What is the Ultraviolet Catastrophe?

YouTube must think very highly of me.

This is a superb, highly detailed account of a topic that is usually glossed over. There are far too many videos on youtube that 'pretend' to explain a topic, but ultimately leave you feeling empty because they have explained nothing. This is the first time that I have seen (and understood) a detailed derivation of the ultraviolet catastrophe and Max Planck's route to a solution. Genius. Thank you for taking the time to make this video.

Would have loved to have seen Plancks "Holy Fook!" expression when he first plotted his function and found it matched experiment.

It’s unbelievable that most text books skip over the detailed math behind the ultraviolet catastrophe. For gods sake this is the origin of quantum mechanics. This is similar to Newton’s observation that apple falls, or Einstein’s derivation of consequences caused by the constant speed of light. You can’t just say speed of light is constant, then something is wrong, therefore time slows down when speed is up. The details are extremely important. Because this detail is skipped, I had the feeling that quantum mechanics is dropped out of nowhere for a long time.

Why am I understanding this... where were you when I was in physics class. You are brilliant!

As someone who studied physics, this is by far the most thorough and yet simply explained video on this topic. It was always glossed over in both my modern physics and quantum courses, thus its significance glossed over. Thank you for this!

"Theoretical physicists wanted more" They always do.

The Ultraviolet Catastrophe sounds like a band from the 60s.

I am bowled over by the depth and clarity of the presentation. When I was studying engineering at the Indian Institute of Technology, the instructor spent a half hour on this topic, skipped the Raleigh -Jeans derivation entirely, and went straight to Planck's formulation. I was dissatisfied at that time with the transition but, after decades, have finally found a satisfying exposition. Thanks so much. I am certainly going to subscribe.

This is really wonderful STEM-to-STEM exposition. This is a hard level to hit square in the nuts, and you did it. Well done sir.

This is the third time I very carefully went over this presentation. My compliments and immense gratitude to the author, especially for rigorous derivation and historical content — simply amazing !!!!

My mind blew up and then reformulated itself... you are never to old to confront your long forgoten nightmares and finally see a glimer of light that says all is not lost. I will now go back to the begining, a time I left behind 40 odd or more years ago and perhaps enjoy a stress free journey where not completely understanding is OK but enjoying the trip non the less. Thank you.

I've studied this stuff, but I finally feel I understand it after this video. I've long been confused by mixing up quantisation of energy levels in atoms with Planck's idea. I understood how the Schrodinger equation gave rise to discrete energy levels for bound electrons, and that the difference in energy levels gave rise to the discrete frequencies associated with spectral absorption and emission lines. Having encountered these concepts before Planck's black body function, I'd always assumed that the solution to the ultraviolet catastrophe was something to do with quantisation of frequencies. But there's still an infinite number of frequencies or vibrational modes, even though the frequencies are limited to stationary wave values. I've finally realised that Planck's solution was to quantise the amount of energy in each mode ! With classical waves of a given frequency the amplitude is continuously variable, so the energy is too. I finally get that the energy within any mode for EM waves is not like that. It's split across a discrete number of quanta. Then the energy conservation principle dictates how the energy is statistically distributed across the modes, just like with the Boltzmann distribution for gases in statistical mechanics. Essentially the discrete number of quanta plays the same role as the discrete number of molecules in a gas. (Which probably explains why I've heard the term "photon gas"). Eureka! In turn, I've realised Einstein didn't discover quantisation with his analysis of the photoelectric effect, it was already there in Planck's work. Einstein simply intuited that energy was transferred to electrons in the same discrete quanta.

I thought Youtube was going to give me some historical background noise that I could relax to and learn about. What I got instead was mini PTSD back to my days of getting a B.S. in Math, where I had feelings of "Oh, I think I get it." and "Wait, could you back up and explain that whole thing again?" and also "Wait, how did you get that equation?". It's like hanging onto a pole for dear life while a tornado barely misses you on it's path of destruction, your house is gone and you got a broken leg or two, but you're still alive. Alternatively, it's like getting shitfaced at a club and being sober enough to get home, but there's puke in your pockets and you'll never fully remember what questionable things happened that night. All this writing and similes aside, I enjoyed watching this video despite the migraine, hunger, and the feelings of loss and confusion that ensued afterward. Good shit, buddy.

Many here will probably know that when Planck was deciding whether to seek a PhD in Physics, one of his advisors told him not to do it because, after Maxwell and Boltzmann, everything that could be discovered in Physics already had been. Around the same time, the great telescope builder George Ellery Hale was told that his desire to build bigger and bigger telescopes only resulted in counting more and more stars and we already knew that space was filled with them. So, bigger telescopes were a waste of money.

This was fascinating and an extraordinarily well-done presentation, marred only by some need to pause a few times to allow my dense brain to catch up, to make sure that I truly understood. Haven't been hit by that feeling (the "slow down, you move too fast" feeling) in a while. Thank you.

Absolutely fantastic video, this was the only one I could find that actually explained why the UV catastrophe occurred and how planck's constant solved it. And you derived everything using maths and physics I (mostly) knew, where my physics teacher refused to even go near this topic. Many thanks!

We need another Max Plank to solve the gravity catastrophe and create a new branch of physics

I learned this topics in a physics seminar a few years ago and roughly have an idea of what's going on in this video. My limited mathematics capabilities at the time did not permit me to understand it in full detail. Thanks for the wonderful presentation, allowing me to revisit this topic with greater depth and getting a more comprehensive understanding!

You’re an excellent teacher. If that is your profession outside YouTube, your students are incredibly lucky.