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Author Topic:   What is "the fabric" of space-time?
Calypso
Junior Member (Idle past 4426 days)
Posts: 28
Joined: 06-05-2006


Message 1 of 327 (457714)
02-25-2008 12:17 AM


I hear a term being thrown around that I don't fully understand called the fabric of space-time. For example when giving an explanation of gravitation it is said that this is caused by the curvature of space-time and that gravitation is the acceleration on a body by way of it falling into something with mass, given that mass tends to curve, or warp this fabric of space.

My question is, what exactly is this 'fabric' we call spacetime? Isn't space supposedly empty? Isn't it near close to a perfect vacuum? If it is empty, what then is the fabric of space? Thanks for taking the time to answer this question.

Edited by Adminnemooseus, : Changed topic title from "A question about space-time" to "What is "the fabric" of space-time?". Also changed a couple of "spacetime" to "space-time" while I was at it.

Edited by Adminnemooseus, : Remember to actually make topic title change.


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Calypso
Junior Member (Idle past 4426 days)
Posts: 28
Joined: 06-05-2006


Message 5 of 327 (457738)
02-25-2008 2:54 AM


Thanks for replying, and no your posts are not confusing at all.

My question isn't so much as to how the analogy applies to the real world, as in how the rubber sheet analogy is used to describe the warping of space, as it is what space is.

In other words, when we say space is warped, what is the substance being warped if space is the lack of any matter in the area? What physically is the rubber sheet analogous to? Is there a physical substance there being warped?


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Calypso
Junior Member (Idle past 4426 days)
Posts: 28
Joined: 06-05-2006


Message 23 of 327 (457847)
02-25-2008 7:50 PM
Reply to: Message 8 by cavediver
02-25-2008 2:59 PM


What are these layers/fields made of? They're not made of anything - they are the underlying reality - everything else is made from, or is an aspect of, these fields. However, they are very familiar - they seem to be objects that we know very well from pure mathematics. Now why should that be...?

Hmm you lost me there I think. Objects that we know from mathematics? Is not mathematics just the language we use to describe what we see out in the universe? So I would think we know these objects from mathematics because we invented mathematics to describe what we see happening in the real world. Correct me if I'm wrong.

Are you asking why they fit a mathematical model so well? Did we not come up with that mathematical model to fit our observations rather than the other way around? Or did I misunderstand what you meant by that question? If so please expound on it if you could? It intrigues me and probably because I think I do not understand it, or what you meant by it.

Also when you said "They're not made of anything - they are the underlying reality - everything else is made from" My question to that would be so mass is warping nothing? How can you warp nothing? I'm having a hard time understanding this concept. I would think if there is nothing there, then there is nothing to be warped or deformed. As far as I see it, mass is warping something is it not?


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Calypso
Junior Member (Idle past 4426 days)
Posts: 28
Joined: 06-05-2006


Message 27 of 327 (457881)
02-26-2008 1:41 AM
Reply to: Message 25 by Chiroptera
02-25-2008 9:09 PM


To be more precise, space-time is a manifold - that is, it is a four dimensional object that has a certain shape. The fact that the shape isn't completely flat is what we call "warped". This "warping" of space-time -- the fact that in places it is very much not flat -- is what we experience as "mass".

Mass doesn't warp space-time. Rather, mass is the warps in space-time.

I've heard it said like this: Mass tells space how to curve, space tells mass how to move,

Or something like that. I'm paraphrasing but this would mean mass does warp space. So is this not correct?


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Calypso
Junior Member (Idle past 4426 days)
Posts: 28
Joined: 06-05-2006


Message 47 of 327 (458060)
02-27-2008 1:16 AM
Reply to: Message 46 by Adminnemooseus
02-26-2008 10:02 PM


Re: Contact with the topic theme has been pretty rare
Well I'd like to take this time to thank the posters that answered the original question for giving it a go at what may seem like a simple topic on the surface but is more complex and less understood than it may seem.

I still feel a bit confused as to why some call this quantum field "nothing". Perhaps that is because it is nothing like anything else we know of?

I feel that if a mass is affecting this quantum field, and that the field in turn affects mass sitting in it and energy propagating through it, then it must be something right?

So far I'm picturing this quantum field, metric, space-time continuum, or whatever its called as something like an EM wave. Where you have this standing wave, and if you want you can modulate it (perturb it, send a gravity wave through it) and it will travel at the speed of light to affect other matter and energy within it. The difference of course being that the EM wave affects things electromagnetically and not gravitationally. Does this sound right? Make sense?

Although I see a problem with it already that the quantum field does not contain any energy and the EM field does. But other than that does it make sense to think of it like that?

Oh also I'd like to add that the way I see it, if it really were nothing, and I mean nothing at all, then why should any object affect another? For example I'm picturing a fictitious universe without this property, where it would seem to me one mass would not affect the other. There would be nothing to warp, so there would essentially be no gravity. Does this make sense?

In our universe, the fabric of space-time that gives rise to gravity is something isn't it? Sure it may have no mass, no energy, no matter, but it does have some property to it which is being warped, and also propagates gravitational waves upon it, thereby perturbing everything in it. Yes?

Edited by Calypso, : No reason given.

Edited by Calypso, : changed something to make it clearer to understand


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Calypso
Junior Member (Idle past 4426 days)
Posts: 28
Joined: 06-05-2006


Message 49 of 327 (458066)
02-27-2008 2:53 AM
Reply to: Message 48 by randman
02-27-2008 2:23 AM


Just saying it does is not an explanation on what the non-physical is. Moreover, the idea that physical things stem from non-physical states is doggone revolutionary whether you admit it or not.

I agree it is revolutionary. Even if it weren't so, or few else agreed, it's still new to me so it's at least revolutionary to me. That is if it is even correct at all!

I ask this because now what about dark energy? Isn't dark energy an intrinsic quality of space that gives rise to the expansion of the universe? Isn't dark energy the energy that pulls the universe apart, and isn't it pervasive throughout the universe?

According to an article in wikipedia:

"The simplest explanation for dark energy is that it is simply the "cost of having space": that is, a volume of space has some intrinsic, fundamental energy. This is the cosmological constant, sometimes called Lambda (hence Lambda-CDM model)..."

Couldn't this mean the fabric of space does indeed have energy? How do we know it doesn't have any energy? What makes it not possible for it to have energy? And wouldn't it be odd to be the only field we've seen to have no energy and yet propagate it throughout? Can a field with no energy even do so? Propagate energy through it?

Edited by Calypso, : typo

Edited by Calypso, : had to change something to make better sense


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