# Expanding Universe vs. Shrinking Matter

 P: 17 After reading about the expanding universe, and the balloon analogy, I found myself wondering about some things. Like many in these forums, I found it difficult to get my head around the concepts. At first I wondered, if space is expanding, and the distance between galaxies is increasing, then are the galaxies themselves getting larger, as well as rocks, trees, electrons, and quarks? It seemed to me that this cannot be. If everything was getting larger, then our measuring stick, or idea of how far away things are, would also be growing with the universe, and we would perceive no expansion at all. (I have since found, through another description of the balloon analogy, with "pennies attached to the surface of a balloon" that my surmise was correct... the expanding universe theory holds that the galaxies themselves are not enlarging). Okay, so far so good, but thinking along these lines led to an alternative model. Is this a fair approximation of what is really happening? Has this been discussed thoroughly before? Is there a flaw in the thinking displayed below?: -Imagine the universe is a static hypersphere, not growing or shrinking. -Viewed from this "universal" perspective, all matter, all galaxies, everything down to quarks is shrinking. -At the same time the speed of light, and the speed of all processes is slowing down by the same factor. -Viewed from the perspective of a person on planet earth (or any intelligent being made of matter somewhere in the universe), because our measuring stick is shrinking with us, our concept of what a meter is remains constant relative to ourselves, but the galaxies appear to be receding. The speed of light also appears to be constant, and all mechanical processes proceed at a "normal" rate, giving no evidence to the shrinking of matter relative to the universe. Does this differ in any way from the expanding universe model, other than simply a shift in perspective? Is it mathematically equivalent? Does it simplify things in a way that makes the process more transparent or easier of comprehension? In short, whaddayathink?
Emeritus
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P: 5,583
 Quote by zadignose After reading about the expanding universe, and the balloon analogy, I found myself wondering about some things. Like many in these forums, I found it difficult to get my head around the concepts. At first I wondered, if space is expanding, and the distance between galaxies is increasing, then are the galaxies themselves getting larger, as well as rocks, trees, electrons, and quarks?
Gravitationally bound systems like galaxies expand only very slightly due to cosmological expansion. The effect is much too small to measure: Cooperstock, http://arxiv.org/abs/astro-ph/9803097v1

With the theoretical caveat given below, things like rocks and trees do not expand. Their sizes are fixed by the sizes of their atoms, and the sizes of atoms are fixed by fundamental constants.

Electrons and quarks are, as far as we know, pointlike particles. Since they have zero size, it doesn't make sense to talk about whether they expand.

http://www.lightandmatter.com/html_b...tml#Section8.2
(subsection 8.2.6, Observability of expansion)

Observations can never distinguish between (1) the possibility that the universe is expanding as measured by a fixed meter stick and (2) the possibility that the universe stays the same size while meter sticks are shrinking. These are not different things. They are the same thing described in different words. However, description #1 is much simpler, so it's the one everyone uses. In description #2, fundamental constants would have to be varying in complicated ways in order to cause atoms everywhere to shrink according to a certain rule.
P: 4,782
 Quote by bcrowell With the theoretical caveat given below, things like rocks and trees do not expand. Their sizes are fixed by the sizes of their atoms, and the sizes of atoms are fixed by fundamental constants.
Just to clarify this a little, the sizes of atoms are set by the details of the electromagnetic force and how it interacts with electrons, protons, and neutrons.

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P: 1,376
Expanding Universe vs. Shrinking Matter

 Quote by zadignose -Imagine the universe is a static hypersphere, not growing or shrinking. -Viewed from this "universal" perspective, all matter, all galaxies, everything down to quarks is shrinking. -At the same time the speed of light, and the speed of all processes is slowing down by the same factor. -Viewed from the perspective of a person on planet earth (or any intelligent being made of matter somewhere in the universe), because our measuring stick is shrinking with us, our concept of what a meter is remains constant relative to ourselves, but the galaxies appear to be receding. The speed of light also appears to be constant, and all mechanical processes proceed at a "normal" rate, giving no evidence to the shrinking of matter relative to the universe. Does this differ in any way from the expanding universe model, other than simply a shift in perspective? Is it mathematically equivalent? Does it simplify things in a way that makes the process more transparent or easier of comprehension? In short, whaddayathink?
I am afraid there is no easy answer to this question.
If you change dimension of length then the question is how do you change other related constants.

For example you suggest that speed of light changes as well. But we can keep it constant and change dimension of time instead. That way geometry of space-time acquires some scaling factor in respect to matter but remains the same otherwise.

Anyways I think that locally there might be no difference (but maybe there is - you might get excess energy that you would have to get rid of). Then globally there would be no difference if the rate of change is exactly the same everywhere. If the change is not the same throughout the universe we can talk about some indirect effects.
 P: 1,464 Eddinton first mused over the idea - in one of his publications he states: "The theory of the expanding universe is also the theory of the shrinking atom" This would seem to be doubtful from the standpoiont of what we know about electrically and gravitationally bound systems. If matter were shrinking a precise balancing of the shrink factor would be required for each atomic composite in order to remain undetectable. Things are much easier if space is expanding
P: 4,782
 Quote by yogi Eddinton first mused over the idea - in one of his publications he states: "The theory of the expanding universe is also the theory of the shrinking atom" This would seem to be doubtful from the standpoiont of what we know about electrically and gravitationally bound systems. If matter were shrinking a precise balancing of the shrink factor would be required for each atomic composite in order to remain undetectable. Things are much easier if space is expanding
Well, it's not "doubtful". It's simply another way of looking at the equations. It's not as beautiful a way of looking at the equations, but it should definitely work, as long as you carry everything through properly.
P: 1,464
 Quote by Chalnoth Well, it's not "doubtful". It's simply another way of looking at the equations. It's not as beautiful a way of looking at the equations, but it should definitely work, as long as you carry everything through properly.
How would you determine that an electron would shrink proportionally with a proton - or that a composite that involves both electric and gravitational binding with various interspacing between the elements would shrink uniformly? This requires a lot of supposition to get to a point that we cannot detect whether the universe is expanding or whether quantum entities are shrinking
 Sci Advisor P: 1,132 Given the expansion of space, would a sufficiently large geodesic dome be ripped apart? How big would it have to be before any stress is noticeable due to expansion? Same concept as the balloon analogy but using rings rather than dimes. Does matter impact the expansion with effects other than gravity? Is the expansion fluid, e.g. does it happen at the same rate through space or does it vary locally?
Emeritus
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P: 5,583
 Quote by -Job- Given the expansion of space, would a sufficiently large geodesic dome be ripped apart? How big would it have to be before any stress is noticeable due to expansion?
Some background on why small structures like atoms and solar systems don't expand:
http://www.astro.ucla.edu/~wright/cosmology_faq.html#SS

The reference to the paper by Cooperstock inside the link gives more details. Basically in an object of size r, you get a fictitious force acting on an element of mass m that goes like $m(\ddot{a}/a)r$, where a is the FRW scale factor, and $\ddot{a}/a\sim H_o^2$. For an atom, the force has no cumulative effect, since the atom is a quantum-mechanical state with a well-defined ground state. For a solar system, there is a cumulative effect, but $H_o^2$ is so small that the effect is many orders of magnitude too small to measure. If you could make your geodesic dome big enough, i.e., it would be of cosmological dimensions, then certainly it would be torn apart, because the large r would result in a large force. In an extreme case, you could imagine a closed FRW cosmology in which the dome has the same circumference as the universe itself, and it would definitely be destroyed.
P: 4,782
 Quote by yogi How would you determine that an electron would shrink proportionally with a proton - or that a composite that involves both electric and gravitational binding with various interspacing between the elements would shrink uniformly? This requires a lot of supposition to get to a point that we cannot detect whether the universe is expanding or whether quantum entities are shrinking
As far as we know, electrons are truly point-like particles. So they wouldn't be shrinking. Rather, it's the electromagnetic force which would be changing through time. It would be sort of a gravitational effect on the electromagnetic interaction. There would have to be a similar effect on the strong nuclear force so that atomic nuclei shrink as well, and on the weak force for symmetry reasons.

The real trick would be insuring that these things change in such a way that atomic spectra and nuclear decay rates are left unchanged.
P: 1,464
 Quote by Chalnoth As far as we know, electrons are truly point-like particles. So they wouldn't be shrinking. Rather, it's the electromagnetic force which would be changing through time. It would be sort of a gravitational effect on the electromagnetic interaction. There would have to be a similar effect on the strong nuclear force so that atomic nuclei shrink as well, and on the weak force for symmetry reasons. The real trick would be insuring that these things change in such a way that atomic spectra and nuclear decay rates are left unchanged.
That was sort of my point - although I expressed it with less precision - also I might comment that the electron is only a point in theory.
P: 4,782
 Quote by yogi That was sort of my point - although I expressed it with less precision - also I might comment that the electron is only a point in theory.
We've been looking for smaller substructure of the electron for some time now, without finding any deviation from it being truly point-like. So it's not just a point in theory, but is extremely point-like experimentally. Whether or not this changes further down is difficult to say.
Emeritus