Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Sorcerer on 10/03/2008 20:20:32
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Hello. I am interesting the follow question: is a Black Hole a point? Tell your opinion. As for me I think a Black Hole has nonzero size. Otherwise it has infinite density. Besides, a doom star must transmit its angular momentum to a Black Hole. But one point is object with zero dimensions and it can’t have angular momentum.
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I think the radius of the event horizon is about 10% that of a similar mass neutron star, what is inside is unknown
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black holes have clearly defined sizes this website gives the dimensions and other properties of simple ones. one with the masss of the sun is aabout a mile radus and the size is a linear function of the mass ie a two solar mass hole would be twice as big.
http://xaonon.dyndns.org/hawking/
Hol;es with angular momentum up to the maximum pssible are a bit bigger around the middle and have more complex event horizons but are otherwise similar.
Most real black holes probably have the maximum angular momentum possible.
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If it had infinite density, then would it not also have infinite gravity?
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The word 'infinite' should be used with care. It is, essentially, a mathematical or philosophical notion and doesn't have a place in the real world. Serious Mathematicians don't even use the word without a load of qualifying statements.
'Limitless' and 'vanishingly small' are less risky concepts.
It is amazing that we brandish the word 'infinity' around on a daily basis when, in fact, it is one of the most difficult concepts around.
If it had infinite density, then would it not also have infinite gravity?
It would be better to say that, as the radius approaches zero the gravitational field at the surface would get higher and higher without limit. Nothing has zero size.
But, for someone at a fair distance away, the field would be the same, of course, whatever the radius. The 'inverse square law', when used casually, assumes a point mass - which is not really the case but allows you to do the sums accurately enough.
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Aren't black holes just rips in the fabric of spacetime?
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There isn't a 'fabric' to space-time - it doesn't appear to be made out of anything that could be 'ripped'.
Space-time, as we know it Jim, breaks down within the Schwarzschild radius/Event Horizon, at least if we rely upon the Lorentz equations (which are pretty much just Pythagoras, with the hypotenuse representing 'c') because you end up trying to get the square root of a negative number for any value within the Rs/EH. Until a workable QM theory of gravity comes along, we're restricted to saying that we cannot describe what goes on within the EH of a BH, as far as relativistic maths is concerned.
Actually, you can use trig functions instead of Pythagoras (which are derived from Pythagoras anyway), which do away with SQRTs of negative numbers, but then you start getting negative time values (which is only to be expected) but in conjunction with positive speeds e.g. the orbital speed at the Rs/EH is less than 'c', so the implication is that the orbital radius where the positive orbital velocity = 'c' is in a negative time rate region, which is confusing to say the least.
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The word 'infinite' should be used with care. It is, essentially, a mathematical or philosophical notion and doesn't have a place in the real world. Serious Mathematicians don't even use the word without a load of qualifying statements.
'Limitless' and 'vanishingly small' are less risky concepts.
It is amazing that we brandish the word 'infinity' around on a daily basis when, in fact, it is one of the most difficult concepts around.
If it had infinite density, then would it not also have infinite gravity?
It would be better to say that, as the radius approaches zero the gravitational field at the surface would get higher and higher without limit. Nothing has zero size.
But, for someone at a fair distance away, the field would be the same, of course, whatever the radius. The 'inverse square law', when used casually, assumes a point mass - which is not really the case but allows you to do the sums accurately enough.
Sophiecentaur: I agree, but aren't leptons considered "point particles". What does that mean?
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Since no one replied to my question, I'll elaborate. The situation with black holes is different from leptons like electrons. At the center of a black hole, physics breaks down. Singularities are places where the laws of physics break down. Electrons, according to the Standard Model, are "point" particles, but I've never heard of anyone suggesting that singularities lurk inside electrons. Therefore, the laws of physics would seem to apply. So how do you deal with 'point' particles that are not supposed to contain singularities?
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The answer in my opinion is NO black holes are not point particles gravity and mass and linked I haven't managed to actually prove my theory however the idea of a point particle seems ridiculous to me not only that but I`ll go as far as to say that the understanding that black holes are swallowing up huge amounts of mass is also incorrect to further object to present theory's hows this a black hole might even be the creation of Solar systems Galaxy's rather than the destruction !
I still need some help in developing my model universe and am interested in anyone who can assist me with this development Please get in contact!
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There are two aspects to the breakdown of the current laws of physics when applied to singularities. One is that you can't do the maths because of the resulting infinities you get when non-zero numbers are applied to zeros. The other is that the laws of physics require four-dimensional space-time to work and singularities, having zero-size, would appear to occupy zero space-time.
Actually, with a black hole, the laws of physics appear to break down at the Schwarzchild radius, not just at the center of the BH - see my earlier post above concerning the rate of time becoming zero at the Event Horizon, effectively removing the 'time' part of space-time.
Although electrons may be regarded as point particles in the SM, it shouldn't be taken too literally - they are not little lumps of matter, with a three-dimensional structure and made out of 'electronite'. Electrons, like the other particles in the SM, are essentially abstract and although we can study and identify their properties we cannot really say exactly how the energy that they are ultimately made out of is structured to produce their properties and behavior. At least as far as I'm aware :)
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To reiterate my answer the idea of resembling a black hole to a single particle is absolutely absurd !
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Hmm, does anyone think Gabe2k2 sounds a lot like some other member? Oh, and he just registered today! What a coincidence!
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Errr hello Evie and with respect to me like some other member I have absolutely no idea who or what your talking about !
I'm from Morecambe North West United Kingdom and a life long astronomer and theorist. I also study artificial intelligence and several other theoretical subjects. So if I resemble someone else then prey tell Who ?
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The very concept of particles in no matter what form as we observe them becomes a blurry subject when applied to a black hole! or for that matter any large gravitational mass as the super compressed mass would be a jumble of well everything !
Theoretically compressed beyond any atomic or subatomic structure we would find on earth !
Forgive me if I`m ` throwing a spanner ` in present or existing theories but I believe and possibly contrary to many that
A) gravity is proportional to mass
B) a black hole a super compressed mass plausibly forming a body made from errr lets say hawkings superstring theoretical particles in a low energy state compacted extremely tightly. Therefore the size of the mass would be again proportional to the forces acting upon it and can be pulled apart again as long as force strong enough to do so. In the example of a black hole the mass is of a much higher density than the observable masses. Again in observation the lower density mass/masses is/are being ripped apart from gravitational forces. The dark center of a black hole merely is the absence of light due to the lack of any reaction from the dense central body and of course with the abundance of light being emitted from the less dense body orbiting the central body further makes it virtually impossible to view the object in the center.
C) in observation there are particles that escape black holes usually and effectively at the poles from the event horizon again this can be explained if gravitational forces act upon objects in a similar way to magnetism ( although I hate to resemble to two forces in any way ). The very existence of these particle's lends credence to this theory and somewhat detracts from the ( 1970`s quantum ) singularity theory ( yeah I know harsh )
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This theory although simplistic alters the entire structure of the universal model with huge amounts of mass Atomic sub atomic etc being compressed at least beyond our atomic understanding to yes! Some kind of super particle but with mass size etc. However the chance of a single "sub atomic super Goo particle " lol structure to be the only existing particles present in something the size of a black hole is astronomically small.
I apologise if this is not as well written as Id like to clarify the subject. It is 1:21 am lol!
I would also state that the zero maths applied to a black hole is simply and purely fictional and merely for the purpose of entertaining science fiction !
Sorry if that last comment sounds harsh !
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Since no one replied to my question, I'll elaborate. The situation with black holes is different from leptons like electrons. At the center of a black hole, physics breaks down. Singularities are places where the laws of physics break down. Electrons, according to the Standard Model, are "point" particles, but I've never heard of anyone suggesting that singularities lurk inside electrons. Therefore, the laws of physics would seem to apply. So how do you deal with 'point' particles that are not supposed to contain singularities?
The lowest mass any black hole could get to is 2 x 10^(-8) kg, as a black hole with that mass would have a Schwarzschild radius (event horizon) of the Planck length (10^(-35)m), below which quantum fluctuations take over and make relativistic calculations unviable. According to the Heisenberg principle, it is impossible to measure position to greater accuracy than the Planck length and the very notion of a distance smaller than this is almost meaningless (due to these quantum fluctuations in spacetime). Hence, a black hole with mass of an electron and radius 10^23 times smaller than this doesn't have any physical meaning.
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Again this may sound harsh rich24 but the maths applied to this subject attempts to prove the singularity theory which it cannot !
To continue the event horizon is again simple to understand and in no way relates to the size of the central body its merely the point where the surrounding body's get completely pulled apart and spin off due to a reduction in mass therefore the inner orbital pathway or event horizon contains actually no mass at all !
Rich 24 I'm extremely impressed as to the amount of maths you have applied to this subject Can you program as I`m gonna attempt at some point to generate a computer model based on the above theories!
if successfull may the program create black holes may create solar systems even galaxy's! dependant on the mass density equations !
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I agree that the only singularity in this case is at the centre of the black hole, where the Schwarzschild metric goes to infinity and the path of any particles is geodesically incomplete. Parts of the Schwarzschild metric also go to infinity at the event horizon, but this is solved through switching to Kruskal coordinates. Even in this coordinate system, there is still a notable difference in the geodesics observed on each side of the event horizon.
Edit: I have done programming in the course of my work, however it may have to wait a while whilst I'm writing up my thesis!
Link to Kruskal depiction of black hole, which solves the problem of singularity at event horizon:
http://en.wikipedia.org/wiki/Image:KruskalKoords.jpg
Richard
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give me a week or too to read up on this lot lol but I'm glad I think you agree !
Dude i was trying to keep it simple lol !
Perhaps its my local but normally I attempt to portray this theory in a overly simplistic manner so as to relate to others without the necessity to be what a PhD mathematician !
Oh other factors of course relate to orbital decay + speed etc got few others again trying to keep the factors down to create a simplistic model or some super cool mathematical path model Im sure you can point me toward ! lol 2:44 am Bed time for me !
In summation I believe there to be constraints on particle compression therefore a blackhole is not a point or subatomic singularity ! hope this answers your question !
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OK in continuation gravity here described as a singularity within a particle above again should not be described as such what we can say for certain is that all known particicles known are effected by measurable gravitational forces although the gravitational force from any known particle is at present beyond our abilities to measure.
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Sorry Gabe2k2, but you're going to have to start including some punctuation in your postings. It's difficult and hard work to figure out exactly what you're saying sometimes and it's likely to lead to misunderstandings.
Heh - it doesn't have to be perfect - mine's not - but some full stops at the end of sentences would really help.
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Thats why I included the comment about the time lol I apologise.
Hell I'm a scientist not a poet lol !
Feel free to punctuate my posts !
You didn't comment as to wether you agree or disagree !