LIGO: Gravity Waves detected

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hanelyp
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Re: LIGO: Gravity Waves detected

Post by hanelyp »

What effect would that gravity wave event have on a nearby nebula or star?
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Tom Ligon
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Re: LIGO: Gravity Waves detected

Post by Tom Ligon »

My guess would be little effect on a nebula unless it was extremely close. A nebula is pretty ... nebulous. Spaces between particles would be too large to get a reaction, although a nebula on the verge of collapse might be triggered to do so just as shock waves will.

I've never tried the calculation but the strain should be easily calculable. The strain here on Earth is a fraction of an atomic nucleus, but closer in it would be much higher. Picture conditions in the core of a star. The core is reacting at a steady rate based on a balance of gravity and radiation pressure, and the density is very high ... . Jiggle that appreciably and the reaction rate is bound to go up. The effects of the compressive phase should increase the reaction rate more than the tensile phase would diminish it. If the effect is strong enough, I can see this touching off the reaction Dr. Bussard told me about for his Interstellar Ramjet Star Killer. You could destabilize the core of a star sufficiently close to the event.

The density of our sun's core is believed to be around 150 x that of water. That still leaves a lot of space between nuclei. It would take less gravitational strain to disturb the balance in denser stars, where little room remains between nuclei.

I can picture triggering an atypical nova. The thing to look for would be a star that was not expected to nova to go ahead and blow. Dr. Bussard thought this would not be a supernova, although if one were about to go off, this might trigger it. What was this news about a GRB a fraction of a second after the gravity wave?

krenshala
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Re: LIGO: Gravity Waves detected

Post by krenshala »

The article I read in Universe Today about the LIGO results mentioned that they detected a faint gamma ray burst from the same direction as the black holes that collided, very shortly after the detection of the collapse via LIGO. My assumption was they were monitoring in the direction of the pair in anticipation of the collapse to get as much corroborative data as possible to go with the LIGO readings. From that article, they were not expecting a gamma ray burst, and other gamma ray detectors did not pick it up. Possible due to how faint it was, possibly because it wasn't really there; more data needed, basically.

Schneibster
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Re: LIGO: Gravity Waves detected

Post by Schneibster »

The most important things about LIGO detecting gravity waves isn't the confirmation of gravity waves, and isn't confirmation of General Relativity Theory. Gravity waves were confirmed long ago, by Joseph Taylor, Jr., and Russell Hulse, in 1974; they received the 1993 Nobel Prize in Physics for the discovery in 1993. They showed that a pair of orbiting pulsars were moving closer together due to loss of kinetic energy by emission of gravity waves. GRT was confirmed even longer ago, in 1919, by Sir Arthur Eddington who showed that the apparent positions of stars whose light passed close to the edge of the Sun in a solar eclipse was modified by the gravity of the Sun. Einstein himself used the rotation of the perihelion of the orbit of Mercury as a stalking horse during his development of GRT, and actually refined his original estimate of

Ruv = Tuv

to the more correct value of

Ruv - 1/2 x R x guv = Tuv

after careful consideration. (Note that he eventually added yet another correction to the formula, yielding the now accepted final value of

Ruv - 1/2 x R x guv + Λ x guv = 8πg/c4 x Tuv

which most will recognize as the Einstein Field Equations.)

The most important things are:
1. Direct detection of gravity waves by Earth-based instruments, and
2. The first direct confirmation of General Relativity Theory in the high-energy regime.

The first unlocks a new era in astronomy, in which gravity observations will complement visual, radio, and X-ray/gamma ray observations and the usual consilience will multiply the information we have about the universe.

The second confirms that GRT operates both in the low energy and high energy regimes, to the extent we can measure it; this is because the collision of two black holes that must have occurred to create the signal detected by LIGO enters the microsecond time regime and involves the multiple-solar-mass energy regime at sub-astronomical unit distances. This indicates that corrections for the high-energy regime will be unnecessary, bolstering theories of dark matter, dark energy, and B-mode polarization of the CMB by primordial gravity waves created by inflation in the ΛCDM model, AKA the "Standard Model of cosmology," and substantially ruling out MOND and other controversial gravity theories involving high-energy corrections to GRT.

It also incidentally confirms, by the time difference in the detection at the two LIGO sites, that the speed of gravity is not infinite. When India gets their act together and constructs a third site, which they are working on, and we actually can make a radio or optical confirmation of the source of a gravity wave, we will be able to definitively state the speed of gravity.

Overall I think this is equal to the detection of the Higgs; I'd hesitate to compare these two steps, though, saying one will have more or less impact in the long term.
We need a directorate of science, and we need it to be voted on only by scientists. You don't get to vote on reality. Get over it. Elected officials that deny the findings of the Science Directorate are subject to immediate impeachment for incompetence.

Schneibster
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Re: LIGO: Gravity Waves detected

Post by Schneibster »

JoeP wrote:How reliable is the above?
It's as reliable as refrigerators, aircraft, or transistors.
JoeP wrote:If they can detect black hole collision from so far away, can other disturbances in the gravity field be detected?
Depends how big they are and how far away.
JoeP wrote:Such as moving a massive object around near the detector? I assume no, but do not understand why not.
It's a matter of scale. If we had a black hole to wave around, and something to wave it with, we could make detectable gravity waves, but that's pretty far from anything we're currently able to do.

Gravity is very, very much weaker than the electromagnetic force; estimates at the atomic scale of the ratio of the strength of electromagnetism compared to the strength of gravity range from 10^39 to 10^47 depending on the masses of the particles involved. The reason that gravity is stronger over astronomical distances is that gravity has no negative. Therefore, gravity just adds up without anything offsetting it. In contrast, the electromagnetic force has positive and negative, and most astronomical objects are approximately electrically neutral, which means there is no net electromagnetic force between astronomical objects.

By simply waving even a very massive object around, say a mountain or an asteroid, near enough to generate a gravity wave that one of the detectors would see, the gravity wave would not be strong enough to be seen by the other detector. They're simply not sensitive enough to detect the waves from a moving asteroid or mountain from far away.
JoeP wrote:Also, does this discovery mean that a particle like the graviton must exist to mediate gravitational force?
No. This discovery does not prove that gravity is mediated by gravitons.
We need a directorate of science, and we need it to be voted on only by scientists. You don't get to vote on reality. Get over it. Elected officials that deny the findings of the Science Directorate are subject to immediate impeachment for incompetence.

Schneibster
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Re: LIGO: Gravity Waves detected

Post by Schneibster »

JoeP wrote:Another thought occurred to me: how does the LIGO team know that the gravity wave detection is due to the merger of two black holes, aside from the energy calculation? It seems to me that they are just picking the most likely explanation as to what most fits the expected space-time distortion and the rough distance of the source.
Sure, but there isn't anything else dense enough to make detectable gravity waves. If Jupiter and Saturn collided and merged, the gravity waves it would make would not be detectable by LIGO, and if there were anything less massive than a couple black holes somewhere close enough to the Solar System to make detectable gravity waves by colliding, we'd be able to see the perturbations in the orbits of the planets. We don't, and that's that.
JoeP wrote:It isn't close enough to get any other supporting data, was it? e.g. gamma burst.
We only have two LIGO detectors; thus, we cannot pin down the exact direction to look in. When we get a third one up and running, then we'll be able to look and see if there's anything happening in the direction the gravity wave came from. Radio triangulation with only two receivers is possible because we look in a limited volume, on the surface of the Earth or within a few kilometers of it. In space, three are required to pin it down. If we watched all of the sky all of the time for GRBs or flashes or whatnot, we might be able to say, "Well, we saw a gravity wave and it was in this area, and we detected a GRB (or saw a flash) right over there that corresponds to it," but we don't have that capability yet either; we just don't have enough telescopes.
We need a directorate of science, and we need it to be voted on only by scientists. You don't get to vote on reality. Get over it. Elected officials that deny the findings of the Science Directorate are subject to immediate impeachment for incompetence.

Schneibster
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Re: LIGO: Gravity Waves detected

Post by Schneibster »

Tom Ligon wrote:This is why I have a problem with gravitons. There's something different about gravity. If gravity were mediated by a particle, even one moving at the speed of light, how would gravity escape a black hole at all? If light can't, why should a graviton?
Actually, if you turn your argument around, you'll see that it's not that there's something different about gravity, it's that we only have half of the story when we talk about gravity.

Einstein's equations break down to a system of ten PDEs that describe it. If you examine Maxwell's original equations, you will find that in fact they also break down, to a system of twenty PDEs. Maxwell's equations are to electromagnetism what Einstein's equations are to gravity. They are the field theory of electromagnetism. Heaviside and Lorentz developed and popularized the form, using four equations, generally the differential form that uses divergence and curl, used in teaching them in modern electronics engineering and electromagnetic physics courses today. But these equations are, in the view of quantum field theory, only approximations.

Dirac developed a quantum theory of electromagnetism; this quantum theory has been integrated with Maxwell's field theory to create the modern quantum field theory of electromagnetism that is taught in standard curriculum today. This theory incorporates not only Maxwell's equations, equivalent to Einstein's, but also a new element, Dirac's quantum theory, which has no equivalent in gravity physics.

The integration of Dirac's quantum theory of electromagnetism with Maxwell's field theory of electromagnetism was enormously difficult; it required the work of three twentieth century geniuses, Richard Feynman, Sin-Itiro Tomonaga, and Julian Schwinger, and earned them a Nobel Prize in Physics. It is called Quantum Electrodynamics, or QED, and was the first quantum field theory ever developed. Unfortunately their approach is not usable with gravity; attempting it yields not merely infinite quantities, which they managed to cancel out in electrodynamics using a process called renormalization, but infinite probabilities, which no one has found an approach to cancel out yet.

So we have a field theory of gravity, but no quantum theory of gravity, because we haven't found a mathematical approach that both allows us to avoid the infinite probabilities, and is experimentally testable. The closest anyone has come is two competing theories called Loop Quantum Gravity and String Theory (a misnomer, it is not a theory, it is a system of physics; it cannot be tested with current technology, and to be a theory something must be testable).

And that is the difference between gravity and electromagnetism (as well as the weak and strong nuclear forces; I could write a fair bit more about the field theory of the strong nuclear force, but I've already written quite a lot for one day).
Tom Ligon wrote:Einstein didn't postulate gravitons, he postulated a distortion of space-time.
Correct: he made a field theory, not a quantum theory, nor a quantum field theory.
Tom Ligon wrote:Gravity isn't emitted from the black hole, the black hole distorts space-time. And as the merger of the two black holes approaches, their furious orbiting shakes the blanket of space-time enough to cause waves.
Correct.
Tom Ligon wrote:Which leaves us still wondering what space-time really is. Quantum entanglement? An ether? The whole idea begs for there to be some edifice out there which still allows Special Relativity to operate as if there were no ether.
If you like string physics, then spacetime (i.e. dimensionality) is the ultimate "stuff" of which everything else is made. So-called "superstrings" are distortions in spacetime + extra dimensions, which in order to exist must resonate to be stable, and which resonate in some or all of these dimensions and form everything we see as matter and energy; they are self-sustaining solitons in these dimensions, wrapped around and moving in these dimensions and remaining in existence because otherwise there would be no mass/energy conservation when they disappeared. Gravity, then, is merely a distortion of spacetime without any distortion of these other dimensions that create electromagnetism and the strong and weak nuclear forces, and electromagnetism and the strong and weak nuclear forces are distortions that involve these other dimensions as well as spacetime. "Gravitons," then, become minute distortions of the spacetime dimensions, and are weak because spacetime is large, and the dimensions warped by electromagnetism and the strong and weak nuclear forces are small. This explains gravity's weakness, along with many other of its characteristics, and also eliminates the infinite probabilities that plague other quantum gravity theories. Unfortunately, this is not a theory; it is only a hypothesis. It's a great explanation, with a lot of really good features, but there's no way to disprove it.
Tom Ligon wrote:I believe gravity is different in kind from the other forces, and until that is accepted I expect it will make monkeys out of the people trying to unify it with the other forces. We're obviously still missing about 96% of physics since we are pretty sure dark matter and dark energy exist, but have no clue what they are, and we base their existence on the fact that gravity does not seem to work like it should. Dark matter is known only as gravity with no visible matter associated with it. Dark energy only because it seems to be an anti-gravity push affecting the expansion of the Universe.
String physics explains why gravity is different in kind: it is distortion of the four large dimensions, space and time, whereas the other forces are distortions of the remaining six plus one dimensions: one for electromagnetism, two for the weak nuclear force, three for the strong nuclear force, and one more that relates the theories of strings that have ends to the theories of strings that link back to themselves. The difference may be because gravity affects time as well as space, and time is different: it is hyperbolically symmetric to the other dimensions, rather than circularly symmetric as the space dimensions are to one another and to time. No one has determined what type of symmetry the additional dimensions postulated by string physics have either to the ordinary spatial dimensions or to time; this is the largest current mathematical problem with string physics.
Tom Ligon wrote:My hope for LIGO is that it turns up something we've been too blind to see, something we are not even looking for. Maybe we'll think it is a malfunction at first, maybe a diurnal zero drift, or noise, and finally realize we've got some signal.
More likely it will supplement and illuminate our findings using light, radio, X-rays, and gamma rays. It's the radiation of the only force but electromagnetism that we can expect to detect at astronomical distances; the strong force is limited by relativity and its own nature to distances around the size of an atomic nucleus, and the weak force is limited by the instability of its bosons to similar distances.
We need a directorate of science, and we need it to be voted on only by scientists. You don't get to vote on reality. Get over it. Elected officials that deny the findings of the Science Directorate are subject to immediate impeachment for incompetence.

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