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A question about time and universe expansion

by Geodesic Worm
Tags: expansion, time, universe
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Geodesic Worm
#1
Aug14-11, 03:36 PM
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I've been looking all over the internet for an answer to this question, and I am yet to find one, so I've decided I'll just have to ask someone. I wasn't sure exactly which forum this thread should go in, but since it involves the expansion of the universe, I figured this would be the best forum for it.

Anyway, could someone, preferably with a good grasp of cosmology explain to me what exactly is meant when it is said that the universe is expanding AND YET we live in a block universe, how can a tenseless universe expand? Wouldn't expansion of the system require time to exist outside the system as opposed to being a feature of the system.

I did assume that the expansion was a referrence to the shape of the universe, in the sense that the further along the time axis you are, the larger the spatial dimensions would be, increasing the potential states for energy and matter to occupy and thus explaining the increase in entropy from low when space was constrained at the big bang to high when space is big and cold (so to speak) and subsequently the apparent arrow of time, etc. However, lately I've gotten the impression from reading up on things that this model isn't the accepted view, so now I'm just lost. Can someone please steer me back on track? Would be appreciated, thanks
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cueball B
#2
Aug16-11, 04:10 AM
P: 9
This is actually a little bit philosofical. You may want to read up on the B theory. The B theory is in short the idea that the future is not less real than the past, just because we know less about it. It does not use tenses, but rather describes events as sooner, before or after or simultaniously. It doesn't mean that nothing happens or things just "freeze". Time is, in such, the forth dimension. Special relativity. So time doesn't have to be outside the system, as you say.

The universe does not simply drift apart. It does so at an accelerated rate. Dark energy is said to fill up the holes in the universe for about 70% and seems to have a great deal of negative pressure.
bapowell
#3
Aug16-11, 12:14 PM
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Quote Quote by Geodesic Worm View Post
Anyway, could someone, preferably with a good grasp of cosmology explain to me what exactly is meant when it is said that the universe is expanding AND YET we live in a block universe, how can a tenseless universe expand?
Where did you hear this terminology: "block universe" and "tenseless"? Neither of these words/phrases is accepted terminology in modern cosmology.

Geodesic Worm
#4
Aug16-11, 12:17 PM
P: 9
A question about time and universe expansion

Thanks for your reply. I get what you're saying, but the thing is, I'm already fairly familiar with the block universe model, and although I'm aware that's more of a philosophical way of looking at the universe than scientific, I was under the impression that most mainstream cosmologists and particle physicists took it to be an accurate representation of the universe, at least based on what we currently know. I'd tend to agree, since most of the arguments against it seem to either be born out of an anti-deterministic desire to maintain freewill, or just plain old arguments from analogy (e.g. the map is not the territory), which whilst poetic and all that, are hardly useful tools for understanding the ontological nature of reality.

My main issue is with the idea that the universe can be both tenseless and yet at the same time be expanding. How would those two ideas be reconciled? Would it be the case that the universe rather than expanding is merely bigger, or perhaps wider, the further one is along the axis of the fourth dimension. And thus when it's said that the expansion is accelerating, wouldn't it be more accurate to say that the angle at which the universe gets wider along the fourth dimension is getting steeper?

If that's not the case then maybe you could tell me where I'm going wrong and help me to visualise it a bit more accurately, thanks again
Geodesic Worm
#5
Aug16-11, 12:19 PM
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Quote Quote by bapowell View Post
Where did you hear this terminology: "block universe" and "tenseless"? Neither of these words/phrases is accepted terminology in modern cosmology.
The terminology is besides the point, as the principle is accepted, regardless of what terminology is used.

And if you're now going to tell me that the principle is not accepted, then all I can say is that scientists need to start being more open about where current research is leading and stop giving mixed messages, it's very off putting to us laymen.
bapowell
#6
Aug16-11, 12:31 PM
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Quote Quote by Geodesic Worm View Post
The terminology is besides the point, as the principle is accepted, regardless of what terminology is used.

And if you're now going to tell me that the principle is not accepted, then all I can say is that scientists need to start being more open about where current research is leading and stop giving mixed messages, it's very off putting to us laymen.
The terminology is not besides the point -- you are using language that is meaningless within the framework of modern cosmology. This is a science forum where we discuss mainstream science. Feel free to indicate what current research you are referring to, and where I might be able to find an authoritative description of the block universe as a proposed model for the physical universe. Mixed messages? I can't answer for that, but there are plenty of resources available in print and on the web that provide information on real science going on in the field of cosmology.
berkeman
#7
Aug16-11, 01:25 PM
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This thread is closed temporarily for Moderation....


EDIT -- re-opened.
berkeman
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Aug16-11, 01:32 PM
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Quote Quote by Geodesic Worm View Post
The terminology is besides the point, as the principle is accepted, regardless of what terminology is used.

And if you're now going to tell me that the principle is not accepted, then all I can say is that scientists need to start being more open about where current research is leading and stop giving mixed messages, it's very off putting to us laymen.
Quote Quote by bapowell View Post
The terminology is not besides the point -- you are using language that is meaningless within the framework of modern cosmology. This is a science forum where we discuss mainstream science. Feel free to indicate what current research you are referring to, and where I might be able to find an authoritative description of the block universe as a proposed model for the physical universe. Mixed messages? I can't answer for that, but there are plenty of resources available in print and on the web that provide information on real science going on in the field of cosmology.
Geodesic, bapowell is the PF Science Advisor who is trying to help you here. Please re-read the Rules link at the top of the page (you agreed to those rules when you joined here). You do indeed need to post links to the terms you are using, and the science we discuss here is mainstream science. You state that the "principle is accepted" -- we will judge that from the links you post.

The PF is a great learning resource. Please post within the rules. Thank you.
Geodesic Worm
#9
Aug16-11, 01:40 PM
P: 9
Quote Quote by berkeman View Post
The PF is a great learning resource.
I beg to differ, it's just another good old boys club, I'm out, bye.

Have fun voting republican.
berkeman
#10
Aug16-11, 01:44 PM
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Quote Quote by Geodesic Worm View Post
I beg to differ, it's just another good old boys club, I'm out, bye.

Have fun voting republican.
Your loss. The rules are the way they are for a reason.
cepheid
#11
Aug16-11, 07:10 PM
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It seems like a shame that we lost a member due to such a drastic failure in communication. He/she thought we were trying to ban certain topics from discussion, when in reality, we were just trying to establish what the heck the topic of discussion was in the first place. Maybe if somebody had said:

We actually don't understand what you mean when you say "block universe" and "tenseless."

or,

We don't really know what you are talking about, even though you seem to be under the impression that we all should. Could you please clarify?"

Then perhaps this thread could have gone somewhere...

EDIT: On the other hand, Geodesic Worm displayed a certain lack of maturity and closed-mindedness, so maybe it wouldn't have helped anyway.
bapowell
#12
Aug16-11, 07:15 PM
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I asked him directly where he heard these phrases. He had ample opportunity to establish a discussion on these topics. He instead chose to be rude and confrontational. The block universe is a philosophical model, and as such, has no place in this forum. There are too many legitimately curious and friendly people on these forums to spend time dealing with people who don't know the difference between science and philosophy, and who are too busy blaming others for the shortcomings in their understanding.
cepheid
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Aug16-11, 07:17 PM
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Quote Quote by bapowell View Post
I asked him directly where he heard these phrases. He had ample opportunity to establish a discussion on these topics. He instead chose to be rude and confrontational. The block universe is a philosophical model, and as such, has no place in this forum. There are too many legitimately curious and friendly people on these forums to spend time dealing with people who don't know the difference between science and philosophy, and who are too busy blaming others for the shortcomings in their understanding.
I didn't know that the block universe was a philosophical model. I thought we were still at the stage of trying to establish what he was referring to, and that he was misinterpreting our request for clarification as a dismissal of his (as yet still undefined) term. So...nevermind.
Chronos
#14
Aug16-11, 10:18 PM
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GW was just spoiling for a philosophical argument and didn't bother to do even the most basic research to correctly phrase whatever 'question' was being attempted. That is a classic 'move the goal posts' strategy. Redefine your terms as the arguments emerge.
ThomasT
#15
Aug16-11, 11:19 PM
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Quote Quote by Chronos View Post
GW was just spoiling for a philosophical argument and didn't bother to do even the most basic research to correctly phrase whatever 'question' was being attempted. That is a classic 'move the goal posts' strategy. Redefine your terms as the arguments emerge.
He posted in the wrong forum -- should have been in GR where they're familiar with the terms "block universe" and "tenseless universe". But I thought his question was clear enough:

Quote Quote by Geodesic Worm
Anyway, could someone, preferably with a good grasp of cosmology explain to me what exactly is meant when it is said that the universe is expanding AND YET we live in a block universe, how can a tenseless universe expand?
It can't. So, if the universe is indeed expanding, then it would be wrong to interpret GR as implying that we live in a block or tenseless universe. (And, yes, interpretations of physical theories are philosophical exercises.)

I'm drawn to threads with the word 'time' in them. I've found that lots of people take it to be a whole lot more mysterious than it needs to be, and I think that that's where the OP was coming from.

Anyway, no big deal. Just too bad that a curious layperson using good syntax and punctuation (they're harder to come by than you might think ) felt the need too leave PF (if that's what happened). One thing I've learned is that one can't have too thin a skin if one is intent on badgering physics professionals with layperson questions. He/she could have clarified matters from the start by simply specifying the meaning of the terms he/she was using. There's probably dozens of threads about a 'block/tenseless' universe in the PF archives. It's certainly at Wiki. And an abstract search at arxiv.org on "block universe" will get a few hits.
Chronos
#16
Aug16-11, 11:49 PM
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The skin of ignorance is thicker than you may imagine. Refusal to accept observational evidence, mathematical rigor or acknowledge widely accepted concepts is symptomatic.
ThomasT
#17
Aug17-11, 01:14 AM
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Quote Quote by Chronos View Post
The skin of ignorance is thicker than you may imagine. Refusal to accept observational evidence, mathematical rigor or acknowledge widely accepted concepts is symptomatic.
I'm not sure what you're referring to wrt this thread. The OP clearly had a problem understanding how a timeless interpretation of GR could be reconciled with our common experience, and the observation that our universe is expanding/evolving. The problem being that there are theoretical physicists and philosophers of science who subscribe to the idea that our experience of time is an illusion. It's a problem of unwarranted reifications of mathematical theories. Depending on one's interpretation, one can get a theory jumping through all sorts of hoops, and then the general public is left wondering what the heck these people are talking about.
IsometricPion
#18
Aug17-11, 01:40 AM
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Quote Quote by Geodesic Worm View Post
My main issue is with the idea that the universe can be both tenseless and yet at the same time be expanding. How would those two ideas be reconciled? Would it be the case that the universe rather than expanding is merely bigger, or perhaps wider, the further one is along the axis of the fourth dimension. And thus when it's said that the expansion is accelerating, wouldn't it be more accurate to say that the angle at which the universe gets wider along the fourth dimension is getting steeper?
So, I suppose the physical content of his questions was something like: Is space-time (as opposed, e.g., only space) expanding? and What is the (local/global) four dimensional geometry of the universe? To which I might answer: "globally, space (alone) is expanding (though quasi-locally time dilation occurs as well)" and "the universe is unbounded (I don't think anything else is mathematically allowed.), so I don't think there is any way one could measure such an angle globally any more than it would make sense to say that the surface of an expanding balloon is making a greater and greater angle with the time axis (i.e., that its rapidity is increasing; which does not make sense because no such concept can be applied directly to space or extended objects, in general). Perhaps if one only considers a finite region of the cosmos your idea would make sense (but in the real world this could be invalid since over small enough scales (10's of millions of light-years or less) the universe may not expand (indeed, we know in some regions it contracts))."


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