Time's arrow may not be as unidirectional as we were led to believe. According to Scientific American, a group of quantum physical researchers at the University of Toronto had observed evidence of what they're calling "negative time"—specifically, of photons exiting a material before they ever entered it, to begin with. It has to do with something called "atomic excitation." From the article (emphasis added):
When photons pass through a medium and get absorbed, electrons swirling around atoms in that medium jump to higher energy levels. When these excited electrons lapse to their original state, they release that absorbed energy as reemitted photons, introducing a time delay in the light's observed transit time through the medium.
Sinclair's team wanted to measure that time delay (which is sometimes technically called a "group delay") and learn whether it depends on the fate of that photon: Was it scattered and absorbed inside the atomic cloud, or was it transmitted with no interaction whatsoever?
[…]
Sometimes photons would pass through unscathed, yet the rubidium atoms would still become excited—and for just as long as if they had absorbed those photons. Stranger still, when photons were absorbed, they would seem to be reemitted almost instantly, well before the rubidium atoms returned to their ground state—as if the photons, on average, were leaving the atoms quicker than expected.
[…]
The time these transmitted photons spent as an atomic excitation matched perfectly with the expected group delay acquired by the light—even for cases where it seemed as though the photons were reemitted before the atomic excitation had ebbed.
So what does this all mean, exactly? That much is as yet unclear. I'm also not sure why physicists would need to look at protons to study negative time when it's just a normal fact of life for people with ADHD and something we've been trying to explain to everyone around us for years.
Previously:
• Flux is a dizzying, dazzling debut novel about trauma, time travel, and 80s cop shows
