Check Digit

I check numbers.

That’s the whole job, in five words. Verification technician, the Institute calls it. I sit at a terminal and make sure the numbers in the big table are the numbers the physicists think they are.

It’s a living. It’s also why I know about check digits.

Here’s how a check digit works. Take a number. Do a little arithmetic on its digits, add them, multiply them, juggle them, and you get a new digit. Append it. Now the number carries its own proof of identity. Mistype one digit and the check fails, and any machine can see something’s wrong with it.

Credit cards have them. Catalog numbers. Serial numbers. Anything that gets made, stamped, and sold, so the clerk can tell the genuine article from a forgery at a glance.

The table doesn’t have them. The table is the constants. c, h, e, the fine-structure constant. The numbers the universe was born with. They’re measured, not assigned. Nobody stamps them. When they go into the table, my department appends a check digit, computed from the digits, so a typo can’t turn a measurement into garbage.

That’s me. The typo catcher.

The cosmological constant sits in the table under Lambda. It’s the smallest number in physics. 1.1056 times ten to the minus fifty-two. So small you’d need a microscope to read it. It’s the number that says the universe is picking up speed. Dark energy. You’ve read the headlines. Nobel, front pages, the works. My department’s job is to make sure the headline’s number is the right number.

Four years I’ve had this job. I caught one typo, and it was mine.

Last Thursday I got bored.

I wrote a new routine. A joke, mostly. The regular routine verifies the check digits we append. The new one worked the other way. It stripped those digits off and ran the bare digits underneath through the check, the same check a credit card has to pass. A stamped number balances. A measurement doesn’t have to. Run a constant through it and it fails. The routine was built to fail on anything that wasn’t stamped.

I ran the table through it for laughs. c, fails. h, fails. G, fails. I threw in Pi for the hell of it. Fails.

Lambda passed.

I laughed. Ran it again. Passed. I ran the strong check, the one with the eleven in it. Passed. Ran it backwards. Passed. A random number passes one check in ten. Three checks, three ways. That’s not random.

A number only passes a check digit if somebody built it to pass. No measurement was ever built to pass.

I called my boss at home and went back to the office to wait. By midnight there were eleven men in the verification room, and none of them were from verification.

Saturday they told us what it meant. Flat, no poetry. The cosmological constant is not a measurement. It’s a serial number. The digits were assigned, not measured. Somebody made a universe and stamped the number on the outside, the way a refrigerator has a plate on the back. They’d cracked the format. The significand reads model and unit. The exponent reads the batch.

Model 1056. Unit 1. Batch 52.

Unit 1. First one off the line.

Genuine, they said. The check digit checks. We’re the genuine article. The number is exactly what it claims to be.

Then they found the catalog.

Model 1056 is called an expansion model. That’s the name, not a description. The spec says an expansion model expands. It starts small, it gets big, and it ends. The spec has a word for the end, coded as dispersed, empty, even. Nothing moving, because nothing’s left. Not a malfunction. That’s the model. The check digit says ours is doing it perfectly, to spec. Every galaxy in the sky is running from us at the speed the spec requires.

Then the bulletin.

Batch 52 was recalled. All units. The bulletin is dated, and the date is the beginning. Thirteen point eight billion years. They stamped the recall before the units had run a second. It says the units show expansion beyond tolerance. The defect is the expansion. The thing that won us the Nobel got us recalled.

It says return the unit. Do not operate. Return for disposal.

And here’s the part the men in chairs sat on for a week. The bulletin has a line in fine print. Every unit in batch 52 is to be returned. Every unit but one.

Unit 1 is to be retained in service pending verification.