If you follow physics, you might recognize what this means: Using lasers and a block of glass, a team of Italian physicists created Hawking radiation.
Black holes are called 'black' because they're not supposed to emit anything. A light bulb, for example, looks bright because it emits photons, the particles that make up light. In Einstein's theory of gravity, which predicted black holes in the first place, black holes can only take things in, and once inside the event horizon—the black hole's point of no return—nothing can escape. That is, the black hole can't emit anything. (The reason for this is wonderful: in the theory, time and space actually trade places inside a black hole. Just like we can only go forward in time, inside a black hole you can only go forward in space! You're forced inexorably to go deeper into the black hole, and even an infinitely powerful rocket is useless up against the laws of space and time.)
But in 1974 Stephen Hawking showed that there was a way. The key is that even empty space is teeming with activity all the time—particles are coming in and out of existence constantly. It turns out particles popping into existence come in pairs (usually, and in any case that can't emerge as single particles because of energy conservation—remember that from the first post?). So let's say a pair of photons popped into existence right at the event horizon. What happens? One falls into the black hole, never to return, while the other can escape. The one that escapes is the Hawking radiation, light created through a quantum process that then escapes a black hole's grasp.
This is a good place to point out a common misperception: black holes are not vacuum cleaners, and they do not "suck" everything around them into the hole any more than the Earth does. In fact, particles, stars, and even other black holes can remain in perfectly stable orbits around black holes for great lengths of time, just like our Moon orbits us.
Now, using high-intensity lasers, physicists have created something like a black hole horizon in the lab. There are, as always, concerns and cautious stories, but this is interesting no matter what. Read the story for more.
Also, the story doesn't have a whole lot of detail about how they actually created the "something like a black hole horizon." If you'd like to know more—and let me tell you it's cool—let me know in the comments and I'll fill you in.
Can they in principle use these lab black holes to investigate the information paradox? I.e. by looking for correlations in the emitted radiation. That would be pretty cool.
ReplyDeleteIncidentally, when Hawking gave a talk on conceding his bet about the paradox, I got to ask him from the audience: "so, does this mean Hawking radiation is wrong?" Fun times.
Hi James—sorry to take a few days to reply. I'm curious to hear what Hawking's response was!
ReplyDeleteRegarding the information paradox, that bet is up in the air.
(For those who don't know, the information paradox is the following: in theory, black holes have only three properties: their mass, angular momentum, and electrical charge. Everything else follows from these. The paradox is that stuff that ends up in a black hole has more information, e.g., physical structure, chemical makeup, temperature, speed, etc. All this stuff gets lost when something falls into the hole. Some argue that Hawking radiation carries that information away, so that it isn't actually lost, but that position remains controversial.)
I never worked on this problem, but I cautiously side with Thorne. The problem is that Hawking radiation isn't obviously carrying information about the black hole away. Rather, it's (arguably) carrying away new information created when the particle pairs come into existence. Preskill (the third party who initiated this round of general relativity bets) has an argument, though.
Regardless, the one thing that's clear about this experiment is that it doesn't involve a black hole. The article makes it sound like this is all cool black hole stuff, but really it's not. In fact, one point is that Hawking radiation need not come from a black hole.
So I doubt it will give us insight into the information paradox. However, it's possible. An interesting point is that in this experiment, the Hawking radiation does carry information about the horizon, the properties of which determine the HR spectrum.