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Offline hamza

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A question regarding gravitons
« on: 28/08/2007 17:44:51 »
Hey guys.. i wanted to know that if gravity and gravitational forces were due to space time warps than what's the use of Gravitons.. i mean what do they do.. if time space is warped and masses attract due to this warpness than there's no "gravity". right?? we stick to the earth just beacause of the warpness.. is that right.. correct me if i'm wrong.


 

Offline lightarrow

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A question regarding gravitons
« Reply #1 on: 28/08/2007 19:42:24 »
Hey guys.. i wanted to know that if gravity and gravitational forces were due to space time warps than what's the use of Gravitons.. i mean what do they do.. if time space is warped and masses attract due to this warpness than there's no "gravity". right?? we stick to the earth just beacause of the warpness.. is that right.. correct me if i'm wrong.
It's an interesting question. We could maybe think of gravitons as quantums of the "warped space time perturbations" which move at light speed. I know nothing about it, however.
 

Offline DoctorBeaver

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A question regarding gravitons
« Reply #2 on: 28/08/2007 22:39:07 »
That's something I've been wondering about too. I've been reading books on particle physics & extra dimensions that talk a lot about gravitons; but none of them say what the theories say about how they work (I don't even know if any theories address that question).

I asked a similar question here a while ago.
http://www.thenakedscientists.com/forum/index.php?topic=8455.0
« Last Edit: 28/08/2007 22:41:01 by DoctorBeaver »
 

Offline Soul Surfer

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A question regarding gravitons
« Reply #3 on: 29/08/2007 10:23:02 »
I have been thinking a bit about this topic again recently and think that there is quite a lot of confusion in people's minds about the topic and that includes the scientists.

Firstly let me give an example from electromagnetics.  A proton attracts an electron by electric charge.  The electron goes into "orbit" around the proton to form a hydrogen atom  there are quite a few different orbitals that the electron could occupy when it does this and the process of doing this causes a quantum of electromagnetic radiation, a photon, to be emitted.  This photon has a particular frequency associated with its energy and that's where Planck's constant comes in.  The photon is the "particle" of pure energy that effectively communicates the electromagnetic force.

All atoms and molecules whenever they interact by the electromagnetic force emit photons  This applies to all chemical reactions and just atoms vibrating with the heat energy they contain.  That is why warm bodies emit infra red radiation and iron rods get red hot in a fire.

Now my understanding of a graviton is that it is, like the photon, the particle of pure energy that mediates the gravitational force so the earth orbiting the sun emits gravitons and very slowly loses energy.  This energy loss can be measured in binary neutron stars and agrees well with the predictions.  Experiments are being carried out to detect the gravity waves "consisting of many individual gravitons"  from objects like this. Just like we detect the photons from the sun as light.

A graviton like a photon can have any energy and this energy probably depends on its frequency and Planck's constant.  But gravitational interactions are very slow indeed  the earth would emit gravitons with a period of one year  The fastest neutron star binaries are a few hundered cycles per second  so the individual gravitons have an extremely tiny energy.  by comparison light's frequency  is in thousands of millions of millions of cycles per second.

Many people think that a graviton is a particle lke an electron that just carries a gravitiational charge and nothing else.  This  this I believe is incorrect.  A particle of gravitiation would in fact be a tiny black hole and such objects may actually form part of the dark matter.  OK Hawking states that small blackholes radiate and that this radiation gets more intense as the hole gets smaller but there is probably a quantum limit where the only thing a black hole can radiate is another black hole.  Now this may be the Planck mass,  which is quite large but we have particles with a tiny mass like neutrinos so my guess it may be very small and way below the planck mass  one way to look at this would be to think at what frequency does a gravition get to have the same energy as the two orbiting particles that emit it.  I have never seen this calulation illustrated.  I know that there is a maximum energy for a photon and this has been discussed recently on these pages.
 

Offline syhprum

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A question regarding gravitons
« Reply #4 on: 30/08/2007 10:09:35 »
An excellent summation of the current thinking on Gravitons
 

Offline DoctorBeaver

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A question regarding gravitons
« Reply #5 on: 30/08/2007 12:39:38 »
But gravitational interactions are very slow indeed  the earth would emit gravitons with a period of one year 

Can you explain in idiot language exactly what the period of a graviton is? And why would the period be 1 year?

Quote
A particle of gravitiation would in fact be a tiny black hole and such objects may actually form part of the dark matter.

If that were the case, wouldn't gravitons absorb other particles and thus become more energetic?
« Last Edit: 30/08/2007 12:41:22 by DoctorBeaver »
 

Offline lightarrow

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A question regarding gravitons
« Reply #6 on: 30/08/2007 16:41:33 »
But gravitational interactions are very slow indeed  the earth would emit gravitons with a period of one year 
Can you explain in idiot language exactly what the period of a graviton is? And why would the period be 1 year?


Gravitons, as mediators of grav. force, would (I say "would" because gravitons are just a speculation) have, like photons, a frequency and a wavelenght. Which is the frequency of a photon? Is the frequency of the moving electric charges which generates that light.

For example: if you take an electron and move it up and down 5*1014 times every second, it generates orange light in every direction; light's frequency of orange light at 600 nm is just  5*1014 cycles/second (= Hz); in the same way, if you take a mass and move it periodically with a frequency ν, it'll generate gravitational waves with that freq. ν.

Earth moves periodically, because it goes around the sun once in a year, so it will generate grav. waves of frequency = 1 cycle/1 year = 1/31536000 = 3.2*10-8 Hz. The period of a wave is the inverse of the frequency.

Actually, to produce grav. waves it's not enough a periodic movement of that kind because it'll need quadrupole oscillations, but this is too complicated to discuss now.

Since the energy of a single particle is hν, the higher the frequency, the higher the energy. For this reason gravitons would have extremely low energies.



« Last Edit: 30/08/2007 16:45:39 by lightarrow »
 

Offline DoctorBeaver

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A question regarding gravitons
« Reply #7 on: 30/08/2007 18:38:12 »
I understand about frequency/oscillation. But why couldn't the period be 1 day instead of 1 year?
« Last Edit: 30/08/2007 18:39:55 by DoctorBeaver »
 

Offline JP

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A question regarding gravitons
« Reply #8 on: 30/08/2007 19:47:33 »
The earth can't generate gravitational waves by rotating since it's essentially spherical.  The distribution of mass needs to be moving in order for gravitational waves to be generated, and while each individual point on the earth might move as it rotates, the total distribution is still the same (a sphere).  However, when it revolves around the sun, the mass distribution is moving in space and therefore can generate gravitational waves.  Therefore you get gravitational waves with the period of 1 year (revolution) as opposed to 1 day (rotation).
 

Offline lightarrow

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A question regarding gravitons
« Reply #9 on: 30/08/2007 19:48:29 »
I understand about frequency/oscillation. But why couldn't the period be 1 day instead of 1 year?
In 1 day earth spin, but in this movement it doesn't change the grav. field around it (assuming a perfect homogeneus sphere), so it couldn't produce any perturbation-->oscillation-->wave of grav. field.
 

Offline lightarrow

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A question regarding gravitons
« Reply #10 on: 30/08/2007 19:49:58 »
The earth can't generate gravitational waves by rotating since it's essentially spherical.  The distribution of mass needs to be moving in order for gravitational waves to be generated, and while each individual point on the earth might move as it rotates, the total distribution is still the same (a sphere).  However, when it revolves around the sun, the mass distribution is moving in space and therefore can generate gravitational waves.  Therefore you get gravitational waves with the period of 1 year (revolution) as opposed to 1 day (rotation).
You have beaten me for 1 minute.  [:-'(]
 

Offline lightarrow

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A question regarding gravitons
« Reply #11 on: 30/08/2007 19:54:38 »
I understand about frequency/oscillation. But why couldn't the period be 1 day instead of 1 year?
In 1 day earth spin, but in this movement it doesn't change the grav. field around it (assuming a perfect homogeneus sphere), so it couldn't produce any perturbation-->oscillation-->wave of grav. field.

In the same way, if you take an homogenously charged sphere and you spin it, it won't produce an EM radiation, just static electric and magnetic fields.
 

Offline DoctorBeaver

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A question regarding gravitons
« Reply #12 on: 30/08/2007 19:58:59 »
OK, thanks guys. I understand now.
 

Offline Mr Andrew

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A question regarding gravitons
« Reply #13 on: 30/08/2007 20:21:37 »
Hamza, to address your original question about gravitons and the warping of spacetime it necessary to recognize that gravitons are, by necessity, incompatible with the general theory of relativity (which deals with the warping of spacetime by mass).  This is because gravitons violate the equivalence principle of gravity and acceleration, the very foundation of general relativity.  This principle states that gravity and acceleration are identical, that there is no way to physically discern the difference between the two in a closed system (Einstein's elevator thought experiment for example).  Gravitons provide a way to do this by making gravitational attractions no longer equivalent to accelerations.  They are two totally different, contradicting theories.

Now, since, if general relativity holds true, there can be no gravitational force mediator, and assuming the potential existence of a unified theory of forces, this means that because the other forces would then be equivalent to gravity, there can be no mediating particles for them either.  Also, accepting general relativity and the possibility of a grand unification theory suggests that charges should warp spacetime also, in a way that only affects other charges though (like a massless charged particle in a gravitational field is unaffected, a chargeless mass is unaffected in an electric field).
 

Offline syhprum

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A question regarding gravitons
« Reply #14 on: 30/08/2007 20:58:15 »
The earth can't generate gravitational waves by rotating since it's essentially spherical. 

Although the Earth on its own would not produce any gravitational waves the Earth Moon system must produce some at 3.85*10^-7 Hz
« Last Edit: 30/08/2007 21:00:40 by syhprum »
 

Offline DoctorBeaver

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A question regarding gravitons
« Reply #15 on: 30/08/2007 23:27:25 »
The earth can't generate gravitational waves by rotating since it's essentially spherical.

Although the Earth on its own would not produce any gravitational waves the Earth Moon system must produce some at 3.85*10^-7 Hz

 ???
 

Offline Mr Andrew

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A question regarding gravitons
« Reply #16 on: 31/08/2007 04:48:16 »
Think of a bowling ball on a large trampoline.  If that ball was rotating, like the earth, then the trampoline doesn't move but if there are two balls, the one revolving around the other, then the trampoline is forced to change and this change might be considered a wave (I'm not familiar with the mechanics behind general relativity).
 

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A question regarding gravitons
« Reply #16 on: 31/08/2007 04:48:16 »

 

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