Could gravity waves be faster than light?

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Re: Could gravity waves be faster than light?

Postby BurtJordaan on October 18th, 2017, 4:25 am 

BurtJordaan » 17 Oct 2017, 15:37 wrote:
ralfcis » 17 Oct 2017, 15:16 wrote:The ligt from the start of the explosion had already occurred before they could catch it.

Correct, but I would not describe the merger as an explosion, just the creation of an extraordinary hot, large neutron star, that will 'shine' in many wavelengths for many days (or longer). They have already measured the cooling down in the first day or so, according to the articles that I have seen so far.

I now think you are also close to correct about some sort of explosion, because I have read further:
https://www.space.com/38471-gravitational-waves-neutron-star-crashes-discovery-explained.html wrote:The researchers estimated the merger generated a jet of material that shot outward at nearly the speed of light, moving down a path tilted about 30 degrees away from the line of sight from Earth. All of the light that the researchers detected came from a cocoon of material surrounding this jet. They estimated that about 30 percent of future neutron-star mergers will generate bright gamma-rays detectable from Earth.
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Re: Could gravity waves be faster than light?

Postby jocular on October 18th, 2017, 8:15 am 

BurtJordaan » October 18th, 2017, 4:25 am wrote:[
https://www.space.com/38471-gravitational-waves-neutron-star-crashes-discovery-explained.html wrote:The researchers estimated the merger generated a jet of material that shot outward at nearly the speed of light, moving down a path tilted about 30 degrees away from the line of sight from Earth. All of the light that the researchers detected came from a cocoon of material surrounding this jet. They estimated that about 30 percent of future neutron-star mergers will generate bright gamma-rays detectable from Earth.

Is that interesting in its own right? We have a collection of matter traveling at near to the speed of light ** wrt to neutron star source and almost anything else it happens to encounter.

I wonder what the make up of this matter is (plasma?), how big and expansive it is and what will be the result of any encounter with objects in its path.

**seems very unique to me (it will presumably continue on its way for ever if it meets no obstacles.Are there many more of these around if neutron mergers are common events?)
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on October 18th, 2017, 4:43 pm 

A very good article on the neutron star merger is available here.
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Re: Could gravity waves be faster than light?

Postby jocular on October 18th, 2017, 6:49 pm 

BurtJordaan » October 18th, 2017, 4:43 pm wrote:A very good article on the neutron star merger is available here.


Yes ,interesting and educational days ahead.

Will it further our understandings of Black Holes, I wonder? Do they remain as dark as ever despite this?

For example will this multimessenger technology cast any new light on Hawking radiation itself?
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Re: Could gravity waves be faster than light?

Postby ralfcis on October 18th, 2017, 7:53 pm 

Similarly, the luminosity of the electromagnetic signal and its delay relative to a gravitational wave can be used to probe the physics of gravity (such as the equivalence principle) in ways that were not possible through either type of observation alone.


So doesn't this and the 1.7s delay of the gamma ray burst after the gravity wave not signify gravity waves are faster than light (which is the title of this thread)? So light travels slower than c? I would think there would have reacted a little more to this.
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Re: Could gravity waves be faster than light?

Postby BurtJordaan on October 19th, 2017, 12:56 am 

The gravitational waves originate in the wildly changing curvature just outside the orbit of the two merging stars, while the gamma ray burst comes from when they are (almost?) fully merged, probably from near the center of the merger.
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Re: Could gravity waves be faster than light?

Postby ralfcis on October 19th, 2017, 9:48 am 

Well that definitely kills my theory.
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Re: Could gravity waves be faster than light?

Postby mitchellmckain on October 19th, 2017, 9:48 pm 

By the way...

Because light is a wave, velocity is not as straightforward for it as it is for a solid object. The speed at which the crests of the wave move is called the phase velocity and this is not always equal to c, the physical constant known as the speed of light (in a vacuum). The refractive index of materials like water (1.333), glass (1.52), and air (1.0003), is the factor by which the phase velocity of a light wave is less than c in that material.
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Re: Could gravity waves be faster than light?

Postby Braininvat on October 20th, 2017, 12:11 am 

N is also dependent on frequency. Why prisms work.

Cherenkov radiation is another consequence of phase velocities slower than c. If a charged particle passes through a medium, going faster than the phase velocity of light in that medium, then you get that eerie blue light. While I don't fully grasp the phenomenon, I find it amazing.

Correct me if I'm wrong, but isn't phase velocity the velocity of ANY phase of the propagating waveform? It doesn't have to be just the crests?
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Re: Could gravity waves be faster than light?

Postby mitchellmckain on October 20th, 2017, 4:08 am 

Braininvat » October 19th, 2017, 11:11 pm wrote:N is also dependent on frequency. Why prisms work.

Cherenkov radiation is another consequence of phase velocities slower than c. If a charged particle passes through a medium, going faster than the phase velocity of light in that medium, then you get that eerie blue light. While I don't fully grasp the phenomenon, I find it amazing.

Correct me if I'm wrong, but isn't phase velocity the velocity of ANY phase of the propagating waveform? It doesn't have to be just the crests?


In fact, since it is frequency dependent, the phase velocity would only be the velocity of that frequency component. The whole wave moves together at the phase velocity as long as there is only a single frequency in the light wave.
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