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

Argument against the existence of black holes?

  1. Sep 13, 2008 #1
    I had a brief conversation with a professor of mine and he presented, in short an argument against the existence of black holes. I'm sure you've heard it or a variation of it. It goes something like this: An advisor and his student are near a black hole. They are both wearing a watch, the same watch, synchronized to the same time. The advisor doesn't like his student though. He propels his student into the black hole past the event horizon. On the advisor's watch, he sees the student fall into the black hole and die in a finite amount of time. But the student going deeper and deeper into the black hole, the gravity becomes immense, and time slows to such a degree it takes him an infinite time to fall all the way in. Mind you, he has gone all the way past the event horizon. Thoughts?
     
  2. jcsd
  3. Sep 13, 2008 #2

    Jonathan Scott

    User Avatar
    Gold Member

    The advisor does not actually "see" what is happening, but rather sees increasingly delayed (and red-shifted) images of what was happening earlier. However, if he calculates the student's location and time based on those images and extrapolates forward in time, he will calculate that in his own frame of reference, the student would have reached the event horizon in a finite time. The contradiction is therefore the result of a not very meaningful mathematical calculation, rather than an actual observation.

    This is in many ways just another example of the way in which relativity means that different observers observe the same events, but assign different locations and times to them in different frames of reference.

    However, I personally still think black holes are probably nonsense for different reasons. Even if GR remains accurate in such extreme cases, Einstein's equations do not uniquely determine the physical radial coordinate without additional boundary conditions, and when Karl Schwarzschild himself first presented his solution (in a paper available in translation at arXiv:physics/9905030), he used a different coordinate for the coordinate distance to the Euclidean origin and his "r" coordinate was merely a mathematical convenience for simpler calculation, valid only for r > 2Gm.

    So far, I've not seen any totally convincing proof either way, although I've seen some surprisingly heated opinions where people claim in both directions that it's obvious - given their own personal physical interpretation of some undeniable mathematical fact. On the basis of simplicity, I'm inclined to accept Karl Schwarzschild's own model, which doesn't include black holes, but there could be some argument that would convince me otherwise.
     
    Last edited by a moderator: Sep 14, 2008
  4. Sep 13, 2008 #3

    mathman

    User Avatar
    Science Advisor
    Gold Member

    It looks to me like the time sensations have been switched. The outside observer sees the infalling object take an infinite amount of time to fall in, while the person falling in takes a finite amount of time to pass the event horizon and get killed.

    There seems to be much observational evidence for black hole existence, particularly gigantic (millions to billions of solar mass) objects at the center of galaxies.
     
  5. Sep 14, 2008 #4

    Jonathan Scott

    User Avatar
    Gold Member

    That is evidence for black holes only if you assume (a) that GR still holds in those cases and (b) that Hilbert's reinterpretation of the Schwarzschild radial coordinate as a physical radius is meaningful.

    Note for example that if GR is right but Hilbert was wrong, then such objects would be not-quite-black but incredibly red-shifted and compact, but they would for example be able to have significant intrinsic magnetic fields, as they would not be susceptible to the "no hair" theorem. Many black hole candidates show signs of strong magnetic fields, and although it is plausible that these could arise from the accretion disk, there is experimental evidence that the properties of the observed fields do not correlate well with the properties of the accretion disk, for example in the case of the gravitationally lensed quasar Q0957+561, where the magnetic field seems to be associated with the central object. This evidence has been used to promote another alternative theory to black holes known as a MECO (Magnetospheric Eternally Collapsing Object), but it also supports GR with Karl Schwarzschild's original interpretation of the radial coordinate.
     
  6. Sep 15, 2008 #5
    Each black hole is remnant, cooled nucleus of an exploded star and has nuclear density.
     
  7. Sep 15, 2008 #6

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    If a black hole is formed during stellar collapse, then, according to an observer falling with the surface of the remnant, the density of the remnant rapidly exceeds nuclear density.
     
  8. Sep 15, 2008 #7
    Falling matter on the black hole produces micro-quasar or quasar. Connected to the size of black hole.
     
  9. Sep 15, 2008 #8

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Could you give a reference?

    And what does this have to do with the density of the remnant?
     
  10. Sep 15, 2008 #9
    A remnant density is decreasing.
    go through Google about micro-quasars.
    in the case of quasars of course the event is same and large-scaled
     
    Last edited by a moderator: Sep 15, 2008
  11. Sep 15, 2008 #10

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    As the black hole forms, the mass of the remnant increases
    This is not a satisfactory response. Let me remind you of some of the rules

    https://www.physicsforums.com/showthread.php?t=5374

    here at Physics Forums,
     
  12. Sep 22, 2008 #11

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    These ideas have been thoroughly discredited; see

    https://www.physicsforums.com/showthread.php?t=141985&highlight=Abrams

    http://arxiv.org/abs/gr-qc/0608033.
     
  13. Sep 22, 2008 #12
    A better argument against the formation of event horizons in gravitational collapse is given here:

    http://arxiv.org/abs/gr-qc/0609024

    See Section 7 on page 10 and further.
     
  14. Sep 22, 2008 #13

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Better in that this paper doesn't make undergraduate mistakes, but it is still highly speculative and controversial, and has yet to be accepted by the physics community. Also this paper is not classical, i.e., its claims are based on quantum effects. I have mentioned this paper on Physics Forums several times, e.g.,

    https://www.physicsforums.com/showthread.php?p=1534827#post1534827.
     
  15. Sep 22, 2008 #14

    Jonathan Scott

    User Avatar
    Gold Member

    George, I don't agree. Neither that thread nor the article justifies the use of Hilbert's assumption about the radial coordinate; they merely find fault with other aspects of the relevant papers, and I find the extremely defensive and abusive nature of the responses (especially from "tessel" quite extraordinary in itself).

    I've answered the same point in more detail in another thread at https://www.physicsforums.com/showpost.php?p=1884298&postcount=6
     
  16. May 8, 2011 #15
    Wouldnt this be the oposite? The professor would see the student get closer and closer to the black hole but his light would slow down as gravity started to effect it. Eventually the light from the student would slow to a stop as he reached the event horizon and the professor would never actually see the student go into the black hole. He would only see the students light lingering just ouside the event horizon. The student on the other hand would approach the event horizon and eventually be sucked in and killed, yet to him his watch still appears to be running normal even though time is altered by the mass of the black hole. Im not an expert in physics or math, but i am doing research for an argumentative speech over black holes and i am having trouble finding points and counterpoints for this matter. Ive seen that black holes are science fact now, but ive also seen that their existence is still a matter of speculation. Can anyone help me disprove them or prove them in lamens terms.... while keeping in mind that i know practially nothing about physics or math. And my only real knowledge in either subject is what i can picture in my mind, not prove through equations.

    ..be gentle >.<
     
  17. May 8, 2011 #16
    So?

    If you put in additional boundary conditions you still get a collapse to a black hole.

    There are also two different statements:

    1) any collapsing object will turn into a black home
    2) black holes don't exist

    1) is a somewhat controversial, but there is no way I can see around 2). You can solve Einstein's equations using something other than schwarzchild conditions and you get a collapse to a singularity.

    Simple,

    Do a coordinate transformation to Kruskal-Szekeres coordinates

    see

    http://en.wikipedia.org/wiki/Kruskal-Szekeres_coordinates
     
  18. May 8, 2011 #17
    a) yes b) no.

    In fact when you do black holes, there is interpretation as a "physics radius". R is just a coordinate, and you can use any other,

    Not true. Kip Thorne worked this out in the 1970's, and wrote a book about this called the membrane paradigm. To summarize, because the time coordinate slows down, you can treat the surface of a black hole "as if" it as a conducting surface at which you can attach a magentic field.

    That's because the magnetic field is generated by a dynamo centered on the black hole. See Kip Thorne. I really don't take any of the MECO papers seriously, because they ignore Thorne's work in the 1970's. Unless someone explains why Thorne's arguments and mechanisms don't work, I don't see any reason for the MECO speculation.
     
  19. May 8, 2011 #18

    FtlIsAwesome

    User Avatar
    Gold Member

    Welcome to PF, unedjoocated.

    unedjoocated, twofish, I'm not sure if you've noticed, but this thread is ~3 years old, so some of the information may be outdated.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Argument against the existence of black holes?
  1. Black Holes Don't Exist? (Replies: 10)

  2. Black holes cannot exist (Replies: 22)

Loading...