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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

#331

Post by kamaal »

jerf wrote: post #175
kamaal wrote: post #141

Earlier quoted context omitted.

Our power generation stations are the black hole equivalent to the caveman with only access to generating fire through rubbing stones. Based on what level of civilization you are. Rubbing two black holes in for a ping, might be the same as rubbing two stones for a spark. Advanced civilization go really advanced, to a point their activities would be undetectable to us or would appear to us the nature of reality itself…

"Advanced civilization go really advanced, to a point their activities would be undetectable to us or would appear to us the nature of reality itself." This is science fiction, not an argument. We have no rational reason at the moment to believe this is the case, or even possible. What we do in fact have is an increasing trend towards efficiency . Projecting that out along crazy growth curves suggests that advanced a…

>>This is science fiction, not an argument. We have no rational reason at the moment to believe this is the case, or even possible.

There are not only rational reasons, but even evidences to support what I'm trying to say.

Look at any insect colony or bacteria, they don't even recognize our presence, let alone our technology.

>>What we do in fact have is an increasing trend towards efficiency. Projecting that out along crazy growth curves suggests that advanced aliens are likely to be more horrified by such a waste of negentropy than we are.

We the advanced aliens to ants, are indulging waste and plastic pollution like never before. And ants the aliens to bacteria might appear the same.

Efficiency and waste are very relative terms based on what level of abundance or austerity on is supposed to live on.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#332

Post by nitrogen »

bbcbasic wrote: post #325
nitrogen wrote: post #66

Earlier quoted context omitted.

Is your speculation that the gravity wave detectors would be able to detect the changes in gravity caused by movements of people and things? Submarines already do this to detect other vessels AFAIK.

Surely you are thinking of Sonar?

No, this came up on Hacker News recently: https://news.ycombinator.com/item?id=10810390

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#333

Post by tedd4u »

evanpw wrote: post #280
theophrastus wrote: post #260

Earlier quoted context omitted.

Here's my re-statement of this confusion, isn't everything we can experience embedded in time-space, including the LIGO experiment itself? So how is there any relative shift allowed to be detected when everything we know is fundamentally intrinsic to time-space? That is, I too would appreciate having this mis-conceptualizing, of mine, cleared away.

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…

Thanks for this explanation. The universe is a pretty freaking amazing place.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#334

Post by yk »

guscost wrote: post #319
tfgg wrote: post #301

Earlier quoted context omitted.

(None of my points below say the graviton is massless, just that it's not crazy. As another post says, this new observation probably confines the graviton mass to be less than 10^-55 grams) > If the massive gravitron was leaving a black hole it would be slowed by the black hole's gravity. A graviton wouldn't be able to escape a black hole. A photon can't, and it's massless. The gravity of a black hole is actually a s…

> A graviton wouldn't be able to escape a black hole ... the curvature of the spacetime around the black hole But isn't the curvature of spacetime around the black hole supposed to be the effect of its interaction with the graviton?? Is this where the translation from GR -> QM breaks down?

> Is this where the translation from GR -> QM breaks down?

Sort of, to get a graviton you introduce perturbations on a background metric. (Basically small wiggles of spacetime around an 'average.') You don't do anything like that when you solve the Einstein equations. Consequently, the background spacetime ( that is, the black hole) is not really made of gravitons. (At least in some sense.)

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#335

Post by amelius »

semi-extrinsic wrote: post #307
zoke wrote: post #222

Earlier quoted context omitted.

I recall reading some years ago that gravitational wave would be used to prove multiverse theory. How would that scale compared to bh-bh or ns-ns mergers? Also, have read today that this discovery backs inflationary theory, how so? It seems highly unlikely that they could say a specific bh-bh merger was the cause. It seems implied they are triangulating the source, with two detectors?

AFAIK no multiverse theory has yet been put forth that is experimentally testable (even in theory given infinite time, energy etc.) So it's not a proper (falsifiable) scientific theory at present, merely a (in my opinion wild) conjecture.

How about a theory where spacetime touches upon another spacetime and interacts with it, perhaps through gravity?

Or if spacetime folds back onto itself?

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#336

Post by ScottBurson »

pbhjpbhj wrote: post #324
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…

>how far we are from being able to create and detect gravitons // Surely we create gravitons whenever we move a mass just like we create photons whenever we move a body that interacts electromagnetically? Isn't the point that we're constantly exchanging gravitons with all matter as they mediate gravitational attraction.

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.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#337

Post by drx »

mehwoot wrote: post #310
drx wrote: post #252

Earlier quoted context omitted.

This would be true in a static universe, but, during the 1.2 billion years the waves have been traveling, the universe was experiencing accelerating expansion. For example, the edge of the observable universe is about 46.5 lightyears away, while the universe is thought to be 13.8 billion years. https://en.wikipedia.org/wiki/Observable_universe#Misconcept...

is about 46.5 lightyears away I assume you mean 46.5 billion?

Yeah, thanks! I can't edit it any more, unfortunately.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#338

Post by delecti »

fsloth wrote: post #275
wuliwong wrote: post #268

I am not sure why but I am really hung up on the quote “Finally, astronomy grew ears. We never had ears before.” They are detecting gravitational waves not sound waves.

Any vibration is just a signal. We don't actually have a direct experience with a sound, hearing is our brains interpreting the nerve signals generated by tiny organelles jiggling in our ears. What is concrete then, is only the shape of the signal, but not the medium through which it propagates. This device just acts like a gigantic hearing device. Except it's not pressure waves, but the fabric of the universe which…

> Anyway, I was a bit irritated of this same phrase, but because I tought radio astronomers had been listening to skies for quite some time now.

Radio waves are light too though. Or at least they're photons.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#339

Post by swombat »

platz wrote: post #247
swombat wrote: post #230

Earlier quoted context omitted.

Actually, we have ample proof of the distortion of spacetime in a gravity well - gravitational lensing. It's an observed effect around very massive objects and we have been able to see it at work very well. Also, arguably, the fact that we're not falling towards the sky is itself evidence of a spacetime gradient near the Earth, but that was also explained by Newton's Law of Gravitation. But back in 1916, Einstein als…

Agree... my question, though poorly worded, is less about proof of spacetime gradients (they do in the ways you describe). It's more about understanding what the measurable effects of a gravitational well on earth has on the LIGO experimental setup (or a similar one with infinite precision), in the absence of gravitational waves.

Well, something like LIGO can only measure gravitational waves, because it looks for changes in the geometry of spacetime. If you were to move the LIGO in and out of Earth's gravitational well, I guess then it would record a shift.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#340

Post by rattray »

auntienomen wrote: post #208
kkylin wrote: post #200

A conceptual issue that some of the commenters may have missed is that part of the detection is done by matched filtering ( https://en.wikipedia.org/wiki/Matched_filter ), in which it is necessary to have a good idea of the signal you're looking for. This detection has built upon analytical and numerical advances in relativity. While people may not know about the prevalence of e.g. binary black hole collisions, they…

Yeah, too many LHC reports have primed people to expect counting experiments where the scientists struggle to get to 5 sigma. The waveforms we're talking about here have a signal to noise ratio over 20.

Sorry, what does that ratio imply?
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