Andreas Osiander (1498 – 1552) was a Lutheran theologian who is best remembered today for his preface to Nicolaus Copernicus’s (1473 – 1543) book on heliocentric astronomy: De revolutionibus orbium coelestium. The preface, originally anonymous, suggested that the model described in the book was not necessarily true, or even probable, but was useful for computational purposes. Whatever motivated the Lutheran Osiander, it was certainly not keeping the Pope and the Catholic Church happy. It might have been theological, or it could have been the more general idea that one should not mix mathematics with reality. Johannes Kepler (1571 – 1630), whose work provided a foundation for Isaac Newton’s theory of gravity, took Copernicus’s idea as physical and was criticized by no less than his mentor, Michael Maestlin (1550 – 1631) for mixing astronomy and physics. This was all part of a more general debate about whether or not the mathematical descriptions of the heavens should be considered merely mathematical tricks or if physics should be attached to them.
Osiander’s approach has been adopted by many others down through the history of science. Sir Isaac Newton—the great Sir Isaac Newton himself—did not like action at a distance and when asked about gravity said, “Hypotheses non fingo.” This can be roughly paraphrased into English as: shut up and calculate. He was following Osiander’s example. It was not until Einstein’s general theory of relativity that one could do better. Even then, one could take a shut up and calculate approach to the curved space-time of general relativity.
Although atoms were widely used in chemistry, they were not accepted by many in the physics community until after Einstein’s work on Brownian motion in 1905. Ernst Mach (1838 – 1916) opposed them because they could not be seen. Even in the early years of the twentieth century Mach and his followers insisted that papers discussing atoms, published in some leading European physics journals, have an Osiander-like introduction. And so it continues: in his first paper on quarks, Murray Gell-Mann (1929) introduced quarks as a mathematical trick. If Alfred Wegener (1880–1930) had used that approach to continental drift it might not have taken fifty years for it to be accepted.
We see a trend: ideas that are considered heretical or at least unorthodox—heliocentrism, action at a distance, atoms, and quarks—are introduced first as mathematical tricks. Later, once people become used to the idea, they take on a physical reality, at least in people’s minds.
In one case, the trend went the other way. Maxwell’s equations describe electromagnetic phenomena very well. They are also wave equations. Now, physicists had encountered wave equations before and every time, there was a medium for the waves. Not being content to shut up and calculate, they invented the ether as the medium for the waves. Lord Kelvin (1824 –1907) even proposed that particles of matter were vortices in the ether. High school text books defined physics in terms of vibrations in the either. And then it all went poof when Einstein published the special theory of relativity. Sometimes, it is best to just shut up and calculate.
Of course, the expression Shut up and calculate is applied most notably to quantum mechanics. In much the same vein as with the ether, physicists invented the Omphalos … oops, I mean the many-worlds interpretation, of quantum mechanics to try to give the mathematics a physical interpretation. At least Philip Gosse (1810 –1888), with the Omphalos hypothesis, only had one universe pop into existence without any direct evidence of the pop. The proponents of the many-worlds interpretation have many universes popping into existence every time a measurement is made. Unless someone comes up with a subtle knife[1] so one can travel from one of these universes to another, they should be not taken any more seriously than the ether.
The shut up and calculate approach to science is known as instrumentalism—the idea that the models of science are only instruments that allow one to describe and predict observations. The other extreme is realism—the idea that the entities in the scientific models refer to something that is present in reality. Considering the history of science, the role of simplicity, and the implications of quantum mechanics[2] (a topic for another post), realism—at least in its naïve form—is not tenable. Every time there is a paradigm change or major advance in science, what changes is the nature of reality given in the models. For example, with the advent of special relativity, the fixed space-time that was a part of reality in classical mechanics vanished. But with an instrumentalists view, all that changes with a paradigm change is the range of validity of the previous models. Classical mechanics is still valid as an instrument to predict, for example, planetary motion. Indeed, even the caloric model of heat is still a good instrument to describe many properties of thermodynamics and the efficiency of heat engines. Instrumentalism thus circumvents one of the frequent charges again science: namely that we claim to know how the universe works and then discover that we were wrong. This is only true if you take realism seriously and apply it the internals of models.
The model building approach to science advocated in these posts is perhaps an intermediate between the extremes of instrumentalism and realism. The models are judged by their usefulness as instruments to describe past observations and make predictions for new ones; hence the tie-in to instrumentalism. The models are not reality any more than a model boat is, but they capture some not completely determined aspect of reality. Thus, the models are more than mere instruments, but less than complete reality. In any event, one never goes wrong by shutting up and calculating.
Additional posts in this series will appear most Friday afternoons at 3:30 pm Vancouver time. To receive a reminder follow me on Twitter: @musquod
[1] The Subtle Knife, the second novel in the His Dark Materials trilogy, was written by the English novelist Philip Pullman
[2] In particular Bell’s inequalities.
Great post!
Regarding the instrumental versus realist, I think philosopher Ian Hacking has a good compromise: something is real if it produces effects. So atoms might be considered hypothetical creatures until they get thrown at stuff and produce effects that can be measures.
As to Isaac Newton, I have never heard that Newton did not like action at a distance. Rather, after being criticized by Cartesians for his “occult” science he covered himself by saying, whatever the cause, this is how it behaves. In the third edition of Optics, Query 31, Newton really gets into the action at a distance with short range forces.
The ether was believed to have real effects; namely all of electromagnetism and confirmation of Maxwell’s equations was taken as confirmation of the ether hypothesis. And then the ether went away. The same argument could be made for caloric. The Carnot principle was taken as evidence for the existence of caloric. There is no logical positivist criteria for saying something is real.
Your description of the many worlds hypothesis is terribly flawed, to the point of being a straw man. Many worlds does not postulate entirely new universes “popping into existence” every time a “measurement” is made. It takes the wave function as having physical existence, so the single universe contains many, seemingly separate versions of the world that come about as interacting wavefunctions decohere.
I am not convinced that many worlds is entirely correct, but it certainly seems closer to being correct than an arbitrary postulation of wavefunction collapse.
“seemingly separate versions of the world that COME ABOUT as interacting wavefunctions decohere.” The COME ABOUT seems remarkably similar to popping into existence.
But, however you slice and dice it, the many-worlds interpretation has many worlds for which there is no real evidence. They are postulated to make people’s classical intuition happy. I see many-worlds and physically collapsing wave-function as both flawed. As I said, wave functions are a property of the observer-quantum system and not the quantum system by itself. If you accept the correspondence principle this is forced by the properties of classical probabilities.
I would also ask the question: Is there any empirical test that would separate many-worlds from wave function collapse? It basically comes down to opinion which is not very interesting. The only reason I discussed the interpretation of quantum mechanics is that it fits in with the idea of instrumentalism discussed in the previous post.
If people want to believe in many-worlds that is fine by me just realize it is metaphysics not science.
The phrase “pop into existence” implies that it did not exist before. This is not the case in many worlds; nothing new is ever required to “pop into existence.” The appearance of many separate worlds is due to the time evolution of interacting wave functions, as different superpositioned states decohere and cease to interfere with each other.
I would like to know where you are finding all of these people whose classical intuition selects many worlds over wavefunction collapse. Wavefunction collapse was invented to maintain the classical “truth” that a measurement has one result. It has a whole host of mathematically and physically ugly features, including being non-local and non-unitary.
There is experimental evidence that decoherence occurs; it is an established phenomenon. The existence of decoherence, which gives the appearance of wavefunction collapse, makes the postulation of an actual collapse unnecessary. It’s just not parsimonious. The Copenhagen interpretation, to paraphrase Occam, multiplies entities beyond necessity. Occam’s Razor has been put in mathematically rigorous form (minimum message length, and more broadly Kolmogorov complexity), so it does not in fact come down to mere opinion.
Again, it is not clear to me that the specific description of many worlds is the best way to think about quantum mechanics; but it is certainly better than actual wavefunction collapse.
The collapse of the probability occurs with measurements in either classical or quantum systems. In quantum systems it implies the collapse of the wave function.Decoherence is independent of wave function collapse. Even if the state has decohered it is still necessary to determine which of the decohered state the system is in. So the many worlds interpretation does not eliminate the need for wave function collapse or equivalently determining which world we are in.
Decoherence is just the statement that contributions to a measurement are added incoherently if an additional measurement can separate the contributions.