The Most Powerful Particle Ever Seen（原声文稿）

Right now, particles from space are slamming into the air high above you and shattering into showers.

Some of that spray reaches the ground and goes straight through you, dozens of particles every second. You have been standing in this rain your whole life.

Almost every drop of it is tiny.

But in the early hours of October 15, 1991, at a U .S.

Army test site in the Utah desert, A detector caught the biggest drop anyone has ever measured.

One single particle, tens of thousands of times smaller than an atom, carrying the energy of a baseball thrown at about 60 miles an hour.

That's almost 50 million times the energy of the most powerful protons our machines have ever produced.

Unlike the Strangelit, a particle that has never been found, this one was actually detected. And it's a problem.

It was measured far beyond the limit physics predicted and no confirmed source has been found.

Then, in 2021, it happened again.

This time, the particle appears to come from a nearly empty region of space. How powerful was it, really?

Why does physics say it can't have come from far away? And if it came from close by, where's the gun?

In 1991, at Dugway Proving Ground, the University of Utah was watching the desert sky with a detector called Fly's Eye.

Its main eye was 67 mirrors, each tucked inside what Quanta Magazine describes as a rotating can cut from culvert pipe.

By day, the cans turned face down so the Sun couldn't blow out the sensors.

On clear, moonless nights, about one hour in 10, they turned up.

To see what they were watching for, zoom out from you, about 10 miles straight up.

A cosmic ray, a particle from space moving at nearly light speed, hits an air molecule and smashes it apart.

The pieces hit more molecules, and those pieces hit more.

Think of the break in a game of pool, if every ball that got hit shattered into new balls that kept breaking.

In a split second, one particle becomes a pancake of billions racing toward the ground, and the nitrogen it passes gives off a faint ultraviolet glow.

That October night, the moon had set and the sky was clear.

A shower came down about eight miles away, and only one of the detector's two eyes saw it. Nobody noticed.

The same magazine reports the track turned up in the recorded data the following summer, and the team spent another year convincing themselves it was real.

At its peak, that single particle had become more than 200 billion. Its energy?

About 320 quintillion electron volts.

Nothing else Flizei ever recorded reached even a quarter of that.

That, to this day, it is the most energetic particle of any kind ever recorded.

It became known as the Oh My God particle, a name that appeared in an article in 1994.

That article also called it a proton, although its discoverers never claimed that. Remember that.

So how much energy is that, squeezed into something smaller than an atom?

The particle first appeared in print in 1993.

In one sentence, the Utah team tacked on to a summary of other work in physical review letters.

It began, an outstanding event of 3 times 10 to the 20th electron volts. Outstanding is one way to put it. Let's build a ladder.

The first rung you already know, a baseball at about 60 miles an hour, packed into one particle. The The second rung needs a unit.

An electron volt is the energy one electron picks up crossing one volt.

A a a battery gives each electron about one and a half.

The 1991 particle carried about 320 billion billion.

Third rung are best machines.

Our most powerful protons came from the large Hadron Collider switched off this summer for an upgrade.

6 .8 trillion electron volts each.

Our particle carried almost 50 million times as much.

And if it was a proton, its collision with a single particle of air was more than 50 times as energetic as any proton collision the LHC ever made.

Fourth rung, a race against light. Nothing can outrun light.

So, all that energy only squeezes a particle closer to it.

If it was a proton, it fell short of light speed by about four trillions of a trillionth.

Race that proton against a beam of light for a whole light year, and the light wins by about the width of a virus.

To pull one centimeter ahead, light would need roughly a quarter of a million years. Time stretches, too.

If it was a proton, a journey of a hundred million light years would have felt, to the particle, like about two and a half hours.

With a clock like that, it seems it could have come from anywhere, could it?

In 1995, the Utah team published the full paper, under a title that begins, Detection of a Cosmic Ray with Measured Energy Well Beyond the Expected Spectral Cutoff. Expected by whom?

To find out, zoom out again, into the space between galaxies.

It's filled with light left over from the Big Bang, about 400 photons in every cubic centimeter, including the one in front of your nose. To your eyes, it's invisible.

To a proton moving this fast, it looks like a beam of gamma rays.

Picture a toll road with a booth every 16 million light years or so, each one taking about a fifth of whatever you carry.

Travel far enough and you arrive with small change, however rich you set out.

People call it a cosmic speed limit, but nothing gets slowed down.

What it caps is energy, and the booths only charge travelers above about 50 quintillion electron volts.

Heavy nuclei don't escape either. The same light breaks them apart.

In 2008, the successor to Fly's Eye in the same Utah desert saw it.

Above that energy, the number of particles drops sharply. The limit is real.

The oh my god particle arrived with about five times that energy.

Arriving that rich, it can't have passed many booths.

The discoverers calculated that its source should lie within roughly a hundred million light years.

Beyond our galaxy, but practically our neighborhood, they called it strong evidence for a nearby source.

Then, two of them searched the catalogue straight back along its path and found, in their words, no likely astrophysical source. If it came from close by, where's the gun?

In 1984, the astrophysicist, A. M. Hillis, pointed out a simple rule.

Natural throws charged particles with magnetic fields, like a hammer thrower spinning before the release.

And a field can only keep pushing while it can hold on.

To throw something this hard, you need a magnet that is either incredibly strong or incredibly big.

So every suspect has to pass three tests. Is it powerful enough? Is it close enough? And does it sit where the particle came from? come?

Our own galaxy fails the first test.

Its magnetic field is far too weak to hold particles like these, and the most energetic cosmic rays lean away from its center. Crossed out. Now climb from small to big.

The expanding shells of exploded stars, like Cassiopeia A, fail the first test too.

They make the ordinary rain, but even the most generous Centaurus calculation falls more than 60 times short of our particle, crossed out.

Giant black holes firing jets from the hearts of galaxies, like Centaurus A, pass the first two, a perfect machine on paper and close by.

But traced straight back, Centaurus A fails the third.

It sits on the far side of the sky from where our particle came in.

Galaxies bursting with newborn stars, like M82, the cigar galaxy, are the best statistical hint we have.

But M82 sits 37 degrees off our particle's path, set it aside.

And the giants, the glowing lobes of radio galaxies, are, on paper, the best fit of all.

But the textbook example, Cygnus A, is 760 million light -years away.

day. It fails the second test.

Far too many toll booths. Most of these suspects aren't proven innocent. They just don't fit.

Trace the particle straight back and nothing in that direction is close enough or powerful enough to have fired it.

Then in the early hours of May 27th, 2021, a much bigger detector in the same desert caught one that came close, about 240 quintillion electron volts.

The University of Utah compared it to a brick dropped on your toe.

The researchers named it Amaterasu after the Shinto Sun Goddess.

It appears to come from the local void, a region with almost no galaxies.

The team's paper offered three explanations, stronger magnetic bending than we think, a nearby source we haven't spotted, or a gap in our physics.

Toshihiro Fuji, who led the study, said in Osaka Metropolitan University's announcement that no promising astronomical object matches its direction, suggesting, in his words, possibilities of unknown astronomical phenomena and novel physical origins beyond the standard model.

In the University of Utah's announcement, Telescope array physicist John Matthews said that for both particles, you trace the path back and find nothing powerful enough. What the heck is going on?

And just like in 1991, nobody knows what this particle was.

The detector ruled out a gamma ray, but couldn't tell a proton from a heavier nucleus.

So how do you find the gun when you don't even know what it fires?

One clue comes from the South Pole.

A sky full of high -energy protons should also make a faint trail of neutrinos, the way a fire makes smoke.

In 2025, IceCube, a neutrino detector buried in the ice there, looked for that smoke, found none, and concluded that, under standard assumptions, protons can be at most about 70 % of the highest energy cosmic rays.

Other measurements suggest most of them are heavier nuclei, though exactly which is still debated. And the 1991 particle?

The one that 1994 article called a proton?

Its discoverers wrote that it could have been a proton, a heavy nucleus, or even a gamma ray. That hasn't changed. Here's the twist. We may not even know what hit us.

is, every race against light in this video assumed a proton.

If it was an iron nucleus, it was a heavier bullet, a little slower.

Light would gain its centimeter in about 80 years.

And at the same energy, magnetic fields bend iron about 26 times more than a proton, so its path could have been bent far off course.

In January 2026, a team at the Max Planck Institute for Physics simulated Amaterasu's journey through magnetic fields, assuming it was an iron nucleus, and found that nearby galaxies, such as M82, could have launched it.

Yes, the galaxy we set aside for the 1991 particle is back, this time for the 2021 one. Other teams have suggested other options.

The authors themselves point out that if the particle turns out lighter or its energy is pinned down more precisely, the answer swings back toward the void.

So far, no other team has confirmed it.

So after all these years, how close are we to the gun?

Next week marks 35 years since that night in the Utah desert.

The oh my god particle is still the most powerful particle ever measured.

It arrived far beyond the limit physics predicted. And no confirmed source has been found.

not for the 1991 particle and not for the one in 2021.

Now zoom all the way back in to you.

The same rain is passing through you right now.

Somewhere out there is something that can throw a single particle with tens of millions of times the energy of our best machine's protons or something we don't yet understand.

For another particle story, watch our video, The Most Dangerous Particle in the Universe.

In 1991, a detector in the Utah desert caught one bullet.

Since then, hundreds more particles have crossed the limit, and not one has beaten it.

We keep catching the bullets, we have never found the gun.