How Quantum Physics Debunks Determinism | George Ellis

  • 18-Apr-2022

Well, thank you all for coming. I hope this will be interesting. So this course, is obviously intended as an antidote to the very famous book chance and necessity by Jacques many, which I'm sure many of you will have read. He was a Nobel prize-winning molecular biologist.

But in this book, as one can tell by the title, he treats these as the only two causal categories in the universe are the things that chance or their necessity. This is a big mistake because there's a huge amount of evidence of purpose. Everywhere, and I just look around you this year, computer the screens there is evidence of purpose all around us in the universe.

And so he was missing out one of the major causal categories that clearly is causally effective in the real universe in which we live. And so we need a bigger causal framework than he was using to make sense of things now, I'm not going to claim to solve the hard problem of consciousness, and I'm, not going to solve the problem of free will. But I will provide a framework in.

Which the latter problem looks a lot better than if you don't adopt this kind of framework, and I hope that'll become clear. So this session randomness in the universe things are not determinate. And the take-home message is that randomness occurs in the universe. Physics does not determine a unique outcome from initial conditions. Now I hasten to say, some of my physics colleagues do not agree with this and people like my friend, martin Reese who's, the recent president of the royal society believes. That if we had sufficient computing power, and if we could gather enough data at the start of the universe, we would know everything that happens in the universe at future times from that initial data.

This goes back to la. Plus the idea that the universe is deterministic why? Because at the basis, the physics of the universe is what the physicists call Hamiltonian dynamics.

It is a determinate physical system. The initial data given the physics dynamics determines the outcome. It's very strange that. People should hold to this because it's over a hundred years since we've known about quantum mechanics.

And we've known that the universe is not determinate, so it's kind of paradoxical that people should still be holding on to that not only that. But at least 50 years ago, the idea of chaos and in determinism, even in Hamiltonian systems was also understood. Now the references for this section of the course, quantum randomness, any text on basic quantum physics. So for instance, Richard Feynman's book, six.

Easy pieces chapter. Six talks about quantum and discernment or a much more recent book, general Melbourne's book, Schrdinger's machines, the quantum technology that is reshaping, everyday life. Chapter one talks about it. And then the other thing I'm going to concentrate on is microbiological randomness and there's. A wonderful book on this by peter Hoffman called life's ratchet, how molecular machines extract order from chaos and there's an as we will be developing this? Firstly, at the foundational. Levels quantum physics says, the game, the idea of determinism won't start for foundational reasons, it's, not true in the real universe in which we actually live the question is what about randomness in biology.

Now, digital computers I'll talk about this are totally deterministic. And this carries a heavy price. If you are programming a digital computer, those of you who've engaged in program will know if you just get one stop for a full stop wrong and put a comma in this place, the whole. Thing comes to a grinding hot, an error message comes up the screen, and it doesn't work. And so the way that digital computers work with programs that are totally deterministic is not a very good way for biology to work and biology does not work in that way, there's a huge amount of randomness at the bottom levels of biology and biology has understood this. It is developed in order to live in this environment and to take advantage of it.

So biology, just doesn't just treat randomness as an enemy that. Has to be controlled biology uses randomly at the micro levels as a tool in creating what the biology wants and that's. What this book is about life's ratchet, how molecular machines extract order from chaos? Now, where do complex systems come from the emergence of complexity is unpredictable from the initial data in the universe, and I'll make this explicit as we're going, so I'm going to talk about unpredictable emergence of complexity at the universe.

And the foundational reason is that quantum. Physics is unpredictable and Vienna, Heisenberg and Feynman. And all the others say that at the foundations, the true nature of physics is that it is not deterministic, and it's. Not a question that we don't have enough data. If we could find enough data, we would be able to predict quantum physics, says, it's, not that there are hidden variables missing variables, quantum physics, says by the very foundational nature of quantum physics. What happens in the universe? The microscopic scales cannot be described.

In a deterministic way and many of you probably know that, but I want to emphasize it because it's absolutely key. Now, the absolute foundational experiment in quantum physics is the two-slit experiment. You've got a source on the left, a first screen, which has a source in it.

And it can be either particles that then goes the waves spread out to a second screen where there are two slits. And they have to be an appropriate distance part. They have to be very, very small for you to see this. And from those. Two slits waves spread out, and they hit then the final screen, the question of which quantum physics was trying to discover way back. A hundred years ago is light wave or particles. And if life was waved, you get bars of light sections where interference takes place constructively, namely, there's a series of waves from the two slits.

And they either add up or they destroy each other where they add up. You get a bar of light where they destroy. You get a bar of dark. And that is constructive and destructive.

Interference showing that light is a wave, but under the right circumstances, light is a particle. And if you have particles going through those two slits, you get those light and dark things, but you get it building up in a particulate manner. But light is actually also from the quantum viewpoint, photons, its particles and the trick.

And the thing is to get the source of light to reduce the intensity of the lord further and further so that instead of millions of photons coming through any second you. Reduce it until you're emitting one photon at a time. And when you do that that photon goes through the double slit, and it ends up somewhere on the screen, which you cannot predict, and it is impossible as far as quantum physics is concerned. You send one photon through it goes through these two slits. It will appear on the screen at a point, which cannot be predicted. What can pre-predicted is statistics of what will happen.

And when you send many particles through the particles, which make up life. Make up light when you have enough of them, they combine and form what looks like a wave pattern. But the individual particles coming through end up on a screen at a place that cannot in principle, be detected. This applies to waves and particles and the waves.

It might be light, but it might be also electrons. And one of the discoveries foundational discovery of quantum mechanics was that light behaves as a particle or a wave under certain circumstances things that we had previously thought of as. Particles like electrons behave, either as a particle wave also under the right circumstances. And so you get this idea that particles or waves of particles, which way matter behaves. It depends on the context. And so the discovery of quantum physics is that all particles behave like waves under certain conditions and like particles under other conditions.

And this is the wonderful experiment by Dr, tonomiura. And it shows the buildup of the interference pattern of single electrons on the left. Hand side, there are 200 top left particles, and it looks like just a random pattern on the screen. That's number b, number c. You've got 6, 000 ones, and you're beginning to see light and dark patterns showing up number d is 40 000, and you're beginning. Now really to start to see it and in e, you're really seeing now that interference pattern building up and that's when you've got 140 000 photons, when you've got this set up the individual photons or the individual electrons, or you can do it with even.

Heavier particles people have done it with fullerenes molecules that are quite heavy, each individual particle there's, no way to tell where it will end up on the screen. But the pattern builds up. And the pattern is an absolutely 100 predictable patterns. And the pattern that eventually emerges is the classical interference pattern, which we started off with. And that is the basic feature of quantum uncertainty. It's, not possible it's. Not just that we don't have enough evidence.

People have tried to find. Out have we been missing some variable, which will determine where it ends up, and they have failed to find any such variable now, there's a similar thing that happens with an excited atom. If you excite an atom by heating, it up it was in a ground state. It goes to an excited state.

It then sits in that excited state. And eventually it emits radiation. It might be a visible light. It might be x-ray, depending on the frequencies involved to continue watching this video click, the link in the top left or. In the description below or visit for more debates and talks from the world's leading thinkers on today's, the biggest ideas.

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