# If light experiences gravitational redshift as said by GR

1. Jun 1, 2004

### touqra

If light experiences gravitational redshift as said by GR, then, where did the difference between the initial and final energy, $$E = \frac {hc}{\lambda}$$ go?

From Hubble expansion, there is also redshift. Where did the energy difference go?

2. Jun 2, 2004

### Chen

Radiation? (I'm guessing)

3. Jun 2, 2004

### TeV

where redshift energies go to

In the simplest case (For that ,imagine two equal photons emited in opposite directions from the massive object):In cowering the difference between inital and final gravitational field strenght of the source of the gravity potential.Accompaning mass of the *emitter* before and after changes.Total energy of the system remains conserved of course.

As of from Hubble expansion red shift,and the question: Where did the energy difference go?:I would say nowhere.Only the density of the energy of the Universe should change.No?

cheers

4. Jun 2, 2004

### Matrixman13

I would think that it goes to space itself. (If there is such a thing)

5. Jun 3, 2004

### Nenad

E = hc/lamda

when you think of your equation, you notice that the energy is less when the photon of light is emmited back to earth. The reason for this is because of the Compton effect, and photon momentum. Since a photon with energy has a mass, when it strikes an object, some of its energy is lost since the collision is not perfectly ellastic. This would cause a shift to the red side of the spectrum.I think Let me thisnk about that one for a while, Ill get back to you.

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