Gravitational Waves – useful or wasteful?

Gravitational waves (GWs) are predicted by Einstein’s theory of general relativity. They are described as ripples in spacetime that propagate at the speed of light through space. They can apparently also be described as “graviton particles” that transfer gravitational energy, similar to photons that transfer electromagnetic energy.

Gravitational waves transfer energy quite differently to the way photons do. GWs are neither absorbed, nor reflected by matter, but pass straight through them, losing only a tiny amount of their energy. Also, while photons are emitted in legions just about everywhere in space, GW-emitting bodies are scarce, at least the ones that emit strong enough GWs to give us any hope of detection. As I understand it, GWs loose amplitude directly proportional to distance traveled, just like light waves.

GW detectors are huge (and very expensive) contraptions, mostly buried below the surface of Earth, e.g., the LIGO facility. LIGO stands for Laser Interferometer Gravitational-wave Observatory. In about 2 years of working at near-full sensitivity, LIGO has registered no GWs. Plans are now to build an even larger and more expensive GW detector in space, called LISA (Laser Interferometer Space Antenna).

GW’s have been detected indirectly as the ‘anomalous’ in-spiraling of two pulsars orbiting each other. The rate of in-spiral matches the predictions of general relativity almost precisely, which predicts that the “lost energy” is radiated away as gravitational waves. Scientist are fairly optimistic that GWs exist and that it is just a matter of having a sensitive enough detector and then wait for an event that radiates GWs and is close enough so that we can detect it.

My question: are GW detection attempts not a huge waste of resources, while there are other more pressing needs?

SL

49 COMMENTS

  1. Generating a gravity wave. If a large mass is shaken rather violently it should generate a spatial disturbance. The sun is a rather large mass, about 1.9891*10^30 kg, and a radius of 6.955*10^8 meters. Now the gravitational conditions at the surface or 695500 km from the center may be determined.

    Surface acceleration, Sa, = 274.38 meters/ss
    Escape velocity, Ve, = 617.79 km/s
    Time, T’, = 0.999997876656339 seconds/proper second

    Note that a proper second may be read from a clock about 1 light year distant from the sun and at rest with the sun, proper length is a rule in the same location.
    Now to get is shaken, not stirred, at +/- 1000 km at about 10 times per second. Woops both GR and SR says that is a no no, but both allow me to replace the sun with a neutron star of the same mass and much smaller radius and obtain the same results at the same distances from the center. And they allow that to be shaken.

    At 694500 km, +1000 km.

    Sa = 275.17388 meters/ss
    Ve = 618.2369 km/s
    T’ = 0.999997873598969

    At 696500 km, -1000 km

    Sa = 273.5956 meters/ss
    Ve = 617.3486 km/s
    T’ = 0.9999978790493

    The peak to peak time variation is 5.192*10^-7 seconds which is the same variation in length as seen compared to the proper rule. These variations are propagated away from the mass at c.

    Meanwhile at earth orbit, 150133300 km from the center of mass all is quiet, the ripples will take about 8 minuets to arrive so that the gravitational conditions are;

    Sa = 0.588840465 cm/ss
    Ve = 42.04868 km/s
    T’ = 0.999999990163505

    Finally the first peak arrives.

    Sa = 0.588848095 cm/ss
    Ve = 42.488172 km/s
    T’ = 0.999999990163439

    And then the next.
    Sa = 0.5888326210 cm/ss
    Ve = 42.0485371 km/s
    T’ = 0.999999990163570

    At earth orbit the peak to peak time variation is 6.5*10^-14 as is the peak to peak length variation. These are small quantities and they continue to fall off by 1/4th every time the distance is doubled so at the intergalactic distances that we are trying to measure GWs the variations are all-most impossibly small even for super massive events.

    The values of Sa, Ve and T’ fairly well describe the gravity well, and Ve and T’ show a rather neat relationship. If you pick a point r at some distance from a mass the gravitational time dilation is equal to the time dilation of an object traveling at a relative velocity of Ve.

    Thanks. Con Morton

  2. Jim,

    I also said in my most recent response: “Since Jim and I both agree the discussion above is sufficient, there is no reason to resume this circular dance, even though Jim has invited me to do so.”

    So since your latest posting is a repetition of old arguments and accusations, I will counter a couple of personal points and one scientific point and exit this thread. (I admit it. I am rehashing old stuff. If you hadn’t criticized me personally, I would not have replied at all.)

    (1) General relativity is not quite a century old, so what’s wrong with pointing out that no observation has challenged it in that time? Theories gain credibility as they survive more and more challenges. Of course that does not mean that they will survive future challenges. You incorrectly imply that because I give GR great credence, I am rigidly assuming that it will never need to be modified.

    (2) As for “famous” scientists, whenever I cite them, it is always in the context of their work, not as authority figures. Their fame rests on the success of that work, so they have earned much more credibility than you or any other challenger who has yet to achieve that level of success.

    One bit of science: Repeating previous discussion, you write, “There is no unambiguous observational support for the existence of energy-bearing gravitational waves.” I agree and reiterate that absence of evidence is not evidence of absence. There have been no observations to date that would be expected to produce such unambiguous evidence.

    [Emphasis added in edit, because your post states, “What sort of evidence could prove something doesn’t exist if there’s already no evidence that it exists?” The following paragraph responds directly to that question.]

    When we have an observation that would unambiguously be expected to produce detectable gravitational waves by present or future instruments, that will provide evidence toward settling the argument. [Detection will support the theory; lack of detection will support the challenge.] Until then, you have made your points, and I, like everyone else reading this, have not been persuaded.

    Evidence, Jim, not bluster or attacking your critics, is the only way to persuade me. So please let things rest until we have evidence to discuss. We’ve been going in circles long enough.

    [Note to other readers: If Jim decides to insult me or demean me in response to this, as he sometimes does when people give up on having a discussion with him, please recognize that my failure to respond does not mean concurrence or inability to defend myself. It’s just that I’ve had enough.]

    Fred Bortz — Science and technology books for young readers (www.fredbortz.com) and Science book reviews (www.scienceshelf.com)

  3. Fred, when you say:

    “My argument rests on the success of a nearly a century of physical theory and observation that supports general relativity.” (emphasis added)

    you neglect to emphasize “nearly a century”, or to repeat your frequent enumeration of famous scientists, which you’ve employed elsewhere to support your position. That would have been a more pertinent response to my response to you, although admittedly, it would have undermined your argument. And you might have explicitly conceded that in your more recent message you’ve acknowledged that my position is more than “only a dispute based on not believing in gravitational waves” (a paraphrase), as if I’m taking some sort of religious position. All of this is just to clear away the peripheral objections you’ve raised that might discredit my argument without addressing it. Let’s address it.

    You claim that I’m “disputing arguments that have such powerful and long standing observational support.” There is observational support for the interpretations of GR that derive from its characterization as a geometric distortion or curvature of spacetime. There is no unambiguous observational support for the existence of energy-bearing gravitational waves.

    You say I’m “in the position of challenger and thus needs to cite observations that demonstrate errors or at least problems with the theory if [I] expect to be taken seriously.”

    I’ve done that. I’ve pointed out the truism often lost on mathematical physicists, that mathematics can be ambiguous in its relation to the physical world; I’ve said I can see no rational explanation of a physical transition from a theory of gravitation as a geometric distortion or curvature of spacetime to force, energy, and/or the production of energy-bearing waves; and I’ve claimed that no one has offered a coherent description of such a transition except by reference to abstract and ambiguous equations. That’s the problem. You can list all the famous scientists that share your expectation, you can count all the years they’ve been confidently expecting verification, but no one has explained how curvature can produce energy, rather than merely redirect it.

    “Of course that interpretation will be subject to change if the theory is overthrown by clear evidence. But at this point, no such evidence exists.” What sort of evidence could prove something doesn’t exist if there’s already no evidence that it exists?

    “Why is it so disturbing to you that people demand evidence when you are challenging a theory with so much observational support?” Again, there is no unambiguous observational support for the aspects of GR that are based on the association of gravitation with force and/or energy. You’re demanding evidence that energy-bearing gravitational waves don’t exist? So far the lack of evidence for their existence has only resulted in efforts to re-calibrate expectations. How long can that continue?

    Unless someone can specifically show how the field equations require that gravitation as a geometric distortion or curvature of spacetime produces energy-bearing waves – without introducing force “through the back door”, there is neither evidence nor theoretical support for gravitational waves. And no amount of ridicule or invoking time-honored authority can make 0 > 0.

  4. To repeat from long ago, which Jim has just echoed:

    “My argument rests on the success of a nearly a century of physical theory and observation that supports general relativity.” (emphasis added)

    So when Jim counters with “A modern scientific argument rests on observations and interpretations,” he seems to be supporting me, not disputing me.

    In this case, he is disputing arguments that have such powerful and long standing observational support to have earned the designation of “theory” (rather than “hypothesis,” “conjecture,” or “proposal”). He is in the position of challenger and thus needs to cite observations that demonstrate errors or at least problems with the theory if he expects to be taken seriously.

    He has cited no such observations, only an interpretation which no one else finds persuasive. Without evidence to support his thesis while exposing flaws in the the theory, it seems that everyone else is persuaded by existing theory and not Jim’s conjectures. I agree with Jim that evidence can change that, but the absence of evidence is not evidence of absence.

    Unfortunately for Jim, the absence of evidence is all he can offer in support of his challenge. He notes that gravitational waves have yet to be observed, despite strong theoretical indications that they exist.

    In the one observation we were discussing so long ago in this thread, the absence of detection could be legitimately (and was) interpreted as placing the event far beyond the detectable range.

    Of course that interpretation will be subject to change if the theory is overthrown by clear evidence. But at this point, no such evidence exists.

    Jim, your “elusive” points are, at best, an unsupported proposal. Why is it so disturbing to you that people demand evidence when you are challenging a theory with so much observational support?

    Everyone agrees that this difference of interpretation will eventually be resolved by evidence, as discussed elsewhere in this long thread and others. That is the thrust of what people will discover “by pressing and holding the up-arrow.”

    Since Jim and I both agree the discussion above is sufficient, there is no reason to resume this circular dance, even though Jim has invited me to do so.

    Fred Bortz — Science and technology books for young readers (www.fredbortz.com) and Science book reviews (www.scienceshelf.com)

  5. Fred has written:

    Jim attacks with ad hominem nonsense:

    “When all else fails your arguments rest on Famous Names, not reason.”

    My argument rests on the success of a nearly a century of physical theory and observation that supports general relativity as described by Einstein (hence his fame) and elaborated on by Hawking (whose fame rests on his own impressive body of work and his remarkable biography).

    My point has eluded you, and therefore strikes you as nonsense. In modern science, it doesn’t matter if your argument rests on a thousand years of physical theory and the opinion of every physicist who’s ever lived, famous or not. A modern scientific argument rests on observations and interpretations, not its longevity or pedigree. One person can undo the interpretations of millennia, and of countless brilliant predecessors. By your standards, as expressed in your repeated references to the time the idea of energy-bearing gravitational waves has prevailed, and the preeminence of those who’ve supported the idea, physics would still be in lock-step with Aristotle and Ptolemy.

    More from Fred:

    Jim’s only dispute with gravitational waves is that he doesn’t believe in them.

    Again, my point, my dispute has eluded you. (My dispute is available for anyone to see by pressing and holding the up-arrow.) Evidently, you sometimes (at least) read challenging arguments inattentively.

  6. I think it is useful as a super sensitive detector for the earth’s seismic activities.
    Nothing will be wasted. It can be used to warn an impending tsumani and earth quake. But not for the detection of the gravity waves.

  7. SL:

    While the search for gravitational waves is fully expected to bear fruit, based upon all the other successful tests of General Relativity, it can still be considered to be both a test of General Relativity and an additional astronomical tool. In fact, the fact that it can be seen as both, in my opinion, makes it even more valuable.

    For instance, the Gravity Probe B satellite was created and launched with full expectation that it would not measure anything new, since the parameters (of parameterized post-Newtonian gravity*) it would be sensitive to have already been determined to at least as high precision. However, it was considered to still be well worth it, since it would be a more direct measurement of some of the more novel predictions of General Relativity (like frame dragging).

    Of course, the worth of basic scientific investigations are all in the eye of the beholder. :-)

    David

    * Parameterized post-Newtonian gravity is a tool for clasifying nearly all contenders for General Relativity’s crown, and is particularly useful in helping researchers quantitatively see how much uncertainty exists with regard to “validating” General Relativity. (After all, one can never prove a theory, or model. One can only show that it has yet to be invalidated, since it has been upheld by all tests thus far.)

  8. Fred wrote: “So far, the evidence supporting general relativity also leads the physics community to conclude to the contrary–that gravitational waves ought to exist and merit additional research to test the theories even further.”

    I would go one step further – that gravitational waves are ready to be exploited as observational tools. If it was just to test general relativity, I would have thought it a waste of money!

    SL

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