What is the physical interpretation of the huge red shift of the CMB? It
can't mean extreme recessional velocity since it's here, everywhere, in
every direction. AG
Since the CMB isn't receding, what is the physical interpretation of its
huge red shift? AG
It's all relative. We're receding, if you insist on "somebody is
receding". The bit of the CMB we see is a further away bit every day. Its
photons have traveled to us thru space that has been expanding as they
traveled.
Brent
Since I am free to choose any observer is receding, I did. But more
important is your model of the photon. Since the wave property of light is
an ensemble property, what allows you to claim they lose energy as the
universe expands? AG
Suppose you and a pro-baseball pitcher are standing alongside a road
playing catch. When you catch his fastball it has an energy of 70J and
stings thru you glove. Now his throw is little off and instead going to
you, it is caught by a kid in a passing car going the same direction as the
throw. But when the kid catches it bare handed it doesn't even hurt
because it's only got an energy of 2J. How did the ball loose energy?
Brent
Good question. The ball caught by the observer in the moving car didn't
lose all of its kinetic energy, and kept moving with the car after being
caught, whereas all the kinetic energy of the ball was disappated into
recoil, sound waves, and heating of the material in the glove, when the
ball was fully stopped by the guy on the ground catching the ball. Now
that I've answered your question, tell me how a point particle, the photon,
can get it wave stretched by an expanding universe. AG
You didn't answer it correctly. You overlooked the impetus the ball adds
to the car increasing the energy of the car/ball system.
*I gave you a good approximate answer. You're just nitpicking. The ball
never comes to a complete rest wrt the ground when caught by the observer
in the moving car. Hence, this is the main source of the "loss" in kinetic
energy. What part of my explanation do you not understand? AG *
That the photon gets its wavelength stretched during it's long travel from
the CMB is obvious in the inflating balloon model. As space expands it
stretches the photon traveling thru it.
*This is not an explanation. An individual photon has no identifiable wave.
Wave extend to spatial infinity. You're just repeating something you've
heard before, and believe. AG*
*Since photons travel at light speed, from the pov of external observers,
using the LT, they have zero length. So, when you speak of their wave
lengths, do you really know what you're referring to? AG*
Brent
*I sympathize. It's a monumental task to show, how something without
length, a photon, can be stretched. AG *
What do you make of the wavelength?
Brent
*I tend to thInk of a photon's wavelength as a quantum number which defines
its energy, and it has that name because when interacting with other
photons an interference pattern is manifiested, similar to deBroglie
wavelength of material particles. But there's no infinite extention in
space like a classical wave; nor is it a pulse with some dominant
frequencies. So what it actually IS I can't say, particularly since it has
no measureable length. But since a cosmological red shift for galaxies is
observed, I can't deny that reddening occurs as photons exist and travel
within an expanding universe. But we need a model for that occurrance, and
simply asserting that a photon's wave is "stretched" as spce expands, is
just silly story which avoids serious analysis. AG*
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