Black Holes, no hair, gravitational waves.

[Sorcerer]

I was reading through this article: http://www.einstein-online.info/spotlights/bh_uniquenessand it stated :

 

 

 

So how do black holes become simple? How does a cigar-shaped object that collapses to form a black hole lose all its cigar-like properties? In general relativity, there is a natural mechanism for simplifying the complicated geometric structure of certain regions of space: The emission of gravitational waves can carry away complicated features, with the waves either escaping into deep space or being swallowed by the black hole.

 

What is the need for gravitational waves? Gravity acts uniformly in all directions dependent on distribution of mass, any shaped object would be pulled inwards first at its "complicated features", eventually all features would be scaled down so much that they would be negligible. At some point they would fall behind an event horizon and be pulled into a singularity, which is the most uniform object possible, having no dimensions at all that can differ in any way.

 

Why are gravitational waves needed to remove the "hair", isn't a singularity as bald as it gets. How are features "carried away", why do they need to go "away", why aren't they just integrated into the singularity, since regardless of starting shape, all singularities have exactly the same shape, or lack of it. Why speculate gravitational waves are produced if they're swallowed by the black hole, isn't that redundant and against Occam's razor? What if they're always swallowed, how does that change anything?

 

Isn't it more like how every car that goes to the compactor, no matter how different, comes out a cube? Can you extend the analogy, what would be the gravitational waves, differing forces on the compactor?

 

If gravitational waves remove "hair", could we deduce the shape of the object that created them? Could we create them on purpose to encode and send a message over vast distances? How resistant in the information they contain to degradation, how does it compare to a radio wave?

 

If the concern is the loss of information, why not assume the information is hidden behind the event horizon, trapped in a singularity. If the black hole does evaporate, say via hawking radiation, what prevents that information from being returned. What if Hawking radiation was influenced, by information stored on the horizon?

What if we DON'T find gravitational waves, how long should we look?

Edited January 9, 2016 by Sorcerer

[EdEarl]

What if we DON'T find gravitational waves, how long should we look?

Until someone explains why we cannot find them, because there is no way to prevent everyone from trying to find them, as long as there is a possibility they exist and might be found. Someone will be curious and try.

Edited January 8, 2016 by EdEarl

[Mordred]

Variations in gravitational potential would propogate outward as a gravity wave.

 

I would suggest googling key words when your stuck on them. Here is

 

No hair theorem. Though I did find your statement "Isnt a singularity as bald as it gets" hilarious.

 

 

https://en.m.wikipedia.org/wiki/No-hair_theorem

Edited January 9, 2016 by Mordred

[Sorcerer]

Variations in gravitational potential would propogate outward as a gravity wave.

 

I would suggest googling key words when your stuck on them. Here is

 

No hair theorem. Though I did find your statement "Isnt a singularity as bald as it gets" hilarious.

 

 

https://en.m.wikipedia.org/wiki/No-hair_theorem

I worded that carefully, glad you spotted it.

Do you think it'd be funnier if they were both naked and bald?

[MigL]

An excellent book which details the history and theory of black holes is Kip Thorne's 'Black Holes And Time Warps'.

I can't recommend it enough. Its very informative and not math intensive.

 

Incidentally Thorne is a student of J.A. Wheeler, who coined the 'no hair' term.

[ajb]

What is the need for gravitational waves?

 

Gravitational waves fall out of general relativity upon linearisation. If gravitational waves are not realised in nature then this would be awkward for understanding how general relativity has been such a good theory.

 

These waves can carry energy, momentum and angular momentum. They can allow systems to stabilise. For example physically it is expected that any black hole will quickly settle down to a Kerr (or maybe Reissner–Nordström) black hole via 'ringing gravitational waves'. Proving this mathematically and indeed that Kerr black holes are stable (ie, the end result of this 'ringing') has not been proven. (That is your homework for this week!)

 

If the concern is the loss of information, why not assume the information is hidden behind the event horizon, trapped in a singularity. If the black hole does evaporate, say via hawking radiation, what prevents that information from being returned. What if Hawking radiation was influenced, by information stored on the horizon?

This is the question that many people would like to answer.