The story takes us to Quantumland, where Alice encounters a world of electrons and photons, wave functions, the Pauli Principle and the Uncertainty Principle. For the most part these are true. We find Alice on a dull, rainy day as she watches uninteresting TV programs which leads her to daydream about doing something interesting. As Alice continues watching the TV screen becomes fuzzy and she finds herself being pulled inside, tumbling headlong into a new world - a world where electrons always bounce and wiggle so that they can remain small, where rabbits run headlong at locked doors and pass through unharmed eventually , As the subtitle says, this is an allegory of quantum physics. As Alice continues watching the TV screen becomes fuzzy and she finds herself being pulled inside, tumbling headlong into a new world - a world where electrons always bounce and wiggle so that they can remain small, where rabbits run headlong at locked doors and pass through unharmed eventually , where no matter what path Alice takes, she always ends up where she is supposed to be.

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By Maria Popova As a lover of science and of all things Alice in Wonderland , imagine my delight at discovering Alice in Quantumland: An Allegory of Quantum Physics public library — an imaginative and unusual quantum primer by particle physicist Robert Gilmore, who has under his belt experience at Stanford and CERN.

Gilmore writes in the preface: In the first half of the twentieth century, our understanding in the Universe was turned upside down. The old classical theories of physics were replaced by a new way of looking at the world — quantum mechanics. This is in many ways at variance with the ideas of the older Newtonian mechanics; indeed, in many ways it is at variance with our common sense.

Nevertheless, the strangest thing about these theories is their extraordinary success in predicting the observed behavior of physical systems. However nonsensical quantum mechanics may at times appear to us, that seems to be the way that Nature wants it — and so we have to play along. Such analogies can never be very true to reality as quantum processes are really quite different from our normal experience.

This Quantumland shows the essential features of the quantum world: the world that we all inhabit. He cites godfather of quantum mechanics: Neils Bohr … is said to have remarked that anyone who did not feel dizzy when thinking about quantum theory had not understood it. There, we follow her as she visits the Heisenberg Bank and the Mechanics Institute, learning about the curiouser and curiouser behaviors of particles.

She marvels at the Uncertain Accountant, whose attempts to balance books are befuddled by energy fluctuations driven by the Heisenberg Uncertainty Principle. The State Agent shows her that, thanks to the Pauli Exclusion Principle, a particle can be two places at once. She knew from the notice outside that it must be.

Whatever your problem is, I am sure that between us we will be able to assist you, if you would just wait a moment while we finish our shots. Both men turned back to the billiards table. The Classical Mechanic took careful aim, clearly judging all the angles involved to within a tiny fraction of a degree.

At last, he very deliberately played his shot. The ball bounced to and fro in a remarkable series of ricochets, ending in a collision with the red ball and knocking it squarely into the center of a hole. If you do things that way you can produce any result you choose.

His companion did not respond, but took his place at the table and made a vague stab with his cue. The ball shot off in every direction at once, so that there was no part of the table where [Alice] could say definitely that the ball had not gone, though equally she could in no way say where it actually was.

After a moment the player went over and peered into one of the pockets, then reached in and drew out a red ball. I live in the sea and am equally at home upon the land. But this is as nothing compared with the number of worlds which we all inhabit, for we are all citizens of many worlds — many, many worlds. The quantum rules … apply to the whole world, to everything. There is no limit to the idea of the superposition of states. When an observer looks at a superposition of quantum states you would expect him or her to see all of the effects that are appropriate to the selection of states present.

This is what does happen; one observer does see all the results, or rather the observer also is in a superposition of different states, and each state of the observer has seen the result that goes with one of the states, in the original mixture. Each state is simply extended to include the observer in the act of seeing that particular state.

This is not the way that it seems to us, but that is because the different states of the observer are not aware of one another. When an electron passes through a screen with two slits in it, then it might pass through to the left or to the right.

What you observe to happen is pure chance. You might see that the electron has gone to the left, but there will be another you that will have seen the electron go to the right. At the point at which you observe the electron, you split into two versions of yourself, one to see each possible result. The world has split into two worlds with slightly different versions of you in them. To understand what made that encounter possible, Alice visits the State Agent, who presents her with an apparatus for seeing the virtual particles of antimatter.

This had a transparent visor which entirely covered the front, and there was a long cable attached to a socket at the back. The cable snaked away along the path by which he had come until it was lost from sight in the distance.

Just put this on, and you will see the world of virtual particles. It was large, and it looked very complicated and even, she felt, a little sinister. However, if this was going to reveal the virtual particles she had heard mentioned so often, she was prepared to try it.

She put the helmet on her head. It was very heavy. The Agent reached across to the helmet and made some adjustment at the side of her head, where Alice was unable to see. The view through the visor clouded over with little sparkling dots and… When her view through the visor cleared, it had dramatically changed.

Alice exclaimed aloud in annoyance at losing the fascinating picture. I had intended to make it coin-operated, you see. The anti-Alice would travel along until it collided with an Alice and the two mutually annihilated one another, converting their energy back to photons. How it would appear to you is quite different, quite different altogether. For you the annihilation would come before the creation of course.

You are experiencing events in reverse order after all. I would have expected you to see that for yourself. As far as your companion was concerned you and the anti-Alice were both utterly destroyed and your mass energy was carried off by high-energy photons. Both were dressed in long frock coats and narrow trousers, and both had bushy side whiskers.

Both wore waistcoats, each with a gold chain attached to a watch which its owner had obviously checked recently against a reliable standard clock. These two were not actually identical to one another, since only particles are completely identical, but they were certainly very much alike. They were obviously both honorable, honest, and reliable as well as being competent and conscientious observers. If they were to say that they had seen something, no one would dream of disputing it.

Alice in Quantumland: An Allegory of Quantum Physics is absolutely fantastic in its entirety, certain to engage the simultaneous states of entertainment and education with unequaled grace.

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Alice in Quantumland: An Allegory of Quantum Physics






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