The last major prediction of Einstein's theory of General Relativity, gravitational waves, was the most controversial and difficult to verify of them all. It wasn't until 1993 that gravitational waves were indirectly observed in the behaviour of neutron star binaries, and not until 2015 that they were finally directly detected. Even Einstein himself for a time had doubts that they were real, and he even attempted to publish a paper that tried to argue that gravitational waves were a mere artefact of the mathematics, which turned out to be flawed. Oddly enough, it was Richard Feynman, who is much better known for his work on quantum electrodynamics, who came up with an argument that convinced many of the doubters. Rather than arguing the mathematical subtleties of relativity, he came up with a physical explanation that not only demonstrated that gravitational waves must carry energy, but later inspired the design of LIGO, the first apparatus that detected gravitational waves directly. Paul Halpern has an article where he tells the whole story. From the article:
Enter Richard Feynman, who had distaste for unnecessary abstraction. If gravitational radiation is real, it must convey energy. Rather than debating the technical question of whether or not the pseudotensor definition of gravitational energy was correct, he turned instead to a far more intuitive line of reasoning, what has come to be known as the "sticky bead argument."
In his thought experiment, Feynman imagined a thin stick on which one mass is fixed and a second mass, slightly separated from the first, is free to slide back and forth, like a curtain on a rod. These two masses would be analogous to a pair of charges embedded in a vertical receiving antenna used to pick up radio signals. Just as a pulse of electromagnetic radiation would cause such charges to oscillate, the same would happen in the "gravitational antenna" if a gravitational wave passed through—with the maximum effect occurring if the wave were transverse: at right angles to the stick. Upon the impact of a gravitational wave, one of the masses would accelerate relative to the other, sliding back and forth along the stick. The rubbing movement would generate friction between the free mass and the stick, releasing heat in the process. Therefore the gravitational radiation must convey energy. Otherwise, how else did the energy arise?
(Score: 0) by Anonymous Coward on Thursday March 09 2017, @01:25AM (2 children)
I get that they observed a signal that matched what is expected from a BH-BH inspiral really well, but don't think it can be considered confirmed until they detect such a signal along with something else (eg a corresponding gamma wave burst). Otherwise the entire thing seems kind of circular. Also, I don't think I am alone in this thinking and that is why no Nobel prizes were given out for it.
(Score: 2, Informative) by Anonymous Coward on Thursday March 09 2017, @03:06AM
1. If the science is correct (there's always a chance it's not ...) then these were stellar black holes, i.e. remnants of an earlier binary star system. Except for a few leftover planets and asteroids (whose total mass is typically very insignificant when compared to their stars), there's literally nothing else around that could produce electromagnetic radiation. The black holes sure won't, by definition. And even if there's a lot of planets and stuff: they'd have been circling the binary for a long time now, why should they stop doing so and turn into radiation? They're only concerned with the mass at the center of their orbits, and that mass just became *smaller* by ~3 solar masses.
Your demand could only, possibly, be fulfilled if one/both black holes had accretion discs (and possibly not even then). But accretion discs are *very* unusual for stellar black holes, to say the least.
BTW: For a few weeks there was an uncertain candidate for a very weak GRB, but further analysis ruled that out quite conclusively (we're very uncertain about where in the sky GW happened, so there's a lot of probabilities involved ...)
2. I also do not see how there is circular reasoning: relativity gave a prediction of and details for BH-BH mergers even though *all* of its more egregious predictions (black holes per se, gravitational waves, time dilation, contraction of lengths ...) were unknown at the time and had never been observed. Now, decades later, an observation has been made that pretty exactly matches the prediction.
I do not see the circularity here, how did you reach that conclusion?
3. Not getting a Nobel Prize directly after your discovery is the norm.
It typically takes between 10 and 20 years after a discovery to receive a Nobel Prize in physics. 2013's Nobel for the Higgs Boson was a fluke in that regard (discovery in 2012, initial theory in 1964, Nobel was for both). Einstein, on the other hand, got his Nobel in 1921, 16 years after publishing the original article (for explaining the photoeletric effect, not for relativity)
I'm mostly certain that there's a Nobel in the making for the detector teams, give it a few more years, let them find a few more GW events first, let a few more detectors come online giving us actual astronomical capabilities. Einstein would perhaps get his second Nobel for relativity too, but he's dead already and thus not eligible anymore.
(Score: 0) by Anonymous Coward on Thursday March 09 2017, @02:07PM
The predominant reason that the Nobel wasn't given out for it last year was that the official announcement and paper came out just as, or just after the nomination and selection process began. Those "in the know" in the field knew several months before that this discovery was going to be announced, but they wouldn't have considered it until it was official.
(Score: 5, Interesting) by MichaelDavidCrawford on Thursday March 09 2017, @02:51AM (5 children)
Dr. Feynman taught a "class" for one hour each week called "Physics X", in which there were no grades, no homework, no exams, no reading and no credit. He encouraged us to ask any question we wanted - even outside of physics - but our questions must not require him to work out any math. It's not like he knew how but he wanted us to gain an intuitive feel to the solutions to our problems.
I didn't believe in the indeterminacy of QM, being completely convinced of the deterministic clockwork universe. I understood QM well enough to get good grades but regarded it as delusional. Dr. Feynman convinced me of the reality of QM's randomness, largely through chalkboard drawings of the two slit experiment.
If we can somehow tell which slit the photon goes through, then the interference fringes go away. But still I didn't buy it. What conviinced me was that the experiment could be done with electrons. With a very low-current electron gun - a hot, charged filament - we can observe the shot noise of individual electrons jumping off the filament. But we don't know which slit the electron passed through, and so we get the fringes.
Yes I Have No Bananas. [gofundme.com]
(Score: 0, Disagree) by Anonymous Coward on Thursday March 09 2017, @04:27AM (4 children)
Intuition is the wrong way to approach any even halfway complicated physics situation. Even without getting into QM, Special Relativity or Electricity and Magnetism, it's easy to get yourself convinced about what the results should be and not understand why the result is different.
If you want to get good at physics or the math that's required to do it, you really ought to learn to ignore intuition and focus on the equations. After you've got those results, then you can focus on whether the units come out and whether the predictions match the results.
One of the reason why so many people drop out of physics early on is that it's not what most people would consider to be intuitive and they fight mightily to deal with things that in many cases don't make sense in the context of their lives.
(Score: 5, Insightful) by maxwell demon on Thursday March 09 2017, @05:04AM (3 children)
As a physicist, I disagree. Intuition is a very valuable tool. Note that with mathematics, you can go wrong in a lot of ways. Usually intuition tells you that you are wrong. If you don't have intuition, you'll happily produce wrong results and not notice it.
Of course intuition has to be trained. It is not as if we were born with intuition. And of course intuition can go wrong. But if your calculation goes against your intuition, it's a sign that you should look at the calculation again. Either to find the error in the calculation (the most likely case if your intuition is well-trained), or to get your intuition right. And the best way to train your intuition is to look at specific cases.
One of the reasons why so many people drop out of physics is that they never gain any intuition on it, and happily accept whatever results their flawed calculations spit out, even if they are so obviously wrong that they are screaming for correction.
But of course the #1 reason people drop out of physics is that they don't grasp the mathematics. Which again is mostly a lack of developing intuition for it.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 0) by Anonymous Coward on Thursday March 09 2017, @08:06AM (2 children)
I think I agree with you, but I find your view unclear.
"intuition", in this context, is our ability to assign value to a mathematical statement before understanding all the details of the construction of that mathematical statement.
our brains have intuition for euclidian geometry and constant gravitational fields. we spent millions of years climbing trees, we spent hundreds of thousands of years throwing rocks and balancing ourselves on two legs, I find it very likely that some of the relevant physics is actually hard wired in our nervous system.
to be successful in classical physics, we just need to be able to properly associate the relevant math to this existing intuition.
however, we are also able to develop intuition about phenomena outside of regular human experience.
I was told explicitely that people who work on quantum physics experiments develop intuition about quantum physics after a reasonable amount of time.
also, when someone is working on quantum physics, they are using mathematical objects defined in different contexts, for which they probably already have an intuition (for instance complex numbers are quite natural for talking about plain old electricity, which again you can do in the lab).
I'm not sure my comment makes it clear enough, but I think it's different enough from yours to matter.
(Score: 0) by Anonymous Coward on Thursday March 09 2017, @02:15PM
The intuition that you describe goes back to the days of Euclid and was, in fact, so hard wired into our guts that we were locked into that mode of thinking and mathematics for a thousand years. Around Galileo's time people started trying to work in observations, but we were still locked into our intuitive view of the universe. It wasn't until people like Riemann said "Because we can't make a self-consistent geometry with only those five axioms, what happens if we take that troublesome one and consider what happens if parallel lines do intersect . . ."
(Score: 2) by Immerman on Thursday March 09 2017, @03:26PM
>"intuition", in this context, is our ability to assign value to a mathematical statement before understanding all the details of the construction of that mathematical statement.
I disagree. I would say intuition in this context is developing an understanding of the mechanisms in play, independent of the mathematics. A hunter doesn't need to understand the mathematics of the aerodynamic and gravitational influences on his arrow, he just needs to develop a reliable intuition of how he's required to aim to hit the desired target.
Similarly when solving a physics problem, well-developed intuition will let you know roughly where the solution lies and what it will look like before you've done any of the math. Mathematics is then the path taken to verify that you're actually correct, and get the precise details of the solution.
Now, knowing how to do the math reliably can be an valuable path to developing that intuition, to say nothing of pushing past it into the unknown. But a selection of good illustrative examples can also go a surprisingly long way toward developing that intuition, even without knowing any of the math.
(Score: 4, Informative) by stormwyrm on Thursday March 09 2017, @08:14AM
Numquam ponenda est pluralitas sine necessitate.
(Score: 0) by Anonymous Coward on Thursday March 09 2017, @01:18PM (2 children)
supposedly the detector is anchored to earth in a complex gravitational system AND rotating.
i suppose to be conclusive the detector (mirrors?) would need to ping pong light between the lagrang points?
as long as the gravity wave detector is anchored to earth and detection can be interpreted as light NOT having a constant speed and thus not being a universal constant?
(Score: 0) by Anonymous Coward on Thursday March 09 2017, @03:15PM
Your post has interesting technical jargon that, when combined, do not make for a comprehensible statement/question. Are you saying that to be conclusive you need to be in some sort of universal rest frame? I don't know where to go with the last sentence.
(Score: 4, Interesting) by Immerman on Thursday March 09 2017, @04:26PM
I think I kind of get where you're coming from, and the answer is basically no.
All the rotational behavior of Earth happens on a nice regular cycle - if light had a non-constant speed, such as if it had a preferred direction of travel, the interferometer would show that as it rotated into and out of alignment with that direction, and you'd get a constant low-frequency signal with a 24-hour cycle. We're not detecting that.
Alternately, if the speed of light varied with time but not space, then the interferometer would detect nothing at all since the photon in each arm would remain traveling at the same speed as it's tin in the other. So long as they both make the round trip in the same amount of time, it doesn't matter how fast they're moving.
Instead what was detected was an brief, high frequency signal that rapidly increased in intensity and suddenly vanished - the "death scream" of a pair of black holes spiraling into a rapidly deepening gravitational field until they made contact and merged.
Basically, if an interferometer detects a signal then you know one of two things: either the length of one arm changed with respect to the other, or the speed of light changed between the two arms arm. It's not beyond imagining that light speed could change like that, but we have no theoretical basis to believe that it's possible. And if that somehow *were* the case, the signal detected would mean that every once in a long while something happens to cause the speed of light to oscillate rapidly, with a definite directional bias or highly localized effect(only one arm), and a rapidly increasing magnitude, and then suddenly stop.
You're offering a wildly speculative explanation without any theoretical basis as an alternative explanation for a signal that matches exactly what the theoretical predictions say that the gravitational waves from a black hole merger would look like.
It's not *impossible* that you're wrong, and looking for alternative explanations is an important part of science, but in this case you'd need to offer a pretty solid alternative theory with a strong amount of experimental evidence (because General Relativity already has a whole lot of evidence backing it) to have any chance of being taken seriously.
As for Lagrangian interferometers - I don't see that they'd really solve anything, other than determining whether the signal was confined to the planet itself. There are some decent arguments in favor of space-based interferometers, but they mostly revolve around the fact that bigger detectors detect lower-frequency waves, and that to detect the gravitational waves emitted from sources visible in other ways, such as known binary stars within our galaxy, we need an interferometer with arms ~10x longer than the distance between the Earth and the Moon.
Going all the way out the the Lagrange points would actually be an easy way to maintain at least approximate alignment over time, but would make such a stupendously large interferometer that it would be detecting too low a frequency to pick up on any of the predicted strong sources we can see.
Plans such as LISA call for more cleverness in maintaining alignment at the desired size - it calls for putting three solar-orbiting satellites in a giant equilateral triangular formation trailing behind the Earth in it's orbit, but all in different orbital planes so that they form a triangle that kind of wobbles it's way through space while maintaining constant distances. It's actually kind of wild to watch the animation near the top of the Wikipedia article:
https://en.wikipedia.org/wiki/Laser_Interferometer_Space_Antenna [wikipedia.org]
https://en.wikipedia.org/wiki/Laser_Interferometer_Space_Antenna [wikipedia.org]
(Score: 0) by Anonymous Coward on Thursday March 09 2017, @10:42PM
Was evolution willing to pay the cost of expanding our intuitive perception enough to understand the universe? There certainly is no need of that for our species to be able to gather food and reproduce. As a theoretical physicist, I see future work being very non-intuitive.
The circular thought process that concerns me is there has never been an independent measurement of time. Think about that before you react.
The possibility that time in an emergent property and not a fundamental physical property leads to issues of verifying predictions coming from General Relativity that don't depend on the theory itself.