No, I'm not actually going to conduct an experiment to determine whether Reiki actually works. I am, however, going to propose an experiment that might show whether there's something to the whole Reiki concept.
According to The International Center for Reiki Training's FAQ, "Reiki is a Japanese technique for stress reduction and relaxation that also promotes healing." More specifically, Reiki is "spiritually guided life force energy" that reduces stress, relaxes, and promotes healing.
We'll not dispute the potential to reduce stress and relax; evidence has shown that many phenomena can have these effects via the placebo effect. If someone believes in a treatment, then receiving the treatment will likely relieve stress and relax them whether there's anything to it or not.
Healing promotion should be testable, but it would require a double-blind, placebo-controlled study that's well beyond the scope of me or most of my humble readers (you are humble, aren't you?).
No, let's focus on the "Reiki is spiritually guided life force energy" part. After all, it's the part that could win a million bucks from James Randi (that could be used for charity, if you're too selfless to want it for yourself).
It seems reasonable that if this "spiritually-guided life force energy" exists, there should be some way to detect it. The spiritual sort of people who believe in Reiki will likely assert that technological efforts to detect this energy would be fruitless (since it's "spiritual"), but shouldn't competent Reiki practitioners be able to detect the energy they're "spiritually guiding".
So, what test scenarios might we devise to test whether Reiki practitioners can detect "life force energy".
Well, one possibility is to test whether they can detect a living creature inside a closed container. Place a test animal like a mouse inside a box that is made of thin material yet reasonably proof against transmitting sound or vibration. Have similar boxes that are empty. Reiki practitioners should presumably be able to identify the box containing a live animal with greater accuracy than individuals with no belief in Reiki, right?
Another possibility would be to test practitioners to determine whether they can tell if someone has recently experienced Reiki treatment. After all, someone who has recently received Reiki should be more relaxed and less stressed, and this should be evident in their "life force energy", shouldn't it? Recruit a "believer" willing to accept a Reiki treatment. At the beginning of an hour, the test Practitioner should examine the untreated patient to get a baseline feel for the patient's "life force energy". The test Practitioner will visit the patient after 15, 30, 45, and 60 minutes to determine if the patient has received treatment. A second Practitioner may actually perform a Reiki treatment on the patient during one of the intervals. The test Practitioner should be able to determine at what interval, if any, the patient received treatment, right? After all, the patient's "life force energy" will be changed by the treatment, won't it? If you can't detect such a change, how can you know that the patient needs treatment?
These are just a couple ideas that came to me pretty quickly. I'm sure that real Reiki practitioners who wanted to demonstrate just how effective and useful Reiki treatment is could come up with scenarios acceptable to the James Randi Educational Foundation and win a million dollars for themselves or their favorite charities.
What are you waiting for guys?