Few of us really understand the weird world of quantum physics – but our bodies might take advantage of quantum properties
By Martha Henriques
If there’s any subject that perfectly encapsulates the idea that science is hard to understand, it’s quantum physics. Scientists tell us that the miniature denizens of the quantum realm behave in seemingly impossible ways: they can exist in two places at once, or disappear and reappear somewhere else instantly.
The one saving grace is that these truly bizarre quantum behaviours don’t seem to have much of an impact on the macroscopic world as we know it, where “classical” physics rules the roost.
Or, at least, that’s what scientists thought until a few years ago.
Quantum processes might be at work behind some very familiar processes
Now that reassuring wisdom is starting to fall apart. Quantum processes may occur not quite so far from our ordinary world as we once thought. Quite the opposite: they might be at work behind some very familiar processes, from the photosynthesis that powers plants – and ultimately feeds us all – to the familiar sight of birds on their seasonal migrations. Quantum physics might even play a role in our sense of smell.
In fact, quantum effects could be something that nature has recruited into its battery of tools to make life work better, and to make our bodies into smoother machines. It’s even possible that we can do more with help from the strange quantum world than we could without it.
At one level, photosynthesis looks very simple. Plants, green algae and some bacteria take in sunlight and carbon dioxide, and turn them into energy. What niggles in the back of biologists minds, though, is that photosynthetic organisms make the process look just a little bit too easy.
It’s one part of photosynthesis in particular that puzzles scientists. A photon – a particle of light – after a journey of billions of kilometres hurtling through space, collides with an electron in a leaf outside your window. The electron, given a serious kick by this energy boost, starts to bounce around, a little like a pinball. It makes its way through a tiny part of the leaf’s cell, and passes on its extra energy to a molecule that can act as an energy currency to fuel the plant.
Photosynthetic organisms make the process look just a little bit too easy
The trouble is, this tiny pinball machine works suspiciously well. Classical physics suggests the excited electron should take a certain amount of time to career around inside the photosynthetic machinery in the cell before emerging on the other side. In reality, the electron makes the journey far more quickly.
What’s more, the excited electron barely loses any energy at all in the process. Classical physics would predict some wastage of energy in the noisy business of being batted around the molecular pinball machine. The process is too fast, too smooth and too efficient. It just seems too good to be true.
Then, in 2007, photosynthesis researchers began to see the light. Scientists spotted signs of quantum effects in the molecular centres for photosynthesis. Tell-tale signs in the way the electrons were behaving opened the door to the idea that quantum effects could even be playing an important biological role.
This could be part of the answer to how the excited electrons pass through the photosynthetic pinball machine so quickly and efficiently. One quantum effect is the ability to exist in many places at the same time – a property known as quantum superposition. Using this property, the electron could potentially explore many routes around the biological pinball machine at once. In this way it could almost instantly select the shortest, most efficient route, involving the least amount of bouncing about.
Quantum physics had the potential to explain why photosynthesis was suspiciously efficient – a shocking revelation for biologists…