Thursday, May 3, 2012

Entangled minds

Sometimes people use quantum entanglement as an explanation for psychic communication between minds.  The idea is that my neurons are entangled with yours, and whatever my neurons see would be the same as yours.

Being a physicist, I know that's wrong.  Even if psychic communication exists, quantum entanglement would utterly fail to explain it.  But at the same time, as a physicist, I feel compelled to get the technicalities right.  There's a nagging technicality here: Yes, our neurons are in fact entangled.  But that doesn't mean what you think it means.

Most people are told that entanglement is about correlations over large distances.  What someone measures here will be the same as what someone measures over there.  But what you may not have known is that entanglement is also about anti-correlations over large distances.  What someone measures here could be the opposite of what someone measures over there.

So suppose that I feel a twinge of sadness.  I interpret this to mean that you are experiencing sadness right now, because my sad neuron must be correlated with your sad neuron.  Except, maybe they're anti-correlated.  Maybe you are feeling the exact opposite way, and your neuron is happy or whatever?

Or suppose that I think happy thoughts.  Surely happy thoughts are correlated with happy things in the world via entanglement, so if I think positive thoughts I will attract good things to me.  Except, maybe my happy thoughts are correlated with the opposite, and are actually attracting bad things to me?

So if we have two neurons, are they correlated or anti-correlated?  Under carefully-controlled experimental conditions, involving small numbers of particles (ie much fewer than the number of particles in a neuron), and isolating those particles from the random interactions with the outside world, physicists can produce things that are definitely correlated or anti-correlated.  But under any less-controlled conditions, it's essentially random.  There's no way to know.  Every time it happens, it will be different.  It will be completely unpredictable.  On average there will be no correlation at all.  We say that the neurons are decoherent.

(Because there is no observable correlation, some physicists would say that the neurons are not entangled.  This appears to contradict what I said, that the neurons are entangled but decoherent.  We're not really saying different things, we're just using different words to communicate the same ideas.)

Trying to explain psychic ability by quantum mechanics is no better than trying to explain it by thermodynamics.  Thermodynamics is all about the random motion of molecules.  Thermodynamics says that there is a miniscule chance that the molecules in my neuron will just happen to move in the same way as molecules in your neuron!  But out of all the ways molecules could move, why should we single out this particular way, except that it makes us feel fuzzy inside?

Some other gross simplifications I've made:

1. To speak of "same" and "opposite" results presumes that there are only two possible configurations.  I'm sure that neurons are complicated enough that they have a very large number of configurations.  If each neuron has three possible configurations, then we have nine total possible combinations.  Because the neurons are entangled, some of these combinations are more likely than others, but all the probabilities themselves are essentially random.

2. There's no reason to think that entanglement should only involve two things.  In general, entanglement involves every possible configuration of everything.  But imagine that we have just three things: two neurons and my aunt's left foot.  And imagine that each of these has two possible configurations.  Now there are 8 possible combinations.  Some are more likely than others, but the probabilities themselves are essentially random.


Anonymous said...

I'm curious about something. Is there any way that the knowledge THAT there's entanglement could be used to send a bit of data across long distances?

From what I understand, the particulars of spin or whatever is entangled won't work for communication. In other words, reading "left" would be no different than reading "right" because there's no way to say how it was originally entangled. However, is there some means by which one can detect that the other hand has been measured at all? That should be enough to develop a basic communication system. If a reading at one end locks the other end, is there a way for that "locked" state to somehow START an interaction? So, the measuring device would just sit around waiting for that state to be set and ignore completely what it gets set to.

If not, then never mind on that front, but it's something I've been curious about.

miller said...

In principle, there is no way to determine faster than light whether the other particle in an entangled pair has even been measured.

There isn't a direct way to tell if a single particle's state is a "locked" (the technical term for this is a "pure" state). You have to measure many particles, all prepared in the same way, and if they all come out the same way, then they must have been locked. But in the case of a particle whose entangled partner has been measured, some will be locked into state A, and others into state B. In principle, this is indistinguishable from the scenario where the entangled partner has not been measured; the probabilities must be identical.

Anonymous said...

I see, well that shoots that in the foot. Thank you for your response.

Larry, The Barefoot Bum said...

I vaguely recall that we infer "spooky action at a distance" from the correlation between measurements of the properties of entangled particles, not from their individual probability distributions.