General relativity

Gee guys, I just love Dr A.S..  He said the Event Horizon is moving "nearly "  the speed of light.  Lets see .    IF  you are in the EH, inside the black hole is no space, and at least you can not see anything.  On the outside no one can see you, photons can't get out.  So Special Relative only applies on the Event Horizon.     Because in SR you need two Reference Frames that can SEE each other.   There is nothing to see on the inside and they can't see you on the outside.  So all pairs of frames are on the suface and are motionless,  and thus can be going ANY speed relative to something else some place else, say RC easily.  Luckly ofcourse there are no Black Holes !!!!   Only believers in General Relativity believe there are BHs.

There are no black holes? LIGO just detected two of them colliding, after orbiting each other at near the speed of light.

Actually I do accept there is no event horizon and have been an unfashionable advocate of this for years. What falls into a black hole eventually forms a stringball (or the equivalent in your favourite theory of quantum gravity) before being radiated as Hawking radiation. However, the nature of a black hole is that everything that falls into a black hole becomes entirely invisible long before it reaches the stringball.

Looks very solid indeed. Those graphs of the increasing oscillations before merger are very impressive, and they have two of them separated by the right sort of delay, 7ms!

Presumably the delay constrains the location of the source to a circle in the sky, depending on the cosine of the angle to the baseline between the two observatories.

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And here is the answer to your question.

Highly, highly recommended for everyone!

Lets See:  "As I said all you need to create a gravitional wave something exhilarating and so it could be for example a star...."  Direct quote,  READ it for yourself.   Turns out a constant velocity will do.  But that's what one might get from the Univ. of Nottingham.  HIGHLY HIGHLY recomended. !!!! Ofcourse if one believes in GR,  one might say anything,  Like GR is mostly right.   Space is really space-time.    Or ofcourse Black Holes exist, and also Dark Matter.   Singularities are common.   AND these waves PROVE GR.

No, a constant velocity does not produce gravitational waves. Acceleration is needed.

Please show your proof that a constant velocity doesn't work. !  Or are you saying that a constant velocity does not exist ?   I would be happy to do the same with a true example, just ask. 

Well, if an object moving at a constant velocity radiated gravitational waves, so would an object that is standing still!

But I imagine we would agree a static object can have a static gravitational field (i.e. no gravitational waves).

It's difficult to make the negative rigorous in GR, because the space between masses can have any sort of gravitational waves from elsewhere passing through it, but I can point out that when people do the calculations for an accelerating mass (eg orbiting), gravitational waves appear, but not when they do the calculations for masses that are not accelerating.

So you AGREE, constant velocity creates a gravitational wave. If it is moving relative to you and towards you the wave increases and  decreases.  If there is no relative motion the WAVE is flat.   So the guy that said one needs  acceleration was wrong.  Thanks.

No, that is not what is called a wave.

A key difference is that gravitational waves contain energy, so they take energy from the internal energy of their source (typically this involves the decay of an orbit). This energy can be absorbed, but only a tiny amount as far as I understand.

It is only if a mass is deflected by another mass that there is some radiation of gravitational waves (because the masses are accelerated).

If you are not happy with a Flat wave or a Single Cycle wave, why don't you define a wave for us.  Try not to use the word acceraleration.   I am sure you see why.

Perhaps you should first define what you mean by 'gravitational wave'. I'd assume it is not clear to all. At least I can't understand what RPaulB means.

Fair idea, infact a great idea.  To me a gravitational wave is the density of gravitons in a give volume over time.  And the direction of each graviton may be different. I assume someone else does not see it that way.  I can not speek for them but it may be a change in density of space over time, what ever that means.  That can be, time changes it rate; space curves in a 4th dimension; the density of space per unit volume changes; OR...  Sorry i started that, but you see how lost I am.  Please tell us some one.

By analogy with electromagnetic waves, the density of gravitons (if anyone had a quantum gravity theory that worked) would be a key part of it, but not the whole story. Obviously the direction of motion of the energy is important. There is surely some other sort of phase information, but I am not familiar with spin-2 theories, and it would probably be different to EM radiation which is a spin-1 theory.

Still not clear ?   An X wave is the density of X in a given volume over time.   Alasre, if that still isn't clear what is your defination of a wave that's clearer.  Elroch, X can be any thing, with or with out spins. Normally a particle has a 1/2 spin, 2 particles systems whole spins , 3 half again. If your wave has spin it must be a particle, say like space particle wave !  Directions are nice , if you use the Y direction , do you also count the waves in the  -Y direction ? They may be doing more to your Y wave than Y is. Electromagnetic waves are particles that are similar to a wave. They are not waves of particles.   Those Waves must be infinite or STOP.  If they stop they do not represent that particle well at that point.   Be sides how does energy at rest that is about to be a photon "START" to move as a wave at a velocity of C, without accelerating ?  Waves are concepts in math, not nature !

To be honest, I'm not sure, do I understand you at all, Elroch and RPaulB. I'm not even sure, should I comment something or not, because it could end up that I'm talking something I can't afford at the moment.

Nevertheless as RPaulB asked it, I've thought gravitational waves as some kind of quantity that describes change in the energy of the orbital motion of the system. I.e. something that is needed to change the current gravitational field (or more specific the metric). (Observation: orbital period of binary neutron stars)

Further, the observation of this kind of change of the gravitational field should be some kind of measurement of metric. And this maybe means, one should observe how an object changes when the metric changes. This should lead one to the equation of geodesic deviation. (See e.g. this article or this one about that.)

But both of you are talking about spin... I'm sorry, I haven't seen how spin is affecting to the metric tensor and to geodesic deviation. Maybe someone could give a good mathematical definition of that?

It's great you answered.  You understand at least as well as I do, and I would include Elroch too, but he can do that.   You can see how easy it is to miss understand.  I was trying to tell Elroch I don't think spin has anything too do with a wave, and now I ended up talking about spin.  Orbital motion does produce waves,  BUT waves do not have to come from orbital motion.    My point was there is nothing uncommon about a wave. Waves don't prove anything special.  But please don't  feel bad, after rereading your comments,   I don't understand where you are going either,  Sorry. What One needs is all the luck I seem to have in what I say.  So good luck.  I mean "  Space is a particle "  , how lucky can one get.  It's properties are those of any other particle.  ASK some one what the properties of space are, see what answers you get.  I just had dumb luck.

More dumb luck !!!   "An X wave is the density of X in a given volume over time. "  So the Particle X is space this time.   Space itself prduces waves.  Nothing to do with gravity though.  The density of space per unit volume changes.   Not possible ?  Well there was no space at the start of the BB,  Later , about 100,000 years there is space between each Superemass particle, think of them as galaxies, This is  the first time gravity and a photon can get from galaxy to galaxy because there is enough space now to do that.   Still later ,there is more space per unit volume right up to today when there could be 2 cubic meters of space per each cubic volume. The extra space is produced by stars, even right now.  Initially space was produced by the decay of supermass to the unit mass and then to a space particle,  technically from (EEE) to (HHH) to (LLL).  And then go right up to the edge our universe today and ONE Planck's length beyond the edge there is no space still.  If a photon goes there it would return to  Zu as borrowed energy.  Zu was here before the BB ofcourse.  No force is needed to produce the wave.  Space always flows from high density to low density via a boson called a Spon. If there is mass in the space ,it moves freely if the space moves.  A force is only needed to move mass  "inside " a space particle.  INSIDE, ofcourse is the only space we see.   NOW that is what I call really dumb luck !!!!

We are talking about General Relativity, one of the great theories of physics that has proven entirely successful in its domain. The discussion wandered a little into the accepted idea that underlying general relativity is a quantum theory. This however, is a theory that is not known, has no plausible tests at present and the candidate theories are very difficult to calculate with. Despite that both string theory and loop quantum gravity have had some success at attacking problems associated with black holes, where gravity meets quantum mechanics and throws in a large does of thermodynamics. None of us fully understand this (I can infer that, because no-one does).