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A wal
  • A wal
  • Cambridge
  • United Kingdom

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Can Anyone Answer These Black Hole Questions?

I think there's something very wrong with relativity but don't worry I know how to fix it. Instead of treating acceleration due to energy (special relativity) as a special case within the generalised structure of gravitationally curved space-time (general relativity), they should be put on an equal footing. They become two sides of the same acceleration coin. Gravity is considered an inward curvature of space-time, pulling objects together, but you can just as easily view energy as an outward curvature of space-time, pushing objects apart. There is absolutely no difference between following a straight line in curved space-time and following a curved path in flat space-time. They're physically equivalent. Tomato, tomato.

1. Three ships approach a 'black hole'. One ship continuously accelerates at a constant rate to keep itself stationary relative to the 'black hole'. One ship cuts off its engines and free-falls. The last ship accelerates away from the hovering ship and steadily increases its acceleration at an ever increasing rate so that it's always moving away from the hovering ship at exactly the same speed as the free-falling ship is in the opposite direction. From the perspective of the hovering ship the other two ships are continuously becoming more length contracted and time dilated to keep their relative velocities below the speed of light. According to the standard description if we then switch to the perspective of the ship that's accelerating away from the black hole there's no contradiction between the two frames of reference, which is right. This is special relativity. Now if we switch to the perspective of the free-falling ship then according to the standard description it's perfectly okay for the free-falling ship to reach and cross the event horizon despite the fact that it can never happen from the other two ships, or any other objects perspective. It's a direct contradiction. They have to use multiple coordinate systems to describe the whole thing...

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Closing Statement from A wal

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Pabitra Mukhopadhyay: Yes but all that assumes that it's possible to reach an event horizon in the first place. Using any valid coordinate system it isn't possible to reach an event horizon, or a singularity. Singularities are single points in time as well as space and the event horizon is just what they look like from a distance. At the event horizon length contraction and time dilation would be infinite, just like reaching a relative velocity of the speed of light, and the black hole becomes a singularity. As you move away it covers more time and space as it gets less length contracted and time dilated, and always by the same amount. This makes them perfect four dimensional spheres. In GR they're cone shaped.

They are no points in the universe where the rules of SR break down.

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    Apr 28 2013: Why? A black hole is a gravitational/spacetime singularity. A gravitational singularity or spacetime singularity is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system. For an object that crossed event horizon (which is no physical boundary) and entered a black hole, by definition it has reached a state of being where laws of Physics break down, let alone co-ordinate system.
  • Apr 28 2013: These are a long way away - How do we experiment? What are the equations you are using and how do you plug in the numbers? Space travel is best experienced at the movies. Lots of energy, lots of time, and don't forget cosmic radiation.
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    Apr 28 2013: A wal, you mentioned in your other thread that you have posed these questions on a science site where you sought answers from physicists and were not satisfied at the responses you got. Would you mind sharing which sites you have tried? I ask this because I have wondered which the best such science forums are.

    I know the American Physical Society has a great site, as does NASA, but those are not forums.