Light can theoretically zip around the universe forever without breaking down. That's because it's long been believed that the photon — the elementary particle that makes up light and other electromagnetic radiation — has no mass. But physicist Julian Heeck wondered what would happen if it turned out that photons did have mass, and it seems that they'd still stick around for a long time: Heeck calculated that, with mass, a photon would live for at least 1 quintillion (or, a billion billion) years before breaking down.

To the photon, it's just a brief three years

At least, it would last that long from our perspective here on Earth. Because the photon would experience time from its own frame of reference — traveling at around 186,000 miles per second — it would only feel that time as a brief three years.

To determine the particle's minimum lifespan, Heeck looked to data gathered on the early universe by NASA's COBE satellite. The data all lined up with what was predicted by the Standard Model of physics, but by using a previously calculated maximum mass for photons — an incredibly light 10-54 kg — he was able to determine the particle's shortest possible lifespan.

Heeck, who is currently a PhD student at the Max Planck Institute for Nuclear Physics in Germany, had his work on the lifespan of photons published earlier this month in Physical Review Letters. Some variables that could have further shortened the photon's lifespan were left out, and he says that more detailed work ought to be done. "A massive photon sounds crazy and exotic," Heeck writes, "but it really is not." He suggests that though it may be a curiosity, it's one worth investigating.