Strangeness Minus Three Horizon


Strangeness Minus Three

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Archive programmes chosen by experts.

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For this collection, Prof Alice Roberts has selected

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

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More Horizon programmes and other BBC Four Collections

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are available on BBC iPlayer.

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

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

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

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together.

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

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at the root of the apparent paradox.

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And then...

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

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And you put the work aside and do something else,

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

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Apparently, the mind works on these things unconsciously

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once it's been fed.

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

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Usually it turns out that it's nonsense!

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Sometimes it's right.

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

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

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

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

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I find I'm quite prolific with ideas.

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

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

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I don't have the right statistics.

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

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and get some criticism,

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and listen to myself explaining them to somebody else.

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I want to find out whether they are right or wrong

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and I have to do it in that way,

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Two years ago, Gell-Mann and Ne'eman

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

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

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

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the particle and of the transformation of our ideas

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now that it's been found.

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

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physicists, Richard Feynman.

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Progress in physics seems to come in fits and starts.

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The really great pinnacles, the revolutionary discoveries,

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the great transformations of ideas, come very infrequently.

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

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

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and gravitation,

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Maxwell's theory of electricity and magnetism,

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

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the theory of quantum mechanics.

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I think we're due for a new one.

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

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during which we discover the ultimate understanding of the forces

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between nuclear particles.

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

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a long preliminary process of gathering information,

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sorting it down a little bit

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and getting it prepared to be understood.

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For example, for the law of gravitation there was first

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the observations of the motions of the planets,

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then a certain amount of partial understanding,

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

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

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But the final ultimate law of gravitation required

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all this preliminary jockeying of the data around

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to understand it partially.

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

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nuclear interaction,

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is preceded by a partial summation of the information

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

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important and dramatic reshufflings of our understanding.

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So, that I think we're almost ready

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to get the answer to the big question.

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

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this partial understanding that we've just achieved.

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Some time ago, things looked pretty simple.

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

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

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

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

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the nuclear problem just to understand the simple law of force

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between neutron and proton.

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

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inversely as the square of the distance,

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or some other beautifully simple thing

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was all that had to be found out.

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

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

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all looked a little more complicated.

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Ultimately, that it was extremely complicated,

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that it was a s complicated as it could be,

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that the force between neutrons

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and protons depended on practically everything

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

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

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

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

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complicated as it can be,

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

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Now, when a thing looks complicated

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

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

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And, as a matter of fact, there was

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direct evidence that pieces were missing

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in the fact that in cosmic rays,

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the fast particles which come from the outside somewhere,

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in a study in cosmic rays,

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it was found that there were some new particles,

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other particles beside the neutron and proton.

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First there were some mesons,

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which were partially expected, and then there

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were another group of heavier objects,

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one of which was called the lambda meson.

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And it was found to disintegrate into a proton

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and one of the mesons sometimes.

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

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The cosmic rays also discovered still another particle called

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a cascade particle which itself disintegrates into a lambda.

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Now, progress with cosmic rays was very slow

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

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which produce particles as fast and as energetic

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as those in a cosmic ray,

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

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rather than having to wait

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

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In addition, we've developed better instruments

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for observing the particles,

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instead of cloud chambers, bubble chambers.

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And with these bubble chambers and modern accelerators,

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the progress in finding new particles has rapidly increased.

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Five years ago, we were up to 30 particles.

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Now, we have 90 particles.

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So, the problem has got a little more complicated.

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We used to just worry about how the things acted.

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

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we have to go back a step.

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

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and then, how does this stuff act.

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

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in other words, what kind of a world,

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what the particles are that are in the world.

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First thing turns out that they come in families.

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For example, the neutron and proton are very similar.

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

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But the most remarkable characteristic is this.

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That although the forces between neutrons and protons

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and protons and protons are very complicated,

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the force between a neutron and proton

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and between a proton and proton are the same.

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That's a very mysterious accident.

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

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of course, are different.

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One is charged and one is neutral.

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

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has one peculiar characteristic.

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

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

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

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

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The fact that we use the word "symmetry" here

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is a kind of technical use of that word.

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

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

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something to and it doesn't make any difference.

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

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Something I can change something, do something to it,

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and it still looks the same.

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And we use the same word in the physics sense

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to represent the fact that

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

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So, neutron and proton together form a family

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as far as nuclear forces are concerned.

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And it turns out that the cascade particle

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

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

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

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

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Besides families, we found out that there are hierarchies

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between these particles.

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

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

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it takes a third of a billionth of a second.

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

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nuclear particles, that's very slow.

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It should happen almost a billion times more rapidly

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if there weren't something in the way.

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

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Prof Gell-Mann, here at Caltech,

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invented a method of description which describes this situation.

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

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has difficulty into disintegrating into a neutron and proton

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and he makes the rule

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that if you want to disintegrate with change of character,

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it should be slow.

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And thus, is able to associate character,

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a kind of character to the different particles,

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in which he gives a numerical number.

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

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this is strangeness one.

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

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but that's just an accident of history.

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

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disintegrate into neutron and proton,

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it disintegrates slowly into a lambda,

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and then the lambda into neutron and proton.

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

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being two steps removed in the slow disintegrations

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to the neutron and proton.

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

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There's these families, for interchange,

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and there are these hierarchies associated with the strangeness.

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

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For instance.

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

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might make no difference in nuclear forces?

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Or some other possible combinations.

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

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or something like that, into certain particular combinations,

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it makes no difference.

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

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

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of what's called "group theory".

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Group theory is something that mathematicians have analysed a lot

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the problem of what happens if you exchange

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one thing with another and then something with something else.

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What is the net result of all that?

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So, that the mathematicians have prepared for the physicists

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

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

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have been suggested to understand the way the world works

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and in each case, sometimes, you would predict something

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that wasn't exactly in accord with experiment

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and it didn't look very hopeful.

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

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trying it together, we tried many combinations,

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we came to the conclusion that there probably wasn't

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any other symmetry in the system.

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The problem is very hard.

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Why should it be hard?

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If a thing is symmetrical, ordinarily,

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with one glance of the eye

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you could see immediately that it's symmetrical,

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

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at the character of the particles

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that are discovered and see the symmetry?

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There are two reasons.

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First, the symmetry is not perfect.

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

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

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because the two protons interact electrically

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while the neutrons don't,

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

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The electricity is only one or so percent

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However, we know already,

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because the masses of these particles are so different,

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that any other symmetry that must be there

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

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To look for a somewhat symmetrical thing takes more skill

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than to notice a symmetrical thing.

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

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If you had a vase which you knew was nearly symmetrical

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

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

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the pattern of symmetry,

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

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it gets somewhat difficult.

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For example, there was known a set of four particles

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in addition to this set,

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

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

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that were similar for such exchanges

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and there was part of a suggestion,

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there was a suggestion made by Gell-Mann

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and independently by Prof Ne'eman

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of a certain particular pattern of interchanges

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among all these particles

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

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but would only permit these four

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provided these three and another pair and...

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

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

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and a little bit about that

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and were rather reluctant to suggest that it was true

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because there were so many missing pieces it was unbelievable.

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However, when these particles turned out to exist

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and to fit their triangle of interconnections,

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

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

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In order to make this theory right, however,

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this particle here was missing.

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Now, many of the other symmetry systems predicted new particles

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

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the particles had no particular special properties

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and one could make an accident

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that nature did have a particle

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something like what you are looking for.

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But this new particle that was predicted

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by the Gell-Mann-Ne'eman theory

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was very peculiar and unique in its characteristics.

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

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a negatively charged particle with strangeness -3,

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which means that it would only be able to disintegrate

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in three steps before it got to neutron and proton.

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This was so unique and definite a prediction

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

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So, the very interesting question was,

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

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a new kind of additional symmetry among the particles,

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an additional fact to simplify our understanding,

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by which the families of two, three and so on

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can be combined in one element, two elements,

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and thus take on 90 particles

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and replace them by two, three or four groups?

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

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

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This was a moment that is characteristic of physics

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that's one of the big thrills and mysteries.

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

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

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How is it...?

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

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what nature is going to do in situations

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that he's never looked at before

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and here is an example of it.

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With many strange particles,

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by looking at those which you have seen already,

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it is possible to guess

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

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

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

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To look for this particle is a typical,

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dramatic scientific investigation,

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

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to see whether nature recognised their ingenuity.

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And she did.

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The particle was found.

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

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you were waiting for your predictions to be checked?

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Oh, my confidence had its ups and downs.

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

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

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

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besides the existence of omega minus

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and some of those were being confirmed.

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

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

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How much is do you fight for your theories

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if it looks as if they have been proved wrong?

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

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..a really reliable experiment has definitely contradicted something.

0:17:180:17:25

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

0:17:250:17:28

and you try a different tack.

0:17:280:17:30

But if it's a very complicated experimental situation,

0:17:300:17:34

the theory looks particularly beautiful,

0:17:340:17:36

you might hope that there is

0:17:360:17:37

something the matter with the experiment.

0:17:370:17:39

They are awfully difficult in this field.

0:17:390:17:40

They take a long time and they are very expensive

0:17:400:17:43

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

0:17:430:17:46

so that it quite often happens

0:17:460:17:48

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

0:17:480:17:52

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

0:17:520:17:56

Yes, I am terrified of putting forward a theory

0:17:560:18:00

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

0:18:000:18:01

Your reputation?

0:18:040:18:05

No, it's just a personal quirk.

0:18:050:18:07

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

0:18:100:18:13

to worry about that.

0:18:130:18:15

There are lots of scientists who speculate quite freely

0:18:150:18:19

and don't worry very much about whether their predictions

0:18:190:18:22

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

0:18:220:18:26

In other things, too?

0:18:260:18:28

Yes, it carries over into all kinds of things.

0:18:280:18:31

It must be deeply rooted somewhere in my character.

0:18:310:18:34

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

0:18:340:18:39

I would go to a party

0:18:390:18:41

and then would come back and spend a sleepless night

0:18:410:18:44

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

0:18:440:18:46

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

0:18:460:18:50

Well, you could do that.

0:18:500:18:51

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

0:18:510:18:55

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

0:18:550:18:58

studying a problem if I were better organised.

0:18:580:19:00

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

0:19:000:19:04

What do you do with most of your time?

0:19:040:19:06

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

0:19:060:19:09

I do an awful lot of reading.

0:19:090:19:11

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

0:19:110:19:16

Customs of primitive people,

0:19:160:19:18

languages and the relations among them.

0:19:180:19:21

You are always looking for patterns in nature?

0:19:230:19:26

Yes.

0:19:260:19:27

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

0:19:280:19:31

Patterns in the elementary particles.

0:19:310:19:33

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

0:19:330:19:37

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

0:19:370:19:40

What's so special about the patterns in physics?

0:19:400:19:43

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

0:19:450:19:48

are very special.

0:19:480:19:50

The whole universe is made up of these little particles.

0:19:500:19:52

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

0:19:520:19:56

the same laws hold.

0:19:560:19:58

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

0:20:000:20:03

..we are made up of.

0:20:040:20:06

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

0:20:060:20:11

along with the laws of electromagnetism and gravity,

0:20:110:20:14

determine how the...

0:20:140:20:16

how all the bits of the universe work.

0:20:160:20:19

They determine the behaviour of matter

0:20:190:20:22

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

0:20:220:20:25

Of course, you never get a final answer.

0:20:250:20:29

We just keep going from one approximation to another,

0:20:290:20:32

getting to understand things better and better.

0:20:320:20:35

How many more useful years do you think

0:20:350:20:37

you have as a theoretical physicist?

0:20:370:20:38

Oh, I don't know.

0:20:380:20:40

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

0:20:400:20:42

so that we give me -4 years,

0:20:420:20:44

but I guess I still have a few anyway.

0:20:440:20:47

At the end of...

0:20:490:20:51

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

0:20:510:20:55

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

0:20:550:20:59

Maybe it has already happened.

0:20:590:21:00

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

0:21:000:21:03

Do you get into heated arguments?

0:21:030:21:05

Oh, we have wonderful arguments!

0:21:050:21:07

Back and forth.

0:21:080:21:09

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

0:21:090:21:12

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

0:21:120:21:15

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

0:21:150:21:18

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

0:21:180:21:21

"Yes, it will be perfectly all right."

0:21:210:21:23

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

0:21:230:21:25

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

0:21:250:21:30

What about your relationship with Ne'eman?

0:21:320:21:34

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

0:21:340:21:38

this year.

0:21:380:21:39

You know, we started completely independently and...

0:21:390:21:43

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

0:21:430:21:48

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

0:21:480:21:52

..it crossed his preprint in the mail.

0:21:540:21:57

He was working at Imperial College London and...

0:21:570:22:01

when I sent off my paper, I got his

0:22:010:22:04

on the same subject with about the same ideas -

0:22:040:22:06

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

0:22:060:22:09

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

0:22:110:22:16

and I imagined he must be rather a fascinating person

0:22:160:22:18

and it turned out to be very true.

0:22:180:22:20

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

0:22:200:22:24

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

0:22:260:22:30

how did you come to be interested in particle physics?

0:22:300:22:33

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

0:22:330:22:36

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

0:22:360:22:39

I came to London to do physics

0:22:390:22:41

and the reason I had accepted this idea

0:22:410:22:43

of becoming a military attache in England

0:22:430:22:45

was that it was given to me as an opportunity

0:22:450:22:49

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

0:22:490:22:53

And I was interested in general relativity.

0:22:530:22:56

I knew that Bondi was in London

0:22:560:22:58

and there was a good group working in general relativity,

0:22:580:23:01

so I came to England to do that.

0:23:010:23:03

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

0:23:030:23:10

I realised that there was really no hope

0:23:100:23:12

to combine a job of a military attache in Kensington

0:23:120:23:15

with studies at King's,

0:23:150:23:16

which was on the other side of Trafalgar Square,

0:23:160:23:18

so I looked for something nearer

0:23:180:23:20

and I found the Imperial College

0:23:200:23:22

at five minutes' walking distance from the embassy,

0:23:220:23:26

so I went to Imperial College and I found Salam.

0:23:260:23:31

I think I was really lucky, in fact.

0:23:310:23:34

Probably...

0:23:340:23:35

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

0:23:350:23:39

if...

0:23:390:23:40

Well, I might have been in...

0:23:400:23:42

done interesting things in general relativity,

0:23:420:23:44

but I think elementary particle physics is...

0:23:440:23:48

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

0:23:480:23:53

really to get to work with Salam

0:23:530:23:56

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

0:23:560:24:02

and the whole choice of my subject was influenced

0:24:020:24:07

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

0:24:070:24:12

he believed in symmetries in general

0:24:120:24:15

as a possible answer to problems in elementary particle physics

0:24:150:24:21

and I got very interested in that.

0:24:210:24:25

How old were you when you joined Salam?

0:24:250:24:27

Oh, I...

0:24:270:24:29

Well, about 33...

0:24:290:24:31

32, 33, I think.

0:24:310:24:33

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

0:24:330:24:37

Well, I had asked myself that question.

0:24:370:24:40

I thought, in fact, that this was

0:24:420:24:45

probably the last chance I had to go into physics,

0:24:450:24:48

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

0:24:480:24:52

And, er...

0:24:520:24:54

It was like a challenge and...

0:24:540:24:56

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

0:24:560:25:01

I got thinking about this question,

0:25:010:25:03

whether there is really a limiting age,

0:25:030:25:05

whether one has to be really young.

0:25:050:25:09

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

0:25:090:25:14

young in a material sense.

0:25:140:25:16

I think that within ten years

0:25:160:25:18

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

0:25:180:25:23

You've asked all the questions

0:25:230:25:24

and you've either found answers or not.

0:25:240:25:26

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

0:25:260:25:31

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

0:25:310:25:35

Two years...

0:25:350:25:37

Well, nothing really.

0:25:370:25:38

It was last week that was extremely bad.

0:25:380:25:41

We...

0:25:410:25:42

I was attending a conference at Miami and Maurice Goldhaber,

0:25:420:25:47

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

0:25:470:25:51

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

0:25:510:25:55

and were not finding anything.

0:25:550:25:58

I was a bit shocked and I came back here

0:25:580:26:02

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

0:26:020:26:07

so I told him about these results

0:26:070:26:10

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

0:26:100:26:17

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

0:26:170:26:21

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

0:26:220:26:26

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

0:26:280:26:31

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

0:26:310:26:35

undertaken in the last ten years.

0:26:350:26:37

I first became interested in the omega minus

0:26:370:26:40

while attending an international conference

0:26:400:26:43

on high-energy physics in Geneva in 1962,

0:26:430:26:46

precisely two years ago.

0:26:460:26:48

This was a most stimulating conference

0:26:490:26:51

in that the discovery of many new particles was presented.

0:26:510:26:54

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

0:26:550:27:00

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

0:27:000:27:03

You may recognise this pattern

0:27:070:27:09

as something similar to which Feynman drew.

0:27:090:27:12

This is the cascade star.

0:27:120:27:14

Murray Gell-Mann was also in attendance at this conference

0:27:160:27:20

and he immediately grasped the significance of the discovery

0:27:200:27:23

of the cascade star, namely it had strangeness -2

0:27:230:27:27

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

0:27:270:27:31

The mass difference between this and this is 147.

0:27:320:27:36

The mass difference between this and this is 145,

0:27:360:27:39

these being very close to the same number.

0:27:390:27:42

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

0:27:420:27:48

namely a triangle.

0:27:480:27:49

Unfortunately, there is only...

0:27:510:27:52

There is a missing member.

0:27:520:27:54

Gell-Mann called this the omega minus.

0:27:540:27:56

Since it occurs at the apex of the triangle,

0:27:570:28:01

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

0:28:010:28:05

..and a mass where the mass difference between this

0:28:070:28:11

and this had to be 145,

0:28:110:28:13

giving 1,675.

0:28:130:28:17

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

0:28:200:28:23

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

0:28:240:28:29

in that if they omega minus were found,

0:28:290:28:32

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

0:28:320:28:36

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

0:28:360:28:41

then it would have the effect of disproving the theory.

0:28:410:28:44

It had a definitive answer,

0:28:440:28:46

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

0:28:460:28:50

But as an experimentalist,

0:28:500:28:51

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

0:28:510:28:55

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

0:28:550:29:00

of the order of a few years to perform.

0:29:000:29:02

Therefore, before embarking upon such an experiment,

0:29:020:29:05

one thinks about it very carefully.

0:29:050:29:07

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

0:29:080:29:12

has been extremely successful in his field.

0:29:120:29:14

His batting average has been very high,

0:29:140:29:16

so that one felt there was probably

0:29:160:29:19

quite a bit of truth in it to begin with.

0:29:190:29:21

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

0:29:220:29:25

I discussed it with my colleagues

0:29:250:29:28

and we decided that it would probably be worthwhile

0:29:280:29:30

to perform this experiment.

0:29:300:29:32

The question now was to obtain

0:29:320:29:35

the necessary tools to go about performing this task.

0:29:350:29:39

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

0:29:390:29:44

It is half a mile in diameter

0:29:440:29:46

and is enclosed in an underground concrete tunnel

0:29:460:29:49

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

0:29:490:29:54

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

0:29:540:29:58

Then they smash into a metal target

0:29:580:29:59

from which there are emitted all sorts of particles.

0:29:590:30:03

You can realise the precision needed

0:30:030:30:05

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

0:30:050:30:09

81 thousandths of an inch in height.

0:30:090:30:12

The Ks that emerge from this slit

0:30:120:30:13

then enter the 80-inch hydrogen bubble chamber.

0:30:130:30:16

Then they are photographed as they react

0:30:160:30:18

with the protons in the hydrogen atoms.

0:30:180:30:20

MACHINE CLANKS STEADILY

0:30:220:30:26

1,000 photographs are taken every hour

0:30:410:30:45

and these can be scanned for various particle patterns.

0:30:450:30:49

Since Gell-Mann had given us

0:30:490:30:52

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

0:30:520:30:58

we were now in a position to predict the decay patterns

0:30:580:31:02

of the omega minus, the patterns the omega minus track

0:31:020:31:06

would leave in decaying in the hydrogen bubble chamber.

0:31:060:31:09

Here is such a pattern.

0:31:110:31:12

The incoming particle, the K minus, comes in

0:31:140:31:18

and interacts with the proton in the hydrogen atom.

0:31:180:31:21

It makes many prongs,

0:31:210:31:23

among which is the omega minus with strangeness -3.

0:31:230:31:28

The omega minus then decays into a particle

0:31:290:31:34

with strangeness 0

0:31:340:31:36

and a neutral particle with strangeness -2.

0:31:360:31:39

A neutral particle, a particle with zero charge,

0:31:400:31:43

does not leave a bubble track in a bubble chamber.

0:31:430:31:47

This neutral particle could then decay

0:31:470:31:50

into another neutral particle with strangeness 0,

0:31:500:31:54

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

0:31:540:31:59

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

0:32:000:32:05

The lambda.

0:32:050:32:07

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

0:32:080:32:13

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

0:32:130:32:18

This is a pattern for the omega minus decay.

0:32:200:32:24

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

0:32:240:32:29

we look for both this pattern and its variations.

0:32:290:32:32

It was one thing the project these patterns.

0:32:330:32:36

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

0:32:360:32:40

to build a chamber, to get the pictures

0:32:400:32:43

in which one would look for patterns,

0:32:430:32:45

patterns which no-one else had ever seen

0:32:450:32:48

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

0:32:480:32:52

Patterns predicted by particles which had been seen.

0:32:520:32:55

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

0:32:570:33:03

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

0:33:030:33:08

It certainly wasn't smooth sailing.

0:33:080:33:10

We had many difficulties, technical.

0:33:100:33:13

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

0:33:140:33:17

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

0:33:170:33:23

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

0:33:230:33:28

until, in January, we were able to

0:33:280:33:31

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

0:33:310:33:35

We worked a little bit harder,

0:33:350:33:36

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

0:33:360:33:39

and, by late January,

0:33:390:33:41

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

0:33:410:33:45

until, finally, we were able to obtain

0:33:450:33:48

something of the order of 100,000 pictures.

0:33:480:33:51

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

0:33:510:33:54

again, looking for these patterns.

0:33:540:33:57

We scanned 10, 20, 30,000.

0:33:570:34:00

Still no omega.

0:34:000:34:02

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

0:34:020:34:08

that number stays in everyone's mind around here -

0:34:080:34:11

and finally we found the omega.

0:34:110:34:13

And here is a photograph of the omega.

0:34:130:34:15

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

0:34:160:34:21

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

0:34:210:34:26

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

0:34:260:34:30

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

0:34:300:34:35

We were exuberant.

0:34:350:34:36

I mean, the Friday that it was found,

0:34:360:34:38

we just stood around looking at each other,

0:34:380:34:41

a bit numb at the beginning,

0:34:410:34:43

then finally everyone broke out into smiles

0:34:430:34:45

and someone started to do a dance.

0:34:450:34:48

It was very happy.

0:34:480:34:49

In fact, in our exuberance,

0:34:490:34:51

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

0:34:510:34:54

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

0:34:540:34:58

But it was a very peculiar feeling.

0:34:580:35:00

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

0:35:000:35:05

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

0:35:050:35:08

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

0:35:080:35:12

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

0:35:120:35:15

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

0:35:150:35:20

Other people may think they know.

0:35:200:35:21

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

0:35:210:35:24

We knew.

0:35:240:35:25

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

0:35:280:35:32

What does it mean?

0:35:320:35:34

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

0:35:340:35:39

I think, today, nobody knows.

0:35:410:35:42

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

0:35:420:35:46

or more completely understand,

0:35:460:35:48

the fundamental laws of interaction of the nuclear particles

0:35:480:35:51

and this is a vital step forwards to that understanding,

0:35:510:35:54

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

0:35:540:35:58

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

0:35:580:36:02

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

0:36:020:36:07

It's analogous to the discovery of the periodic table

0:36:080:36:11

by Mendeleev a century ago.

0:36:110:36:14

He discovered at that time that various chemical elements

0:36:140:36:17

came in families and that there were relations among them

0:36:170:36:20

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

0:36:200:36:23

This was extremely important in the development of science

0:36:230:36:28

and the bringing about the ultimate understanding

0:36:280:36:31

of the behaviour of atoms.

0:36:310:36:33

But the real understanding of the reason why sodium

0:36:330:36:36

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

0:36:360:36:39

in the chemistry of the various elements existed,

0:36:390:36:42

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

0:36:420:36:47

and this knowledge required

0:36:470:36:49

a complete transformation of ideas about nature,

0:36:490:36:52

a complete change of the philosophical position.

0:36:520:36:55

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

0:36:550:37:00

the principle of uncertainty of Heisenberg had to be discovered,

0:37:000:37:04

the whole understanding of the relation of cause and effect

0:37:040:37:10

had to be modified with the principle of indeterminacy.

0:37:100:37:13

And so it is going to be here.

0:37:130:37:15

We will not understand, really, what...

0:37:150:37:17

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

0:37:180:37:22

until we understand the nuclear interactions,

0:37:220:37:25

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

0:37:250:37:29

transformation of ideas somewhere along the line.

0:37:290:37:32

We already see some of the difficulties.

0:37:340:37:36

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

0:37:360:37:40

is not a perfect symmetry.

0:37:400:37:42

If it were, the statement would be that the replacement

0:37:420:37:45

of one particle by another would make no change.

0:37:450:37:48

For example, the replacement of a neutron by a lambda

0:37:480:37:50

should make no change.

0:37:500:37:52

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

0:37:520:37:56

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

0:37:560:37:59

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

0:37:590:38:01

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

0:38:010:38:05

Physicists are happy with a perfect symmetry.

0:38:050:38:08

To say something is absolutely true and absolutely symmetrical

0:38:080:38:11

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

0:38:110:38:17

If a thing were completely unsymmetrical

0:38:170:38:19

then there would be nothing to say.

0:38:190:38:20

But by what kind of a view is a thing

0:38:200:38:24

that is only partly symmetrical natural,

0:38:240:38:28

is a thing that is only partly symmetrical beautiful?

0:38:280:38:31

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

0:38:310:38:35

the artists feel that the camellia,

0:38:350:38:37

in its partial but near symmetry, is especially beautiful

0:38:370:38:41

and far more beautiful than a perfect geometrical pattern.

0:38:410:38:44

But physicists feel that a partial symmetry

0:38:440:38:47

is an indication that some deeper

0:38:470:38:49

and more profound description of nature

0:38:490:38:51

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

0:38:510:38:55

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

0:38:570:39:01

We're kind of stuck.

0:39:010:39:02

We need a new idea.

0:39:020:39:04

Before we'll really get the nuclear forces understood,

0:39:040:39:07

some great new idea is required.

0:39:070:39:08

Looking for symmetry is an old one.

0:39:080:39:11

Poincare suggested it, Einstein used it,

0:39:110:39:15

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

0:39:150:39:18

But the only information that we're accumulating,

0:39:200:39:22

the places where they were really getting stuck,

0:39:220:39:25

understanding the relation of these particles

0:39:250:39:27

is somewhere where we are missing...

0:39:270:39:30

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

0:39:300:39:35

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

0:39:350:39:38

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

0:39:380:39:42

you try again and again.

0:39:420:39:44

But the great discovery always involves

0:39:440:39:46

a great philosophical surprise.

0:39:460:39:48

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

0:39:500:39:53

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

0:39:540:39:56

in a thoroughgoingly different idea.

0:39:560:39:58

How strange it is. Listen to this.

0:39:580:40:00

How much is known after 200 years of studying physics?

0:40:000:40:02

How much is known about electrons, light, everything?

0:40:020:40:06

And in order to understand the nuclear forces,

0:40:060:40:09

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

0:40:090:40:12

a completely different view about everything that we know already,

0:40:120:40:16

philosophically, that is.

0:40:160:40:17

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

0:40:170:40:21

in which everything that we've already found out about

0:40:210:40:24

is the way it is.

0:40:240:40:25

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

0:40:250:40:28

then falls into place.

0:40:280:40:30

It's a very hard job.

0:40:300:40:31

It's lots of work.

0:40:310:40:33

So, what do we do it for?

0:40:330:40:34

Because of the excitement,

0:40:340:40:36

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

0:40:360:40:39

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

0:40:400:40:44

..new view of nature.

0:40:460:40:47

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

0:40:470:40:50

the peculiarity of the way she works.

0:40:500:40:53

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

0:40:530:40:56

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

0:40:560:41:00

the thing that makes me go on...

0:41:000:41:02

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

0:41:030:41:07

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

0:41:070:41:11

and find that to really catch on,

0:41:110:41:13

they have to polish their mind to the very last.

0:41:130:41:16

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

0:41:160:41:20

These discoveries cannot be made twice.

0:41:200:41:22

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

0:41:220:41:26

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

0:41:260:41:30

more than once.

0:41:300:41:32

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

0:41:320:41:35

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

0:41:350:41:40

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

0:41:400:41:43

about the nature that he lives in.

0:41:430:41:46

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

0:41:470:41:49

they can't appreciate the search.

0:41:490:41:51

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

0:41:530:41:57

between the nuclear forces is going to be so wonderful?

0:41:570:41:59

How do we know it isn't going to be

0:41:590:42:01

some complicated, dirty or simple thing?

0:42:010:42:03

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

0:42:030:42:05

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

0:42:050:42:08

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

0:42:080:42:10

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

0:42:100:42:12

How long is it going to take?

0:42:120:42:15

Do we have all the clues?

0:42:150:42:16

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

0:42:180:42:23

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

0:42:230:42:24

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

0:42:240:42:26

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

0:42:260:42:28

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

0:42:280:42:30

Question.

0:42:300:42:31

Do we have enough facts from experiments so that,

0:42:310:42:34

after this thing is discovered,

0:42:340:42:35

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

0:42:350:42:38

How far before? In 1964.

0:42:380:42:40

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

0:42:400:42:44

I think that we now know enough

0:42:440:42:46

that if, with a sufficiently clear reasoning,

0:42:460:42:49

we could come to the answer.

0:42:490:42:50

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

0:42:500:42:53

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

0:42:530:42:57

we'll look back and we'll see

0:42:570:42:58

how a perfectly sensible, logical line of reasoning,

0:42:580:43:01

from the present position,

0:43:010:43:02

could have brought us to the present understanding.

0:43:020:43:04

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

0:43:040:43:07

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

0:43:070:43:10

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