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Author Topic:   What is "the fabric" of space-time?
Calypso
Junior Member (Idle past 4383 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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Adminnemooseus
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Message 2 of 327 (457716)
02-25-2008 12:32 AM


Thread moved here from the Proposed New Topics forum.

  
Organicmachination
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Posts: 105
From: Pullman, WA, USA
Joined: 12-30-2007


Message 3 of 327 (457719)
02-25-2008 12:55 AM
Reply to: Message 1 by Calypso
02-25-2008 12:17 AM


Fabric of Space-Time
The simplest explanation is this:

The three dimensions of space and the one dimension of time are intertwined and form a smooth fabric, what we call the fabric of space-time. Gravitation is caused by the presence of matter on this fabric. Consider a bowling ball on a taught rubber sheet. When the ball is placed on the sheet, the sheet bends downward, and the ball sinks. Now, a coin or another ball dropped on the edge of this hole starts falling inwards. This is how gravity works. Any star or planet or anything bends space-time downwards, and gravity is us falling down that slop to the bottom of the pit.

Was that too confusing? I hope I answered your question.


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Dr Adequate
Member (Idle past 279 days)
Posts: 16112
Joined: 07-20-2006


Message 4 of 327 (457722)
02-25-2008 1:05 AM
Reply to: Message 1 by Calypso
02-25-2008 12:17 AM


It's a metaphor. People are trying to explain spacetime to you as though it was a thing sitting in space (which obviously it isn't) because that's all the analogies there are. What else can we compare it to except some thing? But a thing (anything, any thing) sits in spacetime, and there the analogy breaks down.

What we can compare it to, which is not misleading, is the predictions made by mathematical models, which introduce no ontological claims about the things they're modelling: that is, they tell you how spacetime works without making any claims about how it's like a rubber sheet, etc.


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Calypso
Junior Member (Idle past 4383 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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fallacycop
Member (Idle past 4748 days)
Posts: 692
From: Fortaleza-CE Brazil
Joined: 02-18-2006


Message 6 of 327 (457745)
02-25-2008 5:24 AM
Reply to: Message 5 by Calypso
02-25-2008 2:54 AM


Is there a physical substance there being warped?

No.

Analogies can be dangerous. This analogy with a fabric can help you understand that space is warped by the presence of mass (Actually, it is more complicated then that, and things like momentum and pressure also contribute to the warping of space). But it can also give you the false impression that there must be some sort of physical substance that get warped. It mustn't. To better understand what meant by warping, think about the following questions.

Is the ratio between the circunference and the radius of a circle necessarily always equal to 2pi?

Is the sum of the three angles of a triangle always equal to 180 degrees?

Answer to both: Only if the space is flat!

For instance, we know that the surface of the Earth is not flat, even if we completely neglect mountains and other local features, because the Earth is a sphere.

Now make an equilateral triangle by starting ant the north pole, moving 10 000 kilometers southward all the way to the equator, then move another 10 000 kilometers eastward, and complete the triangle by moving 10 000 kilometers northward.

There you go, your triangle has three 90-degrees-angles for a total of 270 degrees!


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johnfolton 
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Message 7 of 327 (457783)
02-25-2008 2:45 PM


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.

We'll if e=mc2 then you can not travel faster than lights speed however spacetime is expanding faster than light speed even though lights speedlimit is not violated.

They talk of dark matter guess God is not politically correct but something not nothing is believed to be causing nothing to expand faster than light.

P.S. Now if you could travel faster than light could you follow the light all the way back to the source. T=0? If you could travel faster than light would time end going toward the future or would it circle back to T=0?

If string theory is right then space time left to itself might it not circle all the way back to T=0 ? however how is that possible with space time expanding (dark energy ? God) causing the heavens to be stretching?


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cavediver
Member (Idle past 2871 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 8 of 327 (457785)
02-25-2008 2:59 PM
Reply to: Message 1 by Calypso
02-25-2008 12:17 AM


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?

The fabric is reality itself :) There is actually only the fabric and nothing else. Admittedly, the fabric has multiple layers called fields, and it is one particular special layer that is usually referred to as the 'fabric of space-time', and the other layers give rise to what you would call matter and forces. In some ways, these matter and force layers are more simple, and we have a fairly good quantum understanding of these layers. The 'space-time' layer is more tricky, and we have yet to get a good consistent quantum description (although we do have some good ideas.) Our goal in theoretical physics is to have a single simple description of the all of the layers as one unified super-layer - a unified field.

How do these layers give rise to what you would call particles, matter and empty space?

Empty space is easy, the layer is simply flat in that region. You might think of a single particle as a bump in the layer, a point where the layer is raised up with respect to its neighbouring points. So a single electron would be a bump in the electron layer. An entire planet would be a huge extended bump across multiple layers, involving the electron, photon, quark, gluon layers, and several more. These munmps would then induce a bump in the space-time layer.

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?

The 'space-time' layer is called the metric, and it essentially defines a number associated with pairs of points in our layers. We call this number 'distance' and so this metric layer actually gives shape and form to our layers. A bump induced in this layer is essentially changing the distance between points around this bump, and thus 'warping' and 'curving' this shape and form. At the level of General Relativity, we say that mass is telling space-time how to curve. But from the point of view of the layers, bumps in layers rather unsurprisingly cause bumps in other layers.

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...?


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randman 
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Message 9 of 327 (457801)
02-25-2008 4:08 PM
Reply to: Message 8 by cavediver
02-25-2008 2:59 PM


and the other layers give rise to what you would call matter and forces.

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...?

So they have energy but no matter? Can you have potential for work from energy without physical existence (matter)?

Certainly, it contains specific design though, right?

Pure math isn't really a physical science, and yet describes how physical qualities come into being from a non-physical (no matter) state? Isn't that an immaterial design giving rise to the physical aspects of the universe?

Seems like you are saying there is a pre-existing design, which is really the fundamental state of the universe, and derived from this design is a secondary state, matter/material.

Edit to add: the definition of energy from a physics standpoint: does energy need a physical system to be defined as energy? If there is no matter, where is the physical quality of the system to define it as energy, or do we need to revise the way energy is defined?

Edited by randman, : No reason given.


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cavediver
Member (Idle past 2871 days)
Posts: 4129
From: UK
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Message 10 of 327 (457806)
02-25-2008 4:39 PM
Reply to: Message 9 by randman
02-25-2008 4:08 PM


So they have energy but no matter?

Neither - both are concepts that arise from the fields.

Certainly, it contains specific design though, right?

I'm not sure what this means, but I certainly do not see it containing any type of design. Mathematics is many things, but it is not 'designed'...

Seems like you are saying there is a pre-existing design, which is really the fundamental state of the universe, and derived from this design is a secondary state, matter/material.

There is an underlying state, yes, but hardly a design, whatever that is. If anything, I see existence as a necessary, unaviodable state.


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Admin
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Message 11 of 327 (457808)
02-25-2008 4:46 PM
Reply to: Message 9 by randman
02-25-2008 4:08 PM


This thread is not about design.

I thought you might also be drifting off-topic in the Universe Race thread. If there are topics you'd like to discuss for which there are no active threads, please propose new topics over at Proposed New Topics.

No replies to this message, please.


--Percy
EvC Forum Director

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randman 
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Posts: 6367
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Message 12 of 327 (457811)
02-25-2008 5:11 PM
Reply to: Message 10 by cavediver
02-25-2008 4:39 PM


Cavediver, they exist as something, right? Let's go with no energy and no mass, right? But they exist as something since they can be mathematically described, right?

How would you characterize that something? As mathematical principles and design?

Note to admin: if you want to ban me for the word "design", so be it. All I am talking about is they have specific, predictable characteristics. We can use a different word than "design" if that sets off emotional alarm bells, but the doggone thread is about what the fabric of space-time consists of. Just saying it comes from nothing when clearly that nothing, despite having no energy and matter, can be mathematically descibed and has some degree of predictability needs more clarification.

Maybe we use a different word than "design"? I am open to that. It exists as principles which have the ability to give rise to physical things....whatever. The point is not the lingo, but the fact these "principles" have no matter or energy, and yet have the ability to give rise to matter and energy.

Is that really off-topic?


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randman 
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Posts: 6367
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Message 13 of 327 (457812)
02-25-2008 5:14 PM
Reply to: Message 10 by cavediver
02-25-2008 4:39 PM


I'm not sure what this means, but I certainly do not see it containing any type of design. Mathematics is many things, but it is not 'designed'...

Use a different word then. What I am getting at is that whatever this is, it isn't nothing. It's nothing physical, sure. But it does give rise to the physical aspects of the universe, right?

Call it information if you want. Call it X. It doesn't matter because I am just trying to get at what we do know about it. I think we know it's not physical, not matter and energy, but that it is potential.

How would you describe it?


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New Cat's Eye
Inactive Member


Message 14 of 327 (457814)
02-25-2008 5:17 PM
Reply to: Message 12 by randman
02-25-2008 5:11 PM


The point is not the lingo, but the fact these "principles" have no matter or energy, and yet have the ability to give rise to matter and energy.

Your cells have no brain or heart, yet they have the ability to give rise to brains and hearts.

So what?

Haven't you ever heard of emergent properties?

Edited by Catholic Scientist, : typo


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fallacycop
Member (Idle past 4748 days)
Posts: 692
From: Fortaleza-CE Brazil
Joined: 02-18-2006


Message 15 of 327 (457815)
02-25-2008 5:20 PM
Reply to: Message 7 by johnfolton
02-25-2008 2:45 PM


If you only made sense...

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