Photosynthesis almost seems like it should be magic. Just putting a plant outside in the Sun causes it to generate the energy it needs to survive, grow, and reproduce. It seems like a simple combination of light and chemistry shouldn’t be able to do that.

But, obviously, it can. We’ve even long known the broad strokes of how—photons from the Sun (or from a grow light) hit chlorophyl in the leaves of a plant and cause a chemical reaction. That reaction turns water and CO2 into glucose, which is then converted into the chemical energy that powers the plant.

Interestingly, however, we didn’t know exactly what it would take to trigger that reaction until very recently. We’ve had our predictions—based on the way the whole process works, we assumed that it would only take one photon to kickstart the whole thing. And we’ve done some tests—though, many were done with lasers, which are fundamentally different from sunlight. But we didn’t know for sure, until now.

“A huge amount of work, theoretically and experimentally, has been done around the world trying to understand what happens after a photon is absorbed. But we realized that nobody was talking about the first step. That was still a question that needed to be answered in detail,” Graham Fleming, one of the lead authors of a new study on the subject, said in a press release.

“No one had ever backed up that assumption [that one photon would kickstart the whole process] with a demonstration,” Quanwei Li, first author on the study, added.

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