Butting heads with some pro-homeopathy guy.

My recent post about homeopathy for the Young Australian Skeptics attracted some pro-homeopathy guy in the comments thread. It’s a skeptics website, obviously; I’m not sure exactly what he response was expecting to receive.

So, you know, supposedly homeopathy is real, and I’m a mean old bigot. How does it work? Supposedly, the water has a “memory” of the substances you originally put in it, supposedly just like how a piece of ferromagnetic iron “remembers” the Earth’s magnetic field when you heat it up and allow all those magnetic dipoles to align with the Earth’s magnetic field.

Well, I thought a little bit of pwnage was in order. Cue this response:

If water has a magical “memory” of the substances put in it prior to dilution; what is the physical mechanism by which this “memory” occurs? What degrees of freedom do those water molecules possibly have that could store information for an arbitrarily large period of time at room temperature?

If you could “write” information onto water molecules that persisted for an arbitrarily long time at room temperature without decoherence or thermal noise, using a real physical mechanism that actually existed, kind of like ferromagnetism, imagine what we could do with it!

Water data storage, water “hard disks” with enormously high densities, scalable quantum memory as cheap as water. If you want more songs on your iPod, you just put more water in it! Water-based quantum computers that never exhibit decoherence – even at room temperature, or an incredible water-based version of spintronics. Water-based communication with enormously high bandwidths! The potential would be incredible!

A water molecule really doesn’t have that many degrees of freedom. Certainly there are rotational and vibrational degrees of freedom in the molecule, but they’re not isolated thermally from the environment, and any information encoded on them would be destroyed very, very rapidly, just by stochastic thermal fluctuations. The story is much the same for the positional and translational degrees of freedom of the atoms within the molecule.

Electron-spin degrees of freedom? Well, maybe, but those will decohere very rapidly, too, and in any case, spin-flipping would require an applied magnetic field. Similarly for some sort of use of the nuclear spin of hydrogen-1 (with spin-1/2) in natural water. Decoherence times for a nuclear spin will certainly be longer than electron-spin states, but they will still only be milliseconds or seconds at the most, and you’d still need an applied magnetic field to set up the spin states.

How many bits of information do you need to store the “memory” of the original substance, anyway?

I haven’t yet heard the response.

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