Cumrun Vafa: String Theory | Lex Fridman Podcast #204

The following is a conversation with Comrade Vafa, a theoretical physicist at Harvard, specializing in string theory. He is the winner of the 2017 Breakthrough Prize in Fundamental Physics, which is the most lucrative academic prize in the world. Quick mention of our sponsors: Headspace, Jordan Harmage's Show, Squarespace, and Allform. Check them out in the description to support this podcast. As a side note, let me say that string theory is a theory of quantum gravity that unifies quantum mechanics and general relativity. It says that quarks, electrons, and all other particles are made up of much tinier strings of vibrating energy. They vibrate in 10 or more dimensions, depending on the flavor of the theory. Different vibrating patterns result in different particles. From its origins, for a long time, string theory was seen as, uh, too good not to be true, but has recently fallen out of favor in the physics community, partly because over the past 40 years it has not been able to make any novel predictions that could then be validated through experiment. Nevertheless, to this day, it remains one of our best candidates for a theory of everything, or a theory that unifies the laws of physics. Let me mention that a similar story happened with neural networks in the field of artificial intelligence, where it fell out of favor after decades of promise and research, but found success again in the past decade as part of the deep learning revolution. So, I think it pays to keep an open mind since we don't know which of the ideas in physics may be brought back decades later and be found to solve the biggest mysteries in theoretical physics. String theory still has that promise. This is the Lex Fridman Podcast, and here's my conversation with Comrade Vafa. What is the difference between mathematics and physics?

Well, that's a difficult question, because in many ways, math and physics are unified in many ways. So, to distinguish them is not an easy task. I would say that perhaps the goals are ma- of math and physics are different. Uh, math does not, uh, care to describe reality, physics does. That's the major difference. But a lot of the thoughts, processes, and so on, which goes to understanding the nature and reality are the same things that mathematicians do. So, in many ways, they are similar. Uh, mathematicians care about, uh, deductive reasoning, and, uh, physicists, or physics in general, we care less about that. Uh, we care more about interconnection of ideas, about how ideas support each other, or if there's a puzzle con- uh, discord between ideas, that's more interesting for us. And part of the reason is that we have learned in physics that the ideas are not sequential, and if you think that there's one idea which is more important and we start with there and go to the next idea and next one and deduce things from that like mathematicians do, we have learned that the, like, the third or fourth thing we deduce from that principle turns out later on to be the actual principle. And, uh, from a different perspective starting from there leads to new ideas which the original one didn't lead to, and that's the beginning of a new revolution in science. So, this kind of thing we have seen again and again in the history of science, we have learned to not like deductive reasoning because that gives us a- a bad starting point to think that we actually have the original thought process should be viewed as the primary thought and all these are deductions, like the way mathematicians sometimes does. So, in physics, we have learned to be skeptical of that way of thinking. We have to be a bit open to the possibility that what we thought is a deduction of a hypothesis actually the reason that's true is- is the opposite, and so we- we reverse the order. And so this- this switching back and forth between ideas makes us more fluid about, uh- uh, deductive fashion. Of course, it sometimes gives a wrong impression, like, "Physicists don't care about rigor, they just, you know, they just say random things, you know, they are willing to-