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Author Topic:   Is Infinity Real?
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 46 of 48 (600174)
01-13-2011 4:15 AM
Reply to: Message 45 by Rrhain
01-13-2011 2:05 AM


But a de Sitter universe has no matter.
No, but I have plenty of extensions of de-Sitter that do...
While it certainly seems like we are becoming a de Sitter-style universe due to the expansion of the universe and the dominance of the cosmological constant, we aren't there now.
This isn't relevant. The point is that I have plenty of examples of past infinite space-times that do not reach any point of equilibrium.
But that said, if the universe were infinitely old, why haven't we achieved de Sitter status yet?
I'm not sure what you mean by "de-Sitter status". Yes, under certain behaviours of dark energy, the Universe will approximate de-Sitter behaviour, but that is not the point. I raised de-Sitter, as stressed above, simply to give an example of a past-infinite cosmology that does not approach equilibrium, not because our Universe maybe approaching the *future* state of de-Sitter. If we did live in a de-Sitter-type cosmology, which we probably don't based on evidence, then we would exist at some finite time following the de-Sitter "pinch", the pinch being what we think of as the Big Bang. The bulk of the infinite past would be the collapsing phase of de-Sitter, prior to the pinch.
If there's an infinite amount of energy to be had, where is it?
Distributed over a spatially infinite Universe. You just need to start thinking of densities rather than absolute quantities.
Classic Second Law. There is no perfect system. All processes bleed energy that can never be recovered.
Can never be recovered? There's that equilibrium again that doesn't necessarily exist. I would be careful about trying to use conventional concepts of thermodyanamics in a cosmological setting. Most need careful revision.
Except I've already stated that I do think that infinity does exist.
Yes, I appreciate that. That is why I stressed that my comment was relevant to the topic, rather than our own particular discussion.

This message is a reply to:
 Message 45 by Rrhain, posted 01-13-2011 2:05 AM Rrhain has replied

Replies to this message:
 Message 47 by Rrhain, posted 01-15-2011 1:10 AM cavediver has replied

  
Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 47 of 48 (600529)
01-15-2011 1:10 AM
Reply to: Message 46 by cavediver
01-13-2011 4:15 AM


cavediver responds to me:
quote:
I'm not sure what you mean by "de-Sitter status".
A universe which, for all intents and purposes, is devoid of matter.
quote:
Yes, under certain behaviours of dark energy, the Universe will approximate de-Sitter behaviour, but that is not the point.
Incorrect. That is precisely the point: The universe is expanding...and accelerating at that. Thus, if things keep going the way they are, the universe will be a pretty good approximation of a de Sitter universe: No matter. There will come a point where the only observable universe we will be able to see is the Local Group since we are gravitationally bound. Everything else will have been lost to the expansion of the universe.
If there were an infinite amount of time, why hasn't it happened yet?
Again, that goes back to the concept of a process that somehow manages to kickstart a new instanton. A perfect process that never fails, never loses energy.
quote:
quote:
If there's an infinite amount of energy to be had, where is it?
Distributed over a spatially infinite Universe.
You're misunderstanding my question. I'm referring to this posited process that can somehow create an instanton with enough energy to create a universe. With an infinite amount of time, that requires an infinite amount of energy. But the First Law says that everything has to be somewhere. So where is it? If it is infinitely distributed, how did it manage to get here from everywhere else?

This message is a reply to:
 Message 46 by cavediver, posted 01-13-2011 4:15 AM cavediver has replied

Replies to this message:
 Message 48 by cavediver, posted 01-15-2011 6:19 AM Rrhain has not replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


(1)
Message 48 of 48 (600548)
01-15-2011 6:19 AM
Reply to: Message 47 by Rrhain
01-15-2011 1:10 AM


cd writes:
I'm not sure what you mean by "de-Sitter status".
Rrhain writes:
A universe which, for all intents and purposes, is devoid of matter.
Ok, fair enough. As long as you realise that this is not the defining characteristic of de-Sitter space...
Incorrect.
Jesus, Rrhain, do you really think so? Do you not think for a moment that maybe I know a little bit about this subject and maybe I'm not wrong?
If there were an infinite amount of time, why hasn't it happened yet?
Did you not read my description of de-Sitter space? I would have thought that given you are so comfortable with the term, you would understand it. Read what I said again, go and study de-Sitter space, and hopefully the light-bulb will ping on.
Here's my text again:
cd writes:
If we did live in a de-Sitter-type cosmology, which we probably don't based on evidence, then we would exist at some finite time following the de-Sitter "pinch", the pinch being what we think of as the Big Bang. The bulk of the infinite past would be the collapsing phase of de-Sitter, prior to the pinch.
Before making a fool of yourself by telling me I'm wrong, make sure you understand the above. If you don't know what I mean by the "pinch", you should not be using the term de-Sitter at all, other than in the context of asking questions. And if that goes for de-Sitter, it goes a million times for "instanton". Fucking Wikipedia and pop science articles. Just because they use a technical term doesn't mean that when you use it, you'll magically look knowledgeable.
I'm sat here face-palming, trying to work out how to explain the role of instantons in quantum cosmology to someone who thinks I don't understand something as relatively trivial as de-Sitter space!!!
Screw you guys, I'm going home...
[ABE]not that you deserve it, so it's really for everyone else, but here's an image of what the de-Sitter space-time looks like - time vertical and only one space-dimension shown. Hopefully that will sufficiently illuminate what I'm saying...
Edited by cavediver, : No reason given.
Edited by cavediver, : 'cos no matter how pissed-off I get with incompetent students, I'm still helplessly driven to teach them... grrr...

This message is a reply to:
 Message 47 by Rrhain, posted 01-15-2011 1:10 AM Rrhain has not replied

  
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