How does an expanding space time explain this?

Started by Solitary, September 16, 2015, 04:53:09 PM

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surreptitious57

So the Big Rip is certainly a possibility as the very fabric of spacetime is stretched apart by cosmic expansion whilst the
Universe carries on expanding beyond light speed. Although this is not the most probable scenario. That was an eternal
Universe with alternating Big Bangs and Big Crunches. However the observation of gravitational waves occurring during
inflation has since invalidated this. These are quantum fluctuations happening in the fabric of spacetime. How it shall all
end or if it will end at all while very interesting is entirely academic. Since homo sapiens will be extinct long before then
A MIND IS LIKE A PARACHUTE : IT DOES NOT WORK UNLESS IT IS OPEN

josephpalazzo

Quote from: surreptitious57 on September 24, 2015, 02:48:06 AM
So the Big Rip is certainly a possibility as the very fabric of spacetime is stretched apart by cosmic expansion whilst the
Universe carries on expanding beyond light speed. Although this is not the most probable scenario. That was an eternal
Universe with alternating Big Bangs and Big Crunches. However the observation of gravitational waves occurring during
inflation has since invalidated this. These are quantum fluctuations happening in the fabric of spacetime. How it shall all
end or if it will end at all while very interesting is entirely academic. Since homo sapiens will be extinct long before then

There are many cosmological models at play. The mainstream one is the Big Bang theory. What we really don't know is: what happened at very small scale since we don't have a quantum theory of gravity; will the universe continue to accelerate indefinitely.  Of course there are other questions, more on the fringe of speculation: do we live in a multiverse and are there extra dimensions. So yeah, those questions are academic. But physicists are driven by the actual situation that you one theory, general relativity, to explain large distances, and a totally different theory, quantum mechanics, to explain the very small distances, and the consensus is that there should be one theory - this is reminiscent to pre-Newton times when people believe there were two separate kinds of realm: the terrestrial and the heavens.

Baruch

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Baruch

So that is how Munch's friends get pumped ... the space-time inside their biceps etc is expanding? ;-))
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josephpalazzo

Quote from: Baruch on September 27, 2015, 05:49:22 PM
So that is how Munch's friends get pumped ... the space-time inside their biceps etc is expanding? ;-))

You've got that wrong: Dark Energy is for expanding, but Dark Matter is for clumping up.

Unbeliever

Quote from: surreptitious57 on September 24, 2015, 02:48:06 AM
How it shall all
end or if it will end at all while very interesting is entirely academic. Since homo sapiens will be extinct long before then

Well, Homo Sapiens wasn't here for most of the past history of the universe, but we still find it very interesting. So just because we won't be around to witness the future of the universe doesn't mean we don't find that interesting, as well. Why does our presence or absence mean anything at all where such questions are in play?

God Not Found
"There is a sucker born-again every minute." - C. Spellman

Baruch

Per the Easter Egg at the end of the postlude ... humans evolve into Vorlons, and so exist for a very long time.
Ha’át’íísh baa naniná?
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surreptitious57

Our presence in the Universe matters to us both for reasons of self preservation and because we
can actually investigate it also. Though as for it itself it does not require us at all. It is simply the
sum of all its parts and so then from a purely materialistic perspective it makes no difference if it
supports intelligent life or not. Because only intelligent life could actually be concerned about that
For the Universe is incapable of such abstract thinking. Despite us actually being part of it as such
A MIND IS LIKE A PARACHUTE : IT DOES NOT WORK UNLESS IT IS OPEN

Unbeliever

I've come to think that it may be easier to consider that the cosmic density is decreasing, instead of the cosmos expanding. We still don't know for sure that the universe is absolutely flat. It may be closed on itself on a truly humongous scale. Our ability to measure the flatness isn't perfect, so it could still be curved on a scale we can't yet fathom.
God Not Found
"There is a sucker born-again every minute." - C. Spellman

josephpalazzo

Quote from: Unbeliever on October 23, 2015, 07:31:38 PM
I've come to think that it may be easier to consider that the cosmic density is decreasing, instead of the cosmos expanding. We still don't know for sure that the universe is absolutely flat. It may be closed on itself on a truly humongous scale. Our ability to measure the flatness isn't perfect, so it could still be curved on a scale we can't yet fathom.

Present theory considers that Dark Energy Density (DED) is a constant in the Einstein's Field Equations (EFE). So as the universe expands, the Dark Energy increases with the increasing volume. Nevertheless the EFE does not exclude that the DED could be varying in time. This would allow a universe to expand, then contract, then expand and so on. Pretty much like the human heart. In such a scenario, the universe is eternal as it has no beginning, no ending, and no Big Bang to start it all.

Baruch

Ha’át’íísh baa naniná?
Azee’ Å,a’ish nanídį́į́h?
Táadoo ánít’iní.
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Don't do that.

josephpalazzo

I met Neil once at a seminar. He's a charming fellow. But he has a naive view of Relativity. He believes it's the most beautiful and self-consistent theory. I pointed out to him that Einstein made a leap of faith in his derivation - I have a blog on that. We ended up to agree to disagree.

Baruch

Quote from: josephpalazzo on October 25, 2015, 07:51:53 AM
I met Neil once at a seminar. He's a charming fellow. But he has a naive view of Relativity. He believes it's the most beautiful and self-consistent theory. I pointed out to him that Einstein made a leap of faith in his derivation - I have a blog on that. We ended up to agree to disagree.

Einstein had very good physical intuition ... and was lucky.  Faith had nothing to do with it.  His personal overweening self confidence helped him, but it turned off the people around him.  Only another completely overweening person like Bohr could stand up to him.

Don't relativists and QM-ists never mix well?  This is a continuation of the one on one debates between Einstein and Bohr.  The QM-ists won that round, and I suspect they will again ;-)  See as per a recent good video on Einstein ... he had a neo-Kantian prejudice, not really a Machian ... and this happened to work in his case, but only at the beginning.  Afterward it was a hindrance.  On the other hand it is MHO that the "shut up and calculate" QM-ists are ignoramuses, or savants, not real physicists.  Feynman was of this ilk.  Ask Bethe what Feynman was like as a grad student.  Einstein was the opposite, he was actually bad at math, and needed constant assistance.
Ha’át’íísh baa naniná?
Azee’ Å,a’ish nanídį́į́h?
Táadoo ánít’iní.
What are you doing?
Are you taking any medications?
Don't do that.

josephpalazzo

Quote from: Baruch on October 25, 2015, 11:03:33 AM
Einstein had very good physical intuition ... and was lucky.  Faith had nothing to do with it.  His personal overweening self confidence helped him, but it turned off the people around him.  Only another completely overweening person like Bohr could stand up to him.

Don't relativists and QM-ists never mix well?  This is a continuation of the one on one debates between Einstein and Bohr.  The QM-ists won that round, and I suspect they will again ;-)  See as per a recent good video on Einstein ... he had a neo-Kantian prejudice, not really a Machian ... and this happened to work in his case, but only at the beginning.  Afterward it was a hindrance.  On the other hand it is MHO that the "shut up and calculate" QM-ists are ignoramuses, or savants, not real physicists.  Feynman was of this ilk.  Ask Bethe what Feynman was like as a grad student.  Einstein was the opposite, he was actually bad at math, and needed constant assistance.

The irony about Einstein is that I think he never really understood QM, though he contributed immensely, and his misunderstanding is not out of the ordinary as most QM pioneers didn't understand it either (it took a good understanding of QFT to see where QM fits in the grander scheme of things, circa 1970's). Nevertheless, Einstein's misunderstanding spurred on a whole cottage industry (EPR, Bell's theorem, and the never ending hopeless search for nonlocality).

BTW, my PhD thesis was based on Bethe's groundbreaking paper on the reference spectum for nuclear matter.