history of the speed of light and how its speed was determined

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Just letting you know I am currently working on a follow up to this video with more recent experiments on determining the speed of the light. Stay tuned

Worth mentioning : XVIIth century judge Fermat (of famous math conjecture fame) had the intuition that light takes the shortest route in TIME between A and B. This implies a finite speed. From this principle, Descartes and Snell independantly derived the law of refraction, fundamental to lens design.

Timestamps for each speed of light experiment Ole Romer 1:04 James Bradly 5:12 Hippolyte Fizeau 7:53 Leon Focault 12:15

Hi Paul, thanks for another fantastic video! I think there is a slight error in your explanation of Romer's data... the apparent period should depend on the relative velocity of Jupiter/Io and Earth, not upon their distances (as suggested at 3:05). This would mean the apparent period is larger when earth is moving from J to K, and smaller from F to G. Consider: if Earth were stationary at K, the apparent period would = true period, despite light taking longer to travel a greater distance. It seems analogous to the Doppler effect: when source and observer are moving apart, the apparent f decreases (hence apparent T increases)

My high school physics teacher explained Foucault's method to me in 1983, and it was my first experience of finding out that something that seemed unknowable to mere mortals like me was actually a simple matter to explain and understand. I had that same experience again as an undergrad when I asked my biology prof how we knew about transmembrane cell proteins. (The amount we seemed to know about molecular cell structure baffled me.) In about one minute he explained freeze-fracturing to me. It was so simple! So I went into research. I think people might be surprised how much they can understand if they just have the confidence to ask, and if they ask someone who is good at explaining things. Kids, ask your teachers how we know the things they are teaching! (But don't be a snot about it... that won't help.)

Excellent presentation! Easily one of the best I've seen on the subject. I'm just a hack layman on physics, but I do relish videos like this. Thanks a million!

This is amazing! This video definitely deserves more views! Thank you.

Wow. At age 65, I am suddenly a high school student studying a subject that teenaged-me dismissed as boring. Thanks for that!

A fabulously clear explanation of how Roemer calculated the speed of light! Worth it for that alone! Ty

This video deserves more attention. You guys really helped me with my uni report on thr measurment of light speed

Good job. Very nice explanations. You provide the right insight without going into much detail.

excellent video, thank you for investing your time and effort on this. I am sure that with time this will become a very popular channel.

Excellent! A bit closer to understanding the speed of light! Thank you!. Absolutely fantastic! Thank you so much. Keep them coming..

Good watch after videos about the Maxwell's equations and his realisation that light is but an electromagnetic wave.

Thank you for great video. We learned about the early scientists at school, and I was amazed, and still am, at the intellect and the determination of Rømer, Bradley and Fizeau, and many others, using basic astronomical equipment etc. I mean, if I'm correct, Fizeau's mirror was five and a half miles away, and he was using something like an oil lamp or a candle. I know there was not a lot of light pollution in thise days, but still!

This video is such a good explanation that you appreciate the genius of the scientists who study nature and become more aware of our universe. Now if we could have an explanation of quantum entanglement and quantum measurement like this, that would be brilliant. But the finest minds are still pondering what quantum mechanics means.

Excellent video. Subscribed!

Excellent! A fine blend of mathematics and ordinary human language. Well done! I quickly subsccribed.