Expanding Universe Illusion Theory

[Spyman]

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

AFAIK, the Heat Death is currently favored by our observations, althought a Big Rip is not entirely ruled out.

 

From my understanding the cosmological constant is used for when the expansion is accelerating at a constant rate leading to not bound systems to drift apart and eventually reach and pass their cosmic horizons, whereas phantom energy causes the expansion to accelerate at an accelerating rate, leading to bound systems being ripped apart.

 

 

"If the acceleration continues indefinitely, the ultimate result will be that galaxies outside the local supercluster will move beyond the cosmic horizon: they will no longer be visible, because their line-of-sight velocity becomes greater than the speed of light. This is not a violation of special relativity, and the effect cannot be used to send a signal between them. (Actually there is no way to even define "relative speed" in a curved spacetime. Relative speed and velocity can only be meaningfully defined in flat spacetime or in sufficiently small (infinitesimal) regions of curved spacetime). Rather, it prevents any communication between them as the objects pass out of contact. The Earth, the Milky Way and the Virgo supercluster, however, would remain virtually undisturbed while the rest of the universe recedes. In this scenario, the local supercluster would ultimately suffer heat death, just as was thought for the flat, matter-dominated universe, before measurements of cosmic acceleration.

 

There are some very speculative ideas about the future of the universe. One suggests that phantom energy causes divergent expansion, which would imply that the effective force of dark energy continues growing until it dominates all other forces in the universe. Under this scenario, dark energy would ultimately tear apart all gravitationally bound structures, including galaxies and solar systems, and eventually overcome the electrical and nuclear forces to tear apart atoms themselves, ending the universe in a "Big Rip"."

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

 

 

"Theories about the end of universe

The fate of the universe is determined by the density of the universe. The preponderance of evidence to date, based on measurements of the rate of expansion and the mass density, favors a universe that will continue to expand indefinitely, resulting in the "big freeze" scenario below. However new understandings of the nature of dark matter also suggest its interactions with mass and gravity demonstrate the possibility of an oscillating universe.

 

Big Freeze or Heat death

The Big Freeze is a scenario under which continued expansion results in a universe that asymptotically approaches absolute zero temperature. It could, in the absence of dark energy, occur only under a flat or hyperbolic geometry. With a positive cosmological constant, it could also occur in a closed universe. This scenario is currently the most commonly accepted theory within the scientific community. A related scenario is Heat death, which states that the universe goes to a state of maximum entropy in which everything is evenly distributed, and there are no gradients — which are needed to sustain information processing, one form of which is life. The Heat Death scenario is compatible with any of the three spatial models, but requires that the universe reach an eventual temperature minimum.

 

Big Rip: Finite Lifespan

In the special case of phantom dark energy, which has even more negative pressure than a simple cosmological constant, the density of dark energy increases with time, causing the rate of acceleration to increase, leading to a steady increase in the Hubble constant. As a result, all material objects in the universe, starting with galaxies and eventually (in a finite time) all forms, no matter how small, will disintegrate into unbound elementary particles and radiation, ripped apart by the phantom energy force and shooting apart from each other. The end state of the universe is a singularity, as the dark energy density and expansion rate becomes infinite. For a possible timeline based on current physical theories, see 1 E19 s and more."

http://en.wikipedia.org/wiki/Ultimate_fate_of_the_Universe#Theories_about_the_end_of_universe

[DanielC]

AFAIK, the Heat Death is currently favored by our observations, althought a Big Rip is not entirely ruled out.

 

From my understanding the cosmological constant is used for when the expansion is accelerating at a constant rate leading to not bound systems to drift apart and eventually reach and pass their cosmic horizons, whereas phantom energy causes the expansion to accelerate at an accelerating rate, leading to bound systems being ripped apart.

 

I'm sure you are right. The end-state of the universe is not my area of astrophysics. I'm more familiar with things like stars, white dwarfs and neutron stars. I want to go into exoplanet research. I know GR, but the things you normally learn when you study GR are mainly the Big Bang and lack holes. I don't think the terms "Heat Death" or "Big Rip" ever came up in class.

 

So let's see, in that case the end of the universe will be a bunch of massive objects flying around in big empty space (planets, white dwarfs, neutron stars, BHs). Eventually the BHs evaporate, but other than that I can't think of anything interesting happening in the universe as it slides toward increasing entropy.

Edited October 31, 2010 by DanielC

[lemur]

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.

Do you think I am talking about gravitational lensing occurring somewhere outside the Milky Way galaxy? I know there are gravitational lensing effects noted that take place in circumscribed areas far from Earth, but I am talking about the possibility of the Milky Way itself creating a gravity-web that has an effect on the appearance of light that reaches it from the outside. How do you think such an effect could be controlled for if everything observed outside the galaxy was taken at face value?

 

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.

Which math? Are you going to "cobble" some up to somehow prove your point?

 

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").

Gravitation can cause redshift along with motion/velocity and universal expansion. Gravity doesn't alter the speed of light, supposedly, to cause the redshit. Rather it compresses the spacetime the waves are traveling through, resulting in frequency compression - wait, that would be blueshift, wouldn't it? Oh well, the point was that gravity can alter the frequency of EM radiation waves.

 

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.

No, I'm just hypothesizing that light might change trajectory in an organized way when it reaches the galactic perimeter. This could, in turn, alter the apparent distance and spatial relations of the objects if the effect was similar to that of light penetrating the surface of water, where you're observing from under water.

 

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.

Did God make light change speed and direction when it goes from one density medium to another?

 

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?

If I accepted what someone told me based on the fact that they had studied, would I be doing science or authoritarian-trust? You may be right, but I need to see the reason to accept it. Excuse me for being critical. All I did was think about the charge-relationship between protons and electrons and hypothesize that if the two were disassociated in a plasma state, the opposing charges would still tend to cause the two types of particles to basically circulate around each other, which could cause some shielding effects, albeit less than when the atoms are completely integrated with coherent electron orbits/clouds. I don't mind being wrong, but you didn't provide real reason, just authority-based claim. I asked what happens to the electrons in the plasma and you haven't answered that yet, as far as I know.

 

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.

Maybe you haven't been out of school long enough to get over the ego trip of who gets to lecture who on what. I am happy for you to lecture me on how astrophysics works, but do not expect me to accept anything and everything you say on the basis of your credentials, whatever those may be. When you provide clear specific reasons why I am wrong, I recognize that. I may not be as learned as you but I'm far from stupid. All I do is provide my reasons for thinking the way I do and look for better reasons to replace them and evolve a higher level of understanding. This does not occur from someone telling me that they have a degree that I don't.

 

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.

No, all you did was tell me I was wrong about the planets eventually falling into the sun. So I revised my hypothesis to them drifting into space. Now you tell me they're going to shift orbit outward but not drift away. So will they stabilize into some permanent recursive orbits then, without falling or drifting?

 

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.

Is there any way to measure mass of a distant object except using Newton's inverse square law? If not, don't you see that the measurement technique itself assumes that the mass of objects is proportional to their distance and velocity from another body? Therefore, if a denser object exerted more gravitation than a less-dense object of the same mass, you would still measure its mass according to its gravitation. You have no other way to measure mass except as a function of gravitation, right? Therefore, you cannot but assume the gravitational characteristics indicate the mass and not the density, correct?

 

 

[DanielC]

Lemur,

 

You have spent the last week or two basically arguing that you can overthrow the last 80 years of astrophysics progress without even bothering to grab a physics book and learn how anything works. Instead of calling you an idiot, I have taken a lot of time out of my astrophysics work to explain to you a lot of elementary physics, like pressure, orbits, electromagnetic force, nuclear burning, and so on. These are all things that I understand very deeply. When I pointed out one area where I am not entirely knowledgeable, you proceeded to insult me, saying that I just take equations on faith, while ignoring the dozen times where you just blindly took a vague physical notion on faith and tried to apply it in an inapplicable context. Btw, I do know the derivation of electron degeneracy pressure, but I can still say that I don't know the subject as deeply as the others. Nobody is an expert on everything.

 

I am very busy doing astrophysics. I've taken some time to come to this forum to help people who want to ask an astrophysicist how something works. I think that the time I've spent with you was wasted.

 

Do you think I am talking about gravitational lensing occurring somewhere outside the Milky Way galaxy?

 

No, I never had that impression. You were proposing that the Milky Way somehow caused a really weird type of gravitational lensing that somehow (1) made things look further way, (2) made things look like they are moving, and above all, (4) did all these things in a finely-tuned way that was direction dependent, causing one galaxy appear to move much faster than one standing right next to it in our field of view, and do this billions and billions of times, in a way that is precisely tuned so as to make us believe that the universe expansion follows a pattern of deceleration, followed by constant expansion, followed by deceleration, in a way that just happens to fit the effects of a gravitational constant. Oh, and lets not forget that this magical gravitational field must also be intelligent enough to make the galaxies that are less evolved, an show less metallicity, and greater star formation, also appear to correspond to the galaxies that are further away and receeding faster.

 

Lastly, let's not forget that seeing galaxies move apart is just ONE piece of evidence that the universe is expanding. There is also the fact that GR (which is well tested) predicts that the universe should be expanding or contracting, and that the cosmic microwave background provides a key piece of evidence for the Big Bang theory. Thus, by proposing that the universe is not actually expanding, you are implying that GR is wrong. Trying to prove that you have a better theory than GR would be a bit of a challenge.

 

Which math?

 

You don't think astronomers use math?

 

Let me show you a very simplified data set, and I'd like you to try to explain it using your magical-gravity theory. You don't have to give me the answer. Just think about it and try to explain it mathematically with pencil and paper:

 

You observe four galaxies, all next to each other. In each one you see a Type Ia supernova with identical light curves. Those supernovae have luminosities of 1.0, 0.25, 0.11 and 0.06, in some appropriate luminosity scale. You use the Doppler shift tof these galaxies to get their speed relative to you. They are 2 km/s, 3.5 km/s, 5 km/s and 6.5 km/s respectively.

 

I'll show you how you could explain this in simple terms:

 

The Type Ia supernovae have identical light curves, so we know that their inherent brightness is the same. So we can use the inverse luminosity square law to find the relative distance of these galaxies:

 

sqrt(1/1.00) = 1.00 D

sqrt(1/0.25) = 2.00 D

sqrt(1/0.11) = 3.01 D

sqrt(1/0.06) = 4.08 D

 

Where D is some unit of distance. So that's how we estimate their distances. Now we look at the radial speeds we got from the redshifts: 2 km/s, 3.5 km/s, 5 km/s and 6.5 km/s. We notice that galaxies farther away seem to move faster. We make this more precise by estimating the relationship between distance and speed:

 

v = 1.5 (km/s)/D

 

This is the equivalent of the Hubble constant in the real universe. Now we combine this with General Relativity, and specifically the Friedmann equations[/b] to determine the expansion of the universe.

 

This simplified example is the most basic bit of cosmology that your theory needs to explain. I have not introduced complications like dark energy. You need to think about how you would explain these observations quantitatively in a universe that works the way you propose.

 

 

No, all you did was tell me I was wrong about the planets eventually falling into the sun.

 

I did much more than that. You just happen to ignore stuff you don't want to hear. I said that there were various effects that were far more important than friction from the interstellar medium, and I spent an inordinate amount of time trying to explain this very elementary concept because you don't want to understand how anything works.

 

Now you tell me they're going to shift orbit outward but not drift away.

 

See? You don't listen. That is not what they said. I said that the sun losing mass will not cause them to drift away. But there are other things in the universe that might. For example, planet-planet interactions can cause planets to be ejected, and so can close encounters with other stars. I think that your problem is that you want a simplistic explanation that considers only one factor and ignores everything else. The universe rarely works that way. The sun losing mass will cause planet orbits to expand. Chaotic gravitational interactions can cause planets to come closer, or be ejected.

 

Is there any way to measure mass of a distant object except using Newton's inverse square law?

 

Yes. You can look at the luminosity of a galaxy to figure out how many stars it has, you can look at the colour of stars, which also gives you an indication of how much mass they have. We also have many tests that confirm General relativity: Pulsar timings, gravitational lensing near the sun, and GPS satellites (which wouldn't work if general relativity was wrong). GR has been confirmed to work to extremely accurate levels of precision, and you can derive Newton's inverse square law as a low-gravity approximation to GR.

 

You have no other way to measure mass except as a function of gravitation, right?

 

Don't you realize that all your arguments are based on ignorance? I'm tired of this. I've spent way too much time being polite to you while you try to convince me that you can overthrow astrophysics without knowing the difference between an object in orbit and a light gas floating by waving your hands in the air and saying that it's all just energy that ultimately came from the Big Bang.

Edited October 31, 2010 by DanielC

[lemur]

You have spent the last week or two basically arguing that you can overthrow the last 80 years of astrophysics progress without even bothering to grab a physics book and learn how anything works. Instead of calling you an idiot, I have taken a lot of time out of my astrophysics work to explain to you a lot of elementary physics, like pressure, orbits, electromagnetic force, nuclear burning, and so on. These are all things that I understand very deeply. When I pointed out one area where I am not entirely knowledgeable, you proceeded to insult me, saying that I just take equations on faith, while ignoring the dozen times where you just blindly took a vague physical notion on faith and tried to apply it in an inapplicable context. Btw, I do know the derivation of electron degeneracy pressure, but I can still say that I don't know the subject as deeply as the others. Nobody is an expert on everything.

 

I am very busy doing astrophysics. I've taken some time to come to this forum to help people who want to ask an astrophysicist how something works. I think that the time I've spent with you was wasted.

You seem to have shifted from discussion-of-topic mode to ego-defense mode. If you want measurable evidence that this is true, count the number of times you used "I," "my," etc. and how you've taken a "who's-right?" attitude toward me, claiming that I am now challenging "80 years of astrophysics" etc. I think what you fail to understand is that orthodoxy is not the best or only approach to exploring knowledge. You seem to have grown irritated with discussion so you've decided to promote orthodoxy, basically telling me to go get the degree you did so I will accept that you are right about everything you say and stop exploring these concepts critically. Sorry, but you could be Moses coming down the mountain with video footage of a talking burning bush and I would still ask you what the ethical logic in the ten commandments is. I just like knowing why and how, not just what and who says so.

 

No, I never had that impression. You were proposing that the Milky Way somehow caused a really weird type of gravitational lensing that somehow (1) made things look further way, (2) made things look like they are moving, and above all, (4) did all these things in a finely-tuned way that was direction dependent, causing one galaxy appear to move much faster than one standing right next to it in our field of view, and do this billions and billions of times, in a way that is precisely tuned so as to make us believe that the universe expansion follows a pattern of deceleration, followed by constant expansion, followed by deceleration, in a way that just happens to fit the effects of a gravitational constant. Oh, and lets not forget that this magical gravitational field must also be intelligent enough to make the galaxies that are less evolved, an show less metallicity, and greater star formation, also appear to correspond to the galaxies that are further away and receeding faster.

Why is it that when you're looking underwater, you don't consider it implausible that objects appear to be different sizes and distances than you would expect if you were viewing them in the air? If a wave is amplifying and distorting the image of one rock and the trough of the wave makes the rock next to it seem smaller and farther away, you don't question how the water so "finely tunes" the distortions it causes. I honestly don't know whether the Milky Way could distort light that is reaching it's edges from outside, but I just don't see it as implausible considering how common optical distortion is in water and basically any other substance where light can pass through relatively transparently while being subject to intensified electromagnetic (and on the galactic scale) gravitation.

 

Just answer one simple question for me. Could gravitation at the galactic scale have similar optical effects as electromagnetism has at the level of water or other transparent substances?

 

Lastly, let's not forget that seeing galaxies move apart is just ONE piece of evidence that the universe is expanding. There is also the fact that GR (which is well tested) predicts that the universe should be expanding or contracting, and that the cosmic microwave background provides a key piece of evidence for the Big Bang theory. Thus, by proposing that the universe is not actually expanding, you are implying that GR is wrong. Trying to prove that you have a better theory than GR would be a bit of a challenge.

Calm down. You don't have to establish the dominance of GR and absolute faith in possible alternative explanations to explore them. The OP just postulated something they wanted to discuss, so I thought why not actually entertain the hypothesis instead of burying it under piles of orthodox reasoning that contradicts it.

 

You don't think astronomers use math?

I have no doubt that you can do math. What I questioned was whether you could recognize when the results you derive from math are an artifact of assumptions inherently built into the formulas and equations. I asked twice whether there was any way to measure the mass of a star or planet except by looking at its gravitation, but got no response. I asked if the measurement of mass was based on the assumptions built into Newton's inverse square law that only takes into account the distance between bodies and you failed to comment. Are you avoiding touching that question for a reason?

 

The Type Ia supernovae have identical light curves, so we know that their inherent brightness is the same. So we can use the inverse luminosity square law to find the relative distance of these galaxies:

Why isn't the light curve affected by doppler shifting? Or is it and you can just tell from the shape of the curve that it is a shifted variation of another curve? I'm glad you have experience with these things because they address questions I've thought about informally, such as why people always seem to apply doppler shifting to visible light, but I never read anyone talk about gamma-rays or x-rays redshifting to the visible spectrum, for example.

 

This simplified example is the most basic bit of cosmology that your theory needs to explain. I have not introduced complications like dark energy. You need to think about how you would explain these observations quantitatively in a universe that works the way you propose.

Well, I really haven't proposed any universal theory of "how the universe works." But to answer your question, I think you would have to start by considering all possible optical effects of gravitation as light passes through a galaxy's worth of matter. The best I can do is to repeat my earlier question about comparing optical effects of water molecules to that of galactic matter.

 

See? You don't listen. That is not what they said. I said that the sun losing mass will not cause them to drift away. But there are other things in the universe that might. For example, planet-planet interactions can cause planets to be ejected, and so can close encounters with other stars. I think that your problem is that you want a simplistic explanation that considers only one factor and ignores everything else. The universe rarely works that way. The sun losing mass will cause planet orbits to expand. Chaotic gravitational interactions can cause planets to come closer, or be ejected.

I did think about all these things, but I thought that the sun's behavior would influence such occurrences.

 

Don't you realize that all your arguments are based on ignorance? I'm tired of this. I've spent way too much time being polite to you while you try to convince me that you can overthrow astrophysics without knowing the difference between an object in orbit and a light gas floating by waving your hands in the air and saying that it's all just energy that ultimately came from the Big Bang.

There you go acting like I'm trying to overthrow a regime and you are the great-defender of that regime. All this is is a forum discussion. Stop inflating it to an epic battle between orthodoxy and infidels.

 

 

 

 

 

[DanielC]

You seem to have shifted from discussion-of-topic mode to ego-defense mode.

 

You started insulting me after I took a lot of time from my work to help you.

 

you've taken a "who's-right?" attitude toward me, claiming that I am now challenging "80 years of astrophysics" etc.

 

But you are, and you don't even seem to realize it. And if you are going to basically claim that modern astrophysics is wrong, you should at least know enough to realize that planets are not held up in space by pressure, and a few other elementary facts about physics. Read a textbook. Then make a coherent argument.

 

and stop exploring these concepts critically.

 

But you are not exploring anything critically. You are taking vague concepts that you heard somewhere on faith, without wanting to know how they work, and using that to develop your hypotheses. Instead of calling you an idiot, I very patiently explained a lot of elementary physics concepts like the fact that pressure is not the reason planets are in orbit. And then you accused me of taking formulas on faith. Don't you realize what you did? I have gone through the derivation of just about every key formula in astrophysics, because I want to understand at a deep level. On the other hand, you have a vague notion of things like pressure, which you take on faith, without knowing how they work. I did not insult you for that, but tried to explain, and in turn you accused me of taking things on faith. Between the two of us, you are the one who takes things on faith. You think you are thinking critically, while you just take vague physical notions on faith as if they were magic. How did you expect me to react? I think I deserve an apology.

 

Why is it that when you're looking underwater, you don't consider it implausible that objects appear to be different sizes and distances than you would expect if you were viewing them in the air?

 

(1) As I've said before, you don't measure distance in astronomy by looking at sizes. (2) Being underwater does not make it look like objects in the air are moving radially away from you at various velocities following a power law.

 

you don't question how the water so "finely tunes" the distortions it causes.

 

But water does *not* finely-tune its distortions to make it look like they follow some other set of physical laws. For example, it does not cause rocks that are geologically younger to look further away, or to look like they are moving faster than rocks that are geologically older. The distortion that water makes looks exactly the way you would expect from refraction. The bending of light that water causes does not discriminate between different types of rock on the sea floor.

 

Think about all the other things we use to tell the age of a galaxy: Young galaxies are bluer because they have more star formation. Young galaxies have a lower portion of heavy elements than old galaxies. Quasars are the brightest objects in the universe, and they only occur at extremely high redshifts. At the earliest universe, the youngest galaxies don't have definitive shapes like the Milky Way, you can see that they are just forming. Now try to imagine how the Milky Way could generate some sort of lensing effect that could discriminate these things to fool us. And then you have to explain why these independent measures of age are correlated (e.g. why stars with the highest star formation also have fewer heavy elements).

 

 

Just answer one simple question for me. Could gravitation at the galactic scale have similar optical effects as electromagnetism has at the level of water or other transparent substances?

 

You'll need to define the words "similar" and "galactic scale". Being inside the Milky Way will not make supernovae look like they follow a power law.

 

You don't have to establish the dominance of GR and absolute faith in possible alternative explanations to explore them.

 

I do not rely on faith, and I don't take GR as the be-all and the end-all. But to claim that it is wrong, you has to provide supporting evidence that is commensurate with the nature of the claim. For example, saying that GR is incomplete because it conflicts with quantum mechanics and it gives infinities inside a black hole is entirely reasonable. But if you were to claim (for example) that gravity doesn't make time dilate, you'd have to explain the results of many experiments that show that it does. And if you are going to claim that the expansion of the universe is not real, you will really have to explain all the experimental data that we have that tells us that it is, from the distance-dependent speed of galaxies, to the cosmic microwave background.

 

 

I asked twice whether there was any way to measure the mass of a star or planet except by looking at its gravitation, but got no response.

 

No response?!!! You asked if we had other ways to measure mass (you didn't say "star or planet") and I told you about the mass-luminosity relationship that we can derive from basic physics, the mass-colour (i.e. effective temperature) relationship, and about using light to count the number of stars in the galaxy. I also told you about tests of GR that do not involve the inverse square law, like tests based on time dilation, and how you can derive Newton's inverse square law from GR.

 

Also, Newton's inverse square law was never an article of faith, even before GR. Astronomical observations taken by Tycho Brahe, later studied by Johannes Kepler, indicated that planets move in elliptical orbits, following Kepler's laws. Then Newtonian gravity was able to explain these observations. Newton showed how you could derive all of Kepler's laws from an inverse square law. Then came GR, which made a whole set of new predictions, such as the precession of the periphelion of Mercury, the bending of light, the existence of white dwarfs, the existence of neutron stars, the expansion of the universe, the cosmic microwave background, and time dilation by gravitational fields. Please listen, this is an important point: These were all predictions. None of these things had been observed before Einstein. The GR equations predicted these things, and when physicists went to look for them, they found them, in exactly the way that GR predicted, to a very high accuracy. This gives us a great deal of confidence that GR is an apt description of gravity.

 

Why isn't the light curve affected by doppler shifting? Or is it and you can just tell from the shape of the curve that it is a shifted variation of another curve?

 

Doppler shift makes light look redder or bluer. The light curve of a Type Ia supernova has nothing to do with colour. A Type Ia SN gets very bright very quickly, and then gradually decays in intensity over a period of about 100 days or so. If you plot the intensity of the light against time, you get a curve with a particular shape. All Type Ia supernovae already have more or less the same luminosity, but by looking at the shape of this curve, you can figure out, within something like 2% error, what the luminosity of the supernova was.

 

Another way to measure distance is using Cepheid variables. This is a type of star that pulsates, so its luminosity goes up and down. The period of pulsation tells you its luminosity. Again, since Doppler shift only makes things bluer or redder, it cannot make the pulsation period look different. Cepheid variables and Type Ia supernovae are known as "standard candles". These are the things we use to measure the distance to far-away galaxies.

 

I'm glad you have experience with these things because they address questions I've thought about informally, such as why people always seem to apply doppler shifting to visible light, but I never read anyone talk about gamma-rays or x-rays redshifting to the visible spectrum, for example.

 

Doppler shift happens to every wavelength. We focus on visible light and radio because those frequencies are easier to observe. Gamma rays and x-rays don't penetrate Earth's atmosphere, so you need space telescopes for those. So you only use those frequencies for things that you really cannot investigate otherwise.

Edited October 31, 2010 by DanielC

[lemur]

But you are not exploring anything critically. You are taking vague concepts that you heard somewhere on faith, without wanting to know how they work, and using that to develop your hypotheses. Instead of calling you an idiot, I very patiently explained a lot of elementary physics concepts like the fact that pressure is not the reason planets are in orbit. And then you accused me of taking formulas on faith. Don't you realize what you did? I have gone through the derivation of just about every key formula in astrophysics, because I want to understand at a deep level. On the other hand, you have a vague notion of things like pressure, which you take on faith, without knowing how they work. I did not insult you for that, but tried to explain, and in turn you accused me of taking things on faith. Between the two of us, you are the one who takes things on faith. You think you are thinking critically, while you just take vague physical notions on faith as if they were magic. How did you expect me to react? I think I deserve an apology.

I will not pretend that I think I'm perfect or that I have expertise in your field. My critical thinking is not epic imo; it's just my approach as opposed to acceptance of any and all orthodoxy. I'm trying to base my learning on reason instead of source-validation. I just explained that so you wouldn't take it so personally. I value your explanations and discussion and I don't see you as mindlessly spouting knowledge you've learned dogmatically. I will apologize for my contribution to this bickering we've gotten into because I don't find it enjoyable or productive. I'm sorry if I haven't been as alert to the nuances of many of your explanations as you would have liked. Remember that I do not have the training that you do, so some things you say might not immediately register with the same level of relevance that you have been trained to be aware of.

 

(1) As I've said before, you don't measure distance in astronomy by looking at sizes. (2) Being underwater does not make it look like objects in the air are moving radially away from you at various velocities following a power law.

I never said that water optics is a perfect parallel. It's just an easily accessible example I could cite to explain what I was getting at. I really don't know how to specify the parameters of gravitational optics from inside a galaxy, but to entertain the logic of the OP, I just hypothesized that it was possible.

 

Think about all the other things we use to tell the age of a galaxy: Young galaxies are bluer because they have more star formation. Young galaxies have a lower portion of heavy elements than old galaxies. Quasars are the brightest objects in the universe, and they only occur at extremely high redshifts. At the earliest universe, the youngest galaxies don't have definitive shapes like the Milky Way, you can see that they are just forming. Now try to imagine how the Milky Way could generate some sort of lensing effect that could discriminate these things to fool us. And then you have to explain why these independent measures of age are correlated (e.g. why stars with the highest star formation also have fewer heavy elements).

The shape argument is the most convincing. Color is suspect because of the possibility of doppler-shift.

 

You'll need to define the words "similar" and "galactic scale". Being inside the Milky Way will not make supernovae look like they follow a power law.

By "galactic scale," I meant that there is a relatively dense array of stars/matter that create a certain "gravitational density" the way many molecules hang together as a gas-cloud or liquid.

 

No response?!!! You asked if we had other ways to measure mass (you didn't say "star or planet") and I told you about the mass-luminosity relationship that we can derive from basic physics, the mass-colour (i.e. effective temperature) relationship, and about using light to count the number of stars in the galaxy. I also told you about tests of GR that do not involve the inverse square law, like tests based on time dilation, and how you can derive Newton's inverse square law from GR.

Instead of throwing a barage of unexplained reasons at me to overwhelm me with a preponderance of knowledge, you would be more successful by choosing a specific mass-estimation method and explaining how it triangulates mass by avoiding the assumption of Newton's inverse square law equation. That way, I could see that the inverse square law mass coincides with some other test, e.g. on involving luminocity - and how. Remember how falsification works because it's very convincing. If you give an example of a case that would falsify the method and show how the test fails, I would see how I was wrong. Right now, I can trust you that I'm wrong, but I can't really be reasonably convinced because you didn't explain it to that level of depth. If you don't have the patience to do that, it's fine. No one says you are required. But then don't expect me to trust what you are saying on faith either, just because you have a stack of textbooks on your shelf.

 

Also, Newton's inverse square law was never an article of faith, even before GR. Astronomical observations taken by Tycho Brahe, later studied by Johannes Kepler, indicated that planets move in elliptical orbits, following Kepler's laws. Then Newtonian gravity was able to explain these observations. Newton showed how you could derive all of Kepler's laws from an inverse square law. Then came GR, which made a whole set of new predictions, such as the precession of the periphelion of Mercury, the bending of light, the existence of white dwarfs, the existence of neutron stars, the expansion of the universe, the cosmic microwave background, and time dilation by gravitational fields. Please listen, this is an important point: These were all predictions. None of these things had been observed before Einstein. The GR equations predicted these things, and when physicists went to look for them, they found them, in exactly the way that GR predicted, to a very high accuracy. This gives us a great deal of confidence that GR is an apt description of gravity.

I still don't see where these observations would fail to confirm the predictions if a less massive and more dense body of matter exerted more gravitation than a less dense body of the same mass. You would simply assume that the denser body had a greater mass if its gravitational behavior approximated that of a more voluminous body with the same mass, no?

 

Doppler shift makes light look redder or bluer. The light curve of a Type Ia supernova has nothing to do with colour. A Type Ia SN gets very bright very quickly, and then gradually decays in intensity over a period of about 100 days or so. If you plot the intensity of the light against time, you get a curve with a particular shape. All Type Ia supernovae already have more or less the same luminosity, but by looking at the shape of this curve, you can figure out, within something like 2% error, what the luminosity of the supernova was.

Based on theoretical methodology, no?

 

Another way to measure distance is using Cepheid variables. This is a type of star that pulsates, so its luminosity goes up and down. The period of pulsation tells you its luminosity. Again, since Doppler shift only makes things bluer or redder, it cannot make the pulsation period look different. Cepheid variables and Type Ia supernovae are known as "standard candles". These are the things we use to measure the distance to far-away galaxies.

Doesn't doppler-shifting of light waves correspond to compression/expansion of the waves that would also correspond to time dilation/compression? If 1000 waves expand slightly to occur over a longer distance, and the speed of the waves remains constant, the 1000 waves will take longer to pass as when they were compressed, right?

 

Doppler shift happens to every wavelength. We focus on visible light and radio because those frequencies are easier to observe. Gamma rays and x-rays don't penetrate Earth's atmosphere, so you need space telescopes for those. So you only use those frequencies for things that you really cannot investigate otherwise.

But why shouldn't gamma rays and x-rays redshift to visible frequencies?

 

 

[Spyman]

Oh well, the point was that gravity can alter the frequency of EM radiation waves.

LOL - Everyone can easily scroll up to your post #23 and read what you actually said:

 

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.

Which are totally wrong on at least three accounts as I told you in my post #24.

 

The decent thing to do would be to admitt your fault instead of twisting words and trying to change what you meant afterwards.