Black holes present a very interesting dilemma to physicists. On the inside is matter of some sort which must be in some configuration, but because gravity is so strong we cannot glean any information about the internal state. However, this also presents a couple of problems: If a black hole has no internal states, then dropping a box of gas into the black hole should result in a net decrease in the entropy of the universe—violating the second law of thermodynamics. If the black hole does have internal states and thus entropy, these cannot be seen from the outside since general relativity demands that the horizon be smooth. Yet we also know that black holes glow (called Hawking radiation) due to particles being produced in pairs at the event horizon. One particle with negative energy falls into the hole, the other with positive energy is radiated away from the hole. Thus the amount of matter in the hole goes down and energy is conserved. These particles are entangled (i.e., their quantum states are inextricably linked) yet as the black hole decays away to nothing the radiation is, in the end, entangled with … nothing. This, combined with the smooth event horizon is paradoxical since we know that quantum mechanics conserves information, yet here information appears to be destroyed. Whenever paradoxes arise in physics it indicates we don’t know something, and in this case that is probably quantum gravity. The reason Hawking and others have been able to predict so much about black holes is that everything happens on the event horizon, where the curvature of space is small and quantum gravity is expected to be irrelevant. Read the rest of this entry »

Americans who travel abroad for the first time are often shocked to discover that, despite all the progress that has been made in the last 30 years, many foreign people still speak in foreign languages.

While quoting Dave Barry is always an exercise in sheer comic bliss, here he has put his finger on something eternal, something existential, something irritatingly true.

And that is, other people are so terribly, awfully … other. Read the rest of this entry »