Quantum Theory Cannot Hurt You_ A Guide to the Universe - Marcus Chown [27]
There is a ghostly web of quantum connections crisscrossing the Universe and coupling you and me to every last bit of matter in the most distant galaxy. We live in a telepathic universe. What this actually means physicists have not yet figured out.
Entanglement may also help explain the outstanding question posed by quantum theory: Where does the everyday world come from?
WHERE DOES THE EVERYDAY WORLD COME FROM?
According to quantum theory, weird superpositions of states are not only possible but guaranteed. An atom can be in many places at once or do many things at once. It is the interference between these possibilities that leads directly to many of the bizarre phenomena observed in the microscopic world. But why is it that, when large numbers of atoms club together to form everyday objects, those objects never display quantum behaviour? For instance, trees never behave as if they are in two places at once and no animal behaves as if it is a combination of a frog and a giraffe.
The first attempt to explain the conundrum was made in Copenhagen in the 1920s by quantum pioneer Niels Bohr. The Copenhagen Interpretation, in effect, divides the Universe into two domains, ruled by different laws. On the one hand, there is the domain of the very small, which is ruled by quantum theory, and on the other there is the domain of the very big, ruled by normal, or classical, laws. According to the Copenhagen Interpretation, it is when a quantum object like an atom interacts with a classical object that it is forced to stop being in a schizophrenic superposition and start behaving sensibly. The classical object could be a detecting device or even a human being.
But what exactly does a classical object do to stop a quantum object from being quantum? Even more importantly, what constitutes a classical object? After all, an eye is just a big collection of atoms, which individually obey quantum theory. This turns out to be the Achilles’ heel of the Copenhagen Interpretation and the reason it has always appeared to many to be a very unsatisfactory explanation of where the everyday world comes from.
The Copenhagen Interpretation divides the universe, arbitrarily, into two domains, only one of which is governed by quantum theory. This in itself is very defeatist. After all, if quantum theory is a fundamental description of reality, surely it should apply everywhere—to the atomic world and the everyday world. The idea that it is a universal theory is, in a nutshell, what physicists believe today.
It turns out we never observe a quantum system directly. We only observe its effect on its environment. This may be a measuring device or a human eye or, in general, the universe. For instance, the light from an object impinges on the retina of the eye and makes an impression there. What the observer knows is inseparable from what the observer is. Now, if quantum theory applies everywhere, we have a quantum object observing, or recording, another quantum object. The central question can therefore be restated: Why do weird schizophrenic states fail to impress themselves on, or entangle themselves with, the environment, whereas everyday one-place-at-one-time states do? An example may help.
If a high-speed subatomic particle flies through the air, it knocks electrons from any atoms it passes close to. Imagine it was possible to see a 10-centimetre-long portion of its track. And, say in that 10 centimetres the particle has a 50 per cent chance of interacting with one electron, kicking it out of its parent atom.
The particle, therefore, either knocks out an electron or doesn’t knock out an electron. But because the event of knocking out an electron is a quantum event, there is another possibility—the superposition of the two events. The particle both knocks out an electron and doesn’t knock out an electron! The question is: Why, when this event entangles itself with the environment, does it not leave an indelible impression? As luck would have it, it is possible to actually