In today's blog we talk to Dr. Avshalom Elitzur, PhD from Tel Aviv University, and founder of the Israeli Institute for Advanced Research
David: What have you learned by studying the quantum world that should be passed on to the next generation?
Avshalom: Good. First of all, let's say something about quantum mechanics. I guess your audience is pretty learned and erudite about physics. But just let us remind ourselves what is quantum mechanics. We've been accustomed to the reductionist approach. Every time that you want to understand something, break it to its smallest parts. Then you're going to see simpler and simpler laws more and more basic. And then you build the more complex phenomena on them. This is how it works in chemistry, biology, and so on. Another thing is that the laws that you find when you go to the most elementary level are most precise. You have no friction. You have no all kinds of artifacts, so they are becoming more precise, and on them you can build your understanding of our everyday world, which is less precise. It worked beautifully until quantum mechanics came, and then we saw something which was extremely frustrating. Things are not precise like in classical physics. When you know the initial conditions of any event, and you use the right equations of motion, then you can predict what is going to be the state at every moment later, and so on. Even in relativity, which was extremely revolutionary. It is still classical in this respect. Not so in quantum mechanics. Quantum mechanics tells you that if you did not measure a particle, then some of its values are uncertain. Uncertain, not in the sense that you don't know where it is, or what is its momentum, or what is its spin. The particle itself doesn't know. In other words, it is in a superposition. So once again, when I throw a dice, and I don't know whether it's heads or tails, It's kind of superposed only in my ignorance. But in the quantum world it is indeed both heads and tails. You can prove that when you do an experiment with interference, and so on. That's extremely frustrating. And it comes within the uncertainty principle which says that if you don't like this uncertainty, then you can make a measurement, but then uncertainty will increase in a conjugate variable. So now you know precisely where is the particle. But its momentum becomes uncertain, and it has different velocities, or even opposite ones. It opened for us new ways of understanding nature in all kinds of respects.
Thanks to quantum mechanics, we understand chemistry. We didn't understand why the electrons orbit around the nucleus without falling into it. Why you have these shells, special shells with these numbers of electrons, and so on. So quantum mechanics solved this mystery and many other mysteries. It gave us wonderful technology every time that we use transistors, imaging and so on. We are using quantum mechanics now. Again, however, there are great riddles about which we are still in the dark. While quantum mechanics has solved many riddles, it presented us with paradoxes still unresolved. Quantum mechanics tells us that we know very little about the universe. We are only at the very beginning. We don't know what to expect. There are amazing discoveries waiting for us.
And now something personal. I believe that I belong to a small team which is coming close to the solution of these paradoxes. Yeah, I know that I'm not very modest. My mentor, Yakir Aharonov, was my PhD advisor many years ago, and he is now 92, but just as active as ever, making amazing discoveries about which I will be happy to talk about if you are interested.
David: Absolutely. I just wanted to ask one thing. When you say that we are imprecise or uncertain, this uncertainty seems to come in at the most basic level in quantum theory, in the sense that once we decide that particles are to be described by waves, then we have inevitably a spread in positions and in momentum. So, isn't that an uncertainty that's sort of trivial by construction?
Avshalom: Some people are happy with that. I mean, the contradiction is already there, and it's still driving us, at least me, nuts. I mean, there are so many experiments that tell you that the particle is a particle just like a marble. It hits an atom; it smashes it. Think about a neutron when you produce an atomic bomb, when you make nuclear fission, then what does the neutron do? Just comes like a bullet, and it's extremely precise, hits the nucleus, breaks it, smashes it. So this is a particle.
The same particle can spread in many directions, give rise to diffraction, interference. It has wavelengths and it resides in all those places which you could know, it could be a huge sphere expanding over millions of light years, and it's a real wave in some way, because it can give rise to interference. But then, at the end you get again one single particle which actually behaves as if it went through a straight line from the origin. That's the momentum uncertainty which now vanishes, and it tells you: No, I've been always on this path. But then you have to say: No, you haven't, because you have been making an interference experiment with 2 slits millions of kilometers apart, you would once again behave just as if you were awake. So that's the beginning of the problem.
Conceptually, a wave is a wave, a particle is a particle, they are extremely opposite. And how can something be both depending on different experiments, or change itself as long as you did not measure it. It's been an expanding wave. And suddenly it says, no, I'm just a miserable little particle which went right on. That's one problem. But there are others. First of all, there is something irreversible here. I mean, there is randomness, because we have been used to that fact once you learn all the details. This is what physics taught us, and this is what made physics so beautiful. If there were some planets in the 18th century which don't orbit, according to what Newton told that planet to go. I believe it was Uranus. So then you say it can be so. Let's look. Let's make a calculation, assume that Newton is correct, and then lo and behold, you discover a new planet. This is what you're doing, particle physics and so on. Physics works, physics and mathematics work beautifully. And now somebody tells you have a wave, billions of kilometers wide, but once you make a measurement, the correct measurement it will all vanish. There will be no trace of it. So we can say you are losing a lot of information in terms of physics. This is against unitarity, and nothing remains. It's completely irreversible. When I spill milk, so you say, no use crying over spilt milk, but in principle, milk could come back with the correct technology. You can bring all the molecules back into the glass of white, clean milk. You can do that when you have collapse of the wave function, if that thing exists. So that's one problem.
Here's another problem. This huge wave is spread all over. The moment you discover the particle in one place, it must vanish in all others, or vice versa. If it's in many places, let's say 2, and you find out that it's not in one of them, then it collapses, it materializes, it's definite in the other. This is the Elitzur-Vaidman test experiment. If you know the interaction free measurement now another guy is unhappy, Einstein and special relativity. Nothing can go faster than light. So you have different parts of the wave function, which are very remote from one another. The moment you perform a measurement on one part, then all other parts must change accordingly. This has led later to the Einstein-Podolsky-Rosen Paradox. So we are left with a huge number of paradoxes. Waiting for the solution is very frustrating. But at the same time it's fun. It's challenging.
David: So you don't believe in the collapse of the wave function?
Avshalom: Actually, I do. I do think that there is something very mysterious. I do believe that the wave function is real. It's not just a mathematical abstraction, I mean. It's not that the particle may be in this slit or that slit when you make interference experiments on a single particle, it turns out that a final position depends on whether 2 slits are open or where they are, what are the sizes. So billions of slits, and so on. So wave function is real. Once you make a measurement no trace of the wave function. There have been some theories, a guide wave hidden variables which say that some wave without energy and momentum somehow remains. But you will never find it. That's not physics anymore. So collapse of the wave function, I do believe that is part and parcel of quantum mechanics. Something is changing, something is irreversibly changing. There is a real loss of information, of Unitarity. And it goes contra to relativity theory.
David: So how do we resolve this?
Avshalom: Okay, so it's a long story. Let me say something. About some 40 years ago. Even more, Aharonov brought something new which is not known. It's old, but he brought it in a very fresh way to quantum mechanics. Classical physics is time symmetric, that is, take simple interaction. Two balls colliding with one another, say there is no friction, then it runs. If you run it forward and backwards and show it to another physicist, they are the same. Okay, just like mirror symmetry. If you reflect something by mirror, then left turns into right, right turns into left. But laws of physics are invariant up down. So the laws of physics are invariant in space. They're also invariant in time. Not always, but with the basic, most basic interactions they are invariant. Said Aharonov: Let's use this in quantum mechanics, but in a very radical way. And here it goes.
And with this we begin when you make a measurement on a particle. The particle changes, there is collapse of the wave function. It becomes precise in one variable, becomes uncertain, in the other, variable. Whether it's position, momentum, or something like that. So there is a change following the measurement. But who says that the change is only following the measurement? In other words, how do you know that it goes only forward in time? In classical physics we know that's the case. If I saw a rock on the window or on the fish tank behind me, then it will break, following throwing of the rock. You will never see a window being smashed before the rock has hit it. So there is cause and effect in our macroscopic world. It turns out that in quantum mechanics it's completely symmetric. If you make a measurement, you affect the previous states also, not only the future states of the particle, but also the previous ones. In other words, the effect of the measurement goes in both directions of time, forward and backwards. There was a similar idea by Feynman and Wheeler in their absorber theory, but it was in classical electromagnetism.
Aharonov proposed the Tsvf two-state vector formalism which says that every time you make a measurement, the effect of measurement goes on both sides both to the future and to the past. Now that's crazy enough, because you can't affect the past. Otherwise, it would do silly things like killing our grandfathers and giving rise to all kinds of silly paradoxes. In quantum mechanics It happens without paradoxes. Why is it interesting? First of all, suppose that you make 2 measurements on a particle one in the morning, one at evening. What happens at noon? It turns out that at noon the state of the particle is affected by both measurements, the one in the past and the one in the future. Now suppose that you made 2 non-commuting measurements. In the morning you measured the particle's position. At evening you measured its momentum, or vice versa. According to the Tsvf, the state of the particle at noon is such that both its position and momentum are precise in apparent contradiction to the uncertainty principle. For example, take say, measuring a spin, so you measure spin along X and Y. They're again non-commuting. So once you measure one of them, you're making the other uncertain, but between them, in the time interval between them both spins are accurate. Is it contrary to the uncertainty principle? No, because you don't do it in real time. You just conclude by the mathematics that there was something very interesting going on between the 2 measurements.
Now, what do we do with it? We want to prove it, that you allow things to go backward and forward in time. You know the EPR paradox. I mentioned it earlier. You have 2 particles. I can put those keyboards in, and they are very far apart, and you give them to Alice and Bob. And then Alice measures this spin or that spin, and Bob makes his own measurement, and they are doing it at the same time. By Bell's inequality you show that actually the result of the spin, whether it's up or down for Alice or Bob depends on the choice of measurement which Alice or Bob has made. You know, wherever they are. Very far. So something went faster than light between them, not information, but something, some kind of effect. That's amazing. But once you allow things to go backwards in time then what seemed to be non-local in space is now completely local in space-time, in 4 dimensions. You have this kind of zigzag, you know, going back to the past, and then coming back to the other particle that can solve many other problems. How does the effect not diminish with space? You know EPR has something interesting in it.
Contrary to Newton's inverse square law, it doesn't matter whether the 2 particles are centimeters apart or light years apart. The correlation is full. How come that it overcomes all the noise? How come that it can locate the other particle? Once you allow this to go in 4 dimensions, then you solve this problem. But there are other things that you want to measure. But here's the problem. The question is, how do you prove it? I mean, the mathematics is simple. It shows that the state in between is the product of the 2 measurements. But now you have to prove it, that this is physics, not only philosophy. How do you prove it? Here is how you can prove it. You can make a measurement. You can make a measurement at noon, because then the state would not be between measurements, but upon measurement. So that's a problem. The mathematics tells you that something very interesting is going on, but there is a trick. You can measure it because it then won't be upon it, but would be between measurements. So then Aharonov made the next step and devised weak measurement which is a genius idea.
We were always concerned about measurement. Why does it give us such imprecise results? The proposition was that perhaps we should make the measuring apparatus more precise. I want to say no, make it less precise, make it completely imprecise with a lot of noise. What do you gain by this? If you measure one particle, then there's almost no information. If, however you measure many, many particles, a huge ensemble of particles, then, by a simple law, Schrodinger's formula, the signal overcomes the noise, and then you get a value, and it's very sharp. So it turns out, and this has been validated that the particle can when you make weak measurements have precise values in non-commuting variables.
Is it enough? The method has been criticized. People say you're playing with noise, and so on. One of us managed to overcome this problem too, and I can talk about it later. But let me say another thing. So we have 2 games, a few games already. We can kind of outsmart the uncertainty principle. We can explain non-locality by invoking the 4 dimensions. But here comes something very, very interesting, and I believe that this is a completely new physics.
You have initial boundary conditions, initial and final. Morning and evening. We call it pre and post selection. Sometimes the result that you get at evening, there is an expectation, you know what you are likely to get and what you are not likely to get. Suppose that that evening when you made the final measurement, you got a result, an outcome which is rare. So now you have a rare pair of pre and post selections. Let me give you an example. Suppose I send a particle this way, so it's most likely to end up there, but it may end up here and up here. You pick the cases in which it went to a very unlikely place. It turns out that the physics in between these 2 states is a very unique one. Nature is behaving like somebody takes a loan and he can't give it back. So the guy takes another loan and another loan, and sometimes makes it kind of a lie until they manage to return the loan. Okay? Sorry for the analogy, but it turns out that nature is doing something similar. The physics in between these, this pair of initial and final conditions goes as far as to give you values which are not familiar to physics. Momentum can become too large, too small. Even mass can become negative, energy can become negative. Now, you know, physics doesn't know anything like negative mass. It will lead to all kinds of paradoxes. Negative energy has to do with cosmology, and so on. It turns out that according to the mathematics, that there is, there are unique states in which the particle has a negative mass. That means that if that particle hits say, a mirror or a detector pointer, rather than the pointer being pushed, it is being pulled because negative mass gives you a negative momentum. How can you prove that? Once again you can do weak measurement, and weak measurement, as you know, has not been accepted by everybody. Then Aharonov and Vaidman, some 10 years ago, or a bit more, found out that there are some cases in which you can make an ordinary projective measurement. A bit complex. But you can do that. This is how you do it. You take another particle. You entangle it with your test particle. You wait until you get your result, your rare results. At the evening. Then you go back to the test particle that you left at noon. You measure it, and lo and behold, you get something very strange. Now this is not weak measurement, this is ordinary measurement. So a few years ago, a team and myself, there was also a paper with Aharonov. We published in Nature Scientific Reports, an article in which a proposal for an experiment which showed that indeed, in such cases you're going to see very odd phenomena. And then we teamed with the Japanese research team of Okamoto and Takeuchi. And lo and behold, we got the results which confirmed this.
So I would argue the following. You probably remember the case of Dirac, when he, one of the pioneers of quantum mechanics, tried to work out a relativistic computation of the electron motion and he got a strange result by the mathematics of 22 outcomes. So in one of them the electron had a positive charge. So electron cannot have a positive charge that was back in the beginning of the 20th century. And people advised him not to publish this paper. It's ridiculous. An electron can't have a positive charge. And he published it. And 5 years later Anderson had discovered the positron. With all honesty, I think that this new step is just as revolutionary. It turns out that you know just by the time symmetry of quantum mechanics that matter sometimes has these odd properties of having even negative mass, or too large mass, or too small mass, all kinds of strange spins. So it's a plethora of new phenomena being now discovered, being verified, coming from many laboratories and I find it very exciting.
David: What kind of problems would this solve? This is a new kind of matter. Would it help us understand the difference between matter and antimatter?
Avshalom: So many I mean, I don't know. First of all, there are several branches of physics about which I don't know much, particle physics, the standard model. But people there, you know, feel sometimes stuck in several problems. The progress is not great in cosmology, and so on, I would say that it has bearings on all branches of theoretical physics. We have this apparent contradiction between quantum mechanics and relativity that can help so the implications are huge. Let me say something. Have you been interviewing Aharonov himself? And perhaps you want to. He will tell you that the most fascinating thing goes much beyond physics to questions about ourselves, questions which are considered to be given to psychology or philosophy. For example, do we have free choice? He believes that he can prove genuinely genuine free choice by using this time symmetric formalism. And now, as you know, apparently for many people quantum mechanics has nothing to do with biology. You can't apply quantum mechanics to biology, because living organisms are too warm, too wet. So you can't have pure states there. Today, we know that it's not the case. If you want to understand the wonderful thing called photosynthesis, you need quantum mechanics, and very likely in some other biological functions, smell, and so on. And you know that for Japan some Nobel laureates for many years are advancing the idea that in our brain there are some quantum mechanical processes which can account for our capability of solving problems, mathematical genius, genius in general, inspiration, and so on. So it goes. Very likely it may even have bearings on these issues, which has always been considered very remote from physics.
David: I know you're interested in consciousness, and in many ways the time of conscious experience is, or seems to be, at odds with the time of physics. Hasn't your work in quantum physics added to that tension?
Avshalom: Yeah, not in quantum physics as in relativity theory. Let's remember that relativity theory says something very awkward about time. You know, we are talking now, and we have begun. And we talked before that. So time for us is passing. Time is moving. Time is flowing. According to relativity that's completely wrong. Time is not moving. Time cannot move. Time is a dimension. If you look at the universe correctly, according to special and general relativity, it is 4 dimensional, and it is a block universe. So imagine different places in the universe. Here, Andromeda, some other galaxy. They all coexist. They have the same degree of existence. The fact that I don't know what happens in other galaxies doesn't matter, just they all exist. They are not accessible to us.
David: I don't see the tension that you're suggesting.
Avshalom: No, attention. It will come in a minute. Now, think about different times. The past is normally gone, the future we don't know anything about. So they are not real, future is not. We don't know whether what is going to happen with the election in the United States, or what's going to happen in this miserable part of the world in which I live, we don't know. According to relativity, all those future states are already there, and past states are already there. Our forefathers, and so on, are still there. They are just in another place in time. Do you see the tension now? You and I.
David: I don't see any tension. I could imagine a situation where you know I'm reading a novel, and the same is true about the novel. I only experience the page that I’m reading, that page is my present, the events that are happening on that page. I will experience the events of the future. When I read the other page, the pages with higher numbers, and from my perspective experiencing what is on one page, I will say I don't know what the future is. The future is not real. It's not real for me. I will experience it when I get there, yet all of the book exists, and so I don't really see any tension at all.
Avshalom: Gonna get there. You're already there. I mean, look, we are world lines. Think about it right? We are world lines. We are 4 dimensional from birth to death, and we intersect, get far from one another. But we are world lines, so there is not one Avshalom talking with one David over time. There are zillions of Avshaloms at every moment. And now, during this conversation, there are zillions of Avshaloms and Davids, each of them frozen in their own time. So the end of this conversation is already there. What you're going to do tomorrow is already there. The future David is there. Do you believe in that?
David: If the experiments support the theoretical framework in which these ideas live, you have confidence in those ideas. How do you understand the experiments of Special and of general Relativity?
Avshalom: You're absolutely correct. I sometimes teach it in classroom. You want to show a Lorentz contraction. So you use this, you know, model of this exercise of the tunnel and the spacecraft, which are the same length. If we could, perhaps we can one day use a Powerpoint, so I love to show it on a Powerpoint. So you have a spacecraft, and you have a tunnel for washing spacecraft. So the spacecraft goes very fast, almost near to the speed of light, so you can close the 2 doors of the tunnel and wash it for a brief time. Now, on the spacecraft, and you say, no, it's a tunnel which shrank so the 2 doors cannot close at the same time. And indeed, the guy sitting, the lady sitting on the spacecraft will say you cheated. You didn't close the 2 doors at the same time. So actually, what it means is that all events are there, opening this door, closing this door and that, and you only pick according to reference frame. It amazes me that it doesn't bother you. I taught now almost 40 years. I find it completely silly. And it turns out that Einstein was unhappy about that. You know that he had a long, many years debate with his friend Michele Besso, in which Besso was a very close friend, helped him in formulating both special and general relativity, and told him there is something missing there. He had a debate with Henri Bergson, the philosopher, and then, when Besso died, he wrote this ridiculous condolence letter to his son. He said he's still there. The difference between past and future is an illusion. Okay. He himself told Rudolf Carnap that the fact that the moving now has no meaning is a matter of painful but inevitable resignation. So it was painful for him.
Now can I disprove it? Have I been able to disprove it? I would be dancing on the roofs and on my way to Stockholm. Can I say that it's dumb? And very likely there is something missing in physics. Yes, this is what I say. Very likely there is something called becoming which says that every moment, actually Aharonov himself has another paper along these lines, every moment, like the moment you are now rubbing your fingers is new. It's created new in some way. Is there some higher time, some upper, higher time dimension. I'm not getting into it but you, and now feel that this moment is unique, and then it will turn into past, and another new future will come. Perhaps there is something like that, the motion of the now. Perhaps there is some real creation in our universe.
First of all, quantum mechanics tells you that. Well, it doesn't tell you, but it hints towards that. Okay, if there is a particle and you send it, and it goes like a wave, and it will not materialize in any place until you make a measurement. That's very similar to how we experience the now, there are many possibilities open. They are there, I mean. Once again I have to ask. We have been acquainted only, you know, a few minutes ago, but I really want to ask you, David, how do you feel comfortable with the fact that tomorrow in this room there will be not David, and no matter what you do you can’t change your future. I mean you think you can change it, but I will prove to you. You may say you know that tomorrow I'm not going to be in this room. Of course, you know what Einstein's answer will be, and yours too, that it was predetermined. It's all there that your very decision not to be in this room because we talked about it, is already there. No, I can't refute it.
David: If we combine general relativity with the many worlds version of quantum theory, then we have choices again in some sense, despite all events being out there and fixed.
Avshalom: Did you mention many worlds?
David: Yes.
Avshalom: You know Lev Veidman? We worked on interaction free measurement, and whom I like very much. We are real friends. He loves many worlds. That's one of the dumbest ideas. Come on, now, what do you give me? There are zillions of Davids now at this moment, because the universe has branched and branched. Can you think about this cosmic multitude of Davids? One is doing like that. One is scratching his nose, and so on, and so on, and zillions of Avshaloms arguing with them, doing all other things. You can never prove it, you can never disprove it. It's only metaphysics.
David: But for theorists who love simplicity, economy and elegance…
Avshalom: What is the simplicity here? Is this elegant? What's elegant in it?
David: It is economic theoretically in that it just requires the Schrodinger equation. You don't have to add anything else, whereas you have to add something else in order to achieve collapse.
Avshalom: No, you don't have anything, just zillions of universes, multi zillions of zillions of them. It's so ridiculous, you know. Let me tell you something. When I was young, when I was a kid, I said, I'm going to solve all the problems of physics. I'm going to be the next genius, the next Einstein, and I'll get many Nobel prizes, and so on, and then, you know, in time, you say well, I'll be more modest. I'll solve this problem and that problem, and so on, and you become more realistic. But still the ambition is there.
Every time that I hear that a good physicist believes in the many words I say, good! One less I mean, this guy is already out. Don't tell Vaidman. It will turn you mad. I mean, this is not science. When you see those many worlds people, some of them are extremely bright. Everett himself was the genius. It's not physics anymore. Physics is something about which you can make experiments. You can make observations. But when somebody invokes something like that...
David: I was always interested in the tension between quantum physics and general relativity, but then I started to pay attention to people, and I started to hear the conversations, and I always got the impression that people were very much on a broad spectrum often on very opposite sides, opposite ends. People on one end would say that those people over there are completely crazy. I don't understand why they believe that, and vice versa. It seemed to me that this wasn't likely to generate progress.
Avshalom: The question I asked is, can you propose to me a new experiment? Can you surprise me? Can you? You know Popper. Karl Popper told me all so much about science. He says, can I disprove your theory? And of course you can do that with many worlds, so it doesn't really give us an advance, and these people are very bright, but…
David: Some physicists say it's time to throw Popper out the window.
Avshalom: Shouldn't I advise every student in, in every discipline, to study Popper? It's good.
David: I agree.
Avshalom: Life, for your freshness of mind, for your interpersonal relationships. No, take Popper seriously, but it's very good for science. If you have a theory which explains everything. And this is what the many worlds interpretation is doing. Lev Vaidman thinks that this is actually the end of physics. There are a few things that we have to solve. But that's it. We have solved it. I prefer, and this is what I like about my mentor's work, the Tsvf, It keeps presenting you with new and surprising ideas. You get new experiments. Their bearings are very far reaching, so I would say that this is much better. So I think that.
And then there is a problem of consciousness which apparently lies outside of physics. We have inner experiences which are not accessible. I can study you as a physical object. So then, I know better than you. I may know better than you what happens in your brain when you see red or blue, when you taste something sweet or sour, and so on. But I can never be sure, even when I know everything that goes on in your brain. What is your inner experience? Do you know? Perhaps you experience blue as I experience yellow, and then that's it. And actually, I don't know whether you have any such subjective experiences in theory. You could be just, you know, physical, very precise, physical system brought about by evolution by Darwin's evolution, doing exactly the same things, laughing, crying, and so on, without having any experiences. Why do we have this inner experience? Why do we have this thing called consciousness. There is no answer to that. Even some of the greatest minds in physics admit it.
David: Solve the mind-body problem.
Avshalom: I don't know. All I suggest is that there is a problem with time. Okay, we don't understand time. You may think that we do. But today it is becoming the fact that we experience time in a completely different way than space, and we do feel that every moment there is something new. Perhaps the two riddles are somehow linked. Think about it. Simplest case: I throw a cannonball, so Newton's equations tell me where this cannonball is going to be. The parabola at every moment right? But in this equation there is no hint to the fact that these states are coming one after another. It is just like a map. The map tells you this is the altitude, latitude, and so on. But it doesn't mean that east comes before west. They all coexist. But we know when you watch a cannonball that actually you have these moments, one after another, and it's absent in the equations of physics. This progression of the now. We don't have to this day, but if physics is correct, we may have a complete description of what happens in your brain, neuron to neuron, synapse to synapse, up to the single neurotransmitter molecule. Even more. Is there still something missing there that is you?
David: Why is physics giving us these strange ideas about time? This directionality doesn't matter in the laws of physics. Why is it doing that? If ultimately there is a strong directionality, there is becoming, why this tension?
Avshalom: Good question. Physics is not comfortable with the asymmetry of time. Everywhere you look at the universe, you see cups of coffee becoming cold, not warm. The second law of thermodynamics holds for all the galaxies. And there is a huge literature about that. Some people say that it has to do with the initial conditions of the universe. It somehow began in the Big Bang. And then it's very convenient, because you can't ask questions about what happened before the Big Bang, because there was no time. Cosmology tells you that this is where you can't advance much further. So why was the big bang so orderly, and then from then on order is going down, and entropy is increasing, so that could be one possibility. There is another possibility proposed by Roger Penrose. It's a minority opinion that once you have a good theory of quantum gravity which will bring together general relativity and quantum mechanics, then there will be a small error of time. With every revolution we have to make a sacrifice. We made sacrifices for absolute time and space and relativity, we sacrificed certainty in quantum mechanics. Penrose says, we may have to sacrifice time symmetry, we, it may turn out that in every single interaction, although we think it is symmetric, there is a very tiny arrow of time which then gives rise to cups of coffee cooling, and so on. You may be correct. But you see, there are so many unresolved issues in present day physics. This is why I think that our view of time, that the reason why Einstein was never happy with this consequence of relativity. I mean that there is indeed something very interesting about time.
I have a toy model of my own. It's not a theory, it's a kind of model because it's not yet mathematical. I do believe that time is progressing, that the now is really moving, and then people say, but what's your parameter? You may need a higher time. I have no answer to that. But what I'm saying is the following: I think that the future really doesn't exist. That is contrary to what you've said. What you're going to do tomorrow is really open, and it's not there, you still can affect it. But then, if the future doesn't exist, if the events of the future do not exist, then, according to Mach, there is also no space time there. When you have no events. If you have no events, then you have no space, and you have no time. Space and time are relative to the events. So is it possible? And it's just, you know, a hypothesis, speculation that our universe is growing also in the time direction. It's not only expanding, but every moment you have, we have a new moment. And out of there, there is nothingness. It's not that there is empty space into which our world lines grow, but that's the edge of the universe. Why I think it's interesting? Because then the interaction between wave functions goes on outside of space time about which we don't know anything. Then, once there was this interaction, there is space time. It's only intuitive. I don't have a precise mathematical model.
David: Do you see at an intuitive level some resolution to the conflict between GR and quantum physics?
Avshalom: Sure. Sure, here it is. Here it is. I mean, you say, how come that particle here and that particle there? How did they sense one another when there is such a huge space between them? How about the wave functions? You know this way, which the particle is not really here and not really there. But it's in all those places. We think that these wave functions interact in empty space. And then something happens. How about these wave functions interact in the future outside of the present, in the future, where there is no space time, they interact and then spacetime is created around them. Do you realize that if that is correct, we may explain attraction, like in gravity or repulsion, in electromagnetism, attraction and repulsion? Who knows. Perhaps the key for a unified theory of all the forces lies here in the assumption that interactions, quantum mechanical interactions, precede space, time and spacetime emerges out of them. I know that it's very speculative, and I have to go into more detail.
David: This sounds a lot like the transactional interpretation.
Avshalom: Yes. First of all, I like very much, John Kramer. I met him a few years ago and our work is in many ways akin to his. You know he gave a very beautiful exposition to the Elitzur-Vaidman experiment, and he related to some of our paradoxes of the quantum liar paradox, and so on. Yes, just like Aharonov, but in a different way. He conceived the idea that you may explain several problems in quantum mechanics by invoking this kind of symmetry and things going backwards in time. Retrocausation, as people call it. So I think that he made a very bold step. I know that he's still active, and I'd like to follow what he's doing, or what people are doing along this interpretation of quantum mechanics.
David: I have a couple last things. I don't want to keep you much longer than I already have. What do you make of the fact that the equations of GR look like the equations of thermodynamics?
Avshalom: Which equations?
David: The Einstein field equation looks like an equation of state. The equations of things falling into black holes look like the equations of the 1st law of thermodynamics, the second law, etc.
Avshalom: Oh, that's beautiful! There is something very profound here. First of all, look how great is general relativity. General relativity brings its own end, because it makes a prediction that there are black holes. If there are no black holes, then general relativity is wrong. If there are black holes, General relativity is wrong again, because whatever happens within, beyond the event horizon, is beyond relativity theory. It gives you all these infinities and so on. So that's a problem. Now, ever since, due to the late Jacob Bekenstein as well as Stephen Hawking, it turned out that black holes are thermodynamic objects. They do produce entropy, they do produce heat, they do evaporate. And how this is done? You just have to bring together quantum mechanics and general relativity, and then, lo and behold, you get thermodynamics. So you see that the great 3 theories of physics, quantum mechanics, relativity theory, and thermodynamics, are somehow linked in a way that we don't understand, but they're obviously linked in a very profound way. So there is a new physics there beyond the event horizon about which we don't know.
Many years ago I wrote a modest article which showed the following, that there are 3 prohibitions of physics, one by relativity theory on things propagating faster than light, one by quantum mechanics about certainty, and the 3rd by thermodynamics of entropy going down in a closed system, and I showed that if you violate one of these prohibitions, you are violating the 2 others. So it was again, kind of an intuitive paper, but I think that it's another hint that we are very far from a good understanding of the laws of nature. We have these great theories of cosmology, relativity, quantum, but they are extremely incomplete, and there are good hints how they can come together, and advances are made in these very days.
David: One last thing. How have people reacted to your work? Are you happy with the way the community has interacted with you? Have they given feedback that's enlightening? What's the reaction?
Avshalom: You know, I'm not very young anymore. I'm 67. My academic life has been somewhat turbulent, but that’s because it was unusual. I never finished high school. I just made my PhD, and then I never got tenure in Israeli University, and one of the reasons people said is that “He's strange. He has strange ideas, and he has papers in biology, evolutionary theory, philosophy. It couldn't be serious.” You know what? I couldn't care less. I mean, okay, when you don't have tenure, it's not very convenient. But, on the other hand I was fortunate to know some of the greatest geniuses of our time. Some of my own students are geniuses themselves. I'm so proud of them now, having distinguished professors in universities, and we are still working. We have to hope for is that the leaderships of this world, for you in the United States, for us in Israel as well, that we won't have these lunatics who are now leading the world, and that we will have better place where people don't kill one another. But learning to appreciate...
David: And think about interesting things.
Avshalom: Absolutely.
David: Well, thank you so much.
Avshalom: Been a real pleasure. Thank you and talk to you later.
David: Thank you, Professor!