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Like a black hole looks like this, what does a white hole looks like?

The reason I ask is because I would've imagined that it would look like the exact opposite, i.e. piercing out upwards. But it seems it's the same as black hole in the regards that it also has a mass, so.. I'm slightly confused, how does an "opposite" of black hole look like on graph?

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  • $\begingroup$ A white hole is just a black hole running backwards through time. So you would simply reverse the time axis in the drawing (so it would indeed look the same but pointing up instead of down, as you imagined). $\endgroup$ – lemon May 30 '15 at 12:00
  • $\begingroup$ Don't forget that white holes remain hypothetical. PS: I prefer this depiction of a black hole, because we're plotting the coordinate speed of light. This is zero at the event horizon, and I can't see how it can ever be less than zero. $\endgroup$ – John Duffield May 30 '15 at 12:21
  • $\begingroup$ @lemon Thanks, that answers it. I have a follow up: does that make white holes an object with a negative mass? Or does that mean that white holes simply can't exist (in our universe) because they're objects that actually require that time flows backward for them (w.r.t to everything else in our universe)? $\endgroup$ – laggingreflex May 30 '15 at 12:24
  • $\begingroup$ @laggingreflex They have ordinary (positive) mass. And what I mean is that they are mathematically equivalent to a black hole running backwards through time. That doesn't mean that they require time to flow backwards to exist - just that if you were to watch a black hole backwards it would look like a white hole. $\endgroup$ – lemon May 30 '15 at 12:30
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It would look exactly the same. Your images are called an "embedding" diagram (or at least, an artist's impression of one...). They visualise the curvature of spacetime near a black hole, by drawing a surface in ordinary Euclidean space $\mathbb R^3$ with the same curvature. The classic is "Flamm's paraboloid" -- you can look it up.

Now the choice to orient the funnel this way is purely aesthetics: it points 'downwards', and resembles the traditional gravitational "potential well" from Newton's gravity. But we could flip the surface upside down and its curvature would be exactly the same. That is, you could also draw a black hole as an upside-down funnel. But a white hole has the same curvature as a (same-sized) black hole. And so its embedding diagram(s) are identical.

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