Wednesday, January 25, 2017

All Leak, No Information

The post title could describe a government official's dream -- a leak to reporters that satisfies their desire to find out things official spokesmen don't say but which contains no actual information whatsoever. But I'm referring to the problem that a black hole causes in the universe, as outlined very clearly in physicist Sabine Hossenfelder's recent Starts With a Bang entry at Forbes.

A black hole is what's left after a gigantic star blows up -- a core of matter compressed so much and so dense that nothing, not even light, escapes its gravitational field. Although theorized for some time, black holes weren't confirmed until scientific instruments were developed that were able to measure the gravitational effects they produced.

All well and good, except that Stephen Hawking led a team that showed black holes would in fact emit some radiation -- it would "leak," so to speak, out of them. This Hawking radiation is completely random, forming no waves or anything like that. What it means is that over time, even black holes evaporate and dissipate the energy they have built up. That time is exceedingly long but finite, and the universe has a lot of it to give.

By itself that's no problem, and in fact it helps square things with the second law of thermodynamics about how everything eventually runs down. The problem crops up when we consider, as physicists do, the way that particles and radiation are "information carriers." By information, they don't mean knowledge or facts from a book, but something sort of like the history of the particles and energy under consideration. Hossenfelder's example is a book burned to ash. If the smoke and the ash are retained, it is theoretically possible that the book could be reconstituted from them, since the atoms making up the smoke and the ash are the same as those that made up the book, only transformed by the application of heat. Of course, she notes, theoretically possible doesn't mean easy or in this case at all likely. Some future level of technology might be able to pull off the trick, but not today's.

This same principle, that natural processes can run backward or forward, applies to everything, even Donald Trump's hair. Theoretically, it should be possible to determine what material actually makes up the hair and how it was created but as a wise man once said, that could take years and cost millions of lives, so it probably won't ever be attempted. Non-physical qualities, such as Cory Booker's self-respect, aren't subject to these laws and may appear or disappear as needed.

Hawking radiation escaping from a black hole has no information. Nada. Zip. There is no way to determine whatever it was that fell into the part of the black hole from which the radiation leaked. The process can't run backwards, which is against the rules. Hossenfelder gives brief outlines of four main theories about what's going on with the information but notes none of them come to any real conclusions. She's pessimistic about any near-future breakthroughs in the matter.

Obviously the problem will be "solved" on that day in the far future when the last black hole has completely evaporated -- but there probably won't be people around to witness that or even anything remotely like days, for that matter. So in the meantime it's sitting around and scratching heads and noodling on keyboards and doodling on notepads and a lot of "What-ifs?" and "Do-you-thinks?" Because despite the rock solid opinion by some that we understand everything about the way the universe works, reality reminds us that some of the information we require for that to be true is on a need-to-know basis.

And according to the universe, we don't need to know. Yet.

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