Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: diegostation on 20/10/2005 20:28:05
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I heard in some TV show that it is impossible to destroy a black hole and that once a black hole forms it will last forever, is this true?
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"Black Holes are Forever" - wasn't that the theme song to a James Bond film?
According to one of Stephen Hawking's most famous theories, black holes emit radiation, which takes energy, so the mass of the black hole gradually (over a very, very long time) evaporates away (i.e. as it turns in to energy to produce this radiation).
But that's only a theory, and the bit about it evaporating away to nothing is still controversial. So maybe a black hole does last forever. The problem is, nobody actually knows for certain. (Modern cosmology, using general relativity to try to explain the universe, is full of uncertainties.)
I just did a quick search for more info, and found the following site, which looks pretty good to me:
http://cosmology.berkeley.edu/Education/BHfaq.html#q2
"Eagles may soar, but weasels don't get sucked into jet engines."
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Originally posted by diegostation
I heard in some TV show that it is impossible to destroy a black hole and that once a black hole forms it will last forever, is this true?
<http://curious.astro.cornell.edu/question.php?number=163>
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Do black holes have a definite life? Everything appears to live and die. Do black holes also die? If so, what can be its cause?
Yes, even a black hole has a finite life. This discovery came about when Stephen Hawking discovered that black holes should radiate energy due to quantum mechanical processes. This radiation is called Hawking radiation. As a black hole radiates energy, it shrinks and the more it shrinks, the more it radiates (this is the nature of the radiative process) and so finally it will completely evaporate. However, the timescale for this is extremely long: a black hole of the mass of the Sun will take more than a billion times a billion times a billion times a billion times a billion times a billion times the age of the universe to evaporate completely! So it is not a process which has any significant effect for the black holes we find in astrophysical situations.
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One reason black holes appear to live so long is that the gravitational field they create is so great that its time rate from our perspective appears to be zero. If you could watch the universe from inside a black hole (and you can't) you would see galaxies be created and die almost instantly.
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What happens to all the stuff that falls in?..I mean....where does it all go ? I know things get squished...and then what ? is it compacted into nothingness or somethingness ?
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Dave - why can't you watch the universe from inside a black hole (well, from inside its event horizon)? I thought you could (briefly, before you’re sucked to the centre).
Neil - a black hole is a "singularity" - it has zero size, it takes up no volume in space, but it does have mass (so its density, i.e. mass/volume, is "infinite"). So, mathematically at least, it would appear that anything falling into a black hole does get compacted into, quite literally, “nothingness”. But what that really means, who know?
It’s possible to theorise that the singularity acts as a “wormhole” (to a parallel universe or to the past, say), so maybe whatever falls into one appears in some other place (or time). Look at the “wormholes” bit in the link that I posted above (20 Oct). In fact, read that whole link – it looks like quite a good short introduction to black holes.
Just thought of an analogy for black holes … Black holes are like cosmic landfill sites. All the debris of the universe is dumped there, and you never see it again.
(Hmmm, I wonder if there are cosmic tramps who hang around on the fringes of the event horizon with their cosmic shopping trolleys, hoping to grab any useful objects before they disappear into the hole?)[xx(]
"Do infants enjoy infancy as much as adults enjoy adultery?"
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That is a great link Paul...thanks.
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Originally posted by Solvay_1927
Dave - why can't you watch the universe from inside a black hole (well, from inside its event horizon)? I thought you could (briefly, before you’re sucked to the centre).
Neil - a black hole is a "singularity" - it has zero size, it takes up no volume in space, but it does have mass (so its density, i.e. mass/volume, is "infinite"). So, mathematically at least, it would appear that anything falling into a black hole does get compacted into, quite literally, “nothingness”. But what that really means, who know?
It’s possible to theorise that the singularity acts as a “wormhole” (to a parallel universe or to the past, say), so maybe whatever falls into one appears in some other place (or time). Look at the “wormholes” bit in the link that I posted above (20 Oct). In fact, read that whole link – it looks like quite a good short introduction to black holes.
Just thought of an analogy for black holes … Black holes are like cosmic landfill sites. All the debris of the universe is dumped there, and you never see it again.
(Hmmm, I wonder if there are cosmic tramps who hang around on the fringes of the event horizon with their cosmic shopping trolleys, hoping to grab any useful objects before they disappear into the hole?)[xx(]
"Do infants enjoy infancy as much as adults enjoy adultery?"
I suppose that just before gravity ripped you to shreds you could see the universe ourside appear to speed up. Perhaps enough time to see spiral galaxies actually rotate a little. I never envisioned enough time to enjoy much of a view. Also, I am not familiar enough with optical effects to know how severe the distortions would be of the light coming in. I imagine something like looking up the spout of a funnel with light pouring in from the top. What a view that would be. I don't believe in the worm hole stuff for black holes. Just because something has a huge amount of gravitational attraction does not automatically mean that it has worm hole properties. It might be cool but I think it is just one of those interesting science fiction devices to make time travel possible. Jump into a black hole and the universe will appear to you to race into the future. If you could get out of the black hole you would appear to have traveled into the future. You can't go back though. Time has moved on.
I think space/time is being created all the time. It is being created faster where there is less gravitational influance. Accelleration either by rocket or gravitional fields slow the creation of space/time for the object experiencing the accelleration. The faster you go or the greater the gravitational field you are in means the shorter you become in the direction you travel and the slower time is felt by you.
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Surely, if the Big Bang theory is accepted insofar as before matter formed, the universe comprised merely energy - doesn't that imply that any material that falls into a black hole will be turned into energy? That way a point which has no size makes sense & infinite density doesn't happen. As a non-physicist, that seems logical to me so long as matter that has been transformed into energy still retains its gravitational attraction. I believe the equations allow for that.
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The faster you go or the greater the gravitational field you are in means the shorter you become in the direction you travel and the slower time is felt by you
So how does spaghettification occur if you become shorter?
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From Paul's link...
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The horizon is in a certain sense sitting still, but in another sense it is flying out at the speed of light.
Now I'm even more confuddled! [xx(]
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It is generally accepted that black holes emit Hawking radiation and would very very slowly evaporate if placed in a very cold empty space but this cannot be observed. The problem is that black holes of any size are very cold indeed and the bigger they are the colder they are. The smallest black holes that are likely to be made in our universe at the moment are stellar mass black holes as big stars collapse into surpernovae. If one of these were put into a very empty bit of the universe it would still be colder than the cosmic microwave background and would therefore still be getting bigger by absorbing that energy so it would be still getting colder. The universe has to get a great deal older (millions of times!) before stellar size black holes start to evaporate and then they take loads of orders of magnitude longer than that to go out in a blaze of particles.
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evolution rules in all things
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Would such blackholes be connected to "whiteholes" by way of wormholes, that is a spacetime construct which has reverse characteristics of blackholes and with the resulting destruction of the connecting blackhole?
Doc
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Not sure I understand what you are getting at there so can't attempt to answer the question
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Ian (& Lars) - re: white holes and wormholes - see the link near the top of the page (2nd posting in the discussion).
Paul.
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Similar to the Einstein-Rosen Bridge concept.
Doc
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Black holes, white holes, and wormholes. I have had another look at the books and the notes above and thfeel that it would be worthwhile putting a few more thoughts down.
The main reason that I feel that talking about a singularity at the centre of a black hole is a cop out is that we live in a dynamic physical universe and a singularity is a mathematically single static state and as such does not make any physical or thermodynamic sense.
The event horizon defines the edge of a black hole in our universe and the rules for its growth and decay have been explained reasonably well and are as much as we can observe in our universe.
The interesting thing is what happens when you go inside the black hole. Current descriptions assume a singularity and describe the process of falling to ste singularity they dont look at the physis of a large amount of material collapsing as the singulatiy forms.
I'll post this now and contiue in another message after I've had my lunch
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Now, consider a black hole that is just forming as highly dense msterial in a neutron star collapses. One other way of defining the size of the black hole is the "orbit" of the photons as they are emitted from the surface collapsing material inside the hole. Let us for the moment ignore other stuff falling into the hole. Initially the orbits just go out to the edge of the hole as the material collapses but as collapse progresses, the gravitational field increases and the photons cant get out quite so fat so we have a new event horizon inside the old one ie our new black hole just contains another black hole and a few nbits and pieces that were left behind that will eventually fall into this new hole. plus of course the Hawking radiation of this new black hole. Inside this new black hole just the same thing happens and so on its black holes all the way down but as the collapse progresses the black holes get smaller and the hawking radiation gets more and more intense until it eventually saps the energy of collapse and reaches some sort of stable state. This is not a static singularity but a very violent and dynamic thing similar to a white hole.
So if you consider the sequence of event horizons that you pass as you fall down the gravitational potential well as being a wormhole and you consider the eventual state of the material at the bottom to be a whitehole you doo go into a black hole through a wormhole and get to a whitehole.
Now what would be the effect of more material raining down on to this whitehole. This would further increase the gravitational field and the object would have to get smaller and even more violent.
Now as holes get more and more massive at some point the laws of physics will bhave to bend a bit maybe the increasing field reaches some quantum limit and the radiating process suddenly converts all the energy in the field in the gravitating core into particles we then have the scene set for a "big bang"
Note such a big bang would not burst out of the original event horizon because as far as that is concerned nothing will have changed.
Please note all this is mere conjecture and I am quite happy for it to be proved wrong but I do feel that a lot of the current presenters on the topic have missed something by concentrating on the maths rather than the physics.
Learn, create, test and tell
evolution rules in all things
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Initially the orbits just go out to the edge of the hole as the material collapses but as collapse progresses, the gravitational field increases and the photons cant get out quite so fat so we have a new event horizon inside the old one
Eh? How do you work that out? I accept that if the mass increases, photons will not be able to travel so far from the centre. But the event horizon is the point where the escape velocity exceeds c.If the mass increases, the gravitational field becomes stronger & the event horizon will move further out.
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I agree that if the total mass of the hole ingreases by the addition of material the first event horizon will move outwards but I said at the start of the description let us suspend this for a mopment because it adds unecessary complication to the thinking. What I am describing is what happens INSIDE THIS EVENT HORIZON as the collapsing material gets smaller and more dense.
The same thing happens as a gas cloud collapses to form a star initially the escape velocity is quite low but as it collapses the surface gravitational field increases and thus the escape velocity is greater. At the first event horizon the escape velocity is equal to the velocity of light but as the lump of material gets smaller the escape velocity exceeds that of light.
Now the hawking radiation describes virtual particle antiparticle pairs being forced to travel different paths because an event horizon lies between them. Although both of these different paths now end up in the inner parts of the hole they take different times to get there and thus act as an uncertainty based energy store. As the collapse progresses this energy store gets greeater and greater until a level is reached when almost all the energy in the hole is on he form of virtual particles "evaporating" from and collapsing back into the hole. It is a material like this and not a cold dead singularity that is the final state of the core of a black hole
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I follow your reasoning, but I disagree with your conclusions. I don't see that a succession of increasingly smaller event horizons would be created. If, as is the case, the event horizon is the distance from the centre of the black hole where the escape velocity exceeds c, how can there be more than 1 of them? The escape velocity doesn't increase, decrease & then increase again as you move away from the centre.
Then, of course, there is the matter of spatial & time co-ordinates swapping so that the singularity lies in your future & is thus inescapable. Are you suggesting that these co-ordinates repeatedly swap back & forth as you approach the centre?
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At the first event horizon the escape velocity is equal to the velocity of light but as the lump of material gets smaller the escape velocity exceeds that of light.
The escape velocity at the distance where the original horizon was will increase, yes. But all that means is that the point at which escape velocity = c will move further from the centre.
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No! the escape velocity increases continuously as you head towards the centre if the escape velocity is greater than c you don't get as far as the horizon but you DO get somewhere before falling back. A bit like how high a ball goes depends on how hard you throw it.
The current imagery shows shese event horizons collapsing down to a quiet singularity at a mathematical point from which nothing escapes. I suggest that it is much more dynamic and extends ofer a certain amount of real space than this and could (at least in part) be studied theoretically using the laws of physics of which we are familiar.
My feeling is that it would become an intense ball of energy very well at equilibrium similar to the starting point of our big bang. All it then needs is a process to abruptly remove the restrainig field to end up with a big bang and lo and behold we have a fully fractal universe consiting of black holes forming, exploding internally and evaporating and we live within one of them
A new form of the Fred Hoyle contiuous creation universe that incorporated big bangs :-)
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Originally posted by Soul Surfer
My feeling is that it would become an intense ball of energy very well at equilibrium similar to the starting point of our big bang. All it then needs is a process to abruptly remove the restrainig field to end up with a big bang and lo and behold we have a fully fractal universe consiting of black holes forming, exploding internally and evaporating and we live within one of them
A new form of the Fred Hoyle contiuous creation universe that incorporated big bangs :-)
Would we have to go as far as you suggest?
Would we indeed need to remove the restraints on a black hole (i.e. Allow matter to escape beyond the event horizon), or simply allow that a big bang could be an exploding bubble, but contained within the event horizon, before falling back into the core of the black hole and becoming a big crunch?
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No! the escape velocity increases continuously as you head towards the centre if the escape velocity is greater than c you don't get as far as the horizon but you DO get somewhere before falling back. A bit like how high a ball goes depends on how hard you throw it.
Ian - I fully accept that. But it doesn't alter what I said. The event horizon is the distance from the centre at which the escape velocity = c. You can't change the definition of it simply to fit in with a different theory.
As such, if the mass (& consequently the gravitational force) increase, that distance will increase proportionally. There cannot be a point inside the diameter of the event horizon where the escape velocity = c. It must steadily increase as you near the centre; therefore within the event horizon the escape velocity must always be greater than c. If you're suggesting that there are radii where the escape velocity suddenly increments (similar to the energy levels in the orbital shells of electrons) then maybe you're right; my knowledge of quantum physics isn't sufficient to argue for or against that.
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My feeling is that it would become an intense ball of energy very well at equilibrium similar to the starting point of our big bang. All it then needs is a process to abruptly remove the restrainig field to end up with a big bang and lo and behold we have a fully fractal universe consiting of black holes forming, exploding internally and evaporating and we live within one of them
I've come across theories similar to this before & I don't have a problem with them. I know it has also been postulated that the total mass of the universe may be sufficient for it to be 1 all-encompassing black hole & that the "edge" of our universe is the event horizon.
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I don't think that I ever said or suggested that the escape velocity suddenly increased at any point in fact precisely the opposite I described a contiuous process of gradually increasing escape velocity. Let me put what I am trying to say a different way just insde the event horizon a photon can just about get to (but not cross) the event horizon into our universe. If it originates from deeper inside the hole it can't get near the event horizon into our universe but it CAN travel some distance and take some time about doing it
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If you could watch the universe from inside a black hole (and you can't) you would see galaxies be created and die almost instantly.
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I suppose that just before gravity ripped you to shreds you could see the universe ourside appear to speed up.
It depends on the size of the black hole. In the case of a super-massive black hole the gravitational force at the event horizon would be negligible. You could, in theory, hang around there quite a while before gravity sucked you in.
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Going off at a slight, but related, tangent, what happens when two large black holes of similar mass collide. In the final result, one would expect an even larger black hole to be created; but during the process of collision, as the separate black holes approach each other, one would expect a region of space between them to exist with reduced gravitational force, and even a point that is possible between the converging black holes where there would be zero nett gravity, and a trajectory between the two black holes where a projectile could pass being equally attracted to both black holes, and so engulfed by neither.
At some point in time, as the black holes are sufficiently close that their original event horizons would overlap, but they are still distinct and separate gravitational attractors, one would expect this path of balanced gravity would actually be inside the spheres that once defined the respective event horizons of the black holes. What would be the effect of this collision on matter that had previously been trapped by the event horizon, and upon new matter entering the system?
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I don't think that I ever said or suggested that the escape velocity suddenly increased at any point in fact precisely the opposite I described a contiuous process of gradually increasing escape velocity. Let me put what I am trying to say a different way just insde the event horizon a photon can just about get to (but not cross) the event horizon into our universe. If it originates from deeper inside the hole it can't get near the event horizon into our universe but it CAN travel some distance and take some time about doing it
I fully accept all that. But I still don't understand how you can say that this would cause a succession of smaller & smaller event horizons inside the original 1.
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OK heres a third way of trying to describe the same point that I am trying to get over
An event horizan is an area of space beyond which it is impossible to go beyond once one has entered it even if one was able to travel at the spped of light or use a light beam. As you go deeper into a black hole the distance that light can get becomes less than when you have just entered the hole, so going into a black hole is not like going into a sphere within which there is a strongly gravitating object and one could in theory move around inside this sphere it is a one way trip all the way down but because of this "contraction of event horizons" the horizons would eventuially he hot enough to sap the energy of the hole to become a dynamic and stable object and not a static mathematical singularity.
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...but because of this "contraction of event horizons"...
I'm fine with everything you say until you get to the part I've quoted. By the very definition of an event horizon, there can be only 1 per black hole. I'll grant that what you say subsequently sounds plausible; but do you think that maybe "event horizons" is not a good choice of name for what you're trying to describe?
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Originally posted by Soul Surfer
OK heres a third way of trying to describe the same point that I am trying to get over
An event horizan is an area of space beyond which it is impossible to go beyond once one has entered it even if one was able to travel at the spped of light or use a light beam.
Actually, I was thinking a little more about this, and with my limited understanding, do not see this to be true.
As I understand the definition of an event horizon, it is the point in space at which the escape velocity is equal to the speed of light, such that anyone entering beyond the event horizon will never be able to escape the pull of the black hole. It is not a point one may never rise above, it is merely a point which if one were to rise above, one would inevitably fall back to. Thus, a body just below the event horizon may emit light, and that light might be seen by someone outside the event horizon (albeit, such an observer must also be be doomed to fall into the event horizon themselves), but that light simply could never travel an infinite distance away from the black hole, since it will inevitably be drawn back to the black hole.
As I say, it is my limited understanding of things, but it seems subtly different to what I understand others to have said, and even the underlying assumption in some of own previous speculations on the matter.
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I agree that there is only one event horizon with our universe. but say you entered a very large quiet black hole like the ones in the middle of many galaxies. (they are so big that you could get inside without being spaghettified by the gravity gradient) what you see would be a smallish "universe" (cos you can't see out)containig a few particles possibly and having one black hole in the middle of it. As you progressed on your way down the plughole you would keep seeing much the same thing untill you came to the "singularity" as suggested by most experts on the subject. Or as I am suggesting a hawking radiation fuzzball of energy caused by the intense gravity gradient. This would have incredibly high energy states existing for a long time near the centre in which conditions would be ideal for the creation of a new big bang as a quantum uncertainty "accident"
One of the suggestions for the existence of our universe is that it started as a quantum mechanical fluctuation in the vacuum and grew from that. In the vacuum as we know it this would seem to be an impossibly unlikely event but in the conditions that I described above it would seem to be much more probable and possibly inevitable.
Learn, create, test and tell
evolution rules in all things
God says so!
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Now that I can go along with - & no succession of event horizons! I'm not enough of a physicist, especially in areas such as Hawking radiation, to know whether or not it's possible.
Another_someone - I don't believe that is the case. As far as I'm aware, the maths says that within the event horizon, spatial & time co-ordinates swap. Therefore space becomes time & vice versa (sort of). So, for any object inside the radius of the event horizon the singularity lies in its future & the event horizon in its past.
I realise that the maths also work "back-to-front" (I forget the scientific term for this) which would allow for backward travel in time; but I don't believe they allow for a sudden flip. Therefore, if the calculations say something is travelling forwards in time, that is the direction in which it must continue.
This seems to me to preclude the possibility of anything emerging from behind the event horizon.
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Originally posted by DoctorBeaver
Another_someone - I don't believe that is the case. As far as I'm aware, the maths says that within the event horizon, spatial & time co-ordinates swap. Therefore space becomes time & vice versa (sort of). So, for any object inside the radius of the event horizon the singularity lies in its future & the event horizon in its past.
I realise that the maths also work "back-to-front" (I forget the scientific term for this) which would allow for backward travel in time; but I don't believe they allow for a sudden flip. Therefore, if the calculations say something is travelling forwards in time, that is the direction in which it must continue.
This seems to me to preclude the possibility of anything emerging from behind the event horizon.
Thanks for the clarification – although I use that term loosely.
I have seen mention of that transposition of space and time within a black hole elsewhere, but I do not regard it as exactly intuitive (at least to my diminutive mind), which is why it was not what came to mind when I made my earlier comment.
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but I do not regard it as exactly intuitive
There's nothing even remotely intuitive about relativity or quantum theory! [xx(]
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A singularity as expressed as time is 1 to infinty so jump in enjoy the ride and travel to the end of the universe the quick way.
Tomorrow lies outside our universe without it there would be no tomorrow.
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A singularity as expressed as time is 1 to infinty so jump in enjoy the ride and travel to the end of the universe the quick way.
That sounds very profound but I'm not sure it actually means anything. Can you clarify it please
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Originally posted by DoctorBeaver
Now that I can go along with - & no succession of event horizons! I'm not enough of a physicist, especially in areas such as Hawking radiation, to know whether or not it's possible.
Another_someone - I don't believe that is the case. As far as I'm aware, the maths says that within the event horizon, spatial & time co-ordinates swap. Therefore space becomes time & vice versa (sort of). So, for any object inside the radius of the event horizon the singularity lies in its future & the event horizon in its past.
I realise that the maths also work "back-to-front" (I forget the scientific term for this) which would allow for backward travel in time; but I don't believe they allow for a sudden flip. Therefore, if the calculations say something is travelling forwards in time, that is the direction in which it must continue.
This seems to me to preclude the possibility of anything emerging from behind the event horizon.
Sorry about coming back to this again after all this time, but I was looking around at various sites on Special Relativity (yes, I know that gravity is about General Relativity, not SR; but as far as the swap between time and space dimensions, it should be the same).
From what I now think I understand, the flip between time and space is a local phenomena (i.e. subject to the frame of reference of the observer), not an absolute swap. Thus, if someone who is outside the event horizon is close enough to someone inside the event horizon, the frames of reference of observer to subject should be sufficiently close (i.e. within the light cone – see, I can use big words too, just don't ask me what they mean [:)]) that they would not perceive a time/space swap. It is only to an observer who is sufficiently far away from the subject that the subject would be outside their light cone that would then see a swap between space and time in the subject's local co-ordinates.