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"We have detected gravitational waves. We did it."

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SkyWriting

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essentialsaltes

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So how do we know the wave is a gravity wave?
...

How does one know that what is being moved through is spacetime?

Because what was being measured was basically the length of a long tunnel. The tunnel itself is not changing size (although it must be a headache to deal with expansion due to temperature changes, or random vibrations -- a key technical challenge is to eliminate or deal with the noise caused by extraneous sources) so the changes in length of the tunnel are due to changes in spacetime. It is not so much a 'wave of gravity' as a ripple in spacetime that spreads from the source, causing minute changes in rulers and clocks as it passes through.

My pal Dr. Robert Hurt helped create these visualizations:

 
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essentialsaltes

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"I think they are assuming the velocity of the gravitational waves in order to find the location of the event...."

Explain how that works?

It's something like counting seconds from a lightning flash to find the distance.

Let's say you and your buddy are in your different homes during a thunderstorm. You're not watching it, but you can see the light flashes and hear the thunder. You're talking on the phone when there's a flash.

Your buddy says it took three seconds from the flash to the thunder, and you say it took two seconds from the flash to the thunder. So you know that you are closer to where the lightning hit. If you know the speed of sound, and the relative distance between you and your buddy, you can start to track down exactly where the flash was (even though you didn't directly see it).

I think with just two detectors it will be hard to pinpoint, but possibly they get some orientation/polarization information from the detectors that will help make the direction more clear.
 
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essentialsaltes

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So your suggesting the finding will go unchallenged and people must just accept their findings on faith?

My, that's a lot of words to cram in my mouth.

Unlike, say, cold fusion, this result is not just being announced by a press conference, but also with a peer reviewed paper in Physical Review Letters, one of the most well-respected journals in physics. This result has already been challenged by experts.

It is not so much faith as trust. Trust that people who know what they are talking about, know what they are talking about.

That said, this discovery is likely to lead to the development of additional instruments of this type and sensitivity, which should lead to independent verification of similar events. So if you're not going to build your own, you can patiently await others to do so. Assuming you trust them.
 
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Willis Gravning

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They had a live Q&A session at that site and they gave some information about how distance and direction of the event that triggered the wave was determined. Since the detector has an x And y axis a general direction could be determined. I suppose the amount of energy might yield the distance. They said approximately three solar masses of matter was converted to the energy contained in the gravity wave...wow!
 
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Michael

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Thank goodness we have you here Michael to always correct those silly professional scientists.

Yep, lucky you. I picked out the rotten section of the Bicep2 paper for you on the first read through within the first couple
of days of the release of the paper, and *months* before it all turned to dust. :) Meanwhile, Guth was publicly giving us all some song and dance about why it was Nobel Prize worthy material, and Linde was popping champagne on Youtube. :) Section nine was a complete disaster.

You'll be happy to know however that the LIGO paper passed the first read through critique quite well.
 
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Loudmouth

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Explain how that works?

Just like radio triangulation.

df_triangulation.png
 
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Loudmouth

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Exactly. So how can I test these reported results?

First, get the education needed. Second, ask politely to see their raw data. Third, analyze their methodology and instrumentation.

If you are still unsatisified . . . Fourth, build your own detector.
 
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Loudmouth

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They had a live Q&A session at that site and they gave some information about how distance and direction of the event that triggered the wave was determined. Since the detector has an x And y axis a general direction could be determined.

That makes sense. If the wave were aligned with just one of the limbs in the interferometer then all of the length changes would be detected in that direction. If the event were perfectly in between the limbs, then you would see equal changes in both limbs.

300px-Interferometer.svg.png
 
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dad

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Because what was being measured was basically the length of a long tunnel.
The tunnel is on earth. Something coming in here causes waves. They think it is gravity. I would like to be sure they got that right. They know this..how?
The tunnel itself is not changing size (although it must be a headache to deal with expansion due to temperature changes, or random vibrations -- a key technical challenge is to eliminate or deal with the noise caused by extraneous sources) so the changes in length of the tunnel are due to changes in spacetime.
Spacetime on earth. Now how do you connect that to the universe?

It is not so much a 'wave of gravity' as a ripple in spacetime that spreads from the source, causing minute changes in rulers and clocks as it passes through.
I have no doubts there are ripples out there. The issue is what they are. Also, how far away and etc. I see they claim black holes collided. Did we see the black holes...or do they 'know' those holes exist because they see ripples!!?
 
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essentialsaltes

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The tunnel is on earth. Something coming in here causes waves. They think it is gravity. I would like to be sure they got that right. They know this..how?

In a water wave, it is the water that moves. In a sound wave, it is the air that moves.

In this case, it was spacetime that moved. Our current understanding of spacetime is due to Einstein's general relativity, which shows the connection between gravity and spacetime. In a gravitational wave, it is spacetime that moves. That's what was observed.

I see they claim black holes collided. Did we see the black holes...or do they 'know' those holes exist because they see ripples!!?

We infer the black holes because of the ripples. Not just that there were ripples, but that the shape of the ripples matched the prediction of the theory. The prediction was made before the observation. The observation matches the prediction, which provides additional support that the theory is correct.
 
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