PBS Space Time
2 HN recommenders · recommended in 3 months, 2018–2022
11:48 · 1M views · Mar 22, 2017
A PBS Space Time episode explaining why faster-than-light travel is equivalent to travelling back in time, using relativity and Minkowski diagrams for different observers.
HN points to it in warp drive discussions as a math-free explanation of why superluminal travel causes causality problems.
3 comments from Hacker News
One video with no maths required. this video Without the math you can't get a deep understanding or reason about it too much but you can see the issue.
Here's a good (IMHO) video showing how this works out, by looking Minkowski diagrams for different observers. this video
There's an episode of PBS Space Time about this, "The Speed of Light is NOT About Light" [1], which comes pretty close to making the same points you are making. It might be useful to watch this earlier episode, "Are Space and Time an Illusion?" [2], first. There is a later episode (or maybe a couple of them) that go into how interactions with the Higgs field make it so things with mass travel slowed than the speed of causality. To tie back to the warp drive news, they have an episode that would be a good place to start on warp drives, "Is The Alcubierre Warp Drive Possible?" [3]. There's also "Superluminal Time Travel + Time Warp Challenge Answer" [4], and "Will Wormholes Allow Fast Interstellar Travel?" [5]. A non-warp unknown physics drive that comes up a lot also got an episode, "The EM Drive: Fact or Fantasy?" [6]. There is at least one episode covering interstellar travel without using any unknown physics, "5 REAL Possibilities for Interstellar Travel" [7]. The scope of the series is basically anything vaguely connected to astronomy, cosmology, and quantum mechanics, and the episodes are all pretty short (5-12 minutes), so it is a great thing to watch when you've got a short wait for something. Here's the series home page [8], and their YouTube channel [9]. Also on the PBS streaming app, for those who like to get their physics on their big screen TVs. [1] [LINK] [2] [LINK] [3] [LINK] [4] this video [5] [LINK] [6] [LINK] [7] [LINK] [8] [LINK] [9] [LINK]