Sunday Science Poem: The Irreversibility of Time

Czesław Miłosz’s “This World” (1994)

Telomere_capsIt’s a question you’ve certainly heard before – the laws of physics work just fine when you run time backwards, so why, in the real world, does time only go forwards?

Run a movie backwards, and what you see could never happen in real life: a diver never leaps feet first out of the pool onto the board, while drops of water fling themselves back in. But, as Richard Feynman explained, at the level of atoms and molecules, there is no reason why running the film backward should be absurd – our laws of physics say time is reversible at the microscopic level. Feynman argued that time’s forward motion was a macroscopic phenomenon, rooted in the universe’s relentless increase in entropy. Physicist Lee Smolin has pursued a similar (but in many ways a radically different) idea – the forward flow of time is a consequence of a network of relationships in the universe. He may be right, but for the time being, why time is not reversible is still a deep mystery.

Physics isn’t the only place where reversibility appears to be a mystery. Why isn’t life reversible? Aging and death seem inevitable for us individually, but with each birth, the clock is reset. Biological time is reversed. How is that possible?

We don’t really know. Before your children are born you age twenty, thirty, or forty years. Your DNA has been copied and recopied, accumulating damage, telomeres have shortened, and your cells are on the way towards senescence, and yet each newborn gets a fresh start. Amazingly, each successive generation of children is not born ever more prematurely aged. If the clock can be reset for our germ cells, why can’t we reverse biological time in the rest of our cells?

As Stanford University biologists Thomas Rando and Howard Chang put it:

Despite the apparently unidirectional and inexorable process of aging of individual metazoans, the ability of the aging clock to be not only halted but reversed, or “reset to zero,” is so deeply embedded in the nature of life itself that it should not be surprising. Yet the process appears so mysterious that it is difficult to reconcile with concepts of individual aging.

In “This World”, Polish Nobel Laureate Czesław Miłosz (1911-2004) takes on the perennial longing for reversibility. As time moves on, sorrow, regret, and pain, like age-related damage to our cellular components, take their cumulative toll, and at some point we all wish that we could turn back the clock. (Part way, in any case; once through high school was enough for me, thank you.)

This World

As it turns out, there was a misunderstanding.
Literally speaking, this was only a trial run.
Rivers will immediately return to their source,
The wind is ceasing its circulation.
Trees, instead of budding will proceed to their roots.
The elderly will chase a ball,
Peer into the mirror, and again be children.
The dead will wake up, not understanding.
'Till what's done is, at last, undone.
What a relief! Take a deep breath, all you who are suffering.

“Ten Świat,” Czesław Miłosz, Na Brzegu Rzeki (Kraków: Znak, 1994). Translation by Michael A. White.

Image credit: Telomere caps, by the U.S. Department of Energy Human Genome Program, via Wikimedia Commons.

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