The Fascinating Tale of Measuring Light and Upending Our Understanding of the Universe

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[oxylepy]

"Thus, despite just sitting there on the toilet watching this video" I've been called out 😂

[susanwoodcarver]

This reminds me of the Quote by Sir Terry Pratchett:
"Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first, and is waiting for it."

[forger]

The GPS satellites travel at 14 million meter/HOUR, not per second. It would be quite a feat if we managed to get satellites to a speed of about 5% the speed of light ;)

[ChrisGVE]

One of the best videos of TIFO I have seen, I can't wait for you to tackle other physics topics in the same funny yet accurate matter (I should know I am a physicist). Very well written and delivered as always!

[aaronmicalowe]

It might seem that it has taken a very long time to figure this out, but on the grand scheme of things, we figured it out pretty damn fast!

[HyperactiveNeuron]

Huh. I didn't think I'd get a refresh on physics from Simon today. Someone definitely did their homework.

[DawidUliczny-roeo]

The way I heard that story before was that James Clarke Maxwell calculated the speed of propagation of electromagnetic wave and because it was pretty much spot on the experimental measurements of value of light he surmised that visible light is indeed a form of EM radiation.
Simon, did you do ADR in the bathroom?

[sydhenderson]

I'm thinking Einstein must have been pleased to find out about the Lorentz-Fitzgerald transformation since it would have followed from his thought experiment. I also didn't realize that Galilean relativity played such a vital role for him (and is still valid).

[yobgodababua]

Light (or any electromagnetic radiation) is weird stuff. If you wiggle the electric field of nothingness, that wiggles the magnetic field of nothingness, which wiggles the electric field of nothingness, and thus the wiggle propagates forth through the nothingness. c depends on how fast those wiggles can wiggle each other.

[MLG]

Some easy listening at 6:31am haha.
You’re awesome Simon!

[markf]

as i sit here on the toilet besides the massive amount of energy I contain, there is something else that is about to be released and uncontained. Thanks for the vid Simon, always a good watch.

[Ghostmany]

DJ Cummerbund with yet another banger! I've watched a few of these types of mashes from several other artists on here and I gotta say this guy has the most spot on mixes of all. Beats all smoothly locked together, all pitches perfectly matched, seamless vocal transitions, each mix sounding like it was written as one song start to finish, well done good sir, well done!

[Nazuiko]

I was indeed wondering, where and how did we originally devise or calculate the speed of Light; Perhaps more accurately called "the speed of Causality"

[SterlingGroovy]

Well done Gilles, great script, well done all of you, good work, i really enjoyed video

[kevinbarnard]

For a bit around seventeen mins in, with Simon's accent, I found myself singing Monty Python's Galaxy Song :P

[tomholroyd]

What an amazing AHA! moment that must have been!!!! To realize that when Jupiter is farther away the light takes longer to get here

[BlueMaggard]

Light speed knowledge being illuminating....I can't say it was the best knowledge given in the video, but it made the entire video worth it! <3

[mcleans.]

Hi Simon, this is one of my favorites. Compliments to the writer on this episode.

[jamesmcglew]

24 minutes just so Simon can do a light pun

[PassiveSmoking]

One interesting side note, if Einstein is right then we can't know the speed of light with absolute certainty. The best we can do is measure the speed of a round-trip, light emitting from a source, striking a reflective object like a mirror, and returning to the point of origin. The reason why we couldn't measure the speed of light in one direction is to do so we'd need two perfectly synchronised clocks, one at the source and one at the destination, and that would require us to be able to communicate between the source and the destination instantaneously, which is impossible thanks to the speed of light being finite (in a round trip, I'll get back to that later). or it would require us to synchronise the clocks in one place, then move one of them, but because of time-dilation the instant we start moving one of the clocks, it will go out of synch with the other.

As previously stated, we can measure the round-trip of light with extremely high precision, but that doesn't guarantee that the speed of light is always the same in all directions. It could be, for example, that the speed of the light on the out-bound leg is 1/2 the accepted figure for the speed of light, and that on the return leg its speed is infinite. That would give a round trip that matches the accepted figure for the speed of light, but we would have no way of knowing for sure that the light was always travelling at that speed for its entire journey.

Intuitively, it would seem that the speed of light should be a universal constant in all directions, but it's been demonstrated that the laws of physics don't operate in an intuitive way more than once (for example, the weight of an object has nothing to do with how fast it will fall, though intuitively you'd think that heavy objects would fall faster than light ones). There is no observation you could make or no experiment you could conduct that would prove one way or the other whether the speed of light remains constant.