Harriman doesn’t understand physics
February 8, 2016 Leave a comment
In some respects, physics is not in a very good state. In particular, many physicists are instrumentalists: they see physical theories as instruments for predicting the results of experiments rather than as explanations of what is happening in reality.
There is some resistance to instrumentalism among some physicists and members of the public. But a lot of this resistance takes the form that the laws of physics have to conform to some version of common sense. But common sense is just knowledge that people currently happen to think ought to be uncontroversial. So to say that some idea doesn’t conform to common sense is not particularly relevant to judging that idea. Rather, the idea should be taken seriously as an explanation in its own right. This includes understanding the claims the theory makes about measurement. What sort of physical processes constitute measurements, what sort of limitations do those processes put on what attributes of a system can be measured and so on.
David Harriman is a common sense advocate, and has many of the weaknesses of such people. Harriman writes an article that includes dialogues between a physicist and a layman. The physicist is an intrumentalist and the layman is a common sense advocate.
First, I’ll look at a part of the dialogue about relativity:
P: “There was a theory that treated length contraction and time dilation in that way. It was proposed by a Danish physicist named Hendrik Lorentz. On the basis of his theory, Lorentz derived some of the fundamental equations of relativity before Einstein did. But the Lorentzian theory was rejected and replaced by Einstein’s theory.”
L: “Was Einstein’s theory accepted because it was better able to account for the observed facts?”
P: “Not exactly. The basic advantage of Einstein’s theory is that it’s simpler. He dismissed the idea of explaining the phenomena of relativity by reference to any physical stuff in space (the so-called ether). Instead, we just say that moving bodies appear shorter and moving clocks appear to run slower—as perceived by a stationary observer. In other words, space contracts and time dilates by amounts that depend on the relative motion with respect to an observer.”
L: “But I want to understand the cause of these effects. You say that length contraction and time dilation don’t refer to real physical changes in moving bodies. Do they instead refer to real effects on our measurement of lengths and times? I remember hearing a classical physicist explain that heating a ruler causes it to expand and thereby affects length measurements. Does motion also affect our physical means of measuring lengths and times? If so, I could make sense of relativity theory. There would still be real lengths of bodies and real time intervals; we merely have to account for and subtract the effects of motion on the measurements. After all, the actual properties and relationships of other bodies can’t change whenever I decide to move!”
If I take a picture of a book from two different angles, the measurements I make relative to the sides of the picture may be different, as in the two pictures below:
The book didn’t change as a result of my taking a photo from a different angle. The constitution of the camera didn’t change either, it still operated the same way after I turned it. The only thing that changed was the relationship between the book and the camera. So different relations between two objects can change the results of measurements even if the two systems operate the same way before and after the change. You can tell that the book remains the same because there are features of the book that remain the same in the two photos, such as the length of the bottom edge of the book compared to the letters on the cover. You could say that those are the real measurements of the book since they remain the same in the two photos, but it is also the case that there is a set of objective facts about the results of measurements on the two photos. Physics ought to tell us about both sets of facts. So the results of some measurements can depend on relations between two bodies.
The layman in the section of dialogue quoted above claims that the relationships between body 1 and body 2 don’t change when body 2 moves. This is a bizarre claim since the relative state of motion of two bodies is a relationship between them. So why shouldn’t some measurements change as a result of different states of relative motion? That is the explanation for the difference in length and time measurements given in standard accounts of special relativity, such as Special Relativity by A. P. French. Note also that as in the case of the photos book above, special relativity claims that some features of a system’s behaviour don’t depend on its relations to other objects. For example, if two atoms emit a photon, the time at which I see each atom emit the photon will in general depend on my state of motion relative to the atoms. And the distance I see between the atoms will also depend on my state of motion relative to the atoms. But the quantity where $latex \delta x$ is the distance I measure between the atoms, and is the time between the photons being emitted. Special relativity is different from what people expect from everyday life, but it is consistent and explains the world better than common sense.
In the dialogue on quantum mechanics his confusion is more understandable. The sort of nonsense the physicist in the dialogue utters is not very far from what a lot of physicists say about quantum theory. But this is a problem with how physicists explain the theory not with the content of the theory itself. And there is a notable symmetry between the two sides of the dialogue, illustrated by the quote below:
L: “I still don’t understand. If you observe only specific entities with definite properties, and you know of no mechanism by which an inconceivable ‘nothing in particular’ could suddenly acquire such properties, why not accept the fact that these things possess real attributes before the observation?”
P: “Because we’ve concluded it isn’t possible to develop a theory that explains our experimental results in terms of entities with specific, non-contradictory properties.”
Note that both sides of this dispute talk vaguely about properties, with specifying what properties they are discussing. Neither side gives any explanation of how reality actually works. There is no discussion of any specific experiment, nor of explanations for the outcomes of these experiments. Both sides are discussing the issue entirely in terms of abstractions that float free of all problems, all experimental results and all solutions to problems. There is an explanation of what quantum mechanics says about how the world works. But you can’t understand that explanation by starting with vague mumbo jumbo about properties, as do both Harriman and the standard physicist.