How do you define “real”?
This is a question typically left to the philosophers of the world, or the 1999 cult classic film, The Matrix. However, physicists now have something significant to add to the debate. Under what you would call a non-quantum mechanical definition of real, known as local realism, real is defined as when an object, like a car, has definite properties independent of observation or measurement. Meaning the universe exists external to our minds.
For example, a car can have wheels even when no one is looking. And “local” means that this car can only be influenced by its immediate surroundings. And any measurable influence (causes), under the normal rules of physics, cannot travel faster than the speed of light.
But under quantum mechanics, local realism gets a little dicey. And three theoretical physicists, John Clauser, Anton Zeilinger and Alain Aspect, were recently jointly awarded the 2022 Nobel Prize in Physics for a 1972 experiment, and many subsequent experiments, showing that the local realism view of the universe is likely to be false.
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“This work has made clear what quantum mechanics really means,” said Professor Thors Hans Hansson, a member of the Nobel Committee for Physics, in response to the award.
I’m sorry… What?
Okay, let me explain.
The scientists’ findings show that the universe cannot be locally real, as particles lack definite spin-up or spin-down properties (quantum state) prior to their observation or measurement. Therefore, the simple act of observing a particle changes its state, contradicting the rules of local realism. In other words, the universe is “real,” but only when you’re looking at it.
“The experiments beginning with the earliest one of Clauser and continuing along, show that this stuff isn’t just philosophical, it’s real — and like other real things, potentially useful,” Charles Bennett, an eminent quantum researcher at IBM, told Scientific American.
The Nobel Prize-winning experiments also demonstrated that two particles, regardless of distance apart, can remain entangled in the quantum realm. This contradicts local realism and Einstein’s theory of relativity. Because, as per their assumptions, influences cannot travel faster than the speed of light. In theory, two particles could be at separate ends of the observable universe and continue to be entangled, a concept known as “non-locality.”
“Alain Aspect, John Clauser and Anton Zeilinger have each conducted groundbreaking experiments using entangled quantum states, where two particles behave like a single unit even when they are separated,” wrote The Nobel Prize in a statement. “Their results have cleared the way for new technology based upon quantum information.”
What is ‘quantum state’?
In the field of quantum physics, even legendary Nobel prize-winning theoretical physicist, Richard Feynman, once said: “if you think you understand quantum physics, you don’t understand quantum physics.” But today, we have a much better understanding of what’s happening at the quantum level.
Quantum physics says that the universe is random and that the state of particles, like electrons or protons, can only be predicted using a probability distribution, due to their un-deterministic nature. In other words, we can only predict how particles will behave once observed, within a given probability.
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This theoretical probability distribution is called the “wavefunction,” which holds information like the position and momentum of the particle. But — and this is where it gets tricky — the mere act of measuring, or observing the particle, collapses this wavefunction into a given particle state that we can then observe — a phenomenon known as “particle-wave duality.” This is what, in theory, makes the universe random.
But scientists still don’t understand why or how the wavefunction collapses, an issue dubbed “the measurement problem.” So, what does the particle look like, before it’s been observed? Well, we cannot know, as the particle, before observation, is in a state of “quantum superposition.” Meaning, in multiple (infinite) states, at the same time.
Confused yet? Don’t worry, all you need to know is that nothing is as it seems on the quantum level and that John Clauser, Anton Zeilinger and Alain Aspect’s findings have shaken the science world, tipping reality on its head.
“The burgeoning investments in quantum technologies now occurring all over the world are building on scientific foundations which flow from the pioneering work of Bell, Clauser, Aspect and Zeilinger,” John Preskill, a leading quantum information scientist at the California Institute of Technology, told Scientific American.