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View Full Version : Cosmic Homogeneity does not exist across redshifts but only within them.



kmarinas86
2006-May-01, 07:18 PM
It is apparent that that at higher redshifts we see that there was different structure. But we don't see that there is the same structure over there as here. We know that with increasing redshifts we see a devolution of structure. We see hot, fresh, galaxies way at those distances, that existed long ago baking in the "oven" of a hotter, denser universe. We see that the "oven" existed, but we don't see that oven no longer exists - it impossible to see it as it is now given the vast distances, which are billions of light years. When someone supports the cosmological priniciple it is usually within a certain redshift range where they make their observations. Homogeneity appears when taking samples within a range of similar redshifts. But if the samples span, say from a redshift of 1 to a redshift of 1000, there is a experimentally significant difference in forms. We don't see the very distant galaxies as they are now, but we see them as how they used to be over there. However, the "oven", and galaxies similar to those we see at high redshift may still exist over at those high redshifts - again, we have the same problem - we can't prove that the "oven" doesn't exist today and we can't prove that it exists today. The cosmological priniciple is not only unfalsifiable, it is unverifiable (that is to say in the present moment). It is like a vision ahead of the times to assume the truth value of the cosmological prinicple. The cosmological prinicple may be "confirmed" of course, that is, without being verified.

Nereid
2006-May-02, 07:52 AM
I'm not sure just what you would consider 'falsifiable', or 'verifiable' (or, indeed, just what your statement of 'the cosmological prinicple' would include), but if 'in principle' were part of any falsifiability or verifiability criteria (and not just 'using today's technology'), then there is a very simple method by which 'the cosmological prinicple' can be falsified/verified .... take snapshots of the universe, at z = 0, 1, 2, ... 10 and do so for each year over the next trillion years. Compare snapshots.

Svemir
2006-May-02, 12:35 PM
I think KMarina is talking about information barrier. We can't "verify" that the universe far away has the same structure as it has in our vicinity now because we can only see distant past.
Nothing new in that.
As I posted it earlier, the universe might well be contracting right now and if that happens with, let's say speed of light or higher, we will first know that when the darkness hit us. We will not be aware of that that all stars vanished long time ago (some drastic change in homogenity :-))

Nereid
2006-May-02, 07:04 PM
That may be so .... but if so, then what significance does it have, outside philosophy?

I mean, whether the universe behaves according to the cosmological principle, or turns into a mixture of green cheese and invisible pink fairies the instant it ceases to be observable (by us) is beyond the ken of science, isn't it?