Is faster-than-light communication possible?

The answer to the title question is "No. But also yes." Recently, the 2022 Nobel Prize in physics was awarded to Alain Aspect, John Clauser, and Anton Zeilinger for work related to quantum entanglement and the Bell inequality. Why it was awarded now, instead of 30 years ago, is something I'm not clear on. But …

Ways things can rotate

This is an overview of some of the kinds of rotation an object can undergo, with a focus on astronomical objects. Standard warning: I'm starting to realize that I don't really know enough about physics to write about this. But I try not to let things like that stop me. Things to note: I'm discussing …

Spooky action and quantum marbles

There's a phenomenon in quantum mechanics popularly known as "spooky action at a distance". One manifestation of it is known as the EPR paradox. It's usually explained using a thought experiment similar to the following. Spooky action at a distance "explained" Start with a particle that has a total "spin" of zero. Allow it to …

Black holes – supplement

Here are a few notes about black holes that I think are interesting, but didn't fit in my previous post on the topic. What would happen if… I asked as an example question "What would happen if you tried to escort a small black hole into a large black hole?", but I didn't answer it. …

Black holes

Black holes are well understood by physicists, but I've read too many oversimplified, confusing, and seemingly-contradictory descriptions of them. Over time, I've settled on my preferred mental model of a black hole, one that usually helps me to work out the right answers to questions that non-physicists have about black holes. (An example of such …

Simple orbital mechanics

The Moon is slowly siphoning off the Earth's rotational energy, in a phenomenon called tidal acceleration. This moves the Moon's orbit farther from the Earth. According to Kepler's laws of planetary motion, the Moon must orbit more slowly as it gets farther away. Well, which is it? Is the Moon speeding up, or slowing down? …

How long does it take to fall through a ball of ice?

Planet FrictionlessIceball has a straight, narrow tunnel connecting two points on its surface. How long does it take to slide through the tunnel? Simplifying assumptions As with most story problems, we have to make some simplifying assumptions. But I think they're fairly reasonable. We assume the faller starts out motionless, at one end of the …