If cosmological redshift determines that a emitted photon will have a higher frequency than after it propagates for awhile, doesn't the planck relation tell us that the photon has lost energy? Where does this energy go?
I feel like there is a really obvious answer but I can't think of it....
Potential Energy
Learn what frequency means first.
Photons can travel through space without losing energy. Red shifted light looks that way because it's traveling away from you so the light waves 'stretch' out. It's not until that photon hits something that it gets absorbed
Ya. But Plancks relation says E=hf so how is energy conserved if the frequency is dropping?
Because it does not change. Just set yourself in the relativ motion system of the observer and emitter.
At least not from the relativ motion. It does change because the observer and emitter might be in a different gravitational potential.
the change in frequency comes from the change in observer.
if you are the emitter, the photon has a certain energy when emitted, that doesn't change over time.
if you change frames of reference, energies change accordingly, including the one for photons. It doesn't mean the photons lost energy.
This is just like saying "I claim that at sea level, gravitational potential energy is 0", and then changing our mind and saying "well now I want that to be true but at 10km up in the air"
It's a pretty good question OP.
is wrong, he's confusing the optical redshift with the Doppler-Fizeau effect that is only relevant to phonons.
The loss of energy caused by the redshift is real and caused by the expansion of space, not a consequence of a change of referential.
The answer to this is that energy conservation is a local law and not a global one. It doesn't apply when volumes are not constant in time. Which is why energy has no global meaning in general relativity, unlike work.
light speed is constand lads...
The redshift is caused by distance only, it would be exactly the same if the source traveled toward you. It's caused by space expanding, not by things moving away from you.
Law of conservation of energy.
Photos don't "lose" energy.
They're a cosmological constant.
"c".
we got some good trolling here.
keep it up
here, I'm serious.
The red shift isn't the doppler effect.
there's a redshift due to the metric expansion of space
there's also redshift due to the doppler effect
what's your point?
Now learn attenuation.
This guys right, energy isn't conserved between reference frames. In the frame of a thrown baseball it has no kenetic energy, but in the batter reference frame it does.
You are all wrong. The total energy of all universe is zero, seen by ANY observer.
Really because a neutrino that sees everything moving at .99999c would see everything as pretty energetic
Nope. It would see the total energy as zero.
Rest energy in mass? Regardless of reference frame that is energy.
>mixing up what "energy" means
Brainlets.
Photons have no rest mass
So are you saying that the frequency if the photon is reduced is all reference frames?
That isn't his point. Conservation of energy follows from to time-translation invariance via the Noether theorem. There is no time-translation invariance in GR (at least not always.)
What energy?
undergrad
If a person who is moving away from you punches you in the face, it will hurt less than if a person moving toward you punches you in the face.
Where did the energy go?
E^2=m^2+p^2. This equation is true in any inertial reference frame. If you change reference frames, the changes in energy and momentum compensate each other. Obviously if you switch reference frames, the total energy is going to be different...but so what?