Expanding matter?

[infamous]

You just violated your restriction on the discussion:

If there's no multiverse, the two alternatives are still either a closed or infinite universe. In either case, I didn't feel the need to muddy the water by bringing up the multiverse option. I'm having trouble understanding why you feel that I've violated the discussion. I just wanted to limit the discussion to these two posibilities to establish what I felt was the difference between space and nothingness.

 

If there's no "multiverse" there is no *outside*.

Indeed, and in the absence of an outside, I believe it would be a fair statement to call it 'nothing'. The only point I'm trying to make is that nothingness and space have very little in common. And I believe we agree on this point..................................Infy

[Buffy]

If there's no multiverse, the two alternatives are still either a closed or infinite universe. I'm having trouble understanding why you feel that I've violated the discussion.

Because in my vocabulary these two statements are not equivalent:

• If the universe is closed there is nothing outside.
  
• If the universe is closed there is no outside.
  

Methinks you prefer the former, and I prefer the latter. So no, we don't agree. I'd say that even if your view were "right" we have no way to define what it is or what properties it has any more than we would multiverses or whatever else more complex could be "outside." Most cosmologists favor the notion of "there is no outside" for simplicity.

I just wanted to limit the discussion to these two posibilities to establish what I felt was the difference between space and nothingness.

Cool, but I think this is off on a tangent. To wit, can we for a moment assume that there is an infinite universe. If so, what then is your definition of "nothing" or in that case is it impossible for nothing to exist?

 

I'd argue that the distinction between "space" and "nothing" has nothing to do with whether the universe is closed or open or infinite (and note the last two are not the same thing!). I think we need to define these terms in the absolute or they really do make things more complicated because they have conditional definitions that can jump back and forth between meanings in an unpredictable manner. If there really are two concepts, make up two words otherwise you'll just confuse people...

The only point I'm trying to make is that nothingness and space have very little in common. And I believe we agree on this point...

Yep! Space is a dimension that has mostly nothing in it! But I'm convinced nothing is the absence of any matter, and I don't know what you define it as!

 

The absence of absence,

Buffy

[infamous]

Because in my vocabulary these two statements are not equivalent:

• If the universe is closed there is nothing outside.
  
• If the universe is closed there is no outside.

OK, I see the point you're making. In the case of nothing outside, we would need to accept that space of some sort would exist to accomodate a possible something. In the case of no outside, not even space would exist. So with no space outside to compare with the space inside, the question of a difference between the two makes no sense.

 

 

 

I'd argue that the distinction between "space" and "nothing" has nothing to do with whether the universe is closed or open or infinite

Agreed, now that I understand what scientists mean when they describe the universe as closed, there is NO outside.

 

 

 

 

 

I think we need to define these terms in the absolute or they really do make things more complicated because they have conditional definitions that can jump back and forth between meanings in an unpredictable manner.

Truly, so much of understanding is arrived at thru unit of thought. Until we define words and concepts the same way, misunderstanding is inevitable.

 

 

 

 

 

Yep! Space is a dimension that has mostly nothing in it! But I'm convinced nothing is the absence of any matter, and I don't know what you define it as!

Actually, I visualize space as a volume created by an energy field. I can easily visualize space without the neccessity or presence of matter but not without the presence of an energy field so in that respect, I don't view space as empty or as you define it, "a dimension that has mostly nothing in it". I see space profuse with energy, in fact, my own personal view is that space is created by an energy field and matter is a secondary result of a localized orbital energy flux.

 

..............................Infy

[niin]

But this is *exactly* why I put quotes around the word "momentum": its *apparent* not *actual* relative motion.

So you are saying that the apparent expansion is not real motion and we are not actually moving away from everything faster and faster?

 

This analogy is imperfect because it allows you to keep thinking about space as some sort of physical object that we're physically attached to, and space is really just the "distance between two objects."

That distance is increasing because the whole universe is expanding and everything moves along with that expansion because it always has.

I can think about space as non-physical nothingness, so i don't think the analogy is bad.

If it is just a distance between objects, how can you say the space is expanding. Is it not then the Distance that is getting larger?

Does it not seem more logical to say, that the objects are accelerating and space is not expanding between us.

 

:Only if you and your friend were standing right next to each other, holding hands! Because you're really close, the expansion does not affect you that much--you're too close for its effects to be very measurable--and gravity--holding hands--can completely overpower it. Stand far enough away from your friend and she and the flags will all move away from you at a rate proportional to their distance from you...

What if we are not holding hands (no gravity) and there is no black energy. Would we still move away from each other? At what speed? Accelerating?

 

The reason its counter-intuitive is that nothing here on earth that we can experience is "expansion" so its just plain weird, which makes it easy to say its illogical. But its quite logical once you get the definitions and seems to work exactly like we expect it to out there in the universe.

Well i don't rely on intuition, so that should not affect the discussion.

It is only weird if you believe in it without understanding it.

It seems illogical to me. Maybe it would help if you talked about the definitions.

[Buffy]

So you are saying that the apparent expansion is not real motion and we are not actually moving away from everything faster and faster?

This is the fine distinction "moving away" is translating what we see in to our common experience: If something is getting smaller, we translate this into our common experience of "its moving because its got some energy applied to it, or we're moving for the same reason." But what's going on here is expansion of space. In BOTH cases, *yes* the distance between us and the remote galaxy is increasing, but in this case its *not* "motion imparted by a force" like you would experience say, passing someone in a car. According to Einstein, whether it is expansion or motion under application of force or Harry Potter's wand, its all going to look like motion, and the real distance will increase.

 

Now the reason we know its expansion and not motion under force is that everything from every point in the universe is moving away from everything else. As I described previously if it was force applied by an "explosion" there would be an apparent center that we could identify via triangulation: things at equivalent distances would not all be moving away from us at exactly the same rate. This is the difference that you can percieve that distinguishes expansion from motion.

 

Now note, you're still trying to translate this into motion:

If it is just a distance between objects, how can you say the space is expanding. Is it not then the Distance that is getting larger?

Does it not seem more logical to say, that the objects are accelerating and space is not expanding between us.

"Logical" yes, but only because expansion is so strange. But as I just explained, in order to reconcile what we actually observe--that everything in every direction is receding in *exact* proportion to its distance--it turns out there are only two possible explanations:

• There was a traditional explosion imparting force that is pushing all these objects, AND our little planet *just happens* to be located at the exact center of that explosion, or
  
• it's expansion
  

Think of the odds of the first option being correct, and you see why expansion has become popular!

What if we are not holding hands (no gravity) and there is no black energy. Would we still move away from each other? At what speed? Accelerating?

The expansion could be halted and reversed by gravity. It's the dark energy that's kept it from slowing and stopping and is apparently the cause of the accellerating increase in distances that we are measuring.

 

Hope this clears up some more, but keep asking questions....

 

Like magic only logical,

Buffy

[niin]

Does it not seem more logical to say, that the objects are accelerating and space is not expanding between us.

"Logical" yes, but only because expansion is so strange. But as I just explained, in order to reconcile what we actually observe--that everything in every direction is receding in *exact* proportion to its distance--it turns out there are only two possible explanations:

• There was a traditional explosion imparting force that is pushing all these objects, AND our little planet *just happens* to be located at the exact center of that explosion, or
  
• it's expansion
  

Think of the odds of the first option being correct, and you see why expansion has become popular! :computerkeys:

Only two possible explanations?

What if everything had a repulsive force that correlate with distance. That could explain it?

Actually is that not what black energy is?

 

The expansion could be halted and reversed by gravity. It's the dark energy that's kept it from slowing and stopping and is apparently the cause of the accelerating increase in distances that we are measuring.

I said, what if there was no gravity and no dark matter, but the universe was still expanding. Would the expanding still make everything move apart? Would it go faster and faster?

[Buffy]

Only two possible explanations?

Of the one's we know that are directly relevant here. There are some theories that say that the appearance of increasing distance is an optical illusion (see the thread 3123) but these don't have a lot of supporters, and since they posit no relative movement, thus they'd claim this entire thread was a fantasy! :)

What if everything had a repulsive force that correlate with distance. That could explain it? Actually is that not what black energy is?

That's exactly what Dark Energy is, although its not that "everything has a repulsive force" its that Dark Energy appears to be distributed evenly (or pretty close) throughout the universe.

 

But it wouldn't explain "everything" because unlike the expansion, it is an application of energy, and it battles with gravity which overcomes it.

I said, what if there was no gravity and no dark matter, but the universe was still expanding. Would the expanding still make everything move apart? Would it go faster and faster?

If there was no gravity (dark matter is just matter we can't see, and both the dark and "light" kind create gravity fields), then the Expansion would no longer be slowed and the Dark Energy would not be limited in its application of force, so yes, it would accellerate faster and faster.

 

Luckily for us, gravity does exist, or we'd be in real trouble! :)

 

In a gravity well,

Buffy

[niin]

I said, what if there was no gravity and no dark matter, but the universe was still expanding.

Would the expanding still make everything move apart? Would it go faster and faster?

I meant dark energy when i said dark matter. sorry.

So would it still move apart and would it be accelerating?

[Buffy]

I meant dark energy when i said dark matter. sorry.

So would it still move apart and would it be accelerating?

In theory at least--since this is not something we could observe!--all accelleration of the expansion took place during Inflation during the first fraction of a second after the Big Bang, and in the absence of anything slowing it down (gravity) or speeding it up (Dark Energy), no it would proceed at a constant rate with no accelleration or decelleration.

 

I never bothered to look, but as usual, Wikipedia has got a pretty good page on Expansion of Space that covers what we've been talking about here pretty well.

 

Foot off brake and gas pedals,

Buffy

[infamous]

 

I never bothered to look, but as usual, Wikipedia has got a pretty good page on Expansion of Space that covers what we've been talking about here pretty well.

 

 

Now I'm really confused. The queston of material expansion has always sounded a little weird to me until I read that link you gave from Wikipedia.

 

Quoting Wikipedia; "It is as if without objects themselves moving, space is somehow "growing" in between them".

 

The only way this statement makes any sense to me is; If it appears as if objects themselves are not moving, but the surrounding space appears to be growing, that sounds like both the space inside and outside the proton are growing together. This has really got my head spinning. Help me out here Buffy, how can that statement mean anything else? This brings us full circle, back to my original question. Accepting that space is expanding, what makes the space within particles different from the surrounding space? If there is no difference, then what is preventing expansion of the space within?.......Infy

[Buffy]

Now I'm really confused.

Its okay! It IS confusing!

If it appears as if objects themselves are not moving, but the surrounding space appears to be growing, that sounds like both the space inside and outside the proton are growing together.

Yes, but a couple of things:

 

First off, realize that when you're talking about local space, this "expansion" is very small.

 

Second, you have to keep trying to understand that there's no intrinsic link between the space expanding and what matter does that sits in it.

 

I hate to bring this up, because its a related analogy, and its *not at all* "expansion of space" but maybe it will help you get away from the notion that the expansion has to affect matter directly.

 

You know what a Neutrino is right? The sun produces gazillions of them and billions of them pass right through you every second. In fact at night, those neutrinos are going *all the way through the earth* and *then* going through you. The thing is, they are so small, that the vast space between protons and the electrons whizing around them is like the space between us and the Sun.

 

SO what I'm trying to get across is that you can have *actual matter* that has no ability to push, prod or pull anything that we think of as big matter.

 

Now, completely different, space has no matter at all. There's nothing to push, there's nothing to pull there's nothing to be attached to. So ask yourself the question, if there's no physical connection between space as it expands and the matter that makes up *you*, why should its expansion somehow cause *you* to expand? What I'm trying to get across is that if neutrinos don't do anything to push you around, why should *nothing* push you around? Similar (but watch out, not exactly the same) to the neutrinos, space is expanding through you without touching anything.

 

So to try to answer your hard question:

Accepting that space is expanding, what makes the space within particles different from the surrounding space? If there is no difference, then what is preventing expansion of the space within?

do you see that in saying "expanding the space within" you need to some how explain *why* the electron orbits would expand? We know that takes energy, but there's no source of energy to make it happen because "nothing is expanding" and nothing has no energy.

 

On cosmological scales, stuff is "moving" away because it always has been (again, because of expansion, not an "explosion" so its different). On local scales, gravity and electroweak forces are so much stronger than anything, that even Dark Energy (which *is* energy) can't push them around, let alone "nothing expanding."

 

Pass Go, collect $200,

Buffy

[infamous]

 

So ask yourself the question, if there's no physical connection between space as it expands and the matter that makes up *you*, why should its expansion somehow cause *you* to expand?

The only possible answer to that would be; Action at a distance, which is also something I've yet to understand completely. Truly my friend, I don't want to wear you out with all these abstract inquiries. You're such a good sport about it, I suppose I should give you a little break. I'm going to lay off for a while and let you catch your breath and in the mean time, I'm going to do a little more research about these questions. Thanks for your careful patience, you're the real deal Buffy.....................................Infy

[Qfwfq]

Blame it all on comoving coordinates!

 

It isn't all that meaningful to say that "space is expanding", it's really a pictorial expression rather than a tangible fact. What is physical is the conclusion of the standard model that the size of the universe is increasing. This does not determine the motion of each individual body, even less when interactions other than gravitation are dominant. No object is "anchored to space", as Buffy so prolixly points out.

 

The standard model describes the dynamics of the universe, postulating a few things, and uses comoving coordinates as the most natural choice. Einstein told the journalists it's like a leavening cake with raisins in it and, as usual, this became a fact, ipse dixit, and a universal truth that should be applicable to everything. Instead, it is really just a choice of coordinates, nothing more, nothing less. One may choose a coordinate map according to which space is not expanding, there is ever more of it and distant galaxies have increasing distances. This is no less nor more true than the comoving description, only less handy for defining the dynamic system, the boundary conditions, and solving it.

[infamous]

Blame it all on comoving coordinates!

 

Excellent Qfwfq, I'll dig into this for a while. I think it may hold a few answers I've been looking for............Thanks Q,............Infy