As a diversion from the important topics of shaming, anti-shaming, and anti-anti-shaming, I thought I’d share a little email exchange (with my interlocutor’s kind permission), which gives a good example of what I find myself doing all day when I’m not blogging, changing diapers, or thinking about possibly doing some real work (but where did all the time go?).
Dear Professor Aaronson,
I would be very pleased to know your opinion about time. In a letter of condolence to the Besso family, Albert Einstein wrote: “Now he has departed from this strange world a little ahead of me. That means nothing. People like us, who believe in physics, know that the distinction between past, present and future is only a stubbornly persistent illusion.” I’m a medical doctor and everyday I see time’s effect over human bodies. Is Einstein saying time is an illusion? For who ‘believe in physics’ is death an illusion? Don’t we lose our dears and will they continue to live in an ‘eternal world’?
Is time only human perceptive illusion (as some scientists say physics has proved)?
I don’t read Einstein in that famous quote as saying that time itself is an illusion, but rather, that the sense of time flowing from past to present to future is an illusion. He meant, for example, that the differential equations of physics can just as easily be run backward (from future to past) as forward (from past to future), and that studying physics can strongly encourage a perspective—which philosophers call the “block universe” perspective—where you treat the entire history of spacetime as just a fixed, 4-dimensional manifold, with time simply another dimension in addition to the three spatial ones (admittedly, a dimension that the laws of physics treat somewhat differently than the other three). And yes, relativity encourages this perspective, by showing that different observers, moving at different speeds relative to each other, will divide up the 4-dimensional manifold into time slices in different ways, with two events judged to be simultaneous by one observer judged to be happening at different times by another.
But even after Einstein is read this way, I’d personally respond: well, that’s just one perspective you can take. A perfectly understandable one, if you’re Einstein, and especially if you’re Einstein trying to comfort the bereaved. But still: would you want to say, for example, that because physics treats the table in front of you as just a collection of elementary particles held together by forces, therefore the table, as such, doesn’t “exist”? That seems overwrought. Physics deepens your understanding of the table, of course—showing you what its microscopic constituents are and why they hold themselves together—but the table still “exists.” In much the same way, physics enormously deepened our understanding of what we mean by the “flow of time”—showing how the “flow” emerges from the time-symmetric equations of physics, combined with the time-asymmetric phenomena of thermodynamics, which increase the universe’s entropy as we move away from the Big Bang, and thereby allow for the creation of memories, records, and other irreversible effects (a part of the story that I didn’t even get into here). But it feels overwrought to say that, because physics gives us a perspective from which we can see the “flow of time” as emerging from something deeper, therefore the “flow” doesn’t exist, or is just an illusion.
Hope that helps!
I’ve been thinking about the “block universe” and it seems to me that in it past, present and future all coexist. So on the basis of Einstein’s theory, do all exist eternally, and why do we perceive only the present?
But you don’t perceive only the present! In the past, you perceived what’s now the past (and which you now remember), and in the future, you’ll perceive what’s now the future (and which you now look forward to), right? And as for why the present is the present, and not some other point in time? Well, that strikes me as one of those questions like why you’re you, out of all the possible people who you could have been instead, or why, assuming there are billions of habitable planets, you find yourself on earth and not on any of the other planets. Maybe the best answer is that you had to be someone, living somewhere, at some particular point in time when you asked this question—and you could’ve wondered the same thing regardless of what the answer had turned out to be.