Sunday, January 16, 2011

We'll Never Be Alone

As Brian Greene writes, Albert Einstein needed a gimmick to bolster his theory that the universe had a fixed size and shape. His solution was the cosmological constant, a repulsive gravity that pressed against the gravity that Newton had discovered and kept the cosmos shipshape. While Einstein may have been wrong at first about the size of the universe, he was right about anti-gravity. Scientists now call it dark energy, and it's thrusting the universe away from us at unimaginable speeds, leaving us in the stardust:
If the dark energy doesn’t degrade over time, then the accelerated expansion of space will continue unabated, dragging away distant galaxies ever farther and ever faster. A hundred billion years from now, any galaxy that’s not resident in our neighborhood will have been swept away by swelling space for so long that it will be racing from us at faster than the speed of light. (Although nothing can move through space faster than the speed of light, there’s no limit on how fast space itself can expand.)

Light emitted by such galaxies will therefore fight a losing battle to traverse the rapidly widening gulf that separates us. The light will never reach Earth and so the galaxies will slip permanently beyond our capacity to see, regardless of how powerful our telescopes may become.

Because of this, when future astronomers look to the sky, they will no longer witness the past. The past will have drifted beyond the cliffs of space. Observations will reveal nothing but an endless stretch of inky black stillness.

Especially apt for us Holy Land pilgrims are Greene's reflections on the fragility of empirical knowledge. Remember that he's talking about hundreds of billions of years in the future, when the earth would long since have been engulfed by the sun. Bless him for his optimism about the survival of the species, which, he suggests, would have to have planet-hopped even to confront this dilemma:
If astronomers in the far future have records handed down from our era, attesting to an expanding cosmos filled with galaxies, they will face a peculiar choice: Should they believe “primitive” knowledge that speaks of a cosmos very much at odds with what anyone has seen for billions and billions of years? Or should they focus on their own observations and valiantly seek explanations for an island universe containing a small cluster of galaxies floating within an unchanging sea of darkness — a conception of the cosmos that we know definitively to be wrong?

And what if future astronomers have no such records, perhaps because on their planet scientific acumen developed long after the deep night sky faded to black? For them, the notion of an expanding universe teeming with galaxies would be a wholly theoretical construct, bereft of empirical evidence.
That's where faith comes in handy, as with us who still tell our primitive stories about stars in the night and empty tombs.

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