Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Mark Durre on 08/05/2011 17:30:03

Title: What gravitational waves would you expect from a black hole merger?
Post by: Mark Durre on 08/05/2011 17:30:03

Mark Durre  asked the Naked Scientists:
   
I love your podcasts (http://www.thenakedscientists.com/HTML/podcasts/)! Keep up the good work.

I have a question as to what sort of gravitational wave signal would be expected from (say) the merger of two black holes; would it be a single pulse (a soliton wave) or would you expect something like an earthquake, which rings for a while after the initial shock?

Thanks a lot,

Mark Durré

What do you think?

Title: What gravitational waves would you expect from a black hole merger?
Post by: MikeS on 08/05/2011 17:55:01

To the best of my knowledge, gravitational waves have never been seen.  Maybe they don't exist or are short range.  If they do exist I would expect them to ring for a while.  I wouldn't want to be near a black hole collision, that's for sure.

Title: What gravitational waves would you expect from a black hole merger?
Post by: MikeS on 08/05/2011 18:07:53

I have just had another thought on this.  I don't think gravity waves will be discovered as they will be cancelled by the speed of the passage of time changes (variable time).  In other words gravity waves could exist but would not be observable as a variable time and length wave would cancel them.  They would flow over us unobserved. 

Title: What gravitational waves would you expect from a black hole merger?
Post by: MikeS on 08/05/2011 18:16:55

Let me try to rephrase my last reply better.

I believe the collision that would create a gravity wave would also create an equal and opposite variable time and length wave which would either completely cancel, or at least make undetectable the gravity wave.

Title: What gravitational waves would you expect from a black hole merger?
Post by: yor_on on 08/05/2011 20:10:21

Hi Mark, that's a pretty intricate question. As for yet it's still a theory, highly plausible though. Take a look here Binary black hole merger gravitational waves and recoil in the large mass ratio limit (http://arxiv.org/pdf/1003.0485v1) for some ideas.

As for how to see those waves? In Einsteins universe we're a lot like a jello with all dimensions connected, so even if a gravitational wave may propagate at lights speed in a vacuum you can still imagine it as a 'shiver' in the Jello, just as if you would hit a real jello on the side, to see the kinetic 'energy' move inside it. Like vibrations in a spiderweb. Or you can see it as 'free waves', but as gravity is what defines the SpaceTime we see and know, and as I don't expect any area to be without 'gravity' even when 'unmeasurable' Like inside a geodesic? The Jello for me please :)