Could a contracting Universe create the redshift effect observed by Hubble?

Question

What if we just can’t see far enough and the redshift actually shows the galaxies speeding up towards a gigantic black hole to where everything is converging, repeating a cycle that took place countless times “before” the big bang?

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Even in a contracting Universe, there is a region around the observer where all the galaxies are moving away; the galaxies that are moving towards the observer could be too far to be seen. If we can demonstrate this, we could challenge the conclusion that the Universe is expanding, based on the redshift effect observed in the “nearby” galaxies.

Let’s start with a simpler representation: 1 dimension only (1D). Assume that all the galaxies move along a single line. We could represent an expanding and a contracting Universe as per the images below:

In Situation 1, we have the currently accepted model, where galaxies move away from each other, at increasing speed, which creates the redshift observed by Hubble.

In Situation 2, we assume that in the contracting Universe the galaxies have a speed that is inversely proportional to the distance from the center (as in a sink flow where the particles accelerate towards the drain), galaxies 1 and 3 will display a red shift effect, because they are moving away from each other, while galaxies 4, 5 and 6 will appear with blueshift effect. However, in order to see the blue shifted galaxies it is necessary to see beyond the center of the Universe, which would be not possible either because of the distance or because of the gigantic black hole in the center traps light from galaxies 4, 5 and 6 preventing it from reaching us at galaxy 2.

In fact, assuming that from galaxy 2 we cannot see beyond galaxy 1, it is impossible to distinguish between situation 1 and 2. With this we have demonstrated that for a 1D Universe it is impossible to determine if it is expanding or contracting, simple because we cannot see far enough. What about a 2D space?

Consider two galaxies (1 and 2); consider that they form a angle beta, relative to the center of the universe (assuming that there is one); Consider that galaxy 1 is at the distance r from the center; consider that galaxy 2 is at a fraction of r (say xr) from the center.

We can calculate the distance between galaxy 1 and 2 as follows:

From the equation above we can calculate alfa and from we can calculate d.

We also suppose that the speed along the radius can be calculated with the equation v = c / r, where c is constant.

Therefore we can calculate the position of the two galaxies after a period of time t, and measure the distance d between them to verify if d increases (redshift) of decreases (blueshift).

We can see that no matter what the fraction x is, there is always a minimum value for the angle beta, such that any galaxy within this angle will be moving away from the reference galaxy. Now assume that the universe is so big that we cannot see galaxies beyond beta. In this way, all that we can see is redshifted galaxies!

This means that even for a contracting universe, depending on how far we can see, it is possible to detect only redshifted galaxies. Does not this disprove the theory of expanding universe based on redshift?

Answer 1

Aside from being, I suspect, totally incompatible with GR, the model fails to match observations.

The universe appears to be homogeneous and isotropic. In the model you suggest, Hubble's law would be different depending on which direction you were looking.

In particular, looking away from the black hole, galaxy redshifts would increase to some asymptotic value, whereas looking towards the black hole they would increase to infinity.

If the argument is that the central black hole is so far away that we cannot measure this asymmetry (i.e. well beyond the observable universe, given the homogeneity of the cosmic microwave background - but then does the model have an explanation for the CMB at all?), then the model also needs to explain why galaxies would move in this particular way, since they would not "feel" the influence of the black hole.

Answer 2

For a contracting universe, space would contract as a ratio, and hence even if we could only see a small distance, we would still see blue-shifted galaxies due to the fact that the galaxies further from the hypothetical centre of the universe (see here for why I say hypothetical) would be moving faster than those closer, and hence any two points in space must be moving towards each other. This holds true even in a finite universe, all points appear to contract towards the point of reference, as can be seen in the diagram below.

The distance between Galaxies 1 and 3 and Galaxy 2 is clearly less after contraction than before.

Answer 3

So in this model, all of the observable universe is expanding. It is simply that it is part of a larger universe which is being locally stretched, as part of a an accelerating convergence to a central point.

I think the answer is that we cannot distinguish this model from an expanding universe (assuming the structure of the convergence is very carefully tuned to look like what we see "locally").

On the other hand, it makes no difference as far as the observable universe is concerned, so we have to resort to Occam's razor. The expanding universe is simpler, and arises naturally from our theories of gravity, etc.

Answer 4

A contracting universe is an attractive proposition as it seems to do away with the need for dark energy. Equally a primordial black hole is an attractive proposition as its expansion would seem to indicate that time/events can never be entirely squeezed out of existence.(ie:if time/events ceased to be, there could never be an initial expansion). Both these propositions are currently unproven. A dirty initial expansion seems feasible (ie: one where super massive black holes split from the primordial black hole and seeded the universe, allowing the creation of galaxies which could not themselves have produced black holes of this size in the time available). Obviously we can only observe/photograph what to the observer are present space/ time events (as their light reaches us) which events have taken place previously in the space/time continuum. Presumably a universal gravitational field has always existed within the space time continuum (even inside an event horizon which may have evolved and expanded as the primordial black hole decayed), which will have affected all events and structures in the universe. Cosmic background radiation can perhaps be thought of as the remnant of the original event horizon/expansion now massively red shifted. It is difficult to see how observed red shifts can definitively prove whether the universe is expanding or contracting.