The Black Hole Information Paradox

SPEAKER_1 (0:00)

College football is back, so Hilton called on me, the superstition concierge, to make your fan rituals a reality. Need a room to match your lucky number? We got you. Wanna make sure our team doesn't wash your lucky jersey? Ooh, that smells lucky.

Hilton's unmatched hospitality can keep up with any superstition. Even a marching band wake up call at 555 in 55 seconds. Hit it! When you need a team that will do whatever it takes on game day, it matters where you stay. Hilton, for the stay.

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Matt O'Dowd (1:02)

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Stephen Hawking found a way to vanquish the black hole with his eponymous radiation. But that same radiation threatens the very foundations of quantum mechanics. It may very well be the loose thread that leads to a theory of everything.

Black holes are engines of destruction that remove from our universe anything that crosses their event horizon. But matter and energy aren't erased from existence. They add to the mass of the black hole. And we now know that this mass can escape. It gradually leaks away through Hawking radiation over unthinkably long time scales.

But in a way, that same Hawking radiation may be more destructive than the black hole itself. It may destroy information.

The apparent destruction of quantum information by Hawking radiation defies our current understanding of quantum mechanics. This is the black hole information paradox, and it's one of the biggest unsolved problems in physics.

And the quest for its solution may have completely overturned our understanding of the fundamental nature of the universe. It may have revealed that the universe is a hologram. But I'm getting ahead of myself. First, a quick recap. In recent episodes, we've explored some critical facts about the universe and about black holes. First, we looked at the law of conservation of quantum information. We saw that the very foundations of quantum mechanics demand that quantum information be preserved forever. With perfect knowledge of the current universe, it should be possible to perfectly trace the universe backwards and forwards in time.

The second idea was the no-hair theorem. It states that black holes can only exhibit three properties, mass, electric charge, and angular momentum. The inescapable event horizon shields the outside universe from any other influence within the black hole. At first glance, the no-hair theorem seems to contradict the conservation of information. If we see a black hole, how can we possibly figure out what particles went in to form it? But actually, by itself, the no-hair theorem isn't really a problem because even though the black hole swallows information, that information persists inside the black hole. There's nothing about the law of conservation of information that requires information to remain within our accessible part of the universe, just that it continued to exist somewhere. But this is where Hawking radiation comes in. Hawking radiation is like a cosmic whiteboard eraser. It causes black holes to evaporate into a perfectly random buzz of radiation that contains none of the information about the original contents of the black hole. We went over this in detail previously, but the TLDR.

The gravitational field of a black hole is expected to distort the surrounding quantum fields. That distortion looks like particles flowing away from the black hole, and the energy to create those particles must come from the mass of the black hole itself.

What type of particles? According to Hawking's calculation, those particles should come out with energies that follow the black body spectrum. In other words, Hawking radiation should look exactly like the thermal radiation of heat. Black holes should radiate as though they have a temperature that is inversely proportional to their mass. And the mass of the black hole should be the only thing that determines the nature of the radiation.

The key here is that Hawking radiation doesn't depend at all on what the black hole is made of. The black hole radiates particles, mostly photons, that contain no information. Eventually, the black hole must completely evaporate into those particles, leaving no clue as to what fell into it in the first place. And that's the information paradox.

SPEAKER_1 (4:59)

College football is back. So, Hilton called on me, the superstition concierge, to make your fan rituals a reality. Need a room to match your lucky number? We got you. Want to make sure our team doesn't wash your lucky jersey? Oh, that smells lucky.