Posts Tagged ‘entangled particles’

Of Quantum Mechanics, Cabbages, Kings, and Carpets

September 8, 2015

imagesAstronomer Arthur Eddington said the universe is not just stranger than we imagine, it’s stranger than we can imagine. I’ve written about the biggest question: why does it exist at all? There’s no answer. (It isn’t God, since the same question applies to him.)

Lately I’ve been reading, in Brian Greene’s book, The Fabric of the Cosmos, about quantum mechanics, governing the submicroscopic realm – very different from the physics of our everyday world. And indeed stranger than we can imagine.

Bear with me here:

Unknown-1Heisenberg’s uncertainty principle says one can, for example, know an electron’s position, or its speed, but not both. Measuring the speed makes it impossible to determine its position. The explanation, physicists tell us, is that an electron can be understood as a “probability wave” – it doesn’t actually have a position, merely a sort of mist of possible ones ranging from more to less probable – across the entire universe. It’s likely nearby, but the probability of its being light years away, while exceedingly tiny, is not zero. Measurement causes the probability wave to collapse into a precise location.

Now, a certain experiment created two “entangled” particles, shot out in opposite directions, such that when a characteristic about one, something called “spin,” was measured, that inferentially revealed the spin of the other – seemingly avoiding the uncertainty principle, because with regard to that second particle, nothing has been done to cause its probability wave to collapse. Spin is random, indeterminate until measured – yet what is measured for Particle A will apply to its entangled partner B – instantaneously – even if it’s across the room (or the galaxy).

Unknown-6But in a famous 1935 paper, Einstein, Podolsky and Rosen posited that quantum mechanics cannot be a complete description of reality because notwithstanding the uncertainty principle, a particle must actually have a definite position and a definite speed at a given moment. They couldn’t accept that Particle A would somehow communicate its spin to Particle B, insisting instead that both, when created, must have been somehow pre-programmed to give the result they gave upon A’s measurement.

This seems intuitively reasonable. But guess what? The experiment (I won’t go into the details) says no – proving that the spins of entangled particles are not somehow baked in at their genesis but, rather, become reality – for both – only at the exact instant of measurement – no matter the distance between them.

This mind-bending result might seem to violate not just common sense but the cosmic speed limit (which is the speed of light). However, there is an explanation in Special Relativity: something appearing to be simultaneous from one vantage point may not be simultaneous from a different moving perspective (which I cannot claim to truly understand).

images-1Be that as it may – the described behavior of entangled particles might strike you as so esoteric that it has no relevance to our everyday existence. Yet it goes to the heart of our understanding of reality. Which is a version of “what happens in Vegas stays in Vegas” – that is, what happens in one place is separate from what happens in another place – because there is such a thing as “a place.” Entangled particles belie that notion, and reveal that space – the space we inhabit – is not what our common sense intuition tells us it is. If those particles can do what they do, then what seems to be the space separating them is meaningless – or in effect nonexistent.

Unknown-2This computer and the desk on which it stands seem to be solid objects. But they are comprised of atoms which we know are virtually entirely empty space (or “space”). And the same is true even of the particles comprising atoms. And so on. The more one tries to drill down to the ultimate reality at the heart of existence – its nitty gritty structure at the sub-sub-microscopic level – there’s no there there. I have a sense that the ways in which physicists talk about it are really metaphors. Our grade-school picture of the atom looking like a miniature solar system is such a metaphorical construct.* It’s not reality. Unknown-3And I suspect that, imagining a “Fantastic Voyage” sending super-miniaturized observers down into that realm, they could never be small enough to penetrate to the ultimate substrate of existence.

Yet that literally inconceivable substrate somehow aggregates into the physical world of shoes and ships and sealing wax and cabbages and kings. The mystery is vastly more profound than anything in religion.

To conclude, I will quote the philosopher Woody Allen: “What if everything is an illusion and nothing exists? In that case, I definitely overpaid for my carpet.”Unknown-5

* Might this also be true of the infinitesimally teensy vibrating strings that string theory posits as the ultimate constituents of matter?

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