Life: modern physics can’t explain it – but a new theory, which says time is fundamental, might

Over the short span of just 300 years, since the invention of modern physics, we have gained a deeper understanding of how our universe works on both small and large scales. Yet, physics is still very young and when it comes to using it to explain life, physicists struggle.

Even today, we can’t really explain what the difference is between a living lump of matter and a dead one. But my colleagues and I are creating a new physics of life that might soon provide answers.

More than 150 years ago, Darwin poignantly noted the dichotomy between what we understand in physics and what we observe in life – noting at the end of The Origin of Species “…whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved”.

The importance of time

Isaac Newton described a universe where the laws never change, and time is an immutable and absolute backdrop against which everything moves. Darwin, however, observed a universe where endless forms are generated, each changing features of what came before, suggesting that time should not only have a direction, but that it in some ways folds back on itself. New evolutionary forms can only arise via selection on the past.

Presumably these two areas of science are describing the same universe, but how can two such diametrically opposite views be unified? The key to understanding why life is not explainable in current physics may be to reconsider our notions of time as the key difference between the universe as described by Newton and that of Darwin. Time has, in fact, been reinvented many times through the history of physics.

Although Newton’s time was fixed and absolute, Einstein’s time became a dimension – just like space. And just as all points in space exist all at once, so do all points in time. This philosophy of time is sometimes referred to as the “block universe” where the past, present and future are equally real and exist in a static structure – with no special “now”. In quantum mechanics, the passage of time emerges from how quantum states change from one to the next.

The invention of thermodynamics gave time its arrow, explaining why it’s moving forward rather than backwards. That’s because there are clear examples of systems in our universe, such as a working engine, that are irreversible – only working in one direction. Each new area of fundamental physics, whether describing space and time (Newton/Einstein), matter and light (quantum mechanics), or heat and work (thermodynamics) has introduced a new concept of time.

But what about evolution and life? To build novel things, evolution requires time. Endless novelty can only come to be in a universe where time exists and has a clear direction. Evolution is the only physical process in our universe that can generate the succession of novel objects we associate to life – things like microbes, mammals, trees and even cellphones.

Information and memory

Such objects cannot fluctuate into existence spontaneously. They require a memory, based on what existed in the past, to construct things in the present. It is such “selection” that determines the dividing line between the universe described by current physics, and what Darwin saw: it is the mechanism that turns a universe where memory does not matter in determining what exists, to one where it does.

Life is information. Shutterstock

Think about it, everything in the living world requires some kind of memory and information flow. The DNA in our cells is our blueprint. And to invent new things, such as rockets or medication, living beings also need information – knowledge of the laws of physics and chemistry.

To explain life, we therefore need to understand how the complex objects life creates exist in time. With my collaborators, we have been doing just that in a newly proposed theory of physics called assembly theory.

A key conjecture of assembly theory is that, as objects become more complex, the number of unique parts that make it up increases, and so does the need for local memory to store how to assemble the object from its unique parts. We quantify this in assembly theory as the shortest number of physical steps to build an object from its elementary building blocks, called the assembly index.

Importantly, assembly theory treats this shortest path as an intrinsic property of the object, and indeed we have shown how assembly index can be measured for molecules using several different measuring techniques including mass spectrometry (an analytical method to measure the mass-to-charge ratio of molecules).

With this approach, we have shown in the lab, with measurements on both biological and non-biological samples, how molecules with an assembly index above 15 steps are only found in living samples.

This suggests that assembly theory is indeed capable of testing our hypothesis that life is the only physics that generates complex objects. And we can do so by identifying those objects that are so complex the only physical mechanism to form them is evolution.

We are aiming to use our theory to estimate when the origin if life happens by measuring the point at which molecules in a chemical soup become so complex that they start using information to make copies of themselves – the threshold at which life arises from non-life. We may then apply the theory to experiments aiming to generate a new origin of life event in the lab.

And when we know this, we can use the theory to look for life on worlds that are radically different to Earth, and may therefore look so alien that we wouldn’t recognise life there.

If the theory holds, it will force a radical rethink on time in physics. According to our theory, assembly can be measured as an intrinsic property for molecules, which corresponds to their size in time – meaning time is a physical attribute.

Ultimately, time is intrinsic to our experiences of the world, and it is necessary for evolution to happen. If we want physics to be capable of explaining life – and us - it may be that we need to treat time as a material property for the first time in physics.

This is perhaps the most radical departure for physics of life from standard physics, but it may be the critical insight needed to explain what life is.

Author: Sara Imari Walker

Professor of Physics, School of Earth and Space Exploration, Arizona State University

This article is republished from THE CONVERSATION under a creative common licence. You can find the original article here:life-modern-physics-cant-explain-it-but-our-new-theory-which-says-t...

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Great Mysteries of Physics: will we ever have a fundamental theory of life and consciousness?

What’s the difference between a living collection of matter, such as a tortoise, and an inanimate lump of it, such as a rock? They are, after all, both just made up of non-living atoms. The truth is, we don’t really know yet. Life seems to just somehow emerge from non-living parts.

This is an enigma we’re tackling in the fifth episode of our Great Mysteries of Physics podcast – hosted by me, Miriam Frankel, science editor at The Conversation, and supported by FQxI, the Foundational Questions Institute.

The physics of the living world ultimately seems to contradict the second law of thermodynamics: that a closed system gets more disordered over time, increasing in what physicists call entropy. Living systems have low entropy. A messy lump of tissue in the womb, for example, can grow into a highly ordered state of a foot with five toes.

“We maintain this high sense of order for many, many decades,” explains Jim Al-Khalili, a broadcaster and distinguished professor of physics at the University of Surrey in the UK. “It’s only when we die that entropy and the second law of thermodynamics really kicks in.”

Quantum biology is one approach to understanding how living matter is different from inanimate matter. It is based on the strange world of quantum mechanics, which governs the microworld of particles and atoms. The idea is that living systems may use quantum mechanics to their advantage – promoting or halting quantum processes.

“Evolution has had long enough to fine-tune things or to stop quantum mechanics from doing something that life doesn’t want it to do,” explains Al-Khalili, who carries out research in the area. “It’s a newish area of science.”

One example, albeit still controversial, is photosynthesis, the process in which plants or bacteria absorb particles of sunlight, photons, and convert it to chemical energy. Some physicists think a quantum property known as superposition – allowing a particle to be in many possible states, such as taking different paths, simultaneously – enables this process.

“A lump of energy [such as a photon] just randomly bouncing around should just be lost as waste heat,” explains Al-Khalili. “There’s a quantum mechanical explanation for how that photon follows multiple paths simultaneously.”

Al-Khalili and his colleagues are now using quantum biology to try to understand DNA mutations – a core part of life – and they’ve made some intriguing discoveries already. And while he isn’t convinced the approach will ever be able to explain consciousness, he argues we cannot rule it out.

Sara Walker, an astrobiologist and theoretical physicist working as a professor at Arizona State University in the US, favours another approach, however. She is trying to create a new physical theory of life based on information theory – which takes information to be real and physical.

Information seems to be crucial to life. Living organisms have an inbuilt set of instructions, DNA, which non-living things simply don’t have. Similarly, when living beings invent things, such as rockets, they rely on information, such as knowledge of the laws of physics, stored in their memory.

We can use the current laws of physics to predict how a planet evolves over time, for example whether and when nearby objects are likely to crash into it. But we can’t use the laws to explain how and when intelligent beings arise and decide to build rockets and satellites which they launch into orbit around the planet.

“I do think that there are laws of physics that are yet undiscovered that explain the phenomena of life, and I think those have to do with how information structures reality in some sense,” explains Walker.

Walker thinks that living organisms are more complex and difficult to assemble from fundamental building blocks than inanimate, naturally produced objects, such as simple molecules. And when simple living beings exist, they seem to generate even more complexity – either by evolution or through construction.

So Walker thinks life generates a sudden boost in complexity which may have a threshold that could be a fundamental feature in the physics of life. Another central part of her theory is time. “The deeper in time an object is, the more evolution is required to produce it.”

Walker has designed an experiment to look at how molecules are built up by joining smaller pieces together in various ways. She says the team hasn’t found any evidence that molecules with high complexity can be produced by non-living things. The ultimate goal is to pinpoint an origin of life in which a chemical system can generate its own complexity.

Not only could that help us understand how life arises from non-living building blocks, we could also use it to search for life on other worlds in the cosmos.

Author: Miriam Frankel

Podcast host, The Conversation

 You can read a transcript of the episode here.

https://cdn.theconversation.com/static_files/files/2605/MoP__Ep5_-_...

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