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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

#61

Post by davrosthedalek »

Steuard wrote: post #56
Roodgorf wrote: post #49

Are there any potential competing theories this detection could also support? I'm wondering how much room there is here for confirmation bias, but I suppose that's a pretty hard thing to measure without the benefit of hindsight.

Even before this discovery, it's been pretty solidly established that any alternative theory to General Relativity would need to behave essentially identically to GR in the limits where we've been able to test it. So, for example, the "low energy limit" of string theory is general relativity (plus other content, in most cases). I'm not sure whether the loop quantum gravity folks have a working low-curvature limit yet…

Well, they extracted a lot from the waveform: Distance, the two masses, the resulting mass. I could imagine that a competing theory gives the same waveform maybe with different values for these parameters.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#62

Post by mikeash »

drx wrote: post #54
mikeash wrote: post #39

Earlier quoted context omitted.

Is there any idea how far away these black holes were? It would be interesting to know the volume of space it can potentially detect evens.

TFA says "they had heard and recorded the sound of two black holes colliding a billion light-years away" and "1.2 billion years ago". And from the paper: "The source lies at a luminosity distance of 410+160-180 Mpcc corresponding to a redshift z=0.09+0.03-0.04.". ( https://dcc.ligo.org/LIGO-P150914/public ) Which corresponds to 1.337+0.522-0.587 billion ly (or between 750.2 million and 1.859 billion ly).

Oops, missed that. Thanks!

Looks like there are roughly three million galaxies within a billion light years. Seems like lots of space for black hole pairs to live in. I suppose over the coming years, these gravity wave observatories will nail down just how common they are.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#63

Post by krapp »

omgitstom wrote: post #27
pinkrooftop wrote: post #18

Would it be possible to listen for information transmitted via gravitational waves? Would there be any benefit over radio?

I think if you really wanted to think outside of box for this, quantum entangled particles is your best bet for instantaneous low energy communication

No it isn't. Quantum entanglement doesn't allow for instantaneous communication[0][1].

[0]http://curious.astro.cornell.edu/about-us/137-physics/genera...

[1]https://physics.stackexchange.com/questions/78118/quantum-en...

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#64

Post by bzbarsky »

Steuard wrote: post #51
elorant wrote: post #15

Are gravitational waves supposed to be that weak or is it because of the distance between us and those black holes? Do they lose power as they travel through space?

Both! As others have said, intensity (power per unit area) decreases according to the same inverse square law that governs most effects due to localized sources in three dimensions of space. In this case, you're looking at a distance of over a billion light years, and then squaring it: that's a pretty enormous "per unit area"! But gravity itself is also a tremendously weak force compared to the others. That may seem…

LIGO is measuring wave amplitude, which is the square root of the power. So the thing it measures actually goes down linearly, not as inverse square.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#66

Post by nitrogen »

oldmanjay wrote: post #46
shmerl wrote: post #37

Earlier quoted context omitted.

> No one would have looked at the first computer and envisioned an iPhone. Not really. Portable computers were envisioned quite a long time ago.

Not before they were solid state. Computers had their own buildings and relied on glass tubes for operation. Screens weren't on the radar. Operators were highly educated. But technology did bring us to a point where the vision became more focused, and led to what we have today. There are many possible paths to rebutting my statement, which to be clear is idle morning musing, but your objection doesn't hold water.

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.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#67

Post by dragonwriter »

pinkrooftop wrote: post #18

Would it be possible to listen for information transmitted via gravitational waves? Would there be any benefit over radio?

> Would it be possible to listen for information transmitted via gravitational waves? Would there be any benefit over radio?

Well, if you observe a meaningful, non-natural gravity wave signal, you know that you've discovered not merely another technical situation (which you'd know if you detected the same thing in radio waves), but a phenomenally advanced one.

So, if not an advantage, there is at least a meaningful difference.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#68

Post by jerf »

CGamesPlay wrote: post #24
pinkrooftop wrote: post #18

Would it be possible to listen for information transmitted via gravitational waves? Would there be any benefit over radio?

The amount of energy needed to transmit via a gravitational wave is INSANE. It would involve very rapidly accelerating and decelerating a black hole / neutron star. While it might be possible to do this, it's not within the realm of something we could accomplish without several orders of magnitude technology improvements, and possibly may not be physically possible at all (moving object that heavy that quickly might…

Even if it were possible, what sort of crazy alien would it take to burn 3 solar masses of negentropy to basically run a ping, compared to the amount of data that could be transmitted with electromagnetic waves with 3 solar masses of negentropy? It's literally dozens of orders of magnitude in difference. Any aliens that are that bad at engineering probably aren't going to grow to the point that they can shake neutron stars several times per second.

Re: Physicists Detect Gravitational Waves, Proving Einstein Right

#70

Post by snowwrestler »

pavpanchekha wrote: post #2

I remember learning about the LIGO experiment back when it was being built, a decade ago, and at the time it seemed so amazing: a giant tube of vacuum, sealed underground and so sensitive that it could detect animals walking nearby, listening to the moving and twisting of space itself… I guess we're finally seeing that with immense human ingenuity and the most careful of engineering, the universe will offer its secre…

Well we've accounted for about 5% of the universe--the stuff we know about.

Dark matter (about 25%) seems to only interact gravitationally, which means that we've just, today, proven that we have an instrument that could possibly observe it directly. To date, all our evidence for dark matter is indirect--observing the otherwise unexplained behavior of normal matter. Today is the gravitational equivalent to Galileo pointing his first telescope at the night sky.

Dark energy (about 70%) still seems to be a total mystery.

And of course there is our inability to reconcile quantum mechanics with gravity. With each further proof of the correctness of each of those theories, the mystery of their apparent incompatibility deepens.

All of these factors lead me to believe that we may still have a long way to go in our understanding of the physical universe. I hope I'm right.

This is also why I believe it is so important to pursue nuclear energy. If we do invent further theories and experiments, it's likely that they will require even greater energy levels than we can create now, and potentially imply even greater dangers. If we can't learn to manage nuclear physics in a practical, routine way, we'll never have a hope of going beyond it (if indeed there is a "beyond.")

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