Can photons reach back in time?

Like most of my posts, this one is free and reasonably non-technical; my few premium posts have technical content. (Audio version below.) I considered sending this post back in time to make up for the major delay in publishing it – but I hope that readers with a fair degree of foresight will have looked ahead and seen that it was going to be worth waiting for. This is quite a long read – but its implications are rather important. So I hope you’ll stick with it. To hear an audio version of this post (45 mins), click the arrow below: 1× 0:00 -44:55 Audio playback is not supported on your browser. Please upgrade. Just a reminder: To see a full list of posts in sequential order, with a brief summary of each, go to https://ihs.ac/s.php . Background In 1801 Thomas Young changed the course of science forever, by the simple act of shining a light through two closely-spaced slits in a card onto a screen beyond. In this one apparently trivial step he established that light travels in a w ... Read full article.