“This is going to have a bigger impact on science and human understanding, in many ways, than the first discovery of gravitational waves. We’re going to be puzzling over the observations we’ve made with gravitational waves and with light for years to come.” -Duncan Brown
Detecting black holes and the gravitational wave signals from them was an incredible feat, but doing the same thing for neutron star mergers is a true game-changer. Instead of fractions of a second, neutron star mergers show up for up to half a minute. Unlike black holes, there’s an electromagnetic counterpart. Because of that, we can verify that the speed of gravity really is identical to the speed of light: to better than 1 part in 1,000,000,000,000,000.

All massless particles travel at the speed of light, including the photon, gluon and gravitational waves, which carry the electromagnetic, strong nuclear and gravitational interactions, respectively. Image credit: NASA / Sonoma State University / Aurora Simonnet.

And perhaps most spectacularly, we can bring the electromagnetic and gravitational-wave skies together for the first time. Even though LIGO has seen more merging black holes, the fact is that there are more merging neutron stars. The key, now, is finding them. We live at a moment where gravitational wave astronomy is just in its infancy, giving us a whole new way to look at the Universe.

The galaxy NGC 4993, located 130 million light years away, had been imaged many times before. But just after the August 17, 2017 detection of gravitational waves, a new transient source of light was seen: the optical counterpart of a neutron star-neutron star merger. Image credit: P.K. Blanchard / E. Berger / Pan-STARRS / DECam.

For the first time, we’re doing it. Here’s the incredible science of what we’re actually learning, and what the future of gravitational wave + electromagnetic astronomy now holds.


  1. #1 Steve Blackband
    October 17, 2017

    So they shifted the frequencies of the gravitational waves to the audio so that you can ‘hear’ the collision.

    Do you think this is helpful or misleading?
    *and was what you hear real time?”

  2. #2 Michael Kelsey
    SLAC National Accelerator Laboratory
    October 17, 2017

    @Steve Blackband #1: In fact, there isn’t any shifting involved! LIGO’s sensitivity range is right around 300 Hz (spanning a few tens of hertz up to a few kilohertz), which is exactly the range of human hearing (middle C is 256 Hz).

  3. #3 CFT
    October 17, 2017

    IF gravity traveled at the speed of light, how do you explain the actual orbits of planets around the sun? Interesting things happens if you put your propagation effects at c. Unfortunately stable planetary orbits is not one of them, orbital calculations depend upon gravity being much faster than c to nearly instantaneous in order to work at all. The Earth also orbits a location that is approximately 20 arc seconds ahead of where the sun appears in the sky, where it actually is, not where the light which we are just receiving some eight minutes later shows it to be.
    Lets get skeptical and use Occam’s razor to clear the air a bit instead:
    What did LIGO actually detect? The laser wiggled (effect). The effect was attributed to gravity waves (cause). It is now admitted that what was detected was propagating at c. What was actually detected? Gravity waves traveling at the speed of c, which is in disagreement with our own planet’s orbit, or just an electromagnetic effect to begin with? There is also the problem that gravity travels at c in Einstein’s math only because he wanted it to, the equations are coordinate dependent, you get differing speeds for gravity unless you cherry pick your coordinates specifically to get c. There has been a lot of debate on this by physicists.
    Ethan admitted the reason they could even ‘detect’ orbiting black holes to begin with is because they created such powerful gravitational waves. How much less powerful are the gravity waves of neutron stars? Magnitudes? Considerably? If LIGO had troubles with detecting black holes, would it not have even more trouble with detecting something far less massive? The sudden pivot to detecting orbiting neutron stars seems a bit suspect, combined with claims of c propagation for the gravity waves. In any case, something has got to give theoretically. I have no trouble picking an initial side. I’m siding with direct evidence of our own planetary motion requiring faster than c propagation of gravity, over a highly inferred and indirect evidence based off a theoretical template in a computer processed ‘wiggle’ of something much farther away.
    This to me seems much like the point of contention with BICEP2. Polarized dust WAS actually found (effect). Assumptions were made about (cause) how and when it was polarized. The assumptions turned out to be wrong. The tragedy of BICEP2 wasn’t that it didn’t turn out the way they wanted, it was that not a single purportedly brilliant person on the entire research team, or even one of their financial backers asked the obvious question the entire projected revolved around “How will we be able to discern the causes of the polarization?”
    The same obvious question is there again. “How do you know what is causing your laser to wiggle?” You have a connection between a subject (neutron stars) and your detector now, but is it what you want it to be? Or is it something more mundane?

  4. #4 Michael Kelsey
    SLAC National Accelerator Laboratory
    October 17, 2017

    @CFT #3: What an awesome demonstration of ignorance.

    “Gravity” doesn’t “travel at the speed of light,” any more than a _static_ (i.e., unchanging) electric or magnetic field travels at the speed of light. If you actually studied the physics you so blithely distain, you’d already know this.

    The gravitational field of the solar system is essentially fixed (the movement of the Sun’s barycenter is tiny compared to the sizes of any of the planets’ orbits). The same is true, of course, for the orbits of all the planetary moons about their primaries. Consequently, the orbit of the Earth and other planets is perfectly described by a Keplerian ellipse. In Newtonian language, we can say that the force between the Sun and Earth is instantaneous. In Einsteinian language, we say that the solar system metric is static to high precision. The observable outcome is the same in both cases, and in both cases can be derived quantitatively by someone who can handle the maths. Your statements demonstrate clearly that you either can’t, or just don’t want to because it doesn’t fit your argument.

    What does travel at the speed of light (as measured to within +/- half a part in 10^15) are _disturbances_ in gravity, such as gravitational waves.

    The interferometer didn’t “just wiggle,” as your willful ignorance would have it. The mirrors (not the laser, another demonstration of your ignorance) moved in a very specific oscillatory pattern, with a frequency which increased over time in a very specific, continuous way. What is observed, measured, is not just the movement, but the very specific time history of that movement. Your sidestepping of those quantitative technical details (here as in so many other of your ranting posts) demonstrates that you are either ill-equipped to understand them, or you do understand them but deliberately confabulate in order to support a false narrative.

  5. #5 MobiusKlein
    October 17, 2017

    Uh, CFT, I think the compounding of events – Gravitational Wave, Gamma Ray Burst, and the correlated Optical detection pretty much seal it as a legitimate detection.

    Going forward, there will either be more detection with all the parts, or not. The GRB within seconds of the gravitational wave detection is pretty strong evidence.

  6. #6 CFT
    October 17, 2017

    Dearest Michael,
    You lost me the very moment you called me names…many months ago. I certainly would never take you seriously if you told me the sky was blue at this point. Incompetent experts such as yourself should be cleaning toilets until you develop a semblance of humility, not advising people on anything. Now please, go pound some sand.

  7. #7 Michael Mooney
    October 17, 2017

    @MK #4: ” In Newtonian language, we can say that the force between the Sun and Earth is instantaneous. In Einsteinian language, we say that the solar system metric is static to high precision.”

    I really enjoyed that. Pick your language and your theoretical paradigm. Make your argument from that bias.

    What happened to the scientific method?!

  8. #8 CFT
    October 17, 2017

    @MobiusKlein #5,
    What their ‘detection’ reveals in terms of by optical and radio is not in contention, those are electromagnetic in nature. What they claim they are detecting on their laser seismograph is. The fact they are claiming detection of gravity waves at c means it could be something other than gravity waves. The math is not convincing me, as it does not stipulate gravity even travels at c unless you choose very specific parameters BICEP2 was claiming a positive detection at sigma 7. Do you know what the statistical odds of that being wrong are? 1 in 10 billion, and they were wrong.
    Forgive me for my skepticism, but no, I don’t believe their ridiculously high claims of their calculations certainty, they aren’t very credible at this point. Blowhards like Michael Kelsey having such peculiar overreactions to being questioned only further convinces me something odd is going on.
    If Michael actually was half as informed as he claims, he would have known the argument I was using to challenge the assertion of gravity waves in a vacuum traveling at light speed was actually not even mine, but someone else with considerably more expertise. In other words, he accused me of making up an actual position taken by one of the finest astrophysicists of the twentieth century who in fact worked alongside Einstein himself, A.S. Eddington.
    “The statement that in the relativity theory gravitational waves are propagated with the speed of light has,
    I believe, been based entirely upon the foregoing investigation; but it will be seen that it is only true in a very
    conventional sense. If coordinates are chosen so as to satisfy a certain condition which has no very clear geometrical importance, the speed is that of light; if the coordinates are slightly different the speed is altogether
    different from that of light. The result stands or falls by the choice of coordinates and, so far as can be judged,
    the coordinates here used were purposely introduced in order to obtain the simplification which results from
    representing the propagation as occurring with the speed of light. The argument thus follows a vicious circle.”
    —A.S. Eddington, The Mathematical Theory of Relativity
    As I said,
    Cherry picked coordinates to get the predetermined results you want doesn’t prove anything, except that it is just a math push determining your speed of gravity to be c. If you pick some other coordinates, your speed will vary.

  9. #9 Ragtag Media
    October 17, 2017

    @CFT #6 (?)
    Go easy on Michael, after all he does work for you as a tax payer. Michael is an employee of a US Govt scientific institution and can provide vital input.
    He can be a bit salty at times but that’s understandable because of all the testosterone fostered penis measuring contest that has gone here in the past.

    Men in the science community should follow some of the decent lessons from physical sports teams in our society where we disagree, give some hard hits, and then shake hands and move on. Holding long term grudges does no one ESPECIALLY the truth any justice.

  10. #10 Michael Mooney
    October 17, 2017

    If there is an undetected (by instruments, of course) omnipresent field/medium, that would explain how everything is connected and that direct connection would explain how the force of gravity could be instantaneous.Then we could throw out “spooky action at a distance” as a problem… which resulted in GR.

    Notice the opening “If.” Yes, I do theoretical physics too… even without credentials! (It’s not illegal, except in mainstream physics) “The fabric of spacetime”… so malleable in response to mass… is a story like “the Emporer’s New Clothes.” Only idiots can’t see it. It’s the ultimate hypocrisy in science today.

  11. #11 Alby
    October 17, 2017

    No mathematical or velocity or superluminal speed need be applied to what need not move to be ever present. While such a supposition supervenes even need for an initiating isolated theoretical all inclusive big ‘bang[‘ singularity as a hypothetical a point of origin; even such an singular originating coalescence required prior gravitational and space presence. Also, there are no “holes” in space and space is also not “black”. Such seeming appearances result from telescopic limitations.

    Since there are no “holes”in sqace -nor would they be sustained by the tremendous pressures within galaxies- what is being observed is other than as hypothesized and widely accepted. What is deemed to be “black” seems so, because so does space so appear. However space also has no color.’The APPARENT darkness is due to telescopic equipment limitati0ns unable to detect and record the full spe4ctrum and breadth and origins of spatial antecedents and content.

  12. #12 CFT
    October 17, 2017

    @Ragtag Media #9,
    With due respect,
    I’ll change my stance on Michael when he changes his tone, and learns to argue his point, not talk down. Elitist snobbery is for badly behaved aristocrats, not civil servants.

  13. #13 Frank
    October 18, 2017


    You need to take a good look at ALL your past/present comments in this blog before blaming anyone for talking you down!

    You are obviously someone who see all discussions as a fight for personal honor. I am pretty sure other readers of this blog prefer FRIENDLY DISCUSSIONs instead!

  14. #14 Frank
    October 18, 2017

    @CFT #6:

    I think that comment alone is good enough reason to get you banned from this blog you need to realize well!

  15. #15 Alan G.
    October 18, 2017

    “Scientific discussion”

    “I do not think those words mean what you think they mean.” – Inigo Montoya (paraphrased)

  16. #16 John
    October 18, 2017

    Steve Blackband,

    Yesterday, in the Comments of the Week thread, you appeared to invite comments about the relationship between Science (primarily Physics in this blog) and Philosophy. So, at the risk of antagonizing those few remaining readers I have not yet irritated, the below is a brief reply. If I misinterpreted, please excuse this response.

    Scientific Realism is, I think, better understood in a historical context. It originated as a response to Scientific Positivism/Empiricism, another interpretation of what distinguishes Science from other intellectual disciplines. That school of thought came about as the result of Einstein’s publishing of “On the Electrodynamics of Moving Bodies”, his Special Theory of Relativity (SR) in 1905. Also published in 1905, “Does the Inertia of a Body Depend Upon Its Energy Content?”, Einstein determined a relationship between mass and energy.

    SR and E=mc^2 were Revolutionary Science, and criticized for violating Immanuel Kant’s categoric scheme that was a (if not the) contemporary philosophic world view. At that time, and to many people now, the three-dimensionality of space, Euclidean geometry, and the existence of absolute simultaneity were thought to be needed to understand Nature, and none of them should be altered by empirical findings. SR delivered a shock to physicists and to scientifically minded philosophers, and did not just point out surprising new facts, nor merely require strange new concepts. It revealed a disturbing lack of clarity within familiar concepts, such as simultaneity and length.

    This sets the stage for the logical positivists/empiricists. Their goal was to build a new-and-improved version of empiricism, one that would make the philosophy and the world safe for science. The central principle of logical empiricism is that any cognitively meaningfully statement must be either analytic or a claim about experience. I shall not present an exposition of what an analytic statement might be, but if you are due for some penance, feel free to ask. Science deals with facts, hence the “claim about possible experience”.

    Once science is rooted in just the facts, the meaningfulness of a statement depends upon verification. By verification the positivists mean a method for finding its truth or falsehood. Since to be cognitively meaningful is to be either true or false, if there is the right sort of method for testing truth or falsehood, the statement will be meaningful.

    Okay. All good, clean fun, and useful in clearing away some of the underbrush of 19th century European philosophy. Clarity uber alles, eh?

    Now try to shoehorn the Bag Model of Quark Confinement into a vision limited by observation. Assuming it to be true, not only are quarks unobservable, but cannot be individually observed. Is that model of (presumed) quark confinement science, or not?

    Scientific Realists find ways to relax many of the constraints which the Positivists had insisted science embrace. The Realists can then say, as the Positivists cannot, that science theorizes about quarks the same way as it theorizes about macro-sized objects. So unobservable objects are, in this philosophical POV, not second-class citizens. Of course, there’s a price to be paid. The distinctive virtues that science attained, due to its tight connection to experience are forfeited, and metaphysical possibilities made possible.

  17. #17 CFT
    October 18, 2017

    Frank #14,
    A personal attack is not how you respond to an answer you think is incorrect. If you disagree, say you disagree and explain why coherently, that’s all.
    Michael took the first shot. I responded. Every time Michael takes a kick at me under the table, I’m going to kick back twice as hard and try to make him reconsider his clumsy approach to disagreement.
    The advice I gave him also wasn’t arbitrary.
    I’ve taken it myself.
    I cleaned over 40 toilets a day when I was a teenager, I worked at a fancy hotel near Santa Barbara on the housekeeping staff, and yes it did teach humility, as I believe was my parents intention. When you come home from work exhausted and the skin on your hands is raw from having been in Brasso polish and cleaning solvent, and your back is killing you from having been bent over most of the day scrubbing and making beds, you realize this is all some people will ever know until they die, and you begin to look at the smug self-entitled folk of the world a little differently. I don’t care what you know, or what your position is, If you talk down to me I’ll suggest you to go scrub some toilets too. I’ve had to clean up after some of the biggest stars in Hollywood, quite literally, and in the process quickly lost any sense of awe I ever had with fame or celebrity. Cleaning up other people’s shit does wonders for gaining perspective.

  18. #18 JimV
    October 18, 2017

    As I understand it, Einstein’s General Relativity (GR) says that if our sun suddenly disappeared, it would take about 8 minutes for the lack of its gravitational effects to be felt by the Earth. However, the Sun has been in place for a long time, and it’s gravitational effects have long since propagated throughout our galaxy and beyond. (As it moves with and within our galaxy the effects sweep along with that motion but so does our solar system.) (Recall that according to GR, the effects are a strong local warping of space-time that constrains the orbital motion of nearby objects. This warping may vary slightly as the Sun itself orbits the center of mass of the solar system, but a) this is not a large effe

    I read at another site that the equations of GR have been used to calculate (numerically) the orbits of the planets of our solar system for the next 5 billion years, and they all stayed in the same orbits. (This assumed no outside interference.)

  19. #19 JimV
    October 18, 2017

    To continue where I was somehow interrupted:

    a) this is not a significant effect compared to planet orbital radii; and b) it is a cyclic effect which is part of the existing orbits.

    I will also add, there is an immense amount of evidence for GR. E.G., our GSP system would not work accurately until GR calculations were used in it.

  20. #20 Alby
    October 19, 2017

    Any premise of orig9ns need incorporate adequate inducements for such an fcvcurrence.

  21. #21 Alby
    October 19, 2017

    Any premise of origins need incorporate original inducements.
    Gravity as an all pervading static state is not reasonably viewed as having once been confined singularly with space when both are diverse in function and as such not be subject to an intense coalescence, apart from some prior inducing overpowering factor. able to resolve mutual functional virtual incompatibility.

  22. #22 Michael Kelsey
    SLAC National Accelerator Laboratory
    October 19, 2017

    @John #16: Not irritating at all! I wish I had a good enough grounding in philosophy (and the history of philosophy) to engage in a meaningful debate. On the other hand, this is an opportunity for me to learn about stuff I have had less touch with.

    You used an example to make a point that I think is not quite correct. First, in describing empiricism (which I _think_ i my own philosophical basis) you wrote, “Science deals with facts, hence the ‘claim about possible experience’.”

    Later, using the example of the quark model, you questioned whether, in dealing with “unobservable entities,” it counted as (empirical) science at all. I think this misses the point. Scientific theory deals with “unobservable entities” all the time, in many fields. Atoms, electrons, electric and magnetic fields, various energy potentials, those are all _unobservable_ in the 18th century sense of directly impinging on our senses.

    The test of whether a scientific theory is empirical or not (i.e., whether it is “really science”) is whether it can be used to quantitatively _predict_ observable results. QCD uses the unobservable quarks and their interactions to make definite, quantitative predictions about things like the mass of the proton, lifetimes and decay channels of various particles (yes, there’s a philosophical chain of inference involved), even predicting new particle states before they were observed.

    Whether the underlying invisible entities are real or not is, philosophically, an ontological problem; more pragmatically, it’s a question of how well the theory actually works. We treat electric and magnetic fields as real, even though they’re not directly observable to our senses, because electrodynamics works _perfectly_ every time it is applied to an observable situation, and has done so for a century and a half and counting. We treat atoms and electrons as real for the same reason. Perhaps quarks seem less real to you (and to most people) because they don’t directly impact day to day life, and because QCD has only been around for fifty years?

  23. #23 Narad
    October 19, 2017

    Incompetent experts such as yourself should be cleaning toilets until you develop a semblance of humility, not advising people on anything. Now please, go pound some sand.

    It’s idiocy such as this that makes me happy that SWAB will cease to exist on SB (along with SB itself) at the end of the month. Enjoy Forbes, CFT.

  24. #24 John
    October 20, 2017

    Michael Kelsey,

    “… this is an opportunity for me to learn about stuff I have had less touch with.”

    That’s kind of you.

    My (limited) exposure to physicists persuades me that philosophy and physics are seldom pursued in tandem.

    In re the scientific stature of unobservables: The logical positivists were able to integrate them into Science by the use of the analytic truths which have equal standing with observables (ref prior post) in their Received View of Theories where theoretical propositions such as the bag model of quark confinement are given a partial observation interpretation by inference to their relationship to other, observable phenomena.

    In contrast, you, I, and all (LOL! both) physicists I know are Popper’s intellectual children.

  25. #25 CFT
    October 20, 2017

    Look in the mirror snowflake, and then keep scrubbing. Acting snobby while blaming others is not a winning combo. You are going to have to learn to share the playground of ideas a bit, it doesn’t belong to you.
    The moment Ethan had his Forbes site, this one became an afterthought, a neglected stepchild he didn’t really care about anymore, and he wanted out of. Guess why?$?

  26. #26 CFT
    October 20, 2017

    @John #24,
    If you are truly Popper’s intellectual children, you realize the importance of falsifiability. Inflation theory, String Theory can’t be falsified, at all. Sabine Hossenfelder has pointed this out to Ethan several times…and he has agreed with her in personal discussion, but then glossed over it in his PR (things are fine) narrative on this and the Forbes site.

  27. #27 John
    October 20, 2017


    Yes, I am comfortable with the notion that a “scientific” theory can not be proved, but it can be falsified. That criterion of falsifiability means that to be a scientific theory, the theory can and should be tested by experiment.

    But what does one say about a theory that has been repeatedly tested using techniques independent of each other, and the results (observations) of those tests have been as predicted by the theory? I don’t know about you, but sooner or later I’d say it’s correct, or even True, with a capital “T”. I’d only start to discount its truthfulness if there started to accumulate observations that fell sufficiently far outside the theory’s prediction that they couldn’t be honestly attributed to experimental error. The first time some weird anomaly was reported, I’d go back and try to rework the observations within the theory, not instantly drop the theory, wouldn’t you? Of course you would! Good physical theories are not found in the bargain bin at Walmart.

    If that paragraph didn’t sound vaguely familiar, it should have. Newton’s law of universal gravitation produced accurate predictions for more than 200 years. When the observations (empirical tests) of the orbit of Uranus were observed to deviate from the predictions derive from that theory, first too fast and then too slow, instead of dropping the theory, in 1846 a scientist, Urbain Le Verrier, proposed the deviations could be resolved within the Newtonian theory. He suggested that the gravity of a farther, unknown planet was disturbing Uranus’orbit. He crunched the numbers (although it must have been a bitch to do back then), and Galle and d’Arrest saw Neptune where the “rethought” Newtonian theory said it was supposed to be. It wasn’t until the turn of the 20th century that the illumination provided by Newtonian Physics was to be clouded by the ultraviolet catastrophe and the curious case of the missing ether.

    All theories operate successfully with domains. QM, SR and GR are physical theories that are less inaccurate than Newton’s. They pass many more tests. Does that make them True? Technically no, but not only are all four scientific theories, you can safely rely on them every day.

  28. #28 John
    October 21, 2017


    I think you’re overlooking some of Ethan’s poste opinions about String Theory.


  29. #29 Alby
    October 22, 2017

    Factual cosmological antecedents are not entirely telescopically observable being only inferred from keen visual observations and collaborative deductions..

  30. #30 CFT
    October 22, 2017

    @John #27,
    When the ‘working story’ you tell yourself can’t be falsified, and you can just ‘change it’ to agree with whatever you like, you aren’t going to be able to break out of your epi-cycles. This is why I don not like group-think consensus and despise the Bayesian mindset which is turning the scientific community into a self congratulatory echo-chamber of self referential paper writers.
    There is good news for the future however:
    Scientists eventually die, and someone else is going to come along who doesn’t give a rat’s ass about the political consensus of experts and their overly convoluted ‘stories’, and do something else.
    This is what happened when a couple of bicycle builders from Ohio somehow managed to figure out what the rest of the scientific community could not.
    Science advances one funeral at a time.

  31. #31 CFT
    October 22, 2017

    @Alby #29,
    Try harder. Random word generators are only good for spam.

  32. #32 Jose
    October 29, 2017

    The detection of the gravitational waves produced by the merger of two neutron stars –GW170817– has allowed scientists to fix at 70 km/s per megaparsec * the value of the increase in speed of the expansion of the universe in the 130 million light years that separate us from the origin of said merger.
    As these calculations approach the speed of light throughout the age of the universe, we can do the inverse calculation to determine the average increase in the velocity of expansion so that the observable universe is of the age stated by the Big Bang Theory.
    The result is 300.000 km/s /(13.799/3,26) Mpc =70,820 km/s Mpc. https://molwick.com/en/gravitation/072-gravitational-waves.html#big-bang

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