Quantum biologists argue that life is influenced by the small, strange world of quantum mechanics. But not everyone is convinced.
Imagine a cat trapped in a box with a small vial of acid. Attached to the acid is a bit of radioactive material, which shoots off particles such as electrons ‒ we call this radiation. Attached to the radioactive material is a device that can measure the electrons shooting out, and, after a certain number of electrons are lost, the device will drop a hammer, break the vial of acid and kill the cat.
This was the thought experiment that Erwin Schrödinger proposed in 1935 as a way of thinking about the absurd implications of a then-new and strange field of physics: quantum mechanics.
The oddity of quantum mechanics suggests that the world of very small particles behaves in completely unintuitive ways, and is entirely dependent on probability. The radioactive material next to Schrödinger’s cat behaves likewise. After a certain amount of time it has probably lost half of its electrons, but any single electron could be still in the material or it could have shot off. Strangest of all, quantum mechanics says that it’s both. Particles, according to quantum mechanics, can be in two places at once.
So after you’ve calculated that the final electron has most likely shot off, is the vial of acid intact? Is Schrödinger’s cat alive or dead? Surely it must be one or the other. Right?
Well, until you open the box and “collapse” the possibilities down to either one or the other, quantum mechanics says that the cat is both dead and alive.
Schrödinger’s cat was one of the first explorations of the line between the quantum realm and ours. There seems to be some line, some edge that separates the world that we know and can measure absolutely, and the quantum realm.
Nine years after writing about his cat, Schrödinger proposed another strange idea. In his paper What is Life?, he suggested that life could walk that edge, existing both in our world and the quantum world. This idea, popularised by Schrödinger, didn’t gain much traction until the 1990s when a couple of scientists, Professors Johnjoe McFadden and Jim Al-Khalili at the University of Surrey, picked up the idea and began work in the new field of quantum biology.
“Of course, everything around us is made of molecules, atoms, etc.; their properties depend on quantum mechanics,” McFadden said. “The structure of atoms is entirely quantum mechanical. Everything depends on quantum mechanics. But what we’re saying about life is something different from that trivial observation.”
McFadden and Al-Khalili, along with a small but growing number of other researchers, have linked quantum mechanical processes to photosynthesis in plants, mutations in our DNA, bird migration, our sense of smell, and how enzymes in our cells speed up chemical reactions ‒ something that is essential for us to live. Because enzymes work with single, tiny molecules, yet are essential to building large organisms, they may straddle that quantum line.
Enzymes speed up chemical reactions in our body. Reactions that could take minutes, hours, even years, occur in a split second. How exactly they do this is still a mystery. According to McFadden, it has to do with an effect known as quantum tunnelling. Not only can particles be in multiple places, they can cross seemingly impossible barriers – except that the word “cross” isn’t exactly correct.
For instance, imagine that you have lost your keys. You know that there is a possibility they’re in the kitchen or the living room; you don’t know where, but once you look for them they’ll pop up in one of those two areas. The difference is that, in our world, the keys have always been sitting there, in the couch cushions or on the countertop. Whereas in the quantum world, the particles are both in the cushions and on the countertop, and in a hundred other areas, walls be damned.
McFadden and other quantum biologists say that it is this tunnelling effect that allows electrons to hop around molecules in your cell, and which enzymes can use to overcome molecular barriers with astonishing speed. Tunnelling electrons might also play a role in the electron transport chain, a series of cellular pumps and machinery that creates ATP, the molecule that gives us energy to do everything from digest dinner to run a marathon.
“I’m a biologist, not a physicist, so I’m fairly uncertain of my [physics] grounds,” McFadden said, describing his early work on quantum biology in the late 1990s. “So I got in touch with the physics department here at the University of Surrey and they asked me to give a seminar on this — which I did. I gave a lunchtime seminar, which was received fairly skeptically by the physicists in the audience.”
But McFadden’s seminar did attract the attention of one physicist, Jim Al-Khalili, and the two began working together to see if this new field “had any legs”.
They decided it did, and together they hosted a quantum biology conference in 2012 with about 40 people in attendance. In 2014, McFadden and Al-Khalili co-wrote a book about quantum biology, Life on the Edge: The Coming Age of Quantum Biology. McFadden says that, since 2012, the field has grown to a few hundred people, but many are still skeptical.
Professor Hans Westerhoff, a biologist and biochemist at the Free University of Amsterdam and the University of Manchester, is one of those skeptics. “It’s not completely impossible that some of the things [quantum biologists] put forward are right, but it’s unlikely,” he said.
Westerhoff studies systems biology, a field that looks at the complex interactions in biological systems, and explores many of the same questions that quantum biology does. For many of these questions, Westerhoff thinks that systems biology can provide an answer without needing to invoke the strange world of quantum mechanics.
“All this weirdness that [McFadden] is talking about, or at least most of it, you don’t need that,” Westerhoff said.
And Westerhoff is not the only one. Professor Mathew Cobb, a biologist at the University of Manchester, said in an email that he “said all that he had to say” in a recent review of McFadden and Al-Khalili’s book, in which he wrote: “As an experimentalist, I am less impressed by the power of theory and would have preferred to see the authors revelling in our current ignorance. After all, the most important words in science are ‘we don’t know’.”
Still, even quantum biology’s detractors give it credit for some biological effects. For instance, Westerhoff said that quantum tunnelling does seem to be involved in the electron transport chain, and that there is strong evidence that quantum mechanics plays an important role in photosynthesis. For many other topics, Westerhoff says that while he disagrees with quantum biology, it brings up interesting questions that continue to advance science.
“They could turn out to be right, and so it’s very good that they bring this up, and that, therefore, people try to find out whether this is true or not,” Westerhoff said. “That’s unlikely, but experiments will have to decide.”
Experiments and time: that’s what’s needed before we can understand how big a role quantum mechanics plays in biology. It is hard to tell if quantum biology is a vibrant new field of study, or a small idea that may fade into the background. For now, Schrödinger’s big idea, just like his cat, is both.
Edited by Andrew Katsis and Ellie Michaelides, and sponsored by Jacey Ashton