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SteveinLondon
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When light is red shifted due to the expansion of the universe, it loses energy (E=hf). Doesn't the "conservation of energy rule" apply in this case? Where does all that energy vanish to?
SteveinLondon said:When light is red shifted due to the expansion of the universe, it loses energy (E=hf). Doesn't the "conservation of energy rule" apply in this case? Where does all that energy vanish to?
SteveinLondon said:When light is red shifted due to the expansion of the universe, it loses energy (E=hf). Doesn't the "conservation of energy rule" apply in this case?
marcus said:The CMB ancient light is redshifted by z=1100. Therefore it has lost some 99.9% of its energy and nobody can say where "it went".
salvestrom said:Back into the vacuum tends to spring into my mind. The constant vacuum energy has to come from somewhere, plus it is the origin of the photon in the first place. It may be overly obvious to connect the two, but I'm assuming some relatively straight forward maths would reveal if one can account for the other. We have estimates for total energy, the photon contribution and the amount of expansion since last scattering...
marcus said:I played around with that as a conjecture some back in 2004 or so. jokingly calling it the "marcus conjecture". the vanished CMB energy went into the "dark energy" of the new space.
It doesn't add up. No professional-grade math connects one to the other AFAIK. It is just an appealing idea that has not amounted to anything (AFAIK!)
SteveinLondon said:When light is red shifted due to the expansion of the universe, it loses energy (E=hf). Doesn't the "conservation of energy rule" apply in this case? Where does all that energy vanish to?
BillSaltLake said:Is energy also non-conserved in GR due to local curvature? For example, If a system consists of a hollow spherical reflector with lots of photons bouncing around inside, and it collapses to a BH, does the equivalent gravitational mass of the system change as measured by a distant observer?
Wood_Pecker said:Can this question be usefully reversed? Could some of the observed red shift be the result of photons shedding energy in some way that is difficult measure on human timescales? Could this hypothesis help to explain the observed increase in the rate of expansion of space-time?
Interesting thought. If a distant galaxy is accelerating away at a current speed of 0.9c and if I am traveling in a spaceship towards the galaxy at 0.9c, what I would see is the "normal" light without any shifts right? Is the photon assumed to "not lose energy at all" or "gain energy" in this case? In either case, the relative velocity has something to do with the perceived energy loss/gain of energy of the photon.anorlunda said:I don't think so. If we were in a spaceship moving at a substantial fraction of c, then even distant light from far galaxies dead ahead of us would be blue shifted. From that I conclude that the photon doesn't shed energy along the way, but that the Doppler shift is proportional to the speed difference of the light emitter and the light receiver.
Chronos said:Redshift is a frame dependent measurement. If you were approaching a distant galaxy at the same speed as it is receeding, you would see no redshift. The problem arises when you try to compare photon energy in different reference frames. It is sort of like a baseball player chasing a line drive. If you run toward the ball it hits your glove with more force than it does if you catch it running toward the fence. A stationary observer, however, would perceive no difference in the kinetic energy of the baseball.
All forms of redshift have nothing to do with a change in the state of the photon. Instead it is related to the relative position and orientation [frames of reference] of the emitter and absorber in curved space-time.
The standard {cosmological} convention is that of the conservation of energy-momentum, (GR), which results in fundamental particles having constant mass. Therefore, atoms are defined to provide regular clocks and fixed rulers by which the universe can be measured. [wikipedia]
Photons are measured by those atoms, as the frequency of emission, determined in the laboratory, is compared to the frequency of absorption, the result is they are found to lose energy, i.e. red-shifted.
If another convention is chosen, such as the conservation of energy, it is the photon that remains constant in energy and hence frequency and the masses of atoms, and therefore atomic clocks and steel rulers that change over cosmological time. There are theories that take such an approach, such as
here.http://en.wikipedia.org/wiki/Self-creation_cosmology
ConformalGrpOp said:Adrian- A blue shift generally implies a relative motion of the observer in the direction of the source of the light wave. The observed blue shift is due to the fact that as the observer moves toward the source, the source appears to be emitting photons at a faster rate, or probably more correctly, the observer is running into photons emitted by the source at a faster rate than the photon were emitted. So, to the observer, it appears that the light from the source has a higher energy (frequency), than would be observed if the observer was not moving toward the source.
ConformalGrpOp said:Drakkith, Indeed, I miswrote. The observed blue shift is, of course, the result of the shorter wavelength of the EM in the frame moving towards the source. Adrian was concerned with where the energy came from. Clearly, I was a bit hasty in articulating the explanation and wasnt careful to properly explain the basis of the observation of blue shift in the moving frame, and I can be faulted for not adequately (specifically), articulating why the observer in this frame would observe the photons to have a higher energy than would be observed in the same inertial frame as the source. (Its all because the rain drops were falling on my head!) :) Thank you.
An attractive idea. I would expect that once a spherical universe starts to contract, the photon's energy would be "gained back" (it't wavelength would shrink) and thus never was lost. To me it makes sense to think of it as being some kind of a potential energy, which varies with the scale factor.Chronos said:Obviously spacetime is not conserved in an expanding universe. I've always been attracted to the idea that expansion dilutes energy. An ink dot on a balloon starts out as ... a dot, but, grows as the balloon is inflated. All the ink is still there, just spread out.
Tanelorn said:If we were able to match the relative velocity of the orignal emitting atoms then we would measure the same photon frequency and energy.
However, to do this in our current frame of reference we would have to greatly exceed the speed of light.