# I Particle accleration under gravitational waves?

1. Feb 16, 2017

### AAB1994

I have been through following papers for research:

1)http://cdsads.u-strasbg.fr/cgi-bin/..._paper=YES&amp;type=PRINTER&amp;filetype=.pdf

2)https://arxiv.org/pdf/gr-qc/9905054.pdf

Conclusion of the second paper given above states the following:

"
In this case the
external action (the gravitational wave) amounts to a time variation of the frequency
parameter of the initial system (charged particles in a magnetic field), so that in the
overall system the equilibrium at rest (x
1 = 0) is unstable. Any deviation from this
state, however small, is sufficient to lead to a rapidly increasing displacement along
the peprendicular direction (Landau and Lifshitz 1976). Further analysis shows that,
in any of the above propagation cases, the overall result would be an exponential
increase of the perpendicular energy of the particles involved in this interaction, as a
function of the affine parameter and, hence, of their proper-time as well.
"

From the conclusion I can understand that gravitational blueshift may be the reason for increasing frequency but what could be the reason for perpendicular displacement of particles and exponential increase in perpendicular energy?

2. Feb 16, 2017

### Staff: Mentor

Gravity waves are things like water waves (driven by gravity and different densities of water and air). Gravitational waves and gravity waves are different things.
The calculations? If the energy given to the particle grows with displacement and speed of the particle, you can get such a result.

3. Feb 17, 2017

### Android Neox

Gravitational waves cause relative motion between points at different phase. But, for each observer, spacetime defines stationary. As a gravitational wave passes, each point will feel nothing because the point will remain stationary and move with the wave. When you have two points at different parts of the wave (as with LIGO) the difference in "stationary" becomes visible.

4. Feb 18, 2017

### AAB1994

So they is no net change in energy? And by that explaination what causes the damping of gravitational waves ?

5. Feb 18, 2017

### AAB1994

By energy given do you mean energy of gravitational waves? And so there shouldnt be a change in particles perpendicular energy if the gravitational wave is constant ?

6. Feb 18, 2017

### Staff: Mentor

I asked the same question once in this thread. The answer I got was:

7. Feb 18, 2017

### AAB1994

Than should i or should not trust sources of above papers?

8. Feb 18, 2017

### Staff: Mentor

No, you didn't. You asked about damping of gravitational waves by passing through vacuum (which was a hypothesis of a non-standard theory of gravity, not GR). GR says there is no such damping.

The papers linked to in the OP talk about a possible damping of gravitational waves by passing through plasma with charged particles and magnetic fields. That is a different question.

AndroidNeox is not describing what you are asking about. He is describing gravitational waves passing through vacuum. You are asking about gravitational waves passing through plasma with charged particles and magnetic fields.

The hypothesis of damping of gravitational waves by passing through plasma (because of energy transferred from the waves to the plasma) seems plausible, and appears to me to be consistent with the general GR description of gravitational waves. It would be hard to test, though.

9. Feb 18, 2017

### Crowxe

I'm sorry as this may not be in direct relation to this thread but i had to ask 1) what's the difference between gravity waves and gravitational waves? and 2) regarding LIGO the gravitational waves observatory that had recently measured a "stretch in space" , couldn't it be just a stretch and contraction of earth itself? (it was tiny measure by photon diameter fraction) as result of the increase and decrease of gravity caused by the two black holes that were spinning around each others?

10. Feb 18, 2017

### Staff: Mentor

https://en.wikipedia.org/wiki/Gravity_wave

https://en.wikipedia.org/wiki/Gravitational_wave

No. The earth itself does stretch and squeeze as a result of the passage of the GW, but LIGO is carefully designed to not respond to such changes in the Earth or its supporting structure, so that the signal it detects is in fact due to changes in curvature of spacetime itself.

11. Feb 19, 2017

### AAB1994

But can anyone tell me why there is increase in perpendicular energy?

12. Feb 19, 2017

### Staff: Mentor

According to the papers, it looks like that energy comes from the energy carried by the gravitational wave.

13. Feb 20, 2017

### AAB1994

But why is it increasing in perpendicular direction and not in parallel and would this be the laudau damping effect?

14. Feb 20, 2017

### Staff: Mentor

Because gravitational waves are purely transverse, so they can only add energy in the perpendicular direction.

I am not familiar enough with the paper's subject matter to say.

15. Feb 27, 2017

### AAB1994

And also could anyone tell me why gravity waves frequency has to be double of larmor frequency for energy of gravity waves to pass onto particels?

16. Feb 27, 2017

### Staff: Mentor

Gravitational waves, not gravity waves.
Gravitational waves have a 180 degree symmetry: rotate them by 180 degrees around their propagation axis and they look the same. To stay in phase with the oscillations, you need two oscillations of the gravitational wave per oscillation of the particle: forward and backward motion are symmetric.

17. Mar 2, 2017

### AAB1994

So is it safe to assume that particles accelerated by gravitational waves may generate more electromagnetic radiation than the radiation of electromagnetic field creating the larmor precession on them. And Does it mean net increase in electromagnetic energy which is most certainly accompanied with net decrease in gravitational energy of accelerated particles ?

And would this theory work if the objects generating electromagnetic radiation and gravitational energy in the first place are same?

18. Mar 2, 2017

### Staff: Mentor

It is a net decrease in the energy of the gravitational waves.
The whole idea here is the reaction of charged particles to gravitational waves passing through their region in space. They cannot be the source of the gravitational waves.

19. Mar 10, 2017

### AAB1994

I will rephrase my question with few more points in a hypothetical situation:

If a trains of objects with mass and quadruple movement were rotating in same circumference or path of current loop and had a spiral inside them then what would be the conditions under following situations.

1)As per the conditions( frequency of gravitational waves double than larmor frequency and parallel propagation) of paper discussed above could there be an acceleration of particles in spiral?

2) Depending on the direction of current in current loop could the energy be highest at center of spiral after acceleration of particles from gravitational waves?

20. Mar 10, 2017

### AAB1994

I mean spiral object inform of a conductor

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