I don’t think there is a true ELI5 answer, at least, I can’t think of one. The basic concept involves general relativity, and while there are ways to simplify i

I don’t think there is a true ELI5 answer, at least, I can’t think of one. The basic concept involves general relativity, and while there are ways to simplify it (i.e. no math) it’s still complicated. This does an ok job: https://physics.stackexchange.com/questions/128075/how-would-wormhole-based-ftl-violate-causality https://physics.stackexchange.com/questions/128075/how-would... Better job, but less accessible: https://physics.stackexchange.com/questions/52249/how-does-faster-than-light-travel-violate-causality https://physics.stackexchange.com/questions/52249/how-does-f... The classic version involving FTL ships: http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-ti... A little math, but useful because it applies to the ability to send signals FTL, regardless of means: https://www.quora.com/Why-would-traveling-faster-than-light-make-me-go-back-in-time https://www.quora.com/Why-would-traveling-faster-than-light-...