# Radiation - temperature - frequency

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1. Feb 13, 2016

### Brian E

Hi.

Dunno if this makes much sense.

If radiation is emitted from a star with a certain frequency, does that frequency change, if that radiation travels through areas of different temperatures?

2. Feb 13, 2016

### Drakkith

Staff Emeritus
It does not.

3. Feb 13, 2016

### Brian E

Let me explain my confusion.

I'm pretty sure, that waves in water and waves in spacetime (radiation) should not be considered to be similar in behaviour. Anyway, I will try to use waterwave to explain my point.

I read somewhere, that the frequency of waves in water, among other things, depends on the depth of the water. If I have a tank of water and drop a stone in it, it will produce a wavepattern. If I then heated the water up, the water would grow in volume and the depht would increase. In that case, would the frequence of the waves not change. I know that spacetime is not water and your answer made me understand, that heat does not affect spacetime.

4. Feb 13, 2016

### jbriggs444

Yes, shallow water waves propagate with a speed that depends on the depth of the water. As they pass over a shallower area, they slow down. As they pass over a deeper area, they speed up. But this does not change their frequency. It changes their wavelength.

In steady state, the number of wave crests entering a region per unit time has to equal the number leaving. Otherwise, the region would either run out of wave crests to emit or would pile up an infinite number of them. Neither situation is possible.

Last edited: Feb 14, 2016
5. Feb 13, 2016

### Brian E

Oh I see. Thank you very much for the answer :-)