First there was Schrödinger's Cat, now there's Schrödinger's dollar.
Schrödinger's Cat is a thought experiment developed by physicist Erwin Schrödinger and used to illustrate the random quality of quantum mechanics. Imagine, he said, a cat in a box with a vial of poisonous gas and a bit of radioactive material, such as uranium. Uranium emits alpha particles, but at random intervals. A Geiger counter placed inside the box detects when an alpha particle is emitted. If one is detected, the poisonous gas gets released and the cat dies. If the Geiger counter doesn't detect a particle, the cat lives.
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A mathematical formula describing this experiment says that there is not a definite state (dead or alive), but two states that have a certain probability. The "real" state is known only when someone opens the box and looks in on the cat. This paradox has been explored by physicists for decades.
To explore this thought experiment, conceptual artist Jonathon Keats built a box, but instead of putting a cat inside, he put money. Keats, who is known for combining art and science, calls the box a "quantum ATM."
"The technology exists for the sake of bringing people into this parallel world to explore the nature of money," Keats told Discovery News.
The ATM will operate just like any other financial institution, Keats said. People can deposit dollars and have them assigned to an account. But that's where things differ: while the deposit is being processed, a uranium-glass sphere will randomly emit an alpha particle. Instead of releasing gas, the particle will fire into a cylinder inscribed with 7 billion microscopic squares, each one associated with an account number. When that particle hits a box, the depositor's account will be credited.
However, it's impossible to know without looking inside the apparatus which square the alpha particle has hit. And in fact, Keats set up a steel cylinder around the apparatus so that the particle can never be observed. In quantum mechanical terms, the particle is in a state called superposition - meaning that it could be in any of the 7 billion squares. Mathematically, it is described as taking all of the possible paths and so Keats' ATM credits all 7 billion accounts with the deposit. The cash itself will effectively be in a superposition until someone observes where the particle went.
Because the cash is effectively in all seven billion accounts, each dollar deposited could be withdrawn from any one of them. So if I deposit $1 and get 20 friends to withdraw a dollar, we could pool our resources and get a nice bottle of wine. All these "superposed" dollars are just as real as the initial one deposited.
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And lest one think that superposition is just a mental shorthand for "I don't know where it is," it's important to note that such states have been seen and actually made - atoms, photons, and even an object large enough to see with the naked eye have been put in states where they were in two places at once.
One question is whether anyone would take money from the Quantum Bank. The bank itself can issue notes that are "one quantum" and set to be worth one dollar. "They are perfectly good if anyone would take them." Keats said, just like any other currency.
The ATM will consist of a box on one side where people deposit the dollars and another from which they take the quanta. "In the future, I hope to fully automate the system in such a way that the dollar bills are shredded and the quantum bills are printed as they're dispensed," Keats said.
He noted that at one time local banks issuing banknotes was a common practice - a modern national currency didn't appear in the United States until the Civil War, and the Federal Reserve wasn't created until 1913. In some countries, foreign currencies are used routinely alongside the national ones - dollars are widely accepted in the Caribbean, for example. Bitcoins are an attempt to build an alternative to national currency that can be accepted anywhere, and some merchants accept them.
"By actually spending this money we're asking what we mean by superposition," Keats said.
The ATM will be installed in the basement of 20 Rockefeller Plaza in New York on June 11.
Credit: Jonathan Keats