The end of cosmology...?

[Baby Astronaut]

A decade ago astronomers made the revolutionary discovery that the expansion of the universe is speeding up.

 

The quickening expansion will eventually pull galaxies apart faster than light, causing them to drop out of view.

That's the intro key concepts from a Scientific American article titled

The End of Cosmology?

 

The article goes on to explain that most of the universe will disappear from view, and asks "what has the universe already erased?"

 

Surely many here are familiar with this, but I'd like to hear your thoughts on it.

[npts2020]

I dont like the idea of neverending expansion. If the universe is ever expanding, what occupied whatever there was before our universe got there? Is there truly a state of nothingness or is it just our lack of ability to percieve what is in "space" (and is there any difference)? I guess one could concievably create "space" from energy (matter included) to conserve the idea that you cant create something from nothing or destroy something without ending up with the constituent pieces but exactly what is the nature of that so-called space? In my humble non-scientific opinion this problem is tied into where the conjectured majority of the universe lies, or the nature of dark energy. At any rate the time scale you are talking about is many orders of magnitude greater than the estimated current age of universe.

[Baby Astronaut]

What I don't understand is how space is *something* when it is nothingness? If you took away all the energy, and you were the only thing (on a ship) moving in that void, wouldn't you be able to travel anywhere in that nothingness? I know every point would be identical in comparison, but still, wouldn't you be moving through "space"?

 

And because you would be moving, time would also exist.

[Martin]

BabyAstronaut,

I think the key concepts header to a SciAm article like that is not written by scientists---it is written by the editors of the magazine.

 

For that matter, when a scientists submits an article to SciAm it may get substantially rewritten. The first thing you need to do, if you can, is find the original version. In this case it was an article written in 2007 with the same title by the same authors that was published in a professional journal (General Relativity and Gravitation a.k.a. GRG)

 

I read the original article. It's great. I respect Larry Krauss, the lead author with co-author Robert Scherrer. He's a top scientist as well as being a pretty good popular-style writer. Their GRG article is online. I'll get the link. Go there and click on PDF and you get the whole article.

 

http://arxiv.org/abs/0704.0221

The Return of a Static Universe and the End of Cosmology

Lawrence M. Krauss (1,2), Robert J. Scherrer (2) ((1) Case Western Reserve University, (2) Vanderbilt University)

5th prize 2007 Gravity Research Foundation Essay Competition, to appear, GRG October 2007

(Submitted on 2 Apr 2007)

 

Abstract: "We demonstrate that as we extrapolate the current LambdaCDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our 'island universe' will be fundamentally incapable of determining the true nature of the universe, including the existence of the highly dominant vacuum energy, the existence of the CMB, and the primordial origin of light elements. With these pillars of the modern Big Bang gone, this epoch will mark the end of cosmology and the return of a static universe. In this sense, the coordinate system appropriate for future observers will perhaps fittingly resemble the static coordinate system in which the de Sitter universe was first presented."

 

Parts of the article will be too technical, so just skip them. Part will be accessible. At least you are getting what Larry Krauss actually wrote, not what some editor turned it into.

 

================================

 

I have mixed feelings about the SciAm, and the quality and reliability of what you get there. Some articles are carefully written and not misleading---and they can be enormously valuable.

 

I suspect however that some other articles may be just warmed-over sensationalized pot-boilers. SciAm must have to struggle to stay solvent, with competition from Discovery and New Scientist and the science series they put on TV. A lot of which I tend to think is trash. It must be tough. I don't blame them if they don't always do a perfect job.

 

=================================

 

But one of the sentences in that "key concepts" header is pretty embarrassing. Krauss and Scherrer should never have allowed the editors to tack that on to their article! It is very misleading!

 

This sentence will undoubtably confuse a lot of people:

 

The quickening expansion will eventually pull galaxies apart faster than light, causing them to drop out of view.

 

There is too much wrong with that sentence for me to want to criticize it in a systematic way. Instead, what I suggest you do is read a GOOD SciAm cosmology article---the one I have a link for in my sig. The URL starts out astro.princeton.edu.

It is clear and careful and well-illustrated. It won't get you started on the wrong track by carelessly worded statements. (at least I hope not! )

It is by a world-class cosmologist named Charles Lineweaver. I suggest you have a look at it and then come back with questions.

Edited September 10, 2008 by Martin

[npts2020]

It is possible that space is "nothingness" simply from our inability to percieve it. Dont forget that far more of our universe is unknown than known. One of my favorite subjects in this vein is how does gravity or magnetism seemingly work at a distance with nothing but a "field" in between. What is the exact mechanism of that field? Is it instantaneous or does it have a speed like light?

[Gilded]

It is possible that space is "nothingness" simply from our inability to percieve it. Dont forget that far more of our universe is unknown than known. One of my favorite subjects in this vein is how does gravity or magnetism seemingly work at a distance with nothing but a "field" in between. What is the exact mechanism of that field? Is it instantaneous or does it have a speed like light?

 

The mechanism of those fields is rather well understood actually. There are mediating particles, and neither electromagnetic interaction nor gravity is instantaneous. Recently the "speed" of gravity was measured to be around c. And I'd rather not call space "nothingness" as it has various measurable characteristics. Nothingness is a rather abstract human concept.

 

I dont like the idea of neverending expansion. If the universe is ever expanding, what occupied whatever there was before our universe got there?

 

There doesn't need to be anything outside it. A rather good analogy is that the universe is a balloon, and that the perceived 3D space is reduced to two dimensions; the balloon's surface. Let's say there are dots on the balloon; as the balloon expands the dots get separated more and more, just like galaxies are doing according to our observations. The inside or outside of the balloon do not correspond to any physical location. In this model the universe wraps around itself.

[Baby Astronaut]

Wow thanks for the insight, Martin. I hadn't realized their articles submissions were of previously existing articles (but often commercialized for SciAm).

 

I'm reading your link now.

 

OK read the link.

 

I think much confusion from terminology would be avoided with a name change. For example, the Big Puff would be more self explanatory than Big Bang.

 

And redspan would mark itself as being different than redshift. A doppler effect would mean the light is redshifted by the source's movement away from the viewer, where a cosmological expansion would mean the light is redspanned, or stretched, along the way by the increasingly expanding space between the source and the viewer.

 

Now I have some questions from reading the article.

 

1. How can light lose energy from being stretched by space expansion? It would seem the space is sucking up the energy somehow.

 

2a. If the universe were like a balloon, can't we just take a shortcut through the balloon to reach the other side? The diameter would be shorter distance than the circumference.

 

2b. Are there any galaxies/stars in between the the opposite sides of the "balloon" universe? I'd think so, if it were like a raisin muffin expanding.

 

3. If all of space is bathed in the radiation from the cool afterglow of creation, why hasn't that afterglow instantly dispersed long ago? If the universe is really self-contained, I'd imagine that the (microwave background) radiation simply can't escape.

 

4. If space is really self-contained, and you'll appear at your starting point if you traveled in a straight line, isn't this compatible with how the illusion of a ship rising on the ocean horizon is used to explain the Earth's curvature? If you could observe a spaceship far away on the universe's balloon shape, wouldn't you see the craft "rising" out of empty space?

 

5. When they say that distant galaxies are moving away from us at over the speed of light, and vice versa, don't they really mean half that speed? For example, the combined speeds of expansion between us and them add up to the speed faster than light. More precisely, the speed at which expansion moves us away, plus the speed at which expansion moves them away, equals the higher speed.

Edited September 11, 2008 by Baby Astronaut
multiple post merged

[big314mp]

1. Interesting point. Someone will have to explain this for me.

 

2a. That's the general idea behind wormholes. To continue the analogy, it would be like a small hole poked in one side of the balloon, connected by a straw, to a hole on the other side of the balloon. The holes representing black holes, and the straw representing the worm hole.

 

2b. For the balloon example, there is no "inside" the balloon. This is where the analogy falls apart. It breaks down, because the balloon is a 3D structure. You have to consider the balloon analogy as if you were an ant on the surface of the balloon. To an ant, the question of what is "inside" the balloon is nonsensical, as the ant can't perceive the additional dimension of it's universe.

 

3. I can't answer this any better than you already did .

 

4. What you have to consider is that EVERYTHING happens within the plane of the balloons surface. Imagine you are in (I say "in" this time to highlight the fact that you have to ignore the 3D aspect of the balloon for this analogy to work...however don't misinterpret this as being inside the balloon, we are still on the surface) the balloon universe, and you shine a laser pointer off into the distance. To your eye, the laser pointer will go in a perfectly straight line. However, to an outside observer, the laser pointer beam will bend to follow the curve of the balloon (imagine how the prime meridian is a straight line, which still follows the curve of the earth). On Earth, light goes in a straight line independent of the Earth's surface. Thus a ship following the curve of the earth will seem to rise up. If the light were to also follow the curve of the Earth, this effect would not exist.

 

5. You can examine physics from any reference point. Your premise is based on physics calculated at the half way point between our galaxy and another galaxy. It is simpler to just assume we are stationary and calculate the motions of other galaxy's, than it is to say we are moving, and then calculate the motions of other objects based on that moving perspective.

[big314mp]

I drew a picture for #4. The one on the left is the traditional "Earth", where light can leave the surface. The one on the right is the balloon universe, where light is bound to the surface.

[Baby Astronaut]

I'm beginning to understand. Thanks for drawing the pics, big314mp. You even put a figure of me on them

 

About the balloon universe, now that I'm looking at it in better perspective, a few things strike me as very odd.

 

A. If light really does follow the surface, how can we ever tell it's curved? We'd be fooled into thinking the photons arrived from straight on.

 

B. How do we know the light that greets us is on its first voyage around the balloon? It could be on its third or fourth trip around (perhaps the universe expanded slower back during those few earlier voyages).

 

C. Where on the balloon are the oldest galaxies/stars in relation to our cosmic neighborhood?

 

D. The shortcut distance through the balloon is still immense. I'll assume the wormhole travel is supposed to be instantaneous. If so, why cut "through"? Wouldn't it be just as quick to have the wormhole cut across, following the universe's curvature, if wormhole travel is in fact instantaneous?

[Gilded]

Whoops. Silly post deleted.

 

Well, anyways...

 

A. If light really does follow the surface, how can we ever tell it's curved? We'd be fooled into thinking the photons arrived from straight on.

 

I don't think "fooled" is the right word. At least I'd say sailing around the world in an apparently straight line is a worse case of being fooled.

 

B. How do we know the light that greets us is on its first voyage around the balloon? It could be on its third or fourth trip around (perhaps the universe expanded slower back during those few earlier voyages).

 

Actually, I think since certain wrapping CMB patterns haven't been observed it might point to an open universe rather than a closed one like the mentioned wrapping sphere. Then again, it might've just not had the time to do that. But whether the light has traveled "round" the universe should be visible from the wavelength shift.

 

C. Where on the balloon are the oldest galaxies/stars in relation to our cosmic neighborhood?

 

I'm not sure how to pinpoint them on the surface, but it's not like the universe has an exact set of coordinates. Anyway, they're far away from us.

 

D. The shortcut distance through the balloon is still immense. I'll assume the wormhole travel is supposed to be instantaneous. If so, why cut "through"? Wouldn't it be just as quick to have the wormhole cut across, following the universe's curvature, if wormhole travel is in fact instantaneous?

 

It isn't cutting through as much it is folding through. Imagine a stretch of paper representing a section of space. There's an ant at one end and a sugar cube at the other end. For the ant to get to the sugar cube in minimal time it should obviously move to it in a straight line. However, if this paper is folded into a ring so that the ends meet, the ant suddenly finds itself at the sugar cube without having to move at all.

(Of course to actually do that the sugar cube should be glued to the paper. )

Edited September 12, 2008 by Gilded
multiple post merged

[Baby Astronaut]

It isn't cutting through as much it is folding through. Imagine a stretch of paper representing a section of space. There's an ant at one end and a sugar cube at the other end. For the ant to get to the sugar cube in minimal time it should obviously move to it in a straight line. However, if this paper is folded into a ring so that the ends meet, the ant suddenly finds itself at the sugar cube without having to move at all.

 

Here are two problems I find with the folded paper analogy.

• If you did fold space, it would seem you'd also fold a good portion of its surrounding material, such as if you grabbed a point on a blanket and dragged it to another point -- large portions of the blanket will follow along.
  

• Even then, if you were to drag one point to another, you just traveled the distance anyway, so what's the point of going back and cutting through the paper (or blanket)?
  

[big314mp]

• If you did fold space, it would seem you'd also fold a good portion of its surrounding material, such as if you grabbed a point on a blanket and dragged it to another point -- large portions of the blanket will follow along.
  

• Even then, if you were to drag one point to another, you just traveled the distance anyway, so what's the point of going back and cutting through the paper (or blanket)?
  

 

Well, you don't really "drag" the blanket the way you are imagining. The closest I can visualize it is that you have a tangled blanket, and then you are punching holes in it.

 

So, you aren't really "folding" the universe. The folds are already there, as are the holes in the blanket (which are thought to be black holes).

 

This is a bit hard to visualize, but imagine the balloon universe again. If you are on the surface of it (since this is a 2D universe) there is no "above" or "below" the surface of the balloon. Such an point is nonsensical, because the place doesn't exist. Measuring the distance to such an imaginary point is equally nonsensical, as such a distance doesn't exist. Extend the analogy to a path through this "imaginary space", and it is equally nonsensical to speak of the distance that one travels through a wormhole.

 

As Gilded said, when a wormhole is made connecting two points in space, the two points are, quite literally, right next to each other.

[Norman Albers]

We are working toward a synthesis of relativistic analyses of 'spacetime' and the quantum vacuum, which is not nothing!

[npts2020]

The mechanism of those fields is rather well understood actually. There are mediating particles, and neither electromagnetic interaction nor gravity is instantaneous. Recently the "speed" of gravity was measured to be around c.

 

The mechanism might be well understood by someone but that is not me. I will accept this for now but would be interested in how the speed of gravity was figured out.

 

 

And I'd rather not call space "nothingness" as it has various measurable characteristics. Nothingness is a rather abstract human concept.

 

Could space be what is created when a photon or subatomic particle finally "dies" when it loses all of its energy?

 

There doesn't need to be anything outside it. A rather good analogy is that the universe is a balloon, and that the perceived 3D space is reduced to two dimensions; the balloon's surface. Let's say there are dots on the balloon; as the balloon expands the dots get separated more and more, just like galaxies are doing according to our observations. The inside or outside of the balloon do not correspond to any physical location. In this model the universe wraps around itself.

 

I dont like it. You are creating something (space and at a prodigious rate I might add) from nothing (universal acceleration?). While what you say about the spots on the ballon might be true for those spots, it is not true of the entire system. Does the system operate with different rules from the spots? Unfortunately, it is easier to poke holes in a theory than it is to actually craft a valid alternative. That is where I am now on this subject, sorry.

[big314mp]

Could space be what is created when a photon or subatomic particle finally "dies" when it loses all of its energy?

 

Particles don't die, and photons don't lose energy (barring red shift effects). Photons can be absorbed, but that is different.

 

The mechanism might be well understood by someone but that is not me. I will accept this for now but would be interested in how the speed of gravity was figured out.

 

Gilded can probably explain this better than me, but imagine the solar system, using the "rubber sheet" analogy of space time. The sun sits in the middle and creates a depression, and the planets circle the sun. Now let's say the sun vanishes. Einstein calculated that the speed of the resulting "gravitational wave" moves at the speed of light.

 

I dont like it. You are creating something (space and at a prodigious rate I might add) from nothing (universal acceleration?).

 

You can hardly call a vacuum "something". But the idea that the universe has to expand into some space, is merely a limitation of the human mind.

 

While what you say about the spots on the ballon might be true for those spots, it is not true of the entire system. Does the system operate with different rules from the spots?

 

Clarify this please.

[Gilded]

The mechanism might be well understood by someone but that is not me. I will accept this for now but would be interested in how the speed of gravity was figured out.

 

Well actually it isn't a very conclusive measurement, but it is consistent with general relativity predicting gravity to propagate at c.

 

"In September 2002, Sergei Kopeikin and Edward Fomalont announced that they had made an indirect measurement of the speed of gravity, using their data from VLBI measurement of the retarded position of Jupiter on its orbit during Jupiter's transit across the line-of-sight of the bright radio source quasar QSO J0842+1835. Kopeikin and Fomalont concluded that the speed of gravity is between 0.8 and 1.2 times the speed of light, which would be fully consistent with the theoretical prediction of general relativity that the speed of gravity is exactly the same as the speed of light."

 

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

[Norman Albers]

General Relativity starts from and assumes a Lorentz metric form as the basis of spacetime, "far from sources".

[npts2020]

I dont like it. You are creating something (space and at a prodigious rate I might add) from nothing (universal acceleration?).

 

You can hardly call a vacuum "something". But the idea that the universe has to expand into some space, is merely a limitation of the human mind.

 

The expansion of the universe is caused by something (supposedly vestiges of the big bang), where does this energy go? Why have we not observed parts of the universe moving at different speeds, from gravitational or magnetic effects, that are the same distance from us? Is there any such thing as a true vacuum (in other words prove there is no ether)? Does the absence of anything we can detect at present mean that there is nothing there (exactly where is all of the missing univese anyway)?

 

While what you say about the spots on the ballon might be true for those spots, it is not true of the entire system. Does the system operate with different rules from the spots?

 

Clarify this please.

 

See above.

[big314mp]

Ah, thanks for the clarification.

 

I hate to disappoint, but this is moving out of my area of knowledge, so I will address these as best as I can.

 

We don't really know what causes the expansion of the universe, although scientist posit something known as "dark energy" to be behind it. Of course, we know nothing about it, and have no evidence of it.

 

Gravity cannot affect a vacuum, so there is no effect of gravity on the expansion of space. Where gravity plays a role is in holding together things in the universe. The milky way, for example. It is held together by gravity, so there is no observed expansion of the milky way. Galaxies far away from us are to far to be held by our gravity (or us by them) so we move away from each other.

 

Vacuum is kinda hard to describe, as it is a seething mess of quantum particles known as virtual particles. To say "there are no particles at all in this space" implies a little too much knowledge of things, so there are particles that pop in and out of existence in the vacuum.

 

On the issue of the ether, it simply isn't needed. Ether does not show up in any equations of physics, and there are no experiments that show its presence. Therefore, it either doesn't exist, or it does exist and doesn't affect anything, in which case it is irrelevant.

 

Most scientist would say the ether doesn't exist, and justify that position using occam's razor:

 

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

[npts2020]

Thanks for the clarification. I dont claim to have the greatest knowledge of cosmology but the whole idea of a "vaccuum" really bothers me. I have read about virtual particles in a vaccuum but where do they come from? Are they something being created from nothing? I am aware that human knowledge (especially this human) on this subject is rudimentary at best but why is it that most physicists have discarded the idea of some kind of ether, Einstein himself did a lot of work on it I have heard?

[big314mp]

The ether idea was mostly discarded after the michelson-morley series of experiments, where they tried to determine the effect of the ether on two beams of light:

 

http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment

 

This experiment was designed to measure the motion of the ether relative to the earth. No motion was found, so the existence of the ether was put to rest.

 

Virtual particles are a quantum effect stemming from (I will do horrendous injustice to QM here) the notion that you cannot know with certainty that there are no particles in such and such a space. It is equivalent to saying that you know the position and momentum of a particle with certainty. Someone explained it to me as, "If quantum mechanics doesn't forbid it, then it most certainly happens."

 

And yes, these particles are created from nothing, but they must also return to nothing very quickly. The more massive the particle created, the shorter the time it exists.

[Norman Albers]

Now think about and explain the electric permittivity of the vacuum, and its magnetic permeability ( which I consider to be derivative) . Hang in here, folks. This is where theories collide.

Edited September 16, 2008 by Norman Albers

[npts2020]

Thanks for the link. What I wonder most about the Michelson-Morley experiments, is why anyone would think that the ether would have any measurable effect on photons to begin with? I mean, it has been since their time that we have even been able to measure the effects of gravity on them. Imho ether is neither provable nor disprovable with our current state of knowledge, it is inferred from the lack of other explanation of exactly what "space" is. I am aware of the "virtual particles" that are supposed to appear and disappear in so-called empty space, my question is where do they come from (or go to)? Are we violating physical laws temporarily by creating something from nothing? Is the creation/destruction action perfect (no other particles or forces involved before or after) if so how do we even know of their existence? I accept that my view could be completely wrong about this but these questions, plus the fact that a large percentage of the universe has never been directly observed, are the basis of my belief in ether.

[Norman Albers]

I think you state very well our predicaments in theory.