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Why No One Has Measured The Speed Of Light

Veritasium · 24.3M views · 2020-10-31 · 19:05

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Overview

Veritasium explains why the one-way speed of light has never been measured, only the round-trip speed, since measuring it requires synchronized clocks that assume the answer. It explores the implications for relativity.

On Hacker News

Used as the standard reference in threads about light speed, clock synchronization and untestable assumptions in physics.

Recommended by 6 HN people across 7 months · HN mentions 2020–2024

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What people said

jerf · 2023-09 · Strong recommendation

The video in question for reference: [LINK] Interestingly, when I saw that I figured this channel for a goner because he was going to turn to the darkside, but quite contrary to expectations I feel like his channel has actually blossomed since then. His older videos are fine, but often just explaining concepts that you can find a lot of other explanations on, but some of his recent videos have rocked the boat even among physicists and IMHO he was ultimately proved to be correct for them. I particularly point at his videos about how nobody has measured the one-way speed of light ( [VIDEO] ), which was well-known among people very very deep in the field of relativity but not very well known outside of that (even amongst physicists in other fields, let alone lay people) and the electricity videos he's done in the last year ( [LINK] , [LINK] ) which attracted a whole whackload of "debunking" videos, which were themselves wrong (the best "bunking" video, if I may call it that, is probably AlphaPheonix's: [LINK] , since he actually set up the experiment, albeit on a smaller scale). They aren't all of that caliber, but the knot theory video was very good too and not something I've seen a hundred times elsewhere, and the airships video that preceded that one clearly had a high degree of research put into it beyond just the hype.

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travisgriggs · 2021-11 · Strong recommendation

I love Veritasium. Derek has done a number of videos that are awesome like this. The videos are great and educational, but he also manages to subtly weave in an almost spiritual subtext to them as well. For example, in this one, you learn about imaginary numbers in some cool ways, history, how awesome e^ix is, etc, but also this yen-yang balance between embracing not only what is real but taking a chance on what is imaginary. Some of my other favorites: - [LINK] - [LINK] - [LINK] - [LINK] - [VIDEO] I think he’s going to lose the $10,000 bet on the car though.

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aemreunal · 2020-12 · Strong recommendation

Veritasium recently published a video [1] on why the speed of light can't be measured one way, only two ways (i.e. the speed it travels from point A to point B then back to point A). While I'm not privy to all the physics details of it, I found the video very compelling even as a thought experiment. [1]: [VIDEO]

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Sources

Video by Veritasium, played through YouTube.

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