Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Will a blackhole shrink spacetime?

  1. Jan 28, 2004 #1
    I haven't understood this concept properly...

    When a star becomes a blackhole and then eventually reaches singularity, does it shrink the space-time it previously occupied..along with it's own contraction? or is the previously occupied spacetime available for other particles to fillup ?
     
  2. jcsd
  3. Jan 28, 2004 #2

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    one of our best experts around here is a woman who goes by the name of Nereid (so you two are namesakes in a sense because a nereid is a seanymph, also let us not forget, a type of snail.) so I am tempted not to reply and let Nereid have a go at this. she is around, so lets wait a mo.
     
  4. Jan 28, 2004 #3

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    Re: Re: Will a blackhole shrink spacetime?

    Well Nereid's not around after all. But you will probably get a ton of answers from other people, a kind of dogpile of people wanting to reply. Personally I want to get away from thinking of space as a substance. In one's house it actually IS like a resource, there is only so much of it---limited storage space---and you use it up by putting things in it. But in the world at large it isnt like that.

    But already you are not thinking of space as if it were a fixed amount of material. Good. You are imagining that various processes could make there be more or less of it. I agree. For instance, in some models of the universe all the space we can see expanded from a small volume, and (if we are not good) will someday collapse back down. That possible collapse (way way in the future) is rather like the collapse of a star to form a black hole.

    So I think space must be a very dynamic changeable thing, able to ripple and bend and extend and contract, although fortunately we dont have the means to mess around with it so we dont see nearby space do that.

    If something the mass of our sun would collapse to a BH it would have an event horizon (the black sphere you mustnt touch) that was roughly 4 miles in diameter. So it would start out normal sun size say which is about 1 million miles diameter (or 900,000 anyway) and collapse down to less than 4.

    Nobody honestly knows what goes on inside the event horizon. You cant see in. There may be a zero-volume "singularity" in there, where all the material went. Nobody understands how all that material could occupy zero volume and nobody really understands singularities.
    When there is a quantum theory of space and gravity maybe singularities will look different to us and be easier to understand.
    (this is starting to happen now).

    So you can say, look the million mile diameter thing collapsed down to 4 miles----now we have all that extra empty space where we can put things! So the collapse freed up space. Like when you take a lot of stuff to the Salvation Army. I guess it is all how you look at it. I dont feel I really understand space and there is a lot of room for people to have different views. Sorry not to be conclusive. Maybe other people will give more definite answers
     
    Last edited: Jan 28, 2004
  5. Jan 29, 2004 #4

    Stingray

    User Avatar
    Science Advisor

    The volume is infinite before and after if that's what you're asking (I mean that with the black hole being the only thing in the universe).

    If you talk about a collapsing star with cosmology taken into account, then I'm skeptical as to whether a normal black hole singularity can ever form in the first place. I've never seen any work on it (doesn't mean it doesn't exist!).

    There will exist some state which asymptotically approaches the usual picture of a black hole, but I don't know about the whole singularity business. As far as I remember, all the singularity theorems require that the universe admits Cauchy surfaces, which may not be true...
     
  6. Jan 29, 2004 #5
    Re: Re: Re: Will a blackhole shrink spacetime?

    You can't use euclidean geometry to calculate a blackhole's diameter. the circumference may be 4*pi miles, but that does not make the diameter 4 miles. Black holes are determined by non-euclidean geometry. The actual radius ( and by extension diameter) could very well be infinite because of the warping of space in the presence of such a large mass. The mathematics actually break down in the interior (meaning the pseudo-Riemannian tensor that reality is described as under GR) however the conceptual ideas shouldn't (unless black hole interiors manage to refute GR, though we would never be able to tell if they did).
     
  7. Jan 29, 2004 #6
    Firstly, Stars do not create Blackholes. I know the Chandra Limit is devised to produce the Equations, but its incorrect.

    Blackholes>> CREATE Stars. Stars emerge out from the Electromagnetic Vacuum via what is termed Blackholes. Here is a good recent paper that gives some insights into a Blackhole 'Bubble' emerging out of the Vacuum:http://uk.arxiv.org/PS_cache/hep-th/pdf/0311/0311011.pdf

    All the evidence is pointing to a new understanding of Star formation and Blackhole's at Galactic cores hold all of our milkyways Stars into 'stiff' Galaxies so to speak.

    The 'singularity' you quoted is actually the individual singularity at the heart of every Galaxy, which in evolutionary terms is the Vacuum the Galaxies emerge from, if one reverse's Einsteins feild Equations, one can derive a Universe with Galactic singularities, not Universe 'singularity'.
     
  8. Jan 30, 2004 #7
    Don't listen to ranyart. He's been pushing that theory for a while but that doesn't make any sense given the number of blackholes that should exist if that was the case (given the number of stars out there). Stars are formed from gravitational compression of gases. We have photos of this taking place in nebuli.
     
  9. Jan 31, 2004 #8
    Re: Re: Will a blackhole shrink spacetime?


    Possible potential there for the theory, but the flaws in that statement just hurt my brain.
     
  10. Feb 1, 2004 #9
    I had no right to impose my theory on anyone here, so I WILL delete it and say no more, but just say a little on your post.


    You say:given the number of blackholes that should exist if that was the case (given the number of stars out there). Given that Stars create Blackholes according to the 'Chandra' interpretation?, all Galaxies that have Blackholes at their Core's would have to have evolved from a Star. In the early Universe there lays a problem, namely that the formation of complete Stars precedes blackholes, and thus preceeds Galaxies by default!.

    Now the creation of particles preceeds Stars(particulates of Gas composition) the Quote:Stars are formed from gravitational compression of gases. We have photos of this taking place in nebuli. end quote, I understand the process of stella nebuli, this occurs within Galaxies? nevertheless, at the early Universe in Big-Bang models, the phase of matter would have to be in a Gas state. The radiation period can only occur at a time when Stars have formed (Stars Shine) What you seem to be implying, and can correct me if so?..is that Molecular Clouds existed in an extremme enviroment after the Big-bang, quite close to the 300,000 yrs of Matter/Radiation creation period.

    Certain types of elements exist at certain times, Stars distribute these elements out into the cosmos, the compression function needed to overcome the Expansive force which is occuring early on in the Big-bang model, would be insufficient to form Protostars? this is theorized to have taken millions of years? yet the density of matter/Gas?..(which is being highly expanded as a remnant of Inflationary Dynamics) would mean that the thermal/Time/scale evolution would far outrun the condensation rate needed to instigate Gravatational Collapse. Quote:gravitational compression of gases?..The expansion rate in the early Universe far outways the compression rate.

    Check the figures yourself, the transition from Inflatory/Big-Bang to Radiation Phase does not match, the Gas would have to be a Solid and a Liquid for the states of matter to have evolved, thats in the model you are detailing.
     
  11. Feb 2, 2004 #10

    I tihnk you're referring too the Chandrasekar Limit, which was just a solution of einstein's field equation for what amount of mass could keep itself from collapsing inward to zero volume. Its a concequence of general relativity as are blackholes. You can't toss out the solutions to the equation as invalid unless you first toss out the equation from which the solutions come.
     
  12. Feb 2, 2004 #11

    Stingray

    User Avatar
    Science Advisor

    Actually, the Chandra limit gives the maximum mass of a white dwarf. More massive stars could collapse to either neutron stars or black holes. There's no equivalent limit for when a black hole must form. The derivation is actually more statistical mechanics than GR...

    Ranyart, there have even been explicit simulations showing exactly how the first stars would have formed in the early universe (from Tom Abel and collaborators). It all works out fine with the very first star appearing near z=60 or so. This is long after inflation has stopped, so the models are independent of it. Inflation could be completely wrong, and the result I just stated would still hold.
     
  13. Feb 2, 2004 #12

    1)I have certainly not tossed out any of Einsteins Field Equations.
    2)The consequence of Relativity and then Blackholes came through QM interpretations by Shwarztchild in the early part of the last century(albeit the interpretations followed the GR equations).
    3)Dirac solutions can merge and evolve( Dimensionally exchange) with a Einstein-Friedman-Walker model.
    4)My theory is only an extension to Einsteins GR, it has implications,Subramanyan Chandrasekhar is one of my hero's, and I certainly do not propose that his Limits be corrected.

    The problems lay in the deep rooted perception humans impose into reality in order to..well I presume to feel imoportant?..or significant, which I do believe we are, but the perception is responsible for many mis-guided notions within space and spacetime.

    Observation is Paramount! Perception is Observation!
     
    Last edited: Feb 2, 2004
  14. Feb 2, 2004 #13

    Being specific helps your case.
     
  15. Feb 2, 2004 #14
    Of course, and if I was not so busy I would love to clarify some perceptional insights linked to our position within a spacetime that imposes a 'one-way' observational constraint, but I take your point that I am not given theoretical reasons backed with hard facts, but this is out of choice, not out of ignorance

    I have to go for a short while, but I will return ..but for now


    Is Time 'observer' Dependant?..or is Observer 'Time' Dependant?

    If I place a geddanken thought experiment here, are you willing to participate in giving explanations according to SR-GR?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Will a blackhole shrink spacetime?
  1. Are blackholes (Replies: 7)

  2. The shrinking universe (Replies: 17)

  3. Are Blackholes? (Replies: 2)

  4. Betelgeuse shrinking (Replies: 3)

Loading...