Stationary Centre of Universe Defined?

[Ziggurat]

From my perspective there seems to be a “faith” in math required that I don’’t have.

Physicists have faith that the world is logical, quantifiable, and consistent. Can you accept those premises? Because beyond that, there's no faith involved.

General relativity is a mathematical theory, as is the rest of physics: it must be in order to be logical and quantitative. If something follows from the math, then it is a requirement of the theory. No faith is needed. The only way that such a mathematically required result can not match the real world is if one (or more) of the foundational assumptions of the theory is wrong. But it's the theory, not the math, which is to blame in such a case.

But even then, we don't just throw the theory out, because there's a difference between being wrong and being inaccurate. Newtonian mechanics is wrong. But it's also very accurate for a lot of stuff, so as long as we don't work with situations which expose those foundational assumptions to be wrong, then we can rely on its conclusions. General relativity is an enormously successful theory, and it makes extremely accurate predictions which we can and have tested and found to agree with reality. Given those facts, it is not a matter of faith, but rather the simplest logical conclusion, that it is likely accurate even in areas which we cannot directly test, such as for the universe as a whole (because the universe should be consistent). If so, then certain aspects of cosmology become necessary conclusions. It is not ultimately math which we need to have faith in, but the concept of consistency in the universe. The universe could be inconsistent. But I'm willing to assume it is not.

Now, could GR be wrong? Absolutely. It probably is. But the thing about successful physics theories (and right or wrong, GR is without a doubt successful) is that if they're proven wrong, it's usually in a manner which preserves them as excellent approximations over some range of phenomena. Hence, Newtonian mechanics is an excellent low-mass, low-density approximation of the universe. Special relativity extends this approximation to high velocities. General relativity extends this further into high mass densities and strong gravitational fields. When each of these successive theories was formulated, most of the conclusions of previous theories remained essentially valid, at least as close approximations. The same will likely be the case with general relativity: whatever replaces it (if it is ever replaced) will likely leave most of GR's conclusions intact, and hence much of modern cosmology will probably remain correct. It doesn't take faith in math to reach that conclusion: one need only consult the historic record to determine that this is the most likely outcome.

 

[lionking]

Thanks for such a good post zig. Duly nominated.

 

[Marcus]

Yes, great posts, very educational for us lurkers.

 

[sol invictus]

I can accept a “chicken from an egg" universe but as I understand some they say there was a something from nothing creation and expanding space/time is continuously being created from nothing. My brother used to jokingly ask why a chicken mushed-up in a blender doesn’t turn back into an egg.

That touches on a very deep question, which is why the entropy of the universe is increasing. Entropy can be thought of as a measure of disorder (a teenager's room tends to rapidly increase in disorder, and it takes work to put it back in order) or as a measure of likelihood (the teen's possessions, if distributed randomly around the room, are very unlikely to be sorted in the appropriate drawers). That kind of increase in disorder happens spontaneously, and it's why the mushed up chicken doesn't turn back into an egg. It takes work - correctly applied - to make that happen.

We know the universe is getting less ordered with time (its entropy is increasing), and by the same token we know that the very early universe had extremely low entropy. So we can translate the question of why the entropy is increasing into another question - why was the entropy so very low at times near the big bang? There is no satisfactory answer known.

Regardless of whether it was a singularity or not, if it’s expanding now it must have been smaller before. If it expands uniformly the expansion must be always centred relative to the smaller pre-expansion.

Your problem is that you cannot conceive of an expansion that isn't centered somewhere. That's your own limitation, and until you get your head around it you aren't going to understand any of the answers we're giving you.

By the way, even without fancy things like spacetime curvature one can have an expansion with no center. In other words its possible to imagine an explosion taking place in ordinary 3D space which has no center and no edge (although you have to grant me that the explosion involved an infinite amount of stuff). I can explain that if you're interested, it might or might not help.

 

[Towlie]

Thanks for such a good post zig. Duly nominated.

Ditto.

 

[AntiTelharsic]

"Everything starts somewhere, although many physicists disagree."
-- Terry Pratchett, "Hogfather"