Knowing the one-way speed of light

Holy smokes it's another masterpiece. Light is such a tricky subject to understand.

your videos have repeatedly inspired me to re-engage with scientific learning. you make scientific understanding feel within reach of anyone, not just labs with big grants. also you are precise, but also humble. thanks for publishing your videos.

The overly clever setup of the beam splitters, detectors and the clock reminds me of how designers of perpetual motion machines try to hide the energetic symmetry of their devices behind complex mechanics. The end result is the same: you just can't cheat your way around conservation laws and symmetries.

Nothing but garbage on TV tonight, what a brilliant timing!

This is a great a great video! I want to point out that you missed a simple (yet arguably not obvious) way to make opposing anisotropy locally: make the spring-mass setup MOVE! Or equivalently, make the wave generator move, so that it excites a different mass at each time step. From the resting frame of the wave generator the wave propagation is then opposing anisotropic. You might say that this makes no sense in the setting of the EM field because the field cannot have absolute motion. However, this is exactly the ether interpretation of the EM field (and spacetime itself): opposing anisotropy in the speed of light can be explained by assuming an absolute rest frame (the rest frame of the ether aka the rest frame of the CMB) and anisotropy resulting from motion relative to it.

The best explanation of 0ermittivity and permeability ever, and the analogy with mechanics made so clear the concepts of isotopi and anisotropy of the material... literally wow, You deserve an honorary Professorship

i think people are too afraid of "unsolvable" problems like this. if our current model does not predict any effects from this hypothetical and we do not observe any effects to prove our model wrong in that regard, it truly does not matter what the answer is. its like trying to prove the existence of an unobservable god with science. i appreciate the insight on how a closely related problem is much more approachable

Fascinating! The examination of the asymmetric spring analogy was very intuitive

The moment you said a spring with a different constant on one side than the other, I instantly realized as it vibrated, it would grow in vibration in a single direction and I was like: “Free energy machine!!!” 😂

wow i’m so glad i didn’t click away after the first half lmao first half was amazing (for the viewer that’s not familiar w the conclusion) just excellent motivational context-building but the second half was an amazing next layer deeper of thought experiment / pre-analysis

And this, ladies and gentlemen, is how you explain in a easy way something hard to understand. What a great video!!!

If in a Frame of Reference there is a shift in time as a function of shift in space, then light would effectively travel at different speeds depending on the direction it travels. This is exactly what happens in the equation t’ = gamma(t-vx/cc). In a moving Frame of Reference, time is shifted proportional to distance. It’s the x in the special relativity time dilation equation. Therefore the speed of light is different in the 2 directions depending on the Frame of Reference.

Well done. It's one thing to argue that we cannot measure the speed of light in a single direction (always requiring a reflection), but quite another to assert that the speed of light in one direction could be different from the speed of light in the other. While the E=cp explanation is much simpler, I very much enjoyed the full exploration of the possibilities of anisotropy. Recall that it was Maxwell's equations that eventually led to special relativity, where only the Lorentz transformation could account for a constant speed of light. So if Maxwell's equations are fundamentally true (omitting quantum perturbations), then even if you can postulate the speed of light being different in opposing directions, it's impossible to model it in a self-consistent way.

I thought about this some time and realized that no matter what I try, I always end up with a two-way speed of light in the end. And I had some really crazy ideas that would be practically impossible to do even if we had access to materials that literally have unrealistic properties.

Now I am imagining that little green fempto-pulsed laser blip surfing a gravity wave and I am very happy with that. Thank you for the spring mass analogy. Love when EE concepts match up pretty well to mechanical concepts. Gives more intuition about the more abstract concepts which can be powerful. Love your videos by the way. Optics was one of my favorite courses in college and these videos solidify fundamental teaching while at the same time not shying away from more advanced concepts and topics. At the end of our course, our professor talked some about non-linear optics but treated it as dark magic. Would be awesome to explore some experiments or topics in that realm if your equipment would allow.

Huygens Optics Video: My favourite kind of photons 🤗

Wow! I love hove how concise yet clearly and detailed you describe such complex topics. You are great educator.

once again, what a brilliant video. one way speed of light is such a complex thing to wrap my head around, when I'm thinking about it i always get lightheaded.

I haven't been this excited for a video in a long time

A couple points: 1) the expansion of space has the effect of slowing light in that the frequency is reduced and energy isn’t conserved. 2) the moving mass you mentioned in the end of the video you say we would not be able to detect, we do detect with LIGO. You are describing gravitational waves. I must say, I thoroughly enjoy your videos sir. Thank you and I always look forward to seeing the next! 👍🏻👍🏻