WE ARE born. We die. We call the span that separates these events time. Its passage is perhaps the most fundamental feature of our human experience, yet we are incapable of saying exactly what it is. Worse – the laws of physics don’t help. That time exists is undeniable, but the way we experience it makes no sense. “There’s an old joke about time – it’s nature’s way of keeping everything from happening at once,” says physics Nobel laureate Steven Weinberg of the University of Texas, Austin. To us mortals, time is the passage of the sun and seasons, the progressive wrinkling of our skin as we age – irreversible markers of a present that is moving forwards, and a future that is ineluctably becoming the past. Unlike space, time has a natural order. If A influences B, then B is always later in time. This is the central feature of time as we perceive it: as a flowing entity that orders our lives.
Einstein is referring to the “block universe” conception of spacetime. It’s hardly surprising that he accepted it, since although it came from the work of others (principally from Hermann Minkowski, one of Einstein’s teachers) it is the framework in which his own theories of special and general relativity are most naturally expressed.
The block-universe view of physical reality contains time, but in a way remarkably different to our usual conception. It presents a four-dimensional view in which all events across time and space are on an equal ontological footing, with no sense in which present events are judged more “real” or “actual” than past or future ones. It is also very difficult to recover any meaningful sense in which time “flows”.
Einstein has not been not alone in finding this view — where the distinction between past, present and future is not a fundamental feature of reality — to be a great comfort when reflecting on the loss of loved ones.
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