Physics, Biochemistry, Cell, Biology, Research Understanding the origins of life | Sara Walker

Im. Sarah walker and i am a theoretical physicist by training and i work in the field of astrobiology and think a lot about the nature of life and the original life in the universe and im. Looking forward to discussing these ideas with all of you today, um, so the first part of this academy is going to be focused on the universal laws of life um. So how do we actually identify whether there are universal principles that underlie all life in the universe? Um and i wanted to start by first explaining where the quote that is sort of inspired the title of this academy came from so theres. This very well known book, a brief history of time by stephen hawking, where he mentions that, even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe, and i thought this quote was particularly relevant to what new physics might underlie life and help explain life in the universe, because right now were in a state in physics where Our theories, not only do we need to ask questions about where our equations come from, but we also need to recognize that they dont explain us, and so in my field that i was trained in theoretical physics, weve had a huge amount of success about describing reality At a really fundamental level, in terms of understanding the fundamental forces of nature and realizing that certain unifications of them say, for example, the unification of electricity and magnetism um in the 1800s, leading to electromagnetism or, more recently, the electro weak force and the standard model.

Particle physics have been really successful at describing reality, and we think that we can keep going um to whats called the theory of everything um. But of course, as david krakauer, the president of santa fe institute points out. The theory of everything is a theory of everything, except those things that theorize um, and so all of these sort of laws that weve come up with are actually inventions of biology and they dont describe the biology um that you know has actually come up with these Ideas so im really interested in trying to uncover whether there are deep principles that also explain life and some of the things that id like to talk about with you all today are that some of the things that life does seem to challenge the laws of physics. As we understand them now and might actually demand entirely new principles and frameworks, now, why do we think that this approach might even work um? Well, i am, as i mentioned, uh trained in theoretical physics, so i have very much have this bias um that we have um uh in my field. Um thinking that mathematical principles, uh should applies pretty much to everything in the universe and there should be a fundamental understanding as possible, um and so albert einstein kind of puts this idea very nicely that the general laws on which the structure of theoretical physics is based. Um claim to be valid for any natural phenomena whatsoever and it with them.

We should be able to describe a theory of every natural process, including life by pure deduction, so ive added the emphasis of life, because obviously thats missing from our current descriptions of physics. Theres. No explanatory framework for what life is um, but i wanted to just emphasize that this is very much the mindset of um traditional approaches to physics, so im still maintaining this mindset that we can find universal principles um whether or not thats. The case is still subject of open debate, so maybe life just doesnt conform to the kind of understanding of reality that we get from physics. I am optimistic that it will um, but it might look quite different um, but its still open possibility that it doesnt um. So one of the things i wanted to start with saying, where sort of the dichotomy is between the way weve done, physics for the last 300 years or so, and what new principles might be necessary to explain life um is uh to think about sort of the Difference between how we think about dynamics um in life and what life does as an evolutionary system, um and uh, how we think about things in physics, and so this quote. Um now comes from a nobel laureate, frank wilczak, who was one of the pioneers that really led to the success of the standard model of particle physics, and he points out in one of his papers that since newtons time, we divide the description of the world into Dynamical laws that, paradoxically, live outside of time and initial conditions upon which those laws act um – and this was in part what you know.

This observation is one of the reasons that stephen hawking made this point about what breathes fire into these equations, because they dont exist inside the universe by our current descriptions, nor do the initial conditions. So these are sort of boundary conditions we need to put on the universe in order for our physics that we have currently to work now. This gets really interesting when youre talking about biology, because the newtonian paradigm and the way that we kind of construct all of the theories of physics that we have to date are based on this idea that we have an initial state and some fixed law of motion. So an example would be say: newtons law of gravitation, which explains say planetary motion, or some of you may be familiar with the formula. F equals m a force equals mass times acceleration right, so the theres, no um change in the actual equation. What changes the variables in the equation, so the law itself is fixed and should apply to any massive object um. So these are sort of the ideas that were first established by newton, and we still use today and um. Part of the challenge here is that if you want to explain how the world exists as it exists, now you have to use um one rule, um and sort of fine tune, the initial state to explain the details and features of the universe today. So, for example, if i want to explain how it is that im here, um at this festival, talking to all of you right now, um somehow the initial imprint of that information had to be in the initial state of the universe and then was generated basically by The laws of physics operating on that initial state, so this is kind of an extreme view, but this is one interpretation that you could have um and many people do by taking sort of the the standard, um laws of physics as we understand them and then interpreting How they apply as an explanatory framework, now the difference with biology that we see is really we have sort of evolution if you will in biology.

So you can start from one initial state or many initial states and end up in many different final states, and what do i mean by that? Well, we have something that we call sort of genetic heredity as an example, you have common ancestors, for example, with. Maybe your cousins and your aunts and uncles and things but youre all very different, even though you kind of descended from similar genetic lineage and so part of the idea that people have talked a lot about. Is that biology? Has this kind of multiple histories or possible histories and theyre very contingent on the particular environment and particular features of the system under study and the interaction between those? And so we dont really seem to have this kind of application of a fixed law as being applicable to biology, and this idea, of course goes back quite a long way to the invention of evolutionary theory itself with charles darwin. So he has this beautiful quote. That will this planet has gone cycling on according to the fixed law of gravity, so simple, beginning endless forms, most beautiful and most wonderful have been and are being evolved. So, of course, the newtonian paradigm allows you to take an initial state like say the configuration of planets in our solar system, and once you understand the law of gravitation, you can run that system forward in time and in principle, you should be able to predict where All the planetary bodies will be in the future.

Um now theres obviously challenges of that in practice, because once you start having multiple interacting bodies, theres extra terms in the equations that become more cumbersome to calculate, but in principle, sort of thats the foundation of how we think about things. In physics, we take an initial condition: we have a physical law and therefore we should be able to predict how the system behaves indefinitely um. You can contrast this with darwins endless forms, most wonderful, and so this is kind of a more pictorial visualization of what i was showing on the previous slide, with this idea of the multiplicity of paths that biology takes um. So here we have this um last universal common ancestor, so ill talk about this a little bit more in the second talk we have this morning, but the idea um here is that all life on earth descended from whats called the last universal common ancestor, which was Really, probably a population of cells on early earth and since and thats sort of the first um evidence that we have for life on earth and the first knowledge that we have of a sort of modern machinery that we have in biochemistry today. But since that time. What weve seen is that all of these amazing species that basically cover the surface of our planet, from us to fungi to bacteria and even viruses, and all of these things have sort of descended from this common ancestry and its not just that the biosphere has created A lot of organismal diversity, but its also created a lot of innovation in other things, so, for example, um.

I am you know, sitting here, um talking with you all on a computer, and i have a phone with me and a pen um and a cup, and all of these are technological artifacts that are also the product of the evolution of life. Now a question is, could you predict um say if you knew the the last universal common ancestor and all the conditions on planet earth at that time? Could you have predicted that four billion years later or so or three and a half billion years later, uh a cup would would form right? So so this is sort of the question. So a lot of people that study evolution um think that you couldnt pre specify what is going to evolve. Stuart kaufman is very famous for saying this that evolution is actually not pre stable. You cant predict whats going to happen in the future, and so this is sort of one of the major distinctions between when were talking about, trying to explain life and trying to understand it. With sort of the current paradigms that we have in physics that they dont exactly fit together for this very reason, um and so just to kind of bring the message home a little bit more, its actually related to some very deep paradoxes: um at the foundations of Mathematics and computing, um and sort of the clearest place that we can see this sort of dichotomy um. It was with this nice quote by nigel goldenfeld and carl woes.

Nigel goldenfeld, as a physicist carl woz um, was a biologist famous for discovering the three domains of life are well archaea, the third domain, um and um. What they they point out is that in biology, we encounter a situation where the rules must be self referential. So remember we said in physics the laws are fixed now were saying: the rules are not fixed, but theyre. Actually self referential rules um what they mean by that is the update rules change during the time evolution of the system in a way that they change. As a function of the state and the history of the system, um, and so an example of that is just to think about genomic information inside a cell, so we have genomes inside the cells in our bodies. Not all of the information in the genome is expressed at once um, so it can get read out into proteins which proteins are expressed, actually determines the level of gene expression and so theres. This feedback loop, where the information in the genome specifies whats happening, but then that whats happening specifies whats being expressed as far as the information or you can think about the fact that you know you have thoughts your thoughts um. Maybe if you, if you believe your thoughts, influence your behavior um, you know theres a lot of subject open to debate about that, but that would also be sort of a self responsible dynamic where theres some emergent property of the system.

That then influences the dynamics and what happens next, and in fact i mentioned that this is related to the foundations of computing, because the self referential nature is actually foundational to what turing discovered. As far as the insights around the halting problem and kurt griddles work about sort of the incompleteness of mathematics and so theres, some very deep paradoxes associated with self reference. And this feature that a system might define its own rules and then be able to act on itself, and so this paradox is actually really nicely captured by this um famous illustration by m.c escher, which was trying to capture this idea of self reference. If you have these two hands and one is drawing the other uh, where do you actually say? Um causation starts um and in physics, its very simple where causation starts, we have sort of elementary particles, and then we have laws and everything else is supposed to be derived from that, but in biology it seems that the actual properties of the physical system itself in Part determine how the laws are going to behave in the future, and this is what we mean by saying that biology has a self referential, loop or so um sort of is some kind of capacity to change the rules of the game, its playing um and so Um, so this is sort of one of the most important distinctions between um physics and what might be necessary to explain life.

And in fact, i i want to just point out that the issue with sort of a fixed law of motion and initial conditions is not just problematic for trying to apply the way that weve developed physics historically to life, but its also problematic in some areas of Fundamental physics itself, so i had pulled that quote um from frank wilcheck earlier, but he also points out in the same paper where hes just talking about standard physics. So this is part high energy, particle physics gravity. You know sort of things that we usually think about when were thinking about fundamental theories of reality and where theyre going in the next hundred years. He points out the fundamental laws should no longer admit arbitrary initial conditions and will not take the form of evolution equations, because, even in fundamental physics, these these things are uh problematic, and so one issue just to highlight a specific one. That i already mentioned is this issue of fine tuning, because there are a lot of issues about having to fine tune sort of the initial conditions, to specify kind of what you want to observe and the initial conditions are not given for free. We have to put them in or we have to derive them from another theory, and so these these kind of things become quite challenging if you want sort of an ultimate explanatory framework to continue watching this video click, the link in the top left or in the Description below or visit iai.

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