Books interview with Steven Weinberg: "The history of science can prevent us from making the mistakes of the past"

What inspired you to write this book?

I had been teaching an undergraduate course in the history of physics and astronomy for students who didn’t already know a lot about it. As I taught, I became aware that things in the past were quite different from what I had thought. It’s not true to say that scientists were reaching for the same goals as us and that they were simply not getting as close as we’ve come. In fact, they really had no idea of the kind of things that can be learned about the world and the way to learn it. And

I began to see the history of science not as the accumulation of facts and theories, but as the learning of a way of interacting with nature that leads to reliable knowledge.

It’s surprised me how far the great natural scientists of the past were from anything like our modern conception of science.

Heading to the start of this story, how much do we owe the ancient Greeks?

I think the people of the scientific revolution owed them a tremendous amount, particularly the Greeks of the Hellenistic (roughly the third, second and first centuries BC) and Roman periods. For example, Copernicus did not base his theory of the Earth going around the sun on his own observations or those of his contemporaries in Europe, but on the earlier work of the Greeks, particularly Ptolemy. He saw that Ptolemy’s theory could be rectified and made understandable by just changing the point of view from a stationary Earth to a stationary sun with the Earth orbiting it. The peculiarities of Ptolemy’s theory were simply due to the fact that we observe the solar system from a moving platform – the Earth. But Copernicus made no significant observations of his own: he was relying on what Ptolemy had already done. There are many similar examples, too.

However, while we refer to Isaac Newton’s work to explain the mechanics of motion and gravity in physics courses today, we don’t go back to the Greeks. They are part of our heritage, but their value was mostly in making the scientific revolution of the 16th and 17th centuries possible.

Why were the ancient Greeks able to produce so much important work?

Well, not all of them were. The period that many people think of as the golden age of ancient Greece – the Hellenic period (the fifth and fourth centuries BC), when Athens was at the centre of intellectual life – was not very productive, scientifically. They made some qualitative advances (for example, the philosopher and scientist Aristotle gave a nice argument for why the Earth is a sphere) but the detailed mathematical confrontation of theory and observation we associate with modern physics and astronomy didn’t exist. That began in the Hellenistic period, when the centre of Greek thought moved to Alexandria, and the Greek city-states were absorbed into empires, first the Hellenistic kingdoms and then the Roman empire.

I don’t know precisely why the change happened at that point. Greek thought in general took a less aristocratic tone, and people who did science also began to be concerned with its practical application. They also became much less religious: the religiosity you find in the work of Plato, which is largely gone with Aristotle, seems to be completely absent by the time you get to the great Hellenistics leading up to Ptolemy.

How far did the Middle Ages set the ground for the scientific revolution?

The Middle Ages certainly provided an institutional framework in the form of the great universities. Copernicus was educated at universities in Italy; Galileo taught at Padua and was then a professor at Pisa, although he didn’t teach; Newton was always associated with the University of Cambridge. These universities were offshoots of the cathedral schools that had begun a kind of intellectual revolution in the 11th century in Europe. They kept alive the idea of a rational universe governed by law, and in particular when the teachings of Aristotle became firmly fixed in the academic curriculum, the idea of a rational, understandable world became dominant in European thought.

But it wasn’t a scientific world. No one in the Middle Ages really had anything approaching our modern conception of science, and they made very little progress towards actual scientific knowledge. There were arguments about the possible movement of the Earth, but in the end they didn’t lead to anything like the Copernican theory. The Middle Ages was not an intellectual desert, but it wasn’t a period that resembles either the Hellenistic age that went before or the scientific revolution that came afterwards.

What was the contribution of Islamic thinkers in this period?

After the decline of the Roman empire in the west, science became, I would say, ineffective and largely absent in the Greek half of the Roman empire. You find no scientific work – at least, I’m not aware of any – during about 1,000 years of the Byzantine empire. During that period, science was kept alive in the world of Islam, first in the form of translations of the great accomplishments of the Greeks, and in original work that built on and improved on what the Hellenistic and Roman Greeks had done.

Some of it was very impressive: I think of the work of al-Haytham in optics, who for the first time understood why light is bent when it goes, for example, from air into water. However, although Islamic science in one form or another continued for a few centuries, its golden age was really pretty much over by 1100. If you list the great names of Islamic science, they’re all before that date.

Why that’s the case is an endlessly interesting issue. It may have something to do with the appearance of a fiercer version of Islam: for example, Spain was taken over by people from north Africa who formed the Almohad caliphate, which was extremely repressive. There were episodes in which books of scientific or medical technique were burned by Islamic authorities, and the

11th-century philosopher and theologian Al-Ghazali argued explicitly against science because he saw it as a distraction from Islam.

So had Islamic science run out of steam, or was it suppressed by changes in Islam?

I don’t know the answer, but it’s a similar question to that about Greek science. Did that simply run out of steam around 400 or 500 AD, or was it suppressed by the adoption of Christianity? I think that there are good arguments on both sides of both questions.

Are there any characters in this story that particularly stand out for you?

If I understand that in the sense of who I’d like to have a beer with, Christiaan Huygens is a strong contender. He was a 17th-century Dutch polymath who did a huge variety of things: he discovered the rings of Saturn and the formula for centrifugal force, he invented the pendulum clock... I could go on!

But what stands out for me is that he very explicitly understood the relationship between science and mathematics in a way that had always been muddled. Before him, and perhaps a few other people around at the same sort of time, there had been a large body of thought that felt that science was a branch of mathematics and that its truths could be determined by purely mathematical reasoning. This goes all the way back to Plato, who thought that it wasn’t necessary to look at the sky in order to do astronomy – that pure reason was all you needed.

Huygens specifically said, we can only make our assumptions because we intend to work on their consequences and see if they agree with observation – and if they don’t, we will abandon them. This attitude is one you just don’t find very much before.

I also think I’d have liked Ptolemy: he expressed his joy of astronomy in a way that was lovely. In just a few lines he wrote that, when he studied the wheeling motions of the planets, he felt his feet leave the ground and stood with the gods drinking nectar.

Are there any misconceptions about science and its history that you’d like this book to change?

One misconception that’s been foisted on us by a generation of philosophers of science is the idea of the 20th-century physicist and philosopher Thomas Kuhn that science undergoes discontinuous changes after which it’s impossible to understand the science of a former age. I think that’s wrong. I think that, even though you can marvel at the importance of every great change in physics, you see the roots of that change in what went before – and you don’t forget about it. Indeed, you see the new theory as an improvement on the old theory, not an abandonment of it.

We build on the past, and that, I think, is one of the reasons why the writing of science is different from art history or even political history. We can’t say that the Impressionists were right to abandon the photographic realism of the Romantic period, or that the Norman conquest was a ‘good’ thing. That kind of judgment is silly. On the other hand, we can certainly say that Newton was right and Descartes was wrong about what keeps the planets going around the sun – there is a definite sense of discovering right and wrong.

That’s another important point: science is not just an expression of a cultural milieu, as some historians and sociologists of science have argued. It’s the discovery of truths that are out there to be discovered, and it can help prevent us from making the same mistakes as the past. As I was once crass enough to say, the study of the history of science is the best antidote to the philosophy of science.

To Explain the World: The Discovery of Modern Science by Steven Weinberg (Allen Lane, 432 pages, £20)