Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: DoctorBeaver on 12/10/2007 14:27:42
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There's a thread in Chemistry http://www.thenakedscientists.com/forum/index.php?topic=10738.0 (http://www.thenakedscientists.com/forum/index.php?topic=10738.0) about elements that George & I hijacked into a discussion about neutron stars, and that got me thinking.
OK, so we get main sequence stars. Under certain circumstances, they can collapse to form neutron stars. It has even been conjectured that slightly heavier stars may collapse to form quark stars.
So, if string theory is correct & quarks are made from strings, could there be a situation where they could collapse further to become string stars?
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Yes there have been suggestions that something like this may be possible and could happen to avoid the awkwardness of black hole singularities, however it is important to remember that a neutron star is only a bit bigger than the black hole event horizon of a neutron star mass so the stringy behaviour may only exist behind the event horizon. I am quite happy with black holes and event horizons but I am sure that nature abhors a singularity as a stable and unchanging object. It just doesn't make sense to have a static object like that in a totally dynamic universe. It is obvious that the universe does not work that way so any "sngularity" is bound to be a very brief part of the process.
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I am quite happy with black holes and event horizons but I am sure that nature abhors a singularity as a stable and unchanging object. It just doesn't make sense to have a static object like that in a totally dynamic universe. It is obvious that the universe does not work that way so any "sngularity" is bound to be a very brief part of the process.
On a slight tangent - since time has a very different meaning within an event horizon than without, what is meant by a 'very brief part of the process' - brief in whose reckoning of time?
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Yes there have been suggestions that something like this may be possible and could happen to avoid the awkwardness of black hole singularities, however it is important to remember that a neutron star is only a bit bigger than the black hole event horizon of a neutron star mass so the stringy behaviour may only exist behind the event horizon. I am quite happy with black holes and event horizons but I am sure that nature abhors a singularity as a stable and unchanging object. It just doesn't make sense to have a static object like that in a totally dynamic universe. It is obvious that the universe does not work that way so any "sngularity" is bound to be a very brief part of the process.
I don't think singularities exist. I think there comes a point where no matter how much force is applied, the "stuff" inside a blackhole cannot be compressed further. I don't think "zero size, infinite density" is ever reached.
I don't understand the maths involved, so I can't go into the intricacies of singularities; but I haven't yet seen an explanation in plain English that gives a convincing argument as to why they must exist. All they say is words to the effect that "...eventually it collapses to form a singularity".
As far as I'm aware, if there is an object (or whatever) of finite radius and finite density at the centre of a blackhole, from outside the event horizon we would not be able to tell the difference between that and a blackhole with a singularity.
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The problem is that the mathematical modellers have not got anything that prevents a singularity in a non rotating black hole so they tend to go for that. My experience with mathematicions is that they are often pedantic and bound by their equations and do not explore them to avoid things that are physically nonsensical. However as I have pointed out there can be no such thing as a non rotating or swartschild black hole and suggest that the simplest mathematical solution for the final state of a rotating black hole is a toroidal surface and not the "ring singularity" suggested in the Kerr versions this then starts to sound a bit like the "branes" used in other cosmological models.
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Just because the mathematicians have nothing to prevent it doesn't mean it is inevitable. It just means the maths is lacking.
In what way is it like branes? Do you mean that a brane is formed inside the radius? Or that the singularity is, in fact, a brane?
I know a bit more about blackholes now than I did when you wrote about toroidal surfaces. I'll have to try to find the thread and read it again. I may be able to understand it better now.
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The basic idea I was trying to get over in that post is that space effectively turns "inside out" inside the event horizon of a black hole so as an incredibly hot collapsing rotating ring of particles and energy "cools down" by all the particles going at similar speeds it looks more and more like flat infinite space.
The idea results in what might be called a fractal universe where like the tardis the inside of a black hole looks like infinite space even though it may have a finite size in its parent universe.
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Surely, though, looking out from within the horizon, space would look more-or-less like normal space as there is nothing different about the light crossing the event horizon.
However, I think that looking towards the singularity would be a bit different. Light coming from behind you would become invisible as soon as it went past you. Light travelling tranverse to your line of sight would look pretty normal, and no light would approach you from ahead. (At least, I think that's what would happen)
Obviously, if the blackhole is rotating then it would be a bit different due to spacetime being dragged around with the rotation. I must admit I'm having difficulty trying to visualise how that might look from within the event horizon.
I assume when you refer to "looking like infinite space" you are speaking mathematically & not literally. Is that correct? Or am I missing something?
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From inside the event horizon you cannot see out. You can only see a part of whatever lies at the core. However, high velocities and accelerations slow down time so whatever you see in the distance could be a long time ago. A bit like us looking out in all directions and only seeing the cosmic microwave background at the limits of visibility.
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Why can't you see out? Surely light will still come in.
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The light coming in from the outside looses its coherence by being bent by the gravitational field like a distorting lens so you can't see anything sensible. As you get closer and closer to the event horizon the gravitational distortion gets greater and greater narrowing the angle of sky that you can see out. try looking through a magnifying glass at a distant object from a gradually increasing distance as your eye reaches the focus everthing gets very big and distorted. That's what it's like.
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Ah, OK. I understand now. Thank you.