Updated: Oct 8
Author: Arpan Dey
Leonard Mlodinow  is a physicist, science popularizer and best-selling author. He is the author of the books "The Grand Design"  and "A Briefer History Of Time" , both with Stephen Hawking. He has also written numerous other popular science books, including "The Drunkard's Walk: How Randomness Rules Our Lives" . I have read quite a few books written by him, and I highly recommend reading them (especially the three books mentioned above). In this article, I interview this great physicist, mainly about some big questions of physics. Also, I would like to thank some of my classmates in college for putting forward their questions.
1. It’s true that the Big Bang theory comfortably fits all known experimental data. And the (modern) Big Bang theory is the result of the extrapolation of the predictions of quantum mechanics and general relativity back in time. However, quantum mechanics is incompatible with general relativity at such small scales, and we don’t really know what happens down at a singularity. Considering all of this, how probable is it that one day the Big Bang theory will be proved entirely incorrect?
The original Big Bang theory is a purely classical, that is, non-quantum, theory, based on general relativity. It has been amended to take into account the effects of quantum mechanics and the modern picture is more of what is called "inflation" than the original Big Bang idea. There is a lot of data backing up the inflation theory, but we don’t really understand the details so our understanding certainly may change in the future. But the basics of what we think happened are probably correct.
Recent measurements of the red-shifts of certain supernovas have revealed that the universe has been accelerating for the last 5-6 billion years. Matter has attractive gravitational properties and should, thus, slow down the expansion. A form of matter that would exhibit repulsive gravitational property is needed to accelerate the universe. This is called dark energy. Einstein’s cosmological constant, which he agreed to be the "biggest blunder" in his life and which he added to his theory to "keep the universe static," actually exhibits the properties that are required here. Alan Guth proposed that the universe went through a period of sudden, rapid expansion during the early phase (inflation). This idea is an appealing one since it solves a lot of problems in cosmology. It explains why the universe is homogeneous in all directions. It also explains the flatness problem (why the universe is flat): when a curved surface expands exponentially, it would appear flat. However, there is one common misconception about the inflation theory. It need not be true that inflation happened shortly after the Big Bang. Rather, inflation caused the "bang" in the Big Bang. It is expected that inflation will eventually end in a Big Bang, and so the Big Bang that started off our universe might not have been the beginning, but just the end of inflation in a certain region of space. So anyway, in the end, I think we can safely say that we don't have enough evidence to claim that the basic ideas of the Big Bang theory and/or inflation theory are incorrect. And slight deviations in experimental data can probably be explained by slight tweaks in the theory; the entire theory need not be wrong. But we don't know anything for sure.
2. Do you think we are ever going to find a unified theory of the universe? Will we ever discover the grand design? If yes, would we be able to answer all possible questions about physics (like questions regarding dark energy, the origin of the universe or the nature of quantum mechanics)?
I don’t have an opinion, one way or the other, regarding a unified theory of the universe. It would be nice, but that doesn’t mean it exists. If we did have one, it would in principle be possible to answer all questions, but probably far from practical. Even today we cannot solve the equations of most of our theories, and must resort to approximations and guesses. So calculating, for example, anything about our lives, starting from the first principles of physics, would almost certainly not be possible.
I completely agree that calculating anything about our lives (or that sort of thing) from the first principle of physics would always be impossible, in practice. And as for a theory of everything, well, there may exist no such theory. Maybe there is a limit to our understanding, and some questions will simply remain unanswerable.
3. Do you believe physics should be an empirical science, and the mathematically-elegant theories of quantum gravity (like string theory) which we have today, and which lack experimental support, should be discarded? Or are these theories promising, and it’s too early to expect experimental support because we understand so little about these theories? What is your take on the ultimate goal of science, especially physics?
A theory must make testable predictions and have experimental support to be of any use in science. String theory was promising, but it has been around for several decades now with no real progress with regard to making it testable. So it’s an interesting mathematical exercise and yields some interesting mathematical results that have applications, perhaps in physics, but so far it does not qualify as a theory of the universe.
It's true that string theory has spurred advancements in theoretical mathematics. It has also been of some use to physicists. But as I have stressed again and again in my writings, it probably does not qualify as a scientific theory, mainly due to lack of experimental support. However, the only thing I would like to say is that we can't completely rule out the possibility that it's actually too early to expect experimental support, since we understand so little about string theory. All I am saying, we shouldn't give up on string theory yet. It might be a wild goose chase, but I think there will be a lot of revelations along the way, and it's totally worth it.
4. Do you feel that the universe, deep down, should be completely deterministic and predictable (at least in theory), and that the apparent randomness and chaos has some underlying order which we are yet to fully understand (or which we will probably never understand)?
Yes, I believe that the universe is deterministic, but not in the sense you might think. It is deterministic in the sense that the quantum wave function at any given time can be calculated from the wave function at any other time. And it is from the wave function that we extract all our predictions.
This is a very deep question. First, quantum mechanics doesn't say that the universe can't be deterministic. Certain interpretations of quantum mechanics, like the many-worlds interpretation, are completely deterministic. And in some sense, the universe is deterministic if we can calculate the wave function at any given time from the wave function at any other time. Now whether the measurement of the wave function will give us a definite, particular value or a set of values with different probabilities of occurrence is something that we don't know.
5. Is it probable that a complex system can be fully understood, at least in theory, by studying the simple parts of which it is made? Do we need to formulate an entirely new set of laws that apply to complex systems, or do the same laws apply at all scales?
In principle the same laws apply at all scales, but those laws can look very different at different scales. So it’s not always apparent that the same laws are working. For example, quantum mechanics describes the microworld, and Newtonian mechanics describes the macro world. But you can derive Newtonian mechanics from quantum mechanics, because the macro world is made of many microworlds.
This is probably the best possible answer to the question I've asked. Recently in my college, I attended a talk on pattern formation in Nature, and I learned that similar patterns form at the atomic level and also at much bigger scales, and the same laws are applicable at all scales. However, you must not lure yourself into thinking that if we know the laws that apply at, say, the atomic scale, we can explain systems of much bigger dimensions.
6. How do you define consciousness? What is the difference between sentience and consciousness; can one occur without the other? Can all living beings be considered conscious? If not, how much do we currently know about when and how consciousness evolved in living beings?
I do not know of an adequate scientific definition for consciousness.
I appreciate the honesty in this answer. None of us know what consciousness is. I simply consider consciousness to be that emergent property (of the physical matter of the brain) by virtue of which we have a sense of awareness. Sentience and consciousness, according to me, are the same thing. And all living beings are, to a certain degree, conscious. Of course, the level of complexity is different in different creatures. I don't want to go into discussions of whether it is possible to artificially simulate consciousness and all that. There are a lot of good questions that can be asked here, but let's keep it for another day.
7. Do you agree with the claim that every feeling, every conscious experience can, in theory, be generated by manipulating the levels of different chemicals in the brain? In other words, consciousness is emergent from the arrangement of and interaction between the physical matter that makes up the brain?
Yes, I believe that all our experiences can be derived from the laws of Nature. I do not believe our brains are outside of the laws of Nature.
Thank you for agreeing with me. I think the same. Consciousness is emergent and not fundamental. There's no feeling, no conscious experience, that can't be generated, at least in theory, by manipulating the levels of different chemicals in the brain. It's all happening inside the brain. Of course, the brain is affected by a lot of factors (environmental, genetic etc.). But the point is, all these factors change the physical structure of the brain in some subtle way. It's not always possible to pin down these subtle changes, and often it is not a single change. So when I say there's no feeling that can't be generated by manipulating the levels of different chemicals in the brain, I don't mean to say that we can easily recreate all feelings artificially. All I'm saying is, it's possible in theory.
8. This last question might not be a scientific question, but I would still like to hear your thoughts. Do we have free will?
I do not believe that we have free will. I don’t even think it is possible to satisfactorily form that question. In any case everything we do, or think, is determined by the state of the physical system of our brains and so there is no room for us to change our behavior in a way that violates the physical laws that govern it.
This is reasonable. Neuroscientist David Eagleman says the same thing in his book "Incognito" . And although I have argued that free will might be an "emergent property" of the human brain, now it seems to me this need not be true. I don't have a satisfactory answer to the question of free will (no one does). However, right now I would probably lean more toward the claim that free will does not exist.
 Leonard Mlodinow. Wikipedia. https://en.wikipedia.org/wiki/Leonard_Mlodinow
 The Grand Design. Stephen Hawking and Leonard Mlodinow. Bantam Books. https://www.amazon.com/Grand-Design-Stephen-Hawking/dp/055338466X/
 A Briefer History Of Science. Stephen Hawking and Leonard Mlodinow. Bantam Books. https://www.amazon.com/Briefer-History-Time-Science-Accessible/dp/0553385461/
 The Drunkard's Walk: How Randomness Rules Our Lives. Leonard Mlodinow. https://www.amazon.com/Drunkards-Walk-Randomness-Rules-Lives/dp/0307275175/
 Incognito: The Secret Lives Of The Brain. David Eagleman. https://www.amazon.com/Incognito-Secret-Lives-David-Eagleman/dp/0307389928/