If you work in a city, there’s a good chance you’ve got your morning commute down to a fine art, getting you to the office with your coffee in hand within minutes of that first meeting.
Light, it seems, has you beat.
A recently published experiment conducted by researchers from the University of Toronto in Canada and Griffith University in Australia found that photons traveling through traffic consisting of cold rubidium atoms can leave late and still make it in before the boss decides to dock their pay.
What’s their secret? A touch of quantum uncertainty, it seems.
It’s not the first time light’s time-bending nature has been observed. As far back as the early 1990s, curious leaps in light have been reported in experiments comparing pulses of photons traveling through a medium with those in a vacuum.
In the emptiness of space, all information moves at 186,000 miles (about 300,000 km) per second. No more, no less. Think of it as the speed of causality.
Light is a wave of "causation" between electric and magnetic fields. Without any mass to complicate matters, all photons stick to this universal speed limit.
Throwing a scattering of atoms in their way may delay their journey, but it doesn’t slow them down. The speed of "causation" between the forest of electromagnetic fields and the photon’s own electromagnetic wiggle remains the same, even as the path sends them off in wild new directions.
It stands to reason, then, that a pulse of photons sent surging through a group of atoms should follow the same pattern, with early birds and stragglers and a bulk in the middle ... even if their collective journey is delayed.
For some reason, this isn’t always the case, with baffling instances of the peak of a pulse passing through a medium arriving before a peak moving through nothingness.
One possibility is that interactions between photons and atoms create a statistical shadow, reshaping the graph of photons exiting the medium so that the bulk now arrives towards the front. As likely as this is, other explanations need to be ruled out.
To be clear, nobody is worried about tears in the space-time continuum sending photons flying into the future. Causality is not broken. No wormholes are necessary.
Yet that doesn’t rule out time as a malleable factor.
Taking a different approach to monitoring the pulse, the researchers behind this more recent investigation ‘watched’ the crowd of atoms, measuring the duration of their excited quantum states to determine the timing of photons in the pulse.
This is no simple feat, requiring repeated trials that average out any interference of the environment on the delicate quantum activity.
They found that statistically speaking, photons that arrive early to work have indeed spent "negative" time in traffic.
How is this even possible? Time, like many measures in quantum physics, can get a little fuzzy up close. Heisenberg’s principle of uncertainty still stands – pinning down some measures with increasing precision makes other measures more ambiguous on a fundamental level.
As photons interact with atoms, their shared energy levels resonate with one another like the actions of a parent pushing their child on a swing, matching precisely. Precise energy means the property of time must relax, allowing temporal precision to smear out across the photon’s quantum wave of possibility.
Future experiments could reveal that those arriving late are subsequently carrying that surplus time, confirming that quantum uncertainty is to blame; an excuse we all wish we could give our boss when we miss yet another morning meeting.
This research was published in Physical Review Letters.
Fact-checked by Bronwyn Thompson
