Photons are weird.
We know this. They are massless packets of electromagnetic energy. They travel at light speed. They ignore the rules that keep apples on trees.
But there is a specific quantum trick that breaks the brain even more than wave-particle duality. It involves mirrors. And bananas. Or at least the idea of slicing a photon like an overripe fruit.
Physicists at the University of Oslo asked a question that had never really been asked before. How does one truncate a photon?
If you cut a banana in half, you get two halves. If you cut a photon in half, you do not get two photons.
You get a mess.
“Surprisingly, we will find that a shortened photon is a complicated state involving photon counts up to infinity.”
The researchers simulated removing an optical shutter—a mirror, essentially—while a photon was reflecting off it.
They wanted to see what happens when you interrupt the reflection mid-act.
The Infinite Photon Misconception
The math says the result is a superposition.
In this state, the photon exists in multiple states at once. When you measure it, you might find zero photons. You might find a few. Or, in the extreme theoretical limit, an infinite amount.
Infinite. Photons.
Sounds impossible. It is. But only because of a common misunderstanding.
Johannes Skaar, a theoretical physicist at the University of Oslo and co-author of the study, clarified the confusion. He spoke to ScienceAlert about the limits of the experiment.
The expected number of photons is not infinite.
It depends on speed.
If you remove the mirror slowly, you get a small number of photons. If you remove it quickly, you get a large number. To get truly infinite photons, you would need to remove the mirror in zero time.
That requires infinite speed.
Physics doesn’t allow that.
Why Vacuum Energy Creates Real Particles
So, can you do this in practice?
Yes.
Another myth is that truncating a photon is too difficult to execute. Skaar says that is false.
Photons vary in length. A narrow-band photon can stretch for meters. Or kilometers.
For a photon that long, you do not need an unrealistically fast shutter. You just need to block part of its wave packet.
The mechanism is fascinating. In classical physics, a vacuum is empty. In quantum mechanics, it is not.
The vacuum state contains potential energy.
When the mirror is removed, the process converts that vacuum energy into real photon energy. The truncation doesn’t just chop the light. It creates new light from the void.
What You Actually See
Here is the strangest part.
The state created by this truncation is locally equivalent to simpler states, depending on where you look.
Imagine the region between the mirror and the photon’s path.
To the left of this narrow transition zone, an observer sees a single photon. Normal. Predictable.
To the right, an observer sees vacuum. Zero photons. Empty space.
But in that thin transition region?
It is a brilliant effusion of probability. A mixture state that defies simple counting.
Skaar admitted it is complicated.
It reminds us that at the smallest scales, reality is not solid. It is fluid. It is probabilistic.
We think we understand light.
We don’t.
And if you try to slice it, the universe might just hand you infinity. Or nothing.
Depending on how fast your mirror moves.
