Strangeness Minus Three Horizon

Archive programmes chosen by experts.

For this collection, Prof Alice Roberts has selected

a range of programmes to celebrate Horizon's 50th anniversary.

More Horizon programmes and other BBC Four Collections

are available on BBC iPlayer.

The important thing is first to steep yourself in the problem,

to look at the puzzle, all the pieces of the puzzle.

Turn them around, and look at them in different ways and try to put them

together.

Find out what's missing, what's the...

at the root of the apparent paradox.

And then...

Then, usually, you find you can't do much more.

And you put the work aside and do something else,

and then at an odd moment you may get an idea.

Apparently, the mind works on these things unconsciously

once it's been fed.

At night, you may wake up in the middle of the night and have an idea.

Usually it turns out that it's nonsense!

Sometimes it's right.

And you might have an idea when you're shaving or driving your car.

The strangeness theory came to me when I was explaining a wrong idea to

somebody, I was explaining why that idea wouldn't work.

I made a slip of the tongue, and I had the strangeness theory.

I find I'm quite prolific with ideas.

On the other hand, they tend to be wrong most of the time.

Probably five out of each six ideas - I don't know,

I don't have the right statistics.

But I know that they come to me and if I want to explain them to somebody

and get some criticism,

and listen to myself explaining them to somebody else.

I want to find out whether they are right or wrong

and I have to do it in that way,

Two years ago, Gell-Mann and Ne'eman

predicted the existence of a fleeting particle of matter, which,

if found, would resolve the puzzle of what matter is ultimately made of.

This programme tells the story behind the dramatic two-year search for

the particle and of the transformation of our ideas

now that it's been found.

The programme is introduced by one of the world's leading theoretical

physicists, Richard Feynman.

Progress in physics seems to come in fits and starts.

The really great pinnacles, the revolutionary discoveries,

the great transformations of ideas, come very infrequently.

Perhaps in the last 200 years there's only been half a dozen such things.

You might think of Newton's discovery of the laws of mechanics

and gravitation,

Maxwell's theory of electricity and magnetism,

Einstein's theory or relativity, and, in the 20th century,

the theory of quantum mechanics.

I think we're due for a new one.

I think very soon we'll have another great transformation of ideas,

during which we discover the ultimate understanding of the forces

between nuclear particles.

Now, with every...great pinnacle of discovery, there is

a long preliminary process of gathering information,

sorting it down a little bit

and getting it prepared to be understood.

For example, for the law of gravitation there was first

the observations of the motions of the planets,

then a certain amount of partial understanding,

such as Copernicus's idea that the planets went around the sun,

and later Kepler's discovery that they went in ellipses.

But the final ultimate law of gravitation required

all this preliminary jockeying of the data around

to understand it partially.

In the same way, the future discovery of the laws of nuclear physics,

nuclear interaction,

is preceded by a partial summation of the information

that's available so far, and just recently we've had one of the most

important and dramatic reshufflings of our understanding.

So, that I think we're almost ready

to get the answer to the big question.

What I want to tell you about today is the...

this partial understanding that we've just achieved.

Some time ago, things looked pretty simple.

We just had a theory that the atoms had, on the outside, electrons,

and, on the inside, nuclei, and that the nuclei were made of nothing

but two particles in the world, the neutrons and the protons.

And then, with such a simple picture, just two nuclear particles,

the nuclear problem just to understand the simple law of force

between neutron and proton.

Probably some simple law like the electrical law that the force varies

inversely as the square of the distance,

or some other beautifully simple thing

was all that had to be found out.

So, a programme was launched to study the interactions of neutrons

and protons and it was discovered, as time went on, that it

all looked a little more complicated.

Ultimately, that it was extremely complicated,

that it was a s complicated as it could be,

that the force between neutrons

and protons depended on practically everything

and that it depended on how far apart they were, in a very complicated way.

It depends on which direction they're spinning, what direction

they approach each other relative to the way they're spinning, and so on.

In fact, it depends on everything that it can depend on and is as

complicated as it can be,

except for one little thing, which I'll mention later.

Now, when a thing looks complicated

it's possible that we're looking at it wrong

and that we're missing some of the pieces of the puzzle.

And, as a matter of fact, there was

direct evidence that pieces were missing

in the fact that in cosmic rays,

the fast particles which come from the outside somewhere,

in a study in cosmic rays,

it was found that there were some new particles,

other particles beside the neutron and proton.

First there were some mesons,

which were partially expected, and then there

were another group of heavier objects,

one of which was called the lambda meson.

And it was found to disintegrate into a proton

and one of the mesons sometimes.

Sometimes it disintegrates into a neutron and one of the mesons.

The cosmic rays also discovered still another particle called

a cascade particle which itself disintegrates into a lambda.

Now, progress with cosmic rays was very slow

and was very much speeded up by the development of modern accelerators

which produce particles as fast and as energetic

as those in a cosmic ray,

so that we, so to speak, brought the thing under our own control

rather than having to wait

for the odd fast particle and reaction to occur in nature.

In addition, we've developed better instruments

for observing the particles,

instead of cloud chambers, bubble chambers.

And with these bubble chambers and modern accelerators,

the progress in finding new particles has rapidly increased.

Five years ago, we were up to 30 particles.

Now, we have 90 particles.

So, the problem has got a little more complicated.

We used to just worry about how the things acted.

Now, we have to divide the problem into two parts,

we have to go back a step.

First, we have to decide what there is in the world,

and then, how does this stuff act.

We have to now figure out what the pattern is of available particles,

in other words, what kind of a world,

what the particles are that are in the world.

First thing turns out that they come in families.

For example, the neutron and proton are very similar.

They are the same mass and they have other characteristics in common.

But the most remarkable characteristic is this.

That although the forces between neutrons and protons

and protons and protons are very complicated,

the force between a neutron and proton

and between a proton and proton are the same.

That's a very mysterious accident.

It's only true of the nuclear part of the force, the electrical forces,

of course, are different.

One is charged and one is neutral.

But the nuclear part of the forces, we've discovered,

has one peculiar characteristic.

That is, that you can change a neutron for a proton

and it doesn't make any difference to the force.

We say that the nuclear forces have a symmetry, they have a symmetry

that you can change neutron to proton without making any difference.

The fact that we use the word "symmetry" here

is a kind of technical use of that word.

What is a symmetrical thing, how would you define a symmetrical thing?

One definition is that a symmetrical thing is something that you can do

something to and it doesn't make any difference.

This book, for example, I could turn it over and it looks the same.

Something I can change something, do something to it,

and it still looks the same.

And we use the same word in the physics sense

to represent the fact that

I can change the neutron to a proton and the nuclear forces look the same.

So, neutron and proton together form a family

as far as nuclear forces are concerned.

And it turns out that the cascade particle

is a member of a family of two - one negative and one neutral.

The lambda stands by itself, but there is another particle,

a set of three particles that are similar, that also get exchanged.

And produce a family of the kind that the neutron and proton produce.

Besides families, we found out that there are hierarchies

between these particles.

For example, a lambda disintegrates into a neutron and a meson,

or sometimes into a proton and a meson, and that it does very slowly,

it takes a third of a billionth of a second.

It sounds like that's pretty fast, but for nuclear reaction,

nuclear particles, that's very slow.

It should happen almost a billion times more rapidly

if there weren't something in the way.

In order to analyse this "something in the way" in these disintegrations,

Prof Gell-Mann, here at Caltech,

invented a method of description which describes this situation.

He said that, in a sense, the lambda has a kind of character, that it

has difficulty into disintegrating into a neutron and proton

and he makes the rule

that if you want to disintegrate with change of character,

it should be slow.

And thus, is able to associate character,

a kind of character to the different particles,

in which he gives a numerical number.

He calls this number strangeness, he says this is strangeness number zero,

this is strangeness one.

You'd think actually he'd call it with a minus sign,

but that's just an accident of history.

But then it turns out that the cascade particle here can't directly

disintegrate into neutron and proton,

it disintegrates slowly into a lambda,

and then the lambda into neutron and proton.

So, the cascade particle has a character number minus two,

being two steps removed in the slow disintegrations

to the neutron and proton.

That is some partial analysis of the particles that are in the world.

There's these families, for interchange,

and there are these hierarchies associated with the strangeness.

Question is, is there any more symmetry in this system?

For instance.

Is it possible that an exchange of a neutron with a lambda

might make no difference in nuclear forces?

Or some other possible combinations.

That if you change a P, a proton, to a sigma, a C, a cascade, to a sigma

or something like that, into certain particular combinations,

it makes no difference.

People have tried very many attempts to find such additional symmetries.

In order to help them, they've used the mathematics

of what's called "group theory".

Group theory is something that mathematicians have analysed a lot

the problem of what happens if you exchange

one thing with another and then something with something else.

What is the net result of all that?

So, that the mathematicians have prepared for the physicists

the necessary mathematics, called "group theory", to analyse this.

At any rate, many types of... possible systems of exchanges

have been suggested to understand the way the world works

and in each case, sometimes, you would predict something

that wasn't exactly in accord with experiment

and it didn't look very hopeful.

As a matter of fact, I myself, after playing around with Gell-Mann,

trying it together, we tried many combinations,

we came to the conclusion that there probably wasn't

any other symmetry in the system.

The problem is very hard.

Why should it be hard?

If a thing is symmetrical, ordinarily,

with one glance of the eye

you could see immediately that it's symmetrical,

so why is it that it's not possible to look right away

at the character of the particles

that are discovered and see the symmetry?

There are two reasons.

First, the symmetry is not perfect.

In the case of the pattern that you can replace neutron by proton,

that is very accurate, but it's not exactly perfect in nature

because the two protons interact electrically

while the neutrons don't,

but if we leave out the electricity, it's quite perfect.

The electricity is only one or so percent

However, we know already,

because the masses of these particles are so different,

that any other symmetry that must be there

must be quite a bit off, by 10 or 20%.

To look for a somewhat symmetrical thing takes more skill

than to notice a symmetrical thing.

The other part of the problem is that we have missing parts.

If you had a vase which you knew was nearly symmetrical

and half of it was broken off, or nearly half of it was broken off,

it would be a little bit hard to tell the character,

the pattern of symmetry,

so that, when there is only a limited number of particles,

it gets somewhat difficult.

For example, there was known a set of four particles

in addition to this set,

which belong together in the kind of family that these belong.

Then it became clear that there was another set of three more

that were similar for such exchanges

and there was part of a suggestion,

there was a suggestion made by Gell-Mann

and independently by Prof Ne'eman

of a certain particular pattern of interchanges

among all these particles

which would permit an understanding of what was known so far,

but would only permit these four

provided these three and another pair and...

and still a third particle, all by itself, existed in the world.

They, when they made this up, only knew about this

and a little bit about that

and were rather reluctant to suggest that it was true

because there were so many missing pieces it was unbelievable.

However, when these particles turned out to exist

and to fit their triangle of interconnections,

which they expected would occur, they became more...

ambitious and suggested that, in fact, the theory is right.

In order to make this theory right, however,

this particle here was missing.

Now, many of the other symmetry systems predicted new particles

and many new particles were found, but, in the confusion,

the particles had no particular special properties

and one could make an accident

that nature did have a particle

something like what you are looking for.

But this new particle that was predicted

by the Gell-Mann-Ne'eman theory

was very peculiar and unique in its characteristics.

It had strangeness -3 and this theory predicted that there should exist

a negatively charged particle with strangeness -3,

which means that it would only be able to disintegrate

in three steps before it got to neutron and proton.

This was so unique and definite a prediction

that the theory would be made and broken very easily by experiment.

So, the very interesting question was,

do they have the right pattern? Is there an extension,

a new kind of additional symmetry among the particles,

an additional fact to simplify our understanding,

by which the families of two, three and so on

can be combined in one element, two elements,

and thus take on 90 particles

and replace them by two, three or four groups?

If so, of course, we're making enormous progress.

The big question was, experimentally, does this omega minus exist or not?

This was a moment that is characteristic of physics

that's one of the big thrills and mysteries.

How is it possible, by looking at a piece of nature,

to guess how another part must look, where you have never been before?

How is it...?

It's only in modern times that man has really been able to guess

what nature is going to do in situations

that he's never looked at before

and here is an example of it.

With many strange particles,

by looking at those which you have seen already,

it is possible to guess

that there must be something that you haven't looked at yet.

The reason this is possible is partly man's ingenuity,

but, obviously, more important is nature's inner simplicity.

To look for this particle is a typical,

dramatic scientific investigation,

so the two ingenious men, Gell-Mann and Ne'eman, waited for two years

to see whether nature recognised their ingenuity.

And she did.

The particle was found.

Dr Gell-Mann, how confident did you feel during the two years

you were waiting for your predictions to be checked?

Oh, my confidence had its ups and downs.

There were lots of other things going on besides omega minus.

The search for the omega minus took two years at Brookhaven,

but the theory of the higher symmetry made a number of other predictions

besides the existence of omega minus

and some of those were being confirmed.

A couple of others looked a bit cloudy for part of the time and...

So, I wasn't always sure that it would work out all right.

How much is do you fight for your theories

if it looks as if they have been proved wrong?

Oh, well, it depends a lot, I think, on whether...

..a really reliable experiment has definitely contradicted something.

If that happens then you just drop the theory, it's no good,

and you try a different tack.

But if it's a very complicated experimental situation,

the theory looks particularly beautiful,

you might hope that there is

something the matter with the experiment.

They are awfully difficult in this field.

They take a long time and they are very expensive

and they're very hard to do and to...and to recheck,

so that it quite often happens

that an experimental result that is reported is really not right.

Are you afraid to put a theory forward because it might be wrong?

Yes, I am terrified of putting forward a theory

- that I'm afraid would be wrong. - Why?

Your reputation?

No, it's just a personal quirk.

Probably, I would be a lot happier if I didn't have to...

to worry about that.

There are lots of scientists who speculate quite freely

and don't worry very much about whether their predictions

are related to reality or not, but it bothers me terribly.

In other things, too?

Yes, it carries over into all kinds of things.

It must be deeply rooted somewhere in my character.

I remember in Paris, when I lived there in '59, '60,

I would go to a party

and then would come back and spend a sleepless night

on account of some mistake in grammar that I knew I'd made.

Do you set aside so many hours a day for thinking?

Well, you could do that.

It's not necessarily the time when you get ideas, though.

I'd set aside a certain time, maybe, for...

studying a problem if I were better organised.

Actually, I don't really plan my life very much.

What do you do with most of your time?

Oh, I sort of drift from one thing to another.

I do an awful lot of reading.

Everything I'm interested in somehow smacks of natural history, I guess.

Customs of primitive people,

languages and the relations among them.

You are always looking for patterns in nature?

Yes.

- Now, what's...? - Patterns in the way people think.

Patterns in the elementary particles.

It's all part of the same way of doing things, I suppose.

Trying to spot the law, trying to spot the relationship.

What's so special about the patterns in physics?

Oh, the laws of the elementary particles are...

are very special.

The whole universe is made up of these little particles.

The light from the most distant galaxy shows that there, too,

the same laws hold.

They, too, are made up of the same little particles that we are...

..we are made up of.

And their laws, the laws of the weak and the strong interactions,

along with the laws of electromagnetism and gravity,

determine how the...

how all the bits of the universe work.

They determine the behaviour of matter

and it's fascinating to try to figure out what these laws are.

Of course, you never get a final answer.

We just keep going from one approximation to another,

getting to understand things better and better.

How many more useful years do you think

you have as a theoretical physicist?

Oh, I don't know.

I figured some years ago that I'd probably be through at 30,

so that we give me -4 years,

but I guess I still have a few anyway.

At the end of...

a certain time, most theoretical physicists seem to, er,

lose their flexibility and I suppose that will happen to me, too.

Maybe it has already happened.

What happens when you and, say, Feynman get together?

Do you get into heated arguments?

Oh, we have wonderful arguments!

Back and forth.

"No, you can't do that! It won't work!

"You'll get the magnetic moment of the sigma wrong!" or...

"The decay mode won't be the right one!"

or... "The branching ratio will come out wrong!"

"Yes, it will be perfectly all right."

"You don't understand what I'm doing. I'm really doing it this way."

We don't get mad at each other at all, but we scream and yell and...

What about your relationship with Ne'eman?

Oh, I've had some very fine conversations with him, too,

this year.

You know, we started completely independently and...

In 1961, when I was thinking of the eightfold way, January 1961,

and wrote it up and sent off for preprint...

..it crossed his preprint in the mail.

He was working at Imperial College London and...

when I sent off my paper, I got his

on the same subject with about the same ideas -

the eightfold-way pattern, he called it something else.

And then I was told that he was a colonel in the Israeli army

and I imagined he must be rather a fascinating person

and it turned out to be very true.

And, luckily, he's been able to spend the last year here at Caltech.

Dr Ne'eman, as a colonel in the Israeli army,

how did you come to be interested in particle physics?

Oh, well, this is mainly because of London traffic, really.

- Really? - It's... Yes.

I came to London to do physics

and the reason I had accepted this idea

of becoming a military attache in England

was that it was given to me as an opportunity

to combine it with studies which I had asked for at the time.

And I was interested in general relativity.

I knew that Bondi was in London

and there was a good group working in general relativity,

so I came to England to do that.

Now, our embassy is in Kensington and when I looked and saw London,

I realised that there was really no hope

to combine a job of a military attache in Kensington

with studies at King's,

which was on the other side of Trafalgar Square,

so I looked for something nearer

and I found the Imperial College

at five minutes' walking distance from the embassy,

so I went to Imperial College and I found Salam.

I think I was really lucky, in fact.

Probably...

an extremely lucky thing that happened to me because...

if...

Well, I might have been in...

done interesting things in general relativity,

but I think elementary particle physics is...

more of a frontier now and I was very lucky to...

really to get to work with Salam

because he is certainly one of the best men in that field

and the whole choice of my subject was influenced

by the fact that he was a man who believed in this type of solution,

he believed in symmetries in general

as a possible answer to problems in elementary particle physics

and I got very interested in that.

How old were you when you joined Salam?

Oh, I...

Well, about 33...

32, 33, I think.

Isn't that about the age when most theoretical physicists are giving up?

Well, I had asked myself that question.

I thought, in fact, that this was

probably the last chance I had to go into physics,

but I was afraid that I might have missed the bus, as you say.

And, er...

It was like a challenge and...

On the other hand, after I saw that it was working out well,

I got thinking about this question,

whether there is really a limiting age,

whether one has to be really young.

My theory about it is that you have to be young in the profession,

young in a material sense.

I think that within ten years

you do anything interesting you can do in a certain field.

You've asked all the questions

and you've either found answers or not.

And then you are just really treading on the same ground all the time.

How did you feel during the two-year wait for the Brookhaven results?

Two years...

Well, nothing really.

It was last week that was extremely bad.

We...

I was attending a conference at Miami and Maurice Goldhaber,

the director of Brookhaven, was there and, sitting near the swimming pool,

he was telling me that they had gone through 60,000 feet of film

and were not finding anything.

I was a bit shocked and I came back here

and Gell-Mann was getting ready to go to Japan,

so I told him about these results

and his reply was, "Would Mount Fuji be the right place to jump off from?"

And I said, "I can always go back to the Israeli army."

And then the news came a week later, you know.

For many of us here at Brookhaven on Long Island in New York,

the hunt for the omega minus has been one of the most exciting searches

undertaken in the last ten years.

I first became interested in the omega minus

while attending an international conference

on high-energy physics in Geneva in 1962,

precisely two years ago.

This was a most stimulating conference

in that the discovery of many new particles was presented.

I myself gave a paper reporting the results from here at Brookhaven

in which we reported the discovery of a new particle, the cascade star.

You may recognise this pattern

as something similar to which Feynman drew.

This is the cascade star.

Murray Gell-Mann was also in attendance at this conference

and he immediately grasped the significance of the discovery

of the cascade star, namely it had strangeness -2

and it had a mass which fits very conveniently into the scheme.

The mass difference between this and this is 147.

The mass difference between this and this is 145,

these being very close to the same number.

These particles also fit into a geometric pattern, a very simple one,

namely a triangle.

Unfortunately, there is only...

There is a missing member.

Gell-Mann called this the omega minus.

Since it occurs at the apex of the triangle,

he was also able to determine its strangeness, -3...

..and a mass where the mass difference between this

and this had to be 145,

giving 1,675.

I was struck by the beauty and the simplicity of the scheme.

In fact, this idea was an experimentalist's dream,

in that if they omega minus were found,

it would prove that the theory was correct, that the scheme was correct.

If the omega minus were not found, if it did not exist,

then it would have the effect of disproving the theory.

It had a definitive answer,

there was a definitive result, it had a positive effect.

But as an experimentalist,

I knew that this would take a great deal of effort,

numerous people to work on it, a great deal of money and, above all,

of the order of a few years to perform.

Therefore, before embarking upon such an experiment,

one thinks about it very carefully.

One aspect that was very comforting was the fact that Mr Gell-Mann

has been extremely successful in his field.

His batting average has been very high,

so that one felt there was probably

quite a bit of truth in it to begin with.

Upon returning to Brookhaven, we discussed it with...

I discussed it with my colleagues

and we decided that it would probably be worthwhile

to perform this experiment.

The question now was to obtain

the necessary tools to go about performing this task.

Here at Brookhaven, we have the world's largest proton accelerator.

It is half a mile in diameter

and is enclosed in an underground concrete tunnel

in which there are 240 magnets that guide the protons in a circular path

while they are accelerated until they virtually reach the speed of light.

Then they smash into a metal target

from which there are emitted all sorts of particles.

You can realise the precision needed

when I tell you that the K-beam had to pass this small slit,

81 thousandths of an inch in height.

The Ks that emerge from this slit

then enter the 80-inch hydrogen bubble chamber.

Then they are photographed as they react

with the protons in the hydrogen atoms.

MACHINE CLANKS STEADILY

1,000 photographs are taken every hour

and these can be scanned for various particle patterns.

Since Gell-Mann had given us

the strangeness, -3, and the mass, 1,675, of the omega minus,

we were now in a position to predict the decay patterns

of the omega minus, the patterns the omega minus track

would leave in decaying in the hydrogen bubble chamber.

Here is such a pattern.

The incoming particle, the K minus, comes in

and interacts with the proton in the hydrogen atom.

It makes many prongs,

among which is the omega minus with strangeness -3.

The omega minus then decays into a particle

with strangeness 0

and a neutral particle with strangeness -2.

A neutral particle, a particle with zero charge,

does not leave a bubble track in a bubble chamber.

This neutral particle could then decay

into another neutral particle with strangeness 0,

which could decay into an electron-positron pair...

..and, in addition, a particle with strangeness -1.

The lambda.

And finally, the lambda could decay into two charged particles,

a proton and a pi meson, both with strangeness 0.

This is a pattern for the omega minus decay.

There are variations on this pattern and, in looking for the omega,

we look for both this pattern and its variations.

It was one thing the project these patterns.

It was another thing to perform the experiment, to build the beam,

to build a chamber, to get the pictures

in which one would look for patterns,

patterns which no-one else had ever seen

and patterns which one didn't even know existed, a region unknown.

Patterns predicted by particles which had been seen.

We started to perform the experiment in earnest in November of 1963.

In fact, we started tuning the beam round the clock, 24 hours a day.

It certainly wasn't smooth sailing.

We had many difficulties, technical.

The line-up of the beam had to be constantly checked,

magnets constantly tuned, the chamber had minor difficulties, leaks,

but, finally, we persevered, worked very hard 24 hours round the clock

until, in January, we were able to

start taking a few Ks per picture, one to two Ks.

We worked a little bit harder,

we finally were able to get to three to four Ks per picture

and, by late January,

we were taking 2,000 pictures a roll, a few rolls a day,

until, finally, we were able to obtain

something of the order of 100,000 pictures.

Of course, as soon as we had these pictures, we started scanning them,

again, looking for these patterns.

We scanned 10, 20, 30,000.

Still no omega.

Finally, we went to roll 53 and picture number 97,025 -

that number stays in everyone's mind around here -

and finally we found the omega.

And here is a photograph of the omega.

The pattern is very similar to the pattern I had shown you before.

The strangeness -1, the strangeness -2, and the strangeness 0 particles.

And this little particle, this little three-centimetre particle,

this was the omega, the omega we spent months, years looking for.

We were exuberant.

I mean, the Friday that it was found,

we just stood around looking at each other,

a bit numb at the beginning,

then finally everyone broke out into smiles

and someone started to do a dance.

It was very happy.

In fact, in our exuberance,

we just completely neglected to call Murray Gell-Mann in California.

In fact, he had to call us when he found out about it.

But it was a very peculiar feeling.

It seems to make it all worthwhile, this one to two years' effort.

You sort of stand around, a few of us, and you say,

"At this moment, we few on the face of the Earth,

"we are the only ones who know that this particle,

"this omega that goes this short distance, this particle exists."

Other people may think they know.

Gell-Mann probably thought he knew, but he didn't know.

We knew.

FEYNMAN: That, then, is the story of the omega minus.

What does it mean?

What is the significance of the fact that nature seems to obey this rule?

I think, today, nobody knows.

We will only know, really, when we completely understand,

or more completely understand,

the fundamental laws of interaction of the nuclear particles

and this is a vital step forwards to that understanding,

but it isn't the understanding itself and, until we get that,

we will not really know the meaning of this...the fact

that nature seems to obey the rules guessed at by Gell-Mann and Ne'eman.

It's analogous to the discovery of the periodic table

by Mendeleev a century ago.

He discovered at that time that various chemical elements

came in families and that there were relations among them

and that the chemistry of sodium and potassium, for example, were similar.

This was extremely important in the development of science

and the bringing about the ultimate understanding

of the behaviour of atoms.

But the real understanding of the reason why sodium

and potassium were similar, why the periodicities among the chemistry...

in the chemistry of the various elements existed,

could only come 50 years later with the knowledge of atomic physics

and this knowledge required

a complete transformation of ideas about nature,

a complete change of the philosophical position.

Ideas that were impossible to appreciate at the time of Mendeleev -

the principle of uncertainty of Heisenberg had to be discovered,

the whole understanding of the relation of cause and effect

had to be modified with the principle of indeterminacy.

And so it is going to be here.

We will not understand, really, what...

..what nature, how nature finds... makes this rule

until we understand the nuclear interactions,

and we won't understand those, I'm sure, without a deep and profound

transformation of ideas somewhere along the line.

We already see some of the difficulties.

This law of Gell-Mann and Ne'eman, this symmetry law,

is not a perfect symmetry.

If it were, the statement would be that the replacement

of one particle by another would make no change.

For example, the replacement of a neutron by a lambda

should make no change.

And yet, the neutron and lambda differ in mass alone by some 20%,

so there alone is a change, that when you take neutron

and replace it by a lambda, the mass is different.

So, this symmetry is not perfect, it's an imperfect cemetery.

Physicists are happy with a perfect symmetry.

To say something is absolutely true and absolutely symmetrical

seems to be a succinct, simple and elegant statement of a law of nature.

If a thing were completely unsymmetrical

then there would be nothing to say.

But by what kind of a view is a thing

that is only partly symmetrical natural,

is a thing that is only partly symmetrical beautiful?

Well, the artists say that, in this camellia bush here,

the artists feel that the camellia,

in its partial but near symmetry, is especially beautiful

and far more beautiful than a perfect geometrical pattern.

But physicists feel that a partial symmetry

is an indication that some deeper

and more profound description of nature

is possible, that there is "gold in them thar hills".

So, we've got a peculiar thought to grapple with, this partial symmetry.

We're kind of stuck.

We need a new idea.

Before we'll really get the nuclear forces understood,

some great new idea is required.

Looking for symmetry is an old one.

Poincare suggested it, Einstein used it,

it really came into its own when quantum mechanics was developed.

But the only information that we're accumulating,

the places where they were really getting stuck,

understanding the relation of these particles

is somewhere where we are missing...

some important great idea, we have some prejudice that's in our way.

That's the way it always is in these pinnacle discoveries.

The big pile-up of stuff, all the old things that you've thought of before,

you try again and again.

But the great discovery always involves

a great philosophical surprise.

The pinnacle discovery isn't so much a fact...

..as that it's possible to look at nature

in a thoroughgoingly different idea.

How strange it is. Listen to this.

How much is known after 200 years of studying physics?

How much is known about electrons, light, everything?

And in order to understand the nuclear forces,

it's almost certain that we are going to have to take

a completely different view about everything that we know already,

philosophically, that is.

We're going to have to find another way to look at the world

in which everything that we've already found out about

is the way it is.

And yet, that little detail about what goes on in the nucleus

then falls into place.

It's a very hard job.

It's lots of work.

So, what do we do it for?

Because of the excitement,

because of the fact that each time we get one of these things...

..we have a terrific Eldorado, we have a wonderful...

..new view of nature.

We see the ingenuity, if I may put it that way, of nature herself,

the peculiarity of the way she works.

It takes a terrible strain on the mind to understand these things

and the real value of the development of the science in this connection,

the thing that makes me go on...

..is this...the difficulty of understanding it.

That these apes stand around and look at...nature

and find that to really catch on,

they have to polish their mind to the very last.

We live in a heroic age, we live in a moment that will never come again.

These discoveries cannot be made twice.

One doesn't discover America two or three times in succession, really.

And one doesn't discover the laws of nuclear forces or electricity

more than once.

People say, some people say, our age is meaningless.

Those are only people who don't know what we're doing in this age.

That this age is the age in which mankind is finding out

about the nature that he lives in.

And if they don't understand what's already been uncovered,

they can't appreciate the search.

What makes us so sure that the new discovery of the interrelationship

between the nuclear forces is going to be so wonderful?

How do we know it isn't going to be

some complicated, dirty or simple thing?

We don't know. But we keep on trying anyway.

We're not sure, it's worth the risk,

because it's very likely it'll be peculiar,

and if it is, it'll be very interesting.

How long is it going to take?

Do we have all the clues?

Every time there's been a very great discovery, one can look back and say,

"Why didn't we think of that before?"

Of course, there's a time so far before that you say,

"Well, the reason they didn't think of it

"is they didn't have enough facts from experiments."

Question.

Do we have enough facts from experiments so that,

after this thing is discovered,

people will look back and say, "Why didn't they think of that before?"

How far before? In 1964.

My colleagues don't agree with me, but I think this is the day.

I think that we now know enough

that if, with a sufficiently clear reasoning,

we could come to the answer.

I'll put it another way, when we do finally find the answer,

after the experiments have given us too many clues, a lot of extra clues,

we'll look back and we'll see

how a perfectly sensible, logical line of reasoning,

from the present position,

could have brought us to the present understanding.

I wouldn't have said that before the discovery of the omega minus.

That, to me, is the significance of this discovery.