For us believing physicists, the distinction between past, present and future is only a stubbornly persistent illusion.
We started this series with discussions of the high strangeness of Quantum Physics, with its brain-curdling experimental proofs of such things as particle/wave duality, and the apparent capacity of decisions made in the present to affect a quantum state as it was in the past, effectively undoing events that should already have occurred. It’s as if time, at the quantum level, is either non-existent, or infinitely malleable, and from all the objections of Einstein, Schrödinger et al to these apparent violations of causality and the linear progress of time, one might have assumed that the skeptics had a much more reasonable, much less stupefying model for how the universe worked, and how time, in particular, could be measured and shown to be both immutable and unidirectional. Yet, within the Einsteinian physics of relativity, the picture is no less startling. According to Einstein, not only is time not an absolute, but apt to be perceived quite differently between different observers in different places and states of relative motion, there was also, actually, no such thing as the passage of time. That’s right: time itself is an illusion, a quirk of human perception, with no basis whatever within the equations that explain the universe. If you have trouble squaring this notion not only with such scientific laws as causality and entropy, but your everyday experience of life, you’re far from alone. Even physicists are inclined to doubt it, no matter what the math seems to show, and there’s been some grasping, lately, for a theory that embraces the way we perceive time as objectively valid, without challenging the entire basis of Einstein’s view of the Universe.
First, let’s look at the relatavistic aspect of time, which is absolutely nuts, but provable, and actually the less mind-jarring of the notions we’re discussing today.
When I was a child, I glommed on to a wonderful volume produced out of a BBC series that aired in the Seventies, titled The Ascent of Man, presented by the great historian, mathematician, and humanist Jacob Bronowski. That’s when I got sucked into this intellectual tar pit. One of the chapters covered Einstein’s earliest thought experiments in relativity, when he was still working as a patent clerk in Bern, Switzerland, and I was beguiled by how something so utterly fantastic could be conceptualized by such simple ideas, which clearly, without the slightest understanding of any of the math that goes into them, just have to be right.
The story goes that young Albert was riding in a streetcar, travelling away from a clock tower, when he realized, looking back at the clock face, that if the streetcar could travel fast enough, the clock would seem, from his perspective, to be slowing down. This is because the image of the clock was travelling toward him on waves of light which had a fixed speed, which was very fast – 300,000 Km per second – but still fixed. What if, say, his streetcar was rolling down the rail at 150,000 Km per second? At that point he’d be receding from the clock at half the speed of the light waves it was emitting, and the clock would seem to be ticking at only half its normal speed. The faster one travelled, the more the effect would increase, until if, notionally, you could travel away at the same speed as the light emitted off the clock face – impossible for other reasons that needn’t detain us here – you’d be riding along with the wave, and the clock would seem to have stopped completely. Yet the pedestrian standing a block away would see the device operating as normal. Two observers in two different places, in two different states of motion, were therefore going to perceive time’s passage differently.
You could run the thought experiment from other perspectives. Suppose an observer standing on the corner in Bern was looking through a telescope at a clock sitting on Mars. The Martian clock may have been set at exactly the same time as local clocks before it was launched in a rocket towards the Red Planet, but now, checking it against the local clock tower, the distant clock would seem to be several minutes slow. This is owing to the time it takes for the light to reach the Earth from Mars. Now, imagine somebody else on a spaceship, travelling toward Mars, and halfway there. Imagine too that she has on board a chronometer that was, like the clock on Mars, synched to local Bern time before she blasted off. Now, when she looks at the Martian clock, it shows a different time from what’s observed back in Switzerland, and is not so many minutes slow, compared to the time on her ship’s chronometer. In fact, as she looks back through her telescope at the clocktower in Bern, it’s now running slow too, in exactly the same increment as the one on Mars, and the two planetary clocks seem to be in perfect synchrony, owing to the time it took for light from each of them to reach her at her current position, equidistant from both planets.
There is, in other words, no privileged observer with access to the absolute time on either planet or the spacecraft travelling between them. Everybody sees it differently. The intrepid astronaut servicing the clock on Mars has his own perceptions, with the chronometer on the spacecraft appearing slow, and the clock on Earth slower still. It all depends – or, as they say, it’s all relative.
Let’s return to the guy on the streetcar, looking back at Bern’s clock tower. The faster he goes, the slower the passage of time in Bern will seem to him. The opposite is also true – get him going at a sufficient percentage of the speed of light, and from the perspective of the fellow back in Switzerland, the streetcar isn’t moving forward in time at all. He can see that it’s receding into the distance, but as he manages to catch a glimpse at the rider’s pocket watch through his telescope, he sees that it’s barely ticking. From the perspective on the ground, time has all but stopped for the rider, just as from the perspective of the rider, time has all but stopped on the ground. Yet each has the same subjective experience of local time; for each, time is passing normally, and it’s the other guy whose clock is behaving oddly. It takes a third party perspective to see the difference; the observer on Mars would see the clock on Earth hewing much closer to “normal” time than the one on the relatavistic streetcar screaming off into the cosmic distance. From his perspective, time on the streetcar is going more slowly than time on Earth.
And so it is. For real.
This isn’t just a quirk of perception. The observer on the streetcar isn’t just watching the Earth clock as it appears to slow down; time is actually slowing down for the observer in motion. Does this mean that the faster something goes, the slower it actually ages? Yes. Yes it does. When this was nothing more than a theoretical prediction, it was possible to hope Einstein’s equations were plugging in the wrong variable somewhere, and that time was something real, and absolute, such that what the moving observer perceived wasn’t the same thing as what he actually experienced. Surely, as buddy on the streetcar looked back at the clock ticking in Bern at a rate of one second every 50 years, according to his own watch, he’d age and die in the usual way, and he’d actually be dead after X years as measured back here on Earth, even though we could still see him sitting there motionless through our telescope. It was all just a trick of the light, as it were, right?
But no. The invention of the “atomic clock” settled matters. Atomic clocks can measure time in unbelievably tiny increments, by monitoring the vibrations of atoms like Caesium (in much the same way that wristwatches used to calibrate off of the resonance of vibrating tuning forks, or quartz crystals). In effect, each vibration of the atom is a tick of the clock, and the latest measure time in ticks so short that there are 430 trillion each second. These clocks are so accurate that placed side by side, they’d only disagree by a second or two after several billion years, yet if you keep one stationary, and put one in motion, say by loading it onto a jet, the two will immediately fall out of synch. The one in motion clicks more slowly. The difference is so minuscule that it’s hard to wrap your mind around, but the point is, the variance is measurable. The moving clock is measuring time at a slower rate than the one that’s stationary, and the only difference, after controlling for all other variables, is their relative speed.
So time is indeed relative. The observer’s perception of time is a sort of fluid, malleable thing, and perception dovetails with local reality. By moving at relatavistic speeds, you can change how time, for you, passes, as compared to everybody else.
If you can swallow that, perhaps the next aspect of time as viewed through the Einsteinian lens will stop you in your tracks: according to the physics, when it comes to time passing, perception is all it is. There is no past, present, and future, not really, not the way we think of it. It’s all already there, and never goes away.
The way Einstein conceived of it, every object in space has not just three coordinates corresponding to the the three perceived physical dimensions, but four, because it also has a coordinate in time. When people speak blithely about time being the fourth dimension, this is why. Relativity weaves it all together, so that space and time are all aspects of the same thing, and can’t be separated. Therefore, everything that ever was, or ever will be, is already and perennially in existence, in one huge clump, mixed in with the three dimensions of space, forming one continuous whole that Einstein dubbed “space-time” (so the “space-time continuum” so beloved by the writers of Star Trek is no mere Hollywood invention). It’s a single fabric, if you like, and just as all the space that exists is already out there, so is all the time. I know, it’s crazy, and impossible to understand, but that’s what the equations show, and in fact, as it stands, nothing in the mathematics of physics can account for the perceived passage of time. We may experience time as something that exists only in the present, with the past no longer in existence, and the future yet to be, but there’s no theoretical underpinning to this in modern physics.
But wait, you say, what about the laws of thermodynamics, and entropy, which require that all things must tend from a state of higher order to lower – over time. Shattered glasses never put themselves back together, fading embers never un-combust and turn back into wood, scrambled eggs don’t unscramble, and so on. This proves, does it not, that time has a direction, and that by necessary implication, it also passes? Well, no, not really, comes the answer. For starters, entropy, which seems to determine time’s arrow, is really just a matter of statistical probabilities, and looked at mathematically, it’s not really inevitable, it’s just a question of what’s more probable. Anyway, the equations run just as well in reverse. There’s no real reason, outside of the probabilities, why sawdust doesn’t turn itself back into lumber. Not that there isn’t a time coordinate associated with the dust, and another associated with the lumber, while still another is assigned to the tree the wood came from. It’s just that it’s all already out there, all woven into the fabric of space time.
They call this the “block universe”. In the block universe, a ping pong ball sitting on a table is actually more a long tube than a sphere, its many moments of existence stretched out into a long snaky thing that captures the entirety of its presence in space-time.
I’ve tried to wrap my mind around this, using real-world analogies. Take an old vinyl LP, for example. The needle in the groove is always only at one place, but all the grooves are already there, and the ones that compose track one don’t vanish as the needle moves inward, any more than the grooves of track seven don’t exist yet, even though the needle has yet to reach them. Or imagine a long set of stairs. I may be on the middle step, but the top and bottom steps are both there, one left behind, one still to be reached. Is that what they mean? Are we like needles in a groove, a person climbing stairs, or fish swimming down a pipe?
No, I don’t think so. In these examples, if, say, the LP stands in for space-time, the needle is still only in one place, and moving through it. That doesn’t quite capture it. In the block universe, it’s as if the needle is in all places at once, from start to finish.
I remember trying to articulate this to Kathy one time, sitting by the side of a pool in Antigua, reading, as one does, a book on modern physics. Her reasonable response to my explanation that time is an illusion was “yeah, well, it’s going on two PM and I’m getting hungry”. Right. If the passage of time isn’t real, why do we all perceive it? The only answer on offer, it seems, is that it’s a quirk of the human perceptual apparatus. We see only the now, but that’s our problem. I may think I’m sitting in a swivel chair here in Toronto, but really I’m a sort of fleshy world tube, with my ass end stretching from Grace Maternity Hospital in Halifax to wherever it is down the road that I kick the bucket.
Yet how can that be? Doesn’t that mean that right now, as my tube sits splayed across space-time, I’m also not yet born, and simultaneously already dead? If I’m already dead, how can I perceive anything at all, let alone the supposed illusion of time passing? And what about probabilities, and random chance, central to so much math and physics, both quantum and classical? How can anything be more or less probable, or random, if it already is? Isn’t everything, at that point, a certainty? Isn’t this a purely deterministic view of the Cosmos? Moreover, if everything that ever will be is already sitting out there in this block universe, what do we mean when we say the fabric of space-time is expanding, something that’s been amply proved? Expanding when? It can’t be bigger tomorrow than it was yesterday, since yesterday and tomorrow are mere mental constructs of our little minds – it must already be out there, as big as it’s ever going to get, with my perception of it being smaller than it will be, but bigger than it was, just another illusion, yes? How in blue blazes does a block universe fit with one that’s constantly inflating? How does it fit with the whole idea of a creation moment, for that matter? In the block universe, the Big Bang is something that’s still there at its space-time coordinates! It’s only billions and billions of years in the past because of a quirk in the way we see things! What?
Beats me. I’ll say this, though: whenever a scientific theory starts squaring itself with perceived reality by resorting to “illusion”, or nebulous “forces”, with nothing to back it up, that means there’s something going on that we don’t understand, and it isn’t just rubes like me who’re feeling like physics has taken the easy way out here. An increasing number of theoretical physicists are also balking at the whole block universe idea, and are struggling to come up with something better. You can read about it here, if you have any energy left to keep delving into the madness:
Here’s an excerpt:
Many physicists have made peace with the idea of a block universe, arguing that the task of the physicist is to describe how the universe appears from the point of view of individual observers. To understand the distinction between past, present and future, you have to “plunge into this block universe and ask: ‘How is an observer perceiving time?’” said Andreas Albrecht, a physicist at the University of California, Davis, and one of the founders of the theory of cosmic inflation.
Others vehemently disagree, arguing that the task of physics is to explain not just how time appears to pass, but why. For them, the universe is not static. The passage of time is physical. “I’m sick and tired of this block universe,” said Avshalom Elitzur, a physicist and philosopher formerly of Bar-Ilan University. “I don’t think that next Thursday has the same footing as this Thursday. The future does not exist. It does not! Ontologically, it’s not there.”
I’m with my man Avshalom. Time has to be real. It must really pass. Running the numbers and declaring it to be an illusion strikes me as a rather desperate gambit. There’s something we haven’t yet figured out, that’s all. We need another great leap forward, just like the one that Einstein supplied when dealing with the Universe of Newton. Newton, recall, set out his laws of motion and universal gravitation, but he didn’t really understand what gravity was, or why massive objects attracted each other like magnets. To him, gravity was a “force”, that is, something that happened without him knowing why, exactly. Einstein was able to demonstrate that gravity isn’t a mystical force, it’s just the way things behave when massive objects bend the fabric of space-time towards themselves. A planet orbits a star like a marble circles the inside of a bowl, that’s all. Like so:
That’s been proved. It’s not just an assertion. It was a prediction, and scientific observation, armed with the new idea and knowing what to look for if it was true, proved it.
We need a similar leap to explain time, what it is, and why it works. We’re not there yet. Why should we be? We haven’t really been at this very long. A few centuries, is all. It’s time to stop hiding behind pat explanations that can’t be proved experimentally, like “it must just be an illusion”, and admit that we don’t yet know what’s going on, not with time, and not with anything else, not entirely. Really, it’d be a little weird if we did, wouldn’t it?
 The different effect of gravity at relatively higher altitude will also cause one to go faster than the other, another effect of relativity that we simply don’t have time to explore today!