|
|
Post by Progenitor A on Dec 4, 2010 18:40:25 GMT 1
Simple really
We are told, (and happily repeat the mantra) (don't we) that black holes abound and are singularities with infinite density (isn't it?) with a consequent infinite force of gravity.
This, just thinking about it casually, is nonsense. (Well we all know that infinities in physics are a sure sign that the physicists are lost, and don't know of what they talk, don't we.)
Let me demonstrate this fallacy of black holes.
I will be conservative and say that the force of gravity at the point is not infinite, but very big.
I will take our nearest black hole, some 1600 light years away and ascribe to it a gravity at a point of 1050N
Now that is very large, but a long way shortt of infinity (innit)?
Now , unlike black holes, gravity has been subjected to lots of tests and it has been found, with some reliability that the gravitational force varies as r-2 where r is the distance separaing two bodies.
Now, 1600 light years is a distance of (about)20x 1021 metres
Thats how far away the nearest black hole is from us
So my conseravtive force of gravity 1050N will be reduced as follows when it reaches earth:
1050N/(20x 1021)2
=1050N/400x1042
=1/4 x 106 N
(Note that it doesn't really matter about the acuracy of the arithmetic, infinity is so accommodating)
Now that is quite a lot biger than the 10N acting in the opposite direction (due to earth), innit?
And we should be accelerating like mad toward that Black hole shouldn't we?
Put it another way, once one of our spaceships is out of the earth's gravity, it wil acclerate though space until it is moving at an appreciable fraction of c
Bollocks aint it?
|
|
|
|
Post by Progenitor A on Dec 5, 2010 10:36:20 GMT 1
Evidently my proposition that Black Holes cannot exist is so self-evident that comment is superfluous.
More contradictions of physics soon folks! Keep looking
|
|
|
|
Post by eamonnshute on Dec 5, 2010 16:23:06 GMT 1
Taking more realistic figures, if the black hole has a mass of 1.5 suns (1.5 x 2 x 1030Kg) and the Gravitational constant = 6.6 x 10-11,then the acceleration due to gravity at a distance of 1 metre would be 1.5 x 2 x 1030 x 6.6 x 10-11 = 2 x 1020. This is a lot less than your figure of 1050 !
Black holes are possible even in Newtonian physics. If you throw an object upwards from the Earth then it will escape if the speed is > 11Km/s. For a more massive planet the escape velocity is greater. If the object is big enough then the escape velocity becomes greater than the speed of light, so the object would become invisible.
|
|
|
|
Post by Progenitor A on Dec 5, 2010 17:09:55 GMT 1
Taking more realistic figures, if the black hole has a mass of 1.5 suns (1.5 x 2 x 10 30Kg) and the Gravitational constant = 6.6 x 10 -11,then the acceleration due to gravity at a distance of 1 metre would be 1.5 x 2 x 10 30 x 6.6 x 10 -11 = 2 x 10 20. This is a lot less than your figure of 10 50 ! Yup your figures are fine, for an ordinary mass of 1.5 suns, and as we move through that mass to the centre of gravity the gravitational force reduces to zero. In a Black hole the mass is concentrated into a point and the Gravitational force is infinity at that point (where the centre of gravity lies). If it is infinity there then it remains at infinity as we move radially away F=k/r 2= k/0 = infinity at that point Now this Infinite force will reduce in proportion to r -2At 1 meter distance from a black hole point, the gravitational force is still infinite. An infinite force cannot simply shrink to suit Newtons Laws! The point is that in a Black Hole physical laws break down and this is just one illustration of that breakdown Incidentally the 'infinite' gravitational force means that we have an 'infinite' source of energy in a black hole - more nonsense. Personally I think that the concept of an infinite gravitational force is a nonsense- physical laws cannot cope with such things |
|
|
|
Post by eamonnshute on Dec 5, 2010 17:29:33 GMT 1
In a Black hole the mass is concentrated into a point and the Gravitational force is infinity at that point (where the centre of gravity lies). If it is infinity there then it remains at infinity as we move radially away F=k/r 2= k/0 = infinity at that point You contradict yourself. If F=k/r 2 then F can only be infinite at r=0. At non-zero r the force is finite. |
|
|
|
Post by Progenitor A on Dec 5, 2010 18:06:43 GMT 1
In a Black hole the mass is concentrated into a point and the Gravitational force is infinity at that point (where the centre of gravity lies). If it is infinity there then it remains at infinity as we move radially away F=k/r 2= k/0 = infinity at that point You contradict yourself. If F=k/r 2 then F can only be infinite at r=0. At non-zero r the force is finite. I do not think so k/0 is a mathematical construct, and has (I think) no physical meaning, no reality. What I am saying is that to follow this particular mathematical imperative is absurd. If we have an infinite attractive force, then it certainly does NOT reduce to less than infinity as we move away from it! That concept of an infinite attractive force is surely self-contradictory |
|
|
|
Post by eamonnshute on Dec 5, 2010 18:31:11 GMT 1
k/0 is a mathematical construct, and has (I think) no physical meaning, no reality. What I am saying is that to follow this particular mathematical imperative is absurd. If we have an infinite attractive force, then it certainly does NOT reduce to less than infinity as we move away from it! That concept of an infinite attractive force is surely self-contradictory It doesn't actually matter if the infinities exist or not at r=0 (and it is likely that they do not, in reality), even if the gravity is finite at r=0 black holes are perfectly possible, and expected to exist on theoretical grounds. So what happens at r=0 cannot be used to prove the impossibility of black holes. |
|
|
|
Post by Progenitor A on Dec 5, 2010 18:44:44 GMT 1
k/0 is a mathematical construct, and has (I think) no physical meaning, no reality. What I am saying is that to follow this particular mathematical imperative is absurd. If we have an infinite attractive force, then it certainly does NOT reduce to less than infinity as we move away from it! That concept of an infinite attractive force is surely self-contradictory It doesn't actually matter if the infinities exist or not at r=0 (and it is likely that they do not, in reality), even if the gravity is finite at r=0 black holes are perfectly possible, and expected to exist on theoretical grounds. So what happens at r=0 cannot be used to prove the impossibility of black holes. Yes I agree with you Black holes do exist but we should not blindly accept the mantras that are handed down to us. That is the point of my posting. |
|
|
|
Post by robinpike on Dec 7, 2010 9:19:04 GMT 1
Yes I agree with you Black holes do exist but we should not blindly accept the mantras that are handed down to us. That is the point of my posting. How do we know that black holes exist? |
|
|
|
Post by Progenitor A on Dec 7, 2010 9:33:10 GMT 1
Yes I agree with you Black holes do exist but we should not blindly accept the mantras that are handed down to us. That is the point of my posting. How do we know that black holes exist? ;D Very good point Robin! I am prepared to accept that the evidence adduced by my superiors in that respect has some validity |
|
|
|
Post by robinpike on Dec 7, 2010 10:39:03 GMT 1
The trouble with the evidence is that it is based on deductions. I would be more convinced if we had an explanation for the mechanism of gravity with matter (and with light). It is not that I am arguing for or against black holes, but rather that we are in a position where we do not know. So yes, I think that we should look for evidence of black holes, but we shouldn't be so easily convinced.
|
|
|
|
Post by abacus9900 on Dec 7, 2010 10:43:46 GMT 1
The trouble with the evidence is that it is based on deductions. I would be more convinced if we had an explanation for the mechanism of gravity with matter (and with light). It is not that I am arguing for or against black holes, but rather that we are in a position where we do not know. So yes, I think that we should look for evidence of black holes, but we shouldn't be so easily convinced. What we need is a 'Theory of Everything' which is what, for example, ideas like string theory address. Trouble is, of course, these ideas cannot be tested at the moment. |
|
|
|
Post by speakertoanimals on Dec 8, 2010 18:27:32 GMT 1
The first post is nonsense, because outside even a black hole, the gravitational field depends only on the distance and the total mass. Hence even if our sun suddenlyu became a black hole tomorrow, the gravitataional field at the earths orbit would be the SAME as it is at the moment, and we would continue in our orbit (albeit in the dark).
Saying you can't have infinitely-dense states of matter doesn't get rid of the infinities, as some would have you think.
Okay, what do we know about matter and gravity? As far as we can see, you can keep piling matter up, and the gravitational field gets larger and larger outside the mass. That is the simple, additive nature of gravity.
Okay, so what about the matter that makes up the gravitating body? The outer layers get pulled in by the mass beneath them, hence they have to be supported against that pull, and what supports them is the simple resistanceto compression of the matter beneath them. If we can keep piling matter up, then we can increase the pressure at the centre of the body.
Now we have two choices (keeping to the idea of spacetime being continuous) -- EITHER there is some ultimate state of matter than is incompressible, a maximum density beyond which we cannot go, OR there is not, and at some point the pressure overcomes the resistance of ANY conceivable state of matter, and the collpaee continues without limit, which is the formation of the black hole.
now the existence of an INCOMPRESSIBLE state of matter is just as 'infinite' as 'infinite' density (except it isn't really infinite density, more like it just drops right out of our universe all together). In fact, it is a WORSE infinity, in that incompressible means infinitely strong, and infinitely strong materials violate special relativity, allow instantaneous transmission of signals etc etc.
Whereas the 'infinity' of a black hole is rather tidier, in that even if some freaky weord stuff is going on in there, we can never go visit and come back to report it, it is all safely hidden inside the event horizon, from which there is no escape (Hawking radiation excepted).
As for the first post -- before presuming to make definitive statements about the absurdity or otherwise of fairly basic oncepts in physics, some people should learn to handle the basic equations of newtonian gravity, else they'll just end up looking sillier than they already do........................
|
|
|
|
Post by Progenitor A on Dec 8, 2010 18:33:10 GMT 1
As for the first post -- before presuming to make definitive statements about the absurdity or otherwise of fairly basic oncepts in physics, some people should learn to handle the basic equations of newtonian gravity, else they'll just end up looking sillier than they already do........................ This is the first posting on this thread to indulge in personal attack I wondered when this would appear. You just have no self-control do you? Aspergers I think |
|
|
|
Post by speakertoanimals on Dec 8, 2010 18:48:58 GMT 1
Uh, showing that you don't know what you are talking about when it comes to newtonian gravity isn't a personal attack, it's just pointing out that you don't know what you are talking about. You should really learn to accept your mistakes when they are pointed out, else you will never learn.................
I note that you don't attempt in any way to address the points about physics that I have raised, but nothing new there.....................
|
|
