Ask Ethan: How Do Gravitational Waves Escape From A Black Hole? (Synopsis)

“I think there are a number of experiments that are thinking about how you could look in different frequency bands, and get a glimpse of the primordial gravitational wave background. I think that would be really revolutionary, because that would be your first glimpse at the very first instant of our Universe.” -Dave Reitze, LIGO’s executive director

Black holes are remarkable entities that have puzzled and fascinated us since they were first postulated long before Einstein developed his theory of relativity. One of their fundamental but bizarre properties is the fact that once something crosses or winds up inside the event horizon, it can not only never escape, it heads inevitably towards the central singularity. At that point, the only “information” about the singularity is its mass, charge (of various types), and spin.

Illustration of a black hole and its surrounding, accelerating and infalling accretion disk. The singularity is hidden behind the event horizon. Image credit: NASA.

Illustration of a black hole and its surrounding, accelerating and infalling accretion disk. The singularity is hidden behind the event horizon. Image credit: NASA.

Yet when two merging black holes coalesced together, as seen multiple times by LIGO, the mass of the final black hole was approximately 5% less than the sum of the masses of the two black hole progenitors. If nothing massive or massless can escape through the event horizon, how did this energy get out?

Any object or shape, physical or non-physical, would be distorted as gravitational waves passed through it. Note how no waves are ever emitted from inside the black hole's event horizon. Image credit: NASA/Ames Research Center/C. Henze.

Any object or shape, physical or non-physical, would be distorted as gravitational waves passed through it. Note how no waves are ever emitted from inside the black hole’s event horizon. Image credit: NASA/Ames Research Center/C. Henze.

Our intuitions might lead us astray, but the mathematics provides a straightforward explanation that’s not so different from other physics you might be used to. Come find out on this edition of Ask Ethan!

12 Comments

  1. Omega Centauri

    “I think there are a number of experiments that are thinking about how you could look in different frequency bands, and get a glimpse of the primordial gravitational wave background. I think that would be really revolutionary, because that would be your first glimpse at the very first instant of our Universe.” -Dave Reitze, LIGO’s executive director
    Black holes are remarkable entities that have puzzled and fascinated us since they were first postulated long before Einstein developed his theory of relativity. One of their fundamental but bizarre properties is the fact that once something crosses or winds up inside the event horizon, it can not only never escape, it heads inevitably towards the central singularity. At that point, the only “information” about the singularity is its mass, charge (of various types), and spin.
    Illustration of a black hole and its surrounding, accelerating and infalling accretion disk. The singularity is hidden behind the event horizon. Image credit: NASA.
    Yet when two merging black holes coalesced together, as seen multiple times by LIGO, the mass of the final black hole was approximately 5% less than the sum of the masses of the two black hole progenitors. If nothing massive or massless can escape through the event horizon, how did this energy get out?
    Any object or shape, physical or non-physical, would be distorted as gravitational waves passed through it. Note how no waves are ever emitted from inside the black hole’s event horizon. Image credit: NASA/Ames Research Center/C. Henze.
    Our intuitions might lead us astray, but the mathematics provides a straightforward explanation that’s not so different from other physics you might be used to. Come find out on this edition of Ask Ethan!

    Related

  2. Omega Centauri

    Thanks, Ethan.
    I have a question about other merger observables. If we were so lucky as to be able to observe a merger from close by (say a lightyear), with large telescopes, could we see anything other than gravitational waves? I’m assuming neither has an accretion disk, although that case might be interesting as well.

  3. In the case of the million solar mass versus 1, how much mass is “lost”?
    We also have an end case that I would call perfect aim, i.e. the two BHs centers of mass are aimed directly at each other (i.e. zero angular motion). Rather than spiralling in they merge as fast as possible.

  4. Just on the hardware/measurement end of things,
    For LIGO to have made the discovery they claim, much of the theory used to support that claim can not also be true.
    In hard fact there were no orbiting black holes actually detected/observed. There was merely a template made up of what they imagined what the signal of such a thing would be like, much like the colorful CGI Black holes and space time depictions Ethan favors to decorate his blog with. They didn’t even actually detect their purported circling black holes first to get a signal template from, they made one up. A computer program then tried to find a close match between a very heavily processed (manipulated) signal and a list of imagined templates. To process the signal as claimed, the scientists would have had have known what the cause was for ALL other sources of noise/vibration etc. to a level of accuracy greater than .004 the diameter of a proton measured from a device almost four kilometers long, situated on the face of a heavily populated tectonically active planet. Can we presently do this to this level of accuracy with such a signal to noise ratio? No. You can’t even subtract out the background heat (which we do know about) out of a measurement from a device 4km long down to the level of less than a proton much less everything else (which we don’t know about). It is true you can make your processing algorithm make extrapolations (take guesses) if you like, but in doing so you introduce even more bias into your measurement which is now composed more of computer guesses than actual data.
    .
    On the theoretical side of things, there are a lot of problems as well.
    Gravity ‘waves’ or some intermediary particle like ‘gravitons’ are not compatible with GR. GR makes the assertion that gravity IS the space time curvature due to mass/energy. The curved math makes the curved space, and that’s it, there is no other mechanism, its just a tautology. There are also no carried forces for gravity in GR as there are in Newton’s gravity equations. There is no aether or background particle in GR to be a wave of something. The tensor calculus in GR has no mechanism by which it can stretch or compress space short of vigorous hand waving. There are also no ‘ripples’ in space time to convey such momentary spatial compressions effecting matter as claimed by LIGO, because there is no movement in space time, it isn’t possible (unless you are metaphysically sidestepping into meta time by moving your point of observation about) since the time variable has already been compressed into the spatial geometry of the space time itself, you don’t get to pretend you can pop it back out and have things move about inside the mathematical. space when that degree of freedom is gone.
    .
    It is my strong suspicion that LIGO (much like BICEP2) will eventually have to retract or slowly back away from their initial claims of discovery due largely in part because of the entire experiment being an expensive exercise in confirmation bias. Before you sharpen knives and ridicule is leveled at me for my skepticism, some perspective please, does anyone remember a short time ago “the detection is at the 5–7 sigma level, so there is less than one chance in two million of it being a random occurrence” that BICEP2 claimed? Most of you wanted BICEP2 to be true, and based on past experience with this blog, probably ridiculed those who didn’t share your enthusiastic conviction. How did that work out? Do you honestly think we lucked out that one in two million chance?
    .

  5. Just on the hardware/measurement end of things,
    For LIGO to have made the discovery they claim, much of the theory used to support that claim can not also be true.
    […]
    On the theoretical side of things, there are a lot of problems as well.
    Thank goodness you separated the three ends and sides of things for everyone.

  6. Sarcasm is not an argument. I was pointing out that even for argument’s sake, if LIGO actually could detect ‘gravity waves’ or detect that matter was actually being compressed and stretched by gravity in some undisclosed way, GR would not be able to explain the observation by the very nature of what you claim to be observing. If you want waves of gravity moving about and conveying physical forces in your theory, you can’t have GR too.

  7. Sarcasm is not an argument.
    It’s one way of going about things when someone is so demonstrably both full of themselves and full of sh*t.
    I was pointing out that even for argument’s sake, if LIGO actually could detect ‘gravity waves’ or detect that matter was actually being compressed and stretched by gravity in some undisclosed way, GR would not be able to explain the observation by the very nature of what you claim to be observing.
    Let’s review:
    The tensor calculus in GR has no mechanism by which it can stretch or compress space short of vigorous hand waving.
    Wrong. Proper distance can be well defined in locally flat spacetime. I’m not going to walk you through the derivation of the wave solution and the reduction to two physical degrees of freedom, which can be found in plenty of introductory explanations. Hint: It doesn’t involve really involve “tensor calculus” so much as algebra.
    Most of you wanted BICEP2 to be true
    As has been pointed out the last time somebody trotted out this routine, BICEP2 has f*ck all to do with the LIGO detection. Which reminds me:
    and based on past experience with this blog, probably ridiculed those who didn’t share your enthusiastic conviction.
    You’re starting to sound awfully familiar.

  8. “Sarcasm is not an argument.”
    However your posts are too incoherent to be argued against, since rational discourse can’t work when you are busy being irrational.
    Mockery is the only answer to an incoherent ramble, and incoherent is your only stock in trade.

  9. In hard fact there were no orbiting black holes actually detected/observed. There was merely a template made up of what they imagined what the signal of such a thing would be like,
    Oh not this again. We could make that same statement about most of science. We don’t observe individual atoms using AF microscopy, we merely have a template of what a signal from atoms would be like (and we observe that signal instead). We don’t observe the EM force, we merely have a template of what a signal from an EM force would be like (and we observe that signal instead). We don’t observe brain activity, we merely have a template of what a signal of brain activity might look like (and we observe that signal instead). For that matter, I don’t have any direct evidence of you. I merely have a template made up of what I imagine a signal from another person looks like.
    That’s what science is, CFT: taking an hypothesis, analyzing what signals we would see in the world if that hypothesis were true, and going and looking at/for those signals. When such predictions come true, the hypothesis is considered more confirmed. When the observations don’t match, the hypothesis is undermined. But in many many cases, we don’t actually directly observe the hypothesized law of nature or phenomena, we simply observe some effect we predict it will have on the observable world (in fact, we never “directly observe” a law of nature, we only observe how objects interact).
    I have to ask – are you a creationist or did you get your science education from a private religious school? Because those folks are very into ‘Baconian’ science. They stress the value of direct observation over indirect observations, and they generally think grand theory making should be avoided when at all possible. You sound a lot like them. Is that your background?

  10. They stress the value of direct observation over indirect observations
    Then again, LIGO was a direct observation. CFT seems to have departed, but if the proper-distance approach is unsatisfying, one is still stuck with proper time. It’s linearized GR with a TT gauge, and it’s just fine. The coordinates do not need to change for the effect to be detectable.

  11. Then again, LIGO was a direct observation
    I think he was saying it’s not a direct observation of BH merger. Yes its a direct observation of gravitational waves, but those could (in theory) come from some other phenomenon. That’s true…but that’s always technically true in science; there can always be another explanation. That’s just Hume’s problem of induction. Which scientists don’t typically worry about, and which is particularly dismissable when someone is only using it selectively against the hypotheses and theories they don’t like.

  12. Aye, Zeus could have made LIGO wobble.
    Nobody made it Zeus proof. Or looked to see he wasn’t there.

Leave a Comment

Your email address will not be published. Required fields are marked *

*