- What is real? Let's start with an easy question. Put another way, how do we know what is real and what is merely a creation of our human perception and imagination? - We don't know. We don't know. This is science. I presume we're talking about science. And we believe, or I believe, that there is a world that is independent of my existence and my experience about it and my knowledge of it.

And this I call the real world. - So you said science, but even bigger than science. - Sure, sure. I need not have said this is science. I just was warming up. - Warming up. Okay, now that we're warmed up, let's take a brief step outside of science. Is it completely a crazy idea to you that everything that exists is merely a creation of our mind?

So there's a few, not many, this is outside of science now, people who believe perception is fundamentally what's in our human perception, the visual cortex and so on, the cognitive constructs that's being formed there is the reality, and that anything outside is something that we can never really grasp.

Is that a crazy idea to you? - There's a version of that that is not crazy at all. What we experience is constructed by our brains and by our brains in an active mode. So we don't see the raw world, we see a very processed world. We feel something that's very processed through our brains, and our brains are incredible.

But I still believe that behind that experience, that mirror, veil, or whatever you wanna call it, there is a real world, and I'm curious about it. - Can we truly, how do we get a sense of that real world? Is it through the tools of physics, from theory to the experiments?

Or can we actually grasp it in some intuitive way that's more connected to our ape ancestors? Or is it still fundamentally the tools of math and physics that really allow us to grasp it? - Well, let's talk about what tools they are, what you say are the tools of math and physics.

I mean, I think we're in the same position as our ancestors in the caves, or before the caves, or whatever. We find ourselves in this world, and we're curious. We also, it's important to be able to explain what happens when there are fires, when there are not fires, what animals and plants are good to eat, and all that stuff.

But we're also just curious. We look up in the sky, and we see the sun, and the moon, and the stars, and we see some of those move, and we're very curious about that. I think we're just naturally curious. So, we make, this is my version of how we work.

We make up stories and explanations. And there are two things which I think are just true of being human. We make judgments fast, because we have to. We're, to survive, is that a tiger, or is that not a tiger? And we go. - Act. - We have to act fast on incomplete information.

So, we judge quickly, and we're often wrong, or at least sometimes wrong, which is all I need for this. We're often wrong. So, we fool ourselves, and we fool other people, readily. And so, there's lots of stories that get told, and some of them result in a concrete benefit, and some of them don't.

- So, you said we're often wrong, but what does it mean to be right? - Right, that's an excellent question. To be right, well, since I believe that there is a real world, I believe that to be, you can challenge me on this if you're not a realist. A realist is somebody who believes in this real, objective world, which is independent of our perception.

If I'm a realist, I think that to be right is to come closer. I think, first of all, there's a relative scale. There's not right and wrong. There's right or more right and less right. And you're more right if you come closer to an exact, true description of that real world.

Now, can we know that for sure? No. - And the scientific method is ultimately what allows us to get a sense of how close we're getting to that real world? - No on two counts. First of all, I don't believe there's a scientific method. I was very influenced when I was in graduate school by the writings of Paul Feyerabend, who was an important philosopher of science, who argued that there isn't a scientific method.

- There is or there isn't? - There is not. - There's not. Can you elaborate? I'm sorry if you were going to, but can you elaborate on the, what does it mean for there not to be a scientific method, this notion that I think a lot of people believe in?

In this day and age? - Sure. Paul Feyerabend, he was a student of Popper, who taught Karl Popper. And Feyerabend argued, both by logic and by historical example, that you name anything that should be part of the practice of science, say you should always make sure that your theories agree with all the data that's already been taken.

And he'll prove to you that there have to be times when science contradicts, when some scientist contradicts that advice for science to progress overall. So it's not a simple matter. I think that, I think of science as a community. - Of people. - Of people, and as a community of people bound by certain ethical precepts, percepts, whatever that is.

- So in that community, a set of ideas they operate under, meaning ethically, of kind of the rules of the game they operate under. - Don't lie, report all your results, whether they agree or don't agree with your hypothesis. Check, the training of a scientist mostly consists of methods of checking, because again, we make lots of mistakes, we're very error prone, but there are tools both on the mathematics side and the experimental side to check and double check and triple check.

And a scientist goes through a training, and I think this is part of it. You can't just walk off the street and say, "Yo, I'm a scientist." You have to go through the training, and the training, the test that lets you be done with the training is can you form a convincing case for something that your colleagues will not be able to shout down, because they'll ask, "Did you check this, "and did you check that, and did you check this, "and what about a seeming contradiction with this?" And you've gotta have answers to all those things or you don't get taken seriously.

And when you get to the point where you can produce that kind of defense and argument, then they give you a PhD. And you're kind of licensed. You're still gonna be questioned, and you still may propose or publish mistakes, but the community is gonna have to waste less time fixing your mistakes.

- Yes, but if you can maybe linger on it a little longer, what's the gap between the thing that that community does and the ideal of the scientific method? The scientific method is you should be able to repeat an experiment. There's a lot of elements to what construes the scientific method, but the final result, the hope of it is that you should be able to say with some confidence that a particular thing is close to the truth.

- Right, but there's not a simple relationship between experiment and hypothesis or theory. For example, Galileo did this experiment of dropping a ball from the top of a tower, and it falls right at the base of the tower. And Aristotelian would say, "Wow, of course it falls "right to the base of the tower.

"That shows that the Earth isn't moving "while the ball is falling." And Galileo says no weight is a principle of inertia and it has an inertia in a direction with the Earth isn't moving and the tower and the ball and the Earth all move together. When the principle of inertia tells you it hits the bottom, it does look, therefore my principle of inertia is right.

And Aristotelian says no, Aristotle's science is right, the Earth is stationary. And so you've got to get an interconnected bunch of cases and work hard to line up and explain. It took centuries to make the transition from Aristotelian physics to the new physics. It wasn't done till Newton in 1680-something, 1687.

- So what do you think is the nature of the process that seems to lead to progress? If we at least look at the long arc of science of all the community of scientists, they seem to do a better job of coming up with ideas that engineers can then take on and build rockets with or build computers with or build cool stuff with.

- I don't know, a better job than what? - Than this previous century. So century by century, we'll talk about string theory and so on and kind of possible, what you might think of as dead ends and so on. - Which is not the way I think of string theory.

We'll straighten it out. We'll get on string straight. But there is, nevertheless, in science, very often at least temporary dead ends. But if you look through centuries, the century before Newton and the century after Newton, it seems like a lot of ideas came closer to the truth that then could be usable by our civilization to build the iPhone, right?

To build cool things that improve our quality of life. That's the progress I'm kind of referring to. - Let me, can I say that more precisely? - Yes. (laughing) It's a low bar. - 'Cause I think it's important to get the time places right. - Yes. - There was a scientific revolution that partly succeeded between about 1900 or late 1890s and into the 1930s, 1940s, and maybe some, if you stretched it, into the 1970s.

And the technology, this was the discovery of relativity, and that included a lot of developments of electromagnetism. The confirmation, which wasn't really well confirmed into the 20th century, that matter was made of atoms. And the whole picture of nuclei with electrons going around, and this is early 20th century.

And then quantum mechanics was from 1905, took a long time to develop, to the late 1920s, and then it was basically in final form. And the basis of this partial revolution, and we can come back to why it's only a partial revolution, is the basis of the technologies you mentioned.

All of, I mean, electrical technology was being developed slowly with this, and in fact, there's a close relation between the development of electricity and the electrification of cities in the United States and Europe and so forth, and the development of the science. The fundamental physics, since the early 1970s, doesn't have a story like that so far.

There's not a series of triumphs and progresses, and there's not any practical application. - So, just to linger briefly on the early 20th century and the revolutions in science that happened there, what was the method by which the scientific community kept each other in check about when you get something right, when you get something wrong?

Is experimental validation ultimately the final test? - It's absolutely necessary, and the key things were all validated, the key predictions of quantum mechanics and of the theory of electricity and magnetism. - So, before we talk about Einstein, your new book before string theory, quantum mechanics, so on, let's take a step back at a higher level question.

What is, that you mentioned, what is realism? What is anti-realism? And maybe why do you find realism, as you mentioned, so compelling? - Realism is the belief in an external world independent of our existence, our perception, our belief, our knowledge. A realist, as a physicist, is somebody who believes that there should be possible some completely objective description of each and every process at the fundamental level, which describes and explains exactly what happens and why it happens.

- That kind of implies that that system, in a realist view, is deterministic, meaning there's no fuzzy magic going on that you can never get to the bottom of. You can get to the bottom of anything and perfectly describe it. - Some people would say that I'm not that interested in determinism, but I could live with the fundamental world, which had some chance in it.

- So do you, you said you could live with it, but do you think God plays dice in our universe? - I think it's probably much worse than that. - In which direction? - I think that theories can change and theories can change without warning. I think the future is open.

- You mean the fundamental laws of physics can change? - Yeah. - Okay, we'll get there. I thought we would be able to find some solid ground, but apparently-- - Well, the ground is pretty solid. - The entirety of it, temporarily so. Okay, so realism is the idea that while the ground is solid, you can describe it.

What's the role of the human being, our beautiful, complex human mind in realism? Do we have a, are we just another set of molecules connected together in a clever way, or does the observer, our human mind, consciousness have a role in this realism view of the physical universe? - There's two ways, there's two questions you could be asking.

Does our conscious mind, do our perceptions play a role in making things become, in making things real or things becoming? That's question one. Question two is, does this, we can call it a naturalist view of the world that is based on realism, allow a place to understand the existence of and the nature of perceptions and consciousness in mind?

And that's question two. Question two, I do think a lot about, and my answer, which is not an answer, is I hope so, but it certainly doesn't yet. - So what kind-- - Question one, I don't think so. But of course, the answer to question one depends on question two.

- Right. So I'm not up to question one, yeah. - So question two is the thing that you can kind of struggle with at this time. What about the anti-realists? So what flavor, what are the different camps of anti-realists that you've talked about? I think it would be nice if you could articulate for the people for whom there is not a very concrete real world, or there's divisions, or it's messier than the realist view of the universe.

What are the different camps, what are the different views? - I'm not sure I'm a good scholar and can talk about the different camps and analyze it, but many of the inventors of quantum physics were not realists, were anti-realists. And there are scholars, they lived in a very perilous time between the two world wars.

And there were a lot of trends in culture which were going that way. But in any case, they said things like the purpose of science is not to give an objective realist description of nature as it would be in our absence. This might be saying Niels Bohr. The purpose of science is as an extension of our conversations with each other to describe our interactions with nature.

And we're free to invent and use terms like particle, or wave, or causality, or time, or space if they're useful to us and they carry some intuitive implication. But we shouldn't believe that they actually have to do with what nature would be like in our absence, which we have nothing to say about.

- Do you find any aspect of that, 'cause you kind of said that we human beings tell stories. Do you find aspects of that kind of anti-realist view of Niels Bohr compelling? That we're fundamentally our storytellers and then we create tools of space and time and causality and whatever this fun quantum mechanics stuff is to help us tell the story of our world.

- Sure, I just would like to believe that there's an aspiration for the other thing. - The other thing being what? - The realist point of view. - Do you hope that the stories will eventually lead us to discovering the real world as it is? - Yeah. - Is perfection possible, by the way?

- No. You mean will we ever get there and know that we're there? - Yeah, exactly. - That's for people 5,000 years in the future. We're certainly nowhere near there yet. - Do you think reality that exists outside of our mind, do you think there's a limit to our cognitive abilities, as again descendants of apes, who are just biological systems?

Is there a limit to our mind's capability to actually understand reality? There comes a point, even with the help of the tools of physics, that we just cannot grasp some fundamental aspects of that reality. - Again, I think that's a question for 5,000 years in the future. - We're not even close to that limit.

- I think there is a universality. Here, I don't agree with David Deutsch about everything, but I admire the way he put things in his last book. And he talked about the role of explanation. And he talked about the universality of certain languages, or the universality of mathematics, or of computing, and so forth.

And he believed that universality, which is something real, which is somehow comes out of the fact that a symbolic system, or a mathematical system, can refer to itself, and can, I forget what that's called, can reference back to itself. And build, in which he argued for a universality of possibility for our understanding, whatever is out there.

But I admire that argument. But it seems to me we're doing okay so far, but we'll have to see. - Whether there is a limit or not. For now, we've got plenty to play with. - Yeah. (audience applauding) (audience cheering) (audience cheering) (audience cheering) (audience cheering)