Imagine you are a photon, a packet of light. You are a tiny blip of energy, hurtling through the universe on your own. But you have a twin, another photon to whom you have been intimately connected since the day you were born. Now matter what distance separates you, be it the width of a lab bench or the breadth of the universe, you mirror each other. Whatever happens to your twin instantaneously affects you, and vice versa. You are like the mouse siblings in “An American Tail”, wrenched apart by fate but feeling the same feelings and singing the same song beneath the same glowing moon.
This is quantum entanglement. To non-physicists it sounds about as fantastical as singing mice, and indeed, plenty of physicists have problems with the phenomenon. Albert Einstein, whose own research helped give rise to quantum theory, derisively called the concept “spooky action at a distance.” Quantum entanglement seems to break some of the bedrock rules of standard physics: that nothing can travel faster than light, that objects are only influenced by their immediate surroundings. And scientists still can't explain how the particles are linked. Is it wormholes? An unknown dimension? The power of love? (That last one's a joke.)
Luckily for quantum physicists, you don't always need to explain a phenomenon in order to use it. Ancient humans didn't know about friction before inventing the wheel; doctors in medieval China didn't know about antibodies when they began inoculating people against smallpox 600 years ago. Not knowing what's behind quantum entanglement didn't stop Jian-Wei Pan, a physicist at the University of Science and Technology of China in Shanghai, from rocketing it into space.
In a new study in the journal Science, Pan and his colleagues report that they were able to produce entangled photons on a satellite orbiting 300 miles above the planet and beam the particles to two different ground-based labs that were 750 miles apart, all without losing the particles' strange linkage. It is the first time anyone has ever generated entangled particles in space, and represents a 10-fold increase in the distance over which entanglement has been maintained.
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