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Author Topic: what is gravitational redshift?  (Read 3477 times)

Offline yor_on

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what is gravitational redshift?
« on: 11/03/2012 16:09:14 »
A photon is said to lose energy as it climbs a gravitational field. And it will also be detected as red-shifted by you observing.

So, did it?
How?


 

Offline Pmb

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Re: what is gravitational redshift?
« Reply #1 on: 11/03/2012 16:42:43 »
If the photon is a non-static gravitational field then the energy can change. If the the energy of any particle in a static gravitational field then the energy of a poton does not loose energy as it climbs out of a gravitational field. A derivation can usually be found in a text on GR. The energy of any particle in a static

There is a web site I created to describe gravitational red shift. See http://home.comcast.net/~peter.m.brown/gr/grav_red_shift.htm

It's very mathematical though. I thought I created a web page proving it so but I can't find it.
 

Offline Soul Surfer

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Re: what is gravitational redshift?
« Reply #2 on: 11/03/2012 22:29:40 »
The usual technique for observing gravitational red shift on photons on the earth's surface is the Mossbauer effect using very narrow band gamma ray photons and observing the difference in their frequency after they have travelled some distance vertically upwards or vertically downwards.  The experiment was first done in the 1950s.  It was one of the first lab tests of general relativity.
 

Offline MikeS

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Re: what is gravitational redshift?
« Reply #3 on: 12/03/2012 06:16:12 »
A photon is said to lose energy as it climbs a gravitational field. And it will also be detected as red-shifted by you observing.

So, did it?
How?

No.
It just appears that it has.
This deception is an artefact of the time dilation factor of the gravity well (gravitational gradient).

If an experiment were to be done to test whether a photon looses energy when climbing out of a gravity well the experiment will falsely show a change in energy unless the experiment is corrected to allow for the time dilation factor.
 

Offline Soul Surfer

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Re: what is gravitational redshift?
« Reply #4 on: 12/03/2012 08:30:35 »
An interesting point Mike, but time dilation for a photon causing it to be a lower frequency is a loss of energy.  A massive object slows down and loses energy too but its rest mass energy does not change.  It is just two alternative ways of expressing the same thing.  Frequency and time are inextricably linked.
 

Offline MikeS

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Re: what is gravitational redshift?
« Reply #5 on: 12/03/2012 17:30:39 »
An interesting point Mike, but time dilation for a photon causing it to be a lower frequency is a loss of energy.  A massive object slows down and loses energy too but its rest mass energy does not change.  It is just two alternative ways of expressing the same thing.  Frequency and time are inextricably linked.

It only appears to be a loss of energy when observed from a different time frame.

In the gravity well time passes slower.  A second is 'longer' relative to a distant observer.  There are a certain number of cycles emitted per second.  A distant observer receives less cycles per second as his 'second is shorter in comparison.  There is no actual loss of energy as such it is an effect of different observers having different time dilation factors.  If you consider your local time to be more real than mine then yes, there is a loss of energy but it's all relative.
 

Offline yor_on

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Re: what is gravitational redshift?
« Reply #6 on: 12/03/2012 17:58:47 »
I too see it that way. ( That it shouldn't lose 'energy' I mean :) Because for it to lose any energy it would have to do in in a (intrinsic to it) arrow of time, how would it do that? If a photon isn't a 'particle' though, but more of a 'excitation' in a 'field', that somehow connect  'everywhere'? Then it seems like a symmetry to me.

I'm still getting a headache with this one :)
« Last Edit: 12/03/2012 18:01:18 by yor_on »
 

Offline yor_on

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Re: what is gravitational redshift?
« Reply #7 on: 12/03/2012 18:02:58 »
But it will still be a local definition of the loss. Relative motion will redefine your measurement, as well as a (very) possible expansion. It's weird.
 

Offline yor_on

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Re: what is gravitational redshift?
« Reply #8 on: 12/03/2012 22:20:48 »
If you want to look at it as some sort of 'field' as I do, with excitations, the main idea should be to ignore 'time'. Times arrow is only important macroscopically, above some 'scale/size', as I've started to think of it. But, what creates 'the arrow of time' should be 'field(s)', and they don't 'move'.

In fact, you can always assume relative motion to crave two 'frames of reference' to exist, as long as we're discussing 'inertial frames', aka 'uniform motion. 'Inertial' just means a 'frame of reference' in where you don't feel inertia acting on you,  as earths motion, although we have some 'forces' acting on us as the 'fictitious' Coriolis force, etc. But practically no one on Earth feels any 'inertia' acting on them, and looked on from another planet our earth is 'moving uniformly' in space.

And if 'motion' is a vague expression macroscopically, only definable relative some other 'frame of reference', and nota bene, only arbitrarily at that. Meaning that there is no real gold standard to 'motion'.  If so and excepting accelerations, you then are free to define all uniform motion to yourself, or arbitrarily to any other frame you observe. And it doesn't get simpler by introducing more objects uniformly moving. In fact, 'uniform motion' will always needs a 'reference frame' to exist.

So, what is then a acceleration?
'Gravity'?

And 'gravity' was a 'redshift'?
and a 'slower arrow of time'?

There are a lot of symmetries in those concepts.
And 'motion' becomes a very strange idea.
==

'Inertia' here is me looking at it from 'uniform motion', and that's an 'inertial frame'. In any acceleration you will find inertia acting on you, 'pulling you back' . But there is one way more to define inertia though, after all, it's also 'gravity'. But here we just use it to describe 'accelerating' displacements, ignoring the 'gravity' you already feel.

And one thing more, 'gravity' is very much a geometry, not a 'force'..
« Last Edit: 12/03/2012 22:58:25 by yor_on »
 

Offline yor_on

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Re: what is gravitational redshift?
« Reply #9 on: 12/03/2012 22:47:32 »
Pete, that was one impressive link you've made there.
And it's nice to see your conclusion :)
 

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Re: what is gravitational redshift?
« Reply #9 on: 12/03/2012 22:47:32 »

 

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