APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Comments and questions about the APOD on the main view screen.
User avatar
MarkBour
Subtle Signal
Posts: 1111
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by MarkBour » Fri Feb 12, 2016 5:18 pm

Thank you alter-ego and chris for helping me better understand the evidence here. Yes, chris, I definitely take your point excerpted below:
Chris Peterson wrote:... At this point, claiming that what we observe and interpret as black holes are really something else is kind of like making the claim that what we observe as stars aren't really stars, but rather, plasma bodies which are fusing elements and radiating large amounts of energy!

One of the important conclusions of the discovery is the first direct observation of black holes. Which is a reasonable view.
So, if I'm getting it correctly, one of the nice things about the observations is that they would only be consistent with masses that were very compact. Hence, black holes fit the data like no other type of objects, such as less-dense neutron stars would. That is amazing.

I think a corollary of the above (probably only notable to someone as novice in the subject as myself), is that this event would be the first observation of mass being removed from a black hole. Although in this instance, it was only accomplished with the merger of even more mass into an event horizon, still, something that was within a BH event horizon would no longer be within a BH event horizon. A longer-term larger modelling, then, that simulated the growth of a galactic central black hole to a size of 1 million sols, would therefore, I assume, show that there was a great deal more mass involved in the evolution of the beast than 1 million sols.

One other thing that I think can eventually be shown by the data. The offset of time from the multiple detectors, when there is enough of a signature to believe they are detecting the same event, would measure the velocity of propagation of GWs. It seems to me that with only 2 detectors and one event, one can only put an upper bound on the velocity of the wavefront. Were the detectors aligned perpendicular to the wavefront motion, they would have been simultaneous. Were they parallel to it, they would have measured its velocity. The wavefront must be travelling at most as fast as d/(t2-t1), though (n'est-ce pas?)
Mark Goldfain

User avatar
geckzilla
Ocular Digitator
Posts: 9146
Joined: Wed Sep 12, 2007 12:42 pm
Location: Modesto, CA

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by geckzilla » Fri Feb 12, 2016 9:35 pm

neufer wrote:(unless one is mapping all the events over an extended period of time).
Well, what else would we do with such data? Get on it, astronerds. Where's that third detector?! I want my gravitational wave map. :mrgreen:
Just call me "geck" because "zilla" is like a last name.

User avatar
Chris Peterson
Abominable Snowman
Posts: 15393
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by Chris Peterson » Sat Feb 13, 2016 12:54 am

MarkBour wrote:I think a corollary of the above (probably only notable to someone as novice in the subject as myself), is that this event would be the first observation of mass being removed from a black hole. Although in this instance, it was only accomplished with the merger of even more mass into an event horizon, still, something that was within a BH event horizon would no longer be within a BH event horizon.
Somebody earlier (Art?) said you need to be careful how you think about that sort of thing if you don't want your head to explode. I'm not sure it's reasonable to think of something escaping from inside an event horizon. Any BH pair is giving up energy via gravitational radiation, even before there is a merger- and we have observed that before. Where all that energy comes from is tricky to analyze.
One other thing that I think can eventually be shown by the data. The offset of time from the multiple detectors, when there is enough of a signature to believe they are detecting the same event, would measure the velocity of propagation of GWs.
GR falls apart, and the simulations would fail, if gravitational waves propagated at anything other than c. A confirmation of that may be incidental to other measurements, but I'm not sure anybody has a primary interest in that measurement.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
Chris Peterson
Abominable Snowman
Posts: 15393
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by Chris Peterson » Sat Feb 13, 2016 12:56 am

geckzilla wrote:
neufer wrote:(unless one is mapping all the events over an extended period of time).
Well, what else would we do with such data? Get on it, astronerds. Where's that third detector?! I want my gravitational wave map. :mrgreen:
Advanced Virgo, in Italy, should come online later this year and be operating at full sensitivity within a couple of years. That will make three high sensitivity instruments.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17606
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by neufer » Sat Feb 13, 2016 1:58 am

geckzilla wrote:
neufer wrote:
(unless one is mapping all the events over an extended period of time).
Well, what else would we do with such data?
Well, the first things to do might be to:

1) Check that the "chirps" match up with theory.
2) Categorize the different sources.
3) Attempt to locate the galaxy involved.
Art Neuendorffer

User avatar
geckzilla
Ocular Digitator
Posts: 9146
Joined: Wed Sep 12, 2007 12:42 pm
Location: Modesto, CA

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by geckzilla » Sat Feb 13, 2016 2:36 am

Yeah, something like that quasar map except with various EMS maps lined up with it. Some sources probably originate from where we expect them, like in the cores of massive galaxies, while others surely emanate from unexpected locations.
Just call me "geck" because "zilla" is like a last name.

User avatar
Beyond
500 Gigaderps
Posts: 6889
Joined: Tue Aug 04, 2009 11:09 am
Location: BEYONDER LAND

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by Beyond » Sat Feb 13, 2016 9:28 pm

Click to play embedded YouTube video.
To find the Truth, you must go Beyond.

User avatar
MarkBour
Subtle Signal
Posts: 1111
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by MarkBour » Mon Feb 15, 2016 5:57 pm

Chris Peterson wrote:
MarkBour wrote:I think a corollary of the above (probably only notable to someone as novice in the subject as myself), is that this event would be the first observation of mass being removed from a black hole. Although in this instance, it was only accomplished with the merger of even more mass into an event horizon, still, something that was within a BH event horizon would no longer be within a BH event horizon.
Somebody earlier (Art?) said you need to be careful how you think about that sort of thing if you don't want your head to explode. I'm not sure it's reasonable to think of something escaping from inside an event horizon. Any BH pair is giving up energy via gravitational radiation, even before there is a merger- and we have observed that before. Where all that energy comes from is tricky to analyze.
Well, unless we're the Bene Gesserit, I don't see why. The one fact is pretty simple, of course. If the assumptions and simulation are correct at all, and if you believe that what is inside the event horizon of a BH is still mass, then some of it is no longer there. If it were some quark-filled soup, some of it has been sent away. And one could say that all of the mergers that went in to building up supermassive BHs, were actually events that reduced the total amount of mass in the universe that is currently trapped in BHs.

As two black holes approach one another, they would "pry each other open". There are places where the pull from the two "cores" cancel each other out, Lagrange points, and surrounding them, regions of relatively low gravity. This is pretty well represented in the visualization that was given in the Feb 12 APOD http://apod.nasa.gov/apod/ap160212.html . But here's a nifty question. Even after the two event horizons have merged into one, there should still -- for a brief time, at least -- be a quadrupole inside the BH. A beam of light that aimed exactly at the center of the new BH, traveling perpendicular to the plane of their dance, would pass through, unbent. However, as it passed the plane, it would be affected by the net gravity, tugging it back. A simple answer would be that no, it could not overcome the gravity. But then what of the equal amount of energy that would have been contributed to its flight on the way in? Does that count for nothing?

Could it actually make it through?
Mark Goldfain

User avatar
MarkBour
Subtle Signal
Posts: 1111
Joined: Mon Aug 26, 2013 2:44 pm
Location: Illinois, USA

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by MarkBour » Tue Feb 16, 2016 1:18 am

By the way, in the above, I'm assuming from neufer's earlier post, that the simulation gave us: 36 U 29 => 62 . I'm not claiming to be a person who knows that, just a kiddo who heard it in the conversation, and am relying on it as the basis of my further deductions.
Nitpicker wrote:Is it correct to assume that the gravitational "pull" from a black hole is so great, that no electro-magnetic, nor gravitational radiation can escape its threshold (or event horizon thingy)?
We have lots of observation that shows that gravitation acts on electromagnetic radiation. But your "nor" part assumes that gravitation acts on gravitation. I do not think that will lead to a sensible model. For one, this would lead to black holes having no pull on the space surrounding them.
Mark Goldfain

User avatar
Nitpicker
Inverse Square
Posts: 2692
Joined: Fri Sep 20, 2013 2:39 am
Location: S27 E153

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by Nitpicker » Tue Feb 16, 2016 2:45 am

MarkBour wrote:By the way, in the above, I'm assuming from neufer's earlier post, that the simulation gave us: 36 U 29 => 62 . I'm not claiming to be a person who knows that, just a kiddo who heard it in the conversation, and am relying on it as the basis of my further deductions.
Nitpicker wrote:Is it correct to assume that the gravitational "pull" from a black hole is so great, that no electro-magnetic, nor gravitational radiation can escape its threshold (or event horizon thingy)?
We have lots of observation that shows that gravitation acts on electromagnetic radiation. But your "nor" part assumes that gravitation acts on gravitation. I do not think that will lead to a sensible model. For one, this would lead to black holes having no pull on the space surrounding them.
Yeah, I kinda corrected myself in my next post.

Pianosorplanets
Ensign
Posts: 31
Joined: Tue Jul 14, 2015 1:34 pm
Location: Pennsylvania, USA

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by Pianosorplanets » Thu Feb 18, 2016 7:19 am

OK, sorry before I start. I know I'm a physics idiot. That hasn't stopped me from "trying" to wrap my brain around it. But LIGO's latest "findings" begs a question that I really wish somebody would answer intelligibly for a physics lamebrain like myself. Did or did not Oleg D. Jefimenko and even James Clerk Maxwell (although he worked before Einstein) prove pretty convincingly that Einsteinian Relativity is a pig in a poke mostly stuff stolen from Poincare and disproven by Jefimenko? Meaning that the LIGO detectors would, in fact, provide a much greater donation to mankind as recyclables?

Maybe that question is too big for this forum but having some knowledge of this and yet finding mainstream scientists treating Relativity as if Einstein were a modern Moses down from the Mt. is confusing me greatly.
It takes a lot of stars to make a piano.

User avatar
Ann
4725 Å
Posts: 10911
Joined: Sat May 29, 2010 5:33 am

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by Ann » Thu Feb 18, 2016 7:55 am

Pianosorplanets wrote:OK, sorry before I start. I know I'm a physics idiot. That hasn't stopped me from "trying" to wrap my brain around it. But LIGO's latest "findings" begs a question that I really wish somebody would answer intelligibly for a physics lamebrain like myself. Did or did not Oleg D. Jefimenko and even James Clerk Maxwell (although he worked before Einstein) prove pretty convincingly that Einsteinian Relativity is a pig in a poke mostly stuff stolen from Poincare and disproven by Jefimenko? Meaning that the LIGO detectors would, in fact, provide a much greater donation to mankind as recyclables?

Maybe that question is too big for this forum but having some knowledge of this and yet finding mainstream scientists treating Relativity as if Einstein were a modern Moses down from the Mt. is confusing me greatly.
Think of it like this. There have been huge numbers of carefully carried out experiments to test Einstein's theory of relativity. None have managed to find any cracks or weaknesses in it.

So what would you rather believe, hundreds of top-notch state of the art tests that have all come out in support of general relativity, or Jefimenko?

Ann
Color Commentator

Markus Schwarz
Science Officer
Posts: 224
Joined: Wed Apr 29, 2009 11:55 am
Location: Germany

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by Markus Schwarz » Thu Feb 18, 2016 10:33 am

Pianosorplanets wrote:Did or did not [...] even James Clerk Maxwell (although he worked before Einstein) prove pretty convincingly that Einsteinian Relativity is a pig in a poke...
Actually, it was Einstein who "rescued" Maxwell's equation by introducing his theory of relativity. There are dozens of alternatives to general relativity that were/are studies by physicists. Its' just that they are even more complicated or have been experimentally disproven. As Ann said, Einstein's theory of (general) relativity has been put to the test many times and it passed every time.

daddyo
Ensign
Posts: 78
Joined: Tue Feb 10, 2015 4:48 am

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by daddyo » Thu Feb 18, 2016 8:29 pm

I don't believe anyone's ever directly tested the one-way speed of light anisotropy in a vacuum. I think it's always done with interferometry, using properties of light to measure light, a seemingly bad idea. When that's tested, I'll be a believer in Einstein's magic. The thing is, it can be measured today, but nobody want's to look foolish testing it, and it may be rather expensive since it would ideally be somewhat distant in space.

User avatar
alter-ego
Serendipitous Sleuthhound
Posts: 884
Joined: Mon Apr 21, 2008 4:51 am
Location: Redmond, WA

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by alter-ego » Fri Feb 19, 2016 5:28 am

daddyo wrote:I don't believe anyone's ever directly tested the one-way speed of light anisotropy in a vacuum. I think it's always done with interferometry, using properties of light to measure light, a seemingly bad idea.
It's not "seemingly bad" at all.
All relativity theory would crumble if the speed of light were anisotropic - validation experiments over the last century would have revealed inconsistencies throughout. Regarding interferometry, there is no better path-difference measuring tool. Lasers (standing wave resonators) wouldn't work the way they do if c was anisotropic. To get a false-positive for equal speeds in opposite directions (i.e. no interferometric phase shift), the frequency / wavelength of the light would have to change in just the exact amount to hide the velocity (and distance!) difference. On the contrary, there is nothing better using electromagnetic radiation to test the constancy of c. You might think there's some low-hanging fruit there that's been overlooked, but there isn't. To think otherwise is to vastly complicate an elegant, simple concept. Today, the best and most tested theory of how the Universe works fundamentally rests on that principle - from time dilation (SR and GR), GWs and even particle accelerator experiments. None of the measurements could have been predicted, let alone interpreted, if not for the constancy of the speed of light. It's an incorrect idea to think that one-way velocity timings are required to validate Einstein's "magic".
A pessimist is nothing more than an experienced optimist

daddyo
Ensign
Posts: 78
Joined: Tue Feb 10, 2015 4:48 am

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by daddyo » Fri Feb 19, 2016 5:58 am

I think it's still worth one test of possibly the most direct validation of a fundamental property of relativity. From what I've found, believe it or not, it hasn't been directly tested. I'd really like to be shown otherwise for at least myself. Regarding interferometry, there's more than one way to induce a phase shift.

It took over a hundred years to validate Newton, 200 years ago. His theories held out for quite a while, relativity is still relatively young...

User avatar
Ann
4725 Å
Posts: 10911
Joined: Sat May 29, 2010 5:33 am

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by Ann » Fri Feb 19, 2016 7:02 am

The "problem" with General Relativity is that it is non-intuitive. Its effects are not noticeable on our human scale, size and speed of things. Hence, some people may not "like" GR. We know from our own everyday experience that the more powerful an engine is, the faster it will propel our Earth-bound vehicles. Surely the same rule should apply to our spaceships? Surely achieving near-C speed is only a matter of constructing the right engine and feeding it the right fuel? Surely staying in our own original time frame will be no problem just because we travel at close to the the speed of light or faster? Surely no one has heard of a guy driving an incredibly fast car and returning home younger than his twin brother?

Perhaps it is only the irritating idea of General Relativity that holds us back and prevents us from building the sort of spaceships that would really allow us to travel freely in the galaxy and explore the universe?
Click to play embedded YouTube video.
But the truth is that the unimaginable vastness of the universe is utterly, utterly unlike our own little world. Like it or not, the universe is utterly beyond our imagination.

I can only hope that people will listen to reason and science and respect scientific observation and testing, and realize that flights of fancy are fun, but they are no more than that. They are not reality. Trying to deny all the verifications of General Relativity will not send us to the stars.

Reality isn't like Star Trek or Star Wars, no matter how much we might like it to be.

Ann
Color Commentator

User avatar
alter-ego
Serendipitous Sleuthhound
Posts: 884
Joined: Mon Apr 21, 2008 4:51 am
Location: Redmond, WA

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by alter-ego » Fri Feb 19, 2016 7:17 am

daddyo wrote:I think it's still worth one test of possibly the most direct validation of a fundamental property of relativity. From what I've found, believe it or not, it hasn't been directly tested.
I understand your curiosity, but unlike "direct" gravitational wave detection, the result would neither be exciting nor a surprise. By the way, clock synchronization is a big problem. How does one know how long the one-way time is? The historical measurement of c by the delay in Jupiter's moon's orbital position at different times in Jupiter's orbit (crude accuracy) is the closest example I can think of that deals with different light propagation directions.
Regarding interferometry, there's more than one way to induce a phase shift.
Well not in a vacuum, inertial rest frame. You'd have to invent a non-physical, complicated environment to generate a perfectly self-compensating phase shift to hide anisotropic effects.
It took over a hundred years to validate Newton, 200 years ago. His theories held out for quite a while, relativity is still relatively young...
Agreed. I've stated GR is effectively a middle-aged adult. Sure the transition of Newtonian physics to GR is a good analogy to assume for GR, but the GR may first transition from a classical field theory to one that includes quanta, or it will crack at extreme relativistic conditions that we don't have the technology yet to probe/measure. But it won't be anisotropic behavior of light in our frame of reference and time. The supposition that the magnitude of c is anisotropic in GR is very analogous to suggesting that forces are NOT equal and opposite in Newtonian physics. They are both equally unreal. The impact on Newton's theory is more obvious and maybe silly to you, but the impact on GR is equally silly. It may take decades to ferret out the crack(s) in GR, and it won't be by measuring the one-way speed of light in a flat space-time.
A pessimist is nothing more than an experienced optimist

Markus Schwarz
Science Officer
Posts: 224
Joined: Wed Apr 29, 2009 11:55 am
Location: Germany

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by Markus Schwarz » Fri Feb 19, 2016 9:44 am

daddyo wrote:I think it's still worth one test of possibly the most direct validation of a fundamental property of relativity. From what I've found, believe it or not, it hasn't been directly tested. I'd really like to be shown otherwise for at least myself.
What do you mean by "directly tested"? What do you propose as a Gedankenexperiment?
alter-ego wrote:I understand your curiosity, but unlike "direct" gravitational wave detection, the result would neither be exciting nor a surprise.
There are still a lot of experiments that test the assumptions of Relativity. One standard framework to study Lorentz symmetry violation (end hence violation of Einstein's principle of the constancy of the speed of light) is the standard model extension. This framework can theoretically lead to an anisotropy in the speed of light, which would lead to vacuum birefringence. A former colleague worked on this and obtained incredibly tight bounds the anisotropy of the speed of light.

Buddy
Ensign
Posts: 11
Joined: Wed Sep 10, 2014 4:15 pm

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by Buddy » Fri Feb 19, 2016 7:35 pm

Would any of this energy be converted to radiation? So for example, you detect a gravity wave, get an idea of where to look, then see the radiation pulse follow it? Follow it because presumably gravity waves travel unimpeded, while radiation has the intervening intergalactic medium to slow it down.

User avatar
Chris Peterson
Abominable Snowman
Posts: 15393
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by Chris Peterson » Fri Feb 19, 2016 7:41 pm

Buddy wrote:Would any of this energy be converted to radiation? So for example, you detect a gravity wave, get an idea of where to look, then see the radiation pulse follow it? Follow it because presumably gravity waves travel unimpeded, while radiation has the intervening intergalactic medium to slow it down.
Gravitational radiation is absorbed every time it interacts with a massive object, which results in a conversion to kinetic energy (and ultimately, heat). But the amount of energy thus converted is vanishingly small compared with the original source energy.

Electromagnetic radiation is not slowed down by the intergalactic medium. Like gravitational radiation, it may interact with particles making up the IGM, with a resultant conversion to different energy types and therefore some attenuation of the original energy.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17606
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by neufer » Fri Feb 19, 2016 9:25 pm

Chris Peterson wrote:
Gravitational radiation is absorbed every time it interacts with a massive object, which results in a conversion to kinetic energy (and ultimately, heat).
"Gravitational radiation is absorbed every time it interacts with a massive object, which results in a conversion to kinetic energy" ... but I don't know why it should necessarily end up as heat.

I've assumed that the massive 40kg aLIGO mirrors follow those space time ripples like rubber duckies floating on gentle pond ripples with little in the way of heat or scattered ripples being generated. The mirrors stop moving simply because the ripples pass on and not because there is any real damping involved.
Art Neuendorffer

User avatar
Chris Peterson
Abominable Snowman
Posts: 15393
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by Chris Peterson » Fri Feb 19, 2016 11:19 pm

neufer wrote:
Chris Peterson wrote: Gravitational radiation is absorbed every time it interacts with a massive object, which results in a conversion to kinetic energy (and ultimately, heat).
"Gravitational radiation is absorbed every time it interacts with a massive object, which results in a conversion to kinetic energy" ... but I don't know why it should necessarily end up as heat.
Well, heat is pretty much the endpoint of all energy transformations.
I've assumed that the massive 40kg aLIGO mirrors follow those space time ripples like rubber duckies floating on gentle pond ripples with little in the way of heat or scattered ripples being generated. The mirrors stop moving simply because the ripples pass on and not because there is any real damping involved.
I'm not talking about damping. Parts of the system move. That means work is done. That means energy is required, and the only source of that energy is the gravitational waves. They have to leave the interaction slightly less energetic than when they began. Energy is conserved, after all. And the mechanical energy spent in moving the LIGO components (not to mention the Earth itself) ends up as heat. What else could it end up as?
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
neufer
Vacationer at Tralfamadore
Posts: 17606
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by neufer » Sat Feb 20, 2016 2:00 am

Chris Peterson wrote:
neufer wrote:
I've assumed that the massive 40kg aLIGO mirrors follow those space time ripples like rubber duckies floating on gentle pond ripples with little in the way of heat or scattered ripples being generated. The mirrors stop moving simply because the ripples pass on and not because there is any real damping involved.
I'm not talking about damping. Parts of the system move. That means work is done. That means energy is required, and the only source of that energy is the gravitational waves. They have to leave the interaction slightly less energetic than when they began. Energy is conserved, after all. And the mechanical energy spent in moving the LIGO components (not to mention the Earth itself) ends up as heat. What else could it end up as?
And when a comet comes in from the Oort cloud it speeds up. That means work is done. That means energy is required, and the only source of that energy is the potential energy in the Sun's gravitational field. Energy is conserved, after all.

But when that comet exits the Solar System it slows down thereby giving back that energy to gravitational potential energy. The only way for LIGO to accurately track the ripples in the gravitational wave is for it left motionless and still after the wave has pass...meaning no permanent energy absorbed and no heat.
Art Neuendorffer

daddyo
Ensign
Posts: 78
Joined: Tue Feb 10, 2015 4:48 am

Re: APOD: LIGO Detects Gravitational Waves (2016 Feb 11)

Post by daddyo » Sat Feb 20, 2016 5:14 am

alter-ego wrote:I understand your curiosity, but unlike "direct" gravitational wave detection, the result would neither be exciting nor a surprise. By the way, clock synchronization is a big problem. How does one know how long the one-way time is? The historical measurement of c by the delay in Jupiter's moon's orbital position at different times in Jupiter's orbit (crude accuracy) is the closest example I can think of that deals with different light propagation directions.
I probably hijacked the thread a bit too much, but I really do think that someday the universe will make sense to humans.

Here's an experiment. Two relatively stationary light detectors far away from significant gravitational fields are pulsed from an orthogonal again relatively stationary light source to establish a common time reference at/for the detectors. A high velocity rocket with a light pulse emitter travels down an imaginary line connecting the two detectors. The pulse trips the detectors measuring the elapsed time therefore the speed of light. Compare that to when the rocket was stationary or after the rocket passes. Simple eh? Today's optical emitters/detectors are capable of doing this, already found them. It could be done on Earth, however some theorists may claim Earth's local environment contaminated the result. It would be crazy never to attempt this.