Posts Tagged ‘quantum entanglement’

The eeriest result I’ve seen in years

May 23, 2012 6 comments

Here’s a recent result posted online which, if it’s true, is incredibly eerie.

The upshot of it is that these guys claim to be able to have an experimental quantum entanglement setup that can affect events in the past. Not anywhere in the past, mind you, just specific, isolated events within the same experiment. Still, it’s an amazing result if someone manages to successfully duplicate it.

I rather suspect that they won’t succeed, and that the whole thing will turn out to be dodgy, but here’s the thing: if the result is correct, it probably invalidates the approach that I outlined in the last few weeks of posts. This is because, while the approach I outlined resolves problems with non-locality, it maintains a strict ordering of cause and effect.

I wanted to share with you because in digital physics, we like refutability! There are other discrete approaches in which this kind of result is probably fine, but my favorite model is probably toast.

I’d like to share with you what I think is wrong with this result, but first I should probably summarize the result, for those who don’t want to click around. It works like this:

* Alice and Bob both create pairs of entangled photons.

* One photon from each pair is sent to Victor.

* Alice and Bob make a measurement on their photons.

* Victor makes a decision as to whether to entangle the photons he received or not.

* When we check later, we find that whether Victor decides to entangle or not affects the correlation that Alice and Bob previously saw. Crazy!

So there are multiple reasons to suspect that this research requires more investigation before we know for sure. One is that each experimental pass seems to take place in 14 billionths of a second. That seems to me like a small enough window that experimental error could creep in. Another is that very few particles make it through the whole experimental setup, so the entire result hinges on statistical patterns in the collected data.

However, the thing that I wonder most about relates to the ordering of events. I haven’t gone through the paper yet but I suspect that the catch here is that Alice and Bob’s measurements are compared with Victor’s after Victor makes his decision.

Consider the case where Alice and Bob get to compare results before Victor makes up his mind. In that case, we have information with no quantum ambiguity traveling from the future into the past. My guess is they can’t do that. (If they can, financial trading will never look the same.)

And Victor has to decide first, the whole Alice/Bob/Victor setup only works if we treat it as an entangled system that we can’t touch until the whole trick is over. And that means we have to wonder whether Alice and Bob made a true measurement, if the outcome of it depends on whether we add Victor into the system or not.

In any case, it’s an awesome idea for an experiment. With luck, someone will be out there looking to repeat the result already.