Entanglement

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Their eyes met when both of them looked up at the same moment from the screens they'd been focused on. Maybe it was the contrast between the cold light from their laptops and the warm glow of the coffee shop, or between the abstractions they'd been immersed in--he was a physics postdoc writing a paper on a new test of the Leggett inequality and she was an IT researcher reading Zeilinger's latest piece on quantum teleportation--and their sudden, simultaneous return to reality, but they found themselves instantly attracted to each other. He liked her shy smile and the way the collar of her shirt had slipped to reveal the softness of one shoulder. She was drawn to his shock of mussed black hair and dark, mysterious eyes. Whatever the cause, she felt her cheeks flush a bit and he saw her eyes widen, and he grinned awkwardly while trying to think of what to say, and she realized he was groping for words and found it charming, and smiled invitingly until some words finally emerged, although not the crisp witticism he would have liked.
"Hi," he said, "I'm Bob. What's your name?" Then he blushed, from how blunt and unpolished it sounded, and looked down. She leaned forward and lowered her head to catch his gaze, and with just a hint of laughter in her voice replied, "I'm Alice." Relieved that she hadn't been put off, he looked up again, saw warmth and interest in her face, and surprised himself by asking, "Mind if I join you?" gesturing as if to pick up his laptop. Alice drew a breath and held it for a second, knowing that what she said next could lead on to something completely unpredictable or pop the bubble of light and warmth that seemed to be surrounding them. Bob waited, his fingers curled lightly under the edge of his laptop, watching for a sign from her. He thought he saw a slight shrig and a fleeting smile just before she spoke. "Sure," she said, patting the chair next to her.
As he sat down, he glanced at her computer screen and she looked at his. "That looks familiar," he said. "You're interested in quantum teleportation?" "Yes," she said, I'm part of a group trying to teleport qubits over long distances. You're doing something similar? "Yes," he said, "I'm part of a team that just completed a test of the Leggett inequality." "What did you find," she said. "Einstein was flat-out wrong," he said. "We totally wiped out non-local realism." "So we can't even rely on causality?" she said. "Right," he said with a wry smile. "Everything's random until it's observed. The universe is not deterministic. What's happening now can change what happened in the past." "Where does that leave us?" she asked, with a just detectable emphasis on the word "us". He looked at her for a long time before ansering, looked deeptly, or more accurately, fell into her eyes, feeling a kind of intimacy he'd never experienced before, as if he knew her from the inside, and always had. She felt it too, and gasped. "This is totally out of character," he said, but he learned forward and kissed her, softly at first, but finding her lips soft and responsive, longer and more passionately.
They didn't stay long in the coffe shop, but packed their laptops and walked, and held hands, and talked, and kissed some more, and sometime in the early morning hours climbed the stairs to his apartment. On the walk they traced their histories. They found so many strange parallels, points at which their paths had crossed without their knowing it, times when they might have met if they'd turned left instead of right or arrived a few seconds later or earlier, that they weren't all that surprised to find they'd been born in the same hospital at the same time. "Seriously?" he said. "Boston Children's, March 20, 1990, 1:19 in the afternoon?" "Weird," she replied, "we might have been . . ."  ". . . newborns lying side by side," he said, taking her hand and leading her home.
That first encounter evolved into a deep, moving, sometimes hilarious relationship, during which they always felt inexplicably linked, finishing each other's thoughts, texting or calling each other at the same time, and even when far apart sensing the other's presence.
It ended as suddenly as it had begun. One morning Alice work up and noticed that she felt disconnected, achingly alone even with Bob asleep beside her. He didn't look the same, as if he'd been replaced overnight by an almost-identical stranger. His tousled hair was no longer boyish and charming; just messy. She felt lonely, yet at the same time a tingle of excitement, as if a part of her already sensed something else was coming her way.
When Bob woke up she was gone. He found a note on his laptop. "Dear Bob, I've never felt closer to anyone than I did to you. We shared something incredible. But now it's over and I need to say goodbye. Goodbye." He smiled at the second goodbye. Alice had always been a bit too concrete in her thinking, he reflected. He knew he should feel sad or angry, but found he didn't. What he felt, he decided, was . . . not lighter exactly, but as if he'd been entangled in an invisible web and now, suddedly, it was gone. He got up, brewed some coffee, and typed the finishing touches to the article. "We agree with Zeilinger," he wrote, "that in order to agree with this and previous experiments, we need to abandon certain features of realism. Reality is simply not what it used to be."

About the Author: 
Robert Adler is a science writer based in California and Mexico. Or possibly a Ukranian cartoonist. Or a shepherd from Ulan Bator.

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Quantum Theories

I is for ... Information

Many researchers working in quantum theory believe that information is the most fundamental building block of reality.

Z is for ... Zero-point energy

Even at absolute zero, the lowest temperature possible, nothing has zero energy. In these conditions, particles and fields are in their lowest energy state, with an energy proportional to Planck’s constant.

D is for ... Dice

Albert Einstein decided quantum theory couldn’t be right because its reliance on probability means everything is a result of chance. “God doesn’t play dice with the world,” he said.

A is for ... Act of observation

Some people believe this changes everything in the quantum world, even bringing things into existence.

L is for ... Large Hadron Collider (LHC)

At CERN in Geneva, Switzerland, this machine is smashing apart particles in order to discover their constituent parts and the quantum laws that govern their behaviour.

R is for ... Randomness

Unpredictability lies at the heart of quantum mechanics. It bothered Einstein, but it also bothers the Dalai Lama.

W is for ... Wavefunction

The mathematics of quantum theory associates each quantum object with a wavefunction that appears in the Schrödinger equation and gives the probability of finding it in any given state.

Q is for ... Qubit

One quantum bit of information is known as a qubit (pronounced Q-bit). The ability of quantum particles to exist in many different states at once means a single quantum object can represent multiple qubits at once, opening up the possibility of extremely fast information processing.

F is for ... Free Will

Ideas at the heart of quantum theory, to do with randomness and the character of the molecules that make up the physical matter of our brains, lead some researchers to suggest humans can’t have free will.

G is for ... Gravity

Our best theory of gravity no longer belongs to Isaac Newton. It’s Einstein’s General Theory of Relativity. There’s just one problem: it is incompatible with quantum theory. The effort to tie the two together provides the greatest challenge to physics in the 21st century.

P is for ... Planck's Constant

This is one of the universal constants of nature, and relates the energy of a single quantum of radiation to its frequency. It is central to quantum theory and appears in many important formulae, including the Schrödinger Equation.

A is for ... Atom

This is the basic building block of matter that creates the world of chemical elements – although it is made up of more fundamental particles.

N is for ... Nonlocality

When two quantum particles are entangled, it can also be said they are “nonlocal”: their physical proximity does not affect the way their quantum states are linked.

P is for ... Probability

Quantum mechanics is a probabilistic theory: it does not give definite answers, but only the probability that an experiment will come up with a particular answer. This was the source of Einstein’s objection that God “does not play dice” with the universe.

T is for ... Teleportation

Quantum tricks allow a particle to be transported from one location to another without passing through the intervening space – or that’s how it appears. The reality is that the process is more like faxing, where the information held by one particle is written onto a distant particle.

M is for ... Multiverse

Our most successful theories of cosmology suggest that our universe is one of many universes that bubble off from one another. It’s not clear whether it will ever be possible to detect these other universes.

L is for ... Light

We used to believe light was a wave, then we discovered it had the properties of a particle that we call a photon. Now we know it, like all elementary quantum objects, is both a wave and a particle!

C is for ... Cryptography

People have been hiding information in messages for millennia, but the quantum world provides a whole new way to do it.

S is for ... Superposition

Quantum objects can exist in two or more states at once: an electron in superposition, for example, can simultaneously move clockwise and anticlockwise around a ring-shaped conductor.

Q is for ... Quantum biology

A new and growing field that explores whether many biological processes depend on uniquely quantum processes to work. Under particular scrutiny at the moment are photosynthesis, smell and the navigation of migratory birds.

O is for ... Objective reality

Niels Bohr, one of the founding fathers of quantum physics, said there is no such thing as objective reality. All we can talk about, he said, is the results of measurements we make.

M is for ... Many Worlds Theory

Some researchers think the best way to explain the strange characteristics of the quantum world is to allow that each quantum event creates a new universe.

J is for ... Josephson Junction

This is a narrow constriction in a ring of superconductor. Current can only move around the ring because of quantum laws; the apparatus provides a neat way to investigate the properties of quantum mechanics.

V is for ... Virtual particles

Quantum theory’s uncertainty principle says that since not even empty space can have zero energy, the universe is fizzing with particle-antiparticle pairs that pop in and out of existence. These “virtual” particles are the source of Hawking radiation.

E is for ... Entanglement

When two quantum objects interact, the information they contain becomes shared. This can result in a kind of link between them, where an action performed on one will affect the outcome of an action performed on the other. This “entanglement” applies even if the two particles are half a universe apart.

T is for ... Tunnelling

This happens when quantum objects “borrow” energy in order to bypass an obstacle such as a gap in an electrical circuit. It is possible thanks to the uncertainty principle, and enables quantum particles to do things other particles can’t.

D is for ... Decoherence

Unless it is carefully isolated, a quantum system will “leak” information into its surroundings. This can destroy delicate states such as superposition and entanglement.

R is for ... Reality

Since the predictions of quantum theory have been right in every experiment ever done, many researchers think it is the best guide we have to the nature of reality. Unfortunately, that still leaves room for plenty of ideas about what reality really is!

K is for ... Kaon

These are particles that carry a quantum property called strangeness. Some fundamental particles have the property known as charm!

B is for ... Bell's Theorem

In 1964, John Bell came up with a way of testing whether quantum theory was a true reflection of reality. In 1982, the results came in – and the world has never been the same since!

C is for ... Computing

The rules of the quantum world mean that we can process information much faster than is possible using the computers we use now.

H is for ... Hidden Variables

One school of thought says that the strangeness of quantum theory can be put down to a lack of information; if we could find the “hidden variables” the mysteries would all go away.

B is for ... Bose-Einstein Condensate (BEC)

At extremely low temperatures, quantum rules mean that atoms can come together and behave as if they are one giant super-atom.

G is for ... Gluon

These elementary particles hold together the quarks that lie at the heart of matter.

U is for ... Universe

To many researchers, the universe behaves like a gigantic quantum computer that is busy processing all the information it contains.

S is for ... Schrödinger Equation

This is the central equation of quantum theory, and describes how any quantum system will behave, and how its observable qualities are likely to manifest in an experiment.

X is for ... X-ray

In 1923 Arthur Compton shone X-rays onto a block of graphite and found that they bounced off with their energy reduced exactly as would be expected if they were composed of particles colliding with electrons in the graphite. This was the first indication of radiation’s particle-like nature.

H is for ... Hawking Radiation

In 1975, Stephen Hawking showed that the principles of quantum mechanics would mean that a black hole emits a slow stream of particles and would eventually evaporate.

A is for ... Alice and Bob

In quantum experiments, these are the names traditionally given to the people transmitting and receiving information. In quantum cryptography, an eavesdropper called Eve tries to intercept the information.

I is for ... Interferometer

Some of the strangest characteristics of quantum theory can be demonstrated by firing a photon into an interferometer: the device’s output is a pattern that can only be explained by the photon passing simultaneously through two widely-separated slits.

W is for ... Wave-particle duality

It is possible to describe an atom, an electron, or a photon as either a wave or a particle. In reality, they are both: a wave and a particle.

Y is for ... Young's Double Slit Experiment

In 1801, Thomas Young proved light was a wave, and overthrew Newton’s idea that light was a “corpuscle”.

U is for ... Uncertainty Principle

One of the most famous ideas in science, this declares that it is impossible to know all the physical attributes of a quantum particle or system simultaneously.

R is for ... Radioactivity

The atoms of a radioactive substance break apart, emitting particles. It is impossible to predict when the next particle will be emitted as it happens at random. All we can do is give the probability that any particular atom will have decayed by a given time.

S is for ... Schrödinger’s Cat

A hypothetical experiment in which a cat kept in a closed box can be alive and dead at the same time – as long as nobody lifts the lid to take a look.