It is not until three-quarters of the way through his wonderful and deceptively unassuming new book, Time Travel: A History that James Gleick poses the question that has been haunting his pages from the outset. The question comes in the bald title to chapter 12: "What Is Time?" This is, of course, precisely the conundrum that has preoccupied philosophers and scientists since the disciplines of philosophy and science were instituted, around the fireside at the back of the cave.
Every schoolboy knows, or at least every schoolboy used to know, the tag from Heraclitus that assures us we cannot step into the same river twice. Like so many of the fragments that are all we have of that gnomic thinker’s work, this one looks simpler than it is. Common sense tells us that of course the river is always different, as it endlessly flows; however, common sense stumbles when we dive a little deeper. What is “the river”? It is water, certainly, but is it not also the bed and the banks? If so, all that Heraclitus can safely say is that one cannot step twice into the same flow. And that is just the beginning. What about the river’s name? Surely we can step into “the Shannon” as many times as we wish. And so on.
Heraclitus would have been on safer ground, or in shallower water, if he had stated, more prosaically, that we cannot experience the same event twice. Time, for us, is movement in stasis: we cannot travel backwards or forwards in it but are stuck in the moment, although the moment is always new. This is a profound mystery, and one that the greatest minds throughout history have been unable to make even a start at solving. Einstein’s theory of relativity posits what has come to be known as the block universe, in which everything – everything – has already happened, and time therefore is a delusion of human consciousness. In the relativistic universe we are unborn, living and dead, all at the same . . . well, the same time.
Equations
The equations tell us this is so, and the equations are not to be doubted – until someone comes along with a new set. For now, however, as far as the physicist is concerned, time could as well flow backwards as forwards: it makes no difference to the equations. Gleick quotes Freeman Dyson, that most commonsensical of contemporary savants: “In physics, the division of space-time into past, present and future is an illusion.” And here is Einstein, to back him up: “Time and space are modes by which we think, and not conditions in which we live.” All right, we say, we have heard what you brainy chaps have to say – but how is it that yesterday stubbornly remains yesterday, and tomorrow will remain tomorrow until in due course it becomes today, and then fades into yesterday? Why do the equations not apply to
us
? The philosopher David Hume pointed out that we have no assurance whatever that the sun will rise tomorrow, as it did today and every other day; but it will rise, as we all know, and as Hume himself knew, as he strolled away at the end of his famous game of billiards.
Gleick has read the literature – although that may be too strong a word for the shelfloads of third-, fourth- and fifth-rate books the poor fellow has plodded his way through, on our behalf. He begins, as we might expect, with HG Wells's The Time Machine, in which the nameless Time Traveller mounts an elaborate sort of bicycle and pedals off into the future – never the past – until the second law of thermodynamics puts paid to his fanciful flights. Wells published the novel in 1895, and anticipated Einstein by a decade when in a Socratic exchange his protagonist refutes one Filby, "an argumentative person with red hair", who had challenged the Time Traveller's contention that a cube, "having only length, breadth, and thickness", cannot "have a real existence". Nonsense, expostulates the redoubtable Filby – how easily one falls into the Wellsian style – for of course "a solid body may exist". Here the Time Traveller pounces:
“ ‘Can a cube that does not last for any time at all, have a real existence?’
"Filby became pensive. 'Clearly,' the Time Traveller proceeded, 'any real body must have extension in four directions: it must have Length, Breadth, Thickness, and Duration.' "
The word "duration" conjures the figure of Henri Bergson (1859-1941), the French philosopher who was so famous in his day that a lecture he delivered in New York in 1913 attracted such crowds that the traffic in Manhattan was stopped for hours, and whom the great William James idolised, while confessing, with his usual endearing candour, that "many of his ideas baffle me entirely". In a momentous debate in Paris in 1922, now largely forgotten – although revived in Jimena Canales's fascinating and highly recommended book The Physicist and the Philosopher (2015) – Bergson challenged Einstein on his conception of the nature of time, or, as Einstein would have it, the delusion of time.
"The time of the philosophers does not exist," Einstein declared in the course of the debate, and later added: "There remains only a psychological time that differs from the physicist's." This Bergson regarded as the typical, sterile dogmatism that was everywhere to be met with in the science of the day. Things were to change as the 20th century went on and physics had to come to grips, where it could find something to grip on to, with the seemingly unfathomable implications of quantum theory. "Duration" was Bergson's version of time, which proceeds not in a straight line but wavers and quavers, biting into the future, as he said, in a sort of endless process of creation. Einstein's arguments were strong, however, backed up as they were by experiment, and against them Bergson's could not endure.
Plausible definition
So how far has science got in the search for at least a plausible definition of time, if not an absolute one? Not very. However, even if we do not know what time is, we can at least measure it; indeed, Gleick posits the premise that “Time is what clocks measure”, but goes on to ask, what is a clock? Answer: “An instrument for the measurement of time. The snake swallows its tail . . .” In a footnote here, Gleick, who is possessed of a splendidly dry wit, mentions the physicist Lee Smolin’s attempt to escape this circularity by redefining a clock as “any device that reads out a sequence of increasing numbers”. Oh, yes? “Then again,” Gleick observes, “a person counting to one hundred is not a clock.” Collapse of stout physicist.
In the end, of course, the question of time is in the hands of Thanatos. "Why do we need time travel?" Gleick inquires; his reply to his own question is not cheering: "To elude death. Time is a killer. Everyone knows that. Time will bury us. I wasted time, and now doth time waste me. Time makes dust of all things. Time's winged chariot isn't taking us anywhere good." So get out there and gather those rosebuds while ye may. Time presses.
John Banville's latest book is Time Pieces
