The Uncertainty of Science is the first lecture of a series of thre...
***“I think it's much more interesting to live not knowing than to ...
"John Danz, veteran motion picture theatre owner and philanthropist...
### What is Science? Feynman gives three potential answers to th...
Feynman has another fantastic talk on "What is Science?" [1]. Am...
Technology is the popular definition of science. It corresponds to ...
***"To every man is given the key to the gates of heaven. The same ...
Point Four program was a technical assistance program for developin...
Feynman starts discussing the next aspect of science: **"The pleasu...
Illustration of the ancients view of the Earth. Read on here: [...
The next few paragraphs are great. Feynman puts the old and the mod...
As Feynman makes the point that the elements forming the ancient's ...
Faraday's Chemical History of a Candle is a great read. You can rea...
**Third aspect of science: the scientific method** for finding thin...
Important to remind this today that the pressure of publising has l...
*It was thought in the Middle Ages that people simply make many ob...
#### Where do ideas come from? It was thought that ideas emerged...
*The rules that describe nature seem to be mathematical. This is n...
#### How can an observation be incorrect? Scientists are very care...
The Uncertainty of Science
Richard Feynman
I WANT TO ADDRESS myself directly to the impact of science
on man's ideas in other fields, a subject Mr. John Danz particularly
wanted to be discussed. In the first of these lectures I will talk about the
nature of science and emphasize particularly the existence of doubt
and uncertainty. In the second lecture I will discuss the impact of
scientific views on political questions, in particular the question of
national enemies, and on religious questions. And in the third lecture I
will describe how society looks to me—I could say how society looks to
a scientific man, but it is only how it looks to me—and what future
scientific discoveries may produce in terms of social problems.
What do I know of religion and politics? Several friends in the
physics departments here and in other places laughed and said, "I'd
like to come and hear what you have to say. I never knew you were
interested very much in those things." They mean, of course, I am
interested, but I would not dare to talk about them.
In talking about the impact of ideas in one field on ideas in
another field, one is always apt to make a fool of oneself. In these days
of specialization there are too few people who have such a deep
understanding of two departments of our knowledge that they do not
make fools of themselves in one or the other.
The ideas I wish to describe are old ideas. There is practically
nothing that I am going to say tonight that could not easily have been
said by philosophers of the seventeenth century. Why repeat all this?
Because there are new generations born every day. Because there are
great ideas developed in the history of man, and these ideas do not last
unless they are passed purposely and clearly from generation to
Many old ideas have become such common knowledge that it is
not necessary to talk about or explain them again. But the ideas
associated with the problems of the development of science, as far as I
can see by looking around me, are not of the kind that everyone
appreciates. It is true that a large number of people do appreciate them.
And in a university particularly most people appreciate them, and you
may be the wrong audience for me.
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Now in this difficult business of talking about the impact of the
ideas of one field on those of another, I shall start at the end that I
know. I do know about science. I know its ideas and its methods, its
attitudes toward knowledge, the sources of its progress, its mental
discipline. And therefore, in this first lecture, I shall talk about the
science that I know, and I shall leave the more ridiculous of my
statements for the next two lectures, at which, I assume, the general
law is that the audiences will be smaller.
What is science? The word is usually used to mean one of three
things, or a mixture of them. I do not think we need to be precise—it is
not always a good idea to be too precise. Science means, sometimes, a
special method of finding things out. Sometimes it means the body of
knowledge arising from the things found out. It may also mean the
new things you can do when you have found something out, or the
actual doing of new things. This last field is usually called
technology—but if you look at the science section in Time magazine
you will find it covers about 50 percent what new things are found out
and about 50 percent what new things can be and are being done. And
so the popular definition of science is partly technology, too.
I want to discuss these three aspects of science in reverse order. I
will begin with the new things that you can do—that is, with
technology. The most obvious characteristic of science is its
application, the fact that as a consequence of science one has a power to
do things. And the effect this power has had need hardly be
mentioned. The whole industrial revolution would almost have been
impossible without the development of science. The possibilities today
of producing quantities of food adequate for such a large population,
of controlling sickness—the very fact that there can be free men
without the necessity of slavery for full production—are very likely the
result of the development of scientific means of production.
Now this power to do things carries with it no instructions on
how to use it, whether to use it for good or for evil. The product of this
power is either good or evil, depending on how it is used. We like
improved production, but we have problems with automation. We are
happy with the development of medicine, and then we worry about
the number of births and the fact that no one dies from the diseases we
have eliminated. Or else, with the same knowledge of bacteria, we
have hidden laboratories in which men are working as hard as they can
The Uncertainty of Science
to develop bacteria for which no one else will be able to find a cure. We
are happy with the development of air transportation and are
impressed by the great airplanes, but we are aware also of the severe
horrors of air war. We are pleased by the ability to communicate
between nations, and then we worry about the fact that we can be
snooped upon so easily. We are excited by the fact that space can now
be entered; well, we will undoubtedly have a difficulty there, too. The
most famous of all these imbalances is the development of nuclear
energy and its obvious problems.
Is science of any value?
I think a power to do something is of value. Whether the result is
a good thing or a bad thing depends on how it is used, but the power is
a value.
Once in Hawaii I was taken to see a Buddhist temple. In the
temple a man said, "I am going to tell you something that you will
never forget." And then he said, "To every man is given the key to the
gates of heaven. The same key opens the gates of hell."
And so it is with science. In a way it is a key to the gates of
heaven, and the same key opens the gates of hell, and we do not have
any instructions as to which is which gate. Shall we throw away the
key and never have a way to enter the gates of heaven? Or shall we
struggle with the problem of which is the best way to use the key? That
is, of course, a very serious question, but I think that we cannot deny
the value of the key to the gates of heaven.
All the major problems of the relations between society and
science lie in this same area. When the scientist is told that he must be
more responsible for his effects on society, it is the applications of
science that are referred to. If you work to develop nuclear energy you
must realize also that it can be used harmfully. Therefore, you would
expect that, in a discussion of this kind by a scientist, this would be the
most important topic. But I will not talk about it further. I think that to
say these are scientific problems is an exaggeration. They are far more
humanitarian problems. The fact that how to work the power is clear,
but how to control it is not, is something not so scientific and is not
something that the scientist knows so much about.
Let me illustrate why I do not want to talk about this. Some time
ago, in about 1949 or 1950, I went to Brazil to teach physics. There was
a Point Four program in those days, which was very exciting—
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everyone was going to help the underdeveloped countries. What they
needed, of course, was technical know-how.
In Brazil I lived in the city of Rio. In Rio there are hills on which
are homes made with broken pieces of wood from old signs and so
forth. The people are extremely poor. They have no sewers and no
water. In order to get water they carry old gasoline cans on their heads
down the hills. They go to a place where a new building is being built,
because there they have water for mixing cement. The people fill their
cans with water and carry them up the hills. And later you see the
water dripping down the hill in dirty sewage. It is a pitiful thing.
Right next to these hills are the exciting buildings of the
Copacabana beach, beautiful apartments, and so on.
And I said to my friends in the Point Four program, "Is this a
problem of technical know-how? They don't know how to put a pipe
up the hill? They don't know how to put a pipe to the top of the hill so
that the people can at least walk uphill with the empty cans and
downhill with the full cans?"
So it is not a problem of technical know-how. Certainly not,
because in the neighboring apartment buildings there are pipes, and
there are pumps. We realize that now. Now we think it is a problem of
economic assistance, and we do not know whether that really works or
not. And the question of how much it costs to put a pipe and a pump
to the top of each of the hills is not one that seems worth discussing, to
Although we do not know how to solve the problem, I would
like to point out that we tried two things, technical know-how and
economic assistance. We are discouraged with them both, and we are
trying something else. As you will see later, I find this encouraging. I
think that to keep trying new solutions is the way to do everything.
Those, then are the practical aspects of science, the new things
that you can do. They are so obvious that we do not need to speak
about them further.
The next aspect of science is its contents, the things that have
been found out. This is the yield. This is the gold. This is the
excitement, the pay you get for all the disciplined thinking and hard
work. The work is not done for the sake of an application. It is done for
the excitement of what is found out. Perhaps most of you know this.
But to those of you who do not know it, it is almost impossible for me
The Uncertainty of Science
to convey in a lecture this important aspect, this exciting part, the real
reason for science. And without understanding this you miss the whole
point. You cannot understand science and its relation to anything else
unless you understand and appreciate the great adventure of our time.
You do not live in your time unless you understand that this is a
tremendous adventure and a wild and exciting thing.
Do you think it is dull? It isn't. It is most difficult to convey, but
perhaps I can give some idea of it. Let me start anywhere, with any
For instance, the ancients believed that the earth was the back of
an elephant that stood on a tortoise that swam in a bottomless sea. Of
course, what held up the sea was another question. They did not know
the answer.
The belief of the ancients was the result of imagination. It was a
poetic and beautiful idea. Look at the way we see it today. Is that a dull
idea? The world is a spinning ball, and people are held on it on all
sides, some of them upside down. And we turn like a spit in front of a
great fire. We whirl around the sun. That is more romantic, more
exciting. And what holds us? The force of gravitation, which is not only
a thing of the earth but is the thing that makes the earth round in the
first place, holds the sun together and keeps us running around the sun
in our perpetual attempt to stay away. This gravity holds its sway not
only on the stars but between the stars; it holds them in the great
galaxies for miles and miles in all directions.
This universe has been described by many, but it just goes on,
with its edge as unknown as the bottom of the bottomless sea of the
other idea—just as mysterious, just as awe-inspiring, and just as
incomplete as the poetic pictures that came before.
But see that the imagination of nature is far, far greater than the
imagination of man. No one who did not have some inkling of this
through observations could ever have imagined such a marvel as
nature is.
Or the earth and time. Have you read anywhere, by any poet,
anything about time that compares with real time, with the long, slow
process of evolution? Nay, I went too quickly. First, there was the earth
without anything alive on it. For billions of years this ball was spinning
with its sunsets and its waves and the sea and the noises, and there
was no thing alive to appreciate it. Can you conceive, can you
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appreciate or fit into your ideas what can be the meaning of a world
without a living thing on it? We are so used to looking at the world
from the point of view of living things that we cannot understand what
it means not to be alive, and yet most of the time the world had
nothing alive on it. And in most places in the universe today there
probably is nothing alive.
Or life itself. The internal machinery of life, the chemistry of the
parts, is something beautiful. And it turns out that all life is
interconnected with all other life. There is a part of chlorophyll, an
important chemical in the oxygen processes in plants, that has a kind of
square pattern; it is a rather pretty ring called a benzine ring. And far
removed from the plants are animals like ourselves, and in our oxygen-
containing systems, in the blood, the hemoglobin, there are the same
interesting and peculiar square rings. There is iron in the center of
them instead of magnesium, so they are not green but red, but they are
the same rings.
The proteins of bacteria and the proteins of humans are the same.
In fact it has recently been found that the protein-making machinery in
the bacteria can be given orders from material from the red cells to
produce red cell proteins. So close is life to life. The universality of the
deep chemistry of living things is indeed a fantastic and beautiful
thing. And all the time we human beings have been too proud even to
recognize our kinship with the animals.
Or there are the atoms. Beautiful - mile upon mile of one ball
after another ball in some repeating pattern in a crystal. Things that
look quiet and still, like a glass of water with a covered top that has
been sitting for several days, are active all the time; the atoms are
leaving the surface, bouncing around inside, and coming back. What
looks still to our crude eyes is a wild and dynamic dance.
And, again, it has been discovered that all the world is made of
the same atoms, that the stars are of the same stuff as ourselves. It then
becomes a question of where our stuff came from. Not just where did
life come from, or where did the earth come from, but where did the
stuff of life and of the earth come from? It looks as if it was belched
from some exploding star, much as some of the stars are exploding
now. So this piece of dirt waits four and a half billion years and evolves
and changes, and now a strange creature stands here with instruments
The Uncertainty of Science
and talks to the strange creatures in the audience. What a wonderful
Or take the physiology of human beings. It makes no difference
what I talk about. If you look closely enough at anything, you will see
that there is nothing more exciting than the truth, the pay dirt of the
scientist, discovered by his painstaking efforts.
In physiology you can think of pumping blood, the exciting
movements of a girl jumping a jump rope. What goes on inside? The
blood pumping, the interconnecting nerves—how quickly the
influences of the muscle nerves feed right back to the brain to say,
"Now we have touched the ground, now increase the tension so I do
not hurt the heels." And as the girl dances up and down, there is
another set of muscles that is fed from another set of nerves that says,
"One, two, three, O'Leary, one, two, ..." And while she does that,
perhaps she smiles at the professor of physiology who is watching her.
That is involved, too!
And then electricity The forces of attraction, of plus and minus,
are so strong that in any normal substance all the plusses and minuses
are carefully balanced out, everything pulled together with everything
else. For a long time no one even noticed the phenomenon of
electricity, except once in a while when they rubbed a piece of amber
and it attracted a piece of paper. And yet today we find, by playing
with these things, that we have a tremendous amount of machinery
inside. Yet science is still not thoroughly appreciated.
To give an example, I read Faraday's Chemical History of a
Candle, a set of six Christmas lectures for children. The point of
Faraday's lectures was that no matter what you look at, if you look at it
closely enough, you are involved in the entire universe. And so he got,
by looking at every feature of the candle, into combustion, chemistry,
etc. But the introduction of the book, in describing Faraday's life and
some of his discoveries, explained that he had discovered that the
amount of electricity necessary to perform electrolysis of chemical
substances is proportional to the number of atoms which are separated
divided by the valence. It further explained that the principles he
discovered are used today in chrome plating and the anodic coloring of
aluminum, as well as in dozens of other industrial applications. I do
not like that statement. Here is what Faraday said about his own
discovery: "The atoms of matter are in some ways endowed or
The Meaning of It All
associated with electrical powers, to which they owe their most striking
qualities, amongst them their mutual chemical affinity." He had
discovered that the thing that determined how the atoms went
together, the thing that determined the combinations of iron and
oxygen which make iron oxide is that some of them are electrically
plus and some of them are electrically minus, and they attract each
other in definite proportions. He also discovered that electricity comes
in units, in atoms. Both were important discoveries, but most exciting
was that this was one of the most dramatic moments in the history of
science, one of those rare moments when two great fields come
together and are unified. He suddenly found that two apparently
different things were different aspects of the same thing. Electricity
was being studied, and chemistry was being studied. Suddenly they
were two aspects of the same thing—chemical changes with the results
of electrical forces. And they are still understood that way. So to say
merely that the principles are used in chrome plating is inexcusable.
And the newspapers, as you know, have a standard line for every
discovery made in physiology today: "The discoverer said that the
discovery may have uses in the cure of cancer." But they cannot explain
the value of the thing itself.
Trying to understand the way nature works involves a most
terrible test of human reasoning ability. It involves subtle trickery,
beautiful tightropes of logic on which one has to walk in order not to
make a mistake in predicting what will happen. The quantum
mechanical and the relativity ideas are examples of this.
The third aspect of my subject is that of science as a method of
finding things out. This method is based on the principle that
observation is the judge of whether something is so or not. All other
aspects and characteristics of science can be understood directly when
we understand that observation is the ultimate and final judge of the
truth of an idea. But "prove" used in this way really means "test," in the
same way that a hundred-proof alcohol is a test of the alcohol, and for
people today the idea really should be translated as, "The exception
tests the rule." Or, put another way, "The exception proves that the rule
is wrong." That is the principle of science. If there is an exception to any
rule, and if it can be proved by observation, that rule is wrong.
The exceptions to any rule are most interesting in themselves, for
they show us that the old rule is wrong. And it is most exciting, then,
The Uncertainty of Science
to find out what the right rule, if any, is. The exception is studied,
along with other conditions that produce similar effects. The scientist
tries to find more exceptions and to determine the characteristics of the
exceptions, a process that is continually exciting as it develops. He does
not try to avoid showing that the rules are wrong; there is progress and
excitement in the exact opposite. He tries to prove himself wrong as
quickly as possible.
The principle that observation is the judge imposes a severe
limitation to the kind of questions that can be answered. They are
limited to questions that you can put this way: "if I do this, what will
happen?" There are ways to try it and see. Questions like, "should I do
this?" and "what is the value of this?" are not of the same kind.
But if a thing is not scientific, if it cannot be subjected to the test
of observation, this does not mean that it is dead, or wrong, or stupid.
We are not trying to argue that science is somehow good and other
things are somehow not good. Scientists take all those things that can
be analyzed by observation, and thus the things called science are
found out. But there are some things left out, for which the method
does not work. This does not mean that those things are unimportant.
They are, in fact, in many ways the most important. In any decision for
action, when you have to make up your mind what to do, there is
always a "should" involved, and this cannot be worked out from "if I
do this, what will happen?" alone. You say, "Sure, you see what will
happen, and then you decide whether you want it to happen or not."
But that is the step the scientist cannot take. You can figure out what is
going to happen, but then you have to decide whether you like it that
way or not.
There are in science a number of technical consequences that
follow from the principle of observation as judge. For example, the
observation cannot be rough. You have to be very careful. There may
have been a piece of dirt in the apparatus that made the color change; it
was not what you thought. You have to check the observations very
carefully, and then recheck them, to be sure that you understand what
all the conditions are and that you did not misinterpret what you did.
It is interesting that this thoroughness, which is a virtue, is often
misunderstood. When someone says a thing has been done
scientifically, often all he means is that it has been done thoroughly. I
have heard people talk of the "scientific" extermination of the Jews in
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Germany. There was nothing scientific about it. It was only thorough.
There was no question of making observations and then checking them
in order to determine something. In that sense, there were "scientific"
exterminations of people in Roman times and in other periods when
science was not so far developed as it is today and not much attention
was paid to observation. In such cases, people should say "thorough"
or "thoroughgoing," instead of "scientific."
There are a number of special techniques associated with the
game of making observations, and much of what is called the
philosophy of science is concerned with a discussion of these
techniques. The interpretation of a result is an example. To take a
trivial instance, there is a famous joke about a man who complains to a
friend of a mysterious phenomenon. The white horses on his farm eat
more than the black horses. He worries about this and cannot
understand it, until his friend suggests that maybe he has more white
horses than black ones.
It sounds ridiculous, but think how many times similar mistakes
are made in judgments of various kinds. You say, "My sister had a
cold, and in two weeks ..." It is one of those cases, if you think about it,
in which there were more white horses. Scientific reasoning requires a
certain discipline, and we should try to teach this discipline, because
even on the lowest level such errors are unnecessary today.
Another important characteristic of science is its objectivity. It is
necessary to look at the results of observation objectively, because you,
the experimenter, might like one result better than another. You
perform the experiment several times, and because of irregularities,
like pieces of dirt falling in, the result varies from time to time. You do
not have everything under control. You like the result to be a certain
way, so the times it comes out that way, you say, "See, it comes out this
particular way." The next time you do the experiment it comes out
different. Maybe there was a piece of dirt in it the first time, but you
ignore it.
These things seem obvious, but people do not pay enough
attention to them in deciding scientific questions or questions on the
periphery of science. There could be a certain amount of sense, for
example, in the way you analyze the question of whether stocks went
up or down because of what the President said or did not say.
The Uncertainty of Science
Another very important technical point is that the more specific a
rule is, the more interesting it is. The more definite the statement, the
more interesting it is to test. If someone were to propose that the
planets go around the sun because all planet matter has a kind of
tendency for movement, a kind of motility, let us call it an "oomph,"
this theory could explain a number of other phenomena as well. So this
is a good theory, is it not? No. It is nowhere near as good as a
proposition that the planets move around the sun under the influence
of a central force which varies exactly inversely as the square of the
distance from the center. The second theory is better because it is so
specific; it is so obviously unlikely to be the result of chance. It is so
definite that the barest error in the movement can show that it is
wrong; but the planets could wobble all over the place, and, according
to the first theory, you could say, "Well, that is the funny behavior of
the 'oomph.'"
So the more specific the rule, the more powerful it is, the more
liable it is to exceptions, and the more interesting and valuable it is to
Words can be meaningless. If they are used in such a way that no
sharp conclusions can be drawn, as in my example of "oomph," then
the proposition they state is almost meaningless, because you can
explain almost anything by the assertion that things have a tendency to
motility. A great deal has been made of this by philosophers, who say
that words must be defined extremely precisely. Actually, I disagree
somewhat with this; I think that extreme precision of definition is often
not worthwhile, and sometimes it is not possible—in fact mostly it is
not possible, but I will not get into that argument here.
Most of what many philosophers say about science is really on
the technical aspects involved in trying to make sure the method works
pretty well. Whether these technical points would be useful in a field in
which observation is not the judge I have no idea. I am not going to say
that everything has to be done the same way when a method of testing
different from observation is used. In a different field perhaps it is not
so important to be careful of the meaning of words or that the rules be
specific, and so on. I do not know.
In all of this I have left out something very important. I said that
observation is the judge of the truth of an idea. But where does the idea
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come from? The rapid progress and development of science requires
that human beings invent something to test.
It was thought in the Middle Ages that people simply make
many observations, and the observations themselves suggest the laws.
But it does not work that way. It takes much more imagination than
that. So the next thing we have to talk about is where the new ideas
come from. Actually, it does not make any difference, as long as they
come. We have a way of checking whether an idea is correct or not that
has nothing to do with where it came from. We simply test it against
observation. So in science we are not interested in where an idea comes
There is no authority who decides what is a good idea. We have
lost the need to go to an authority to find out whether an idea is true or
not. We can read an authority and let him suggest something; we can
try it out and find out if it is true or not. If it is not true, so much the
worse— so the "authorities" lose some of their "authority."
The relations among scientists were at first very argumentative,
as they are among most people. This was true in the early days of
physics, for example. But in physics today the relations are extremely
good. A scientific argument is likely to involve a great deal of laughter
and uncertainty on both sides, with both sides thinking up experiments
and offering to bet on the outcome. In physics there are so many
accumulated observations that it is almost impossible to think of a new
idea which is different from all the ideas that have been thought of
before and yet that agrees with all the observations that have already
been made. And so if you get anything new from anyone, anywhere,
you welcome it, and you do not argue about why the other person says
it is so.
Many sciences have not developed this far, and the situation is
the way it was in the early days of physics, when there was a lot of
arguing because there were not so many observations. I bring this up
because it is interesting that human relationships, if there is an
independent way of judging truth, can become unargumentative.
Most people find it surprising that in science there is no interest
in the background of the author of an idea or in his motive in
expounding it. You listen, and if it sounds like a thing worth trying, a
thing that could be tried, is different, and is not obviously contrary to
something observed before, it gets exciting and worthwhile. You do
The Uncertainty of Science
not have to worry about how long he has studied or why he wants you
to listen to him. In that sense it makes no difference where the ideas
come from. Their real origin is unknown; we call it the imagination of
the human brain, the creative imagination—it is known; it is just one of
those "oomphs."
It is surprising that people do not believe that there is
imagination in science. It is a very interesting kind of imagination,
unlike that of the artist. The great difficulty is in trying to imagine
something that you have never seen, that is consistent in every detail
with what has already been seen, and that is different from what has
been thought of; furthermore, it must be definite and not a vague
proposition. That is indeed difficult.
Incidentally, the fact that there are rules at all to be checked is a
kind of miracle; that it is possible to find a rule, like the inverse square
law of gravitation, is some sort of miracle. It is not understood at all,
but it leads to the possibility of prediction—that means it tells you
what you would expect to happen in an experiment you have not yet
It is interesting, and absolutely essential, that the various rules of
science be mutually consistent. Since the observations are all the same
observations, one rule cannot give one prediction and another rule
another prediction. Thus, science is not a specialist business; it is
completely universal. I talked about the atoms in physiology; I talked
about the atoms in astronomy, electricity, chemistry. They are
universal; they must be mutually consistent. You cannot just start off
with a new thing that cannot be made of atoms.
It is interesting that reason works in guessing at the rules, and the
rules, at least in physics, become reduced. I gave an example of the
beautiful reduction of the rules in chemistry and electricity into one
rule, but there are many more examples.
The rules that describe nature seem to be mathematical. This is
not a result of the fact that observation is the judge, and it is not a
characteristic necessity of science that it be mathematical. It just turns
out that you can state mathematical laws, in physics at least, which
work to make powerful predictions. Why nature is mathematical is,
again, a mystery.
I come now to an important point. The old laws may be wrong.
How can an observation be incorrect? If it has been carefully checked,
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how can it be wrong? Why are physicists always having to change the
laws? The answer is, first, that the laws are not the observations and,
second, that experiments are always inaccurate. The laws are guessed
laws, extrapolations, not something that the observations insist upon.
They are just good guesses that have gone through the sieve so far.
And it turns out later that the sieve now has smaller holes than the
sieves that were used before, and this time the law is caught. So the
laws are guessed; they are extrapolations into the unknown. You do
not know what is going to happen, so you take a guess.
For example, it was believed—it was discovered— that motion
does not affect the weight of a thing—that if you spin a top and weigh
it, and then weigh it when it has stopped, it weighs the same. That is
the result of an observation. But you cannot weigh something to the
infinitesimal number of decimal places, parts in a billion. But we now
understand that a spinning top weighs more than a top which is not
spinning by a few parts in less than a billion. If the top spins fast
enough so that the speed of the edges approaches 186,000 miles a
second, the weight increase is appreciable—but not until then. The first
experiments were performed with tops that spun at speeds much
lower than 186,000 miles a second. It seemed then that the mass of the
top spinning and not spinning was exactly the same, and someone
made a guess that the mass never changes.
How foolish! What a fool! It is only a guessed law, an
extrapolation. Why did he do something so unscientific? There was
nothing unscientific about it; it was only uncertain. It would have been
unscientific not to guess. It has to be done because the extrapolations
are the only things that have any real value. It is only the principle of
what you think will happen in a case you have not tried that is worth
knowing about. Knowledge is of no real value if all you can tell me is
what happened yesterday. It is necessary to tell what will happen
tomorrow if you do something—not only necessary, but fun. Only you
must be willing to stick your neck out.
Every scientific law, every scientific principle, every statement of
the results of an observation is some kind of a summary which leaves
out details, because nothing can be stated precisely. The man simply
forgot—he should have stated the law "The mass doesn't change much
when the speed isn't too high." The game is to make a specific rule and
then see if it will go through the sieve. So the specific guess was that
The Uncertainty of Science
the mass never changes at all. Exciting possibility! It does no harm that
it turned out not to be the case. It was only uncertain, and there is no
harm in being uncertain. It is better to say something and not be sure
than not to say anything at all.
It is necessary and true that all of the things we say in science, all
of the conclusions, are uncertain, because they are only conclusions.
They are guesses as to what is going to happen, and you cannot know
what will happen, because you have not made the most complete
It is curious that the effect on the mass of a spinning top is so
small you may say, "Oh, it doesn't make any difference." But to get a
law that is right, or at least one that keeps going through the successive
sieves, that goes on for many more observations, requires a
tremendous intelligence and imagination and a complete revamping of
our philosophy, our understanding of space and time. I am referring to
the relativity theory. It turns out that the tiny effects that turn up
always require the most revolutionary modifications of ideas.
Scientists, therefore, are used to dealing with doubt and
uncertainty. All scientific knowledge is uncertain. This experience with
doubt and uncertainty is important. I believe that it is of very great
value, and one that extends beyond the sciences. I believe that to solve
any problem that has never been solved before, you have to leave the
door to the unknown ajar. You have to permit the possibility that you
do not have it exactly right. Otherwise, if you have made up your mind
already, you might not solve it.
When the scientist tells you he does not know the answer, he is
an ignorant man. When he tells you he has a hunch about how it is
going to work, he is uncertain about it. When he is pretty sure of how it
is going to work, and he tells you, "This is the way it's going to work,
I'll bet," he still is in some doubt. And it is of paramount importance, in
order to make progress, that we recognize this ignorance and this
doubt. Because we have the doubt, we then propose looking in new
directions for new ideas. The rate of the development of science is not
the rate at which you make observations alone but, much more
important, the rate at which you create new things to test.
If we were not able or did not desire to look in any new direction,
if we did not have a doubt or recognize ignorance, we would not get
any new ideas. There would be nothing worth checking, because we
The Meaning of It All
would know what is true. So what we call scientific knowledge today
is a body of statements of varying degrees of certainty. Some of them
are most unsure; some of them are nearly sure; but none is absolutely
certain. Scientists are used to this. We know that it is consistent to be
able to live and not know. Some people say, "How can you live without
knowing?" I do not know what they mean. I always live without
knowing. That is easy. How you get to know is what I want to know.
This freedom to doubt is an important matter in the sciences and,
I believe, in other fields. It was born of a struggle. It was a struggle to
be permitted to doubt, to be unsure. And I do not want us to forget the
importance of the struggle and, by default, to let the thing fall away. I
feel a responsibility as a scientist who knows the great value of a
satisfactory philosophy of ignorance, and the progress made possible
by such a philosophy, progress which is the fruit of freedom of
thought. I feel a responsibility to proclaim the value of this freedom
and to teach that doubt is not to be feared, but that it is to be welcomed
as the possibility of a new potential for human beings. If you know that
you are not sure, you have a chance to improve the situation. I want to
demand this freedom for future generations.
Doubt is clearly a value in the sciences. Whether it is in other
fields is an open question and an uncertain matter. I expect in the next
lectures to discuss that very point and to try to demonstrate that it is
important to doubt and that doubt is not a fearful thing, but a thing of
very great value.


Faraday's Chemical History of a Candle is a great read. You can read it here: [![](]( #### Where do ideas come from? It was thought that ideas emerged from observations, that the simply act of measuring would dictate the laws of Nature. **Today we know that imagination and scientific creativity** play a very important role in the discovery of new ideas, think about P. Dirac (prediction of the positron), or A. Einstein (General Relativity). Scientists have to come up with new ideas, that are different from everything from common belief and that a the same time must be consistent with all the available observations. It is a very interesting type of imagination. ### What is Science? Feynman gives three potential answers to this quesion. For him Science can be: - A special method of finding things out - The body of knowledge arising from the things found out - New things you can do when you have found something out, or the actual doing of new things. This last field is usually called technology Feynman presents his definition of science as an opinion, and opinion of what science can do. Not what science is, since that could be hard to know. Important to remind this today that the pressure of publising has led many people to publish arranged results. Is Science important for those or just a full day job? *It was thought in the Middle Ages that people simply make many observations, and the observations themselves suggest the laws.* Sounds a lot like **Big Data**. Does anyone know what Feynman is referencing here? Technology is the popular definition of science. It corresponds to the body of "new things" that are tangible to every human being. The impact of Science and Technology on human civilisation is undeniable. In the end it woks both ways... Either we derive ideas from the observations (as Kepler did) or we build them from a framework of knowledge and then test them against observations (as Einstein did). Point Four program was a technical assistance program for developing countries initiated in Harry Truman's presidency in 1949 (*Source: Wikipedia*) #### How can an observation be incorrect? Scientists are very careful about the way they create new laws, so thorough about their observations. How come they have to constantly change their laws. For Feynman there are two main reasons for this: 1. Laws are best guesses with the knowledge we have at the time we create them 2. Experiments are always inaccurate Feynman starts discussing the next aspect of science: **"The pleasure of finding things out." ** Scientists do not do research for the sake of finding an practical application to their findings but instead do it simply to satisfy their sheer curiosity. Illustration of the ancients view of the Earth. Read on here: [World Turtle]( ![earthturtle]( "earthturtle") The next few paragraphs are great. Feynman puts the old and the modern views of the world in contrast. The modern view of the world turns out to be much more interesting and exciting than the old view of the world. ***"The Imagination of Nature is far, far greater that the imagination of man."*** As Feynman makes the point that the elements forming the ancient's description of the universe is eerily similar to what we have observed with all our modern technological instruments - we know that there are properties of our universe that exist but we have not discovered a method by which to observe them. Perhaps our five biological senses are not enough. Perhaps we require a sixth sensory input in order to observe the true nature of the universe. With the future discovery of advanced scientific instruments, our current model of the universe could in the end sound just as primitive as that of the ancients. ***“I think it's much more interesting to live not knowing than to have answers which might be wrong. I have approximate answers and possible beliefs and different degrees of uncertainty about different things, but I am not absolutely sure of anything and there are many things I don't know anything about, such as whether it means anything to ask why we're here. I don't have to know an answer. I don't feel frightened not knowing things, by being lost in a mysterious universe without any purpose, which is the way it really is as far as I can tell.”*** - R. Feynman I can't speak for him, but an example would be the extensive observations of planetary positions by Tycho Brahe, which then allowed Kepler to reject Copernicus' theory of circular motion, and verify that elliptical motion matched the observations. **Third aspect of science: the scientific method** for finding things out. All ideas should be tested and observation is the ultimate judge whether a theory is right or wrong. The scientific method constitutes the methods and techniques used for observations and for acquiring new knowledge, you can learn more here: [Scientific Method]( Here is an interesting talk from Feynman about the Scientific method: [![](]( *The rules that describe nature seem to be mathematical. This is not a result of the fact that observation is the judge, and it is not a characteristic necessity of science that it be mathematical.* Is he refering to math beeing an adequate language to describe physical processes? Compared to prosa forms of description? Would the *story telling* like approach in folk psychology be an alternative form of description? What other forms are there? ***"To every man is given the key to the gates of heaven. The same key opens the gates of hell. And so it is with science."*** Feynman believes that the power to create new things enabled by science and technology is of great value. These things can be good or bad but that is not up to the scientist to decide how to control his discoveries. The Uncertainty of Science is the first lecture of a series of three public lectures that R. Feynman gave at University of Washington, Seattle in April 1963. In this lecture Feynman discusses what he believes are the **3 meanings of Science**: 1. A special method for finding things out 2. The knowledge arising from the things found out 3. The new applications you can do with the new knowledge Feynman discusses the 3 points in detail and discuss the fact that uncertainty and doubt in science are essential, because they leave the door open for further investigation and new discoveries. [Richard Feynman - The Uncertainty Of Knowledge]( "John Danz, veteran motion picture theatre owner and philanthropist of the Pacific Northwest, and his wife, Jessie, made a gift to the University of Washington in 1961. This gift was used to establish the John Danz Fund. This fund, an enduring benefit to the University and the state, brings to the University of Washington campus and Seattle community lecturers of national and international reputation. Specifically, the gift is intended to enable the University of Washington to bring ‘distinguished scholars who have concerned themselves with the impact of science and philosophy on man’s perception of a rational universe.’" - Feynman has another fantastic talk on "What is Science?" [1]. Among other things, at a certain point in that talk, this is how he lays out his "best definition of science": "What science is, I think, may be something like this: There was on this planet an evolution of life to a stage that there were evolved animals, which are intelligent. I don't mean just human beings, but animals which play and which can learn something from experience--like cats. But at this stage each animal would have to learn from its own experience. They gradually develop, until some animal [primates?] could learn from experience more rapidly and could even learn from another’s experience by watching, or one could show the other, or he saw what the other one did. So there came a possibility that all might learn it, but the transmission was inefficient and they would die, and maybe the one who learned it died, too, before he could pass it on to others. The question is: is it possible to learn more rapidly what somebody learned from some accident than the rate at which the thing is being forgotten, either because of bad memory or because of the death of the learner or inventors? So there came a time, perhaps, when for some species [humans?] the rate at which learning was increased, reached such a pitch that suddenly a completely new thing happened: things could be learned by one individual animal, passed on to another, and another fast enough that it was not lost to the race. Thus became possible an accumulation of knowledge of the race. This has been called time-binding. I don't know who first called it this. At any rate, we have here [in this hall] some samples of those animals, sitting here trying to bind one experience to another, each one trying to learn from the other. This phenomenon of having a memory for the race, of having an accumulated knowledge passable from one generation to another, was new in the world--but it had a disease in it: it was possible to pass on ideas which were not profitable for the race. The race has ideas, but they are not necessarily profitable. So there came a time in which the ideas, although accumulated very slowly, were all accumulations not only of practical and useful things, but great accumulations of all types of prejudices, and strange and odd beliefs. Then a way of avoiding the disease was discovered. This is to doubt that what is being passed from the past is in fact true, and to try to find out ab initio again from experience what the situation is, rather than trusting the experience of the past in the form in which it is passed down. And that is what science is: the result of the discovery that it is worthwhile rechecking by new direct experience, and not necessarily trusting the [human] race['s] experience from the past. I see it that way. That is my best definition." [1] Feynman, R. P., "What is Science?" The Physics Teacher Vol. 7, issue 6, 1969, pp. 313-320