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# red shift watch

1. When the wavelength is streched because a photon is being emitted away from a large gravitational field, this means its energy is lower, right? Where does the energy go? Some type of photon's g.p.e.?
2. (Original post by mik1a)
When the wavelength is streched because a photon is being emitted away from a large gravitational field, this means its energy is lower, right? Where does the energy go? Some type of photon's g.p.e.?
yeah, i think the photon loses energy as it climbs out of the gravitational field (gpe at infinity=0)
3. Weird, I've never heard of this. Cosmological redshift is caused by the doppler effect though. I suppose what you say makes sense if you use E= hf. However a photon has no mass, and GPE = mgh which means the GPE of a photon is always zero and wouldnt change...*shrugs* meh.
4. (Original post by mik1a)
When the wavelength is streched because a photon is being emitted away from a large gravitational field, this means its energy is lower, right? Where does the energy go? Some type of photon's g.p.e.?
I asked a professor of physics this question a while ago. He says it goes into the gravitational field. The equation for gravitational redshift is a result of the General Theory of Relativity.
5. (Original post by kez-man)
Weird, I've never heard of this. Cosmological redshift is caused by the doppler effect though. I suppose what you say makes sense if you use E= hf. However a photon has no mass, and GPE = mgh which means the GPE of a photon is always zero and wouldnt change...*shrugs* meh.
because photons have energy, they are subject to gravity so a photon climbing out a gravitational potential well (ie - escaping from a star) loses energy as it escapes. e=hc/wavelength so lower energy = higher wavelength = redshift.

i think.
6. Is that why the radiation from empty space (microwaves) has such a long wavelength.. because it 'escaped' the big bang and has been redshited off the visible spectrum?
7. (Original post by mik1a)
Is that why the radiation from empty space (microwaves) has such a long wavelength.. because it 'escaped' the big bang and has been redshited off the visible spectrum?
That would seem to be sensible reasoning? At the point of the big bang there would have been intense gravity and radiation emitted, and combined with doppler effect.

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