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Author Topic:   What is "the fabric" of space-time?
cavediver
Member (Idle past 2914 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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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


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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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 52 of 327 (458190)
02-27-2008 4:32 PM
Reply to: Message 51 by happy_atheist
02-27-2008 3:10 PM


To the people who actually know what they're talking about here, is any of what I said accurate or is it all way off the mark?

The former :)


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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 54 of 327 (458281)
02-28-2008 3:31 AM
Reply to: Message 53 by IamJoseph
02-27-2008 10:03 PM


Duh! If the universe was infinite, it would not be 15 Billion years old.

Why not? An open or flat (hence infinite neglecting topological compactifications) FRLW universe is no different to a closed (hence finite) FLRW universe from the perspective of age. Our Universe could be any of these three (with varying degrees of evidence), and all would have thei earliest point 13.7 billion years ago.

You have obviously forgotten much of your graduate cosmology class...


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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 59 of 327 (458681)
03-01-2008 3:04 PM
Reply to: Message 56 by randman
03-01-2008 2:14 PM


The reality is that the field is non-physical and immaterial

Rubbish - these words don't even begin to apply. If anything, the fields are the only physical, material element of existence.

hence cavediver's admitting it is "nothing"

and where exactly did I do this?


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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 64 of 327 (458721)
03-01-2008 6:43 PM
Reply to: Message 62 by randman
03-01-2008 6:17 PM


randman writes:

hence cavediver's admitting it is "nothing"

and where exactly did I do this?

randman writes:

How about here?

Neither - both are concepts that arise from the fields.

Or here?

What are these layers/fields made of? They're not made of anything

Hmmm, I think I have to repeat...

randman writes:

hence cavediver's admitting it is "nothing"

and where exactly did I do this?

And please stop crow-barring the word "design" into everything - it is meaningless.

randman writes:

The specific information within the force of gravity is at play.

Do you realise how hilarious this is? It's not that you are desperate to find design in every aspect of the Universe - that wouldn't be too bad. It's that you utterly insist that it is there, and the rest of us are too blind, too stupid, or too desperate to avoid any hint of a creator to see it. How can communication be profitable?

How would you describe it?

I've already stated how I describe it - mathematics.


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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 66 of 327 (458726)
03-01-2008 6:59 PM
Reply to: Message 63 by randman
03-01-2008 6:25 PM


So you admit they have no matter or energy, right?

ADMIT??? I'm not admitting anything. A question was asked and I was explaining.

The ocean has waves - does that mean that the ocean is made of waves?

What's your definition of physical then?

That, that makes up the Universe.


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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 95 of 327 (459071)
03-03-2008 3:35 PM
Reply to: Message 92 by randman
03-03-2008 2:56 PM


Now, are you going to answer the question I posed to you?

Are you saying the particles are connected via a field, or not?

Edit to add for more clarity: you say the particles are part of the field.

1. What field?

2. What does it consist of?

PaulK has a very good understanding of what I was saying - you do not, as is abundantly clear by what I am quoting here.


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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 108 of 327 (459131)
03-04-2008 4:35 AM
Reply to: Message 106 by Silent H
03-03-2008 10:23 PM


Re: the gravity of general relativity
As with the original poster, I (mis?)understood General Relativity (GR) to say that mass tells spacetime how to curve, and spacetime tells mass how to move. That creates an image of mass acting on spacetime, or let's say the "fabric" of spacetime.

Yes, this is a reasonable description of GR. GR treats space-time and matter as two different entities. I have been explaining the unified picture, where GR and matter are both aspects of some super-fundemental master field. It is the search for the consistent physical theory of this unification that is at the heart of much of modern theoretical physics.

I thought the idea was that GR replaced the concept of gravity as a force between objects, with gravity as a force between an object and spacetime.

Yes, this is true. But mass acting on space-time is very different. 'Forces' concern action-at-a-distance. Mass at a point acts on space-time at that point. The wider-area effect on space-time has nothing to do with the mass, but the properties of space-time. In the usual ball-bearing on rubber sheet, the ball creates the displacement in the sheet at the point of contact, but the surrounding depression is a result purely of that local displacement and the elastic properties of the sheet - it is nothing to do with the mass itself.

There has been mention that physicists are seeking a "graviton" which would be the gravitational equivalent of the "photon". This confused me as it seems to inherently dismiss GR's implications for gravity, and reasserts the idea of gravity being a force between two objects. Where have I messed up, or is there a disconnect between gravitons and GR theory?

A graviton is simply the smallest possible fluctuation in space-time, a result of applying standard quantum thinking to GR. In terms of the rubber sheet, it is essentially the quantum of displacement. This not so much brings GR 'down' to the level of force, as brings electromagnetism 'up' from a simple 'force' picture, to the level of a geometric theory. And this must happen as we expect all of the fields (space-time, electromagnetism, strong, weak, matter) to be different aspects of the one unified field.


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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 109 of 327 (459134)
03-04-2008 7:17 AM
Reply to: Message 96 by randman
03-03-2008 3:44 PM


Please, no replies to this message that do not bear directly on the topic. --Admin

Randman, the reason I do not like replying to you is the because of the constant misrepresentation - either of myself or of the ideas I have presented. This becomes very tiresome, especially after two to three years of the same.

Just now you have repeatedly and falsely stated that I described the fields as 'nothing'.

Right here you have declared that

Different thread you did the same thing, insisting everything was deterministic.

when I have done no such thing.

You repeatedly ask me questions that I have already answered, claiming that I have yet to answer!

The questions I asked of you are:

...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?

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?

Still waiting for your response.

No, you are not still waiting. You have been told repeatedly. I would describe 'it' mathematically, and characterise that 'something' as mathematics. That is all there is. If you want another word, then it would certainly not be design. If anything, in my mind, it would be inevitability.

How do you define physical?

Already answered. That that makes up the Universe is 'physical'.

Are you ever going to try reading my answers? Or do you just prefer to claim that I haven't answered them?

Edited by Admin, : Add a moderator request.


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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 135 of 327 (459284)
03-05-2008 4:20 PM
Reply to: Message 115 by Silent H
03-04-2008 1:51 PM


Re: the gravity of general relativity
and that's before we introduce the underwater cavediving aspect

My best ideas have always come while decompressing ;) Thanks for the compliment.

GR replaced gravity (force at distance) with mass effecting another entity space-time, however physicists are now trying to merge both entities (mass and space-time) into specific operations of a singular entity which would be a "master field".

Yes - Wheeler long ago wanted to unify matter with the gravitational field, in a study called geometradynamics. It was compelling, but couldn't fully reproduce the properties of fermions (matter). The extended idea is to use separate metter fields that eventually unify with the gravitational field along with the other gauge (photon, gluon, etc) fields.

If this is correct, then I want to ask if this work is a mathematical exercise, that is to say the creation of the simplest mathematical tool (aka model) possible, or is it attempting to describe the "real" nature of natural phenomena? There is a huge difference between convenience and actual understanding.

Good question :) There has been a rather interesting paradigm shift over the past fifty years. Physics was always concenrned with the modelling of the parameters of physical objects with mathematics. This is the core of Gallilean and Newtonian mechanics, Kinetic Theory, and later with Relativistic Mechanics and Quantum Mechanics. However, as we started to look at Quantum Field Theory, we started to notice that it was no longer the parameters of some physical object that was being described mathematically - it was the object itself. An electron is not some 'ball' that has such and such properties. *only* the properties exist. Once we have decribed the properties mathematically, there is nothing left over to say 'and that's the thing we are modelling'. Contrast this with the mechanics of a ball bearing. It is very difficult to convey just how astounding this is - to reach the bedrock of existence to find that we have run out of 'blobs' to describe.

If it is the latter, how are distinctions made between model and underlying reality, beyond calculations fitting results?

Distinctions are not made, as a distinction in many ways would be unparsimonious - none is required. That's not to say we are at the final level, not by any means. But the levels are now simply layers of intertwined mathematics.

As I understand it, if a mass were to suddenly "appear" (let's say an enormously massive particle falls out of an accelerator experiment), then it effects space-time at its what? Surface? Interior? And then the space-time "field" begins to effect other masses (and massless objects too right?) as its warping spreads out at the speed of light?

And if 2+2=5, how would normal arithmetic work? :D

Mass cannot 'appear'. So I cannot describe how space-time would respond because its occurance demonstrates that what we know of space-time is wrong! Mass is simply a measure of the energy in a volume. But yes, disturbances to space-time, say caused by a binary system, propagate outwards at the speed of light.

Normally gravity is represented as a function of two masses

Not quite - the motion of an object through space is purely dictated by the curvature of that space. That space, however, will be curved by both objects.

For example, we would not discuss em attraction as a result of exchanging photons, but as general field effects?

True, except this becomes very difficult, if not impossible, because of the complexity of the situation - this is non-perturbative, or exact, theory. Much easier is to fourier decompose the field and simply work on individual fourier modes. We can then hopefully build these modes back up again to see the big picture. We have a term for these fourier modes - we call them particles :)

If we cannot find a graviton, would that pose a problem?

Individual gravitons are phenomenally hard to detect - we probably never will. We haven't even managed to detect unambiguously an entire gravitational wave, never mind one tiny quantum of such a wave!

he rubber sheet analogy always worked for me on moving masses, so moving objects would have their motion bent by the distortion, perhaps so great as to circle into the mass creating the distortion.

However, I don't understand what is happening on an object which is not in motion. For example I pick up a stone and then let it go. What is space-time doing that makes the originally motionless stone start moving toward the surface? Why does it keep moving?

Excellent question :) (what was that about stupidity?)

All objects have a 4-velocity, and these 4-velocities all have the same magnitude - c. In free space, if you are not being acted on by any forces, your 4-velocity has components (c,0,0,0) which in loose translation means that you are travelling at the speed of light in the time direction. What we call 'motion' is a rotation of this vector out of the pure time direction, so that there is a (very small) component in the spatial directions. Thus it is now clear why there is a limit to 3-velocity - it is simply a projection of a rotating 4-vector of fixed magnitude. Now, in curved space-time, what you think of as your time direction *here*, may well not appear to be the same direction over *there*. So you may well see someone else 'moving' but as far as they are concerned, they are 'still'. The obvious example of this is someone in orbit watching someone falling radially towards the earth. Both have their 4-velocities pointing purely in the time direction (both are 'weightless', i.e. experiencing no forces), but they have very different perceived motion. Both are simply following unhindered their respectives paths through time. Compare this with standing on the Earth. here you are being continually accelerated vertically, and you can feel the accelartive force on your body via your feet from the surface of the Earth pushing you up, as you try to follow your natural path through time, which actually points slightly inwards, towards the centre of the planet. So if straight up through time actually takes you inwards towards the centre of the Earth, then the surface of the earth must be travelling outwards, from a 4d perspective :)


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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 137 of 327 (459288)
03-05-2008 4:37 PM
Reply to: Message 136 by Percy
03-05-2008 4:28 PM


This just bears repeating in case anyone is falling for some of the nonsense spouted elsewhere in this thread.

When a physicist or cosmologist is speaking for a lay audience he may give way to saying things like, "Entanglement operates outside of space and time," but in such cases he's only referring to the layperson's classical understanding of space and time. Entanglement does not operate outside of space/time. After all, entanglement was predicted by the mathematics of quantum theory, our current most fundamental model of space/time.

Edited by cavediver, : No reason given.


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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 139 of 327 (459296)
03-05-2008 5:27 PM
Reply to: Message 138 by randman
03-05-2008 5:20 PM


It exhibits instant action at a distance regardless of time and space

Oh, so you're an expert on quantum field theory, are you? Obviously not, as this is completely incorrect.

Zeilinger says the process is outside space and time. He's not being superfluous there.

No, he's just talking bollocks to impress his lay-audience. He's obviously suceeding.


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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 141 of 327 (459298)
03-05-2008 5:45 PM
Reply to: Message 140 by randman
03-05-2008 5:34 PM


You show me where in any of Zeilinger's published papers that he states that "Entanglement operates outside of space and time,".

Please keep in mind I have read a number of his papers and discussed some of them here

:laugh:

which if my memory serves me state that QM violates local realism or causality or both

Why would we care that QM breaks causality - it is not a relativistic theory!!! What the f'k do you expect? Why are you not pointing out that Newtonian Theory breaks causality? And who cares about Local Realism? That was abandoned long ago.

The trouble, as ever, is you are so far out of your depth it's not funny. The only reason I bother posting is to ensure that the peanut-gallery isn't being taken in by your ill-informed blathering.


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cavediver
Member (Idle past 2914 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 145 of 327 (459306)
03-05-2008 7:07 PM
Reply to: Message 144 by randman
03-05-2008 6:52 PM


You show me where in any of Zeilinger's published papers that he states that "Entanglement operates outside of space and time,".

If we are to discuss the worldview of what constitutes the quantum field as PaulK mentioned, we should approach it with an understanding that the principle of local realism is not valid.

Randman, quoting the words is very easy. Understanding this is a whole 'nother ball game. Leave it to the professionals. What was it I said in my last post?

cavediver writes:

And who cares about Local Realism? That was abandoned long ago.


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