Quote:
Originally Posted by PhantomWolf
Now I have to admit that I'm a chemist not a physicist so this isn't my specialist topic and so one of our physicists might correct me if I misunderstand it, but from my reading of the subject, space is a geometric subsection of spacetime.
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Essentially right. More to the point mathematically, space is a threedimensional "slice" (or "hypersurface") of the fourdimensional spacetime manifold at a constant cosmological time (or even more mathematically, for which every two points have a "space-like" distance, in the sense of SR, i. e. ds^2 < 0).
Quote:
Originally Posted by PhantomWolf
It only deals with shape, nothing else.
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I'm not sure what you mean here.
Quote:
Originally Posted by PhantomWolf
As soon as you add energy or matter to space you get spacetime,
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Now, that's wrong. The question if energy or matter is present has nothing to do with the difference between space and spacetime. The difference is essentially the dimensionality. See above - space is only a 3D "slice" of the 4D spacetime.
Quote:
Originally Posted by PhantomWolf
Also, as far as I understand it, spacetime is infinite as it contains all space and all matter and energy throughout all time.
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That makes spacetime only infinite if space or time are infinite. Possibly both are finite, which would make spacetime finite also.
Quote:
Originally Posted by PhantomWolf
Infinite things cannot be expanded. How do you make infinity bigger?
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Infinite things
can be expanded - by saying what is actually meant with "expanding". In the context of the expansion of the universe, it simply means that the distances between any two points grow with time. And that's also possible in an infinite universe.
Quote:
Originally Posted by PhantomWolf
Space, on the other hand, is merely a volume, it can be expanded.
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Ever it is an infinite volume, yes.
Quote:
Originally Posted by PhantomWolf
As such, as far as I understand it, saying an expansion of spacetime is totally meaningless, we can only talk about an expansion of space.
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Exactly right! Note that I asked MITM several times what "expansion of spacetime" actually is supposed to mean - he didn't answer so far...
Quote:
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Originally Posted by MITM
"Spacetime" is made of real things. It has real mass, and real fields of energy.
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Does anyone understand what it is supposed to mean to say that spacetime "is made of real things" and "has real mass and real fields of energy"???
Quote:
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Originally Posted by MITM
Spacetime can in fact expand as the matter of spactime expands and moves,
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Could anyone please tell MITM that the expansion of the universe does
not mean that matter moves around and expands?
[quote=PhantomWolf;913731]
Space is a finite thing, it has a set volume.
[/QOTE]
Actually, if the universe is flat or open, space has an infinite volume.
No offense intended, but before participating in a BBT discussion, you should perhaps first read up on what the BBT actually says?
http://www.talkorigins.org/faqs/astronomy/bigbang.html
Quote:
Originally Posted by PhantomWolf
Of course I can, you are claiming that an infinite entity can get bigger, that is meaningless.
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No, it isn't. Actually, what is meaningless with the statement "spacetime expands" is that spacetime already includes
all times. It simply
is - talking about changes of a thing which already includes
all times is meaningless.
Quote:
Originally Posted by PhantomWolf
WE AREN"T TALKING ABOUT AN ACCELERATION OF MATTER!!!!!!!!!!!!
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He has been told that about 50 times in this thread, I estimate. So why does he keep repeating that? Probably because he still thinks that the BBT says that spacetime expands, not space, and for him, that means that matter expands. Whereever he got these two strange ideas from...
Quote:
Originally Posted by PhantomWolf
If you put in an accelerating expansion, you get back a negative constant.
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Huh? Actually, what you get back is a
positive (cosmological) constant, a
positive energy density, and a
negative pressure.
Quote:
Originally Posted by PhantomWolf
That means that if GR is correct, and our interpretation of the SN and other data that points to an accelerating expansion of space is correct then there HAS to be a negitive pressure energy involved.
Now having said that, if you want to argue that GR is incorrect and therefore there is no point in putting the data into it, that's fine, argue that. If you want to argue that our interpretation based on the observations is wrong and there is either no expansion, or that any expansion is not accelerating, fine argue that. But if you accept that GR is correct and that space is accelerating in its expansion, then the only answer is a negative pressure energy. Arguing about what that energy is termed as because you don't like it is just plain stupid.
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Quote:
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Originally Posted by MITM
[Vacuums do not possess negative energy, they posses *less* pressure or less energy than other areas, but there is no "negative energy density" inside of a vacuum.
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This seems to be a new straw man by MITM. No one ever said that the vacuum has a negative
energy density. What was said is that there exists
a form of energy in the universe which has a
positive energy density, but a
negative pressure.
I keep wondering if he makes up these straw men intentionally, or because he is utterly incapable of understanding what people actually tell him...
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Originally Posted by MITM
False. The cosmological constant is not "guaranteed" to be "negative pressure energy".
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And that's simply wrong, as can be seen in a number of publications and textbooks on GR. But MITM does not bother to educate himself - he seems to think he already knows everything, better than actual physicists...