How Were Gravitational Waves detected?
By two detectors in the USA, one in Washington State, the other in Louisiana (detecting in one place would have been enough; in two places at the same time, the finding is overwhelming certain; the National Science Foundation of the USA had spent $1.1 billion, over 40 years, on that research). The detectors were simplicity themselves in concept: just a light interferometer to measure the distance between mirrors: light is split, sent in two perpendicular directions, and then re-united with itself. If one of the branches vary slightly in length relative to the other as a gravitational waves passes, an interference will show up. However mirrors hanging from pendulum hanging from pendulums five times, the whole thing in an anti-vibration machine had to be realized in half a dozen places in a chain of reflections and interference.
What are these Gravitational Waves?
As far as existing gravitation theory has it, distortion in space (and, thus time: time and space are related by the speed of light, c).
What Was Detected:
Einstein’s Gravitation Theory says that gravitation “is” the deformation of space(time) it brings. It is this deformation which was directly detected: a part of space in one direction was made shorter than in another direction. That meant a huge gravitational wave had passed.
The formidable event that caused it was the crash and collapse of two black holes into each other, each around 30 solar masses (much more details are known).
Gravitational Waves Were Certain Theoretically, & Already Detected:
We already had evidence for the existence of gravitational waves, both theoretical and experimental. Einstein’s name was rolled out, naturally enough. Because Einstein contributed to the present Theory of Gravitation (I am not anti-Einstein, far from it, but he closely worked with a number of other people, including the towering mathematician David Hilbert, who published his own approach to gravity within weeks of Einstein).
Einstein tends to appear as the cherry on many a cake. Those who celebrate the photogenic cherry, and ignore the cake, will go hungry.
WAVES ARE PREDICTED BY FINITE SPEED FIELD THEORY:
Actually, once one has hypothesized that gravitation is a field propagating at a finite speed, the apparition of waves is automatic.
The reasoning was made first by British and French Eighteenth Century physicists, in the framework of electromagnetic force; the mathematics is exactly the same with gravitation, as both fields vary with the inverse square of the distance. This is what happens in a radio antenna, with electrons going back and forth: the electric field that those electrons create is deformed in such a way that it moves other electron at a distance, back and forth.
The Gravitational Energy Loss Detection Method:
Thus, how do the waves show up? By shaking things at a distance. Using conservation of energy, it means that the field creating system, by moving just so, loses energy to its waves. An obvious case is two neutron stars (“pulsars”) rotating around each other: as they move back and forth, because of said rotation, they create gravitational waves which carry energy away from their system, As this happens, their system loses energy, the two stars should spiral into each other, thus rotate ever faster, and this should be observable, and computable exactly. This, indeed, was thoroughly observed, so we knew the waves were there.
Einstein’s Gravitation Theory is a sleight of hand:
It affects to identify space(time) deformations with gravitation. The idea actually originated with the awesome German mathematician Bernard Riemann, who invented manifold theory in part to point out that any force could be viewed as convergence, or divergence of geodesics (this is an idea that physics has been milking ever since).
This, though, does not answer Newton’s deeper query about the nature of gravitation (see below). It’s a bit as if a creature asked:’What is an arm?’ And one answered:’An arm is what pushes things, and we can detect the deformation the arm brought.’
What is the discovery good for?
Well, first, one has to make sure. Science is about making 100% sure. The present experiment improved some technology far out what anything else required (but then it does open some possibilities!) Just an importantly, now we will be able to check the details of the Gravitation Theory (the big picture was not in doubt; the details are). Ultimately it may be possible to communicate through gravitational waves, etc (although right now the deformation are only of the size of the fraction of a nucleus, and we could detect them!)
Who were the originators of that idea? First Newton himself pointed out that his own theory of gravitation was grotesque (I am paraphrasing). Newton:
“that one body may act upon another at a distance thro’ a Vacuum, without the Mediation of any thing else, by and through which their Action and Force may be conveyed from one to another, is to me so great an Absurdity that I believe no Man who has in philosophical Matters a competent Faculty of thinking can ever fall into it.”
There were actually two problems: that the action was instantaneous, and that it was at a distance without intermediaries. Newton paid attention to the second one, physics, in the last two centuries, solved the first (which was implicit in Newton’s observations).
As I mentioned in passing above, part of Newton’s worries were addressed by the invention of the concept of field. And then by the realization that fields carried energy away in waves. At that point, gravitational waves were automatic… Riemann’s introduction of manifolds, and how to conceptualize forces in them gave the manifestation of its nature to gravitation we presently have, a distortion of space metric (once again, time follows automatically).
It’s important to know who invented what, and contributed most. Because it unveils how ideas appear and evolve. Then, in turn, one can make theories of that, accelerating innovation (don’t forget there is a horse race between innovation and oblivion, on the scale of the entire biosphere!)
Curiously, this is all very useful; GPS with a precision of 30 centimeters has allowed to find out that baboon society is more democratic than ours, in fundamental ways. “General Relativistic” effects (the fact clocks run slow in a gravitational field) make crucial corrections to the GPS computations (otherwise GPS would be pretty useless). So this is not all academic. GPS will soon allow robotic agriculture… among other things.
We still don’t know what gravitation is. However, we can predict more things than Newton did… Even if he did not suspect they were there. This is just the beginning of what could be revealed, if our satanic impulses are kept in check.