Expanding Universe Illusion Theory

[John Phoenix]

Well How about a hypothesis.

 

If those who say the universe is expanding beleive so because the matter seems to be moving away from us, but they do not take into account the destructive forces of black holes that swallow up most matter then their theories could be wrong.

 

I was watching the History channel show that said there is a massive black hole at the center of most galaxies. If this is true, we must Think. What are those black Holes doing? They are swallowing up matter. Galaxies spin in a circular motion.. like the motion of the black hole at it's center. I submit to you that every galaxy is being eaten/swallowed up from within itself.. from its black hole in the center. One day every planet star etc. inside its own galaxy, will be eaten by its black hole. Our own galaxy is right Now shrinking and being swallowed up by the black hole at it's center.

 

Now, as we observe the universe from our standpoint it may indeed look like it's expanding, but it's not this is an illusion.. What we are really seeing are the planets and stars rushing away from us, because the are rushing away to meet their doom at the black hole at it's galaxies center.

 

From our standpoint in space looking outward, the two conclusions may look very much the same. However if you do not take into account this black hole at a galaxies center eating the galaxy up from within, the conclusions of the observations of planets rushing away from us cannot be accurate.

 

Ask yourself these questions. What's faster The speed at which matter seems to be rushing away from us OR the speed at which black holes swallow up matter?

 

So call me a crackpot. To me this is not any sillier than the theory of Dark Matter so believed because the observable effect of light bending in space. Many things can bend light here on Earth and in space. To assume dark matter exists because of this effect is way sillier than my theory.

Edited October 17, 2010 by John Phoenix

[ajb]

Really we should think in terms of clusters of galaxies rushing away from each other. We see galaxies in our local cluster moving towards us, clusters of galaxies also have their own internal dynamics. Galaxies themselves have their own internal dynamics, individual stars maybe moving towards or away from other stars. Planetary systems around stars have dynamics.

 

So I think your idea is incorrect. The supermassive black holes in the centre of galaxies will be influential over the internal dynamics of individual galaxies. However, I cannot see how the fact that supermassive black holes are to be found in the centre of most if not all galaxies would have any effect on the large scale dynamics of clusters of galaxies. They would contribute to the mass, but the fact they are black holes is largely irrelevant.

 

Black holes could be important in cosmology, via providing the missing mass aka dark matter in the universe. Primordial black holes, that is black holes formed in the early universe have been proposed as a possible candidate for dark matter and galaxy seeding. The latter I presume could be seen in the CMBR, but we would have to ask an expert about this.

[John Phoenix]

I didn't know clusters of galaxies were observed moving away from each other. You are right that this observation changes the conclusions. Hey, perhaps there is yet another massive black hole at the center of the universe. I was just going on what the show said ( and didn't say). I give myself an "A" for thinking out of the box with the given info. Ha ha.

Love your avatar. i myself cannot wait for the Christmas special and next season.

[lemur]

I didn't know clusters of galaxies were observed moving away from each other. You are right that this observation changes the conclusions. Hey, perhaps there is yet another massive black hole at the center of the universe. I was just going on what the show said ( and didn't say). I give myself an "A" for thinking out of the box with the given info. Ha ha.

Love your avatar. i myself cannot wait for the Christmas special and next season.

 

Why wouldn't it be the case that galaxy clusters are themselves galaxy-like formations with black-holes in their centers? I don't think the universe has a single center, but it would make sense that all black holes would be centers/drains of matter-energy swirling in, since they could theoretically have enormously large gravitational fields surrounding a volumeless point.

[DanielC]

Why wouldn't it be the case that galaxy clusters are themselves galaxy-like formations with black-holes in their centers? I don't think the universe has a single center, but it would make sense that all black holes would be centers/drains of matter-energy swirling in, since they could theoretically have enormously large gravitational fields surrounding a volumeless point.

 

1. The universe has no centre.

 

2. There is nothing special about a black hole that turns it into some sort of vacuum cleaner sucking up a galaxy. From far away, there is absolutely no difference between orbiting a black hole with 1 million solar masses, or orbiting a stellar cluster with 1 million sun-like stars. Things only look different if you are very near the black hole, where you get an event horizon and probably an ergosphere, but these distances are insignificant compared to the size of the galaxy (a galaxy is about a trillion times larger in diameter than an event horizon or black hole).

[lemur]

2. There is nothing special about a black hole that turns it into some sort of vacuum cleaner sucking up a galaxy. From far away, there is absolutely no difference between orbiting a black hole with 1 million solar masses, or orbiting a stellar cluster with 1 million sun-like stars. Things only look different if you are very near the black hole, where you get an event horizon and probably an ergosphere, but these distances are insignificant compared to the size of the galaxy (a galaxy is about a trillion times larger in diameter than an event horizon or black hole).

 

Maybe not in the sense that gravity fields dissipate at the same rate from their center, regardless of what is emitting the gravitation. But what about the fact that black holes result from stars depleting their energy-generating capacity? In other words, stellar matter maintains volume due to the energy that is being emitted from them. When their energy-output decreases, they collapse into a smaller volume. If you extend this effect to their surrounding space, you could look at entire solar systems and galaxies as having volume resulting from expansionary energy, the big bang being the original prominent one from which all space-time was set into motion.

 

So as stars die and coagulate into increasingly gravitous black holes, they are consuming the energy and motion the big bang set in motion, no? I wouldn't say that black holes are "vacuum cleaners sucking up galaxies" as that implies that the galactic motion and the black holes are not part of the same process. It does seem, however, that galaxies and stars are the result of gravitational coagulation that culminates in total collapse into the black holes at the center of the galaxies. What's more, the growth of such a black hole occurs as part of the larger gravitational-compression/collapse of the galaxy as a whole, therefore the volume of the galaxy is decreasing while the gravitation of the central black hole is increasing. So, in effect, wouldn't it make sense to say that the gravitational attraction between the galaxy and its central black hole is increasing insofar as both the mass/density of the center is increasing AND the radius to the edge of the galaxy is decreasing (along with the relative distances among stars in the galaxy?

 

I know I'm assuming a lot in this post, so please correct those assumptions that are misconstrued. Otherwise, I think the OP has a good point, no?

Edited October 18, 2010 by lemur

[DanielC]

Maybe not in the sense that gravity fields dissipate at the same rate from their center, regardless of what is emitting the gravitation. But what about the fact that black holes result from stars depleting their energy-generating capacity?

 

Do you understand in which sense black holes relate to stars running out of fuel? What could that possibly have to do with the expanding universe?

 

In other words, stellar matter maintains volume due to the energy that is being emitted from them. When their energy-output decreases, they collapse into a smaller volume. If you extend this effect to their surrounding space, you could look at entire solar systems and galaxies as having volume resulting from expansionary energy, the big bang being the original prominent one from which all space-time was set into motion.

 

That doesn't make any sense at all. You are seeing the universe as magic. You need to ask yourself, "WHY is there a connection between energy generation in a star and its volume?" The reason is that a star is a big ball of gas held up against gravity by gas pressure. Nuclear fusion increases the temperature inside the star, which by the ideal gas law will give you an increase in pressure, which is what holds the ball of gas that we call a star. Next to ask yourself if any of this applies to a solar system or a galaxy, and quickly you'll realize that neither one is a ball of gas being held up by gas pressure. Solar systems and galaxies have the shapes they do because the planets/stars are in orbit.

 

So as stars die and coagulate into increasingly gravitous black holes, they are consuming the energy and motion the big bang set in motion, no?

 

No. Stars work by nuclear fusion, not kinetic energy from the big bang.

 

And btw, the vast majority of stars never make black holes. The vast majority (like 95%) will make white dwarfs, and most of the rest will make neutron stars. Only the tiniest fraction of stars (those with masses above about 20 solar masses) will become black holes.

 

 

I know I'm assuming a lot in this post, so please correct those assumptions that are misconstrued. Otherwise, I think the OP has a good point, no?

 

No, he doesn't. You and the OP need to think about what is actually happening physically. Don't just say "stars consume energy and become black holes". Ask yourself, what exactly do you mean by that?What energy do stars consume? Do most stars become black holes? Why are stars held up in the first place? Can any of this be applied to something that is not a star?

 

There is nothing about the physics that you don't know already. I'm sure you already know that stars are powered by fusion, and you already know the relationship between temperature and pressure. If you reasoned through I don't think you should come up with ideas like the solar system shrinking when the sun goes out.

Edited October 23, 2010 by DanielC

[lemur]

That doesn't make any sense at all. You are seeing the universe as magic. You need to ask yourself, "WHY is there a connection between energy generation in a star and its volume?" The reason is that a star is a big ball of gas held up against gravity by gas pressure. Nuclear fusion increases the temperature inside the star, which by the ideal gas law will give you an increase in pressure, which is what holds the ball of gas that we call a star. Next to ask yourself if any of this applies to a solar system or a galaxy, and quickly you'll realize that neither one is a ball of gas being held up by gas pressure. Solar systems and galaxies have the shapes they do because the planets/stars are in orbit.

Gas pressure is the result of kinetic energy of the gas particles colliding with one another correct? Likewise, the distances of planets and other satellites orbiting a star, or stars orbiting the center of a galaxy are also due to the kinetic energy working against gravity, correct? So is it really such a stretch to view orbital distance/velocity as being similar to gas-pressure in creating the volume of a solar system or galaxy? Ok, the planets are stars are not exchanging momentum due to collisions the way you would expect particles in a gas to do, but their velocity nevertheless produces an expansive effect, no?

 

No. Stars work by nuclear fusion, not kinetic energy from the big bang.

I don't know the conditions that caused the big bang to eventually form matter, but the fact that hydrogen fuses into heavier elements makes it possible to view gravitational coagulation as a catalyst for fusion. Thus, the fact that the big bang dispersed energy/matter broadly and with relatively even consistency amounts to a type of energy-potential. In other words, gravity only has the ability to induce fusion because matter was spread evenly so the spreading itself was the fuel for fusion to occur in a slow-crescendo as gasses coagulate and eventually reach a level of compression to "ignite."

 

And btw, the vast majority of stars never make black holes. The vast majority (like 95%) will make white dwarfs, and most of the rest will make neutron stars. Only the tiniest fraction of stars (those with masses above about 20 solar masses) will become black holes.

I knew that, but thanks. Eventually they will become black holes, though, to the extent that they will eventually be pulled into another black hole, correct?

 

 

No, he doesn't. You and the OP need to think about what is actually happening physically. Don't just say "stars consume energy and become black holes". Ask yourself, what exactly do you mean by that?What energy do stars consume? Do most stars become black holes? Why are stars held up in the first place? Can any of this be applied to something that is not a star?

Stars consume dispersion of protons. Protons separated into hydrogen atoms are more widely dispersed than protons that fuse into helium and larger nuclei. So stars literally consume inter-proton repulsion (however they are repelled). The energy that sustains a star at a relatively large volume keeps a good deal of its contents at pressure-levels that slow down the fusion reaction (an assumption, admittedly, am I wrong?). So, as they consume their fuel, they eventually collapse and sometimes supernova or red-giant as a result of the sudden condensation (this is something I haven't read about for a while so I could be mixing some things up). When they finally consume what's left of their fusion potential, they collapse into either white dwarves, neutron stars, or black holes if they have sufficient mass. So apparently there is something collapse-resistant in matter to prevent the cooled stellar matter from collapsing smaller than the Schwarzschild radius in some cases. However, there seems to be something about the gravitation-levels of a certain amount of matter that does causes the matter to collapse/compress beyond that radius, at which point you get a black hole.

 

Can any of this be applied to something that isn't a star? You mean like if elements too heavy to fuse coagulated into a massive, dense lump? I think they could eventually form a black hole, yes, but what is the relevance of that?

 

There is nothing about the physics that you don't know already. I'm sure you already know that stars are powered by fusion, and you already know the relationship between temperature and pressure. If you reasoned through I don't think you should come up with ideas like the solar system shrinking when the sun goes out.

Are there any galaxies without black holes at the center? I would guess that very young galaxies would have yet to develop black holes in the center. However, it makes sense that galaxies are slowly coagulating into smaller areas with denser centers. Could you have a galaxy where the contents reached a point of non-decaying orbit around the center? In that case, could the stars run out of fuel, collapse, and continue to orbit without falling into the center? My impression is that gravity always continues to drive coagulation of matter dispersed by the big-bang in one way or another. Likewise, the kinetic energy of stars and galaxies seems to be a product of the initial big bang and subsequent exchanges of momentum.

 

Why wouldn't the solar system shrink once the sun goes out? Won't the planets slowly decelerate as they encounter occasional friction from various sources? Doesn't solar wind produce a certain amount of thrust for everything orbiting the sun? I know this isn't much, but what could prevent the planets from encountering friction for the rest of eternity? If they are slowing down due to friction, what would prevent their orbits from decaying if there was no thrust to counteract the friction-deceleration? In fact, maybe solar wind clears the orbital paths of the planets by keeping dust pushed out at the heliotrope. Once the sun goes out, that dust might fall back down and result in a lot more friction for the planets and asteroids.

Edited October 23, 2010 by lemur

[DanielC]

Gas pressure is the result of kinetic energy of the gas particles colliding with one another correct? Likewise, the distances of planets and other satellites orbiting a star, or stars orbiting the center of a galaxy are also due to the kinetic energy working against gravity, correct? So is it really such a stretch to view orbital distance/velocity as being similar to gas-pressure in creating the volume of a solar system or galaxy?

 

Yes, it is a very big stretch, and it is wrong. Let's go over this slowly: (1) Yes, gas pressure is the result of particles colliding with each other. (2) An orbiting body has nothing to do with anything colliding with anything. An orbiting body is basically on a free-fall trajectory that takes it around the star. It is not hitting anything. At the same time, the particles inside a gas are not in orbit.

 

Ok, the planets are stars are not exchanging momentum due to collisions the way you would expect particles in a gas to do, but their velocity nevertheless produces an expansive effect, no?

 

Saying "an expansive effect" is a very vague term. It has no clear meaning. This is the sort of thing that can make your physical thinking go in weird directions. The kinetic energy of a planet does not "expand" anything. An orbiting body is basically on a free-fall trajectory, with a centripetal acceleration corresponding to the gravitational force.

 

If it helps, imagine a toy universe where all the particles are point particles, and there are no electromagnetic forces. In this universe, nothing ever "touches" anything else, matter just passes through (point particles never collide) and there is no friction. Imagine that you magically transport the sun to this universe. What would it look like? Well, in this universe there would be no gas pressure, and no friction, so all the particles would simply be in orbit around their common center of mass. There would be no friction to make matter spiral toward the sun. In this universe, the sun's particles would stay in orbit forever and it would never coalesce into a white dwarf. What makes stars work like stars is particles hitting each other. This is the friction that can make things spiral inward, and it is what makes the gas in stars not behave like planets in orbit. The friction between the gas particles makes the gas coalesce, but the kinetic energy imparted by particle collisions makes the gas expand.

 

Does this help at all?

 

I don't know the conditions that caused the big bang to eventually form matter, but the fact that hydrogen fuses into heavier elements makes it possible to view gravitational coagulation as a catalyst for fusion.

 

I have no idea what you mean by "gravitational coagulation", but you are making a very fuzzy connection between gravity and fusion without stopping to think about how it actually works. If you do that, you should expect to reach wrong conclusions.

 

Thus, the fact that the big bang dispersed energy/matter broadly and with relatively even consistency amounts to a type of energy-potential. In other words, gravity only has the ability to induce fusion because matter was spread evenly so the spreading itself was the fuel for fusion to occur in a slow-crescendo as gasses coagulate and eventually reach a level of compression to "ignite."

 

We do have a concept of gravitational potential energy, which you probably remember from school. Gravitational potential energy is indeed the source of the kinetic energy that eventually allows protons to be stripped of electrons, and later, to overcome the electromagnetic repulsion between protons, which is a necessary step for fusion to occur. But again, it is better to think about what the mechanism is, rather than just making a fuzzy jump from gravity to fusion, because not everything that has gravity will have fusion. Planets don't do fusion for example.

 

I knew that, but thanks. Eventually they will become black holes, though, to the extent that they will eventually be pulled into another black hole, correct?

 

No. There is no reason why this should be the case. There is nothing special about a black hole that makes things necessarily fall into it. Just like you wouldn't say that Jupiter will necessarily, one day fall into the sun... Why should it?... Makes sense?

 

Stars consume dispersion of protons. Protons separated into hydrogen atoms are more widely dispersed than protons that fuse into helium and larger nuclei. So stars literally consume inter-proton repulsion (however they are repelled).

 

I cannot think of any sense in which "stars consume inter-proton repulsion". The electromagnetic force doesn't go away, and it is not the source of energy for stars. Fusion provides energy thanks to the strong force. The strong force is attractive, but short range. For very short ranges, it is more powerful than the electromagnetic repulsion. If the protons have high enough kinetic energy, they will be able to get close enough for the strong force to take over. This is what powers fusion (in simplified terms).

 

The energy that sustains a star at a relatively large volume keeps a good deal of its contents at pressure-levels that slow down the fusion reaction (an assumption, admittedly, am I wrong?).

 

Fusion only happens in the stellar core, which is about 1/6th of the star. The interplay between fusion rate and pressure is a bit different from what you suggested. If the fusion rate increases, the pressure increases causing the core to expand. When it expands, it cools down (remember the ideal gas law saying that pressure is proportional to temperature). This means that the particles have less average kinetic energy, and thus fewer of them are able to tunnel through the Coulomb barrier. This is (in simplified terms) how fusion is kept stable.

 

 

So, as they consume their fuel, they eventually collapse and sometimes supernova or red-giant as a result of the sudden condensation (this is something I haven't read about for a while so I could be mixing some things up).

 

All stars become red giants, and this has nothing to do with core collapse. Neither red giants nor supernovae have to do with condensation. A red giant happens when a star starts to run out of hydrogen fuel at the core. It builds a core of helium that is not doing any fusion, and it has a shell of fusing hydrogen. To continue burning, it needs to have a very high pressure + temperature at the core, which makes the core generate a lot of energy, which causes radiation pressure, which makes the star expand.

 

When they finally consume what's left of their fusion potential, they collapse into either white dwarves, neutron stars, or black holes if they have sufficient mass.

 

To be precise, the term collapse is only really appropriate for neutron stars and black holes. The process of becoming a white dwarf is more gradual, non-violent, more like a slow contraction than a sudden collapse.

 

So apparently there is something collapse-resistant in matter to prevent the cooled stellar matter from collapsing smaller than the Schwarzschild radius in some cases.

 

Electron degeneracy pressure keeps a white dwarf from collapse, and a neutron degeneracy pressure keep a neutron star from collapse. In 99.9% of the cases, the star does not collapse into a black hole. Degeneracy pressure has to do with quantum mechanics, and is not related to the temperature of the object.

 

However, there seems to be something about the gravitation-levels of a certain amount of matter that does causes the matter to collapse/compress beyond that radius, at which point you get a black hole.

 

For all degenerate stars (white dwarfs and neutron stars), when you increase the mass, the star actually shrinks, increasing both density, gravitational attraction, and the degeneracy pressure. You can show that, as you add mass, you reach a point where the contraction causes the gravitational attraction to increase faster than the degeneracy pressure. This is the point where you get a collapse.

 

Can any of this be applied to something that isn't a star?

 

Anything that has enough mass and density for the above processes to take place, WOULD be a star. After all, at the most basic level a star is just a really big ball of gas with enough mass that fusion can take place.

 

You mean like if elements too heavy to fuse coagulated into a massive, dense lump?

 

The only elements that cannot fuse are those heavier than iron. If you somehow managed to get a big enough ball of lead and compress it down enough, it would form a white dwarf. But keep in mind that the elements bigger than Helium make up less than 1% of the universe, and the elements bigger than iron are a very small fraction of that, how exactly would you expect to pile and compress a ball of lead? In practice, the only way to make something degenerate like a white dwarf is through the usual star-based process that we are all familiar with.

 

Are there any galaxies without black holes at the center? I would guess that very young galaxies would have yet to develop black holes in the center.

 

No one knows for sure, but it is believed that most galaxies have super massive black holes at the center, even fairly young ones. The super massive black holes appear to form surprisingly early.

 

 

However, it makes sense that galaxies are slowly coagulating into smaller areas with denser centers. Could you have a galaxy where the contents reached a point of non-decaying orbit around the center?

 

Why does that make sense? What do you mean by coagulating into smaller areas? A galaxy is not spiraling inward if that is what you mean. ALL orbits are non-decaying unless you have some sort of friction (for the pedantic reader: please ignore gravitational waves).

 

 

In that case, could the stars run out of fuel, collapse, and continue to orbit without falling into the center?

 

This is the default behaviour. Except that most stars don't collapse, they just gradually form a white dwarf.

 

My impression is that gravity always continues to drive coagulation of matter dispersed by the big-bang in one way or another.

 

This would be wrong. Ignoring some details with gravity waves that really don't matter, once something is in orbit it just stays in orbit unless friction makes it spiral inward. Earth is not spiraling toward the sun.

 

Why wouldn't the solar system shrink once the sun goes out? Won't the planets slowly decelerate as they encounter occasional friction from various sources? Doesn't solar wind produce a certain amount of thrust for everything orbiting the sun?

 

The solar wind would push things outward. If you are going argue solar wind, you would be arguing that orbits should expand. Btw, when the sun enters its giant phase, it will lose significant amounts of mass and this should make the planet orbits expand gradually.

 

I know this isn't much, but what could prevent the planets from encountering friction for the rest of eternity? If they are slowing down due to friction, what would prevent their orbits from decaying if there was no thrust to counteract the friction-deceleration?

 

I want to be very careful replying to this... If you look at the really long term (as in, several times the age of the universe), you can consider the tiny friction in the solar system as a factor that could make the planets or a whole galaxy spiral inward, but if you are going to look at that long term, you have to consider whether the expansion of the universe might not take the same solar system or galaxy and spread it apart before it has a chance to coalesce. If you wait long enough, the expansion of the universe should eventually tear everything apart (except maybe black holes). But if you wait long enough, even black holes will evaporate away by Hawking radiation, so in the really really absurdly long term you should have a universe that is nothing more than a very thinly dispersed sea of elementary particles. This is known as the "Heat Death" of the universe.

[losfomot]

I want to be very careful replying to this... If you look at the really long term (as in, several times the age of the universe), you can consider the tiny friction in the solar system as a factor that could make the planets or a whole galaxy spiral inward, but if you are going to look at that long term, you have to consider whether the expansion of the universe might not take the same solar system or galaxy and spread it apart before it has a chance to coalesce. If you wait long enough, the expansion of the universe should eventually tear everything apart (except maybe black holes). But if you wait long enough, even black holes will evaporate away by Hawking radiation, so in the really really absurdly long term you should have a universe that is nothing more than a very thinly dispersed sea of elementary particles. This is known as the "Heat Death" of the universe.

 

I was under the impression that this is a pretty far-fetched possibility. Clusters of galaxies will probably separate... but our solar system, our galaxy, and even our galactic cluster should hold together regardless of the expansion or 'dark energy'. Is there evidence that the cosmological constant is actually increasing over time?

[lemur]

Yes, it is a very big stretch, and it is wrong. Let's go over this slowly: (1) Yes, gas pressure is the result of particles colliding with each other. (2) An orbiting body has nothing to do with anything colliding with anything. An orbiting body is basically on a free-fall trajectory that takes it around the star. It is not hitting anything. At the same time, the particles inside a gas are not in orbit.

You just perfectly avoided getting my point, why? The point was that the kinetic energy, i.e. momentum, of the objects/particles results in volume of the system. Pressure is basically a function of gravity.

 

Saying "an expansive effect" is a very vague term. It has no clear meaning. This is the sort of thing that can make your physical thinking go in weird directions. The kinetic energy of a planet does not "expand" anything. An orbiting body is basically on a free-fall trajectory, with a centripetal acceleration corresponding to the gravitational force.

When orbiting objects slow down, they fall into the gravity well. If they gain more velocity in a non-downward direction, they gain altitude.

 

If it helps, imagine a toy universe where all the particles are point particles, and there are no electromagnetic forces. In this universe, nothing ever "touches" anything else, matter just passes through (point particles never collide) and there is no friction. Imagine that you magically transport the sun to this universe. What would it look like? Well, in this universe there would be no gas pressure, and no friction, so all the particles would simply be in orbit around their common center of mass. There would be no friction to make matter spiral toward the sun. In this universe, the sun's particles would stay in orbit forever and it would never coalesce into a white dwarf. What makes stars work like stars is particles hitting each other. This is the friction that can make things spiral inward, and it is what makes the gas in stars not behave like planets in orbit. The friction between the gas particles makes the gas coalesce, but the kinetic energy imparted by particle collisions makes the gas expand.

Good description. Now consider that the solar system is de-frictioned by the heliotrope remaining at a far distance from the sun. If the sun would stop radiating energy and solar wind, would the heliotrope not collapse and result in much friction for the planets?

 

I have no idea what you mean by "gravitational coagulation", but you are making a very fuzzy connection between gravity and fusion without stopping to think about how it actually works. If you do that, you should expect to reach wrong conclusions.

Why? Doesn't gravity cause pressure, pressure cause heat, and pressure and heat cause fusion?

 

We do have a concept of gravitational potential energy, which you probably remember from school. Gravitational potential energy is indeed the source of the kinetic energy that eventually allows protons to be stripped of electrons, and later, to overcome the electromagnetic repulsion between protons, which is a necessary step for fusion to occur. But again, it is better to think about what the mechanism is, rather than just making a fuzzy jump from gravity to fusion, because not everything that has gravity will have fusion. Planets don't do fusion for example.

I know that. I was referring to light weight gasses coagulating into stars.

 

No. There is no reason why this should be the case. There is nothing special about a black hole that makes things necessarily fall into it. Just like you wouldn't say that Jupiter will necessarily, one day fall into the sun... Why should it?... Makes sense?

Because without any momentum being added to it, it is in line to. It's just a question of time until the friction it encounters decelerates it to a degenerative orbit.

 

I cannot think of any sense in which "stars consume inter-proton repulsion". The electromagnetic force doesn't go away, and it is not the source of energy for stars. Fusion provides energy thanks to the strong force. The strong force is attractive, but short range. For very short ranges, it is more powerful than the electromagnetic repulsion. If the protons have high enough kinetic energy, they will be able to get close enough for the strong force to take over. This is what powers fusion (in simplified terms).

So just as an object's altitude in a gravitational field exists as potential energy, two protons distance from each other exist as potential energy of fusion. To the extent that protons are separated/repelled from each other as hydrogen, they have the potential to fuse into heavier particles. So when the fusion process merges them and releases energy, the potential energy in their separation/repulsion is expended, no?

 

Fusion only happens in the stellar core, which is about 1/6th of the star. The interplay between fusion rate and pressure is a bit different from what you suggested. If the fusion rate increases, the pressure increases causing the core to expand. When it expands, it cools down (remember the ideal gas law saying that pressure is proportional to temperature). This means that the particles have less average kinetic energy, and thus fewer of them are able to tunnel through the Coulomb barrier. This is (in simplified terms) how fusion is kept stable.

Ok, thanks. Does this present an argument or are you just clarifying the details of how it works?

 

 

All stars become red giants, and this has nothing to do with core collapse. Neither red giants nor supernovae have to do with condensation. A red giant happens when a star starts to run out of hydrogen fuel at the core. It builds a core of helium that is not doing any fusion, and it has a shell of fusing hydrogen. To continue burning, it needs to have a very high pressure + temperature at the core, which makes the core generate a lot of energy, which causes radiation pressure, which makes the star expand.

So fusion just slowly shifts outward due to increasing volume of helium at the core?

 

To be precise, the term collapse is only really appropriate for neutron stars and black holes. The process of becoming a white dwarf is more gradual, non-violent, more like a slow contraction than a sudden collapse.

Sorry, I was using "collapse" to mean the equivalent of "contract." I wasn't thinking about collapsing as rapid contraction.

 

Electron degeneracy pressure keeps a white dwarf from collapse, and a neutron degeneracy pressure keep a neutron star from collapse. In 99.9% of the cases, the star does not collapse into a black hole. Degeneracy pressure has to do with quantum mechanics, and is not related to the temperature of the object.

I was thinking along these lines, but I don't know enough about how the internal structure of particles is defined except for that various levels of sub-atomic particles are defined, like quarks and leptons. I don't understand those, though.

 

For all degenerate stars (white dwarfs and neutron stars), when you increase the mass, the star actually shrinks, increasing both density, gravitational attraction, and the degeneracy pressure. You can show that, as you add mass, you reach a point where the contraction causes the gravitational attraction to increase faster than the degeneracy pressure. This is the point where you get a collapse.

Interesting. Is there an assumption of minimum volume of particles?

 

 

Anything that has enough mass and density for the above processes to take place, WOULD be a star. After all, at the most basic level a star is just a really big ball of gas with enough mass that fusion can take place.

I know, but if the contents were not gas but heavy elements, they wouldn't fuse, would they?

 

 

No one knows for sure, but it is believed that most galaxies have super massive black holes at the center, even fairly young ones. The super massive black holes appear to form surprisingly early.

How so fast?

 

 

Why does that make sense? What do you mean by coagulating into smaller areas? A galaxy is not spiraling inward if that is what you mean. ALL orbits are non-decaying unless you have some sort of friction (for the pedantic reader: please ignore gravitational waves).

If all orbits were non-decaying, how would stars ever congeal in the first place? Friction? Why would friction ever completely disappear in a galaxy/solar-system?

 

 

The solar wind would push things outward. If you are going argue solar wind, you would be arguing that orbits should expand. Btw, when the sun enters its giant phase, it will lose significant amounts of mass and this should make the planet orbits expand gradually.

Ok, no matter. Then they will fall into another gravity well eventually, no?

 

 

I want to be very careful replying to this... If you look at the really long term (as in, several times the age of the universe), you can consider the tiny friction in the solar system as a factor that could make the planets or a whole galaxy spiral inward, but if you are going to look at that long term, you have to consider whether the expansion of the universe might not take the same solar system or galaxy and spread it apart before it has a chance to coalesce. If you wait long enough, the expansion of the universe should eventually tear everything apart (except maybe black holes). But if you wait long enough, even black holes will evaporate away by Hawking radiation, so in the really really absurdly long term you should have a universe that is nothing more than a very thinly dispersed sea of elementary particles. This is known as the "Heat Death" of the universe.

 

But will the galaxies not coalesce into black holes prior to their heat death? Likewise, as they coalesce doesn't their average level of gravitation increase? If it does, couldn't that cause the appearance of expansion as the OP suggested?

[DanielC]

You just perfectly avoided getting my point, why?

 

Perhaps your point was poorly stated. You make several leaps of logic and you use unusual terminology.

 

The point was that the kinetic energy, i.e. momentum, of the objects/particles results in volume of the system. Pressure is basically a function of gravity.

 

Pressure depends on many things, and gravity is but one of them. For example, the solar system and the galaxy are not held up by pressure in any way, manner or form. This is an important point because you are trying to equate the behaviour of a star (which you understand poorly) with the behaviour of the solar system and the galaxy (which is incorrect).

 

When orbiting objects slow down, they fall into the gravity well. If they gain more velocity in a non-downward direction, they gain altitude.

 

The second statement is incorrect. Consider a thrust in the direction opposite to their motion for example.

 

Good description. Now consider that the solar system is de-frictioned by the heliotrope remaining at a far distance from the sun. If the sun would stop radiating energy and solar wind, would the heliotrope not collapse and result in much friction for the planets?

 

You overestimate the density of the interstellar medium. Furthermore, notice that none of this is related to the claims you have been trying to support:

 

1) Friction from the interstellar medium has nothing to do with the gas pressure that is responsible for how stars work.

 

2) Friction from the interstellar medium does not justify you making a connection with how stars work and how a galaxy is held up, and it certainly doesn't justify you using fuzzy terms like "expansionary energy" that have no clear meaning.

 

 

Why? Doesn't gravity cause pressure, pressure cause heat, and pressure and heat cause fusion?

 

Under some conditions. And if you don't stop to think about when that is true and why, you will reach strange conclusions like thinking that what holds stars up and what holds a galaxy up are somehow the same thing.

 

 

I know that. I was referring to light weight gasses coagulating into stars.

 

Note that it is difficult to know how much you know because you've made some strange connections between the pressure that holds a star in place

 

Because without any momentum being added to it, it is in line to. It's just a question of time until the friction it encounters decelerates it to a degenerative orbit.

 

Try to do a calculation comparing friction from the interstellar medium against Jupiter versus the expansion of the universe. Even without the expansion of the universe, can you even show that friction from the interstellar medium will cause Jupiter to spiral inward? After all, you could just as well imagine that the in-falling material would add kinetic energy to Jupiter and raise it to a higher orbit.

 

You are stuck in a mental model where everything naturally tends to "fall to the ground". This may be valid in the limited range of conditions you see on Earth, but you have to be careful extrapolating from that. Material calling from the interstellar medium could just as well push outward as inward. I don't immediately see a fundamental reason why it has to be inward.

 

 

So just as an object's altitude in a gravitational field exists as potential energy, two protons distance from each other exist as potential energy of fusion. To the extent that protons are separated/repelled from each other as hydrogen, they have the potential to fuse into heavier particles. So when the fusion process merges them and releases energy, the potential energy in their separation/repulsion is expended, no?

 

No. The energy from fusion does not come from potential energy due to their repulsion. If you think about that, you'll see it doesn't make sense. We talk about potential energy for gravity, but gravity is attractive, not repulsive. It is fair to say that two hydrogen atoms before fusing have some sort of "potential energy", but this would be driven by the attractive strong force, and not the repulsive electromagnetic force.

 

Ok, thanks. Does this present an argument or are you just clarifying the details of how it works?

 

Just clarifying how it works. Important so we can apply the lessons properly.

 

So fusion just slowly shifts outward due to increasing volume of helium at the core?

 

For the red giant phase, yes. When stars leave the red giant phase, things get more complicated. Stars can go on to burn helium, so you can have a helium-burning core with a hydrogen-burning shell, and for massive stars, they can go on to fuse heavier elements, so you end up with a sort of onion layer with heavier elements being fused further down, and lighter elements being fused in shells.

 

I was thinking along these lines, but I don't know enough about how the internal structure of particles is defined except for that various levels of sub-atomic particles are defined, like quarks and leptons. I don't understand those, though.

 

I can explain degeneracy pressure if you are familiar with the Heisenberg uncertainty principle. Heisenberg said that the more certain the position of a particle is, the less certain its momentum. If you squeeze a ball of matter enough, the space available for every particle decreases. If you do it enough, you can reach the point where Heisenberg's uncertainty principle is dominant and the small confined space for each particle means that there is a very large uncertainty in their momentum. If momentum covers a wide range of values, that means that the average momentum must be high, which translates into high pressure. This is the sort of pressure that keeps a neutron star and a white dwarf from collapsing. Notice that the argument has nothing to do with temperature, so when they cool down they don't shrink.

 

Interesting. Is there an assumption of minimum volume of particles?

 

I'm not 100% sure I understand your question. But perhaps some of what I wrote in the previous paragraph is related to what you asked.

 

I know, but if the contents were not gas but heavy elements, they wouldn't fuse, would they?

 

If they were higher than iron, they wouldn't fuse. Iron is the limit (the most stable element).

 

How so fast?

 

As I understand it, the origin of super massive black holes is a bit of a mystery because they happen so early. The answer probably requires that we understand dark matter, which is responsible for most of the gravity, and which we don't understand well at all.

 

If all orbits were non-decaying, how would stars ever congeal in the first place? Friction? Why would friction ever completely disappear in a galaxy/solar-system?

 

Yes, friction. If it weren't for friction, all orbits would be non-decaying. Friction in a proto-solar nebula is hugely higher than in the solar system today, or the typical interstellar medium. Technically it is not zero, but the time scale for it to have any effect is probably thousands of times the present age of the universe. It is at a point where you have to begin to wonder if other factors like gravitational waves, or disruptions from other stars, or planet-planet interactions, or the expansion of the universe might be more important.

 

Ok, no matter. Then they will fall into another gravity well eventually, no?

 

Not necessarily. I don't see an obvious reason why planets necessarily have to collapse into a larger object at some point.

 

But will the galaxies not coalesce into black holes prior to their heat death?

 

I doubt it very much. Especially for galaxies. In the case of galaxies you can't even invoke friction from the interstellar medium because that medium is part of the galaxy too and it is in orbit around the center of mass, just like the rest of the galaxy. Why should the galaxy coalesce into a black hole?

 

Likewise, as they coalesce doesn't their average level of gravitation increase? If it does, couldn't that cause the appearance of expansion as the OP suggested?

 

No. The gravitational force you see does not change when things coalesce. At a distance you cannot tell the difference between the gravity from a 1-million solar mass black hole and a globular cluster with 1 million sun-like stars. Finally, I don't understand how gravity can give the appearance of expansion. That really doesn't make sense to me at all.

 

I was under the impression that this is a pretty far-fetched possibility. Clusters of galaxies will probably separate... but our solar system, our galaxy, and even our galactic cluster should hold together regardless of the expansion or 'dark energy'. Is there evidence that the cosmological constant is actually increasing over time?

 

You don't need an increasing cosmological constant for this, and I am not aware of anyone suggesting that the cosmological constant is changing in any way.

 

You can roughly think of the cosmological constant as an acceleration term. If space expands with a constant acceleration, then the rate of expansion will increase quadratically without any bound, and at some point the expansion will become significant at the scale of a galaxy, and then at the scale of a solar system.

 

http://en.wikipedia.org/wiki/Big_Freeze

[losfomot]

You don't need an increasing cosmological constant for this, and I am not aware of anyone suggesting that the cosmological constant is changing in any way.

 

You can roughly think of the cosmological constant as an acceleration term. If space expands with a constant acceleration, then the rate of expansion will increase quadratically without any bound, and at some point the expansion will become significant at the scale of a galaxy, and then at the scale of a solar system.

 

http://en.wikipedia.org/wiki/Big_Freeze

 

I'm sorry DanielC, but I am going to have to call you on this one. The link you provided does not support your statement. The 'Big Freeze' is based on stars using up all their fuel, and proton decay. What you are describing is called the 'Big Rip' and is based on the possibility that the cosmological constant is not a constant at all, but is increasing over time.

 

I am used to being humbled, so I won't feel too bad if you prove me wrong on this.

[pioneer]

Special relativity has three equations, one for mass, one for time and one for distance. Although space and time can appear relative to the observer, there is no such thing as relative mass. If mass observation was relative to a given reference, we could violate the conservation of energy simply by picking a relative reference. To maintain the conservation of energy, relativistic mass needs to be absolute, independent of reference. That means that at some level of observation, space and time also need to be absolute and not relative. The three variables move together, so if mass needs to be absolute to satisfy the energy conservation, space and time will also need to line up too. I tend to think since we use relative motion, we don't have the correct reference for absolute mass. Is it possible we are creating relative mass, such that we are in violation of energy conservation?

[lemur]

I can't get into discussion about all your criticisms. Many of them just misrecognize what I'm saying so by the time I clarify and defend my reasoning, it will get very convoluted and probably the maximum post-length will be reached.

You are stuck in a mental model where everything naturally tends to "fall to the ground". This may be valid in the limited range of conditions you see on Earth, but you have to be careful extrapolating from that. Material calling from the interstellar medium could just as well push outward as inward. I don't immediately see a fundamental reason why it has to be inward.

Because gravity is an attractive, centripetal force. I'm not saying that it is impossible that objects can reach orbital equilibrium where they maintain constant distance from each other indefinitely due to frictionless geodesic motion, but to the extent that random particles/object keep falling into more massive ones and causing their gravitational fields to grow in strength and reach, I would expect the coalescence to be a progressive phenomenon. You make a good point about heat-death of black holes, which would raise the question of what process occurs faster, hawking radiation or mass-coalescence and gravitation-increase. Eventually, I could see how if everything has already fallen into black holes, the black holes themselves will slowly radiate into masslessness, but they have to capture all the other matter-energy first, no?

 

No. The energy from fusion does not come from potential energy due to their repulsion. If you think about that, you'll see it doesn't make sense. We talk about potential energy for gravity, but gravity is attractive, not repulsive. It is fair to say that two hydrogen atoms before fusing have some sort of "potential energy", but this would be driven by the attractive strong force, and not the repulsive electromagnetic force.

Put it this way: if it was possible to pull the two protons of a helium atom apart and stabilize them as hydrogen atoms, the process would be endothermic, correct? In fact, wouldn't the amount of energy invested in separating them be equal to the amount that would be released by re-fusing them? Isn't this similar to investing energy in pumping water uphill and then releasing that (potential) energy by allowing the water to flow back down hill and drive a turbine?

 

Just clarifying how it works. Important so we can apply the lessons properly.

I'm sure it is quite important for your self-esteem to establish an asymmetrical relationship between us in this discussion but my interest here is physics, not the social relations of the discussion.

 

For the red giant phase, yes. When stars leave the red giant phase, things get more complicated. Stars can go on to burn helium, so you can have a helium-burning core with a hydrogen-burning shell, and for massive stars, they can go on to fuse heavier elements, so you end up with a sort of onion layer with heavier elements being fused further down, and lighter elements being fused in shells.

And when lead is reached, does fusion continue only now endothermically? I assume this is how uranium and other unstable elements get formed. But you are clearly the expert.

 

I can explain degeneracy pressure if you are familiar with the Heisenberg uncertainty principle. Heisenberg said that the more certain the position of a particle is, the less certain its momentum. If you squeeze a ball of matter enough, the space available for every particle decreases. If you do it enough, you can reach the point where Heisenberg's uncertainty principle is dominant and the small confined space for each particle means that there is a very large uncertainty in their momentum. If momentum covers a wide range of values, that means that the average momentum must be high, which translates into high pressure. This is the sort of pressure that keeps a neutron star and a white dwarf from collapsing. Notice that the argument has nothing to do with temperature, so when they cool down they don't shrink.

Why isn't the average momentum the same thing as heat? Are you saying that due to very high compression, momentum becomes intermittent instead of consistent?

 

As I understand it, the origin of super massive black holes is a bit of a mystery because they happen so early. The answer probably requires that we understand dark matter, which is responsible for most of the gravity, and which we don't understand well at all.

Or the answer could have to do with gravity-related time/light distortion as the overall gravitational characteristics are evolving until the formation of the black hole.

 

Yes, friction. If it weren't for friction, all orbits would be non-decaying. Friction in a proto-solar nebula is hugely higher than in the solar system today, or the typical interstellar medium. Technically it is not zero, but the time scale for it to have any effect is probably thousands of times the present age of the universe. It is at a point where you have to begin to wonder if other factors like gravitational waves, or disruptions from other stars, or planet-planet interactions, or the expansion of the universe might be more important.

Have you thought about what I said about the sun's radiation and the maintenance of the heliopause? It may be that stars create a frictionless bubble using their radiation which permits planets to form stable frictionless orbits while they are radiating sufficient energy to maintain the relative vacuum. In this sense, interstellar space may be much less vacuum-like and chaotic enough to result in very different gravity-space relations as within the heliospheres formed by stars.

 

 

I doubt it very much. Especially for galaxies. In the case of galaxies you can't even invoke friction from the interstellar medium because that medium is part of the galaxy too and it is in orbit around the center of mass, just like the rest of the galaxy. Why should the galaxy coalesce into a black hole?

Because the galaxies are the result of a longer process of coalescence to begin with? If intergalactic gas slowly coalesced into a galaxy, why would that process of coalescence slow and stop and result in permanent orbital equilibrium?

 

No. The gravitational force you see does not change when things coalesce. At a distance you cannot tell the difference between the gravity from a 1-million solar mass black hole and a globular cluster with 1 million sun-like stars.

So you think there is no difference in the spacetime fabric topology of numerous small gravity-wells verses on very large unified gravity well?

 

Finally, I don't understand how gravity can give the appearance of expansion. That really doesn't make sense to me at all.

Because gravity dilates/contracts spacetime. Theoretically, shouldn't each galaxy have a certain gravitational lensing effect due to its gravitational web? As such, isn't observing from inside a galaxy somewhat like observing the outside of a lens from inside of it?

 

 

[DanielC]

Eventually, I could see how if everything has already fallen into black holes, the black holes themselves will slowly radiate into masslessness, but they have to capture all the other matter-energy first, no?

 

No. And in fact, they won't.

 

This is the key point of our discussion, so it is worth making it clear. I know that you want to hear that at some point everything will end up inside black holes, but I'm pretty sure that that isn't true. This is how the long term future of the galaxy is likely to play out:

 

Long after all the stars have died, you have a galaxy full of white dwarfs, with a small number of neutron stars and fewer black holes. Once in a while two white dwarfs come close to each other and exchange momentum, with one being sent outward and the other inward, and some times being ejected. As time goes by, white dwarfs are steadily ejected out of the galaxy while at the same time the smaller, remaining galaxy becomes denser. As the galaxy becomes denser, these close encounters happen more frequently and the process accelerates. At the end of the process you find that the great majority of the white dwarfs in the galaxy have been ejected, while a small fraction have coalesced into the central galactic black hole. In this way, the vast majority of the white dwarfs never end up inside a black hole and they just travel alone through

empty space.

 

 

Put it this way: if it was possible to pull the two protons of a helium atom apart and stabilize them as hydrogen atoms, the process would be endothermic, correct? In fact, wouldn't the amount of energy invested in separating them be equal to the amount that would be released by re-fusing them? Isn't this similar to investing energy in pumping water uphill and then releasing that (potential) energy by allowing the water to flow back down hill and drive a turbine?

 

You said that "the potential energy in their separation/repulsion is expended". This is not true. The energy from fusion doesn't come from the proton-proton repulsion, it comes from the strong nuclear force which is attractive. You can say that before fusion, hydrogen atoms have a form of potential energy, but you cannot say that their repulsion is expended, or that their repulsion is the source of the energy. Quite the opposite, the repulsion serves to decrease how much energy you can get out fusion.

 

 

I'm sure it is quite important for your self-esteem to establish an asymmetrical relationship between us in this discussion but my interest here is physics, not the social relations of the discussion.

 

This is not about my self-esteem. I prefer to clarify and give detailed explanations rather than say "you are wrong, trust me" because if I do that I am not doing my job as a scientist. Sorry if some of that came across badly.

 

And when lead is reached, does fusion continue only now endothermically? I assume this is how uranium and other unstable elements get formed. But you are clearly the expert.

 

Fusion stops at iron. AFAIK heavier elements are produced in supernova explosions.

 

Why isn't the average momentum the same thing as heat? Are you saying that due to very high compression, momentum becomes intermittent instead of consistent?

 

Heat is average kinetic energy per particle, and while it is not the same as momentum, it is correct that they go together. No, momentum does not become intermittent at high compressions. All I tried to say is that the source of pressure is grounded on quantum mechanics and the Heisenberg uncertainty principle rather than the usual ideal gas law. Among other things, it means that no matter how long you wait, the white dwarf will never compress further on its own (unlike a star, which can radiate heat and shrink).

 

 

Have you thought about what I said about the sun's radiation and the maintenance of the heliopause? It may be that stars create a frictionless bubble using their radiation which permits planets to form stable frictionless orbits while they are radiating sufficient energy to maintain the relative vacuum. In this sense, interstellar space may be much less vacuum-like and chaotic enough to result in very different gravity-space relations as within the heliospheres formed by stars.

 

Let's do a calculation: The heliopause is about 153 AU away from the sun. At that distance, the solar wind is about 153^2 = 23409 times weaker than it is here on earth. Actually, it's weaker than that because the particles slow down, but let's use 23400 as our estimate. That means that the force / momentum from the interstellar medium is more than 23 thousand times weaker than the force that the earth already receives from the solar wind. But you don't hear anything about earth spiraling outward due to the solar wind. Earth has been going around the sun for 1/3 the age of the age of the universe and over that scale the effect of the solar wind is not even measurable. That means that if you wait (1/3) x 23400 = 7,700 times the age of the current age of the universe, the effect of the interstellar medium will still be not measurable. There are other effects that will become significant long before you've waited 8,000 times the present age of the universe.

 

 

So you think there is no difference in the spacetime fabric topology of numerous small gravity-wells verses on very large unified gravity well?

 

You can prove that the gravitational force felt by a distant observer is the same, regardless of whether the gravity comes from numerous small gravity wells or one very large one.

 

Because gravity dilates/contracts spacetime. Theoretically, shouldn't each galaxy have a certain gravitational lensing effect due to its gravitational web? As such, isn't observing from inside a galaxy somewhat like observing the outside of a lens from inside of it?

 

Gravitational lensing is a real, but well understood phenomenon. We do not experience gravitational lensing just because we are inside a galaxy. The gravitational lensing we observe is from massive objects lying between us an whatever we are observing. Gravitational lensing will not give the appearance of expansing. It will make objects look deformed, and it can make some galaxies look brighter. But none of that has to do with how we measure the expansion of the universe, which is by taking the Doppler shift of many galaxies and comparing it with luminosity data from Type Ia supernovae.

 

I'm sorry DanielC, but I am going to have to call you on this one. The link you provided does not support your statement. The 'Big Freeze' is based on stars using up all their fuel, and proton decay. What you are describing is called the 'Big Rip' and is based on the possibility that the cosmological constant is not a constant at all, but is increasing over time.

 

I am used to being humbled, so I won't feel too bad if you prove me wrong on this.

 

I am not an expert on cosmology, so I might have used some terms wrong, and I might have some timescales wrong. But I'm fairly confident that you don't need a variable cosmological constant to have galaxies tear apart. The cosmological constant means that the expansion of the universe is accelerating. That tells me that the expansion will become significant at the galactic scale sooner or later. But perhaps I'm wrong...

 

To maintain the conservation of energy, relativistic mass needs to be absolute, independent of reference. That means that at some level of observation, space and time also need to be absolute and not relative.

 

This is not correct. In special relativity, the laws of conservation of mass, energy and momentum are simply replaced by a single law of conservation of the four-momentum tensor, whose magnitude is (E^2 - |pc|^2). This is a quantity that all observers will agree on, and it does not necessitate an absolute space or time. This is akin to conservation of momentum in classical physics. The momentum components in the x, y and z directions need not be conserved, but the total momentum is conserve.

[lemur]

At the end of the process you find that the great majority of the white dwarfs in the galaxy have been ejected, while a small fraction have coalesced into the central galactic black hole. In this way, the vast majority of the white dwarfs never end up inside a black hole and they just travel alone through

empty space.

Interesting. And what do they do after being ejected into "empty space?" Do they not coalesce into new galaxies eventually?

 

You said that "the potential energy in their separation/repulsion is expended". This is not true. The energy from fusion doesn't come from the proton-proton repulsion, it comes from the strong nuclear force which is attractive. You can say that before fusion, hydrogen atoms have a form of potential energy, but you cannot say that their repulsion is expended, or that their repulsion is the source of the energy. Quite the opposite, the repulsion serves to decrease how much energy you can get out fusion.

I think we're talking about opposite sides of the same coin, but maybe I misunderstand. The strong force is attractive, but it can only bond the two protons once they are sufficiently close, right? To get this close, they have to get beyond their electron clouds/shells/whatever. So whatever force causes/allows them to encapsulate themselves with an electron prevents the protons from fusing under low-pressure conditions, right? So by transcending this tendency to repel each other, via electron shells/clouds, protons maintain a form of potential energy of fusion in low-pressure situations, no?

 

This is not about my self-esteem. I prefer to clarify and give detailed explanations rather than say "you are wrong, trust me" because if I do that I am not doing my job as a scientist. Sorry if some of that came across badly.

Fine, apology accepted. Either of us may have insights that the other one lacks, but if we make this into a pissing contest it will only detract from the productivity of the discussion, right?

 

Fusion stops at iron. AFAIK heavier elements are produced in supernova explosions.

why then?

 

Heat is average kinetic energy per particle, and while it is not the same as momentum, it is correct that they go together. No, momentum does not become intermittent at high compressions. All I tried to say is that the source of pressure is grounded on quantum mechanics and the Heisenberg uncertainty principle rather than the usual ideal gas law. Among other things, it means that no matter how long you wait, the white dwarf will never compress further on its own (unlike a star, which can radiate heat and shrink).

Then I don't get how you're saying that Heisenberg uncertainty relates to particle momentum. Do the particles themselves have volume or are they points? If they are pure zero-dimensional points, can they be compressed limitlessly?

 

 

Let's do a calculation: The heliopause is about 153 AU away from the sun. At that distance, the solar wind is about 153^2 = 23409 times weaker than it is here on earth. Actually, it's weaker than that because the particles slow down, but let's use 23400 as our estimate. That means that the force / momentum from the interstellar medium is more than 23 thousand times weaker than the force that the earth already receives from the solar wind. But you don't hear anything about earth spiraling outward due to the solar wind. Earth has been going around the sun for 1/3 the age of the age of the universe and over that scale the effect of the solar wind is not even measurable. That means that if you wait (1/3) x 23400 = 7,700 times the age of the current age of the universe, the effect of the interstellar medium will still be not measurable. There are other effects that will become significant long before you've waited 8,000 times the present age of the universe.

Nice quantification of the issues involved. So the stuff beyond the heliopause is moving very slowly. What do you expect at such a high altitude in a gravity-well? Once that stuff starts to descend into the gravity-well, though, don't you think it will accelerate? By the time it gets to the planets it may have quite some momentum, no?

 

You can prove that the gravitational force felt by a distant observer is the same, regardless of whether the gravity comes from numerous small gravity wells or one very large one.

A distant observer, maybe, but what about the dynamics of the system internally? What about the procession of light through spacetime? Light will change directions much more traveling through a cloud of dents in spacetime than through a single large gravity-well, no?

 

Gravitational lensing is a real, but well understood phenomenon. We do not experience gravitational lensing just because we are inside a galaxy. The gravitational lensing we observe is from massive objects lying between us an whatever we are observing. Gravitational lensing will not give the appearance of expansing. It will make objects look deformed, and it can make some galaxies look brighter. But none of that has to do with how we measure the expansion of the universe, which is by taking the Doppler shift of many galaxies and comparing it with luminosity data from Type Ia supernovae.

I don't know. Personally, I think that gravitational lensing is treated as too isolated a phenomenon. After all, if you look at the variety of optical effects that exist terrestrially, why would you expect in less variety extra-terrestrially? Imo, we're just not able to explore the universe as thoroughly as terrestrial space, so we're somewhat alienated from being able to recognize all the optical variations.

 

This is not correct. In special relativity, the laws of conservation of mass, energy and momentum are simply replaced by a single law of conservation of the four-momentum tensor, whose magnitude is (E^2 - |pc|^2). This is a quantity that all observers will agree on, and it does not necessitate an absolute space or time. This is akin to conservation of momentum in classical physics. The momentum components in the x, y and z directions need not be conserved, but the total momentum is conserve.

 

Thanks, I've never heard of this. I assumed it would be possible to consolidate the law of conservation but I didn't know it had already been done.

[DanielC]

Interesting. And what do they do after being ejected into "empty space?" Do they not coalesce into new galaxies eventually?

 

They don't. Remember that the universe is expanding. If the universe was static, we could conclude that sooner or later they would hit something. But as the universe expands, space just gets emptier and emptier. If you imagine a lone white dwarf that has been ejected from the Milky Way, in theory there is some galaxy "in front", some huge distance ahead. But that galaxy is moving away too, as the universe expands. So as time goes by, the Milky Way is further and further behind, and the galaxy in front is further and further away too, and the white dwarf just gets more and more isolated. It would just be a few white dwarfs that just happen to be flung in the direction of a nearby galaxy that is not receding away.

 

I think we're talking about opposite sides of the same coin, but maybe I misunderstand. The strong force is attractive, but it can only bond the two protons once they are sufficiently close, right?

 

Correct.

 

To get this close, they have to get beyond their electron clouds/shells/whatever.

 

Incorrect. We are talking about protons getting close to each other. Electrons are not involved. The sun's core is a ball of ionized gas where basically the electrons and protons are not bound to each other. What we have to overcome is the repulsive force of two protons, because they both have a positive charge and they repel.

 

Fine, apology accepted. Either of us may have insights that the other one lacks, but if we make this into a pissing contest it will only detract from the productivity of the discussion, right?

 

Keep in mind that I am a graduate student in astrophysics. I try to explain things clearly and politely. I am in this forum in the hope that I can help people understand astrophysics better. I am not here in order to insult people, but if you say something that is wrong in this forum, I imagine that it is acceptable for me to say so. I try to say it politely, but I also try to give enough details that you understand why the universe works the way it does. I hope that you will not take my explanations as an insult. Would you really be happier if I simply said that you are wrong and didn't try to give more details?

 

 

why then?

 

A (core collapse) supernova explosion is a hugely energetic process where atoms nuclei can be banged together with enough force to make them fuse, even if that reaction consumes energy. In a (core-collapse) supernova, a lot of things happen that actually consume energy. For example, at the high energies of the explosion, photons have enough energy that they can actually break apart iron nuclei into smaller pieces, essentially running fusion backward, even though this reaction consumes a lot of energy.

 

The energy source of a core collapse supernova is gravitational potential, which is about 100 times greater than the nuclear energy, so there is plenty of energy to go around to force matter to things that actually consume nuclear energy.

 

As one point of clarity: A core-collapse supernova is one type of supernova. Basically, a "type Ia" supernova is something else, and every other type is ultimately a core-collapse.

 

Then I don't get how you're saying that Heisenberg uncertainty relates to particle momentum. Do the particles themselves have volume or are they points? If they are pure zero-dimensional points, can they be compressed limitlessly?

 

Quantum mechanics models particles as points or waves, not as objects with a definite volume.

 

Heisenberg's uncertainty principle says that a particle's position and its momentum are not definitive quantities that can be known exactly. Let "dx" be the uncertainty in the position of a particle. Let "dp" be the uncertainty in a particle's momentum. Heisenberg's uncertainty principle says that "dx * dp > h" where h is Planck's constant, which is a very small number. For most things in life this relation doesn't say anything interesting. In a white dwarf, electrons are confined within a very small space, of a size comparable to "h", and as they are more compressed, their momentum must be more uncertain, which means that it spans a greater range of values.

 

Nice quantification of the issues involved. So the stuff beyond the heliopause is moving very slowly.

 

The main point is not that it moves slowly, but that it is very thin. The interstellar medium is practically empty. The scale of the interstellar medium having any effect on planets is many magnitudes longer than other effects such as planet-planet interactions or a close encounter with another star causing planets to move out.

 

What do you expect at such a high altitude in a gravity-well? Once that stuff starts to descend into the gravity-well, though, don't you think it will accelerate? By the time it gets to the planets it may have quite some momentum, no?

 

Here is a persistent problem with your thinking: You keep imagining stuff just has a natural tendency to fall toward the sun and that stuff is held "up" by some form of pressure. This is not the case. The galaxy is full of forces, with multiple stellar winds, as well as everything orbiting the galaxy in their own orbits. The heliopause is the point where the solar wind becomes comparable with these other forces. It is wrong to think of the heliopause as some cloud of gas that is stuck with the sun and is just waiting to come down when the sun turns off. The heliopause is where the sun's influence becomes no greater than the other normal effects that you get from other stars, or from each particle having its own orbit around the galaxy.

 

A distant observer, maybe, but what about the dynamics of the system internally?

 

As a way of example: You are sitting on earth. You are not very far from earth. The gravity that you feel is basically indistinguishable from the gravity that you would feel if all of earth's mass was concentrated at a single point at the centre of the earth. Now imagine that you are 3,000 km down into the earth. Now the gravity that you feel is different. Basically you only feel the gravity of the mass that is below you, but as long as you have spherical symmetry, the gravity that you feel is indistinguishable from what you'd feel if all the mass below you was concentrated at a single point at the centre of the sphere. In a similar way, it is not the same thing being in the middle of a globular cluster with 1 million stars, versus being next to a 1 million solar mass black hole. A black hole would give you things like an event horizon. But notice that most of what you have been talking about in your posts have been references to distant observers. For example, look at the following:

 

Light will change directions much more traveling through a cloud of dents in spacetime than through a single large gravity-well, no?

 

This is a reference to what distant observers will see. You are an observing some distant object, and its light could pass through a gravity well formed by either a single huge black hole, or by large number of small stars. To the best of my knowledge, the bending of light would be the same in either case.

 

I don't know. Personally, I think that gravitational lensing is treated as too isolated a phenomenon. After all, if you look at the variety of optical effects that exist terrestrially, why would you expect in less variety extra-terrestrially? Imo, we're just not able to explore the universe as thoroughly as terrestrial space, so we're somewhat alienated from being able to recognize all the optical variations.

 

We can see a heck of a lot of universe. Gravitational lensing has been observed many times, always in accordance to Einstein's field equations. Gravitational lensing is a fairly well understood phenomenon. It is worth highlighting that our understanding of gravitational lensing comes from Einstein's field equations, which have been tested very throughly. Some people have this image of physicists looking up at the sky and assuming that whatever they haven't seen yet must not exist. This isn't how we work. We form a model of the universe, and we test it throughly. It is worth noting that gravitational lensing was predicted by Einstein's field equations, and once physicists saw the prediction, they went to look for it (and they saw it).

[swansont]

Special relativity has three equations, one for mass, one for time and one for distance. Although space and time can appear relative to the observer, there is no such thing as relative mass. If mass observation was relative to a given reference, we could violate the conservation of energy simply by picking a relative reference. To maintain the conservation of energy, relativistic mass needs to be absolute, independent of reference. That means that at some level of observation, space and time also need to be absolute and not relative. The three variables move together, so if mass needs to be absolute to satisfy the energy conservation, space and time will also need to line up too. I tend to think since we use relative motion, we don't have the correct reference for absolute mass. Is it possible we are creating relative mass, such that we are in violation of energy conservation?

 

 

No. Relativistic mass is not invariant between frames (which is one reason why many physicists decry its use) which is because energy is not invariant. Rest mass, however, is invariant, and can be used as a reference between frames. Energy conservation only applies within a frame of reference.

 

But I'm not sure what this has to do with the expansion of the universe. If there is a followup to this it should go in a new thread.

[lemur]

They don't. Remember that the universe is expanding. If the universe was static, we could conclude that sooner or later they would hit something. But as the universe expands, space just gets emptier and emptier. If you imagine a lone white dwarf that has been ejected from the Milky Way, in theory there is some galaxy "in front", some huge distance ahead. But that galaxy is moving away too, as the universe expands. So as time goes by, the Milky Way is further and further behind, and the galaxy in front is further and further away too, and the white dwarf just gets more and more isolated. It would just be a few white dwarfs that just happen to be flung in the direction of a nearby galaxy that is not receding away.

If two balloons were next to each other and shrinking, an observer inside one of the balloons could conclude that they were moving away from each other. If the balloons were galaxies and the decreasing average distance between massive bodies was increasing the average level of gravitation, then the differential between spacetime compression inside and outside the galaxy would be increasing. This, I would expect, would increase the apparent expansion because relative to the speed of light as measured within the galaxy, the speed of light outside it would be (lower? . . . this is where I get mixed up whether higher gravity slows or accelerates light). Still, you get my point: objects may be more distant than they appear and this effect may be steadily increasing causing the appearance of expansion. I didn't make this idea up, it was the OP but I've thought of it before and I don't see how/why it would be excludable.

 

Incorrect. We are talking about protons getting close to each other. Electrons are not involved. The sun's core is a ball of ionized gas where basically the electrons and protons are not bound to each other. What we have to overcome is the repulsive force of two protons, because they both have a positive charge and they repel.

The protons and electrons may not be bound, but that doesn't mean their flows relative to each other and themselves are not influenced by their interactive tendencies. They are, after all attracted to each other by opposite charge. So the ability for protons to come into contact and be compressed beyond their repulsion would still be mitigated by the force required to displace electrons, which probably also has something to do with whether fusion results in helium or a heavier element. I.e. it probably takes more energy to get 3 or more protons next to each other and compressed to the point of fusion than it does for 2.

 

Keep in mind that I am a graduate student in astrophysics. I try to explain things clearly and politely. I am in this forum in the hope that I can help people understand astrophysics better. I am not here in order to insult people, but if you say something that is wrong in this forum, I imagine that it is acceptable for me to say so. I try to say it politely, but I also try to give enough details that you understand why the universe works the way it does. I hope that you will not take my explanations as an insult. Would you really be happier if I simply said that you are wrong and didn't try to give more details?

No, I enjoy reading and responding to your posts. I hope I don't come across as impolite because I tend not to worry about being too polite because I'm not a very hostile person in my core. Nevertheless, I do tend to be fairly free with engaging in conflict with people because of this and it can lead to malice when the conflict is taken as hostility. Let's avoid that if we can;)

 

A (core collapse) supernova explosion is a hugely energetic process where atoms nuclei can be banged together with enough force to make them fuse, even if that reaction consumes energy. In a (core-collapse) supernova, a lot of things happen that actually consume energy. For example, at the high energies of the explosion, photons have enough energy that they can actually break apart iron nuclei into smaller pieces, essentially running fusion backward, even though this reaction consumes a lot of energy.

 

The energy source of a core collapse supernova is gravitational potential, which is about 100 times greater than the nuclear energy, so there is plenty of energy to go around to force matter to things that actually consume nuclear energy.

 

As one point of clarity: A core-collapse supernova is one type of supernova. Basically, a "type Ia" supernova is something else, and every other type is ultimately a core-collapse.

Thanks. I would have guessed about core-collapse causing a sudden increase in gravitation, pressure, and just the impact-force of lots of heavy matter falling long distances at high gravity, so it's interesting to hear that this is why people study in astrophysics.

 

Heisenberg's uncertainty principle says that a particle's position and its momentum are not definitive quantities that can be known exactly. Let "dx" be the uncertainty in the position of a particle. Let "dp" be the uncertainty in a particle's momentum. Heisenberg's uncertainty principle says that "dx * dp > h" where h is Planck's constant, which is a very small number. For most things in life this relation doesn't say anything interesting. In a white dwarf, electrons are confined within a very small space, of a size comparable to "h", and as they are more compressed, their momentum must be more uncertain, which means that it spans a greater range of values.

But how would this alter the overall compression of the particles?

 

The main point is not that it moves slowly, but that it is very thin. The interstellar medium is practically empty. The scale of the interstellar medium having any effect on planets is many magnitudes longer than other effects such as planet-planet interactions or a close encounter with another star causing planets to move out.

And both its slowness and thinness may become fastness and thickness as it descends into the gravity well of a dying/deceased star, no?

 

Here is a persistent problem with your thinking: You keep imagining stuff just has a natural tendency to fall toward the sun and that stuff is held "up" by some form of pressure. This is not the case. The galaxy is full of forces, with multiple stellar winds, as well as everything orbiting the galaxy in their own orbits. The heliopause is the point where the solar wind becomes comparable with these other forces. It is wrong to think of the heliopause as some cloud of gas that is stuck with the sun and is just waiting to come down when the sun turns off. The heliopause is where the sun's influence becomes no greater than the other normal effects that you get from other stars, or from each particle having its own orbit around the galaxy.

I was thinking more that the heliopause was the edge of an energy-bubble resulting from solar wind but also radiation and heat. Lighter gases tend to rise in a gravity-well, no, especially when heated? Solar wind is basically light gas doing just that, right? So couldn't you look at the solar wind as a very thin solar atmosphere that tends to rise due to solar heat? If you light a candle in space, the heat expands outward in a spherical shape. Why wouldn't you see the heliopause as the surface of that sphere for the sun?

 

 

As a way of example: You are sitting on earth. You are not very far from earth. The gravity that you feel is basically indistinguishable from the gravity that you would feel if all of earth's mass was concentrated at a single point at the centre of the earth. Now imagine that you are 3,000 km down into the earth.

I know this is based on Newton's equation which considers only mass and distance. However, don't you think that matter whose mass is spread out less densely has the tendency to cancel out a certain amount of its gravitation. The center of the Earth, for example, is weightless because the gravity from the outer layers of the sphere cancels itself out completely in the center. Nevertheless, the gravity from the North pole is less by the time it reaches the South pole than it would be if the two poles were compressed into the same point, no? So I would actually think that gravitational fields extend farther from denser bodies than more voluminous ones with the same mass.

 

 

We can see a heck of a lot of universe. Gravitational lensing has been observed many times, always in accordance to Einstein's field equations. Gravitational lensing is a fairly well understood phenomenon. It is worth highlighting that our understanding of gravitational lensing comes from Einstein's field equations, which have been tested very throughly. Some people have this image of physicists looking up at the sky and assuming that whatever they haven't seen yet must not exist. This isn't how we work. We form a model of the universe, and we test it throughly. It is worth noting that gravitational lensing was predicted by Einstein's field equations, and once physicists saw the prediction, they went to look for it (and they saw it).

But are there equations and experiments for predicting the effect on light if we were located inside a gravitational lens?

 

 

 

[DanielC]

If two balloons were next to each other and shrinking, an observer inside one of the balloons could conclude that they were moving away from each other.

 

No, he wouldn't, unless he was not a very smart observer. Incidentally, we do not measure the expansion of the universe by seeing stuff shrink. We use various techniques such as Type Ia supernovae, Cepheid variables and Doppler shift to measure distances and speed.

 

Second, galaxies are not shrinking, and gravitational lensing would not make it look like they are. The best analogy I can think of is: If you put a magnifying lens in front of an object, it might make the object look bigger and brighter, but it will not make the object look like it's moving.

 

This, I would expect, would increase the apparent expansion because relative to the speed of light as measured within the galaxy, the speed of light outside it would be (lower? . . . this is where I get mixed up whether higher gravity slows or accelerates light).

 

It does neither. The speed of light is a universal constant. Light is not accelerated or decelerated by gravitational fields. Gravitational fields can bend light, but they do not change the speed of light.

 

Still, you get my point: objects may be more distant than they appear and this effect may be steadily increasing causing the appearance of expansion.

 

This is wrong for a few reasons: (1) We do not (and cannot) use the angular size of galaxies to determine their distance or speed. (2) Even if we did, and even if the galaxy's gravitational field changed their apparent size the way you suggest (it doesn't), that would not make us get the speed wrong, unless this strange gravitational lensing that you propose was also changing in time. (3) And even if we did have this magical, time-changing, gravitational field you propose, it would not make objects further away look like they are moving faster than those nearby. (4) And even if we did have this super-magical gravitational lensing that somehow could discriminate distance to make further-away objects look like they are moving faster, that still would not fit observations because the expansion rate that we measure is not a simple acceleration curve. What we observe is that the very young universe was decelerating, as you would expect in a matter-dominated universe, while the older, more recent universe is accelerating away, and the shift between the two matches that of a universe that is initially matter dominated, and as it expands, the cosmological constant becomes more significant.

 

The protons and electrons may not be bound, but that doesn't mean their flows relative to each other and themselves are not influenced by their interactive tendencies. They are, after all attracted to each other by opposite charge. So the ability for protons to come into contact and be compressed beyond their repulsion would still be mitigated by the force required to displace electrons, which probably also has something to do with whether fusion results in helium or a heavier element. I.e. it probably takes more energy to get 3 or more protons next to each other and compressed to the point of fusion than it does for 2.

 

I'm sorry, but you have no idea what you are talking about. Electrons are not at all involved in the process of fusion, and they have no effect whatsoever on the ability of protons inside a stellar core to come close enough for the strong force to work.

 

 

But how would this alter the overall compression of the particles?

 

I should mention that I am not an expert in quantum mechanics. The Heisenberg principle does not compress particles. It says that when you compress particles, their momentum becomes less certain. And through some calculations that I only more-or-less follow, you can show that this gives you a source of pressure that is independent of temperature.

 

And both its slowness and thinness may become fastness and thickness as it descends into the gravity well of a dying/deceased star, no?

...

I was thinking more that the heliopause was the edge of an energy-bubble resulting from solar wind but also radiation and heat. Lighter gases tend to rise in a gravity-well, no, especially when heated?

 

No. Lighter gases do not rise in a gravity well when heated. This is the sort of thinking that is based on your experience here on earth, sounds intuitive, but has no reality in the near vacuum of space. On earth, and on the sun, lighter gases float. But this cannot be extended to orbiting objects in a solar system.

 

But to make you feel better, lets suppose that if you turned off the solar wind, the interstellar gas would condense around the sun the way you suggest. The pressure from this gas would not be greater than the pressure that earth already feels from the solar wind, right? (otherwise, the solar wind would not be pushing it). So let's take the entire pressure from the solar wind, and instead of being random, lets assume that you put all that energy into slowing down the earth, with perfect 100% efficiency. How long would it take for this pressure to make the earth fall onto the sun? I did a calculation, and the answer was 222,000 times the present age of the universe.

 

Do you now believe me that the friction from the interstellar medium is negligible compared to other factors?

 

I know this is based on Newton's equation which considers only mass and distance. However, don't you think that matter whose mass is spread out less densely has the tendency to cancel out a certain amount of its gravitation.

 

This is not true. This is not simply a supposition that we just make for simplicity, it is something that you can prove by integrating the gravitational force of every infinitesimal mass from a spherically symmetric volume.

 

Look, if there is one thing astronomers should understand, it's gravity, because that is the force that dominates everything in the universe. Astronomers don't just hypothesize about how gravity might work. We have very precise theories of gravity that have been experimentally verified to incredible levels of accuracy.

 

The center of the Earth, for example, is weightless because the gravity from the outer layers of the sphere cancels itself out completely in the center.

 

You can derive this fact from what I said in my previous post. I told you that if you are inside the earth, the gravitational attraction corresponds to the mass in the sphere below you. So as you go down, the gravity you feel drops.

 

Nevertheless, the gravity from the North pole is less by the time it reaches the South pole than it would be if the two poles were compressed into the same point, no? So I would actually think that gravitational fields extend farther from denser bodies than more voluminous ones with the same mass.

 

Gravity does not extend further from denser bodies. If it did, astronomical observations would have revealed that long ago. We have a wide range of both very light and very dense bodies with which to test our theories of gravity, and all tests match our existing theories.

 

But are there equations and experiments for predicting the effect on light if we were located inside a gravitational lens?

 

Einstein's equations are perfectly general. They work just fine for observers inside the galaxy. They can also tell you what an observer entering a black hole would see, or what an observer in an accelerating rocket would see, etc.

[zapatos]

I am not an expert on cosmology, so I might have used some terms wrong, and I might have some timescales wrong. But I'm fairly confident that you don't need a variable cosmological constant to have galaxies tear apart. The cosmological constant means that the expansion of the universe is accelerating. That tells me that the expansion will become significant at the galactic scale sooner or later. But perhaps I'm wrong...

I'm a rookie on these topics so please excuse me if I am out of place here, but as Spyman pointed out in another thread:

 

"Yes, it is normally considered that the expansion of space only happens on very very large scales.

 

But, as I have tried to explain, on smaller scales, things like galaxies, solar systems, molecules and atoms are bound systems, they are held together by forces much stronger than the expansion. The force from Dark energy is not able to continue to expand them, instead bound systems only expands until they reach a slightly larger size where the forces that holds them together counter and stop the expansion.

 

So bound systems don't continue to expand but they are a tiny bit larger due to Dark energy, this tiny bit is so teeny-weeny that it is not measureable and esteemed unimportant.

 

 

The reasoning is not my personal idea, it's a valid scientific conclusion and even mentioned on Wikipedia:"

 

"A cosmological constant has the effect of a repulsive force between objects which is proportional (not inversely proportional) to distance. Unlike inertia it actively "pulls" on objects which have clumped together under the influence of gravity, and even on individual atoms. However this does not cause the objects to grow steadily or to disintegrate; unless they are very weakly bound, they will simply settle into an equilibrium state which is slightly (undetectably) larger than it would otherwise have been."

http://en.wikipedia....ansion_of_space

Edited October 26, 2010 by zapatos

[lemur]

No, he wouldn't, unless he was not a very smart observer. Incidentally, we do not measure the expansion of the universe by seeing stuff shrink. We use various techniques such as Type Ia supernovae, Cepheid variables and Doppler shift to measure distances and speed.

 

Second, galaxies are not shrinking, and gravitational lensing would not make it look like they are. The best analogy I can think of is: If you put a magnifying lens in front of an object, it might make the object look bigger and brighter, but it will not make the object look like it's moving.

If the magnifying glass was changing density, it could make spatial relations outside the lens appear to be expanding or contracting. If a galaxy was contracting, gravitation levels could be rising, which could be steadily increasing the optical-density differential between the interior of the galaxy and the more empty space between galaxies.

 

It does neither. The speed of light is a universal constant. Light is not accelerated or decelerated by gravitational fields. Gravitational fields can bend light, but they do not change the speed of light.

The speed of light is the maximum speed possible in any medium. So C changes in material media, such as water, but also due to gravitation, which is the cause of gravitational redshift, I beleive.

 

This is wrong for a few reasons: (1) We do not (and cannot) use the angular size of galaxies to determine their distance or speed. (2) Even if we did, and even if the galaxy's gravitational field changed their apparent size the way you suggest (it doesn't), that would not make us get the speed wrong, unless this strange gravitational lensing that you propose was also changing in time. (3) And even if we did have this magical, time-changing, gravitational field you propose, it would not make objects further away look like they are moving faster than those nearby. (4) And even if we did have this super-magical gravitational lensing that somehow could discriminate distance to make further-away objects look like they are moving faster, that still would not fit observations because the expansion rate that we measure is not a simple acceleration curve. What we observe is that the very young universe was decelerating, as you would expect in a matter-dominated universe, while the older, more recent universe is accelerating away, and the shift between the two matches that of a universe that is initially matter dominated, and as it expands, the cosmological constant becomes more significant.

Idk, I'm still not convinced that lens-effects couldn't cause some objects to appear to recede faster or slower than others. Remember, I'm not talking about a stable lens but one that is changing shape and density at a variable rate depending on the changing gravitational field relations of the galaxy's constituents.

 

I'm sorry, but you have no idea what you are talking about. Electrons are not at all involved in the process of fusion, and they have no effect whatsoever on the ability of protons inside a stellar core to come close enough for the strong force to work.

Well, what happens to them then? They continue to be negatively charged while the protons continue to be positively charged, no?

 

 

I should mention that I am not an expert in quantum mechanics. The Heisenberg principle does not compress particles. It says that when you compress particles, their momentum becomes less certain. And through some calculations that I only more-or-less follow, you can show that this gives you a source of pressure that is independent of temperature.

So you're another person who accepts the calculations without having an explanatory mechanism for how the process actually works outside of the math?

 

No. Lighter gases do not rise in a gravity well when heated. This is the sort of thinking that is based on your experience here on earth, sounds intuitive, but has no reality in the near vacuum of space. On earth, and on the sun, lighter gases float. But this cannot be extended to orbiting objects in a solar system.

I suppose that buoyancy is the product of heavier particles pushing lighter ones up as they fall, so you have a point. Nevertheless, the sun's radiation is sufficient to push very light particles very far away, correct? Theoretically, shouldn't the heliopause be located at the point where solar radiation drops to a level of energy that is less than the momentum/heat of particles outside the solar system?

 

But to make you feel better, lets suppose that if you turned off the solar wind, the interstellar gas would condense around the sun the way you suggest. The pressure from this gas would not be greater than the pressure that earth already feels from the solar wind, right? (otherwise, the solar wind would not be pushing it). So let's take the entire pressure from the solar wind, and instead of being random, lets assume that you put all that energy into slowing down the earth, with perfect 100% efficiency. How long would it take for this pressure to make the earth fall onto the sun? I did a calculation, and the answer was 222,000 times the present age of the universe.

 

Do you now believe me that the friction from the interstellar medium is negligible compared to other factors?

I suppose the Earth does have a great deal of momentum considering its mass. I suppose I'll have to concede that your idea that the sun will lose mass due to fusion will cause the planets to expand in their orbits and eventually drift off into interstellar space.

 

Gravity does not extend further from denser bodies. If it did, astronomical observations would have revealed that long ago. We have a wide range of both very light and very dense bodies with which to test our theories of gravity, and all tests match our existing theories.

Ok, can't argue with empirical observations. But then, how else do you measure the mass of a body except by its gravitational effects?

 

 

 

 

[Spyman]

The speed of light is the maximum speed possible in any medium. So C changes in material media, such as water, but also due to gravitation, which is the cause of gravitational redshift, I beleive.

1) The speed of light, c, is the physical constant of the speed light through vacuum. The speed of light through different media will be lower, but the value of c does not change.

 

"The speed of light, usually denoted by c, is a physical constant important in many areas of physics. Light and all other electromagnetic radiation always travel at this speed in empty space (vacuum),"

 

"The speed at which light propagates through transparent materials, such as glass or air, is less than c. The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material (n = c / v). For example, for visible light the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200,000 km/s; the refractive index of air for visible light is about 1.0003, so the speed of light in air is very close to c."

http://en.wikipedia.org/wiki/Speed_of_light

 

2) In different media the speed of light is not the maximum speed possible, Cherenkov radiation is emitted when charged particles passes through at speeds greater than the speed of light in that medium.

 

"While relativity holds that the speed of light in a vacuum is a universal constant ©, the speed at which light propagates in a material may be significantly less than c. For example, the speed of the propagation of light in water is only 0.75c. Matter can be accelerated beyond this speed during nuclear reactions and in particle accelerators. Cherenkov radiation results when a charged particle, most commonly an electron, travels through a dielectric (electrically polarizable) medium with a speed greater than that at which light would otherwise propagate in the same medium."

http://en.wikipedia.org/wiki/Cherenkov_radiation

 

3) Gravitational Redshift doesn't change the speed of light, it changes the energy of the lightbeem by increasing its wavelenght, so it looks more red but still travels with c.

 

"In physics, light or other forms of electromagnetic radiation of a certain wavelength originating from a source placed in a region of stronger gravitational field (and which could be said to have climbed "uphill" out of a gravity well) will be found to be of longer wavelength when received by an observer in a region of weaker gravitational field. If applied to optical wave-lengths this manifests itself as a change in the colour of the light as the wavelength is shifted toward the red (making it less energetic, longer in wavelength, and lower in frequency) part of the spectrum."

http://en.wikipedia.org/wiki/Gravitational_redshift

 

 

----------

 

[EDIT]

Here is a great article on the timeline of the Universe:

 

The Great Cosmic Battle

 

The expansion of the Universe itself provides an intensely dramatic example of the ubiquitous struggle between the force of gravity and entropy. As the Universe expands and becomes more spread out, gravity resists this trend and tries to pull the expanding Universe back together. The particular fate which our future holds depends on whether gravity wins or loses this cosmic battle, whose outcome depends on the total amount of mass and energy contained within the Universe. Current astronomical data strongly suggest that gravity has already lost this critical conflict and our fate will be determined by a continued and unending expansion.

http://www.astrosociety.org/pubs/mercury/0001/cosmic.html

Edited October 27, 2010 by Spyman

[DanielC]

I'm a rookie on these topics so please excuse me if I am out of place here, but as Spyman pointed out in another thread:

 

The expansion of the universe is accelerating. Over time it becomes significant at smaller distances.

 

If the magnifying glass was changing density, it could make spatial relations outside the lens appear to be expanding or contracting.

 

No. And astronomers are not so stupid as to be fooled by something as lame as gravitational lensing. Second, notice that you keep invoking more and more magical forms of "gravitational lensing" without actually knowing how it works, in an attempt to force your hypothesis. Gravitational lensing will not give the appearance of an expanding universe unless the astronomer can't do basic math. For one, gravitational lensing will not cause some galaxies to appear to move at different speeds from others, and it certainly will not cause the complex distance/speed relationship that indicates a universe that initially slowed down and later began to accelerate.

 

If a galaxy was contracting, gravitation levels could be rising, which could be steadily increasing the optical-density differential between the interior of the galaxy and the more empty space between galaxies.

 

I'm sorry, but you don't know what you are talking about. You just keep cobbling words together without thinking and I am getting frustrated that you can't be bothered to understand how gravitational lensing actually works, but you continue to insists that for 30 years astronomers have been unable to do math.

 

The speed of light is the maximum speed possible in any medium. So C changes in material media, such as water, but also due to gravitation, which is the cause of gravitational redshift, I beleive.

 

You are wrong, of course. You have not the faintest clue how gravitational redshift works. No, gravity does not change the speed of light, (which is a lower-case "c" btw), it makes photons lose energy causing their frequency to shift toward the red (hence the term "red-shift").

 

Idk, I'm still not convinced that lens-effects couldn't cause some objects to appear to recede faster or slower than others. Remember, I'm not talking about a stable lens but one that is changing shape and density at a variable rate depending on the changing gravitational field relations of the galaxy's constituents.

 

Try for a second to understand the absurdity of what you are suggesting. You are proposing that gravitational lensing does something that it does not do (make light go slower) while constantly changing, in an incredibly fine-tune way so as to make a further way galaxy appear to be receding 10 times faster than another nearby galaxy sitting right next to it on the sky. With billions and billions of galaxies observed, you propose some weird magical gravitational lens with billions and billions of lumps, just exactly located to match the locations of these galaxies, to give the impression of a universe that in earlier times was slowing down, and in more recent times began speeding up, in a way that just happens to fit into a form compatible with Einsteins theory of relativity, which has been tested to an incredible level of precision. In other words, you are proposing that the universe has an incredibly complex and weird set of physical laws, which are finely tuned with the very specific effect of making humans on earth think that the universe actually has a completely different, very precisely measured, set of physical laws.

 

With your line of argument you would be better off saying that the universe appeared last week and that it looks the way it does because God made it look that way.

 

Well, what happens to them then? They continue to be negatively charged while the protons continue to be positively charged, no?

 

Electrons and protons don't lose their charge. That doesn't mean that electrons have anything to do with nuclear fusion. Again, you have no idea what you are talking about, and in your ignorance you keep repeating things that make no sense because you cannot accept it when someone who actually studied the subject tells you that electrons are not relevant for the process of nuclear fusion... Did I mention that I'm frustrated?

 

So you're another person who accepts the calculations without having an explanatory mechanism for how the process actually works outside of the math?

 

Nobody nows everything, and between the two of us, I have gone a lot more deeply into the physical processes than you have, since my field is astrophysics. I bet that I am more familiar with the experimental evidence for particle physics than you are. So don't try to lecture me about understanding physical mechanisms. In this discussion you have shown yourself unwilling to grab a physics textbook to learn anything about how physics works, like how planets stay in orbit, the density of the interstellar medium, the process of nuclear reactions, or the behaviour of gravitational lensing, while I have spent a lot more time than you deserve explaining how all these physical processes work and doing various calculations when appropriate, while you continue to close your mind and insist that whatever half-baked idea just crossed your mind must be correct. It sure must be very easy for you to not feel the burden to prove any of your hypotheses.

 

I suppose the Earth does have a great deal of momentum considering its mass. I suppose I'll have to concede that your idea that the sun will lose mass due to fusion will cause the planets to expand in their orbits and eventually drift off into interstellar space.

 

I did not say that when the sun loses mass it will cause planets to drift into interstellar space. Furthermore, fusion on itself does not cause mass loss. The mass loss is caused by stronger stellar winds during the red giant phase, and the result is that the orbits expand, but not that planets drift off into space. It looks like you haven't actually bothered to read much of the explanations I gave. It looks like I've wasted my time trying to explain science to you. I should spend my time with people who actually came to this forum to learn about science.

 

But then, how else do you measure the mass of a body except by its gravitational effects?

 

You don't measure the mass of almost anything with gravitational lensing. Gravitational lensing is far too weak for that. The way you measure mass depends on the object in question. For planets in the solar system, and for stars in binary systems, you can measure the size and period of some orbits (e.g. the moons of Jupiter allow you to measure Jupiter's mass). Similarly, the rotational speed of galaxies tells you how much mass they have and how it is distributed. You can also derive equations of state for a ball of gas, which allow you to establish a mass-luminosity relationship for stars. Combined with measurements of the mass of the sun, and stars in binary systems, we can effectively deduce the mass of other stars as well. Etc etc.