Tim Maudlin: Quantum Mechanics Explained FROM SCRATCH

**SPEAKER_1** (0:00)
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**Tim Maudlin** (0:30)
But notice the deep problems were about spooky action at a distance, not particularly about determinism. I'm really going to try to do this once properly from beginning to end. What's going on with EPR? What's going on with Bell?

**Curt Jaimungal** (0:46)
This is Tim Maudlin, Professor of Philosophy at New York University, and one of the world's leading philosophers of physics. Today, I'm thrilled to bring you a lecture with the breathing room it requires. To explain quantum physics and what Bell did with zero background knowledge.

**Tim Maudlin** (1:01)
I've been told I have an unlimited amount of time.

**Curt Jaimungal** (1:05)
On this channel, I, Curt Jaimungal, interview researchers regarding their theories of reality with rigor and technical depth.

**Tim Maudlin** (1:11)
Unfortunately, most people haven't understood the EPR paper.

**Curt Jaimungal** (1:15)
This is to set the record straight once and for all on what?

**Tim Maudlin** (1:19)
The great ironic reversal at the end is that Bell undermines Einstein's fundamental thesis. That there's no action at a distance, but he undermines it using Einstein's own tools.

**Curt Jaimungal** (1:34)
Professor, welcome. I'm super excited. Thank you for coming.

**Tim Maudlin** (1:38)
I'm very glad to be here.

**Curt Jaimungal** (1:40)
So this title, as far as I can see, EPR Bell, the completeness of the wave function, spooky action at a distance and all that. That's the title of this. Take it away. The title of the YouTube video may be something that can fit into the character counts of the YouTube video. I went to all that trouble.

**Tim Maudlin** (1:56)
Okay. So let me explain to anybody watching this what this is. It's not a normal back and forth conversation designed that way. It was supposed to be a real careful presentation, a century of Bell's theorem, and then a little bit on the problems that arise because of Bell's theorem. And in preparing for this, I thought, all right, I have a kind of, I've been told I have an unlimited amount of time, which is unlike what I normally have. Usually you have to squeeze it down. And I thought, all right, if I really do have a lot of time, I'm really going to try to do this once properly from beginning to end. What's going on with EPR? What's going on with Bell? What Einstein was thinking? What Bell was thinking? Other things had happened in the meantime. The logic of Bell's argument and the conclusions of it. So that's what this is all about.
I should say that because I want this to be absolutely clear, I've essentially written everything out. Perfect. And it's going to be a little boring because I'm going to be more or less reading what's on the screen unless I riff on something or if Curt has something he wants to interrupt me about and ask me about, which is fine. But don't be surprised if that's what's going on. Okay. So should we begin? Please. Okay. So this comes in various acts, historical acts. I think there'll be some history here that almost nobody listening to this is aware of. Historians of physics are aware of it, but it's not usually talked about. So we're going to start in 1905
The Honest Mirabilis, when Einstein proved that there were atoms and developed the Special Theory of Relativity and proved E equals MC squared. And on top of that, really began quantum theory with his paper on the photoelectric effect. So let's just begin there. So although Planck is usually credited with being the originator of quantum theory because of work he did on thermal radiation in black body radiation in 1900, I think it's really not fair to say that Planck began what became what we now think of as quantum theory. Why? He was doing some statistical calculations in a normal way for a classical physicist doing statistical calculations. He knew what he was trying to get. He was trying to get a certain spectrum of radiation for black body radiation. He found that he could get the right answer out if instead of taking a limit, going to zero, which is what you'd normally do, he stopped at a certain point. And so he stopped. And that point had little finite regions of phase space which were characterized by this Planck constant H. He knew that gave him the result he wanted. It's not clear that he thought that what he was doing was quantizing anything. It's not clear that he had any real physical hypothesis about what he was doing. He just noticed that it worked. So when you really ask who really proposed quantization of a classical quantity, it's Einstein in 1905 Now what was Einstein worried about? He wasn't worried about black body radiation. He was worried about the photoelectric effect. And the photoelectric effect was a known property of certain metals that when light fell on a metal, it created a current, an electrical current. And it was known how that current was related to the light. And it's a very surprising way that it's related to the light. I mean, it's not surprising from a classical perspective that light on a metal might start a current. It's obviously delivering energy to the metal. And you need to deliver energy to the metal intuitively to knock electrons free and get a current going. But the way that that energy translated into current was very surprising. So let's go through the surprise. Classically, you think of light as an electromagnetic wave. And it's characterized by a frequency and an amplitude. The frequency tells you essentially what the color of the light is. And the amplitude tells you what the brightness of the light is. And classically, when you attribute energy to an electromagnetic wave, it depends on both the frequency and on the amplitude. So you can increase the energy by increasing the frequency, and you can increase the energy by increasing the amplitude by making it brighter. So you would think that if light falling on a metal is creating the current, you could increase the current either by changing the frequency and making it higher or by changing the amplitude and making it brighter. But it actually turns out it doesn't work like that.