Still, the X‑ray retains its hold on our imagination

Still, the X‑ray retains its hold on our imagination

Photo by Ricardo Esquivel from Pexels

Originally published 6 November 1995

Stout lit­tle X, with its feet plant­ed firm­ly on the ground and its arms uplift­ed in sur­prise, is our emis­sary to the unknown.

It was the philoso­pher René Descartes, in his book on geom­e­try in 1637, who first used x to stand for the unde­ter­mined vari­able in his equa­tions. Since then we have employed X as an alias when the true iden­ti­ty of a thing is unknown: the mys­te­ri­ous Mr. X, the crea­ture from Plan­et X, secret ingre­di­ent X.

And so it was that when Wil­helm Kon­rad Rönt­gen dis­cov­ered pen­e­trat­ing radi­a­tions of an unknown nature on Nov. 8, 1895, he called them X‑rays.

It turned out that the mys­te­ri­ous rays were not so mys­te­ri­ous as he at first imag­ined; they are of the very same nature as the rays that enter our eyes from the sun, only of a short­er wave­length. Rönt­gen had stum­bled into a pre­vi­ous­ly unex­plored part of the elec­tro­mag­net­ic spectrum.

We live in a sea of elec­tro­mag­net­ic waves, from the very long to the very short: AM radio, FM radio, tele­vi­sion, radar, microwaves, radi­ant heat­ing, vis­i­ble light, ultra­vi­o­let, X‑rays, gam­ma rays, cos­mic rays. The wave­length (dis­tance from crest to crest) of a typ­i­cal radio wave might be as long as a city block. A bil­lion X- ray waves can fit across the head of a pin.

What is it that is wav­ing? Elec­tric and mag­net­ic fields. What are elec­tric and mag­net­ic fields? Things that wave.

That did­n’t help much. Let’s try again.

What are elec­tric and mag­net­ic fields? The things that physi­cists rep­re­sent in their equa­tions by the let­ters E and B. What are E and B? The elec­tric and mag­net­ic fields.

Still unsat­is­fied? That is because you want to see or touch these waves, the way you see and touch waves in water or vibrat­ing piano strings. Can’t be done. Elec­tro­mag­net­ic waves are elec­tro­mag­net­ic waves — and that’s that. Not even physi­cists can tell you much more about them. We see the effects of these pre­sumed waves. The rest we make up. There’s a bit of Alice in Won­der­land in all of this. The grin with­out the cat. But it works.

Elec­tro­mag­net­ic waves are unde­ni­ably real. Turn on your radio. Thaw the ham­burg in your microwave. Look at the X‑ray pho­to­graph that your den­tist made. Nev­er mind that elec­tro­mag­net­ic waves seem spook­i­ly imma­te­r­i­al, evanes­cent, hard to describe in famil­iar terms. We use them. Our equa­tions pre­cise­ly describe their behav­iors. X goes forth in the world as respectable E and B.

The most famil­iar elec­tro­mag­net­ic waves are vis­i­ble light. Ten or 20,000 of these waves would fit across my thumb­nail. They are focused by the lens of the eye and detect­ed by the reti­na. We were born with elec­tro­mag­net­ic wave detec­tors to either side of our noses.

Our bod­ies are less dra­mat­i­cal­ly sen­si­tive to waves a lit­tle short­er than the vis­i­ble, called ultra­vi­o­let. These can change cells in our skin and give us a tan or skin can­cer. We are also sen­si­tive to waves a lit­tle longer than vis­i­ble, called infrared. We feel them as heat.

The rest of the spec­trum, stretch­ing away toward the very long and the very short, was X‑territory — until the late-19th century.

We fol­lowed X into the unknown. Down the spec­trum to longer and longer wave­lengths, and up the spec­trum to short­er and short­er wave­lengths. We learned how to pro­duce each kind of wave, turn it to our pur­pose. We learned how to detect those waves falling upon the Earth from space, and used what we detect­ed to dis­cov­er more about the uni­verse. For exam­ple, spe­cial tele­scopes placed in orbit above the atmos­phere detect Rönt­gen rays from deep space, con­firm­ing, among oth­er things, the pos­si­ble exis­tence of black holes. One of the most promi­nent black hole can­di­date is called, appro­pri­ate­ly, mys­te­ri­ous­ly, Cygnus X‑1.

We are crea­tures of X. We love our mys­ter­ies. When Rönt­gen announced his dis­cov­ery, the news spread like wild­fire. Pub­lic demon­stra­tions sprang up every­where. “Won­drous rays.” “See the bones in your hand.” “Count the coins with­in your purse.”

But now Rönt­gen’s mag­i­cal rays have become com­mon­place, threat­en­ing even. So we turn to oth­er sources of mys­tery. Black hole X‑1. Tele­vi­sion’s X‑Files. X marks the spot.

Rönt­gen’s rays have now been assigned to their appro­pri­ate place in the elec­tro­mag­net­ic spec­trum. They are as well-under­stood as the col­ors of the rain­bow. We should have long since giv­en them a name less sug­ges­tive of mys­tery: Rönt­gen-rays, per­haps, or more sim­ply, R‑rays.

But “X‑ray” march­es on, unmasked. The name retains its hold on our imag­i­na­tions, most like­ly because of the use of the rays in reveal­ing the inte­ri­or of the human body: the clots, can­cers, tumors, malig­nan­cies, and the skele­ton, that Hal­loween cos­tume we wear on the inside all year round, the caus­es and sym­bol of our mortality.

Death, with its grin­ning skull and crossed bones, is the deep­est of all unknowns — the ulti­mate and final X.

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