On 1/23/2014 1:34 AM, Pierz wrote:
Yes, dark energy *is* what he was talking about. Thanks for that clarification. The
original expansion is just a result of the residual inertia of the big bang.
I don't think you can look at it that way. If were just the motion, as away from the
center of an explosion, then even the most distant parts could not exceed c. But if it's
the expansion of space as in the FRW solutions to Einstein's equation then sufficiently
distant parts are receding faster than c.
On Thursday, January 23, 2014 7:40:03 PM UTC+11, Liz R wrote:
On 23 January 2014 20:09, Pierz <[email protected] <javascript:>> wrote:
I once heard a cosmologist say that you can't feel the force of
repulsion due to
cosmological expansion between your fingers because at that distance it
is
imperceptibly small. But if your fingers were at either end of the
universe
you'd feel an immense pressure pushing them apart.
If he's talking about dark energy, fair enough, although since we don't
know what it
is, I'm not sure how he could make that statement with confidence (about
the force
being there between your fingers, I mean).
However, if he wasn't talking about dark energy, I don't understand. I
don't think
that the hubble flow /itself/ involves a force. That is, the contents of the
universe are moving apart (except where they're gravitationally bound) and
they are
interacting via gravity and dark energy, whatever that is.... and that's
all that's
involved. Cosmological expansion is simply movement, galaxies on either
side of the
universe aren't being pushed apart by anything /other/ than dark energy,
and not
being pulled together by anything except gravity (as far as we know). There
isn't a
force of repulsion making the universe expand - apart from dark energy - it
simply
IS expanding.
Of course it depends on what DE is. The most common theory is that it's just the
cosmological constant term in Einstein's equation. If that's the case then it's just
another geometric effect of the dynamics of space. It's not really a "force", it's just
part of gravity.
Brent
WAS he talking about Dark Energy?
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