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Author Topic: Graviton emission and absorption?  (Read 5186 times)

Offline Supercryptid

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Graviton emission and absorption?
« on: 07/12/2005 21:28:04 »
Most people here are most likely familiar with how an atom absorbs a photon. A photon with energy X is absorbed by an electron in orbit around an atom. This electron, now with energy X added to it, jumps to a higher energy state. After another photon with energy X is emitted by that electron, it falls back into its lower energy state once more.

But, once that electron absorbs the photon, what prevents it from re-emitting that same energy as a graviton with energy X instead of a photon with energy X? Neither photons nor gravitons have properties such as lepton number or electric charge which must be conserved. Both of these particles are pretty bare as far as conserved properties are concerned. My guess is that it would have to do with the spin differences between the two particles.

On another note, can an electron in orbit around an atom theoretically absorb a graviton and re-emit it in a similar fashion that some electrons absorb and re-emit photons?

Is there any way to stimulate an excited atom with excess energy X to emit a graviton with energy X?


 

Offline DoctorBeaver

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Re: Graviton emission and absorption?
« Reply #1 on: 07/12/2005 21:57:36 »
Maybe because there isn't actually any such thing as a graviton?
 

Offline Soul Surfer

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Re: Graviton emission and absorption?
« Reply #2 on: 07/12/2005 23:25:46 »
Remember always that the energy levels for emission and absorption have to fit into a classical system even though they are quantised. That is,  electron energy levels and orbit dimensions together with the energy changes between orbits are just as if they were classical non quantised particles.  Quantum theory just overlays this fuzzes it up with uncertainty and places defined values for angular momenta to produce the precise energy levels.

The graviton may be a bit wierd and hypothetical but it does fit into the particle mengerie quite well and seems as least as plausible as other particles that have been suggested theoretically and subsequebtly identified.  The big problem is that the gravitational energy effects in atoms are so tiny that they are totally undetectable with current technology.

I'm not even sure that quantised gravitational interactions are likely to be obseved much in materials as dense as neutron stars which are only a little bit bigger than a black hole with the same mass.  Even then such observations would be very difficult at astronomical distances.



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Offline DoctorBeaver

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Re: Graviton emission and absorption?
« Reply #3 on: 08/12/2005 01:17:54 »
Isn't it hypothesised that releasing gravitons would take an incredible amount of energy? Far more than we can currently generate?
 

Offline Soul Surfer

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Re: Graviton emission and absorption?
« Reply #4 on: 08/12/2005 09:39:48 »
No.  They are like photons and can have very low energies at low frequencies as most gravitational related phenomena are.  Remember the energy of a photon is Plancks constant times the frequency of the radiation. You don't see processes involving individual photons much below 1GHz.  The lowest I can think of at the moment is the 1.4Ghz hyperfine hydrogen line sometimes called the 21 cm line.  I suppose NMR is another case that reaches down into low radio frequencies at low fields but that is a real exception.

Now think of gravitational processes, like things orbiting each other  even a pair of neutron stars in close orbit can only manage a few KHz.  OK we can detect the loss of energy by graviton emission by the decay rate of the orbits but we can't detect the gravitons  - yet, although the latest gravity wave detectors are thought to be getting pretty close to managing it.

An interesting aside is, I tend to wonder if the latest discoveries involving "dark matter" and "dark energy" are someting to do with the basic background radiation of gravitiational waves that must exist in the universe rendering gravitiational fields inneffective at very low values.

This would work in the same way as  the atoms in the air in the room don't all drop to the floor under gravity because they are all batting aroud too fast because they are at room temperature or it is difficult to cool things out in the universe down below a couple of degrees kelvin because the cosmic microwave bacground would warm them up.  The only natural things that are cooler than this are isolated largish black holes and they require violent compressive processes to make them.

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« Last Edit: 08/12/2005 09:56:10 by Soul Surfer »
 

Offline DoctorBeaver

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Re: Graviton emission and absorption?
« Reply #5 on: 08/12/2005 12:41:50 »
I was reading an article on particle accelerators recently & I'm sure it said something about the production of gravitons requiring far more energy than we can achieve.
And isn't 1 of the problems with GUT that we have no means of testing anything to do with bringing gravity into the model as the energy requirements for such an experiment are way beyond our capabilities?
 

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Re: Graviton emission and absorption?
« Reply #5 on: 08/12/2005 12:41:50 »

 

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