http://en.wikipedia.org/wiki/Big_Bang_Theory

Tensor and Van and I began began another discussion in the dark energy thread about the expansion of spacetime. Cougar mentioned it as well. I'm specifically curious about the presumed size of the physical (mass) universe and how that relates to General Relativity and the absolute speed of objects with mass.

As I understand BB theory, there is a presumption of gravitational force (associated with mass in GR) at the moment preceding the singularity. This would seem to suggest the presence of mass, and therefore the presence of the tensor fields of GR. In GR however, nothing with mass can travel faster than light, and in no way could the tensor fields ever "expand" faster than light because objects with mass cannot travel faster than light. I'm therefore very puzzled how the universe can be larger than 27.4 billion light years across if the universe in only 13.7 billion years old. What am I missing that allows any object that contain mass to travel faster than light?

Space between objects expands. This gives the illusion of movement.

__________________
New Orion's Arm Site . The Starlark . Against a Diamond Sky (OA Novella Collection) . OA Flickr set

Define "space" for me in some physically tangible way that relates to GR or QM. how does this expansion affect the expansion of the tensor fields of "spacetime" (as separate from "space")?

27.4 billion light years across

Here's an article by the BA's friend, Robert Roy Britt, that addresses that very question.

Gah! I'll go fix it.

Just an idea, but as far as I know there is no reason that space cannot expand faster than the speed of light. If the big bang created space or if an equivalent event in existing space emerged as a ball of energy without mass, then the superluminal expansion in the first picoseconds could have occurred. After that inflationary epoch, matter could have formed from the energy density.

In this scenario matter would not have to travel faster than the speed of light, and yet would still be evenly distributed across the entire expanding ball after it forms.

I'm very unclear what you are describing when you use the term "space" in terms of "expanding faster than light". If by "space", you are defining some sort of mental concept about a "pure vacuum" devoid of all mass has no speed limit, sure, I'll buy that idea, but I don't see how that idea applies here.

As far as I know, there was never a "time" when "spacetime" (space with particles of mass) did not exist. I say this because the BB theory itself talks about gravitational fields being present throughout the process. "Space" in the sense of a "pure vacuum" may never have existed for all I know. We however are describing the "expansion" of particles with mass, not what can and cannot happen in a "pure vacuum". I really don't understand what you mean when you say "space" is "expanding".

What exactly is expanding if not the mass particles within the tensor field of spacetime?

Is there a mathematical presentation of this idea that you would recommend? I'm having a hard time wrapping my head around the idea, and I'm hoping a mathematical presentation of the idea might answer some of my questions for me.

__________________
The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell

Thanks Tim. You've certainly provided me with a lot of reading material recently.

I'm curious, MITM, why did you start this thread in the ATM section?

As far as I can see, it's a simple question about mainstream physics, well-suited for BAUT's Q&A section (this OP contains no ATM claims, proposals, etc ... as far as I can see).

You've completely lost me I'm afraid ... would you mind explaining what this post of yours has to do with modern (mainstream) cosmology, or GR?

Or, perhaps, you are presenting an ATM idea, dressed up in words that have a slightly-less-than-random relationship with modern physics?

Or maybe you are simply (very) confused about what the concordance model in cosmology (a.k.a. "BB") actually is? Is so, why not start a thread in the Q&A section? Perhaps something like "according to the Big Bang Theory, the universe started with a single point that encapsulates ALL necessary energy to create all matter found in these milions of bilions of galaxies - is this an accurate summary of modern cosmology?" or "according to the Big Bang Theory, is space-time expansion creating matter? or is matter self-creating?"

That's actually a very good question. I suppose I could have started the conversation anywhere. I guess in the back of my mind I suspected that when it came to identifying the actual "cause" of the expansion of "space" (whatever that is), it was going to sound something like:

It is profoundly impossible for the ad hoc "invisible cheeseburger force" to not exist, if we assume the validity of the expansion of space for the simple reason that "invisible cheeseburger forces" are, by definition, the cause of that effect.

I've not had time to really give Tim's first reference a thorough read through, but already I see things headed in that direction. I'll comment more when I've been through the paper, and I have a better idea of how the expansion of "space" (whatever that is) presumably affects real life "spacetime" according to these papers. Are the spaces inside of atoms "expanding" too, or is this a special "peek-a-boo" force that is shy around science labs like DE?

Ok Tim, I need a hand here with a concept/statement that I simply can't make heads or tails of from a physics point of view.

From a QM and GR perspective, I have no idea what they are talking about when they talk about "space" somehow "expanding". Spacetime can "expand" as the particles of mass expand, but the term "space" here has no clear meaning in terms of GR, QM or particle physics. What exactly does that mean? Does the space between subatomic particles expand? Does the earth expand, or does this expansion take place only where we can't test it? How does this author know that the velocity is due to the rate of the expansion of space? Can you define the term "space" here in a way that relates to GR or QM? What is "expanding" exactly?

Mods! I think we need a Food Forum

Can I play the role of Rachael Ray?

They are trying to salvage the "limiting speed" hypothesis of SR theory.

No, I am trying to precisely define what it is that is "expanding" in any physical sense. The term "space" is pretty vague. Does that mean the space inside the atoms are all expanding too?

I am not a cosmologist, so I can only give you the dumbed down version;
yes, the space inside our local group of galaxies is expanding, and the space inside the Earth, and inside atoms; but the expansion is very weak, so cannot overcome the forces which hold those objects together. Gravity, nuclear forces, and so on make sure that these objects do not expand in the same way that the Universe as a whole does.

I beleive that the expansion does actualy inflate atoms, the Earth, and the Local group slightly, so that they are larger than they would be if expansion didn't exist;but I don't think that has been measured (as far as I know). It is an incredibly small expansion on the scale of anything we can directly measure.

__________________
New Orion's Arm Site . The Starlark . Against a Diamond Sky (OA Novella Collection) . OA Flickr set

So what are the particles or fields that are expanding inside this "space" thing, and how would we measure it?

Define "weak" here in some physical way. If it's a "weak" force, how and why would it overcome the tensor fields of "spacetime"?

MITM, can you define what you mean by a "Tensor Field"?

__________________
Some try to tell me, thoughts they cannot defend,... - Moody Blues.

Neptune- The original Dark Matter.

The author feels that this technique of deliberately lying will actually make it easier for you to learn the ideas. - Donald Knuth

No, because that would make physical things get bigger. Some people just need the "expanding space" thing to account for all galaxy speeds of c and above, relative to the earth. This term became popular in the '90s when the high speed galaxies (high redshifts) began to be discovered in large numbers, after we had been told for nearly a hundred years that nothing could exceed c relative to the earth.

Sam5, why don't you create your own thread for your curious interpratations of Relativity?

__________________
Some try to tell me, thoughts they cannot defend,... - Moody Blues.

Neptune- The original Dark Matter.

The author feels that this technique of deliberately lying will actually make it easier for you to learn the ideas. - Donald Knuth

That would be appropriate since it is itself an ATM concept.

__________________
I say there is an invisible elf in my backyard. How do you prove that I am wrong?

Disclaimer: Avatar is not an official NASA image and does not imply any specific interplanetary or interstellar capability.

The Leif Ericson Cruiser

I don't think there is any need to go beyond the common, intuitive understanding that space is what constitutes distance. If here is not there, then something has to lie between them. That something is space. If now is not then, then something has to lie between them. That something is time. And if here & now is not there & then, then something has to lie between them. That something is spacetime. What these things may be, beyond this intuitive grasp that we all have, has been a subject of debate for thousands of years, and the debate goes on even now. See Edward Harrison's discussion of dressed & undressed space, in his excellent book Cosmology: The Science of the Universe, Cambridge University Press, 2000, 2nd ed., chapter 9. A small part of that discussion reads ...

The space of special relativity is "undressed", being nothing more than the basis of flat, unchanging distance. The space of general relativity is dressed, because it is dynamic & changing. This means that in GR the concept of distance is not static; two objects which are at rest, each in its own intertial reference frame, can nevertheless move away from one another. That's what the expansion of space means, at least in the operational sense.

Whether or not the space between subatomic particles expands, or the earth, or solar system or galaxy expand, is entirely dependent on the cosmological model. In the old standard big bang cosmology, the universe banged & then coasted. In that model, the expansion was not associated with any force, so nothing that was bound could expand, not a galaxy cluster, not a galaxy, not a planet & etc. However, the advent of accelerating expansion models has accelerated the confusion over expansion. Cosmological models that include phantom energy as the cause of accelerated expansion can lead to big rip cosmologies in which everything, including the subatomic particles themselves, are ripped apart. Other models continue to maintain bound structures. The current state of observational cosmology is quite unable to constrain the models, so you can delve through the literature and find just about anything.

This may not be the answer you are looking for, but it's a good first crack at it.

__________________
The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell

That nothing could exceed the speed of light relative to Earth was always true of special relativity, but was never true of general relativity.

__________________
The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell

Right, I agree with that.

But I require a definition of "space" that is quantifiably different from "distance". Distance doesn't "expand" on its own accord.

That is sort of a Buddist metaphysical description rather than an actual force/field/particle that I might use to explain the cause of movements of objects in space.

Just to be clear, I'm looking for a description of "space" that is substantively different from "distance". I'm looking for something physical in nature rather than metaphysical in nature so that I can design experiments to "test" the concept.

Sure:

http://en.wikipedia.org/wiki/Tensor_fields