by Thomas O’Dwyer
Our world (made of atoms) is crammed with paradoxes. Particles act like waves, waves like particles And your cat can be dead and alive at the same time. Just step through your looking glass and welcome to the quantum world. “If you think you understand quantum mechanics, you haven’t understood quantum mechanics,” the physicist Richard Feynman once said. Of course, the non-scientific reader may respond, “Why would I want to understand it?” If a genius like Feynman became lost in the twisting labyrinth of the quantum world, abandon hope all ye who expect to become enlightened here.
Quantum theory is famously opaque, and it drew dismissive grumbles from Albert Einstein. He was one of many superior minds who worried that science was abandoning its high road of rigorous clarity to dabble again in the murkiness of faith and superstition by even pondering the notion of quantum reality. Alive-dead animals, parallel universes, the existence of all times past present and future? These were for April 1 spoofs, right guys? Yet, whether one is aware of it or not, quantum mechanics has given us lasers, smartphones and many esoteric electronic components, like tunnelling diodes, from which we build our devices. They come with a weird label that says, we made them, and they work, but we don’t quite know how. Quantum computers will soon solve problems well beyond the reach of present-day digital machines – complex chemical analyses, dynamic biological processes. These will be of use to the pharmaceutical industries, and they will also model complex systems like financial transactions and climate changes.
In May, New Scientist magazine hosted the first in a series of online events that tried to enlighten the locked-down and curious about the present view from the fringes of physics and reality. The forum, Decoding Reality, was a fine effort but left one agreeing with Feynman, that we can’t grasp the answer to quantum weirdness because no one really knows what the question is. Vlatko Vedral, a formidable figure in the quantum physics world, hosted the event lucidly and pleasantly, but one couldn’t avoid the impression that his fingers were twitching to grab a piece of chalk and fill the wall behind him with incomprehensible mathematical squiggles. Quantum physicists addressing the lower orders in plain language can seem like medieval saints who have seen the face of god and must now describe it to the yokel faithful using kitschy holy pictures.
Vedral is a British physicist and professor in the Department of Physics at Oxford University and a Fellow of Wolfson College, Oxford. He is known for researching Entanglement and Quantum Information Theory, which is about as close to the gods of science as one can get. The New Scientist forum took its title from one of his many books, Decoding Reality. Einstein has forewarned us: “God does not play dice with the universe.” And on another occasion, “I cannot seriously believe in it because quantum theory cannot be reconciled with the idea that physics should represent a reality in time and space, free from spooky actions at a distance.” (When you separate two entwined sub-atomic particles and you move both parts away from the other, even to opposite ends of the universe, if you alter or affect one, the other will be identically changed or modified).
Mentioning spooky brings to mind everyone’s favourite scientific concept which they don’t understand – Erwin Schroedinger’s creepy cat, which can be both alive and dead at the same time. How so? A laser, a mirror and two electronic detectors walk into a bar and order the house speciality, Quantum Cat cocktail, which unfortunately is lethally poisonous. They all return to Dr Schrodinger’s laboratory where Herr Doktor connects one detector to a fragile vial of Quantum Cat cocktail and fixes it on his cat. He fires a pulse of light from the laser at the mirror, which is called a beam-splitter and is half-silvered, meaning it can both transmit and reflect a light beam.
When the pulse of light photons hits the mirror, it is either deflected away to hit detector one or passes straight through the mirror to hit detector two. The cat and poison are attached to detector one. If the beam hits that, the vial breaks and the cat dies. If the beam hits detector two, it just clicks, and the cat lives. However, particle quantum mechanics allows the photon beam to undergo interference and travel both paths simultaneously – apparently observing Yogi Berra’s famous advice, “when you come to a fork in the road, take it.” The moment the pulse fires, the cat is both alive and dead. In Schrodinger’s words, the cat’s two realities become entangled in a state called superposition. This state would remain until somebody external observed it and it would then collapse into one or other reality – alive or dead.
Schroedinger devised this thought experiment in 1935 during debates with Einstein, and he intended to illustrate the paradox and the absurdity of applying quantum mechanics from the sub-atomic world to everyday objects. By the 1950s, like many other doubting scientists, Schroedinger had to grudgingly accept that quantum mechanics must in some way apply to the whole universe and experiments would one day confirm it. The mystery deepens when we introduce an observer and then more observers. In his lecture, Vedral introduced Bob, who sees the cat as either alive or dead and the expression on his face, happy or sad, would reflect the cat’s fate. The live cat and the dead cat are entangled in both states, but so too Bob is entangled in two Bobs – one happy and one sad.
If there is yet another observer, Alice, outside the lab, does she see Bob happy or sad? She writes a question for Bob on a note and slips it under the door: “Do you see a definitive state of the cat?” Bob answers “Yes”. Note that if she asks him if he sees a dead cat, she enters that dead-cat branch of the quantum world and becomes entangled, and only the dead-cat reality exists after that. There are two Bobs, and each would feel they exist in their own world. Alice can tell each Bob that there are two of them. She can confirm the state of each cat/Bob as alive/happy and dead/sad. Alice cannot see what is the “true” state of the cat, only that each Bob sees “a definitive state.”
Vedral likened this strange world to the riddle of two brothers, a subject of folklore in many cultures. One man always lies and one always tells the truth. A traveller comes to a fork in the road, where he finds the brothers standing. One path leads to certain death, and the other leads to life and prosperity. The brothers know which route is which, and the traveller, with just one question, has to ask one of them which is the safe road to choose and be certain he’s getting the true answer. The only reliable question is, “If I ask your brother, which is the safe road, what will he tell me?” As Vedral said, “it’s down the rabbit hole from here.” If there’s another observer of the laser-pulse event beyond Alice, he can become entangled and collapse the suspended quantum cat scenario into one or other reality. It’s like a painter who determines to make a perfect picture of his garden, complete in every detail. Having done it, he is troubled; something is missing. Himself. So he paints in an image of the painter painting the scene, and still, something is missing, the artist himself, ad infinitum.
And so the questions swirl endlessly. What does it feel like to be in another universe? What does it feel like to be another Bob? Is it the same as it would feel like to be in a different time since different times are like different states. Quantum science is still too strange for many of us to get a real grasp on it. Still, the scientists are relentlessly closing in on the enigmas, maintaining scientific rigour and discipline in the fog of endlessly evolving theories and possible explanations.
Physics has two main theories to describe reality. The theory of relativity describes events on a large and very large-scale, quantum mechanics describes them at the very small scale. At the sub-atomic level, entanglement and superpositions – quantum mechanics – work just fine. But in “our” macro world, they don’t appear to. It took decades for Schroedinger to accept that his cat thought experiment, which he meant to prove how ludicrous quantum theory was, might be right. We are nowhere near experimenting on a cat-sized entanglement, but scientists are chasing the next milestone to examining entangled states. They are close to testing sample entanglements on a living system, probably a tiny virus, a microscopic scale.
We still have to understand the role of the observer in collapsing entanglements. Must the observer be conscious, or could an artificial intelligence fill the observer role? Moving the theories from a bundle of sub-atomic particles to an incredibly complex concept like consciousness – which we don’t understand – is quite a journey. But consciousness probably is not a fundamental requirement, and using AI could perhaps demonstrate that consciousness is not relevant. After all, reality existed before people. Despite the convoluted efforts of many philosophers to prove that reality only exists because we create it in our minds, scientists, like most of us, believe that what we observe really is out there. When you see a bird fly past your window, you know your cat sees it too. “I like to think the moon is there even if I am not looking at it,” said Einstein.
Evolution may have created a biological system called life, based on patterns of energy endlessly triggering patterns of energy. Our consciousness resembles a pattern of information generated in the brain, which allows us to model the world and ourselves in it. This is either the real physical world or our internal reality where we consider multiple possible pathways from which we select one future over others and then act to bring it about. But in the physicists’ modern concept of the universe, our future already exists – all times, past present and future exist simultaneously. That suggests a predetermined universe with no such thing as a free choice, never mind a free lunch.
As usual, in the ever-changing shambles of the quantum universe, let’s blame Einstein for upsetting all that neat and cosy Newtonian world of the nineteen century where all physics was settled, every atom knew its place, and the steam trains ran on time. He came up with the special theory of relativity which dragged time and space into a shotgun wedding at the speed of light. Three-dimensional space and one-dimensional time weren’t two members of a singles club and happy to stay that way. No, declared Relativity, you’re one four-dimensional entity, and your name is space-time. The past hasn’t all gone away, the present is, well, present, and the future isn’t waiting to be decided. Every single frame of the infinite movie of the universe’s existence already exists and will exist forever.
Einstein was as fond of train stations and clocks as Salvador Dali was of melting watches. First, he would remind us that the speed of light is fixed, constant, immutable. No argument. So, if you are standing on a platform as a train whizzes past, the speed of light coming off the train is the same as the speed of light coming off a stationary train. For one sliver of a second, the driver in front and the guard in the rear coach will be the same distance from you. But the driver is speeding away from you, and the guard is coming towards you. The light travelling from the guard should be the speed of light plus a fraction of the train’s speed. For the driver, the speed of light should be minus a fraction of the train speed.
But wait! The speed of light is fixed, and light travels the same distance to you from the guard and the driver. If you look around for some essential variable, all that’s left is time. The light from the driver must be coming from an earlier point in time than the guard. Here you have three different but simultaneous nows – yours, the guard’s and the driver’s. Apply this principle to our galaxy and the universe. Every object in the vastness is moving at different speeds relative to one another. It’s an infinite multiplicity of nows, all existing simultaneously.
This brings us perilously close to that old philosophical chestnut that causes groans all round when someone starts an argument, with or without a smidgen of religion to heat things up – free will. The future already exists, so everything is preordained even if it hasn’t arrived yet. What will be will be. Thus spake the determinist, rendering your life meaningless. However, we can’t see the future, so we have that encouraging illusion that we have free will and maybe that’s good enough. After the future has arrived and quickly become the past, we can still nurture the warm fuzzy feeling that we made the free choices that got us here.
Yet all is not lost for proponents of real free will rather than fake free will buried in relativity’s determinist creation. Quantums to the rescue! If we add a portion of quantum uncertainty to the boring old determined universe, the picture changes (in theory, at least) to a different model when all possibilities exist, as they did at the Big Bang, where all possibilities that could ever happen existed. The problem remains that, so far, quantum mechanics still describes events at very small scale – general relativity roots for determinism and no free will; quantum mechanics the other way round. What we’re waiting for is another shotgun wedding like Einstein created with spacetime – quantum relativity perhaps. Or how about you, quantum gravity? But no, that’s a hare-sized rabbit hole. Enough is enough.
“The quantum is that embarrassing little piece of thread that always hangs from the sweater of space-time. Pull it and the whole thing unravels.” (Fred Alan Wolf)