Many science fiction and fantasy stories are enveloped in a warm glow, and it’s not just because of nostalgia. Some characters literally glow — from ET’s fingertip to the demon markings in this year’s hit movie K-Pop Demon Hunters.
This glow-up is easy to draw or add in post-production for movie magic. But while we can’t see it unaided, we — and every organism around us — really do produce tiny amounts of light. Scientists still aren’t sure whether these biophotons serve a purpose, or if they’re just glowing motes of cellular junk.
It’s not bioluminescence, a well-known set of chemical reactions, says Catalina Curceanu, who is a nuclear and quantum physicist at Italy’s National Institute of Nuclear Physics–National Laboratories of Frascati. Nor is it thermal radiation — the result of our heat production.
Instead, biophotons are individual photons that appear to be a by-product of normal cellular processes, though it’s unclear how they form, says quantum physicist Christoph Simon, of the University of Calgary in Canada. For example, cells often produce reactive oxygen species, small molecules with highly unstable oxygen atoms that can serve as signals in the cell or can damage other molecules.
When these reactive molecules attack lipids — long links of fatty acids that form things like cell membranes — they produce “a kind of a chain reaction,” Simon says. “When two of those radicals meet and make another radical,” energy is released. That energy might be a photon with a wavelength between 200 and 1,000 nanometers — from ultraviolet through the visible spectrum to near infrared.
Many biophotons will never see the surface of the cell, let alone our skin. Instead, they’re absorbed by the vast forest of proteins, lipids and other cell structures. But some do escape, “about 1,000 photons per square centimeter per second” from our skin, Simon says. It’s about a millionth the intensity of a firefly and can’t be seen with the naked eye, adds Simon, who with colleagues has detected these photons from the skin of live mice.
Germinating lentils and beans also give off biophotons, Curceanu and colleagues found. “It shows some pattern, some complexity … like this signal might be used for something,” she says.
What that something is, though, is a mystery. Many organisms have molecules called rhodopsins that detect light. We have them in our eyes. But the true work of this light might be happening in the shadows.
Some smaller molecules in the body can absorb and reemit light, says Philip Kurian, a theoretical physicist at Howard University in Washington, D.C. The amino acid tryptophan, a building block of proteins, is especially fluorescent.
Kurian and his colleagues have shown that some cell structures like microtubules — which form the structural skeleton in cells — have protein arrangements that could allow tryptophan to act as a quantum information network. The amino acids could share a photon, giving it a chance of being in two different places in the network at the same time, a quantum superposition.
The effect boosts the fluorescence of the tryptophans “and that allows for greater information processing,” he says. So these biophotons could be used to speed information processing in cells — or beyond. This might explain why our brains are capable of so much processing with so relatively little power, Kurian says.
The glow of science fiction is not the light of biophotons, Curceanu notes. “It’s easy to get it wrong on biophotons and to imagine that we are all glowing in some totally not realistic way.” But life does emit a tiny bit of light, and scientists are working to find out why it shines.