Dumb Question

Question about gravitational red-shift

Hi!

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The gravitational red-shift here is due to the loss of energy when escaping from a gravitational field, right?
Is this the one considering the photon to have the equivalent mass of m=hf/c^2 and do the calculation?
I once read about another explanation of the gravitational red-shift due to time dilation at the gravitational field but not considering the energy, is there such an explanation?

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flamethrower ...

Thanks.

Only wish the US would have contributed to keeping Mir aloft. Oh well, egotism
had it's day and a great artifact of the 'space age' is no more.

Sad.

 

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Are these pages any help Dreamsa

http://www.pact.cpes.sussex.ac.uk/users/markh/GR/node22.html

http://background.uchicago.edu/~whu/tamm/webversion/node20.html

The maths is a bit beyond me so I can't tell.

A google search on gravitational redshift returns over 2000 sites so you may find what you need.

 

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Hi!

The maths is also beyond my capibility.

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The problem of the search engine is that they give me too much site that I don't know which one gives me what I want!

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Boris2...
I don't understand the diagram. It show that when the space expand, the light wave also expand with it, why is it so?

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Then why are you wasting your time on this forum when you should be studying your maths? Just joking

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The cosmological redshift is only apparent over very large distances. Local gravity, our solar system and galaxy group, has more influence on these small scales. Keeping that in mind we can do a thought experiment.

If you took a metre rule and tried to measure the comological expansion you would find that your rule was also expanding at the same rate. You too would be expanding at this rate. So for you nothing would change. But to an outside observer you, your ruler would be stretching. The light from the CMBR started with a particular frequency, and hence wavelenght, as it travels through the expanding space it will be stretched just like the ruler.

When we observe the redshift on Earth, we are the outside observer and see the light stretching.

Don't know if this is correct so maybe wait for a better explanation. This is a trifle beyond my understanding.

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I'm not sure about this any more from all the posts now. But if something is moving at a high speed (closer to c), the length of that object will shrink, it wouldn't stretch. But from Einstein, he said that the speech of light is constant for all observers, even if the observer is travelling at the speech of light, he/she will still observer the light as normal, not contracted. The only way to explain this is that the space is stretched. So I guess your explaination of the light been stretched wouldn't work. I still think it's the space that stretches that lengthened the distance between the wave fronts as it is emitted, so as the next wave front is emitted, the distance between the one before is lengthened, thus the increased wave length - just the same for the doppler effect, but instead the object moving away to cause the distance between the two wavefronts to increase, but it's the space that increases.

 

No so I believe. They will observe the <i>speed</i> of light to remain constant, <b>but</b> the frequency will change. It will be blue-shifted in front and red-shifted behind them. But this is doppler shift not cosmological.

We are talking about light so the speed will be c. In your example the object travelling close to c will observe <b>no</b> change in its length, but an outside observer <b>will</b>.

The light <b>is</b> streched, and the frequency lowered, and so appears to us to be red-shifted. This is what cosmological red-shift is.

 

Let's make things clear first!

Let first see whether my understanding now is correct!

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1)Ordinary Dopller shift of light is because the oberver or the source or both are moving with respect to each other, right?

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2)But the red-shift of CMB has nothing to do with the Dopller effect, is this right?

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Ordinary Doppler shift of light is because the observer or the source or both are moving with respect to each other, right?

Correct.

But the red-shift of CMB has nothing to do with the Doppler effect, is this right

Remember, our entire local group of galaxies is moving in a particular direction at about 600 km/s. We are moving through the CMB at this speed. In the direction we are moving the wavelengths of the radiation are squashed together (a blue-shift), making the sky appear hotter there, while in the opposite direction the wavelengths are stretched out (redshift), making the sky appear colder there. This temperature variation on the sky is known as a "dipole." When the dipole is removed, the CMB appears "isotropic," the same in all directions.

You couls say that our motion through the CMB, in effect, is creating a Doppler.

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Hi!

The red-shift I am talking about is this:
When the CMB are first created, the wavelenght is much shorter.
But now it became much longer.
Is this red-shift different from ordinary red-shift?
Or even can I call this red-shift?

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Thanks

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Also

This is the part I do not understand:

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Answer.....

From

http://www.pd.astro.it/E-MOSTRA/NEW/A9002STR.HTM

 

Boris2 ...

Took a look at the link you provided ... interesting, and now I'm even more confused.

All the discussion on this thread led me to believe that the red shift was attibutable to either a doppler effect or the stretching of space. Now the matter of temperature has been brought into the picture ... what's going on?

 

That's actually an easy one to solve: when the volume increases, the temperature of the matter/radiation/... inside decreases.

Bye!

Crisp

 

Crisp ...

Understand that when a fixed amount of a gas expands there is a temperature drop. What threw me is that radiation is affected in the same way.

Or is it that the expansion, and resulting 'thinning' of the matter the universe contains, results in the less energetic, lower frequency, radiation (temperature?)?

And if that's the case, why the bit of 'space stretching the radiation' and lowering its frequency, the 'red shift' aspect?

I just don't get it and haven't been able to find anything that clarifies the question. Any recommendations?

Thanks

 

Chagur,

That noisy, smelly, perferated, electrically compromised, combustionably-insulted POS didn't re-enter soon enough.

And we did monetarily contribute to that noisy, smelly, perferated, electrically compromised, combustionably-insulted POS: we leased space/man-hours/docking rights on that noisy, smelly, perferated, electrically compromised, combustionably-insulted POS.

 

Don't worry about this as it will/has confuse/d you

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Ignore the text in bold and you have it

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Micro wves are a lower frequency than gamma rays and are therefore "cooler" or less energetic. The early universe would have had a lot of gamma rays and therefore been "hot".

Can I interest you in some slightly used grey matter.

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Keep asking as it get my, slightly used, grey matter stirred up

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Boris2 ...

Thanks ... and thanks for the grey matter offer

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Mr. G ...

Glad to see you have such fond thoughts re.Mir.

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But for all its faults, it still had a working toilet and exercise equipment that
didn't have to be constantly repaired.

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As "a great artifact of the 'space age'", I still wish it were up there.

Take care all.

 

But I still do not understand how the gamma rays become microwave!

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Anyone tell me clearly?

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