Free Will and Retrocausality

I discussed yesterday's post on retrocausality with a few people and thought I'd make a quick post to explore an analogy that shows what a successful demonstration of the phenomenon would really mean for free will.

Some of you may be geeky enough to remember the Fighting Fantasy books - one incarnation of the 'choose your own adventure' concept. For those who aren't familiar with them, the books are divided into paragraphs (usually a few hundred) which are numbered; after reading one, you're offered a choice of which paragraph to read next to continue the story. Some choices lead to an ignoble death, some lead to the eventual solution.

When you read a paragraph (let's say #150), you take the information in it, plus any previous information you know, and make a decision on which paragraph to read next (we'll say #200 or #60). In fact it's probably fair to say that you pick the option that seems most sensible - given what you know (i.e. the past). That's analogous to any other decision-making moment. If you'd taken a different route through the story to reach #150, you might know that paragraph #60 means certain death - so you'd pick the other option. You do make a 'real decision'. (In reality, unlike Fighting Fantasy, you can't go back and start again, so you only make one decision in practice - this is really what determinism means.)

Now let's introduce retrocausality. This is very easy to include in our Fighting Fantasy analogy - you can just cheat. You glance ahead, read #60, realise it'll kill you, and go back and pick #200 instead.

What may not be so obvious is that back-in-time signalling has exactly the same effect. The signal from the future changes the information you have, so your decision changes. There's no paradox, because at the time you received your signal from the future, it accurately described what the future would be. However, now knowing that, you can deliberately pick a 'different future'. (It's not even a problem that the future where you sent the signal back is now probably not going to happen - although the explanation of that is more complicated.)

This is really the key distinction between determinism and fatalism, so I'm quite excited about it - if we can really send retrocausal signals, we should be able to thoroughly put the latter to rest.

Retrocausation?

It says something about me that I take breaks from revising for my Biochemistry finals by reading about quantum mechanics. Exactly what it says I'm not sure. :|

John Cramer has published an update on his progress to try to demonstrate retrocausal signalling. I'll summarise in a few sentences for those who don't have time to read the article or prefer a less technical phrasing:

Quantum mechanics allows non-local signalling between entangled particles. This essentially means that an interaction with one particle that changes its state can change the property of its entangled partner at arbitrary distance, instantly (not just at light speed). The 'reality' of this phenomenon is disputed but there is a great deal of experimental evidence that it exists.

If we take two entangled photons and pass one into a long optical fibre, we can delay the arrival of the second photon at its destination by a few microseconds. We detect both photons, but the delayed photon is detected in a specific fashion that changes its state - the non-delayed photon is detected without forcing it to take any particular state.

If the quantum prediction holds, the two photons will always be in the state induced by the measurement of the delayed photon, even though several microseconds passed between the first 'free' detection and the delayed detection.

So what?

Cramer's paper is a progress report and doesn't speculate about applications of the phenomenon if it's demonstrated to be possible, but any number of science fiction authors have considered possible 'future-scope' devices, some more credible than others. I have a feeling Greg Egan wrote one such story, but I don't recall in which collection.

The most obvious application is a device for 'signalling back in time'; by delaying one entangled particle for longer than a few microseconds (this is hard, of course, without breaking the entanglement - the same problem is encountered in quantum computing - but not impossible), i.e. for minutes or hours, we can then 'immediately' receive information on what the state of the future will be. This throws up all sorts of interesting potential paradoxes (although it may simply deal a final decisive blow to the concept of free will).

Spooky Sensing at a Distance

Slightly less obvious is the idea of using the phenomenon as a sensor - fire one photon at a distant object (like an extrasolar planet), and observe how the entangled partner changes. This should in principle reveal information about the 'target', again 'instantly' - even though the sensor photon takes subjective time to reach the target. Only certain kinds of information could be retrieved, but astronomers are very good at making sense of sparse data.

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More obscurely - and perhaps most interestingly, although I have a niggling feeling it may prove to be impossible - one could in theory perform long computations 'without actually performing them, by 'sending the answer back' to the beginning of the computation. If that's really true, then a suitable computer can perform any finite-length computation 'instantly'.

All quiet

Not much to report, really, but I feel like making a post, if only to share the following piece of gratuitous overwriting (from the 29th March issue of Science CiteTrack):

"Investigations of the ecology of planktonic marine organisms run into the problem of reconciling the anonymity of morphological uniformity with the potential for ubiquitous distribution in the continuity of the oceans and the observed genetic diversity."

I have no problem with the use of jargon words where necessary, but it's very important - especially in a general-interest publication like CiteTrack - to be clear and straightforward to avoid putting people off. For example, the above can be rewritten as:

"Investigations into plankton ecology are difficult because different species are similar in shape but genetically diverse, and may be widespread throughout the oceans."

While I'm here I'll also point you in the direction of the remarkably talented Alex Ries, whose xenobiological creativity has earned him a place on my first terraforming expedition...

Praise and giftedness

Arguably most interesting article I have read in some time, "the power and peril of praise". I went through more or less exactly the school experience they describe, and suffered more or less the same consequences. It's only really in the last few months that I've really made any progress on my ability to motivate myself when success is not immediate, and I still have a long way to go.

I'm intrigued though by Dr. Cloninger's observation that there is a distinct cortical region associated with persistence. That sounds like an extremely promising target for TMS. Since the latter is now achievable at home if you have a few thousand to burn, I wonder how long we have before we start seeing parents and/or teenagers trying to boost their study. Frankly I'd rather like to try it myself...

Ribosomes

I don't usually seem to manage to get to the Tuesday lunchtime seminars organised by the Biochemistry department, but I made an exception today for Venki Ramakrishnan's talk on 'Structures of Functional States of the Ribosome', not least because that's exactly the topic I've been revising for the past three days. Venki's lab produces some really amazing videos which I personally find not only scientifically interesting but also quite beautiful.

The fact that cellular processes can be so elegant and yet so reminiscent of mechanical production lines can't help but be good news for nanotechnology too. I begin to understand why some people find it necessary to dream up 'intelligent designers' to explain away the otherwise quite awe-inspiring complexity of life.