Sparked by this thread.
Is it possible to interpret the data for an expanding universe as evidence for the continual collapse of matter instead? So instead of space getting bigger, we, and everything around us. are getting smaller? Is there any way experimentally to distinguish between these two scenarios?
The amount of redshift we observe in distant galaxies requires a very large relative velocity. This couldn’t be accounted for if things were simply staying in place, but shrinking.
The redshift seems to indicate that the observed speed of expansion is roughly proportional to the distance to the object. This is consistent with all of space expanding uniformly. If it were matter that were shrinking, the red shift effect would presumably depend only on the local properties of the observer. It would then seem that the observed red shift would be roughly invariant to the distance.
If you assume the local properties of the shrinking matter were responsible for the red shift, you could get a distance effect if the rate of shrinkage changed regularly over time so that light coming from further away (and therefore longer ago) had a proportionally larger effect.
As discussed in the linked thread, the redshift of distant galaxies is NOT caused by the Doppler effect, but by the apparent expansion of the intervening vacuum during the transit of the light.
The question is, could this apparent stretching of the wavelengths of light from distant galaxies be caused by a shortening of our rulers here on Earth instead?
I’m not clear on what you mean by “the collapse of matter”. Do you mean that [ol][li]bulk massive bodies are getting closer to each other, []molecular and interatomic forces are getting stronger, causing particles to get closer to each other, or []fundamental particles are getting “smaller” and everything else is scaling down proportionally?[/ol]The the case of the first, we’d see the obvious effect on celestical mechanics; depending on the rate of change, we’d see it in the motion of galaxies in the Local Group, within stars in our own galaxy, or in the orbits of the planets. Even a very tiny change–a fraction of several orders of magnitude–would have dramatic and observable results upon the historical motion of celestial bodies. Since this isn’t the case, we’re pretty confident that the ratios between the forces have remained constant since not long after the breakdown of supersymmetry shortly after the birth of the Universe. [/li]
In the second case, the quantum mechanical effects of stuff getting “closer together” (i.e. the probability of interactions becoming “stronger”) would have dramatic and disasterous effects that would be immediately evident. Ditto for the intermolecular electrical forces. Such changes would have dramatic impacts upon the everyday chemistry of…well, everything, making common reactions occur at different rates, or not at all.
Even in the third case, we have the (presumed) invariance of light; if stuff was merely getting smaller, we wouldn’t see (much) of a redshift, and the frequency of shift wouldn’t vary with distance, as contraction should merely be a constant. Instead, we find that things become increasingly redshifted at greater distances, and at some point disappear entirely at the cosmic event horizon (the boundary of the observable universe).
So, we can be pretty confident that we’re not just stuck in a bad Richard Fleischer movie.
Stranger
I don’t think this is true. In a “shrinking matter” universe, redshift would still vary linearly with transit time from the source. And since light moves at a constant speed, the distance of the source determines the transit time.
Stranger, I mean option #3 from your list.
We would see a redshift because our rulers would be getting steadily shorter.
However … presumably in the “shrinking matter universe” the speed of light would need to constantly change as well otherwise it would seem that light was slowly speeding up.
Hmmm … that I don’t like. I can imagine a universe where matter is constantly collapsing. That could be caused by purely local effects. But if it requires the speed of light everywhere in the universe to change smoothly to match, that suggests a violation of causality.
Perhaps the Universe is expanding to us, but collapsing into something else?
(Please don’t ask me what!)
There was a paper published in a reputable, peer reviewed journal that proposed this very idea back in the eighties (IIRC) by two scientists at Princeton (again, IIRC). They wrote the paper, not as a serious theory, but more as a commentary on the state of modern cosmology and the invention of more and more complicated theories being made to explain our observations. It was too long ago for me to remember exactly what their beef was (I think something about inflation theory set them off), but this paper was basically meant as a parody. The paper was scientifically sound however. It explained how larger atoms would have a smaller change in potential energy for electronic transitions, thus making older light (read as light from far objects) look red shifted.
I still have a copy of this paper filed somewhere in a box in my garage (I cited it in a paper I wrote as an undergrad and I don’t throw that kind of stuff away). I’ll see if I can find it.
The redshift in this hypothetical case would be a constant everywhere, though, from the Moon to Sagittarius and beyond. We see no effective redshit to stars locally, as their relative velocities aren’t anywhere near relativisic speeds. The speed of light would be invariant no matter what size you are or in what direction you’re going. That’s a fundamental premise of Special and General Relativity.
There’s no violation of causality here; relativity says that the speed of light must be invariant (the same for all observers) but doesn’t indicate what the speed should be or how changes in physical constants would propagate through spacetime; indeed, the strong equivlence principle (should it be found to hold) argues that any changes in physical laws should be the same everywhere, instantaneously. This might seem like “spooky action at a distance” (to steal a phrase from quantum mechanics) but it doesn’t contradict relativity or causality. It would, however, have very noticeable effects, both in immediate effect and past history, and we’re pretty certain that the fundamental constants of Nature haven’t changed much, if at all, since the known forces fell out and everything else compactified or slid off into an imaginary direction or whatever you like.
It has been suggested that some of the effects of the inflation of the universe resemble a collapsing singularity in reverse, or one collapsing in some extra “spatial” dimension such that there is no bias or gradient. I don’t think any of these speculations was ever given a firm theoretical basis–aside from thermodynamic issues it’s not clear that there would be a practical, measurable distinction between expanding space and being “burped” out of a black hole in reverse–but it’s an interesting notion anyway.
Stranger
I, for one, welcome our Napoleonic overlords.
The size of “rulers” are affected by the various fundamental forces that hold the constituent particles of the rulers together. One can design a variety of rulers which would be held together by a variety of different forces. For all of them to shrink uniformly would then require that all of the four fundamental forces change strength in lockstep, as well. While this can’t actually be disproved, it’s a lot more complicated than calling what we observe an expansion, so that’s what Ockam tells us to do.
I’m not sure about this. (By which I mean, literally, “I’m not sure.”)
Say there were a simple force which is measured as 1/d, where d is the distance between the centers of two objects. (Say all objects are perfect circles for now.) Now at time 1, say two circles are 5 units of distance away from each other. So the force between them is 1/5. Now, say we look at what happens later at time 2, when either:
A. The distance between them has doubled due to expanding space, or
B. The size of the two circles has shrunk by half, due to shrinking objects.
In case A, the distance will now be (measured as) 10, since the “rulers” used by inhabitants of the two circles (didn’t I mention them before?) will not have changed size, but the distance between them has.
In case B, the distance will still be (measured as) 10, since the distance has not changed, but the rulers have shrunk by half.
The force involved, then, comes out “the same” either way. The inhabitants will still say, no matter whether A or B was the case, that the force is to be measured as 1/d. The inhabitants have no way to tell whether A or B was the one that happened, and as far as I can tell from this example, it appears they have no “okham’s razor” type reasons to select one over the other, either. They have no reason to claim in either case that any force has changed.
Well, that’s what it looks like to me, having just thought about it for a second. Maybe a few more seconds will change my mind…
-FrL-