NeuroDojo

"Debunking" a 'Net "psychic," Part 2

How does the Flash Mind Reader work? (If you haven't seen it yet, you may want to scroll down to read yesterday's entry first.)

When I read the instructions, I strongly suspected that the little procedure ("Pick any 2 digit number, add the digits, subtract the total from first number") would give a very limited range of possible answers -- not the range of 100 shown on the page. Not being a mathematician, I had to check this in a "brute force" sort of way.

Using Microsoft Excel, I randomly generated a lot of numbers: over 65,000! I ran them though the procedure asked by the web page, and plotted them all on a histogram. As I suspected, the resulting numbers were not randomly or broadly distributed.

There are only nine possible answers. 9, 18, 27, 36, 45, 54, 63, 72, and 81. All multiples of 9. In retrospect, this isn't a big surprise, as 9 was considered a "magic" number by a lot of mystic thinking types. If you multiply any one digit number by 9, and add the two numbers together, you get... 9! This funny property is also used in this gag (also here). (When I was learning multiplication in school, this trick let me remember my multiplication tables for 9 easily; only the "5 times" tables were easier to learn.)

From here, the rest is easy to decipher. All you have to do is to put up the same symbol for the nine possible answers. Because:

• The multiples of nine are widely spread,
  
• There are 91 distracting "possible" answers,
  
• There are over a dozen possible symbols, and
  
• The symbols change every time you click on the crystal ball (and the page takes you to a new screen to get your "psychic" answer),
  

...The regular, invariant pattern is well concealed. Thus, the webpage creates the powerful illusion of "knowing" your answer -- which is not as wide as you think.

There you have it, folks! Behold the power of science!

Link of the moment: If you liked this journal entry, check out the website of magician James Randi.