Telescopes seek blasts from past

Originally published 12 December 2000

To be human is to be inter­est­ed in origins.

Every human cul­ture has had sto­ries of cre­ation, hand­ed down gen­er­a­tion to gen­er­a­tion from sup­posed ances­tors who were wit­ness­es to the orig­i­nal events, or who were told of the begin­ning by ani­mals or gods.

Then, 200 years ago, humankind made an epic dis­cov­ery: The world is vast­ly old­er than humans and ani­mals. All of human his­to­ry is a blink in cos­mic time. The cre­ation hap­pened bil­lions of years ago, long before there were sen­tient beings to record the rel­e­vant stories.

So, is the cre­ation beyond reach of human know­ing? A time machine would be nice, a way to trav­el back to the begin­ning and wit­ness for our­selves exact­ly what hap­pened. As a mat­ter of fact, such time machines exist. They are called telescopes.

When we look with our tele­scopes into the depths of the cos­mos, we are also look­ing back in time. Because light trav­els with a finite veloc­i­ty — 186,000 miles per sec­ond — it takes time for the light of dis­tant objects to reach us. When we see a galaxy 2 bil­lion light-years away, for exam­ple, we are see­ing that galaxy as it exist­ed 2 bil­lion years ago Earth-time.

And since we live in a typ­i­cal cor­ner of a uni­verse that is gov­erned every­where by the same phys­i­cal laws, that far-away galaxy pre­sum­ably looks pret­ty much like our own galaxy might have looked 2 bil­lion years ago.

If the uni­verse evolves, then we will see the changes as we look into deep space. And if the uni­verse had a begin­ning, then the cre­ation should be vis­i­ble if we look deep enough into time.

When it comes to using tele­scopes as time machines, big­ger is bet­ter. The big­ger the mir­ror of a tele­scope, the more light it col­lects, and there­fore it is pos­si­ble to see more dis­tant, fainter objects. And the big­ger the mir­ror of a tele­scope — all oth­er things being equal — the sharp­er will be the images that we see.

But all oth­er things are nev­er equal. To sharply focus light of a dis­tant object, a tele­scope mir­ror must have a cur­va­ture that is accu­rate to a few tens-of-thou­sandths of an inch. Main­tain­ing that accu­ra­cy means rigid­i­ty, and rigid­i­ty gen­er­al­ly means bulk. But bulk means weight, and weight means sag. Bulk also means dis­tor­tions due to tem­per­a­ture inequal­i­ties. All of which throw an image out of focus.

Assum­ing these prob­lems of grav­i­ty and tem­per­a­ture can be solved, there is still the tur­bu­lence of the Earth­’s atmos­phere. Look­ing out at the uni­verse from the sur­face of the Earth is like look­ing at clouds in the sky from the bot­tom of a sloshy swim­ming pool. For ground-based instru­ments, the sharp­ness of images is more often lim­it­ed by atmos­pher­ic dis­tor­tion than by optics.

Atmos­pher­ic dis­tor­tion can be elim­i­nat­ed by putting a tele­scope in space, which is why the Hub­ble Space Tele­scope, with a mir­ror less than 8 feet across, is cur­rent­ly out­per­form­ing the huge Keck 1 tele­scope on Hawai­i’s Mount Kea with a mir­ror four times wider. But putting tele­scopes in orbit and main­tain­ing them there is huge­ly expen­sive. The Next Gen­er­a­tion Space Tele­scope, now sched­uled for launch around 2009, will cost at least $1 bil­lion dollars.

Mean­while, cheap­er ground-based behe­moths are on the draw­ing boards, most dra­mat­i­cal­ly a Euro­pean ini­tia­tive for an Over­Whelm­ing­ly Large tele­scope, or OWL, with a mir­ror 100 meters in diam­e­ter. This is about 10 times wider than the biggest tele­scopes at work today, with a light gath­er­ing area 100 times larger.

There would be no point in build­ing such a scope unless astronomers were able to com­pen­sate for atmos­pher­ic dis­tor­tion, and for­tu­nate­ly a tech­nol­o­gy to do this is now avail­able, at least in prin­ci­ple. It is called adap­tive optics, and uses high-speed com­put­ers to instant-by-instant mod­i­fy the shape of a flex­i­ble mir­ror to com­pen­sate for atmos­pher­ic tur­bu­lence. The big new ground-based tele­scopes of the future will replace bulk with intelligence.

OWL will require super­com­put­ers many times faster than any that exist today, but the tele­scope’s design­ers are antic­i­pat­ing that com­put­er tech­nol­o­gy will keep up with their plans; pre­sum­ably, by the time OWL opens its pro­posed eye on the uni­verse, there will be com­put­ers fast enough to keep its eye in focus.

And what will OWL and the oth­er planned behe­moths see? Far­ther and deep­er into the abyss of time, to with­in a few hun­dred mil­lion years of the Big Bang. With luck, they will see the first stars and galax­ies being born out of the primeval mat­ter. They will find clues to how an ear­ly uni­verse of smooth radi­a­tion became a lumpy uni­verse of mat­ter. And maybe, just maybe, they will see things that no astronomer has antic­i­pat­ed, per­haps even things that will change our sto­ry of how it all began.

Big­ger, bet­ter tele­scopes are human­i­ty’s way of wit­ness­ing the creation.