Ask Ethan: Why Is The Black Hole Information Loss Paradox A Problem?
“Why do physicists all seem to agree that the information loss paradox is a real problem? It seems to depend on determinism, which seems incompatible with QM.”
There are a few puzzles in the Universe that we don’t yet know the answer to, and they almost certainly are the harbingers of the next great advances. Solving the mysteries of why there’s more matter than antimatter, what dark matter and dark energy are, or why the fundamental particles have the masses they do will surely bring physics to the next level when we figure them out. One much less obvious puzzle, though, is the black hole information loss paradox. It’s true that we don’t yet have a theory of quantum gravity, but we don’t need one to see why this is a problem. When matter falls into a black hole, something ought to happen to keep it from simply losing its information; entropy must not go down. Similarly, when black holes evaporate, a la Hawking radiation, that information can’t just disappear, either.
So where does it go? Are we poised to violate the second law of thermodynamics? Come find out what the black hole information paradox is all about, and why it compels us to find a solution!
It From Bit: Is The Universe A Cellular Automaton?
“I don’t believe that there are objects like electrons and photons, and things which are themselves and nothing else. What I believe is that there’s an information process, and the bits, when they’re in certain configurations, behave like the thing we call the electron, or the hydrogen atom, or whatever.”
In the mid-20th century, computers allowed us to explore a brand new idea: that a discrete space, with a simple set of rules and straightforward initial conditions, could evolve in steps to create a rich, life-like environment. While many of us have played or seen simulations of Conway’s Game of Life, a deeper idea is at the core of such a simulation: that at a fundamental level, the Universe itself may be nothing more than a similar cellular automaton. Started by Ed Fredkin in the 1960s, a simple idea that digital information could represent reality, and that bits of that information in different states and configurations could correspond to what we perceive as different particles in our physical Universe. Developed further by John Wheeler and David Bekenstein, and later taken to a quantum level to incorporate the full nature of the Universe, it’s conceivable that both matter and energy could be illusions. If the “It from Bit” hypothesis is true, only digital information would truly be real.
Is it possible that this is how our Universe actually works at a fundamental level? That the whole shebang is nothing more than a cellular automaton? Paul Halpern explores, and the rest of us get to find out!
Ask Ethan: What Happens When A Black Hole’s Singularity Evaporates?
“What happens when a black hole has lost enough energy due to hawking radiation that its energy density no longer supports a singularity with an event horizon? Put another way, what happens when a black hole ceases to be a black hole due to hawking radiation?”
One of the most puzzling things about Black Holes is that if you wait around long enough, they’ll evaporate completely. The curved spacetime outside of the event horizon still undergoes quantum effects, and when you combine General Relativity and quantum field theory in exactly that fashion, you get a blackbody spectrum of thermal radiation out. Given enough time, a black hole will decay away completely. But what will that entail? Will an event horizon cease to exist, exposing a former black hole’s core? Will it persist right until the final moment, indicative of a true singularity? And how hot and energetic will that final evaporative state be?
Incredibly, even without a quantum theory of gravity, we can predict the answers! Find out on this week’s Ask Ethan.