Now I am going to discuss how we would look
for a new law.
In general, we look for a new law by the following
process.
First we guess it.
(Audience laughs)
Well, don't laugh that's really true.
Then we compute the consequences of the guess,
to see if this law that we guessed was right,
we see what it would imply.
Then we compare those computation results
to nature, or we say compare to experiment
or experience.
Compare it directly with observation to see
if it works.
If it disagrees with experiment, it's wrong.
In that simple statement is the key to science.
It doesn't make a difference how beautiful
your guess is.
It doesn't make a difference how smart you
are who made the guess or what his name is.
If it disagrees with experiment, it's wrong.
That's all there is to it.
Now you see of course, that with this method,
we can disprove any definite theory.
You have a definite theory, a real guess,
from which you can clearly compute consequences,
which could be compared to experiment, and
in principle we can get rid of any theory.
We can always prove any definite theory wrong.
Notice however, were we never prove it right.
Suppose that you invent a good guess, calculate
the consequences to discover that every consequence
that you calculate agrees with experiment.
The theory is then right?
No.
It is simply not proved wrong.
Because in the future, there could be a wider
range of experiments to compute a wider range
of consequences, and you may discover then
that the thing is wrong.
That's why the laws, like Newton's laws for
the motion of planets, last such a long time.
He guessed the law of gravitation.
He calculated all kinds of consequences for
the solar system and so on, compared them
to experiment, and it took several hundred
years before the slight error of the motion
of mercury was developed.
During all that time, the theory had been
failed to be proved wrong, and could be taken
to be temporarily right, but it can never
be proved right, because tomorrow's experiment
may succeed in proving what you thought was
right, wrong.
So we never are right, we can only be sure
we're wrong.
However, it's rather remarkable how we can
last so long.
I mean, have some idea which would last so
long.
I must also point out to you that you cannot
prove a vague theory wrong.
If the guess that you make is poorly expressed
and rather vague.
And the method that you use for kinda figuring
out the consequences is rather a little vague,
you're not sure.
And you just say, I think everything's because
it's all due to Mughals, and Mughals do this
and that more or less.
So I can sort of explain how this works.
Then you see that that theory is good because
it can't be proved wrong.
If the process of computing the consequences
is indefinite, then with a little skill any
experimental result can be made to look like
an expected consequence.
You're probably familiar with that in other
fields.
For example A hates his mother.
The reason is of course, because she didn't
caress him or love him enough when he was
a child.
Actually, if you investigate, you find out
that as a matter of fact, she did love him
very much and everything was alright.
Well then, it's because she was overindulgent
when he was...
So by having a vague theory it's possible
to get either results.
Now the cure for this one is the following.
It would be possible to say, if it were possible
to state ahead of time, how much love is not
enough and how much love is overindulgent
exactly.
Then there would be a perfectly legitimate
theory against which you can make tests.
It is usually said when this is pointed out.
How much love is and so on...
Oh, you are dealing with psychological matters
these things can't be defined so precisely.
Yes, but then you can't claim to know anything
about it.
Now, I want to concentrate from now on, because
I'm a theoretical physicist and more delighted
with this end of the problem, as to how do
you make the guesses.
Now as strictly as I said before, not of any
importance where the guess comes from, it's
only important that it should agree with experiment,
and that it should be as definite as possible.
But you say then it's very simple...
We've set up a machine, a great computing
machine, which has a random wheel in it that
makes the succession of guesses, and each
time it guesses a hypothesis about how nature
should work, computes immediately the consequences
and makes a comparison to a list of experimental
results that it has at the other end.
In other words, guessing is a dumb man's job.
Actually it's quite the opposite and I will
try to explain why.
The first problem is how to start.
You see, I'll start with all the known principles,
but the principles that are all known are
inconsistent with each other, so something
has to be removed.
You see, the problem is not to make, to change,
or to say something might be wrong, but to
replace it by something and that is not so
easy.
As soon as any real definite idea is substituted,
it becomes almost immediately apparent that
it doesn't work.
Secondly, there's an infinite number of possibilities
of these simple types.
It's therefore not unscientific to take a
guess, although many people who are not in
science think it is.
For instance, I had a conversation about flying
saucers some years ago with, Layman.
Because I'm scientific, I know all about flying
saucers.
So I said, I don't think there are flying
saucers.
So, the other, my antagonist said.
Is it impossible that there are flying saucers.
Can you prove that it's impossible?
No.
I can't prove it's impossible.
It's just very unlikely.
That, they say, you are very unscientific.
If you can't prove it impossible, then how
could you say it's unlikely.
That is scientific.
It is scientific, only to say what's more
likely and less likely, and not to be proving
all the time, possible or impossible.
To define what I mean I finally said to him,
Listen, I mean that for my knowledge of the
world that I see around me, I think that it
is much more likely that the reports of flying
saucers are the results of the known irrational
characteristics of terrestrial intelligence,
rather than the unknown rational efforts of
extraterrestrial intelligence.
It's just more likely that's all.
And it's a good guess.
And we always tried to guess the most likely
explanation, keeping in the back of the mind,
the fact that if it doesn't work then we must
discuss the other possibility.
