CARGO CULT SCIENCE by Richard Feynman
Adapted from the Caltech commencement address given in 1974.
During the Middle Ages there were all kinds of crazy ideas, such
as that a piece of rhinoceros horn would increase potency. Then a
method was discovered for separating the ideas--which was to try
one to see if it worked, and if it didn't work, to eliminate it.
This method became organized, of course, into science. And it
developed very well, so that we are now in the scientific age. It
is such a scientific age, in fact that we have difficulty in
understanding how witch doctors could ever have existed, when
nothing that they proposed ever really worked--or very little of
But even today I meet lots of people who sooner or later get me
into a conversation about UFOS, or astrology, or some form of
mysticism, expanded consciousness, new types of awareness, ESP, and
so forth. And I've concluded that it's not a scientific world.
Most people believe so many wonderful things that I decided to
investigate why they did. And what has been referred to as my
curiosity for investigation has landed me in a difficulty where I
found so much junk that I'm overwhelmed. First I started out by
investigating various ideas of mysticism, and mystic experiences.
I went into isolation tanks and got many hours of hallucinations,
so I know something about that. Then I went to Esalen, which is a
hotbed of this kind of thought (it's a wonderful place; you should
go visit there). Then I became overwhelmed. I didn't realize how
much there was.
At Esalen there are some large baths fed by hot springs situated
on a ledge about thirty feet above the ocean. One of my most
pleasurable experiences has been to sit in one of those baths and
watch the waves crashing onto the rocky shore below, to gaze into
the clear blue sky above, and to study a beautiful nude as she
quietly appears and settles into the bath with me.
One time I sat down in a bath where there was a beautiful girl
sitting with a guy who didn't seem to know her. Right away I began
thinking, "Gee! How am I gonna get started talking to this
beautiful nude babe?"
I'm trying to figure out what to say, when the guy says to her,
I'm, uh, studying massage. Could I practice on you?"
"Sure," she says. They get out of the bath and she lies down on a
massage table nearby.
I think to myself, "What a nifty line! I can never think of
anything like that!" He starts to rub her big toe. "I think I feel
it, "he says. "I feel a kind of dent--is that the pituitary?"
I blurt out, "You're a helluva long way from the pituitary, man!"
They looked at me, horrified--I had blown my cover--and said, "It's
I quickly closed my eyes and appeared to be meditating.
That's just an example of the kind of things that overwhelm me. I
also looked into extrasensory perception and PSI phenomena, and the
latest craze there was Uri Geller, a man who is supposed to be able
to bend keys by rubbing them with his finger. So I went to his
hotel room, on his invitation, to see a demonstration of both
mindreading and bending keys. He didn't do any mindreading that
succeeded; nobody can read my mind, I guess. And my boy held a key
and Geller rubbed it, and nothing happened. Then he told us it
works better under water, and so you can picture all of us standing
in the bathroom with the water turned on and the key under it, and
him rubbing the key with his finger. Nothing happened. So I was
unable to investigate that phenomenon.
But then I began to think, what else is there that we believe? (And
I thought then about the witch doctors, and how easy it would have
been to cheek on them by noticing that nothing really worked.) So
I found things that even more people believe, such as that we have
some knowledge of how to educate. There are big schools of reading
methods and mathematics methods, and so forth, but if you notice,
you'll see the reading scores keep going down--or hardly going up
in spite of the fact that we continually use these same people to
improve the methods. There's a witch doctor remedy that doesn't
work. It ought to be looked into; how do they know that their
method should work? Another example is how to treat criminals. We
obviously have made no progress--lots of theory, but no progress--
in decreasing the amount of crime by the method that we use to
Yet these things are said to be scientific. We study them. And I
think ordinary people with commonsense ideas are intimidated by
this pseudoscience. A teacher who has some good idea of how to
teach her children to read is forced by the school system to do it
some other way--or is even fooled by the school system into
thinking that her method is not necessarily a good one. Or a parent
of bad boys, after disciplining them in one way or another, feels
guilty for the rest of her life because she didn't do "the right
thing," according to the experts.
So we really ought to look into theories that don't work, and
science that isn't science.
I think the educational and psychological studies I mentioned are
examples of what I would like to call cargo cult science. In the
South Seas there is a cargo cult of people. During the war they saw
airplanes land with lots of good materials, and they want the same
thing to happen now. So they've arranged to imitate things like
runways, to put fires along the sides of the runways, to make a
wooden hut for a man to sit in, with two wooden pieces on his head
like headphones and bars of bamboo sticking out like antennas--he's
the controller--and they wait for the airplanes to land. They're
doing everything right. The form is perfect. It looks exactly the
way it looked before. But it doesn't work. No airplanes land. So
I call these things cargo cult science, because they follow all the
apparent precepts and forms of scientific investigation, but
they're missing something essential, because the planes don't land.
Now it behooves me, of course, to tell you what they're missing.
But it would be just about as difficult to explain to the South Sea
Islanders how they have to arrange things so that they get some
wealth in their system. It is not something simple like telling
them how to improve the shapes of the earphones. But there is one
feature I notice that is generally missing in cargo cult science.
That is the idea that we all hope you have learned in studying
science in school--we never explicitly say what this is, but just
hope that you catch on by all the examples of scientific
investigation. It is interesting, therefore, to bring it out now
and speak of it explicitly. It's a kind of scientific integrity,
a principle of scientific thought that corresponds to a kind of
utter honesty--a kind of leaning over backwards. For example, if
you're doing an experiment, you should report everything that you
think might make it invalid--not only what you think is right about
it: other causes that could possibly explain your results; and
things you thought of that you've eliminated by some other
experiment, and how they worked--to make sure the other fellow can
tell they have been eliminated.
Details that could throw doubt on your interpretation must be
given, if you know them. You must do the best you can--if you know
anything at all wrong, or possibly wrong--to explain it. If you
make a theory, for example, and advertise it, or put it out, then
you must also put down all the facts that disagree with it, as well
as those that agree with it. There is also a more subtle problem.
When you have put a lot of ideas together to make an elaborate
theory, you want to make sure, when explaining what it fits, that
those things it fits are not just the things that gave you the idea
for the theory; but that the finished theory makes something else
come out right, in addition.
In summary, the idea is to try to give all of the information to
help others to judge the value of your contribution; not just the
information that leads to judgment in one particular direction or
The easiest way to explain this idea is to contrast it, for
example, with advertising. Last night I heard that Wesson oil
doesn't soak through food. Well, that's true. It's not dishonest;
but the thing I'm talking about is not just a matter of not being
dishonest, it's a matter of scientific integrity, which is another
level. The fact that should be added to that advertising statement
is that no oils soak through food, if operated at a certain
temperature. If operated at another temperature, they all will--
including Wesson oil. So it's the implication which has been
conveyed, not the fact, which is true, and the difference is what
we have to deal with.
We've learned from experience that the truth will come out. Other
experimenters will repeat your experiment and find out whether you
were wrong or right. Nature's phenomena will agree or they'll
disagree with your theory. And, although you may gain some
temporary fame and excitement, you will not gain a good reputation
as a scientist if you haven't tried to be very careful in this kind
of work. And it's this type of integrity, this kind of care not to
fool yourself, that is missing to a large extent in much of the
research in cargo cult science.
A great deal of their difficulty is, of course, the difficulty of
the subject and the inapplicability of the scientific method to the
subject. Nevertheless it should be remarked that this is not the
only difficulty. That's why the planes didn't land--but they don't
We have learned a lot from experience about how to handle some of
the ways we fool ourselves. One example: Millikan measured the
charge on an electron by an experiment with falling oil drops, and
got an answer which we now know not to be quite right. It's a
little bit off, because he had the incorrect value for the
viscosity of air. It's interesting to look at the history of
measurements of the charge of the electron, after Millikan. If you
plot them as a function of time, you find that one is a little
bigger than Millikan's, and the next one's a little bit bigger than
that, and the next one's a little bit bigger than that, until
finally they settle down to a number which is higher.
Why didn't they discover that the new number was higher right away?
It's a thing that scientists are ashamed of--this history--because
it's apparent that people did things like this: When they got a
number that was too high above Millikan's, they thought something
must be wrong--and they would look for and find a reason why
something might be wrong. When they got a number closer to
Millikan's value they didn't look so hard. And so they eliminated
the numbers that were too far off, and did other things like that.
We've learned those tricks nowadays, and now we don't have that
kind of a disease.
But this long history of learning how not to fool ourselves--of
having utter scientific integrity--is, I'm sorry to say, something
that we haven't specifically included in any particular course that
I know of. We just hope you've caught on by osmosis.
The first principle is that you must not fool yourself--and you are
the easiest person to fool. So you have to be very careful about
that. After you've not fooled yourself, it's easy not to fool other
scientists. You just have to be honest in a conventional way after
I would like to add something that's not essential to the science,
but something I kind of believe, which is that you should not fool
the layman when you're talking as a scientist. I am not trying to
tell you what to do about cheating on your wife, or fooling your
girlfriend, or something like that, when you're not trying to be
a scientist, but just trying to be an ordinary human being. We'll
leave those problems up to you and your rabbi. I'm talking about
a specific, extra type of integrity that is not lying, but bending
over backwards to show how you are maybe wrong, that you ought to
have when acting as a scientist. And this is our responsibility as
scientists, certainly to other scientists, and I think to laymen.
For example, I was a little surprised when I was talking to a
friend who was going to go on the radio. He does work on cosmology
and astronomy, and he wondered how he would explain what the
applications of this work were. "Well," I said, "there aren't any."
He said, "Yes, but then we won't get support for more research of
this kind." I think that's kind of dishonest. If you're
representing yourself as a scientist, then you should explain to
the layman what you're doing--and if they don't want to support you
under those circumstances, then that's their decision.
One example of the principle is this: If you've made up your mind
to test a theory, or you want to explain some idea, you should
always decide to publish it whichever way it comes out. If we only
publish results of a certain kind, we can make the argument look
good. We must publish both kinds of results.
I say that's also important in giving certain types of government
advice. Supposing a senator asked you for advice about whether
drilling a hole should be done in his state; and you decide it
would be better in some other state. If you don't publish such a
result, it seems to me you're not giving scientific advice. You're
being used. If your answer happens to come out in the direction the
government or the politicians like, they can use it as an argument
in their favor; if it comes out the other way, they don't publish
it at all. That's not giving scientific advice.
Other kinds of errors are more characteristic of poor science. When
I was at Cornell, I often talked to the people in the psychology
department. One of the students told me she wanted to do an
experiment that went something like this--it had been found by
others that under certain circumstances, X, rats did something, A.
She was curious as to whether, if she changed the circumstances to
Y, they would still do A. So her proposal was to do the experiment
under circumstances Y and see if they still did A.
I explained to her that it was necessary first to repeat in her
laboratory the experiment of the other person--to do it under
condition X to see if she could also get result A, and then change
to Y and see if A changed. Then she would know that the real
difference was the thing she thought she had under control.
She was very delighted with this new idea, and went to her
professor. And his reply was, no, you cannot do that, because the
experiment has already been done and you would be wasting time.
This was in about 1947 or so, and it seems to have been the general
policy then to not try to repeat psychological experiments, but
only to change the conditions and see what happens.
Nowadays there's a certain danger of the same thing happening, even
in the famous (?) field of physics. I was shocked to hear of an
experiment done at the big accelerator at the National Accelerator
Laboratory, where a person used deuterium. In order to compare his
heavy hydrogen results to what might happen with light hydrogen"
he had to use data from someone else's experiment on light
hydrogen, which was done on different apparatus. When asked why,
he said it was because he couldn't get time on the program (because
there's so little time and it's such expensive apparatus) to do the
experiment with light hydrogen on this apparatus because there
wouldn't be any new result. And so the men in charge of programs
at NAL are so anxious for new results, in order to get more money
to keep the thing going for public relations purposes, they are
destroying--possibly--the value of the experiments themselves,
which is the whole purpose of the thing. It is often hard for the
experimenters there to complete their work as their scientific
All experiments in psychology are not of this type, however. For
example, there have been many experiments running rats through all
kinds of mazes, and so on--with little clear result. But in 1937
a man named Young did a very interesting one. He had a long
corridor with doors all along one side where the rats came in, and
doors along the other side where the food was. He wanted to see if
he could train the rats to go in at the third door down from
wherever he started them off. No. The rats went immediately to the
door where the food had been the time before.
The question was, how did the rats know, because the corridor was
so beautifully built and so uniform, that this was the same door
as before? Obviously there was something about the door that was
different from the other doors. So he painted the doors very
carefully, arranging the textures on the faces of the doors exactly
the same. Still the rats could tell. Then he thought maybe the rats
were smelling the food, so he used chemicals to change the smell
after each run. Still the rats could tell. Then he realized the
rats might be able to tell by seeing the lights and the arrangement
in the laboratory like any commonsense person. So he covered the
corridor, and still the rats could tell.
He finally found that they could tell by the way the floor sounded
when they ran over it. And he could only fix that by putting his
corridor in sand. So he covered one after another of all possible
clues and finally was able to fool the rats so that they had to
learn to go in the third door. If he relaxed any of his conditions,
the rats could tell.
Now, from a scientific standpoint, that is an A-number-one
experiment. That is the experiment that makes rat-running
experiments sensible, because it uncovers the clues that the rat
is really using--not what you think it's using. And that is the
experiment that tells exactly what conditions you have to use in
order to be careful and control everything in an experiment with
I looked into the subsequent history of this research. The next
experiment, and the one after that, never referred to Mr. Young.
They never used any of his criteria of putting the corridor on
sand, or being very careful. They just went right on running rats
in the same old way, and paid no attention to the great discoveries
of Mr. Young, and his papers are not referred to, because he didn't
discover anything about the rats. In fact, he discovered all the
things you have to do to discover something about rats. But not
paying attention to experiments like that is a characteristic of
cargo cult science.
Another example is the ESP experiments of Mr. Rhine, and other
people. As various people have made criticisms--and they themselves
have made criticisms of their own experiments--they improve the
techniques so that the effects are smaller, and smaller, and
smaller until they gradually disappear. All the parapsychologists
are looking for some experiment that can be repeated--that you can
do again and get the same effect--statistically, even. They run a
million rats no, it's people this time they do a lot of things and
get a certain statistical effect. Next time they try it they don't
get it any more. And now you find a man saying that it is an
irrelevant demand to expect a repeatable experiment. This is
This man also speaks about a new institution, in a talk in which
he was resigning as Director of the Institute of Parapsychology.
And, in telling people what to do next, he says that one of the
things they have to do is be sure they only train students who have
shown their ability to get PSI results to an acceptable extent--
not to waste their time on those ambitious and interested students
who get only chance results. It is very dangerous to have such a
policy in teaching--to teach students only how to get certain
results, rather than how to do an experiment with scientific
So I have just one wish for you--the good luck to be somewhere
where you are free to maintain the kind of integrity I have
described, and where you do not feel forced by a need to maintain
your position in the organization, or financial support, or so on,
to lose your integrity. May you have that freedom.