Comment by Gravityloss

Comment by Gravityloss 6 months ago

16 replies

View on Hacker News

Exactly. The coin flipping example is a very nice way to put it. It works since the coins are interchangeable, you just count the number of heads or tails.

If the coins were of different color and you took that into account, then it wouldn't work.

It's not intuitive to me what gravity has to do with entropy though, as it's classically just a force and completely reversible (unlike entropy)? Ie if you saw a video of undisturbed objects only affected by gravity, you couldn't tell if the video was reversed.

floxy 6 months ago

> Ie if you saw a video of undisturbed objects only affected by gravity, you couldn't tell if the video was reversed.

How does that work with things like black holes? If you saw an apple spiral out of a black hole, wouldn't you suspect that you were watching a reversed video? Even if you take account the gravitational waves?

Reply View 15 replies
  • immibis 6 months ago

    That's the question of why time only goes forwards. It seems to be that the universe started in an extremely low-entropy state. It will go towards high entropy. In a high entropy state (e.g. heat death, or a static black hole), there's no meaningful difference between going forwards or backwards in time - if you reverse all the velocities of the particles, they still just whizz around randomly (in the heat death case) or the black hole stays a black hole.

    Reply View 0 replies
  • Gravityloss 6 months ago

    Classical gravity doesn't work like that. An apple does not spiral into a black hole in space there. It's in an elliptical orbit. (A circle is a special ellipse.)

    Reply View 0 replies
  • kgwgk 6 months ago

    If you saw a comet coming from the sun, or a meteorite coming from the moon, etc. you would also find that suspicious.

    Reply View 12 replies