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Quantum Entanglement: Spooky Action At A Distance - by John Prytz

Actually I quite love this idea of entanglement and to know the properties of something without ever having to actually observe or measure it. Let’s return to my favourite imaginary couple, Jane and Clive, who, as we all know, are a bit weird. So, I can imagine this hypothetical macro example from the Jane and Clive archives, where Jane and Clive agree that on any given day, whatever colours Clive wears, Jane won’t (or vice versa). So, if Clive is dressed in a blue suit, with white shirt and red tie, grey socks and hat, with black shoes, I can be sure, without observing, that Jane’s outfit will consist of nothing that is black, white, blue, red or grey. So, I know something about Jane’s properties without any observation because in this case Jane and Clive were entangled!

 

In actual fact it is way weirder than that. If this were a real quantum  entanglement example, then if Clive and Jane were on opposite sides of the Universe, and Jane had on a green outfit and Clive had on a red outfit, and Clive changed outfits to one of green, then Jane would have to also change, in this case from green to red – instantaneously. Now that’s really spooky!

 

Speaking of clothes, Clive has this daily habit of putting on unmatched socks. If Jane sees Clive’s right foot wearing a brown sock, she doesn’t need to have the IQ of Einstein to figure out that Clive’s left foot isn’t clothed in a brown sock! If Clive only has brown and black socks, Jane knows that Clive’s left foot has a black sock on it.

 

Or, say Jane and Clive are expecting company, but don’t know when that company will arrive. Therefore, one or the other of them has to be home at all times – in case. So, if I see Jane shopping, I know, without personal observation, that Clive is home. Now let’s take a micro example. The vacuum energy spits out a matter-antimatter particle pair, but they separate and escape and head off in opposite directions. Jane captures one in her particle trap (box); Clive gets the other one in his particle trap (box). Jane peeks into the box and sees a positron and says so. That alone spoils the surprise for Clive, for without any need to look; he now knows his box contains an electron.

 

Pick and remove a card from a standard deck. Don’t look at it. Bury it in a time capsule. Send the rest of the unobserved deck of 51 cards via rocket ship off to the Andromeda Galaxy. Leave instructions. Generations upon generations later, with the deck of 51 safely in the Great Galaxy of Andromeda, you’re great, great, great (add lots more greats) grand-person can dig up and look at lone card in the time capsule. Say it is the Ace of Diamonds. You do not now need to observe the original deck in Andromeda to know 1) it contains 51 cards, and 2) that it is missing the Ace of Diamonds! That’s entanglement. And entanglement is something that Einstein called ‘spooky action at a distance’ because you can come by information or knowledge instantaneously – faster than the speed of light. Thus, Einstein was not amused!

 

On the micro level, the example usually given involves electrons (though one can experimentally substitute oppositely polarised photons). No two electrons can be in the exact same atomic ‘orbit’ if they have the exact same quantum configuration – the Pauli Exclusion Principle. One such configuration is called ‘spin’ and there are two mutually exclusive possibilities called ‘spin up’ and ‘spin down’. Any electron is either ‘spin up’ or ‘spin down’ with respect to ‘spin’. So, two electrons can occupy the same atomic ‘orbit’ if one is ‘spin down’ and the other is ‘spin up’. If either electron flips from ‘spin up’ to ‘spin down’, then its orbital partner must instantaneously flip too, but in the opposite manner. One would suspect that even while in their shared atomic orbit, two electrons couldn’t ‘communicate’ quite instantaneously and thus it would still take some finite time for the other’s spin to flip given a flip by its partner. One would think that, but if real entanglement has any validity, that can’t be so.  

 

Separate the two electrons, one ‘spin up’ the other ‘spin down’ and send them travelling in opposite directions so that there eventually becomes a vast distance between them. If later on you observe the spin orientation of one, then you instantaneously know the spin of the other – faster than the speed of light! Where ‘spooky’ comes in is that if one of the isolated electrons flips its spin from up to down, then the other apparently must flip also in response – from down to up. Yet the two are out of touch and out of reach and out of sight, so how do they know each other’s state, and how do they instantaneously communicate that state faster than the speed of light? Something’s rotten somewhere!

 

I can only conclude that since electrons have no free will, no ability to communicate with each other, and can not violate the cosmic speed limit, that once separated and thus isolated they either don’t flip, or it doesn’t matter because observing one will now tell you nothing about the state of the other, and therefore nothing ‘spooky’ happens. It doesn’t matter because once separated, the entanglement is no longer valid – the two electrons are like a divorced couple that have no further interaction with each other.

 

Unfortunately, actual experiment verifies entanglement, and thus spookiness reigns. However, one can not apparently use entanglement to actually communicate anything original apart from knowing the properties of the other unobserved bit, so therefore entanglement isn’t a solution to a superluminal telegraph.     

 

Further readings in entanglement:

 

Aczel, Amir D.; Entanglement: The Greatest Mystery in Physics; John Wiley & Sons, N.Y.; 2002:

 

Clegg, Brian; The God Effect: Quantum Entanglement, Science’s Strangest Phenomenon; St. Martin’s Griffin, N.Y.; 2006:



Science librarian; retired.

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