Brian Greene has written a reflection on cosmology in the New York Times that caught my attention, since it asks some favorite questions: what can we know, and in what sense is it meaningful to say that we know something? Many of us harbor (perhaps unconsciously or unreflectingly) a belief that if something is true, then it can, with enough effort, be discovered — even though there are areas of knowledge where this has been proven not to be so.
One Orthodox catechism notes that the existence of countless angels helps us to remember that there are vast areas of the created world that are not even theoretically accessible to science. I remembered this while reading Greene’s article.
The universe, as we can readily observe, is filled with other stars and galaxies, many of them almost unimaginably far away. But cosmologists now believe that the universe is expanding at such a rate that, in time, distant stars and galaxies will be moving away from us faster than the speed of light — meaning that light from them will never be able to reach us. If we look out into the surrounding universe in the far future, we will see our own galaxy and a few other “nearby” objects floating in a field of total darkness which no technological improvement can ever penetrate. Greene closes with some words which struck me powerfully, whose implications for any theory of knowledge seem clear (though I haven’t been able to resist bold-facing a few phrases):
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.
We’ve grown accustomed to the idea that with sufficient hard work and dedication, there’s no barrier to how fully we can both grasp reality and confirm our understanding. But by gazing far into space we’ve captured a handful of starkly informative photons, a cosmic telegram billions of years in transit. And the message, echoing across the ages, is clear. Sometimes nature guards her secrets with the unbreakable grip of physical law. Sometimes the true nature of reality beckons from just beyond the horizon.
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A further reflection: Greene’s article is based on the idea that we now know many things about the cosmos that in the future will become unknowable — a heavy idea in itself. Is there any reason not to speculate that at some time in the distant past there were things about the cosmos that were knowable but have now become unknowable? And that the physics of today could be the kind of illusory construct that Greene pictures for scientists in the far future who build a cosmology on the world as it presents itself to them?