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Physicists Detect Gravitational Waves, Proving Einstein Right

nytimes.com

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Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#351

Post by contravariant »

sandworm101 wrote: post #288
contravariant wrote: post #279

Earlier quoted context omitted.

>(1) We should see this as some inconsistency in how gravity scales with the mass of a black hole. The larger ones would have proportionately greater 'drag' on leaving gravitrons. Perhaps, no clue how a quantum mechanical gravity would interact with a black hole. >(2) If they are massive, and therefore subject to slowing, shouldn't gravity waves leaving a black hole be subject to some sort of doppler effect? Should w…

If they interact with each other, then wouldn't any "wave" collapse? The particles leave the event in a smooth wave. Then they run into other waves, or each other, or just the background gravity fields. This perturbation should cause them to clump together. So in short order the smooth wave would become large blobs of gravitrons more akin to raindrops than waves. And without anything holding them apart, might not som…

I think what you're trying to describe is something like 'confinement'. I'm not confident that a massive graviton will necessarily lead to confinement, neither gravitons nor confinement are that well understood.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#352

Post by oldo-nicho »

oldo-nicho wrote: post #349

I'm interested to know how they can be so sure that the change in distance between the two arms of LIGO is attributed to gravitational waves? I would of thought that miniscule movements in the Earth's crust would be a more likely culprit.

Ahh, just realised that there are two instruments located on either side of the states, so if both instruments register the same event then it is unlikely to be tectonic movement...

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#353

Post by nikdaheratik »

cdelsolar wrote: post #281
adrianN wrote: post #245

Earlier quoted context omitted.

When one arm gets longer the laser takes a little longer to travel through it. That changes the interference pattern. http://www.phdcomics.com/comics.php?f=1853

Still not explaining it. If spacetime is stretched why doesn't light "speed up" to accommodate for it is what he's asking. I'm assuming it's because the speed of light is invariant to that.

Exactly. The speed of light in a vacuum is constant no matter how quickly/slowly your frame of reference is (Special Relativity). You can think of it as the space "stretching/shrinking" because of the gravitational wave, as that is how it looks from the point of view outside the experiment.

Another way to look at it is to change your reference to be internal to the experiment. You can imagine the experiment moving through space-time at a constant rate of speed. When the gravitational wave hits the experiment its movement through space-time changes an infinitesimal amount (faster than slower as the wave passes, or vice-versa). Since the speed of the light passing through space-time has not changed (due to special relativity), the difference between its start and end points can be used to measure the amount of change caused by the gravitational wave, essentially in the same way you can use a laser to measure the speed of a moving object relative to a stationary object. Only you are basically "bouncing" the laser off of the experiment itself to determine the change.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#354

Post by 1024core »

cdelsolar wrote: post #31
tomp wrote: post #23

Earlier quoted context omitted.

If this events are so rare (that we don't even know how rare they are), how is it possible that they achieved the required certainty (5 sigma)? I guess you could count one looong wave as a series of one-time events/measurements, but it could as well be a loooong interference.

Both detectors detected the same event at slightly different times

About 7ms apart, which ties in well with the distance between the two detectors.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#355

Post by thisrod »

oldo-nicho wrote: post #349

I'm interested to know how they can be so sure that the change in distance between the two arms of LIGO is attributed to gravitational waves? I would of thought that miniscule movements in the Earth's crust would be a more likely culprit.

The LIGO mirrors and beam splitter are attached to Earth very loosely. They hang from towers of pendulums; when Earth moves, LIGO catches up eventually, but over the time it takes a gravity wave to oscillate the components might as well be in orbit.

That is one of the more routine feats of engineering involved.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#356

Post by amelius »

semi-extrinsic wrote: post #345
amelius wrote: post #335

Earlier quoted context omitted.

How about a theory where spacetime touches upon another spacetime and interacts with it, perhaps through gravity? Or if spacetime folds back onto itself?

You are suggesting possible future events that would provide evidence for a multiverse. That does not make something a falsifiable theory. Analogy: it could happen that tomorrow Jesus Christ descends from the heavens and brings the day of reckoning. That would prove Christianity to be true, but the fact that this could happen does not make Christianity a falsifiable theory. A falsifiable theory is a theory that predi…

Ok. What if spacetime folds back onto itself over a very long distance? Wouldn't that be (viewed locally, with our limited instruments) as if another version of spacetime touches upon our version of spacetime?

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#357

Post by undersuit »

other_herbert wrote: post #346
ScottBurson wrote: post #336

Earlier quoted context omitted.

I think you must be right -- but maybe there's some other way to create them, without needing to move a mass. The ability to manipulate gravity itself might be the key to space travel.

Flying cars man! Think of the flying cars! And maybe real hover boards

First we need to find out how to create repulsion. Right now I'm pretty sure a graviton generator would just be a novelty device that weighs more than what it's mass would lead you to think it weighs.

Maybe we could make orbital graviton beam generator that could literally suck an object off the face of the Earth.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#358

Post by IIJamesII »

brudgers wrote: post #204
guscost wrote: post #134

Earlier quoted context omitted.

Unfortunately not-entirely-unreasonable skepticism can be mistaken for hostility by people excited about a potentially groundbreaking result. That said, it sounds like they did a lot more work to eliminate sources of error than you may be aware of. OTOH if seismic resonance was causing the correlation, there would probably be more time between the events at the two facilities. Scientists will try to poke holes in the…

I'm sure I was not clear, since that was the first pass. What the experiment indicates is that the Earth varies in size. Roughly: measured distance of 10^-20 meters 4km is 10^-5 of earth circumference. delta Earth's circumference 10^-25 total distance change in earth's diameter = 10^-18 meters Given the non-intuitive nature of geology[1], I am saying that the possibility that the Earth varies that much in dimension d…

I was also wondering how they successfully rule out other possibilities. Many people seem very eager to believe. Some skepticism here can help aid a more thorough understanding.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#359

Post by nikdaheratik »

platz wrote: post #318
evanpw wrote: post #280

Earlier quoted context omitted.

Another re-phrase: how can we detect that space has stretched out if all of our rulers also get stretched by exactly the same amount? The answer is that we have a ruler that doesn't get stretched in this way: light. The speed of light is a constant dictated by the laws of physics; stretching out our flashlight to twice its normal size wouldn't make the light it emits go twice as fast. So if you just measure the time…

Does this mean that in earth's gravity well, there is an absolute difference in the time light takes to travel compared with light travelling in the void of space? Can we compute the strength of a static gravity field we are inside, by measuring the time that light takes to propagate through it?

The light is constant, which means it moves at the same speed in both cases (assuming the light is in a vacuum). It won't move faster or slower based on the gravity field (other than in the case of black hole where it can't escape at all).

What happens instead is that the speed that an object moves through space-time changes dependent upon gravity. Using an atomic clock, we've actually measured the effect of gravity to show that time moves more slowly down on earth than it does in an orbiting satellite.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#360

Post by celticninja »

undersuit wrote: post #357
other_herbert wrote: post #346

Earlier quoted context omitted.

Flying cars man! Think of the flying cars! And maybe real hover boards

First we need to find out how to create repulsion. Right now I'm pretty sure a graviton generator would just be a novelty device that weighs more than what it's mass would lead you to think it weighs. Maybe we could make orbital graviton beam generator that could literally suck an object off the face of the Earth.

That sounds like a tractor beam to me.
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