Is anything forever?

Is anything forever?
Originally published 10 April 1989

In this day when every­thing seems to break down the day after the war­ran­ty expires, it would be nice to know that some­thing lasts for­ev­er. Unfor­tu­nate­ly, sci­ence seems deter­mined to remove the last ves­tiges of per­ma­nence from the universe.

Stars burn out. Con­ti­nents split and drift. Entire races of ani­mals become extinct. Just ask the dinosaurs. Every­where around us, or so it seems, atoms are falling apart — radon, ura­ni­um, stron­tium 90 — zap­ping us with radi­a­tion. There’s a hole in the ozone. Green­house warm­ing promis­es to melt the polar ice­caps. The Rock­ies will crum­ble, Gibral­tar will tum­ble, they’re only made of clay, and — the song notwith­stand­ing — not even love is here to stay.

Sure­ly, some­thing, some­where endures forever?

How about the pro­ton? Yes, the pro­ton — that lit­tle basic build­ing-block of mat­ter, the most sol­id and sen­si­ble par­ti­cle in the uni­verse. Some­day our sun will die, swelling up to become a red giant and then col­laps­ing heav­i­ly upon itself, but the sun’s pro­tons will stay intact. Some­day you and I will turn to dust, but every pro­ton in our bod­ies (oh, rough­ly 10 bil­lion bil­lion bil­lion) will find some oth­er home.

Around since the beginning

If we under­stand these things right­ly, all pro­tons in the uni­verse today have been around since the first frac­tion of a sec­ond after Cre­ation, when the fun­da­men­tal par­ti­cles of mat­ter con­densed from the flash of the Big Bang. Not long ago physi­cists thought pro­tons would last till the end of time. Now, they’re not so sure. The immor­tal­i­ty of the pro­ton has been called into question.

In under­ground cav­erns all around the world, in Japan, Europe, the Unit­ed States, and the Sovi­et Union, physi­cists are watch­ing for pro­tons to dis­in­te­grate. In this coun­try, the most impres­sive “watch-a-pro­ton-die” exper­i­ment is half-a-mile under­ground in a salt mine near Cleve­land. A huge rec­tan­gu­lar cav­ern is filled with 8,000 tons of water, watched over by 2,048 super-sen­si­tive elec­tron­ic eyes. If a pro­ton falls apart, releas­ing a spray of fast-mov­ing parts, flash­es of light in the tank will announce the event.

But why should pro­tons die? The answer basi­cal­ly is this: Why not? Per­ma­nence is out of fash­ion in sci­ence today. Accord­ing to the new dis­pen­sa­tion, we live in a rag­ing Her­a­clitean fire; every­thing is in flux.

There are good the­o­ret­i­cal rea­sons to believe that pro­tons have finite life­times. Physi­cists, in imi­ta­tion of nature, can pro­duce a whole zoo of exot­ic par­ti­cles — muons, mesons, pio­ns, and so on — and all of them quick­ly decay into less mas­sive com­po­nents. A muon, for exam­ple, falls apart into three par­ti­cles — an elec­tron, a neu­tri­no, and an anti­neu­tri­no. Cer­tain things, of course, remain con­stant in any such dis­in­te­gra­tion, such as the total mass-ener­gy and elec­tric charge.

It is pos­si­ble to imag­ine accept­able ways a pro­ton might decay — into a positron and a pion, for exam­ple. And if nature has no good rea­son for pre­vent­ing it, then why does­n’t it hap­pen? Why does­n’t the whole world of ordi­nary mat­ter just dis­in­te­grate into a show­er of parts?

The the­o­ret­i­cal physi­cists who are seek­ing to uni­fy the forces of nature (with so-called “grand uni­fied the­o­ries,” or GUTs) think they have the answer. Their the­o­ries pre­dict that a pro­ton should live 10 thou­sand bil­lion bil­lion bil­lion years, give or take a fac­tor of 10. That’s long even by Methuse­lah’s stan­dard, but it’s not eter­nal. Cer­tain­ly it’s long enough to keep the uni­verse from pre­ma­ture­ly falling apart.

Getting to the nub of it all

If pro­tons last so long — vast­ly longer than the present age of the uni­verse — then why should we care whether or not they are immor­tal? The answer has to do with the GUTs of the uni­verse. If we can deter­mine the life­time of the pro­ton, we will be clos­er to answer­ing the old­est ques­tions of all: How did the uni­verse begin and how will it end?

So physi­cists have gone under­ground to wait and watch for decay­ing pro­tons — under­ground to keep cos­mic rays (high-ener­gy par­ti­cles from space) from fool­ing their detec­tors. The pre­dict­ed pro­ton life­time of 10 thou­sand bil­lion bil­lion bil­lion years is an aver­age, so if you have 10 thou­sand bil­lion bil­lion bil­lion pro­tons one of them should die every year. To get a worth­while count, how­ev­er, one needs even more pro­tons than that, which is the rea­son for the 8,000 tons of water.

So far, not one pro­ton has been observed falling apart. Maybe the pro­ton has a longer life­time than some peo­ple thought. Or maybe it’s immor­tal. Either way, physi­cists would like to know.

Ques­tions about the begin­ning and end of the uni­verse have always occu­pied human minds. Curi­ous­ly, one of the best ways to answer these ques­tions today is to go down in a deep hole and watch big tanks of water. Of course, one does­n’t actu­al­ly watch; the human eye is not near­ly sen­si­tive enough to see a pro­ton decay. The eyes that watch are elec­tron­ic, and the brains that ana­lyze what the eyes see are com­put­ers. But the brains that ask the ques­tions — the great and deep philo­soph­i­cal ques­tions about where the uni­verse came from and how it will end — are human.

Mean­while, don’t bet on pro­tons last­ing for­ev­er. If you need some­thing absolute­ly endur­ing in your life, put your mon­ey on elec­trons. Appar­ent­ly elec­trons don’t fall apart because there are no lighter par­ti­cles with neg­a­tive charge, and there­fore no way for the total charge in a dis­in­te­gra­tion to stay con­stant. For the time being at least, it seems that elec­trons are here to stay.


To date, despite decades of exper­i­men­ta­tion, there has not yet been any suc­cess­ful obser­va­tion of pro­ton decay. ‑Ed.

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