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Braininvat » September 6th, 2018, 1:38 am wrote:I'm still curious what my infinitely long iron bar does when it's heated. See my two posts that touched on that. Would this changing the metric concept also address the apparent expansion of an infinite bar?
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Braininvat » September 5th, 2018, 6:38 pm wrote:I'm still curious what my infinitely long iron bar does when it's heated. See my two posts that touched on that. Would this changing the metric concept also address the apparent expansion of an infinite bar?
Braininvat » September 5th, 2018, 11:16 am wrote:Our electron orbitals aren't moving away from our quarks and rendering our bodies into cyclotron trash.
Braininvat » September 5th, 2018, 11:16 am wrote: I don't really see any logical contradiction for cosmological scale expansion in an infinite universe, because infinities seem eternally accommodating.
Braininvat » September 5th, 2018, 11:16 am wrote: Only something with a limit cannot expand,
Braininvat » September 5th, 2018, 11:16 am wrote: so I need to understand what the "limit" would be for an infinite universe.
Braininvat » September 5th, 2018, 11:16 am wrote:If you had an iron bar of infinite length, and you heated it up, what would happen to it?
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someguy1 » September 5th, 2018, 5:45 pm wrote:Ok you know what, I'm perfectly correct.
From the Wiki page for the expansion of the universe, and I quote:
Technically neither space, nor objects in space, move. Instead it is the metric governing the size and geometry of spacetime itself that changes in scale.
However, the model is valid only on large scales (roughly the scale of galaxy clusters and above), because gravitational attraction binds matter together strongly enough that metric expansion cannot be observed at this time, on a smaller scale. As such, the only galaxies receding from one another as a result of metric expansion are those separated by cosmologically relevant scales larger than the length scales associated with the gravitational collapse that are possible in the age of the universe given the matter density and average expansion rate.
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A useful visualization is to approach the subject rather than objects in a fixed "space" moving apart into "emptiness", as space itself growing between objects without any acceleration of the objects themselves. The space between objects shrinks or grows as the various geodesics converge or diverge.
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davidm » September 5th, 2018, 8:37 pm wrote:Just to get clear, here are the credentials of the author of the "dot page" that SG disparaged.
And no, pre-emptively, spare me the charge that this is an illicit "appeal to authority." It's nothing of the kind.
davidm » September 5th, 2018, 8:19 pm wrote:
I am in complete agreement with this. With the whole article, in fact. In an infinite space, no object is moving apart into "emptiness." There is no emptiness, just an infinite space with an infinite number of objects, wherein over time distances increase between those objects.
davidm » September 5th, 2018, 7:36 pm wrote:Not only is the above in perfect accord with everything that I have said ...
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someguy1 » September 5th, 2018, 8:49 pm wrote: How can all the distances double yet the space remains the same size?
Wow. We really are done here.
The quote I gave totally falsifies everything you've said.
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davidm » September 5th, 2018, 9:13 pm wrote:Very easily, in infinite space. It's only in finite space that such cannot happen. In finite space, doubling in distance will run up against a limit.
davidm » September 5th, 2018, 9:13 pm wrote:
Yes, we are.
davidm » September 5th, 2018, 9:13 pm wrote:The article supports everything I have said.
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Braininvat » September 5th, 2018, 7:44 pm wrote:Well, sort of. My thought experiment was not notably reality based, but I was trying to get at an expansive effect all along the length of the bar, not at one location. If a uniform heat (yes, I know this requires infinite energy input) were applied, as Positor noted, it would become less dense and, erm, LONGER. But, of course, the bar is already infinitely long. Maybe this just reveals the failure point of preposterous thought experiments. In any case, I am very glad you have made clearer the distinction between actual stretching and changing the metric.
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someguy1 » September 5th, 2018, 9:16 pm wrote:davidm » September 5th, 2018, 9:13 pm wrote:Very easily, in infinite space. It's only in finite space that such cannot happen. In finite space, doubling in distance will run up against a limit.
That's shockingly incorrect. If I double all the distances in a one-inch interval it becomes a two-inch interval. You can't change the size of an infinite universe. You are simply making stuff up now..
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davidm » September 5th, 2018, 9:21 pm wrote:
Tell me, if I double infinity, what do I get? Or what does infinity times infinity equal?
davidm » September 5th, 2018, 9:21 pm wrote:The linked article supports everything I have said.
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However, the model is valid only on large scales (roughly the scale of galaxy clusters and above), because gravitational attraction binds matter together strongly enough that metric expansion cannot be observed at this time, on a smaller scale. As such, the only galaxies receding from one another as a result of metric expansion are those separated by cosmologically relevant scales larger than the length scales associated with the gravitational collapse that are possible in the age of the universe given the matter density and average expansion rate.
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someguy1 » September 5th, 2018, 9:28 pm wrote:You said the universe stretches.
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davidm » September 5th, 2018, 9:35 pm wrote:
I did not say any such thing. Perhaps you are getting this from a science chat forum to which I linked, where an interlocutor invoked an analogy of a piece of rubber stretching. It was an analogy. I, myself, said no such thing.
davidm » September 5th, 2018, 9:35 pm wrote:I'm really tired of your twaddle.
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someguy1 » September 5th, 2018, 11:36 pm wrote:I refer now to @davidm's awful link (he got upset at me when I mocked this link but it's impossible not to) here: http://www.astro.ucla.edu/~wright/infpoint.html
It says: Note that the black dots represent galaxies, and the galaxies do not expand even though the separation between galaxies grows with time.
REALLY? How does that work? How does the distance between two galaxies know to double, yet the matter within each galaxy knows to stay right where it is with respect to its neighbors?
We're often told to imagine dots on the surface of a balloon. But as the balloon expands, so do the dots.
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- SG....It's a change of coordinate systems or a change of metric, same thing. The "distance" changes only because you've changed the metric. You almost got it with everything but your final clause. You can THINK about it as space "stretching," but the math doesn't support that interpretation. The math just says the metric changes. You are making an interpretation, but it's not the only one possible. That's true even in the finite case, but in the infinite case your claim makes no sense. How can all the distances double yet the space remains the same size?
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someguy1 » September 5th, 2018, 10:10 pm wrote:[. I wonder if it's crossed your mind that you have no idea what you're talking about. You don't even understand the pages you're linking because none of them say what you claim they do.
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The size of the box in each view is 78 billion light years. The green circle on the the right is the part of the Universe that we can currently see. In the view on the left, this same part of the Universe is shown by the green circle, but now the green circle is a tiny fraction of the 78 billion light year box, and the box is an infinitesimal fraction of the whole Universe. If we go to smaller and smaller times since the Big Bang, the green circle shrinks to a point, but the 78 billion light year box is always full, and it is always an infinitesimal fraction of the infinite Universe.
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