Entanglement: The Greatest Mystery In Physics
Story: Begin physics lesson: Entanglement is the property of quantum physics which allows for instantaneous movement – regardless of the speed of light. In short, two particles can be generated by a common process (like a photon hitting an excited atom). The properties of these two particles are tied together. When generated, they fly off in opposite directions. If we capture one of the particles and measure its properties, we can say with absolute certainty what the properties of the other particle are. We never have to touch it or see it. What’s better, if we change some property of our particle, we change those properties on the other particle instantly. We can, in theory, change a particle in the Gamma quadrant by tweaking its entangled partner as it passes Earth. End of physics lesson.
Review: In the world of “accessible” science books there are authors and there are Authors. Aczel definitely falls into the latter category. His style shines with the passion he feels for his subjects. When his subject is the precursor to real teleportation, the result is a great read.
Aczel knows how confusing this all is for physicists, so he makes every allowance for us mere mortals. He takes a chronological approach to the story of entanglement, and repeats concepts, definitions, and principles when possible to help the reader grasp the story. And this is a story. Beginning with Thomas Young’s proof that light is a wave in the early 1800s, Aczel takes entanglement from a glint in the eye of a young physicist, through decades of research, to experiments which actually manipulate matter instantly across miles.
For the most part, the story is told in terms of the people who have lived it. Based largely on Young’s work, Max Planck developed Quantum Mechanics in 1900. Niels Bohr tied quantum theory to the atom. With Planck’s Constant and Bohr’s theories, DeBroglie determined how to calculate the wavelength of a particle.
Erwin Schroedinger and his cat squeezed all this together and came up with something unprecedented. Schroedinger proved on paper that a particle in a sealed environment is both a wave and a particle. Observing the particle makes it pick a form – particle or wave. Through all of his work, Schroedinger developed the first theory of entanglement in 1926.
About the same time, Werner Heisenberg demonstrated that we can only know so much about a particle. There’s no way we can know everything about it because measuring one property affects other properties. Then things began to move quickly. Richard Feynman worked out the math required to give an educated guess of where particles went when given multiple paths. Paul Dirac came up with the concept of anti-matter, so a year later Carl Anderson discovered the first anti-particle: the positron. Madame Wu and Irving Shaknov made a positron and electron orbit each other, creating the first artificial element: Positronium. Positronium’s disintegration exactly followed the predictions made by John Wheeler.
Wheeler gave us the concept of the black hole. He and Bohr developed the concept of fission. Wheeler also updated Young’s original experiment and demonstrated that we can make a decision which changes the past. For details on that, you’ll have to read the book.
You may have noticed one name missing from the panoply so far. What about Einstein? His theory of Special Relativity was incorporated into quantum theory early on, so what effect did the century’s most famous physicist have on the state of things? Einstein believed three principles were central to theories of nature: Nature should be described by a deterministic theory – probabilities only demonstrate gaps in human knowledge. The theory should include everything. The theory should be local – events here are dictated by the laws of reality here, and those laws may be different elsewhere.
Einstein disliked quantum theory. He thought it was incomplete. In 1934 he brought in Boris Podolsky and Nathan Rosen. Together they wrote the EPR paper and began an argument which continued through the remainder of the century. EPR claims that hidden variables are required to account for the fact that quantum mechanics is not deterministic. Entanglement was presented as evidence. Entanglement isn’t local if modifying a particle here modifies a particle way over there. We’re missing something.
The ink (and particles) flew for years. Physicists fell into two camps, arguing alternately for EPR and for Quantum Mechanics. Enter John Bell. In 1966 Bell wrote a paper which did two things. It proved that EPR and Quantum Mechanics were mutually exclusive: one or the other can be right, but not both. The paper concluded with some nasty math that included a series of inequalities. Bell explained that if someone could demonstrate an experiment that violated those inequalities, it would also demonstrate that Quantum Mechanics is correct. The race began.
Within a couple of years people were looking at Wu and Shaknov’s Positronium experiment. The idea was that the experiment could resolve Bell’s theorem, but it would have to be repeated because no one was looking for that data when it was done the first time. The primary players to emerge were John Clauser, Mike Horne, Abner Shimony, and Richard Holt. Their CHSH experiment violated Bell’s inequalities by a quantity five times greater than statistically expected. The same experiment refined and repeated by others increased the support of Quantum Mechanics further. Alain Aspect pushed the support of Quantum Mechanics to over 40 standard deviations.
And here’s where science fiction begins to become science fact. Based on the body of knowledge and the experiments to this point, scientists have begun adding new levels of sophistication to their manipulation of entangled particles. Entanglement has been used to send messages between two points. Methods were developed to entangle three or four particles as one. They have demonstrated that particles passing through an experiment will behave differently if a mechanism is added to observe them – even if they’re not observed. The mere existence of a way to observe them changes the results of the experiment. Entanglement experiments have been conducted between cities. There is a great deal of work underway now to develop “quantum encryption.” The value of the encryption particles would not be determined until they arrived at their respected recipients – hacking would be impossible.
So what about teleportation? The good news is that they’ve done it. The bad news is that the largest thing they’ve managed is a subatomic particle. If two particles are entangled – one of which we have, and other being somewhere else – we can determine the properties of our particle and instantly impart those properties on the other particle. The rules of Quantum Mechanics dictate that we have to destroy our particle to get all the measurements. In fact, it’s hard not to destroy our particle before we get all the information we need. But the cool part is that we don’t have to do anything with the information we gather – just gathering it causes the distant particle to transform into what our particle was. And since we have to destroy our particle, we avoid creating a “matter fax” in which we create copies of particles.
We’re still very far from teleporting a jug of fresh milk to the house in the morning, but this book makes you understand just how far we’ve come. You gain a real appreciation of the thought, the lives, and the decades of manpower that have gone into the problem so far. Even though Aczel stops short of saying it, you come away feeling that teleportation on the macro level is an attainable goal.
The style of the book is extremely readable. Aczel includes biographical information on each of the players in the game, so you gain an understanding of their time, their motivation, and you know on what they’re building their work. You don’t need any math skills to follow the bouncing ball. The ideas are clearly presented, repeated as needed, and illustrated with quite a few drawings and diagrams. It’s not every day that a book about physics leaves you feeling like the future’s both exciting and nearly within reach.
Author: Amir D. Aczel
Publisher: Four Walls Eight Windows