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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

#371

Post by elihu »

boardwaalk wrote: post #138

If they build a third observatory, can they triangulate where in the universe the events are occurring?

One would think so. I'm not an expert in this area, but from the descriptions it seems like they would have at least two options for finding the source direction:

One is to compare the arrival time at each of the detectors and infer direction from the speed-of-light delay.

Another option is to measure the difference in relative strength between each of the detectors. I'm assuming the detectors aren't uniformly sensitive; perhaps they're most sensitive to waves travelling in a direction parallel to one arm of the detector and perpendicular to the other, and completely insensitive to waves that are perpendicular to both (i.e. it would affect them both the same and cancel out, or perhaps not affect either of them at all). With multiple detectors at right angles to each other, you can get a pretty good idea which way it came from.

Combining the two methods could give you greater accuracy, and also help to rule out spurious signals that are not gravity waves.

This makes me wonder what you would see if you had a sufficiently accurate directional gravity wave detector and let it run for a long time. Sooner or later, you'd get an actual image, like a telescope.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#372

Post by Crito »

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.

Could such a device be used to increase the reaction mass of your fuel when it exits your engine? A sort of way to cheat F=MA by artificially boosting M, but only after you are in orbit?

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#374

Post by Ensorceled »

JabavuAdams wrote: post #223
JoeAltmaier wrote: post #186

Earlier quoted context omitted.

That always confused me. We have an Oort cloud, whose members we cannot resolve very well/at all. Why do we assume only our star has such a thing? If all stars did, that isn't enough mass to explain dark matter?

> For comparison, the sun makes up about 99.8% of the Solar System mass (500x as much mass as all the planets, dust, etc. combined). That leaves just 0.2% for all the planets, dust, Oort cloud, Kuiper belt, etc. So ... no.

Google "sun percentage mass solar system" and the highlighted answer is "By far most of the solar system's mass is in the Sun itself: somewhere between 99.8 and 99.9 percent."

Please don't just disagree when you don't know what you are talking about.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#375

Post by lmm »

tizzdogg wrote: post #177
lutorm wrote: post #149

Earlier quoted context omitted.

https://www.black-holes.org/gw150914 has some visualization of the event. There is the initial inspiral, and then there is a ringing afterwards. However, the entire event is over in a fraction of a second, which may be a "blip" to humans, but is very long when things happen at the speed of light.

Thanks, that's helpful. It's hard to get my head around the idea that an event so massive can be over so "quickly", without any residual longer-lasting effects.

There's a theorem that black holes have "no hair": two black holes of the same mass, charge and angular momentum are indistinguishable. So the merge must happen instantaneously: if the combined black hole were "sloshing" afterwards that would violate that theorem.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#376

Post by tbabb »

Manishearth wrote: post #367
sandworm101 wrote: post #272

Earlier quoted context omitted.

If the massive gravitron was leaving a black hole it would be slowed by the black hole's gravity. (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, pulling more in. (2) If they are massive, and therefore subject to slowing, shouldn't gravity waves leaving a black hole be subject to some sor…

> We should see this as some inconsistency in how gravity scales with the mass of a black hole. This inconsistency is a part of general relativity (even though gravitons themselves aren't). A black hole does not follow the GM/r^2 gravity law. > 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 we be looking for red/blu…

> and the final series converges.

Or not, and we yell "look behind you!" and then dump the infinities out the window.

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

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#377

Post by smegel »

dbranes wrote: post #256
ScottBurson wrote: post #176

This made me wonder how far we are from being able to create and detect gravitons. The Wikipedia page on gravitons [0] addresses this question: Unambiguous detection of individual gravitons, though not prohibited by any fundamental law, is impossible with any physically reasonable detector. The reason is the extremely low cross section for the interaction of gravitons with matter. For example, a detector with the mas…

Gravitational waves are a prediction of classical linearlized gravity - gravitational waves are to (classical) gravitons what light waves are to photons.

But we have direct experimental confirmation of light behaving light both a wave and as a particle. Do we have any such evidence to show gravity exhibiting particle like behavior?

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#378

Post by Manishearth »

tbabb wrote: post #376
Manishearth wrote: post #367

Earlier quoted context omitted.

> We should see this as some inconsistency in how gravity scales with the mass of a black hole. This inconsistency is a part of general relativity (even though gravitons themselves aren't). A black hole does not follow the GM/r^2 gravity law. > 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 we be looking for red/blu…

> and the final series converges. Or not, and we yell "look behind you!" and then dump the infinities out the window. https://en.wikipedia.org/wiki/Renormalization

Hah, that too :p

When I first learned about renormalization formally (i.e., with equations) I realized it wasn't that bad. But still, pretty sneaky :P

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#380

Post by sandworm101 »

Crito wrote: post #372
undersuit wrote: post #357

Earlier quoted context omitted.

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.

Could such a device be used to increase the reaction mass of your fuel when it exits your engine? A sort of way to cheat F=MA by artificially boosting M, but only after you are in orbit?

No more so than any other means of adding energy to the fuel.
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