Charlotte Higgins - 'There is no such thing as past or future': physicist Carlo Rovelli on changing how we think about time
What do we know about
time? Language tells us that it “passes”, it moves like a great river,
inexorably dragging us with it, and, in the end, washes us up on its shore
while it continues, unstoppable. Time flows. It moves ever forwards. Or does
it? Poets also tell us that time stumbles or creeps or slows or even, at times,
seems to stop. They tell us that the past might be inescapable, immanent in
objects or people or landscapes. When Juliet is waiting for Romeo, time passes
sluggishly: she longs for Phaethon to take the reins of the Sun’s chariot,
since he would whip up the horses and “bring in cloudy night immediately”. When
we wake from a vivid dream we are dimly aware that the sense of time we have
just experienced is illusory.
Carlo
Rovelli is an Italian theoretical physicist who wants to make the uninitiated
grasp the excitement of his field. His book Seven
Brief Lessons on Physics, with its concise, sparkling essays on
subjects such as black holes and quanta, has sold 1.3m copies worldwide. Now
comes The Order of Time, a dizzying, poetic work in which I found
myself abandoning everything I thought I knew about time – certainly the idea
that it “flows”, and even that it exists at all, in any profound sense.
We meet outside the
church of San Petronio in Bologna, where Rovelli studied. (“I like to say that,
just like Copernicus, I was an undergraduate at Bologna and a graduate at
Padua,” he jokes.) A cheery, compact fellow in his early 60s, Rovelli is in
nostalgic mood. He lives in Marseille, where, since 2010, he has run the
quantum gravity group at the Centre de physique théorique. Before that, he was
in the US, at the University of Pittsburgh, for a decade….
Rovelli’s work as a physicist,
in crude terms, occupies the large space left by Einstein on the one hand, and
the development of quantum theory on the other. If the theory of general
relativity describes a world of curved spacetime where everything is
continuous, quantum theory describes a world in which discrete quantities of
energy interact. In Rovelli’s words, “quantum mechanics cannot deal with the
curvature of spacetime, and general relativity cannot account for quanta”.
Both theories are
successful; but their apparent incompatibility is an open problem, and one of
the current tasks of theoretical physics is to attempt to construct a
conceptual framework in which they both work. Rovelli’s field of loop
theory, or loop quantum gravity, offers a possible answer to the problem,
in which spacetime itself is understood to be granular, a fine structure woven
from loops.
String
theory offers another, different route towards solving the problem.
When I ask him what he thinks about the possibility that his loop quantum
gravity work may be wrong, he gently explains that being wrong isn’t the point;
being part of the conversation is the point. And anyway, “If you ask who had
the longest and most striking list of results it’s Einstein without any doubt.
But if you ask who is the scientist who made most mistakes, it’s still
Einstein.”
How does time fit in
to his work? Time, Einstein long ago showed, is relative – time passes more
slowly for an object moving faster than another object, for example. In this
relative world, an absolute “now” is more or less meaningless. Time, then, is
not some separate quality that impassively flows around us. Time is, in
Rovelli’s words, “part of a complicated geometry woven together with the
geometry of space”.
For Rovelli, there is
more: according to his theorising, time itself disappears at the most
fundamental level. His theories ask us to accept the notion that time is merely
a function of our “blurred” human perception. We see the world only through a
glass, darkly; we are watching Plato’s shadow-play in the cave. According to
Rovelli, our undeniable experience of time is inextricably linked to the way
heat behaves. In The Order of Time, he asks why can we know only
the past, and not the future? The key, he suggests, is the one-directional flow
of heat from warmer objects to colder ones. An ice cube dropped into a hot cup
of coffee cools the coffee. But the process is not reversible: it is a one-way
street, as demonstrated by the second
law of thermodynamics…. read more:
