The cover article of the September 30th issue of New Scientist features a Gedankenexperiment that my father, John Cramer, proposed in a talk he gave at an AAAS meeting in San Diego last June.
The article begins:
Ever wish you could reach back in time and change the past? Maybe you'd like to take back an unfortunate voicemail message, or rephrase what you just said to your boss. Or perhaps you've even dreamed of tweaking the outcome of yesterday's lottery to make yourself the winner.
Common sense tells us that influencing the past is impossible - what's done is done, right? Even if it were possible, think of the mind-bending paradoxes it would create. While tinkering with the past, you might change the circumstances by which your parents met, derailing the key event that led to your birth.
Such are the perils of retrocausality, the idea that the present can affect the past, and the future can affect the present. Strange as it sounds, retrocausality is perfectly permissible within the known laws of nature. It has been debated for decades, mostly in the realm of philosophy and quantum physics. Trouble is, nobody has done the experiment to show it happens in the real world, so the door remains wide open for a demonstration.
My father says:
As implied in the article, I have recruited an atomic physics experimentalist (Warren Nagourney) and we have decided to do at least the first stage of the experiment. I now have a LiIO3 non-linear crystal on order that will be needed to do this. We will begin the experiment in a couple of months when the argon-ion laser owned by the UW Atomic Physics group becomes available (sometime around December to February).
Here are the last few slides from his Power Point presentation. They outline the experiment. (Click on them to see bigger versions.)
