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Black Hole Question #8,452,123

  1. Mar 30, 2014 #1
    Requested info for a sci-fi short story I'm writing:

    You are approaching the event horizon of a supermassive (10 billion Solar masses) Schwartzchild black hole in a magical spaceship which is capable of violating the laws of physics. You have not been free falling but lowering into the hole slowly. Inches away from the point of no return, you fire your rockets like crazy to remain at this point.

    From what I have attempted to research over the past three days, remaining at this point just far enough away from the event horizon will result in you being able to view the entire future of the universe pass before your eyes at high speed in a concentrated circular area directly behind you.

    My questions are:

    a. Is this the case? If not, please explain why and correct my terrible layman's knowledge.
    b. If this is the case, is it possible to observe the future of the universe past the point in time where the black hole should evaporate as predicted by Hawking radiation or will your time travel end there?
    c. If this is the case, what will it look like?

    Thanks in advance!
  2. jcsd
  3. Mar 31, 2014 #2


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    close enough for a science fiction story that already includes an impossible spaceship, if you assume a static black hole. You've constructed a situation which allows for an arbitrarily great gravitational time dilation, so you can have an arbitrarily large amount of rest-of-universe time pass in any given amount of shipboard time. (You've also constructed a situation that involves arbitrarily large accelerations and fuel consumption, so it's a good thing your space ship is magical and can violate the laws of physics)
    You never were doing any time travel, just aging much less quickly than the rest of the universe. As the black hole disappears, so to does the gravitational time dilation; eventually your rate of aging comes to match that of the rest of the universe. (A good exercise is to calculate how long it would take for a black hole of ten billion solar masses to decay by Hawking radiation - chances are that black hole decay will be irrelevant to your plot).
    not the case.
  4. Mar 31, 2014 #3
    I'm getting about 2x1097 years.
  5. Apr 2, 2014 #4
    Lower yourself towards the BH with your back towards it. You'll observe the entire universe blue-shifting and getting squished into a structure in front of you. At the same time, all things happening in the universe will appear in fast motion and so by the time you reach the horizon you would have witnessed a huge amount of the universe's history.
    The structure that the blue shift squishes the universe into will look more and more like a single star-like object radiating at very high temperature. The further you get away from the universe (and towards the horizon), the more compressed this star-like object gets and the hotter its spectrum becomes.
    I speculate that the moment you cross the horizon, you'll find yourself in orbit around the star-like object with a regular looking universe all around you - like orbiting a normal, hot star.
  6. Apr 2, 2014 #5
    Last edited by a moderator: May 6, 2017
  7. May 15, 2014 #6


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    My question is: what good is this to your characters? as was pointed out, you are not viewing the future so much as staying nearly the same age while the Universe ages around you. even if you had the energy to pull away from the black hole, you would be in some distant point in the future. Unless that is the plot of your story. IF your characters were attempting to pull off this maneuver to glimpse the future and stay in their own time frame, I don't think it is going to work.
  8. Nov 25, 2014 #7


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    Science Advisor

    On that time-scale, you cannot ignore cosmological effects, such as dark energy tearing apart your black hole.
  9. Nov 25, 2014 #8


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    Gold Member

    It ABSOLUTELY isn't going to work.
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