A Decay a Trillion Times Longer Than the Age of the Universe—Neutrinoless Double-Beta Decay May Hold the Answer to Why We Exist

1. A change a trillion times longer than the universe’s age

A few days ago, I read a news report saying China is accelerating plans for an experiment called “neutrinoless double-beta decay” at the Jinping underground laboratory in Sichuan.

One line of the accompanying text said:

This is the slowest process in nature.

Its half-life is a trillion times longer than the age of the universe.

The universe is 13.8 billion years old. That part is simple; we all know it.

Now multiply that by a trillion.

After so long, the universe itself might no longer be “alive.”

When we say “a hundred years from now,” it already carries the desolation of a human lifetime;

“A thousand years ago” already has the dust of history;

“Hundreds of millions of years” sounds like we are discussing the fate of mountains, oceans, and stars.

On this scale, every human adjective for time feels weightless.

How could scientists possibly know?

None of us can live until that day. Could they simply have made up a number to fool us?

But following this question farther, we discover that its endpoint is not physics, but something I have wondered about all my life:

Why do we exist?

Neutrinos sound tiny, even from their name.

How could they relate to the vast universe—to the enormous question of why our entire world exists?

2. The slowest change in the entire universe

To understand this story, we must first meet two characters.

The first is beta (β) decay.

Protons and neutrons live inside atomic nuclei. Protons carry positive charge; neutrons carry none.

Sometimes a neutron “changes its mind”: it turns itself into a proton, throwing out an electron and an antineutrino at the same time.

This is governed by the weak interaction, the weakest of nature’s four fundamental forces.

“Weak” is not a figure of speech. It really is weak, so this happens extremely slowly.

The second character is double-beta decay.

Its requirements are much stricter.

For some special nuclei, a single change of heart is strictly forbidden by energy conservation. Their only way out is for two neutrons to change their minds together at the same instant, ejecting two electrons and two antineutrinos.

An analogy:

Single-beta decay is like tossing a coin that happens to stand on its edge on a table.

Double-beta decay requires tossing two coins simultaneously: both must stand upright, and they must also collide perfectly in midair.

How low is that probability?

An atom might have to wait 10²¹ years for its turn.

But scientists cannot live for 10²¹ years. How do they “see” it?

The answer is simple:

Strength in numbers works miracles.

If you have only one nucleus with a half-life of 10²¹ years, you will indeed probably never see it decay.

But if you have a huge number of nuclei, everything changes.

We learned Avogadro’s constant in high school: one mole contains 6×10²³ atoms.

A commonly used isotope at Jinping is xenon-136. 136 grams is one mole.

Prepare several tons of this material, and the number of atoms reaches the order of 10²⁶.

What happens when a decay probability as tiny as 10⁻²¹ is multiplied by a base as enormous as 10²⁶?

In this material, dozens to hundreds of decays still happen every year.

A scientist need not wait until the universe ends.

They need only spend a year beside the detector, count its flashes, and work backward with simple division to calculate that half-life a trillion times longer than the universe’s age.

The fate of an individual atom

is diluted by immense numbers into measurable statistics.

But the story does not end there.

The real difficulty is silence.

Earth’s surface is full of background noise.

Cosmic rays are constantly falling. Granite contains traces of uranium. Radon drifts through the air. Even the potassium-40 in our bodies quietly emits signals.

A few dozen real decays a year would be completely drowned in this surging background noise.

So scientists have only one path left:

Escape the surface and go somewhere absolutely quiet.

The Jinping underground laboratory is built beneath 2,400 meters of mountain rock, in Liangshan Prefecture, Sichuan.

The cosmic-ray intensity there is only one hundred-millionth of that at the surface.

Humanity buries its most precise instruments in Earth’s deepest darkness just to witness the rarest loosening of nature’s laws, then wait for the moment when a nucleus gently changes its own fate.

3. Does God really play dice?

At this point, you may ask: Is this decay genuinely random, or have we simply not found its pattern yet?

If there were a pattern, we could prepare in advance and wait for the event, instead of working so hard to find a needle in a haystack.

This question sparked the fiercest fight in twentieth-century physics.

Most “randomness” in everyday life is actually fake.

Coin tosses and dice rolls look unpredictable. But if you knew the force and angle of release, air resistance, and the table’s elasticity, you could theoretically calculate the outcome using Newtonian mechanics.

This randomness arises only because we do not have enough information.

But the quantum world gave an answer that made everyone uncomfortable:

Its randomness is an intrinsic property of the universe.

No hidden clock determines whether a nucleus decays now or ten thousand years later.

Before it actually happens, it is nothing definite—only a cloud of probability.

Einstein deeply disliked this idea. He left the famous line quoted ten thousand times:

God does not play dice.

His bet was that quantum mechanics was incomplete: atoms must contain some secret we had not discovered—hidden variables.

This wager lasted decades, until a physicist named Bell proposed a mathematical criterion that experiments could test.

For the next half century, laboratories around the world pushed this criterion to its limits again and again. The 2022 Nobel Prize in Physics went precisely to the pioneers of this work.

All experiments point in the same direction:

Einstein lost.

The world does not appear random merely because we are ignorant.

At least within the range we can reach, the universe really does roll dice at its foundation. It really contains irreducible probability.

When I first read this history, I felt a kind of sadness.

Einstein is my favorite physicist. He was not insufficiently clever. He simply wanted too badly to preserve a certain world—one where everything has a reason and every outcome can be deduced.

But the universe refused.

It left a crack in its deepest place, and genuine randomness lives inside that crack.

This crack is about to become the central character of the whole story.

4. The missing-antimatter mystery: We should not exist

Now pull the camera back from the nucleus, back to the Big Bang 13.8 billion years ago.

A huge cloud hangs over physics: the mystery of missing antimatter.

According to current theory, in the Big Bang’s first moments, energy turning into matter must obey an iron rule:

Whatever amount of matter is produced,

an equal amount of antimatter must be produced at the same time.

0 = 1 + (-1)

When matter and antimatter meet, they instantly annihilate, becoming pure energy again.

1 + (-1) = 0

If this iron rule were carried out without exception, all matter and antimatter should have destroyed each other in pairs shortly after the Big Bang.

Today’s universe should have been a dead-silent sea of light:

No galaxies, planets, or oceans. No you reading this article, and no me writing it.

Yet we exist.

There are galaxies in the night sky, rocks beneath our feet, and carbon, oxygen, iron, and calcium in our bodies.

This means that in that long-vanished instant, matter exceeded antimatter by roughly one part in a billion.

After every billion matter-antimatter pairs destroyed each other, one matter particle remained, standing alone.

That leftover “one part in a billion”

supports the whole universe we have today.

Where did this one-in-a-billion “unfairness” come from?

Who secretly pressed down on the scales in that instant?

Physicists fixed their suspicion on a particle that looked least like a suspect: the neutrino.

If the particle world were a city:

Electrons would be pedestrians coming and going through its streets.
Protons and neutrons would be sturdy building materials.
Neutrinos would be ghosts.

They pass through everything without knocking, stopping, or leaving much of a trace.

Neutrinos are so light they have almost no mass, so reclusive they barely interact with matter.

At this moment, tens of billions of solar neutrinos are passing unnoticed through your body.

But the Italian physicist Majorana made a conjecture so bold it was almost poetic:

A neutrino is its own antimatter.

Ordinary particles have a strict distinction between matter and antimatter, like two sides of a coin.

But the neutrino might be an exception: both heads and tails.

It can move back and forth between matter and antimatter, giving it the ability, in the universe’s first instant, to secretly tilt the scales just a little.

Ordinary double-beta decay:

0 = 2 + (-2)

Neutrinoless double-beta decay:

0 → 2

This conjecture was beautiful enough to move physicists, but for more than eighty years it remained a conjecture nobody could prove.

Until people realized there was an experiment that could settle it decisively.

5. The decisive blow buried underground

Neutrinoless double-beta (β) decay.

Ordinary double-beta decay ejects two electrons and two antineutrinos.

But if Majorana was right, the two antineutrinos that should have been ejected would recognize each other as their own antimatter inside the nucleus, destroy each other on the spot, and vanish.

Outside, the detector would see only two electrons.

No neutrinos.

Not even one.

If an experiment genuinely observed such an event—even just once—

The conjecture that a neutrino is its own antiparticle would be confirmed.
The golden rule of lepton-number conservation would be broken.
A tear would open in the Standard Model, modern physics’ strongest building.

And cosmology’s crucial missing puzzle piece—why any matter remained after the Big Bang—would quietly fall into place.

For the first time, humanity could answer its oldest question in the language of physics:

Why do we exist?

This is what the Jinping laboratory is doing.

This is why several tons of xenon-136 must be buried beneath 2,400 meters of mountain.

This is why the world’s leading physicists are racing.

They are waiting for a light.

A light that might flash only a few times a year, originating at the universe’s beginning, so faint it almost does not exist.

The circle is tightening year by year.

That moment may very well arrive within the next decade.

It is like a letter the universe spent 13.8 billion years writing before sending to humanity.

And the letter might say:

You can exist

because I once showed a little favoritism.

6. Light is the universe’s cleanest language

I suspect one small question remains unanswered in your mind:

Matter and antimatter annihilate and “become light”—what does that actually mean? Why can light represent energy?

This deserves a clear explanation.

Our bodies, tables, chairs, and stars—all things we can “see and touch”—have a property called rest mass.

Even an electron that is completely motionless carries its own mass.

But photons are different. Their rest mass is zero.

This means they cannot be still. From the moment they are born, they must race at the speed of light.

Once a photon is absorbed—for example, when sunlight falls on your black coat—it simply disappears from the universe, giving all its energy to the coat.

Einstein’s most famous formula is actually a simplified version. The truly complete form looks like this:

Substitute the photon’s value into it, and the formula reduces to an extremely simple form.

In other words, one hundred percent of a photon’s energy comes from its motion itself, without any contribution from rest mass.

So when matter and antimatter annihilate and mass “disappears” from the universe, energy must remain conserved. The energy is passed to photons, which carry all the original matter’s information outward in every direction.

Photons are like the universe’s messengers.

They have no weight, yet carry information, energy, and direction, arriving in our eyes from the far reaches of the universe.

The entire universe

relies on these weightless messengers

to speak to itself.

7. Where did the original energy come from?

If you follow this line of questioning, sooner or later you hit the wall:

Where did that first mass of energy

come from?

I must tell you honestly: current science cannot answer this.

Science is good at answering “how,” not so good at answering “why.”

This does not make science weak.

Quite the opposite: science’s most precious quality is knowing how far it has gone and where it has not yet arrived.

It does not disguise imagination as an answer, or describe the unknown as failure.

At the singularity where time equals zero, relativity and quantum mechanics both fail.

It is a mathematical dead end of infinite temperature and infinite density. Even the word “before” loses its meaning, like asking “What is farther north than the North Pole?”

At physics’ frontier, several hypotheses have been proposed.

Some say the universe is a quantum fluctuation: a quantum vacuum permits energy to be borrowed from nowhere for an extremely brief time.

And the positive energy of all matter, added to gravity’s negative energy, totals almost exactly zero. In other words, the universe might be a perfect case of “something from nothing,” owing nothing at all.

Some say our universe is merely a collision between two branes in higher dimensions. The Big Bang is the ripple that collision stirred in the three-dimensional world. These ideas relate to string theory and brane cosmology.

Some say time has no beginning at all. The universe cycles through countless expansions and contractions, and we merely happen to be in its expansion phase.

These hypotheses all make some sense, but only some.

They remain within mathematics, untouched by experiment.

Human reason hits its ceiling here.

Reason is both great and small.

The position of being human lies precisely where that greatness and smallness are simultaneously true.

Using a few tons of liquid 2,400 meters underground, we can infer the laws of decay over 10²¹ years, and reach back across 13.8 billion years to test the universe’s original favoritism;

Yet we cannot answer why it began.

A hundred, a thousand, ten thousand, even hundreds of millions of years from now, if humanity still exists, people will remain trapped by this same question.

Perhaps they will casually transform planets, travel between galaxies as though taking a walk, and let carbon and silicon breathe within the same body;

They will journey at light speed, no longer chased by time, no longer treating death as fate.

Black holes, dark matter, and dark energy will be no more than childhood exercises to them.

They will view us as ancient children who have only just learned to count.

But returning to this question, they too will be no closer to an answer:

Why does the world truly exist?

It is not that science is insufficiently developed or thought insufficiently profound. It is that a person standing inside the universe can never clearly ask about what lies outside it.

Our perspective has been locked inside from birth.

This is the paradox of existence.

Still, that is not so bad.

Precisely because the ultimate answer is always absent, it becomes a spiritual refuge shared by all humanity.

Every generation has mornings of despair, unbearably boring afternoons, and nights of heartbreak.

At such moments, looking up at the stars and having an enormous, insoluble question to keep you company while you daydream is a kind of good fortune.

Otherwise, if some generation truly completed the universe’s open-world game, wouldn’t later players lose even the pleasure of exploration, left at the finish line to complain:

“That’s it?”

8. Absolute symmetry is another kind of death

I find neutrinoless double-beta decay fascinating not merely because it is cutting-edge, or difficult.

It connects two things on radically different scales.

At one end is an extremely tiny, rare, almost nonexistent event inside an atomic nucleus.

At the other is why the whole universe did not become a sea of light, why matter remained, why life exists.

It is like a thread so fine it is almost invisible, stretching from the darkness 2,400 meters underground to the universe’s dawn 13.8 billion years ago.

Following that thread, let us return to the very first instant.

If matter and antimatter were perfectly symmetrical, the universe would be an ocean of light.

Perfect, pure, eternal, quiet—and utterly lifeless.

That “one part in a billion” of imperfection gave the universe life.

That chance roll of the quantum dice allowed matter to remain.

That crack running through the universe’s deepest place let stars burn, oceans surge, and life open its eyes.

Since childhood, we have been taught to pursue perfection, certainty, and order.

Yet at its beginning, the universe demonstrated something else:

It was precisely that small imperfection,

that uncertainty, that disorder,

that allowed everything to happen.

Absolute symmetry is annihilation.

Absolute certainty is stagnation.

Absolute order is death.

And in that tiny, random, almost nonexistent crack live all possibilities.

Including you.

Including me.

Including us, asking these questions right now.

We do not stand outside the universe, coldly watching its fate.

We are within it.

More precisely:

We are the universe itself.

This is both desolate and comforting.

Desolate because the universe did not write everything in advance: why you came, where you will go, what your life means. It did not begin for humanity, and it will not stop for humanity.

Comforting because meaning may not be a starting point, but a relationship that emerges afterward.

When light leaves a star, it does not know whose eyes it will enter.

When a seed falls into soil, it does not know which tree it will become.

When a river runs toward the distance, it does not know on which morning it will reflect the sky.

They still depart, still grow, still flow.

People are the same:

We do not keep living because we have discovered meaning.

The act of continuing to live itself generates meaning.

9. Hear the Way in the morning, and one may die that evening

We are not born to seek knowledge.

We first come into this world merely to survive: eat, sleep, reproduce, avoid danger.

These are life’s first instructions, simple and powerful.

But humans are strange creatures.

During the long struggle to survive, some people slowly developed a desire unrelated to survival:

They wanted to know.

Why stars shine.

Where matter comes from.

Why they are alive.

These questions cannot give them another mouthful of food or another day of life, yet they refuse to stop.

It was these people who could not stop who looked up at the moon more than two thousand years ago and wrote, “Today’s people cannot see the ancient moon, yet today’s moon once shone upon the ancients”;

It was these people who could not stop who pointed a telescope at Jupiter four hundred years ago and discovered its four moons;

It is these people who cannot stop who bury themselves in darkness 2,400 meters deep to capture an echo from the universe’s beginning that flashes only a few times a year.

They trade a lifetime for an answer.

Confucius said, “If I hear the Way in the morning, I may die that evening.”

I used to think this was metaphorical.

How could anyone exchange an entire life for one morning’s insight?

But now I understand.

This sentence is not about death, but about what is worth it.

If something makes you willing to treat “obtaining it” as reason enough to outweigh everything else, that thing is your “Way.”

It may be something large—

The origin of the universe, the truth of life, a great truth.

Or something small—

A person you have never been able to forget,

Something you are willing to do for a lifetime,

A landscape you want to protect.

It does not need to be understood by anyone.

It only needs to be confirmed by you.

A small dictionary

If these terms ever stopped you

Responsible only for making you understand in a second, not for helping you pass a physics exam.

Beta decay (β decay)

A neutron changes careers and becomes a proton, producing two “attachments” along the way.

Double-beta decay

Two neutrons submit job-transfer requests together. The approval process is so long that even the universe finds it slow.

Neutrinoless double-beta decay

The application is submitted, but the attachments vanish. Physics begins to suspect someone modified the system.

Half-life

Physics’ fig leaf for abandoning predictions of individual fate. You never know exactly which atom will expire on which day, but you know precisely that after this interval, half the stock will have gone bad.

Neutrino

The universe’s invisible person. It came, did not knock, and left no name.

Antimatter

Matter’s mirror image. When they meet, they return to zero as light.

Hidden variables

The official physics term for “There must be an inside story.”

Standard Model

A building one pillar—gravity—short of completion.

Quantum fluctuation

An interest-free microloan in the vacuum.

Singularity

A synonym for a physicist saying, “I can’t keep making this up.”

Symmetry breaking

The universe’s first “unfairness.” Fairness disappeared, and everything else appeared.

The paradox of existence

An eye cannot see itself.

Meaning

A small lamp carbon-based creatures light for themselves in a desolate universe.

Why does the world exist?

The beyond-the-syllabus question shared by all humanity.

The only question every generation can attempt again simply by looking up at the stars.