Why do we care what's inside of a black hole? What can we learn from it?

 VICTOR T. TOTH I.T.  PART TIME PHYSISIST

First of all, Interstellar is a piece of fiction. When the movie was released, it was lauded for its scientific accuracy, so I had high expectations. My expectations were shattered by the absolutely nonsensical “science” of the movie. So please, do not rely on Interstellar as a reference on black holes.


Now let us talk about the “inside” of a black hole for a moment. Presumably, we are talking about the inside of the event horizon. But the event horizon is a really weird thing, a construct of extreme (!) spacetime geometry. Here are a couple of its important properties:
To an observer outside, the event horizon remains forever in the future. It is unobservable, because it has not happened yet.
Things falling towards the event horizon will disappear from sight, but only because of extreme time dilation and the associated redshift; any light from such things gets redshifted to invisibility as they approach the horizon. They will also appear to slow down as they approach, never quite reaching the horizon (which hasn’t formed yet, as you recall.)
An observer who falls towards the horizon will reach the horizon in finite time as measured by his watch. Once the horizon is crossed, however, it (i.e., the horizon) is no longer a geometric object in space. Rather, it is now (from this observer’s perspective) a moment in time. Very specifically, a moment in the past. Hence, there is no returning to the horizon; you cannot go backwards in time.
An observer inside the horizon will inevitably end up at the singularity (which is an unavoidable future moment for such observers, at least in the case of a simple Schwarzschild black hole.) There is no escaping; no avoiding this moment. But attempting to escape by accelerating in any direction actually shortens the time before reaching the singularity.

OK, now that we have dealt with these points, I think it is fairly clear that a) we have a pretty good idea what’s inside a black hole, and b) you really don’t want to go there. Like, ever.

Why do I boldly say that we know what’s inside a black hole? Because black holes, first and foremost, are theoretical constructs. Nobody has seen a black hole yet, by any technical means. We infer the existence of specific black holes by observing their environment: e.g., stellar sized black holes in binary systems, supermassive black holes in galaxies. But inference is not the same as direct observation. A campaign is presently under way to attempt to observe the “shadow” of our very own Milky Way’s supermassive black hole. This campaign, the Event Horizon Telescope, may yield some interesting results in the near future. But for now, black holes are constructs of theory. Everything we know about them comes from equations.

Having said all that… studying the neighborhood of a black hole can be very interesting, especially if it is an active object. You see, the black hole itself may be pretty much invisible, but its neighborhood may contain huge amounts of swirling, infalling matter, producing all kinds of extreme, interesting physics. But no, I don’t think studying the accretion disk (which is what these swirling clouds of matter are called) of a black hole will help us “solve everything or “produce wormholes and stuff”. Rather, they’ll add to our existing body of knowledge of how matter behaves under extreme circumstances. That’s all. Depending on your outlook on life, this may be a lot or it may be a little, but this is what we get.

But for this, we don’t need spaceships. Telescopes (optical, radio, X-ray, etc.) will do just fine. Not that it wouldn’t be cool to have spaceships capable of traveling thousands of light years to the nearest black hole. But we are a very long way away from, never mind that, just traveling to the nearest star a little over 4 light years from here. As a matter of fact, later this year we are approaching the 45th anniversary of the last time a human being has been more than a few hundred kilometers from mother Earth in space (for comparison, the Moon is 385,000 km from here, and a light year is close to 10 trillion kilometers.)

ANAΔΗΜΟΣΙΕΥΣΗ ΑΠΟ ΤΟ QUORA 21/6/2017