Is the Red Shift Evidence of an Expanding Universe or an Illusion?

[ape]

I am curious about the red shift that is claimed to demonstrate that the Universe is expanding.

Is there a direction to this expansion?

Have we looked over our shoulder and seen a whole bunch of stars blue shifted and coming fast behind us or is it red in every direction we look?

Are there other explanations for the wide spread red shift we observe?

If the red shift is all around us and the whole universe is expanding away from us does this place us at the center of the Universe?

Is it possible that the red shift is an illusion similar to the illusion that the Earth is flat?

 

[bapowell]

Is there a direction to this expansion?

The universe appears to be expanding away from us in all directions that we look. From our vantage point, this expansion is said to be isotropic (no dependence on direction) and uniform.

If the red shift is all around us and the whole universe is expanding away from us does this place us at the center of the Universe?

Good question! Given the symmetry of the expansion about our reference point, it certainly appears that we occupy a special place in the universe, perhaps even, the very center as you suggest. However, in a universe that expands uniformly and isotropically, every point enjoys this symmetry -- the universe expands uniformly and isotropically away from every point. The best way to visualize this is with the balloon analogy. The inflating balloon is analogous to an expanding universe. If we arbitrarily choose a point on the balloon, we'll find that all the other points on the balloon expand away from this one uniformly and isotropically.

The Copernican Principle states that Earth is not at the center of the universe. In the 20th century, this principle has been supplanted by the more profound notion that nobody is at the center of the universe (i.e. there isn't one.) This paraphrased statement is known as the cosmological principle, and more formally states that the universe (on average) looks the same to all observers.

 

[daumphys]

In a not moving space, let us think about light property.
Is light property always constant, i.e., always independent on time flowing?
Are there any clear evidence of light property constancy without depending on time?
Is light property always constant, no matter how long it go?

 

[ape]

The universe appears to be expanding away from us in all directions that we look. From our vantage point, this expansion is said to be isotropic (no dependence on direction) and uniform.

Good question! Given the symmetry of the expansion about our reference point, it certainly appears that we occupy a special place in the universe, perhaps even, the very center as you suggest. However, in a universe that expands uniformly and isotropically, every point enjoys this symmetry -- the universe expands uniformly and isotropically away from every point. The best way to visualize this is with the balloon analogy. The inflating balloon is analogous to an expanding universe. If we arbitrarily choose a point on the balloon, we'll find that all the other points on the balloon expand away from this one uniformly and isotropically.

If all space is expanding uniformly and isotropically then the space between the Milky Way and Andromeda galaxies is expanding at the same rate as the rest of space which would make the predicted collision between these two galaxies impossible unless the two galaxies are traveling at a rate that is fast enough to overcome the expansion of space some how.

If space is also continuously accelerating would we not see at some point the Andromeda galaxy slow down, pause and reverse its direction? Could we measure its velocity relative to our galaxy, or at least to our position and determine if indeed there is a change in it's velocity? In which case could we then calculate the exact rate at which the universe is expanding?

Is it possible that the red shift is the result of the movement of our galaxy as a whole combined with our movement within the galaxy?

 

[ape]

Is light property always constant, no matter how long it go?

We can assume it is but how can we be sure?

 

[Nabeshin]

If all space is expanding uniformly and isotropically then the space between the Milky Way and Andromeda galaxies is expanding at the same rate as the rest of space which would make the predicted collision between these two galaxies impossible unless the two galaxies are traveling at a rate that is fast enough to overcome the expansion of space some how.

It's not the speed of the two galaxies which will lead to their eventual collision, but the mutual gravity between them. Locally, gravity is strong enough to overcome any large scale expansion of the universe, so on scales of a few Mpc, it doesn't make much sense to consider the universe expanding.

A slightly different way to think about it is when deriving the dynamics of the universe as a whole, i.e its expansion, acceleration, size, etc., we assume that it is completely homogeneous and isotropic. That is, there are no overdensities or underdensities. Clearly, this is false, as galaxies, stars, planets, and humans are all overdensities! So the mathematical solution of the universal expansion does not make any sense when the assumptions of homogeneity and isotropy are not realized.

 

[iRaid]

The expansion also has to do with the entropy, can't remember exactly how, but it does :p

 

[mistergrinch]

Ape the rate of separation between any two points in the universe increases with separation -- it is only significant on cosmological scales (billions of light years). Think of a rubber band held stationary at one end -- the speed points on the band move increases linearly with the distance of the points from the fixed end. If you think of those points as superclusters of galaxies you'll have a pretty good model of the expanding universe.

 

[Borek]

Have we looked over our shoulder and seen a whole bunch of stars blue shifted and coming fast behind us or is it red in every direction we look?

It is red in all directions.

 

[Radrook]

The expansion, if indeed real, will supposedly gradually place most galaxies beyond our detection sometime in the far future and we will be left with only our local galactic cluster of thirty some members to observe. Beyond that all will supposedly be blackness.

Here's an interesting article:
Cosmologists Predict A Static Universe In 3 Trillion Years
http://www.sciencedaily.com/releases/2007/05/070524094126.htm

 

[Feeble Wonk]

"However, in a universe that expands uniformly and isotropically, every point enjoys this symmetry -- the universe expands uniformly and isotropically away from every point. The best way to visualize this is with the balloon analogy. The inflating balloon is analogous to an expanding universe. If we arbitrarily choose a point on the balloon, we'll find that all the other points on the balloon expand away from this one uniformly and isotropically."

I've heard this example many times, yet it still confuses me somewhat. While each of the points on the balloon are moving away from each other without a specific center ON the balloon, the center of the expansion is IN balloon. How should I interpret that?

 

[bapowell]

The balloon example is a 2D analogy of our 3D universe. There is no IN the balloon to speak of. The 2D universe is the surface. Think of the Earth -- it's a 3D sphere but we humans only really experience the 2D surface (modulo flying airplanes and boring holes through it.)

If our universe is indeed closed, then we occupy the 3D surface of spherical topology. Interestingly, there need not exist a 4th dimension for the 4D sphere to 'expand into'. a 4D sphere. The interesting thing is that there need be no 4D sphere: the surface of a 4D sphere can be topologically defined in only 3 dimensions. For example, a torus, which we are accustomed to visualizing in 3D as a donut, can be consistently defined in only 2 dimensions: take a sheet of paper and logically identify opposite edges. So a 2D sheet, together with rules for how the edges should be identified (a topology), can be made to represent a variety of 3D forms.

 

[Feeble Wonk]

The 2D universe is the surface. Think of the Earth -- it's a 3D sphere but we humans only really experience the 2D surface

I appreciate your effort, but I'm still having trouble with the concept. I realize that you're just trying to convey a mental image here, but we obviously are experiencing a very limited 3D portion of the total 3D spherical earth, which is itself an extremely limited portion of the entire 3D universe.
I simply can't understand how you can bend a 1D line into a circle if there is not (at least) a 2D plane for it to exist in. Yes, you can arbitrarily select a circular sample from the plane, define that as your universe, and try to limit your perspective to the single linear dimension of the circle, but the plane must exist to do so. Doesn't it?

 

[ape]

The expansion, if indeed real, will supposedly gradually place most galaxies beyond our detection sometime in the far future and we will be left with only our local galactic cluster of thirty some members to observe. Beyond that all will supposedly be blackness.

Here's an interesting article:
Cosmologists Predict A Static Universe In 3 Trillion Years
http://www.sciencedaily.com/releases/2007/05/070524094126.htm

Thanks for the article, I found the last paragraph to be especially meaningful.

It is hard to imagine that our current understanding of the Universe may be near sighted and not quite accurate. Such a statement does not mean that we have failed to come a long way in our understanding of things, just that no matter how far we are able to go, we will never be able to observe the situation from a truly objective position.

I have personal reservations about our models when they stray too far from the empirical evidence and into speculations built upon speculations. Having come from a mystical/religious background, which relies so much upon a chain of speculations built on a smattering of empirical evidence, I have become throughly skeptical even about the certainty of our best explanations.

I once came across the idea that the truth of our models is not what is important, but what is important is that our models allow us to make accurate predictions regardless of whether or not they are technically true.

Is this idea correct and is it shared by the physics community at large?

 

[Calimero]

If nothing extraordinary (big rip, for example) happens in the future, it is clear that for observers in the far far future universe will look static, and they will have no means to establish its true nature. You can read original paper http://arxiv.org/abs/arxiv:0704.0221" .

 

[bapowell]

I have personal reservations about our models when they stray too far from the empirical evidence and into speculations built upon speculations. Having come from a mystical/religious background, which relies so much upon a chain of speculations built on a smattering of empirical evidence, I have become throughly skeptical even about the certainty of our best explanations.

I think this is a rather cynical view of the current state of cosmology. In science, or in any inductive program for that matter, one must make assumptions and speculations. However, the hope is that with quality empirical data, these assumptions and speculations can be minimized. I'm curious to hear which aspects of the current standard cosmological model you feel are speculations lacking sufficient empirical evidence.

I once came across the idea that the truth of our models is not what is important, but what is important is that our models allow us to make accurate predictions regardless of whether or not they are technically true.

Is this idea correct and is it shared by the physics community at large?

I suppose it depends on the individual. If you are a statistician, then you probably only care whether the model makes accurate predictions. But as a physicist, I like to think that our current models are more than handy statistical representations. I would hope that they reveal something fundamental and true about what our universe is made of and how it has evolved.

 

[marcus]

I once came across the idea that the truth of our models is not what is important, but what is important is that our models allow us to make accurate predictions regardless of whether or not they are technically true.

Is this idea correct and is it shared by the physics community at large?

I suppose it depends on the individual. If you are a statistician, then you probably only care whether the model makes accurate predictions. But as a physicist, I like to think that our current models are more than handy statistical representations. I would hope that they reveal something fundamental and true about what our universe is made of and how it has evolved.

I like this patient truthful commonsense answer. I'll perturb the discussion a little in the hope of contributing a different angle. It may sound a bit wacky:

what is important about a mathematical model?

Models inspire us with new concepts and ideas. We even add new words to our spoken language in an effort to understand models and how they work.

The human mind, its language, evolves. There are no prior fixed boundaries to thought.

One person can say "this model explains nothing, it merely fits the data and makes correct predictions, but it does not say anything true about nature".

He may not have the necessary concepts to recognize the truth which the model holds.

Another person, or the same person later, may tune into the model and be inspired by it.
Or he may be troubled by some puzzle and be forced to invent another model to cure an apparent paradox or conflict.

The human mind, and its ability to understand nature, evolves----as if walking forwards on two legs----the right foot is the mathematical model that fits the data and the left foot is the verbal understanding of what the model "means".

Sometimes one is ahead somethings the other. When we advance the model we do not care what it "means" (and we may not have words to translate what the model grasps for us) we care only that it fits the data. Then we step forward with the other foot and learn from the model a new idea, and then perhaps go ahead with new intuition.

Walking like this, with two legs, is better than trying to hop along on just one foot.

"Raffiniert ist der Herr Gott, aber boshaft ist er nicht."

This is a faith in the evolution of the human mind that goes on two feet. It is the faith that the mathematical models that we construct will not mislead us and fool us. The universe is not malicious although the mathematical regularities may be subtle and elegant, unintuitive at first. Yet the universe is ultimately understandable. The patterns of regularity are hot deceptive (though they might seem mystifying at first when we don't have the adequate words to say them).
http://math.furman.edu/~mwoodard/ascquote.html

This is to conjecture the idea that what is important about our models is that they are part of a process of growth, of "living up" to the universe.

 

[Feeble Wonk]

But as a physicist, I like to think that our current models are more than handy statistical representations. I would hope that they reveal something fundamental and true about what our universe is made of and how it has evolved.

This is essentially the issue I am struggling with. It seems that there is a subtle, but very real, difference in what is being described by the 1D circle, or the 2D torus, and a physical entity of substance... one that "actually" exists. If we are discussing an abstract mathematical representation, I suppose that the 1D circle can be described as such. Yet, is it "really" there in the absence of a second dimension to exist in? Is our universe an actual, physically extant entity, or rather, is it simply the information.