Hacker News new | past | comments | ask | show | jobs | submit
The most recent Kurzgesagt video (on time travel) https://youtu.be/dBxxi5XAm3U had this passage:

> To explain how this actually works without making a math video, we have to make a lot of physicists grumpy, so please keep in mind that we are simplifying and lying a bit.

And that simplification / lie is that everything moves at the speed of light in spacetime. We are moving at basically 0 in the space coordinates and 1s/s in the time dimension (which is "light speed" in the time dimension). However... (1:45 in the video)

> Photons, light particles, move at the speed of light through space. They don’t experience any time passing because their speed in that time dimension is 0. In the time dimension they are frozen in place. If you see light on earth, from the photon’s perspective it was just on the surface of the sun and then suddenly crashed into your eye with nothing happening in between.

... and this falls into the Lie-to-children domain. https://en.wikipedia.org/wiki/Lie-to-children#Examples_in_ed...

Yeah isn’t it a simplification of the idea an object at rest has has a four-velocity where U^0 = c (so a velocity of c entirely the time direction) but a photon doesn’t have a rest frame to do this calculation?