Why the Speed of Light is the Ultimate Speed Limit | The Physics of the Universe

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How can the speed of light be the same for everyone, regardless of their state of motion? First, investigate how the speed of light is determined. Next, consider the hypothesized medium for light propagation—the aether—which was dealt a fatal blow by the Michelson-Morley experiment in the 1880s. Finally, examine laboratory proof that the speed of light is constant for all observers.

This video is lecture six from the series "The Evidence for Modern Physics: How We Know What We Know"

00:00 How Do We Measure the Speed of Light?
06:27 Proving the Speed of Light is Uniform for All Observers
11:11 Maxwell's Equations and Electromagnetism
12:52 The Michelson—Morley Experiment
19:15 Particle Accelerator Offers Further Proof for Speed of Light
23:41 Is the Speed of Light the Same for All Wavelengths?

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[robertgoss]

I have grown to greatly value your programs. You presentation style and timing are very accessible and in fact, make your lessons a pleasure to watch. Thanks for your hard work, and for making some often knotty subject matter so much more comprehensible.

[willsingourd]

Thank you for this quite excellent vid on the "C" constant along with its bonus, strong History of Science flavor! My subscription was instant, if not as fast...

[popkorn]

Technically, he didn't really answer the question of WHY the speed of light is the limit. I was hoping to see the reasonning of Einstein when he came to that conclusion. Great video though!

[joemug]

This was that totally captivating and interesting. Even though I couldn’t grasp all of it. But I do understand it.

[WooliteMammoth]

Great video...but doesn't answer the question in the title of why the speed of light is the limit. Perhaps change the title?

[aethrya]

Man, I just love Don Lincoln. Fermilab has been a great source of knowledge on physics for me and I have always enjoyed his intellect and dry sense of humor that occasionally comes out.

[hassegreiner]

The major difference between the baseball thrower and lightemission is, that while the speeds of the thrower adds to the speed of the ball, light is just set free to travel at the speed it chooses given the medium - it cannot be affected (bothered) by the speed of its source.

[titleloanman]

Though I don’t implicitly doubt the conclusion of the final experiment, I’m having trouble understanding why it proves that the photon is moving at the speed of light with respect to the electron. It only seems to prove that it moves at the speed of light respective to the stationary detector, irrespective of the speed of the emitter. I don’t see how that experiment is demonstrating the perspective of the emitting electron at all.

[barryzeeberg]

"Why the Speed of Light is the Speed Limit" - but the video showed what the speed of light is, and how it is measured, but not why it is what it is, and not why it is the speed limit.

[CharlesDeMar]

This guy is a good teacher. Altho beyond the scope, my understanding is that measuring the speed of light in one direction is not achievable. It’s measured by round trip b/c of a problem with keeping two separate clocks perfectly synchronized.

[koantao]

I wish I had you as my physics teacher. I had a D in physics, yet I was fascinated by it and still am.

[bloodyorphan]

Loved this Thankyou.

A couple of things, all the standard model particles that "Occlude" need to be the same size (12 Planque ish).

The superposed nature of photon weight versus frequency...
The "Particle" and the QM field wave are always "there" it's the spacial collapse and expansion for the raw weight that is frequency.
So does the entire "magnetic" aperture of the photon disappear and reappear (Polarity question) ?

Lensing is likely another double aperture addition, but if symmetrical flow energy is the vector driver, the "longest" distortion and therefore the lowest pressure is on the wrong side, but the planet side compression is 12 Planque higher than the outside so back to a kissing hawking reaction over time spinning the lowest flow density aperture length to the outside, resetting after frequency cycle completion ? 😁

Love your work DrDon.
Thank you again
Bernhard

[ballsrgrossnugly]

I like the video, it touches on some bigger concepts for anyone coming to physics for the first time.
One thing I noticed, you mentioned that the dark patches on the double slit experiment are the peaks and troughs lining up, but wouldn't they be the double troughs? The grey sections in between would be any combination of peak/trough strength that isn't both 1 or both 0, including a peak/trough line up right on the 50% brightness line.

[NalitaQubit]

Thank you for a your simple way of explaining complex phenomena!

[ttamdude]

Was this done in a single take? My goodness… this is great.

[ERPRocks]

The title is misleading. This video does not say why the speed of light is the speed limit, only that we observe the speed of light to be the same everywhere.

[darkososyt]

Thanks for the video, some good explanations, and there is a lot of them out there. I'm seeing this line of reasoning over and over again, and every time I'm left puzzled. It seems to me we have two different things here.

First, since we don't really have a medium for light, i.e.the very space itself is the medium, and if we suppose it's fixed (although GTR says it's not, but lets leave that aside here), then it's no surprise that it can't be pushed by anything. Because it's not really pushed (or thrown or whatever), it is more generated. That very fact is enough for us to say that the photon could not travel faster than the speed at which the space itself could spread the electromagnetic disturbance (that is very similar to Maxwell's derivation from two different permeabilities). So that part is pretty obvious.

The second part is what puzzles me, and that is hidden inside the following sentence: "..the electron sees photon traveling at the speed of light...". First of all, how we know this? I'd say that is not something that could be deduced from any of these experiments. I know it's one of the conjectures, but could you please say what exactly proves that part? And I think it is crucial. As I see this, that part is what makes the (Einsteinian) relativity so "weird" - it gives rise to time and length dilatation, effectively the usage of Lorentz's transformations.

[sParadox]

Thanks for taking 30 min's of my life to hear all I could 10 years ago.

[maurjoy]

You've convinced me. Though there are caverns in my understanding. But you are a superb narrator.

[antifajesus]

You're a really good presenter and the camera work is getting better thanks for posting