by Ulf Wolf
In fact, by now most scientists agree that quantum mechanics was a greater scientific evolution than the relativity theory. In fact, scientists view Einstein’s gem as the 19th century’s crowning achievement, while they now see quantum mechanics as the 20th century’s crowning achievement.
Simply stated, quantum mechanics is the theory of how the world behaves at a subatomic level.
No Longer Certain
We have all come to regard the physical universe, or nature, as being certain, dependable, and predictable. After all, that’s what our physical laws—gravity and such—are all based on.
But when we enter the tiny quantum world this no longer holds true. Some would say that what happens inside an atom is just plain weird.
Einstein vs. Bohr
A good way to present quantum theory might be to tell the story of a battle. A battle between two of the greatest physicists of the 20th century: Albert Einstein and Niels Bohr.
I am sure that most of you have of Albert Einstein (if not, well, shame on you). Niels Bohr, on the other hand—who was also one of the giants of 20th century physics—is not a household name (so you’re forgiven).
They were both hugely influential figures, Bohr and Einstein. They knew each other well, were fond of each other, and each respected the other deeply. But when it came to quantum mechanics, gloves would come off, for here they were at loggerheads. Here they fundamentally disagreed.
As one of Einstein’s students would later put it, “As soon as quantum mechanics was brought up, sparks would fly. Einstein felt that certain aspects of quantum mechanics—the world according to quantum mechanics—didn’t really make philosophical sense.
“Einstein believed that the world presented by quantum mechanics was too ugly to be true.”
Predictable Nature
As mentioned, for centuries now, scientists have believed that the laws of nature hold firm, that knowing them makes nature predictable. In fact, some go so far as to say that if only we knew enough about the way the world worked, and if we could gather sufficient data, we would be able to predict the future down to the minutest detail.
For it seems obvious that nature is deterministic, that one thing determines another. One thing happens which causes another thing to happen. Hit a gong and a pleasant sound appears. Drop a ball and it bounces.
But quantum mechanics shattered that certainty. It upset people then and it still does now. And Einstein spent most of his life doubting it.
That said, Albert Einstein was, of course, himself an early pioneer of quantum theory. He was the one first to show that light exists as tiny quantum particles—photons. This was before he went on to become famous for his relativity theory: e=mc2 and all that.
Niels Bohr—who developed the theory of quantum mechanics along with Einstein and others—was to become its most prominent champion, while Einstein became its most famous doubter. Now, Einstein didn’t out and out disagree with the theory—after all, he had helped develop it—but he thought the theory was incomplete, and was therefore saying the wrong things about the true nature of reality.
So, what does quantum theory say about the true nature of reality?
What is says is that there is a limit to what we can know about what goes on at nature’s subatomic level. It also says that the universe seems to be run on chance, and that nothing is truly certain.
Which means what, exactly?
Two Gloves
To give you an idea of the difference between the ordinary (macro) world and the quantum (micro) world, imagine that inside a sealed box is an ordinary glove. Now, as gloves go, this glove is either left-handed or right-handed. The obvious way to find out which kind it is, is to have a look.
Opening the box and peaking inside we simply reveal to our senses what nature knew all along: it’s a left-handed (or right-handed) glove. This is the nature that scientists and the rest of us are used to. Certainty.
But in the quantum world it’s not quite as straightforward.
Imagine, instead, that inside the sealed box is a quantum (micro) glove that behaves in the same way as does a subatomic quantum particle. In this case, before we open this box (same as with the macro glove) we know that there is an equal chance that the glove could be left-handed or right-handed. We don’t know which, yet, but we only have to open the sealed box to find out.
But here’s the crux: according to quantum theory not only do we not know which hand the micro glove will fit, it also says that neither does the glove—neither does nature.
In fact, the theory goes on to state that on a sub-atomic level, the micro glove doesn’t really exist one way or the other while the box is sealed; that it is in a ghostly state of in-between left- and right-handed; that it is only once we open the box and take a look (or measurement) that nature makes up its mind and then manifests as one or the other.
In other words, in the quantum world—so says the theory—things are not as simple as to be or not to be, because until the subatomic particle (the micro glove) is observed, nature has not made up its mind one way or the other.
I am sure that you find this odd, and probably believe it not to be true. Well, you would be in very good company as Albert Einstein would be on your side. He just could not accept that nature was not certain.
And that is precisely what he was getting at when he said “God does not play dice.”
As Einstein was wont to point out, fighting quantum mechanics and the idea that nature was uncertain: “If I’m not looking at the moon, does this mean the moon is not there?”
(The answer, truthfully speaking, is yes, that is, in fact, what it does mean).
The thing that Einstein fundamentally hated about quantum mechanics was the element of uncertainty or what he termed indeterminism. This deeply offended his sense of an orderly universe that is fundamentally rational, and his belief that there should always be an ascertainable reason why things occur.
Einstein came down on the side of centuries’ worth of scientists—going all the way back to ancient Greece—who all believed in a deterministic universe; who believed that things happen for a reason; who believed that the secrets of the universe were just waiting to be unlocked. You just have to have your wits about you and take a good look.
The same holds true for most of us today. We are used to the fact that events always occur with well-defined causes. We may not know right away what the causes are, but if we investigate, and gather all the relevant information, we normally rest assured that we can then determine why something happened.
Things don’t occur spontaneously or arbitrarily, they don’t occur for no reason, that was Einstein’s view.
For No Reason
But in the quantum realm things do occur for no (apparent) reason. Generally speaking, from one moment to the next you don’t know precisely what an atom or an electron is going to do.
Indeterminism or uncertainty is the central feature of quantum mechanics.
Einstein did not see eye to eye with that. He championed an “objective reality”—one where you could make a statement about the physical world independent of how (the way in which) you observed it.
And that is where Bohr and Einstein disagreed, their one pivotal disagreement. Bohr would always maintain that the observer, and the way the quantum world was observed, was, if not the only, then at least a vital determining factor of what nature would now make up its mind to be (and so show the observer).
Einstein’s vigorous objections notwithstanding, the quantum theory was a huge success. Mysterious effects like radioactivity could now be understood (and harnessed), and new technologies like microelectronics were being born.
That is not to say that scientists liked what quantum theory said about the uncertainty of nature. In fact, many worried about that. But the theory worked, it produced results, whether you agreed with, or understood it, or not.
And to this day, scientists have no difficulties doing the mathematics of quantum mechanics—it all works just f
ine, but they still find it impossible to understand the full consequences of the theory, what—when all is said and done, at the core—does it really say about nature?
For it seems—contrary to all reason and common sense—that you have to assume one attitude, or outlook, toward small scale objects (the micro world of atoms and subatomic particles) and another when you work with large object (the macro part of nature).
So, that is what the working physicist did: viewed macro nature one way and micro nature another. No, it didn’t really make philosophical sense, and there was always the question of what counts as small and what counts as big, and why do they work differently if big things are just made of lots of small things?
Bohr—perhaps less philosophically inclined than Einstein—arrived at the conclusion that you just have to accept that nature is odd. Quantum theory may not make sense but, look, you can’t argue with its applicability and its success. The theory works, whether ugly or not.
And so, in the end, Bohr’s view of quantum mechanics, which was to be known as “the Copenhagen interpretation,” became the new orthodoxy of the nature of reality. Einstein grumbling and mumbling offstage.
Bohr thought of reality has having two perspectives, that reality contains two alternative dimensions.
And that is the Copenhagen interpretation: Bohr postulated one reality at the microscopic level, where everything behaved like quantum mechanics said—that things were wavy and did not have definite positions or speeds; and then there was another reality at the macroscopic level, obeying classical physics where everything is definite and not so puzzling.
But as someone who constantly worried about what is really going on, Einstein could not let this go. He was determined to solve this apparent contradiction.
His problem, however, was that 1930s’ technology was not up to the job. There was no way to conclusively prove things at this level one way or the other.
So, instead of approaching the problem experimentally, Einstein and his colleagues set out to test nature in their heads to attempt to expose the flaws in Niels Bohr’s philosophy.
The EPR Thought Experiment
Now, remember, we are dealing with intellectual giants here. These were theorists and thinkers that could create and agree upon a mental universe with specific laws—law that could then be tested; a universe that would behave according to these laws when subjected to postulated events and introduced variables.
But even in the elaborate thought-universe of quantum mechanics, Einstein could not disprove Bohr’s view, or improve upon the theory.
Let’s take a look at the most famous of these what they called thought experiments. It was devised and carried out by Einstein and two of his colleagues, Podolsky and Rosen, and thus it has become known as the Einstein-Podolsky-Rosen (EPR) thought experiment.
It can be a little tricky to get your head around, but let’s return to the quantum (micro) glove in the sealed box. So here, again, we have a glove inside a box. And again, imagine that this glove is a tiny quantum particle, only this time we have a pair of particles, and so we have another box, with another glove in it to make up this pair of quantum particles.
Now, we have yet to open either of the boxes or make any measurements of the gloves, so according to Niels Bohr, at this unobserved point, neither of these gloves knows whether it is left-handed or right-handed. They are, both of them, in a strange state of mixture of maybe left and maybe right—if indeed, they are at all.
Here it is important to add that while there are not many things we can know about these quantum particles with certainty, one thing we do know is this: like gloves, they come in (bonded) pairs. But until observed, the pair remains in a strange unknown state as to which of them is right-handed and which is left-handed.
“Okay,” said Einstein, “I don’t believe it, but let’s just suppose it were true, if I open one of these boxes, we will then force nature to make a decision.”
Now, because the gloves—just like the quantum particles—must be a pair, if you discover, upon opening one of the boxes that it is a left-handed glove (particle), the other glove must instantly be(come) the opposite, i.e., right-handed.
In the quantum world left or right translates into polarity: positive or negative, or into which way the particle spins, clockwise or anti-clockwise. If one of the pair is one way, the other one has to be the other way. This has be experimentally proven (without a single deviation) over and over and for so long that it is now accepted as a natural truth.
But here’s the big question: How does the right-handed glove (inside its unopened box) know when we open the left-handed box, and so make sure to be its opposite (inside the still unopened box)?
The only answer is that the gloves obviously, one way or another, communicate with each other. But this communication cannot be via messages (which would themselves be particles of some kind), because, according to Einstein’s theory of relativity, a message-particle cannot travel faster than the speed of light—while the other of the pair instantly (and instantly is a whole lot faster than the speed of light) adjusts to be the opposite of its observed twin. (This is what Doctor Lawson conclusively proved in April of 1999).
Also, were we to open the boxes at exactly the same moment, there would be no time for a message-particle to travel. And still, the quantum gloves would be each other’s opposite.
This, as one scientist put it, “is instantaneous action at a distance, and modern physics, because of Einstein’s own theory of relativity, does not allow for that, because things—even if travelling at the speed of light—has to take time; and instant essentially means no time.
“That is why Einstein said that if you believe quantum mechanics like it is normally understood, then you also believe something that is inconsistent with special relativity, and that just looks wrong.”
Moving On
The (failed) EPR thought experiment—Einstein, Podolsky and Rosen could not disprove Bohr’s take on things—was Einstein’s last and best challenge to the quantum theory, and after 1935 he moved on to other things. Still, he remained unconvinced about Bohr’s quantum theory for the rest of his life, despite Bohr’s efforts to sway him otherwise.
Actually, it really bothered Bohr that he could never convince Einstein; it was a real aggravation to him. Some even say that Bohr felt that he had failed because he could not convince Einstein.
Still, as the quantum theory was refined it became more and more successful, and despite its philosophical difficulties most scientists just got on with it and used deployed in their work.
This thought experiment was to remain a thought experiment for decades since there was no way to physically prove it one way or another, but in the 1960s, John Bell, a physicist from Northern Ireland, moved things on by turning the EPR thought experiment into something that could be practically tested.
And after a few years of refinement, and allowing for lab technology to catch up and be ready for the task, the EPR thought experiment was carried out in the real world.
The Geneva Experiment
This was finally done over a tiny distance by a French team led by Alain Aspect in the early 1980s. The result proved Bohr’s assumption: the observation of one particle did indeed cause the instant “opposition” of the other.
Still, this was not sufficiently convincing for the large majority of the scientific community.
So, we fast forward to 1997, when a team at the University of Geneva lead by Nicolas Gisin attempted the experiment on a much large scale. They wanted to demonstrate that a pair of quantum particles actually do have this strange, unexplainable connection, but this time across a whole city.
For this experiment they first had to create a bonded pair of quantum particles: a pair of photons, particles of light. And, as always and just like gloves, one photon must be the opposite of the other.
The plan was to then separate them by ten kilometers and then measure them at exactly the same moment.
Timed correctly—a
nd being Swiss they had the clocking thing down—there would then be no time for a message to pass between the photons, even at ten times the speed of light.
In this experiment they first isolated one photon and then, by firing it at a non-linear crystal, divided it into two, bonded twin photons—together now forming what they termed a single quantum system.
One of these twin-photons was then sent down one fiber strand to travel about five kilometers to the south, while the other twin-photon was sent down another strand of fiber to travel five kilometers to the north.
At ten kilometers apart, a measurement was made at the exact same time.
Said Nicolas Gisin in a subsequent interview, “Measuring the northbound photon forced it to assume a measurable property, with the effect that instantaneously—in theory, and certainly faster than light in practice—the southbound photon acquired the opposite property—every time.
“The output on one side was always completely random, the outcome on the other side was also always completely random, however, the two outcomes were always opposite. Always. Always.”
Not only did the researchers not know which photon had which property, but according quantum theory, and well confirmed by the experiment, the photons themselves did not know until one of the twins was measured.
One way of stating that is that nature itself does not know what it is until viewed by life.
Bohr 1 - Einstein 0.
So, nature is, if you will, at the subatomic level, and as I’ve pointed out, just plain weird.
Until someone makes a measurement, two bonded photons exist in a tangled-up state, both being and not being at the same time, while also, somehow, being intimately connected whether side by side or across vast distances.
