~ PIERRE ARVAY: Music For Solo Harp
There are seven basics shapes of crystals in nature and a multitude of colours.
The crystals in nature express something about the atoms that compose them.
They help to put the atoms into families.
This is the world of physics in our own century, and crystals are a first opening into that world.
~ KHACHATURIAN: Symphony No.2 "The Bell"
Of all the variety of crystals, the most modest is common salt.
And yet it's surely one of the most important.
This is a small part of the great mine at Wieliczka,
near the ancient Polish capital of Cracow.
Salt has been mined here for nearly a thousand years.
The alchemist Paracelsus may have come this way on his eastern travels.
He changed the course of alchemy after 1500,
by insisting that among the elements that constitute man and nature must be counted salt.
Salt is essential to life and it's always had a symbolic quality in all cultures.
Like the Roman soldiers, we still say "salary" for what we pay a man -
though it means "salt money".
In one respect, Paracelsus was wrong.
Salt is not an element.
Salt is a compound of two elements - sodium and chlorine.
That's remarkable enough that a white fizzy metal, like sodium,
and a yellow poisonous gas like chlorine,
should finish up by making a stable structure - common salt.
But more remarkable is that sodium and chlorine belong to families.
For instance, sodium can certainly be replaced by potassium.
Potassium chloride.
And then, similarly, the chlorine can be replaced by its sister element bromine.
Sodium bromide.
And, finally...
lithium fluoride -
in which sodium has been replaced by lithium, chlorine by fluorine,
and yet all the crystals are indistinguishable.
What makes these family likenesses among the elements?
In the 1860s, everyone was scratching their heads about that.
The man who solved the problem most triumphantly
was a young Russian called Dmitri lvanovich Mendeleev,
who visited the salt mine here at Wieliczka in 1859.
He was 25 then.
A brilliant young man.
The youngest of a vast family of at least 14 children.
The darling of his widowed mother, who drove him through science.
What distinguished Mendeleev was not only genius, but a passion for the elements.
They became his personal friends.
He knew every quirk and detail of their behaviour.
The elements, of course, were distinguished each by only one basic property -
that which John Dalton had posed originally.
Each element has a characteristic atomic weight.
How do the properties that make them alike or different flow from that single gift?
Mendeleev worked at this.
He wrote the elements out on cards,
he shuffled the cards in a game that his friends used to call Patience,
and that is the game that I shall play again.
Mendeleev wrote on his cards the atoms in the order of atomic weights.
Hydrogen he didn 't really know what to do with.
So it's lithium, the lightest that he knew,
then beryllium,
then boron,
then come carbon, nitrogen, oxygen,
and then fluorine.
The next is sodium.
And since that has a family likeness to lithium, we start again up there.
Now, magnesium, aluminium, silicon, phosphorus, sulphur,
and now chlorine.
And sure enough, chlorine stands in the same row as fluorine.
And the next is potassium.
There is potassium, next to lithium, sodium, potassium... calcium.
The fact is that the horizontal rows on this arrangement make sense.
They put families together.
If we arrange in order of atomic weight, get every one, two, three, four, five, six, seven steps,
we start afresh, then we get family arrangements.
And then the first problem.
Because, you see, Mendeleev didn 't have all the elements.
63 out of a total of 92 were known, so sooner or later he was bound to come to gaps.
And the first gap he came to was there
because the next known element, namely titanium,
simply doesn 't have the properties that would fit it there, with boron and aluminium.
So he said, "There's a missing element there. Titanium belongs here."
And indeed it does, with carbon and silicon.
Well, I won 't go on, except just to say that when you go down,
this is where bromine would come in this family likeness.
There were a number of gaps and Mendeleev singled out three.
They stand in these three places.
The one that I've just pointed to... one here in the same row... and one here.
And of them he prophesied that on discovery, they would be found -
not only that they would have the weights that fit into their vertical place,
but that they would have these properties.
For instance, this most famous -
what he called eka-silicon -
he predicted the properties of with great exactitude.
It was nearly 20 years before it was found.
It was found in Germany and called not after Mendeleev but germanium.
Mendeleev had predicted that it would be 5.5 times heavier than water. That was right.
He predicted that its oxide would be 4.7 times heavier than water. That was right.
These forecasts made Mendeleev famous - everywhere except in Russia.
He was not a prophet there because the tsar did not like his liberal politics.
The later discovery of a whole new row of elements
beginning with helium, neon, argon -
enlarged his triumph.
The underlying pattern of the atoms was numerical, that was clear.
And yet that can 't be the whole story.
We must be missing something.
It simply does not make sense to believe that all the properties of the elements
are contained in one number - the atomic weight.
Which hides what?
It must hide some internal structure, some way the atom is physically put together,
which generates those properties.
But, of course, as an idea, that's inconceivable,
so long as it's believed that the atom is indivisible.
And that's why the turning point comes in 1897
when JJ Thomson in Cambridge discovers the electron.
Yes, the atom has constituent parts.
The electron is a tiny part of the mass, but a real part,
and it carries a single electric charge,
and each element is characterised by the number of electrons in its atoms.
And their number is exactly equal to the number of the place in Mendeleev's table
that that element occupies.
The picture has shifted from atomic weight to atomic number.
And that means, essentially, to atomic structure.
Physics becomes, in those years,
the greatest collective work of science.
No - more than that.
The great collective work of art of the 20th century.
~ MESSIAEN: Works For Organ
I say work of art because the notion that there's an underlying structure,
a world within the world of the atom,
captures the imagination of artists at once.
Since the time of Newton 's Opticks,
painters had been entranced by the coloured surface of things.
The 20th century changed that.
Like the X-ray pictures of Rontgen, it looked for the bone beneath the skin,
and for the deeper, solid structure that builds up from the inside.
The total form of an object or a body.
The Cubist painters, for example, are obviously inspired by the families of crystals.
They see in them the shape of a village on a hillside.
A group of women. This is Pablo Picasso's famous beginning to Cubist painting.
A single face.
The interest has shifted from the skin and the features, to the underlying geometry.
The head has been taken apart into mathematical shapes
and then put together as a reconstruction, a recreation from the inside out.
This new search for the hidden structure is striking in the painters of northern Europe.
Franz Marc, for example, looking at the natural landscape.
And, a favourite with scientists, the Cubist, Jean Metzinger.
There are two clear differences between a work of art and a scientific paper.
One is that in the work of art, the painter is visibly both taking the world to pieces
and putting it together on the same canvas.
And the other is that you can watch him thinking while he's doing it.
In both these respects, the scientific paper is often deficient.
It often is only analytic...
...and it almost always hides the process of thought in its impersonal language.
I have chosen to talk about one of the founder fathers of 20th-century physics - Niels Bohr -
who collected pictures here in his house in Copenhagen in Denmark,
because in both these respects he was a consummate artist.
He had no ready-made answers.
He used to begin his lecture courses by saying to his students,
"Every sentence that I utter should be regarded by you not as an assertion, but as a question."
What he questioned was the structure of the world.
And the people that he worked with, when young and when old,
were others who were taking the world to pieces,
thinking it out and putting it together.
He went first, in his 20s, to work with Ernest Rutherford,
who, round about 1910, was the outstanding experimental physicist in the world.
Rutherford was then at Manchester,
and in 1911, he proposed a new model for the atom.
He had said the heavy nucleus is at the centre
and the electrons circle it on paths,
the way that the planets circle the sun.
A nice irony of history that, in 300 years,
the outrageous image of Copernicus and Newton
had become the most natural model for every scientist.
Nevertheless, there was something wrong with Rutherford's model.
The planets as they move in their orbits lose energy continuously,
so that year by year, their orbits get smaller -
a very little smaller, but, in time, they will fall into the sun.
If the electrons are exactly like the planets, then they will fall into the nucleus.
There must be something to stop the electrons from losing energy continuously.
That required a new principle in physics
which limits the energy that an electron can give out to fixed values.
Only so can there be a yardstick, a definite unit which holds the electrons to orbits of fixed sizes.
Niels Bohr discovered the unit he was looking for...
...in the work that Max Planck had published in Germany in 1900.
What Planck had shown, a dozen years earlier,
is that in a world in which matter comes in lumps,
energy must comes in lumps, or quanta, also.
By hindsight, that does not seem so strange.
But Planck knew how revolutionary the idea was the day he had it.
Because on that day he took his little boy for one of those professorial walks and said to him,
"I have had a conception today...
...as revolutionary and as great as the kind of thought that Newton had."
And so it was.
Now, in a sense, of course, Bohr's task was easy.
He had the Rutherford atom in one hand, he had the quantum in the other.
What was there so wonderful about a young man of 27 in 1913
putting the two together and making the modern image of the atom?
Nothing but the wonderful, visible thought process.
Nothing but the effort of synthesis.
And the support of it, in the one place where it could be found,
the fingerprint of the atom,
the spectrum in which its internal behaviour becomes visible to us looking at it from outside.
That was Bohr's marvellous idea.
The inside of the atom is invisible,
but there is a window in it, a stained-glass window,
the spectrum of the atom.
Each element has its own spectrum.
For example, hydrogen has three rather vivid lines in its visible spectrum.
Bohr explained them as a release of energy
when the single electron in the hydrogen atom
jumps from one of the outer orbits to one of the inner orbits.
The red line is when the electron jumps from the third orbit to the second.
The blue-green line - when the electron jumps from the fourth orbit to the second.
The structure of the atom was now as mathematical as Newton 's universe,
but it contained the additional principle of the quantum.
Niels Bohr had built a world inside the atom
by going beyond the laws of physics as they had stood for two centuries after Newton.
He returned to Copenhagen in triumph.
~ CARL NIELSEN: Symphony No.2
Denmark was home for him again.
A new place to work.
In 1920, they built the Niels Bohr Institute for him, where it has been ever since.
It's interesting to trace the steps of confirmation of Bohr's model of the atom
because in a way they recapitulate the life cycle of every scientific theory.
First, the paper.
In that, known results are used to support the model.
That is to say, the spectrum of hydrogen in particular...
...is shown to have lines, long known,
whose positions correspond to quantum transitions of the electrons
from one orbit to another.
The next step is to extend that kind of confirmation to a new phenomenon.
In this case, lines in the higher energy X-ray spectrum.
That work was going on in Rutherford's laboratory in 1913
and yielded beautiful results, exactly confirming what Bohr had predicted.
The man who did that work was Harry Moseley,
who, like Rupert Brooke, died, sadly, at Gallipoli in 1915.
His work, like Mendeleev, suggested some missing elements
and one of them, hafnium, was discovered in Bohr's laboratory.
And just at this moment, when everything seems to be going so swimmingly,
we suddenly begin to realise that the theory is reaching the limits of what it can do.
It begins to develop little cranky weaknesses, a kind of rheumatic pain.
And then... the crucial realisation...
...that we have not cracked the real problem of atomic structure at all.
We've cracked the shell.
But within that shell, the atom is an egg with a yolk - the nucleus -
and we have not begun to understand the nucleus.
~ CARL NIELSEN: Serenata In Vano
Niels Bohr was a man with a taste for contemplation and leisure.
When he won the Nobel prize in 1922, he spent the money on buying a house in the country.
His taste for the arts also ran to poetry.
He said to Heisenberg, "When it comes to atoms, language can be used only as poetry.
The poet, too, is not nearly so concerned with describing facts as with creating images."
That's an unexpected thought.
When it comes to atoms, language is not describing facts, but creating images.
But it is so. What lies below the visible world is always imaginary.
A play of images.
There is no other way to talk about the invisible, in nature, in art or in science.
When we step through the gateway of the atom,
we are in a world which our senses cannot experience.
~ SIBELIUS: Symphony No.6 in D Minor
There's a new architecture there, a way that things are put together which we cannot know.
We only try to picture it by analogy, a new act of imagination.
The architectural images come from the concrete world of our senses
because that's the only world that words describe.
But all our ways of picturing the invisible are metaphors, likenesses,
that we snatch from the larger world of eye and ear and touch.
Once we've discovered that the atoms are not the ultimate building blocks of matter,
we can only try to make models of how the building blocks link and act together.
The models are meant to show, by analogy, how matter is built up.
So, to test the models, we have to take matter to pieces...
...like the diamond cleaver feeling for the structure of the crystal.
The ascent of man is a richer and richer synthesis.
But each step is an effort of analysis, of deeper analysis.
When the atom was found to be divisible,
it seemed that it might have an indivisible centre, the nucleus.
And now it turned out, around 1930, that the model needed a new refinement.
The nucleus at the centre of the atom is not the ultimate reality either.
(Machinery roars) At twilight on the sixth day of Creation,
so say the Hebrew commentators to the Old Testament,
God made for man a number of tools that give him also the gift of creation.
If the commentators were alive today, they would write...
..."God made the neutron."
Here it is, the blue glow that is the trace of neutrons,
the visible finger of God touching Adam in Michelangelo's painting
not with breath but with power.
(Thunderclap)
It was James Chadwick who proved in 1932
that the nucleus consists not only of the electrical positive proton,
but of a non -electrical particle - the neutron.
The neutron, therefore, was a new kind of probe,
a sort of alchemist's flame,
because, having no electric charge,
it could be fired at the nuclei of atoms and change them.
The modern alchemist, the man who, more than anyone, took advantage of that,
was Enrico Fermi, in Rome.
Enrico Fermi was a strange creature.
I didn 't know him until much later because in 1934, Rome was in the hands of Mussolini,
Berlin was in the hands of Hitler,
and men like me didn 't travel there.
But when I saw him in New York, much later,
he struck me as the cleverest man I had ever set eyes on.
Well, perhaps the cleverest man with one exception.
Compact, small, powerful, penetrating, very sporty.
And always with the direction in which he was going
as clear in his mind as if he could see to the very bottom of things.
The neutrons he used you can see streaming out of this reactor.
It's a High Flux Isotope Reactor which has been developed here at Oak Ridge.
Transformation was, of course, an age-old dream.
But to men like me with a theoretical bent of mind,
what was most exciting about the period was that it began to open up the evolution of nature.
I must explain that phrase.
I began by talking about the day of Creation and I'll do that again.
Where shall I start?
Bishop Ussher, a long time ago, said that the universe was created in 4004 BC.
Armed as he was with dogma and ignorance, he brooked no rebuttal.
He knew the year, the date, the day of the week, the hour, which, fortunately, I've forgotten.
But the puzzle remained, oh, well into the 1900s,
because while it was very clear that the Earth was many, many millions of years old,
where did the energy come from in the sun and the stars?
We had Einstein 's equations, of course,
which showed that the loss of matter would produce energy, by then.
But how was the matter rearranged?
Well, that's really the understanding that Chadwick's discovery opened.
In 1939, Hans Bethe for the first time explained...
...in very precise terms...
the transformation of hydrogen to helium in the sun
by which a loss of mass streams out to us as this proud gift of energy.
I speak of these matters with a kind of passion
because, of course, to me they have the quality not of memory but of experience.
Hans Bethe's explanation is as vivid to me as my own wedding day,
and the subsequent steps that followed, as the birth of my own children.
Because what was revealed in the years that followed, and finally sealed in, I suppose, 1956,
is that in all the stars there are going on processes which build up the atoms one by one,
into more and more complex structures.
Matter itself evolves.
The word comes from Darwin and biology,
but it's the word that changed physics in my lifetime.
The first step in the evolution of the elements takes places in young stars such as the sun.
It's the step from hydrogen to helium and it needs the great heat of the interior.
What we see on the surface are only storms produced by that action.
Helium was first identified by a spectrum line during the eclipse of the sun in 1868.
That's why it's called helium. It was not known on earth until then.
What happens in effect is that from time to time a pair of nuclei of hydrogen collide and fuse
to make a nucleus of helium.
In time, the sun will become mostly helium.
And then it'll become a hotter star
in which helium nuclei collide to make heavier atoms in turn.
I've come back briefly to the mine at Wieliczka
because there is a historical contradiction to be explained here.
The elements are being built up in the stars constantly.
And yet we used to think that the universe is running down.
Why? Or how?
The idea that the universe is running down...
...comes from a simple observation about machines.
Every machine consumes more energy than it renders.
Some of it is wasted in friction, some of it is wasted in wear
and, in more sophisticated machines, it's wasted in other ways in which the energy is degraded.
There is a pool of inaccessible energy into which some of the energy that we put in always runs.
Rudolf Clausius put that into a basic principle.
He said that there is energy which is available and there is energy which is not accessible.
That he called entropy.
And he formulated the famous second law of thermodynamics.
Entropy is always increasing.
In the universe, heat is draining into a sort of lake of equality
in which it is no longer accessible.
That was a nice idea a hundred years ago because then heat was thought of as a fluid.
But heat is not material any more than fire is or any more than life is.
Heat is a random motion of the atoms.
And it was Ludwig Boltzmann in Austria who brilliantly seized on that idea
to give a new interpretation to what happens in this machine or a steam engine or the universe.
When energy is degraded, said Boltzmann,
it is the atoms that assume a more disorderly state
and entropy is a measure of disorder.
It is the probability of the state. He put that quite precisely.
S, the entropy, is to be represented as proportional to the logarithm of W,
the probability of a given state.
Of course, disorderly states are much more probable than orderly states.
So, by and large, any orderly arrangement will run down.
But by and large is not always.
It is not true that orderly states constantly run down to disorder.
It is a statistical law, which means that order will tend to vanish.
But statistics do not say always.
Statistics allow order to be built up in some islands of the universe -
here on earth, in you, in me... and in the stars, in all sorts of places -
while disorder takes over in others.
That's a beautiful conception.
But there is still one question to be asked.
If it's true that... probability has brought us here,
is not the probability so low that we have no right to be here?
People who ask that question, always put it in this way:
Think of all the atoms that make up my body at this moment.
How madly improbable that they should come to this place at this instance and form me.
Yes, indeed.
If that was how it happened, it would not only be improbable, I would be virtually impossible.
But, of course, that's not how nature works.
Nature works by steps
The atoms form molecules, the molecules form bases, the bases form amino acids,
they form proteins, proteins work in cells,
the cells make, first of all, very simple animals and then sophisticated ones -
climbing step by step.
Evolution is the climbing of a ladder from simple to complex by steps,
each of which is stable in itself.
Since this is very much my subject, I have a name for it.
I call it stratified stability.
That is what has brought life, not only here, but constantly up a ladder of increasing complexity,
which is the central problem of evolution.
And now we know that that's true not only of life but of matter.
If the stars had to build a heavy element like iron,
a superheavy element like uranium,
by the instant assembly of all the parts,
it would be virtually impossible.
No, no. A star builds hydrogen to helium.
Then, at another stage, in a different star,
helium is assembled to carbon, to oxygen, to heavier elements
and so step by step up the whole ladder to make the 92 elements in nature.
~ SIBELIUS: Symphony No.7 in C Major
We can 't copy the processes in the stars as a whole
because we don 't command the immense temperatures
that are needed to fuse most elements.
But we've begun to put our foot on the ladder, to copy the first step from hydrogen to helium.
This is another part of Oak Ridge where the fusion of hydrogen is attempted.
It's hard to recreate the temperature within the sun, of course -
over ten million degrees centigrade -
and it's still harder to make any kind of container that will survive that temperature and trap it,
even for a fraction of a second.
This is a new kind of physics - plasma physics.
Its excitement, yes, and its importance is that it's the physics of nature.
For once, the rearrangements that man makes run, not against the direction of nature,
but along the same steps which nature herself takes in the sun and in the stars.
Immortality and mortality is the contrast on which I end this essay.
Physics in the 20th century is an immortal work.
The human imagination working communally...
...has produced no monuments to equal it -
not the pyramids, not the lliad, not the ballads, not the cathedrals.
The men who made these conceptions, one after another,
are the pioneering heroes of our age.
Mendeleev shuffling his cards.
JJ Thomson, who overturned the Greek belief that the atom in indivisible.
Rutherford, who turned it into a planetary system.
And Niels Bohr, who made that model work.
Chadwick, who discovered the neutron.
And Fermi, who used it to open up and to transform the nucleus.
And, at the head of them, the iconoclasts. The first founders of the new conceptions.
Max Planck, who gave energy an atomic character like matter.
And Ludwig Boltzmann, to whom more than anyone else
we owe the fact that the atom is as real to us now as our own world.
Who would think that only in 1900 people were battling,
one might say to the death,
whether atoms were real or not?
The great philosopher, Ernst Mach, here in Vienna where I am, said no.
The great chemist, Wilhelm Ostwald, said no.
And only one man... at that critical turn of the century,
stood up for the reality of atoms.
He was Ludwig Boltzmann...
...at whose memorial I have come to pay homage.
An irascible, extraordinary, difficult man.
An early follower of Darwin.
Quarrelsome and delightful and everything that a human being should be.
The ascent of man teetered on a real intellectual balance at that point...
...because had anti-atomic doctrines then really won the day...
...our advance would certainly have been set back by decades and perhaps a hundred years.
And not only in physics, but in biology, which is crucially dependent on that.
Did Boltzmann just argue? No.
He lived and died that passion.
In 1906, at the age of 62, feeling isolated and defeated,
at the very moment when atomic doctrine was going to win,
he thought all was lost... and he committed suicide.
What remains to commemorate him is his immortal formula...
I have no phrase to match Boltzmann 's.
But I will take a quotation from the poet William Blake...
...who begins the Auguries Of Innocence with four lines.
"To see a world in a grain of sand
And a heaven in a wild flower,
Hold infinity in the palm of your hand
And eternity in an hour."
~ SIBELIUS: Symphony No.7