The Ascent of Man (33 page)

Who would think that, only in 1900, people were battling, one might say to the death, over the issue whether atoms are real or not. The great philosopher Ernst Mach in Vienna said, No. The great chemist Wilhelm Ostwald said, No. And yet one man, at
that critical turn of the century, stood up for the reality of atoms on fundamental grounds of theory. He was Ludwig Boltzmann, at whose memorial I pay homage.

Boltzmann was 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 fine 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 would it have been held back, 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 sixty-two, 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,

carved on his grave.

I have no phrase to match the compact and penetrating beauty of 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.

One aim of the physical sciences has been to give an exact picture of the material world. One achievement of physics in the twentieth century has been to prove that that aim is unattainable.

Take a good, concrete object, the human face. I am listening to a blind woman as she runs her fingertips over the face of a man she senses for the first time, thinking
aloud. ‘I would say that he is elderly. I think, obviously, he is not English. He has a rounder face than most English people. And I should say he is probably Continental, if not Eastern-Continental. The lines in his face would be lines of possible agony. I thought at first they were scars. It is not a happy face.’

This is the face of Stephan Borgrajewicz, who like me was born in Poland. In ‘Portrait
of Stephan Borgrajewicz’ it is seen by the Polish artist, Feliks Topolski. We are aware that these pictures do not so much fix the face as explore it; that the artist is tracing the detail almost as if by touch; and that each line that is added strengthens the picture but never makes it final. We accept that as the method of the artist.

But what physics has now done is to show that that is the
only method to knowledge. There is no absolute knowledge. And those who claim it, whether they are scientists or dogmatists, open the door to tragedy. All information is imperfect. We have to treat it with humility. That is the human condition; and that is what quantum physics says. I mean that literally.

Look at the face across the whole spectrum of electromagnetic information. The question
I am going to ask is: How fine and how exact is the detail that we can see with the best instruments in the world – even with a perfect instrument, if we can conceive one?

And seeing the detail need not be confined to seeing with visible light. James Clerk Maxwell in 1867 proposed that light is an electromagnetic wave, and the equations that he constructed for it implied that there are others.
The spectrum of visible light, from red to violet, is only an octave or so in the range of invisible radiations. There is a whole keyboard of information, all the way from the longest wavelengths of radiowaves (the low notes) to the shortest wavelengths of X-rays and beyond (the highest notes). We will shine it all, turn by turn, on the human face.

The longest of the invisible waves are the radiowaves,
whose existence Heinrich Hertz proved nearly a hundred years ago in 1888, and so confirmed Maxwell’s theory. Because they are the longest, they are also the crudest. A radar scanner working at a wavelength of a few metres will not see the face at all, unless we make the face also some metres across, like a Mexican stone head. Only when we shorten the wavelength does any detail appear on
the giant head: at a fraction of a metre, the ears. And at the practical limit of radiowaves, a few centimetres, we detect the first trace of the man beside the statue.

Next we look at the face, the man’s face, with a camera which is sensitive to the next range of radiation, to wavelengths of less than a millimetre, infra-red rays. The astronomer William Herschel discovered them in 1800, by noticing
the warmth when he focused his telescope beyond red light; for the infrared rays are heat rays. The
camera plate translates them into visible light in a rather arbitrary code, making the hottest look blue and the coolest look red or dark. We see the rough features of the face: the eyes, the mouth, the nose – we see the heat steam from the nostrils. We learn something new about the human face,
yes. But what we learn has no detail.

At its shortest wavelengths, some hundredths of a millimetre or less, infra-red shades gently into visible red. The film that we use now is sensitive to both, and the face springs to life. It is no longer a man, it is the man we know: Stephan Borgrajewicz.

White light reveals him to the eye visibly, in detail; the small hairs, the pores in the skin, a blemish
here, a broken vessel there. White light is a mixture of wavelengths, from red to orange to yellow to green to blue and finally to violet, the shortest visible waves. We ought to see more exact details with the short violet waves than the long red waves. But in practice, a difference of an octave or so does not help much.

The painter analyses the face, takes the features apart, separates the
colours, enlarges the image. It is natural to ask, Should not the scientist use a microscope to isolate and analyse the finer features? Yes, he should. But we ought to understand that the microscope enlarges the image but cannot improve it: the sharpness of detail is fixed by the wavelength of the light. The fact is that at any wavelength we can intercept a ray only by objects about as large as a
wavelength itself; a smaller object simply will not cast a shadow.

An enlargement of over two hundred times can single out an individual cell in the skin with ordinary white light. But to get more detail, we need a still shorter wavelength. The next step, then, is ultra-violet light, which has a wavelength of ten thousandth of a millimetre and less – shorter by a factor of ten and more than visible
light. If our eyes were able to see into the ultra-violet, they would see a ghostly landscape of fluorescence. The ultra-violet microscope looks through the shimmer into the cell, enlarged three thousand five hundred times, to the level of single chromosomes. But that is the limit: no light will see the human genes within a chromosome.

Once again, to go deeper, we must shorten the wavelength:
next, to the X-rays. However, they are so penetrating that they cannot be focused by any material; we cannot build an X-ray microscope. So we must be content to fire them at the face and get a sort of shadow. The detail depends now on their penetration. We see the skull beneath the skin – for example, that the man has lost his teeth. This probing of the body made X-rays exciting as soon as Wilhelm
Konrad Röntgen discovered them in 1895, because here was a finding in physics that seemed designed by nature to serve medicine. It made Röntgen a kindly father figure, and he was the hero who won the first Nobel prize in 1901.

A lucky chance in nature will sometimes let us do more by a flanking movement, that is, by inferring an arrangement which cannot be seen directly. X-rays will not show
us an individual atom, because it is too small to cast a shadow even at this short wavelength. Nevertheless, we can map the atoms in a crystal because their spacing is regular, so that the X-rays will form a regular pattern of ripples from which the positions of the obstructing atoms can be inferred. This is the pattern of atoms in the DNA spiral: this is what a gene is like. The method was invented
in 1912 by Max von Laue, and was a double stroke of ingenuity, for it was the first proof that atoms are real, and also the first proof that X-rays are electromagnetic waves.

We have one step more left to take, to the electron microscope, where the rays are so concentrated that we no longer know whether to call them waves or particles. Electrons are fired at an object, and they trace its outline like a knife-thrower
at a fair. The smallest object that has ever been seen is a single atom of thorium. It is spectacular. And yet the soft image confirms that, like the knives that graze the girl at the fair, even the hardest electrons do not give a hard outline. The perfect image is still as remote as the distant stars.

We are here face to face with the crucial paradox of knowledge. Year by year we devise more
precise instruments with which to observe nature with more fineness. And when we look at the observations, we are discomfited to see that they are still fuzzy, and we feel that they are as uncertain as ever. We seem to be running after a goal which lurches away from us to infinity every time we come within sight of it.

The paradox of knowledge is not confined to the small, atomic scale; on the
contrary, it is as cogent on the scale of man, and even of the stars. Let me put it in the context of an astronomical observatory. Karl Friedrich Gauss’s observatory at Göttingen was built about 1807. Throughout his lifetime and ever since (the best part of two hundred years) astronomical instruments have been improved. We look at the position of a star as it was determined then and now, and it
seems to us that we are closer and closer to finding it precisely. But when we actually compare our individual observations today, we are astonished and chagrined to find them as scattered within themselves as ever. We had hoped that the human errors would disappear, and that we would ourselves have God’s view. But it turns out that the errors cannot be taken out of the observations. And that is true
of stars, or atoms, or just looking at somebody’s picture, or hearing the report of somebody’s speech.

Gauss recognised this with that marvellous, boyish genius that he had right up to the age of nearly eighty at which he died. When he was only eighteen years old, when he came to Göttingen to enter the University in 1795, he had already solved the problem of the best estimate of a series of observations which have internal
errors. He reasoned then as statistical reasoning still goes today.