Theory-Change and Scientific Realism

Professor of Philosophy of Science John Worrall on scientific revolutions, continuity of science, and the change of Newtonian physics by Einstein’s theory

videos | August 14, 2018

There’s this nice modernist Enlightenment idea that science is the way to truth, that the Scientific Revolution gave mankind the opportunity – of course, not everybody takes it, – to find out the truth about the universe. There is this couplet by famous poet Alexander Pope “Nature and Nature’s laws lay hid in night: God said, Let Newton be! and all was light”. People thought for a long time that science was just a question of accumulating truth, that you discovered more and more, that Newton discovered the structure of the solar system and the universe more generally, that Fresnel discovered the properties of light, that Maxwell discovered the properties of electromagnetism, it is just adding more and more sometimes called the layer-cake view of the progress of science.

Then along came in the early 20th century Einstein’s theory and even more radically in a way the theory of quantum mechanics, which were completely at odds with Newton’s theory, at least when one looks at them initially. Certainly, the idea of science as a way to truth is certainly challenged by the existence of revolutionary changes, so-called revolutionary changes, like Einstein’s from Newton’s.

They really are quite writing radically different on the surface at any rate. Newton’s theory involves an infinite universe with action to distance, with absolute space and absolute time, two events are absolutely simultaneous or they’re not simultaneous. Einstein theory negates all those things: there’s no action at a distance in Einstein, the world is finite but unbounded, not infinite, and two events can be simultaneously, a function of simultaneity is relativized in Einstein.

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What we’re going to say? Post-modernist and fake-truth people have really jump onto this saying that science is not really supplying standard for truth, there is no truth, it’s just a question of what different people can be, can believe. Some people believe one thing, some could believe another. You can interpret the facts in either way. There are some people who still believe in a classical Newtonian physics. You can accommodate all the data within it.

So, what’s so what’s going on? This is a real challenge to our view that science is a way of finding out the truth. There’s been an over the centuries, but more in particular over the past several decades, various attempts to respond to that problem by philosophers of science. What is to give up on theories as truth-seeking, as being about the truth? We shouldn’t think of scientific theories as even attempting to tell us what the fundamental structure of the universe is like. Theories by definitions postulate some underlying reality that accounts for the observable reality that we see in the laboratory or when we’re making observations.

Newton’s theory postulates that there’s this invisible intangible force of gravity, and it’s that that produces in accordance with the principles he laid down in his theory, the observable orbits of the planets, for example, or how a particular object will move in it in a particular field when subject to a particular force. That one possibility is called instrumentalism. Its most distinguished recent proponent is a philosopher in the States called Bas van Fraassen, Bas Van constructive empiricism. The idea is that science is just about codifying the phenomena. It gets the phenomena, so it certainly isn’t arbitrary or anything. But we can’t really think that off, what all theories say is going on beneath the phenomena, it’s just that they capture the phenomena accurately, but they don’t do any more than that.

There’s been the arrival to that. Some people stick their head in the science and don’t worry about theories change, and they still think of themselves as so-called scientific realist, believing that our current theories are indeed true. But you can’t really have any knowledge of the history of science, it’s not just once people had recognized that on the back of Einstein’s theory there were these radical theories changing science they saw that earlier, there’ve been important changes too.

For example, Fresnel’s theory of light, which was massively successful, postulates the existence of an intangible invisible mechanical medium that is doing the vibrating to produce the way of light. That was completely rejected by Maxwell’s theory of electromagnetism, which just has an electromagnetic field, there’s no underlying medium.

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There have been important changes right through the history of science. If we look at that case that I just mentioned – the switch from Fresnel’s theory of light, which involves this elastic solid medium to carry the light waves, compared to no medium whatsoever, just the electromagnetic field in Maxwell – although that’s a radical change in content, in metaphysics, in a metaphysical picture that you have of those aspects of the universe, there is in fact complete continuity in terms of the mathematical equations, in the equations that Fresnel has, that govern, for example, the relative intensity of light that we get when you send a light wave at a glass interface. Some of the light gets reflected, some gets refracted into the glass. The intensities of the light and the relationship to that planes of polarization – Fresnel had certain famous equations for them. They were completely given again by Maxwell.

The idea is that although we can’t be sure that our scientific theories are correct in terms of their content, given what’s happened in the history of science, in the history of theories change in particular, but there is a reason to think that we’ve at least captured the structure of the universe in our theories, there is something importantly progressive and truth-seeking in science, despite the fact that there have been these radical changes in so-called scientific revolutions.

NASA, for example, the space agency still thinks of themselves as applying Newtonian theory. When they calculate that rocket or projectile motions. I think, that’s a mistake, new technology always applies the best available theories, and in this case, they’re applying Einstein’s theory. But Einstein’s theory itself tells you that the Newtonian predictions will be well within observational error, that is they’ll be as accurate as they could possibly need to be, whenever the velocity of a body that you’re looking at is as a small velocity relative to the velocity of light. Basically, everything in Newton, all predictions get multiplied by a factor, the square root of one minus three squared with the velocity of the light, the velocity of the object that you’re looking at sees the velocity of light, which is, of course, enormous. That quantity is very close to one. The predictions that you get from Newton are all bang on the money, all within any conceivable observational error bars, except when you get very fast-moving objects, which, of course, rockets are not compared to the velocity of light.

There’s a very important continuity in science through scientific revolutions. What one should look to with respect to the problem of scientific realism, what we should think of how science fundamental theories in science relate to the truth is we should look at the history of science and see where we do have continuity. We do have continuity with respect to mathematical structure, we don’t have continuity with respect metaphysical image that theories are giving us. Stick to the structure and just enjoy the metaphysical image, but don’t take it too seriously.

Professor of Philosophy of Science, the London School of Economics and Political Science
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