[OT] Black Holes Merge--Universe "wobbles"

[Kwalish Kid]

Gravity and Straight lines

Well, that's a good question. Gravity determines what a straight line is, so people tend to talk about everything else following the paths that gravity sets out. I'm not too sure of the answer yet, but I should be by this time next year.

One thing I can say is that there are solutions to the Einstein field equations where the universe is expanding and it's not due to gravity. So you can have a world where the underlying grid of spacetime is changing and that determines the direction that gravitation effects will take.

As far as quantum gravity goes... well, there's a lot of work being done. I'm not sure that anyone posits instantaneous gravity effects. Some do propose that gravity creates a preferred reference frame (physicists out there know what I mean)--and that would be a challenge to the special theory of relativity.

Everyone buys that the General Theory of Relativity is a very accurrate theory. Almost everyone thinks it needs to be replaced, of course. I guess that means that everyone thinks that the gravity waves will coincide with light emitted from the region of space where the black holes are merging.

(And in many ways, it is the math that demands this. The mathematical language used means that we can't have gravity moving FTL, or we get different numbers for key predictions. These numbers fall outside the range of data that has been collected from a number of quite accurate sources.)

I recommend Lee Smolin's recent book on physics for further reading. He is currently working with a team to develop a quantization of gravity along traditional lines. They've gotten some surprising success--they were looking for failure!

Of course, Clifford M. Will's classic and easily readable book, "Was Einstein Right?" remains my first recommention.

 

[bolen]

Let me add Kip Thorne's book "black holes and time warps" This is the only popular book which discusses the history of GRT (General Relativity Theory). Of course there is also Hawking's book but I found that raises more questions then it answers.

Let me also add a comment (monto) of John Wheeler. He explains GTR as follows: "Mass tells space how to curve, and space tells mass how to move". By mass here he means Mass-energy. So Masses tell space what a straight line is. In fact relativists, dont veiw gravity as a force. We think of it as the object trying to move in a straight line but the surface it is on is curved (think of drawing a line on a ball).

 

[Airwolf]

I just saw this new story. It is related to the current thread so I will post the link here instead of starting a new thread.

Look out, here comes a black hole

 

[Aaron L]

100 million years from now? I bet we have already gone through the effects of this happening before, maybe several times.

 

[Kwalish Kid]

I just saw a talk by Fotini Markopoulou Kalamara about trying to combine quantum mechanics/field theory with GTR. We were lucky to get her, as she's in this month's Scientific American. See the following link:

http://www.sciam.com/article.cfm?articleID=0007E95C-9597-1DC9-AF71809EC588EEDF&catID=2

Markopoulou Kalamara postulates (if I got her right) that the fundamental units of relationship in spacetime are quantum events. The relationships that we see are actually akin to a thermodynamic effect: the large-scale interaction of quantum events produces what we see as GTR. FTL effects would seem to be possible, but not ever be seen at large distances.

She seems hesitant to put much weight in such postulating, however. Her main work seems to be looking for ways to experimentally test models of quantum gravity. She's willing to abandon much of her own theories based on the outcomes of experiment.

It turns out that in the next 5 to 10 years, there may be some significant results that can be applied to the field. If space is in fact made up of discrete units, there may be an effect on the speed of light at different wavelengths. Effectively, short-wavelength photons will "catch" on the discrete units of spacetime more often than long-wavelength photons. Thus the former will end up slower than the latter. A satellite that will soon be sent up to examine X-rays may provide an opportunity to test this prediction.

 

[bolen]

So is this the woman who is looking for dispersion in the light from far away supernovae due to large scale extra dimensions or the "loop" theories of Ashtekar et al? Is she able to distinguish between these two theories?

 

[Umbran]

4) GW have been seen indirectly. In the 1970's two physicists were observing a Binary pulsar system. Thay saw that the system was loosing energy. This loss of energy exactly agrees with what one would calculate from General Relativity for loss due to Gravitational radiation (gravity waves). They won the Nobel prize in 1996 (I think that is the date) for this.

1993. Russle Hulse and Joseph Taylor. The press release only calls it "indirect proof of the existance of gravitational waves". Proof of the existance of a thing is not quite the same as actually observing the waves.

Thus, LIGO - looking for the actual deformation of the Earth/space caused by gravitational waves.

5) As far as gaming for a realistic sf game. I cant imagine a place in our universe where GW would play a role, unless you are role-playing physicsists doing work on LIGO and I doubt anyone does that.

Well, there are others - You can try David Brin's Earth and Larry Niven's short story, "The Hole Man" for some ideas...

 

[Kwalish Kid]

bolen,

She has come up with a way to generally model the different theories of quantum gravity.

Losely, the universe is modeled as a large spin network, with events being transitions in the nodes of the network. Unitary transformations are found only in local systems where all information is kept from one transition to the next. If you don't know what a spin network is, well, you'll have to look it up yourself. It's math by Roger Penrose, I think, though it might be Oliver Penrose's work, now that I think about it. There is no hamiltonian for the universe, because there is no observer of the whole universe. But there are local density matrices, defined in the lightcones of observers.

Anyway, all the major players in QG can be roughly modelled in this way, they each determine different parameters of the model.

There are empirical predictions that the models make. So, in the next 5-10 years, analysis of light from broad spectrum emissions can be used to distinguish between some theories. Specifically, it can distinguish between those that postulate discrete space vs. those that postulate continuous space.

PS. The proof by Hulse and Taylor can't be too indirect... the Nobel Committee hates theoretical physics.

 

[Gargoyle]

I wish I understood this whole thread.

Here's an RPG idea:

The gravity wave is an event that a ragged confederacy of enslaved alien races has been waiting for. They have rigged a planet-sized sailing vessel designed to catch the gravitational energy that will hurl them at FTL speeds across the galaxy away from their oppressors, a much more militant alien race.

They end up, of course, on Earth and cause a lot of upheaval with their sudden arrival and high technology.

Their enraged enemy, with their even more advanced technology, are in close pursuit , and send a small scout ship to prepare Earth for the invasion.

The player characters are either alien or human freedom fighters. These heroes are determined to find a weakness in the evil alien armada that will be arriving in just a year, all while uniting the various nation-states of the world with the racially and culturally diverse alien refugees.

Far enough from reality?

 

[Umbran]

PS. The proof by Hulse and Taylor can't be too indirect... the Nobel Committee hates theoretical physics.

There's much more meat to Hulse and Taylor's work than the indirect proof of the existance of gravity waves. In many ways, their work isn't really theoretical physics, insofar as it deals with the actual astronomical measurements, rather than construction of theories.