Last week I was inspired by a poorly presented popular physics lecture to review a couple of concepts in modern physics which people tend to think are impossible, but are not. Most laws of physics have loopholes in them - nothing can travel faster than light unless it carries no information or causes spacetime itself to move, time travel seems paradoxical but there are quantum mechanical solutions, energy must be conserved unless the laws of physics themselves can evolve over time, etc.

Continuing with that theme, today I am going to suggest two methods in which psychic events or fortune telling may happen. However I must first add the disclaimer that there is a huge difference between these sort of subatomic oddities and the claims of spiritualists and mediums and their ilk. Remember always that there is a difference between something existing and something not being completely impossible. Please do not interpret this as an endorsement of pay-for-predicting psychics.

After all those disclaimers and explanations, let me move on to the science. The first potential loophole is due to the effects of antimatter. Over sixty years ago, the legendary American physicist Richard Feynman published a series of academic papers in which he set forth methods of calculating reactions of subatomic particles by using diagrams to track individual particles propagating from one point in spacetime to another. However these calculations must include the effects of particles moving both forward in time, and backwards in time. Feynman went so far as to suggest that anti-matter could be viewed as ordinary matter travelling backwards in time, and that the Universe may contain a single electron that zig-zags back and forth in time. 

And that leads to the idea that perhaps by altering the properties of a group of positrons in the present, you could alter their properties at the time they were created. And so in principle you could generate a set of positrons, measure their properties carefully, and then sometime later alter their properties based on the outcome of a lottery or other random event. Then the altered properties propagate backwards in time to their origin, and the measurements you made initially reflect an event that hasn't yet happened. This would be true fortunetelling.

But unfortunately it doesn't work. As with the faster-than-light communications using entangled particles, the properties would be random and just taking measurements would collapse the system. Although the positrons may propagate backwards in time, the information they carry is randomized and of no use.

A closely related method involves the transactional interpretation of quantum mechanics. Although we have known for nearly a century how to use quantum mechanics to do calculations, we do not understand why it works. The most popular interpretation claims that there exist virtual systems, and when an observer views them one becomes real and the others disappear. This has both philosophical and physics based problems, and many experts in this field do not believe that this is the true mechanism behind quantum mechanics. In the transactional interpretation, which is too complicated to review in detail here, quantum mechanical systems are composed of two waves - one moving forward in time as in the standard interpretations, but also one travelling backwards in time. As with the positron system described above, this would allow for fortunetelling if this wave could be used for carrying information. However once again, (so far as I know) there is no method of taking information from this backwards propagating wave as it is also a random process.

Which then leads to the method which I believe does work for fortunetelling, but it owes more to stage magicians and mentalists than to serious science (although it does qualify as fortunetelling in my opinion, since even the psychic doesn't know that no prediction has been made). 

Suppose that you write down a prediction for which playing card will be selected by a test subject. The subject then selects the card, and you reveal that the prediction you made is correct. You remember writing it down, and at no point do you change your prediction. Is this a proof of psychic ability?

In theory this can be done using quantum mechanics and no trickery. In principle, you can divide yourself into 52 virtual copies of yourself, in a similar manner to creating both a dead and a live virtual cat in Schrodinger's famous thought experiment. (and I must stress that not everyone believes that humans can be made into a quantum state, even though they generally accept that cats can...) Each virtual copy of you writes down a different playing card. Meanwhile the test subject is also divided into 52 virtual copies, each of which selects a different card from the deck.

Now if the two systems are entangled correctly, then each of your states is matched up with one of their states, and when this joint wavefunction collapses, both systems simultaneously collapse to the same state. If the test subject collapses to the state in which they selected the three of clubs, then your wavefunction also collapses to the state in which you predicted the three of clubs, and everyone is amazed. Even more astonishing, since the other 51 copies of yourself have disappeared, you don't even know or remember that they ever existed. Your own memory tells you that you made a single prediction that turned out to be true. And every time you repeated this experiment, you remember making a single prediction that turned out true. You would be confident in declaring yourself to be psychic!

This is simply a quantum mechanical variation on the standard magicians' method of "multiple endings". Of course no one has ever created a quantum mechanical system using something as large as playing cards or prediction slips. Many people do not believe that humans can be part of a wavefunction, although no proof exists that they cannot be. However these are technical problems, rather than a definitive proof that this experiment is impossible. So perhaps fortunetelling is not impossible after all?

Given the nature of this article, I do feel obliged to add once more that I am not claiming that psychic phenomena are real, or that any of these suggestions form definitive proof that such things are possible. They are at the extreme end of speculation and philosophy. I merely present them as ideas to be debated and discussed, and another example of the beautiful mysteries of quantum mechanics.