Allan Sandage died this month at age 84. While not generally known by the public, Sandage was legendary among those who study the sky. He was the successor to Edwin Hubble -- the amateur-boxer-turned-astronomer who made the astounding discovery that the universe is expanding.
Everyone knows about the Big Bang. (Well, almost everyone. I receive several e-mails a month from people who simply cannot believe that all existence began as a tiny pinprick). But a single lifetime ago, no one knew that the universe was in a state of explosion, with galaxies receding from one another as space expands like a middle-age paunch.
Hubble was the first to uncover this profound truth, which is often cast as the greatest scientific revelation of the twentieth century. He did so by measuring two simple properties for a sample of galaxies: their distances and how quickly they were moving away from us. In 1929, Hubble published a straightforward diagram that graphed results for two dozen nearby galaxies. His plot showed that the cosmos was crudely akin to the aftermath of a hand grenade explosion, with galactic shrapnel fleeing our vicinity as if we had bad breath.
This analysis implied something stunning. Using a bit of imagination and some simple arithmetic, Hubble ran the explosion backwards in his mind and calculated that the pin on the grenade had been pulled about 2 billion years ago. Before that, there was no universe.
Well, that was wrong. Even in 1929, scientists knew that the Earth was older than 2 billion years, so something was clearly fishy with Hubble's result. A few believed that the basic premise of a cosmic starting pistol -- a universe boiled up in a Big Bang -- was in error. But most figured that the difficulty was technical: Hubble had miscalculated the distances to his galaxies.
Hubble died suddenly in 1953, and his disciple Allan Sandage assumed the arduous task of getting better distance measures for galaxies -- objects that were 100 thousand times farther than the stars blinking above your head at night. For years, Sandage used the 200-inch telescope on Mt. Palomar to do this. Eventually, space-based observatories - including the orbiting telescope that bears Hubble's name -- were conscripted by Sandage's competitors in pursuit of the same goal. Determining accurate galactic distances is a black art, and one of astronomy's toughest enterprises, but the current estimate is that the time since the Big Bang is just shy of 14 billion years, or roughly three times the age of the Earth.
Measuring the correct age of the universe was difficult, but some astronomers have been busy with an even trickier effort: determining if the expansion is slowing down or otherwise.
Why should you care? Because gauging the changing rate of expansion might tell you the long-term fate of the cosmos. In particular, will it continue to expand indefinitely, or ease to a stop, shift into reverse, and doom everything and everyone to a massive, future implosion -- a Big Crunch?
To the amazement of just about all earthly sentients, it turns out that the universal expansion is actually speeding up, not slowing down. Space is being enlarged at an ever-increasing rate by something called dark energy.
No one knows what dark energy is -- the name is merely a blind for our ignorance -- and its behavior is as uncertain as its nature. But we now believe that there are but two likely scenarios for the universe's future: Either dark energy will continue to assert its mysterious self with greater and greater strength, eventually causing galaxies, stars, planets, and every atom of your body to blow apart a few tens of billions of years from now (the technical term for this disconcerting event is "the Big Rip"), or the cosmos will enjoy a more sedate future, expanding without limit as it gradually becomes less energetic.
It's the latter scenario that is currently the bettor's favorite -- a universe that slowly winds down. Stars will die, and fewer and fewer replacement stars will be born. Eventually, most of the dead stellar hulks will flee their dark galactic homes. In ten thousand trillion trillion trillion trillion trillion trillion trillion trillion years, the last black hole will expire. After that, as far as we know, nothing more happens.
Nothing except this: The expansion discovered by Hubble and calibrated by Sandage and others will not stop. The cosmos -- having become nothing more than a thin soup of cold, atomic particles, punctuated by the inert corpses of former stars and planets -- will continue its mindless growth.
So this, then, is the story of the universe. A Big Bang, a hundred billion years of light, life, and late-night television, and then an infinitude of nothingness. Am I getting through to you? Not a long time -- not a really long time -- but an infinitude.
A flash of activity, followed by never-ending darkness. Our universe is destined to spend eternity in hell, without the fire.
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