Scattered dots of light can tell us a lot! If you find a photon of a frequency that's only produced by, say, a CO2 molecule, you can prove that CO2 existed 50 m

Scattered dots of light can tell us a lot! If you find a photon of a frequency that's only produced by, say, a CO2 molecule, you can prove that CO2 existed 50 million years ago. Ok wow, probably not too useful. Collect a bunch of photons, count how many indicate CO2 and how many indicate O2, and you can figure out the composition of Earth's atmosphere. All of this using single photon detections!