Quantum Entanglement

by Ira Mark Egdall

Nature is not only stranger than we imagine, it is stranger than we can imagine.

– J. B. S. Haldane

You want wild and crazy? Forget jumping out of an airplane or going out with that nose-pierced, body tattooed delinquent with the multi-colored hair your mother hates. Just look at reality.

I’m talking about the reality revealed by so-called quantum entanglement, where two particles — no matter how far apart — are intimately and instantly connected.

Take two entangled photons moving in different directions. Per conservation laws, if one is vertically polarized, the other must be horizontally polarized, and vice-versa. So when you measure the polarization of one photon, you instantly know the polarization of the other.

So what’s the big deal? Einstein and his colleagues Podolsky and Rosen (EPR) argued each photon had a certain polarization before you measured it. All the measurement did was reveal what that polarization was all along. And once you measured the first photon, you knew what the second photon’s polarization was.

But quantum theory says a photon’s polarization, like its other variable attributes, is in a kind of limbo. Its polarization is undetermined until it is measured. In other words, a particle’s attributes like polarization are not programmed in advance. They exist only after measurement.

Physicists have since conducted a number of tests to find out whether this is true. These Bell experiments show quantum theory is right. A particle’s variable attributes are not pre-programmed. They are random — determined in the act of observation itself.

So in the above experiment, the polarizations of both photons start out indeterminate, in quantum limbo. The act of measuring the first photon sets its polarization — and the polarization of the second photon. Instantly. Across space. No matter how far apart the two particles are. Something here can and does influence something way over there. In zero time. The universe is “non-local”.

This quantum reasoning also applies to a particle’s location. As Rosenblum and Kuttner wrote in their book, Quantum Enigma, a particle “was not there before you found it there. Your happening to find it there caused it to be there.”

Whoa. Our universe is wilder than we can imagine.

Caveat: Arguments against the completeness of quantum theory and the interpretation of Bell experiments remain topics of ongoing physics discussion and research. David Bohm’s so-called Causal Interpretation of quantum mechanics is the most famous non-local hidden variable theory (there are a number of others). Bohm’s theory reproduces the predictions of quantum mechanics without resorting to probabilities. In Bohm’s clever but convoluted construct, a particle’s attributes are pre-programmed, known before measurement. Based on an idea from Louis de Broglie, a hidden “guiding wave” traveling faster than light governs the motion of a particle. However, the theory remains non-local.

What do you think? I welcome all comments — pro and con.

My website: marksmodernphysics.com

You can also follow me on Twitter@IMEgdall