Physics and Philosophy Part One

KEVIN HARRIS: Bill, it has been almost 10 years since your debate with Sean Carroll, and nearly 500,000 people have watched that exchange on YouTube, so it continues to be an influence. He was recently interviewed by Neil deGrasse Tyson, and they were complimentary of you despite their obvious naturalistic disagreements. Let’s look at some excerpts from that interview. But first, perhaps you can once again reflect on that influential debate.

DR. CRAIG: This was a debate on the existence of God and modern cosmology. I prepared extremely hard for this debate. I talked to quite a number of physicists about the arguments that I was going to be offering. I read Sean Carroll's literature carefully to interact with it. I even brought up things in the debate that he wasn't aware of; for example, Aaron Wall's theorem concerning the generalized second law of thermodynamics and the implications for the beginning of the universe, and offered a critique of Carroll's model of the universe that he developed with Jennifer Chen, his graduate student. And he did not respond to that critique in the debate. In the debate, I decided I would defend a very modest contention; namely, that the existence of God is more probable given the evidence of contemporary cosmology than it would have been without it. Now, that's almost a no-brainer. You almost don't need to argue for that; it's so obvious. Just think of 19th century physics before the discovery of the Big Bang and the origin of the universe at a point in the finite past, or the discovery of the fine-tuning of the fundamental constants and quantities of nature. I think clearly God's existence is more probable given the evidence of contemporary cosmology than it would have been without it. But one thing I didn't anticipate in the debate is the degree of authority that is an aura around a professional scientist like Sean Carroll. I'm not impressed with that aura myself because as a philosopher I realize that scientists when they speak on issues of philosophy and theology are really just like laymen; indeed, they are laymen when they speak in those fields. But I think for the average person, scientists are like the high priests in our contemporary culture, and if they say something is true then they don't need to prove it. They don't need to give the evidence or arguments, they just need to assert it and people believe that. I think that Carroll profited in the debate from this aura of authority that attends a natural scientist in our culture.

KEVIN HARRIS: You'll appreciate this first clip as deGrasse Tyson and Carroll give a little history lesson on natural philosophy and philosophy in general. Let's go to the clip.

DR. TYSON: First, natural philosophy – I last saw that term with, you know, 17th, 18th century philosophers. Natural philosophy was the then term for what today we would call physics. There’s political philosophy and religious philosophy. Natural philosophy was physics. So why isn't that just physics, professor?

DR. CARROLL: There's a joke in philosophy circles that once an area of philosophy starts making progress, it gets spun off to a completely different field so it never looks like philosophy actually makes progress. But you're right. Newton, Galileo, those folks would have called themselves philosophers. The idea of a physicist hadn't been invented yet. And we're at a point in physics right now where questions like “What is an observer?”, “What is infinity?”, “Why is the past different from the future?”, “What is emergence?” These are physics questions.

KEVIN HARRIS: They seem to be more appreciative of philosophy than many popular physicists – a few I can think of right off the top of my head. Carroll mentioned several philosophical questions that physicists work on today that you've also worked on.

DR. CRAIG: Yes. Historically, for example, Isaac Newton's masterpiece The Principia Mathematica – the full title was Mathematical Principles of Natural Philosophy. That's what he was doing in doing his physics. Today, science continues to be permeated with profound philosophical questions so that one of the most interesting and vibrant subdisciplines of philosophy is philosophy of science. I have found in particular the nature of space and time to be an especially fascinating philosophical question. But in addition to physics, there are other fields, too, like biology and the cognitive sciences which also raise profound philosophical questions that are explored by philosophers who specialize in those subdisciplines.

KEVIN HARRIS: As you pointed out, Sean Carroll has written on the many-worlds hypothesis, and deGrasse Tyson asked him about it in this next clip.

DR. TYSON: Remind us of the many-worlds hypothesis because I think that's now a hundred years old. Right? We're on the centennial decade of the major discoveries of quantum physics – the 1920s. So if you can just remind us what the many-worlds . . . I think it was once explained to me and I said, “What are you smoking?” I think I’m sure that's what I said. Tell us.

DR. CARROLL: When we teach undergraduates quantum mechanics, we say that a quantum system has two different ways of evolving. There's one way it can evolve when you're not looking at it (and that's what Schrödinger and Heisenberg and their friends figured out back in the day).

DR. TYSON: Just to be clear. Just to be precise. I know how you're using the word “evolve” but to a biologist the word “evolve” means something completely different. You mean it unfolds.

DR. CARROLL: Yeah. It changes. It has its dynamics, whatever it's doing, whatever its behavior is. But then there's a whole another way that we need to describe that behavior when we make a measurement – when we observe the system. Famously in quantum mechanics, you can't predict deterministically precisely with 100% confidence what answer you're going to get. You can predict a probability distribution over different possible answers. So what is going on with this weird thing? You don't expect measurements and observations (looking at things) to be part of the fundamental nature of reality. Right? It never was before quantum mechanics came along. So you can ask yourself what if all of that was unnecessary. This whole idea that we need a separate rule for what happens when we measure something. What if you just erase that from the rules of quantum mechanics? The answer is that what you find is that every possible measurement outcome comes true but in a different world – in a different part of the overall quantum universe. You get parallel worlds where different measurement outcomes are true. If you have an iPhone, you can download an app called Universe Splitter. And if you're ever stuck on what decision to make (“Should I have a hamburger?” “Should I have pizza for dinner tonight?” Or whatever) ask the Universe Splitter and it will come back with an answer, and you can be guaranteed that there's a whole other universe which you can never interact with or talk to in which you do the opposite thing.

DR. TYSON: And it split in that instance? At the decision instance.

DR. CARROLL: In that instance. Yes. It's a physical quantum process.

KEVIN HARRIS: Well, no doubt it's a very complicated hypothesis. Go to town on it.

DR. CRAIG: What they are talking about here is a physical interpretation of quantum physics. The mathematical equations that are the core of quantum mechanics are susceptible to at least nine different physical interpretations, and the many-worlds hypothesis is one such physical interpretation. Nobody knows which, if any, of these physical interpretations is true because they're empirically equivalent. But what the word “evolve” in this context indicates is that there is a sort of dynamic element in quantum physics. That is to say, as quantum measurements are made the universe literally splits into different worlds with different values of the measurement. And as deGrasse Tyson rightly said, you want to know what someone's smoking when they offered this interpretation of the mathematics of quantum mechanics! It is outrageous to think that every time a mouse observes the universe, the universe splits in two. So this is a hypothesis that is not taken all that seriously by contemporary physicists. It also gets the probability distributions wrong for quantum mechanics. But it's important to understand that there's another hypothesis that goes by the same name – the many-worlds hypothesis – and this one is taken more seriously. It is a hypothesis about cosmology or astronomy which says that the universe that we observe is just a tiny part of a much wider collection of universes that make up what's called “the multiverse.” So the many-worlds hypothesis in this respect means that we inhabit just one world in this plenitude of other worlds that go to make up this world ensemble of many universes.

KEVIN HARRIS: It doesn't surprise me a bit that there is an app for that! There's an app for everything. The Universe Splitter – you can actually download and get it on your phone. Neil deGrasse Tyson, by the way his co-host is comedian Chuck Nice. He's very funny and very smart. He reads a question from a listener in this next clip.

CHUCK NICE: My question pertains to Dr. Carroll's research which says that the universe is infinitely old and Big Bang is just one of many events resulting from quantum fluctuations of a vacuum energy in a cold de Sitter space. Please throw some light on what kind of space is this? How can I visualize it better in order to understand it more fully?

DR. CARROLL: Yes. This is all driven by the very famous philosophy question: Why is the past different from the future? Why is there an arrow of time? Because the fundamental laws of physics have no arrow of time in them. The answer is entropy and the second law of thermodynamics. The universe used to be more organized – lower in entropy. The whole history of the universe is just entropy increasing, disorder and chaos developing all around.

CHUCK NICE: We're all gonna die.

DR. CARROLL: It's not your fault necessarily, but you're contributing to the disorder and chaos all around us. And that started about 14 billion years ago near the Big Bang. At the moment of the beginning of the universe, our universe was exquisitely orderly. It doesn't necessarily look that way, but you run through the numbers and it's true. Why? Why is that true? Why was the early universe so orderly? I've long wondered about this, and I wrote a paper years ago now with a woman who was a graduate student of mine at the time, Jennifer Chen, where we proposed that the Big Bang was not the beginning of our universe. Other people propose that in different contexts, but we made the case that you don't need a fine-tuned, special, organized, low-entropy beginning of the universe. The universe can be eternal. It can last forever. But what happens is it empties out, just like our universe is doing. A universe can be completely empty. The future of ours will be. But it still won't be perfectly quiet. There are still quantum fluctuations that can lead to whole new universes coming into existence. And, as that happens, they all start in low-entropy conditions and the entropy grows and gives that little part of the universe an arrow of time. The fun part is the far, far past the same thing happens but in the other direction. So there's sort of a symmetric shape to the universe where the future is a story of more and more universes being created, and the arrow of time pointing in that direction. The past is a story of more and more universes being created with people in them who think that we are in their past.

KEVIN HARRIS: The arrow of time. Entropy. And the Carroll-Chen model comes up in this question.

DR. CRAIG: Yes. Here's one of the philosophical issues on which I differ with Professor Carroll. I do not think that you can answer the question of the arrow of time by appealing to the second law of thermodynamics and entropy increase. The direction of entropy increase is at best evidence of which direction of time is the future, but it doesn't determine which direction is the future. Theoretically, if you have entropy increasing from one direction to the other, the direction of entropy decrease could be called the future and the direction of entropy increase could be called the past. So thermodynamics itself is at best evidence of the directionality of time, but it does not determine it. I think to do that you need to have objective temporal becoming which is of necessity unidirectional. Carroll then asks the question: Why is it that as you recur into the past entropy decreases until you get to this extremely finely tuned low-entropy state at the beginning of the universe? And this is where he mentions the Carroll-Chen model as an attempt to explain this fine-tuning and the origin of the universe. On this model, what he argues is that the universe is sort of like this hourglass. We live in the top half of the hourglass where the direction of time runs from the neck of the hourglass upwards. But he says at some point in our past the arrow of time flips over and runs in the other direction so that people in the lower lobe of the hourglass think of us as being in their past because the direction of time is different. And what I argued in the debate (and he never answered) is that if you think that the direction of time is determined or defined by the second law of thermodynamics and entropy increase then in no sense are the people in that lower lobe in our past. Rather, what you would have would be two universes with a common beginning at the neck of the hourglass – a kind of forked beginning. So you don't avoid the beginning of the universe, and you don't have an eternal past universe. You have two universes with a common beginning point. On the other hand, if you say, well, no, no. You're right, Craig. The direction of time is independent of thermodynamics and entropy increase, and therefore this lower lobe really is in our past. Then the problem is that the model is in flagrant conflict with the second law of thermodynamics because it says that in this lower lobe you have entropy decreasing over indefinite time until you finally get to this neck in the hourglass. And this causes all sorts of physical dislocation. So it turns out that the model is either physically impossible because it contradicts the laws of thermodynamics or else it implies the very beginning of the universe that it sought to avoid.

KEVIN HARRIS: Your debate with Sean comes up in this next question. Let's go to that clip.

CHUCK NICE: This is Doug from Frisco, Texas. Doug says, “I thoroughly enjoyed Sean's debate on God and cosmology against William Lane Craig. Although I'm still trying to get my head around everything Sean explained. One amongst many arguments I found interesting was Sean's rebuttal against Mr. Craig's [teleological] argument that the finely tuned universe was evidence for the existence of God. I don't recall the specifics, but I believe Sean stated that in some models the probability of a finely tuned universe approaches one and then it's . . .” Oh, man, he must have cut and pasted because it drops out. The finely tuning universe approaches . . . Then he says, “Could Sean once again go through the perspective of the fine-tuned argument? I also reject the teleological argument but for more simplistic reasons than my flawed brain can rationalize.”

DR. TYSON: Just for context, William Lane Craig is a proponent of basically a God-created universe. He's not the Bible-thumping person in such a conversation as others might be. He's trying to stay grounded in the natural world, taking you to a precipice where you say, “OK, God must be there.” I'm pretty sure Sean wouldn't debate just anybody on that subject. So William Lane Craig has some debating respectability in that regard. Did I characterize that correctly?

CHUCK NICE: So what you’re saying is: Sean, you're not gonna throw down with Pat Robertson or Jimmy Swaggart?

KEVIN HARRIS: Before Sean addresses the question, let me ask you: What do you think of their characterization of you, Bill? You're not a bible-thumper, but you're grounded in the natural world and respected.

DR. CRAIG: I really appreciated Neil deGrasse Tyson's generous comments in that regard. I have always loved science since I was a boy, and I've made a genuine effort to understand the framework of the worldview of contemporary physics and biology. So I appreciate their remarks that this deserves to be taken seriously and not just laughed off.

KEVIN HARRIS: Their attitude toward Christians may be revealed here as well. Their derision towards the late Pat Robertson and Jimmy Swaggart. It's pretty evident. But those men are not scientists or philosophers. Your thoughts?

DR. CRAIG: I've said in the past – and I repeat – that I think it is a tremendous embarrassment that somewhere around 50% of Christian pastors in this country believe that the universe was created just a few thousand years ago. I do not think that they understand or realize the discredit that they are bringing upon the Christian faith by advocating such a preposterous position and the obstacle to evangelism that they are erecting and putting in the path of people who want to come to Christ.

KEVIN HARRIS: By the way, Chuck was, I think, trying to say “teleological” argument. He may have mispronounced that.

DR. CRAIG: Either he or it might have been the questioner. I didn't get the impression that the questioner was the sharpest knife in the drawer by some of the things that he said.

KEVIN HARRIS: Could have been either one.

DR. CRAIG: I think that this Chuck Nice actually shows himself to be a rather bright fellow with some real insights in this interview.

KEVIN HARRIS: OK, we are out of time so let’s stop right there. But we are going to pick it up on the next podcast and continue this discussion with Dr. Craig. Reasonable Faith with Dr. William Lane Craig.^[1]