On 6/4/2025 6:15 PM, Alan Grayson wrote:
On Sunday, June 1, 2025 at 5:38:51 AM UTC-6 John Clark wrote:
On Sun, Jun 1, 2025 at 3:16 AM Alan Grayson <agrays...@gmail.com>
wrote:
/> But the question persists; when photons redden as the
universe expands, where does the lost energy go? AG/
*The energy doesn't go anywhere, it's just destroyed,*
*I don't get it. How can energy be destroyed? Destroyed by what? AG*
Think of it this way. You're floating in space. Space is filled with
randomly distributed tennis balls and they are all slowly receding away
from one another. So the further away they are, the faster they are
receding from you. A mile away they are receding at 1mph. Two miles
away they are receding at 2mph. Ten miles away they are receding from
you at 10mph, etc. This is uniform expansion of tennis ball
distribution. You take your tennis racket and hit a 130mph smash. It
goes flying off thru space, passing by the slowly moving tennis balls.
But at 100 miles the tennis balls are going 100mph and your ball is only
going by them at 30mph. At 125mi your ball is only passing the other
balls at five mph. So will it take your ball another hour to reach the
balls going 130mph? No it will never reach the balls going 130mph, it
only asymptotically approaches them.
When you hit the ball you gave it a big chunk of kinetic energy relative
to you and the balls near you. Now the ball is essentially stationary
relative to the balls around it. What happened to that kinetic energy?
Nothing...but it's relative. So it still exists relative to you. But
in fact it also has the same kinetic energy relative to any other balls
that are 130mi away /in any direction/. Every ball has that kinetic
energy relative to other balls 130mi away. So the kinetic energy is not
really located just relative to you. It's been absorbed into the
overall expansion of tennis balls.
Brent
*energy is not conserved at the cosmic level. Noether's theorem
says if there's a symmetry, then there's a corresponding
conservation law (but the reverse does not necessarily hold, if
there is a conservation law there may or may not be a
corresponding symmetry). *
*
*
*In the case of energy Noether says the corresponding symmetry is
time, at the cosmic scale if energy is conserved then the universe
should look the same from one time to another, but if the universe
is expanding it doesn't look the same from one time to another,
and if the universe is accelerating then time is even less
symmetrical. So energy is not conserved globally, however it's
still true that at the local level if things are at thermal
equilibrium then the amount of energy entering a finite volume of
space will equal the amount of energy leaving that volume.*
*
*
*John K Clark See what's on my new list at Extropolis
<https://groups.google.com/g/extropolis>*
7ma
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