It all adds up to a very Big Bang

Originally published 27 May 1996

“Pro­fes­sor, that stuff you spoke of in class this morn­ing — about the begin­ning of the universe…”

Yes?

“Well, you know how you said that the uni­verse began 10 or 15 bil­lion years ago as an infi­nite­ly small point…?”

Yes, that would appear to be the case. An explo­sion from a point of infi­nite ener­gy. Space and time expand­ing from noth­ing. Mat­ter coa­lesc­ing from cool­ing radi­a­tion. Stars, galaxies…

“To tell the truth, I’m hav­ing a hard time believ­ing it. I mean, the idea that every­thing that exists today, the bil­lions and bil­lions of galax­ies, stars, and plan­ets, life, every­thing, was con­tained with­in some­thing no big­ger than a pin­prick. I mean, come on…do you real­ly expect me to swal­low that?”

You will recall that I list­ed some pret­ty con­vinc­ing evi­dence: The galax­ies are rac­ing apart, as from a pri­mor­dial explo­sion; the amount of hydro­gen and heli­um in the uni­verse is just what the­o­ry pre­dicts for a Big Bang begin­ning; and, not least, we see the flash of the Big Bang in every direc­tion of space, with pre­cise­ly the pre­dict­ed characteristics.

“Yeah, I know. I under­stand most of that stuff. But I keep com­ing back to the idea of the whole uni­verse con­tained with­in a pin­prick. I mean, it’s impos­si­ble to imagine.”

It is dif­fi­cult to imag­ine, I’ll grant you. But not impos­si­ble. Math­e­mat­i­cal­ly it works out. Math­e­mat­ics is a big help to the imagination.

“It sounds impossible.”

Let me tell you a sto­ry. More than 2,000 years ago in Alexan­dria, Egypt, there were two fel­lows, named Eratos­thenes and Aristarchus. They were excel­lent mathematicians.

Eratos­thenes was a geo­g­ra­ph­er. He imag­ined that the Earth was a sphere. He fig­ured out how to mea­sure the size of the sphere by using shad­ows cast by the sun at Alexan­dria and anoth­er place down the val­ley of the Nile. He used some math­e­mat­ics that at the time was pret­ty advanced stuff — geom­e­try, trig.

He cal­cu­lat­ed the size of the Earth and got it near­ly dead-on, with­out ever leav­ing Alexan­dria. That’s what I mean about math­e­mat­ics being an aid to the imagination.

Then Aristarchus used the size of the Earth to fig­ure out the sizes and dis­tances of the sun and the moon. He observed eclipses of the moon, and mea­sured the time it takes the moon to move through the shad­ow of the Earth. Then he did some high-pow­ered math­e­mat­ics with cir­cles and tri­an­gles. Accord­ing to his cal­cu­la­tions, the sun is many times big­ger than the Earth.

Aristarchus told his fel­low Alexan­dri­ans about his dis­cov­ery. If the Earth is the size of a grape, he may have said, then the sun is the size of a mel­on. They laughed. Any fool can see that the sun is tiny com­pared to the vast, wide Earth. Why, for heav­en’s sake, one can cov­er up the sun with the tip of one’s lit­tle fin­ger, but trav­el across the Earth for weeks with­out ever leav­ing Egypt.

The sun big­ger than the Earth? No way, it was sim­ply impos­si­ble to imagine.

“But…”

And Aristarchus got one cru­cial obser­va­tion wrong, through no fault of his own. In fact, the rel­a­tive sizes of the Earth and sun are more like a grape and a wash­ing machine, some­thing every school child accepts today.

The moral of the sto­ry is — the “impos­si­ble” can turn out to be true.

“But the whole uni­verse con­tained with­in a pin­prick? It vio­lates com­mon sense.”

Ein­stein once said that com­mon sense is the col­lec­tion of prej­u­dices we acquire by age 18. I’m not telling you to believe the Big Bang if you don’t want to, but keep your options open. One gen­er­a­tion’s impos­si­bil­i­ty often turns out to be the next gen­er­a­tion’s com­mon sense.

“You’re ask­ing me to take it on faith?”

Yes, on faith. But not on blind faith. As we saw this morn­ing, there is impres­sive obser­va­tion­al evi­dence. The cal­cu­la­tions are based on Ein­stein’s gen­er­al the­o­ry of rel­a­tiv­i­ty, which has many impor­tant suc­cess­es to its cred­it. Then there’s the record of suc­cess by the suc­ces­sors of Eratos­thenes and Aristarchus. Just think of all the sci­en­tif­ic dis­cov­er­ies that were thought to be non­sense in their time. The Earth going around the sun. The evo­lu­tion of life over bil­lions of years. A chem­i­cal blue­print for a human being in the DNA of a sin­gle micro­scop­ic cell.

And besides, it’s a won­der­ful, won­der­ful sto­ry — a uni­verse unfold­ing from a math­e­mat­i­cal point!

“Yeah, it’s an won­der­ful sto­ry, all right. But…”

But?

“But I still don’t believe it.”