During the summer after  the war I had some documents to write and work
to finish up,  so I went back to Los Alamos from Cornell, where I had taught
during the year. In the middle of my work I had  to refer to a document that
I had written before but couldn't remember, and it was down in the library.
     I went down to get the document, and  there was  a soldier walking back
and forth, with a gun. It was a  Saturday, and after the war the library was
closed on Saturdays.
     Then I remembered what a good friend of mine, Frederic de Hoffman,  had
done. He  was in  the Declassification Section. After  the war the army  was
thinking of declassifying some documents, and he had to go back and forth to
the library so much -- look at this document,  look  at that document, check
this, check that --  that  he was going  nuts!  So he  had a  copy of  every
document -- all the secrets to the atomic bomb -- in nine filing cabinets in
his office.
     I went  down  to his office, and the lights  were  on. It  looked as if
whoever was there -- perhaps his secretary -- had just stepped out for a few
minutes,  so I waited. While I  was waiting I started to  fiddle around with
the combination  wheel on one of the filing cabinets. (By  the way, I didn't
have the last two numbers for de Hoffman's safes; they were put in after the
war, after I had left.)
     I started to play with one of the combination wheels and began to think
about  the  safecracker books.  I thought to  myself, "I've never  been much
impressed by the tricks described in those books, so I've never tried  them,
but let's see if we can open de Hoffman's safe by following the book."
     First  trick,  the secretary:  she's  afraid she's  going to forget the
combination, so  she writes  it down somewhere. I started to look in some of
the places  mentioned in the book. The desk drawer was locked, but it was an
ordinary lock like Leo Lavatelli taught me how to open -- ping! I look along
the edge: nothing.
     Then I looked through the secretary's  papers. I found a sheet of paper
that all the secretaries had,  with the  Greek  letters carefully made -- so
they could recognize them  in mathematical formulas -- and named. And there,
carelessly written along the top of the paper, was pi = 3.14159. Now, that's
six digits, and why does a secretary have to know the numerical value of pi?
It was obvious; there was no other reason!
     I went over to the filing cabinets  and tried the  first one: 31-41-59.
It didn't open.  Then  I  tried  59-41-31. That  didn't  work  either.  Then
95-14-13. Backwards,  forwards, upside down, turn  it this way, turn it that
-- nothing!
     I closed  the desk drawer and  started to walk  out  the door,  when  I
thought of the safecracker books again:  Next, try the  psychology method. I
said  to  myself,  "Freddy de Hoffman  is just  the  kind  of guy  to  use a
mathematical constant for a safe combination."
     I went back to the first filing cabinet and tried 27-18-28 -- CLICK! It
opened! (The mathematical constant second in importance to pi is the base of
natural logarithms, e:2.71828...) There were nine filing cabinets, and I had
opened the  first one, but the document I wanted was  in another one -- they
were in  alphabetical order by  author. I tried the  second filing  cabinet:
27-18-28 -- CLICK! It opened with the same, combination. I thought, "This is
wonderful! I've opened the secrets to the atomic bomb, but if I'm ever going
to  tell  this story, I've  got to make  sure that  all the combinations are
really the  same!" Some of the filing cabinets were  in  the next room, so I
tried 27-18-28 on one of them, and it opened.  Now I'd opened three safes --
all the same.
     I thought to myself, "Now I could write  a  safecracker book that would
beat  every one, because at the beginning I would  tell how  I  opened safes
whose  contents  were bigger  and more  valuable  than  what any safecracker
anywhere  had opened -- except for a life, of course -- but compared  to the
furs  or  the gold bullion, I have them  all beat: I opened the safes  which
contained  all  the secrets  to  the  atomic  bomb:  the  schedules for  the
production  of the plutonium, the purification procedures, how much material
is needed,  how the bomb  works, how  the  neutrons  are generated, what the
design  is, the dimensions -- the entire  information that was  known at Los
Alamos: the whole shmeer!"
     I went  back to  the second filing  cabinet and took out the document I
wanted. Then I took a red grease pencil and a piece of yellow paper that was
lying around in the  office and  wrote,  "I borrowed  document no. LA4312 --
Feynman the safe-cracker." I put the note on top of the papers in the filing
cabinet and closed it.
     Then I went to the first one I had opened and wrote another note: "This
one was no  harder  to open than the other  one -- Wise  Guy" and  shut  the
cabinet.
     Then in the  other  cabinet,  in  the  other  room, I wrote, "When  the
combinations are all the same, one is no harder to open than another -- Same
Guy" and I shut that one. I went back to my office and wrote my report.
     That evening  I went to the cafeteria and ate supper.  There was Freddy
de Hoffman. He said he was going over to his office to work, so just for fun
I went with him.
     He started to work, and soon he went into the other room to open one of
the  filing cabinets in  there -- something  I hadn't counted  on  -- and he
happened to open the filing  cabinet I had put the third note in,  first. He
opened the  drawer, and  he saw this foreign object in there --  this bright
yellow paper with something scrawled on it in bright red crayon.
     I had read in books that when somebody is afraid, his face gets sallow,
but I had never seen it  before. Well, it's absolutely true. His face turned
a gray, yellow green -- it was really frightening to see. He  picked  up the
paper, and his hand was shaking. "L-l-look at this!" he said, trembling.
     The note said, "When  the  combinations are all the  same,  one  is  no
harder to open than another -- Same Guy."
     "What does it mean?" I said.
     "All the c-c-combinations of my safes are the s-s-same!" he stammered.
     "That ain't such a good idea."
     "I-I know that n-now!" he said, completely shaken.
     Another effect of the blood draining  from the  face must  be  that the
brain doesn't  work right. "He signed who  it was! He signed who it was!" he
said.
     "What?" (I hadn't put my name on that one.)
     "Yes,"  he  said,  "it's the same  guy  who's  been  trying to get into
Building Omega!"
     All during the war, and  even after, there were these perpetual rumors:
"Somebody's been trying to get into Building Omega!" You see, during the war
they were doing experiments for the bomb in which  they wanted to get enough
material together for  the chain  reaction to  just get started.  They would
drop one  piece of material  through  another, and when it went through, the
reaction  would start  and they'd measure how many  neutrons  they  got. The
piece would  fall through so  fast that nothing should build up and explode.
Enough of  a reaction would begin, however,  so they could tell that  things
were really starting correctly, that the  rates were  right, and  everything
was going according to prediction -- a very dangerous experiment!
     Naturally, they were  not  doing this experiment in  the middle of  Los
Alamos, but off several miles, in a canyon several mesas over, all isolated.
This  Building Omega had its  own fence around it with guard towers. In  the
middle of the night when  everything's  quiet, some  rabbit comes out of the
brush and smashes against the fence and makes a noise. The guard shoots. The
lieutenant in charge comes  around. What's the guard going to say -- that it
was  only  a rabbit?  No. "Somebody's been trying to get into Building Omega
and I scared him off!"
     So de Hoffman was pale and shaking,  and he didn't  realize there was a
flaw in  his logic: it was not clear that the same guy  who'd been trying to
get into  Building Omega  was the same guy who was standing next  to him. He
asked me what to do. "Well, see if any documents are missing." "It looks all
right," he said.  "I don't see  any missing." I tried  to  steer  him to the
filing cabinet I took my document out of. "Well, uh, if all the combinations
are the same, perhaps he's taken something from another drawer."
     "Right!" he said, and he went back into his office and opened the first
filing  cabinet and found the second note I wrote: "This  one  was no harder
than the other one -- Wise Guy."
     By that time it didn't make any difference whether it was "Same Guy" or
"Wise Guy": It was  completely  clear to  him that it  was the  guy  who was
trying to  get into Building Omega. So  to convince  him to open  the filing
cabinet with  my first  note in it was  particularly difficult, and I  don't
remember how I talked him into it.
     He started to  open it, so I began to walk down the hall, because I was
a little bit afraid that when he found out who did it to him, I was going to
get my throat cut!
     Sure enough,  he came  running down  the hall after me,  but instead of
being angry, he  practically  put  his  arms  around  me  because he was  so
completely  relieved that  this terrible burden  of the atomic secrets being
stolen was only me doing mischief.