4 ms·
In general, most laws of physics are reversible, so extrapolation backwards is as accurate as extrapolation forwards. In the case where it's just mostly motion
by FreeFull 8y ago
In general, most laws of physics are reversible, so extrapolation backwards is as accurate as extrapolation forwards. In the case where it's just mostly motion and gravity, we can do it rather accurately.
- darkerside 8y agoI know that, but that makes the assumption that the flight path was unaffected by external forces. How is this distinguishable from, say, an alien spacecraft seeing it was spotted, boomeranging around the Sun, and exiting the solar system? *Wow, sorry. Guess I'm a conspiracy nutjob for skiing an innocent question.
- yongjik 8y agoTheoretically we can't distinguish them. But then again, if CCTV shows a hooded guy exiting your shop's front door at 4 am, it would be safe to assume that the same guy entered the shop some time before that, even though theoretically it could be an alien lifeform teleported into your shop out of thin air. It's never aliens. (Until we actually find them, of course.)
- darkerside 8y agoSeems more akin to saying, since we see this runner on the track, he must have been running around the track for an undeterminable period of the past time. It's just as possible that the runner just started running when you saw him. All I wanted to know is if we observed the past path or inferred it. Seems a valid question to me, but whatever.