Never believe an experiment until it has been confirmed by a theory

Supposedly Sir Arthur Eddington said this, and supposedly he was at least partially joking.  I like to think he was only half joking, though, because there’s a pretty big nugget of truth in this supposedly backwards statement.  It’s really just an obnoxious way of stating another favorite adage of scientists: Extraordinary claims require extraordinary evidence.

If someone tells you the result of an experiment, and that result fits nicely in with a previously-established theoretical framework, you should be more inclined to believe it than you would be for a claim that does not fit into such a framework.  In so doing, you’re just being a good Bayesian reasoner, taking into account both your prior knowledge and the information contained in the new experiment.

Take, for instance, the idea that cell phones cause cancer.  Maine is considering a law requiring warning labels to this effect.  The epidemiological evidence is, to say the least, mixed.  I find the “don’t believe an experiment until it’s confirmed by a theory” maxim to be a pretty convincing argument against the idea tha there’s any risk: as far as I know, no one has proposed a plausible mechanism by which the microwave radiation emitted by cell phones could cause cancer.  As Bob Park has been pointing out in his What’s New column for quite a while now,

Cancer agents break chemical bonds, creating mutant strands of DNA. Microwave photons cannot break chemical bonds.

I’m terribly ignorant about biology, so maybe this argument is all wrong, but it sounds convincing to me.

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Ted Bunn

I am chair of the physics department at the University of Richmond. In addition to teaching a variety of undergraduate physics courses, I work on a variety of research projects in cosmology, the study of the origin, structure, and evolution of the Universe. University of Richmond undergraduates are involved in all aspects of this research. If you want to know more about my research, ask me!

8 thoughts on “Never believe an experiment until it has been confirmed by a theory”

  1. I think Sagan’s statement is more appropriate than your title. While the Eddington quote is good for those who a) know Eddington and b) actually work in science, it can give a false impression to those outside of science.

    For example, when debating homeopathic “medicine”, one often hears lines like “science can’t explain it, but there was a time when science couldn’t explain continental drift” and similar arguments. The correct response is “the problem is not that science can’t explain it; the problem is that it doesn’t work”. In fact, a pretty good definition of science is “learning how to explain things we couldn’t explain before”. In other words, stuff we don’t (yet) understand is the bread and butter of science; if science understood everything, it would no longer exist as a discipline or way of working, but as just a body of knowledge.

    Of course, Bayes comes to the rescue for things like cold fusion and homeopathy. As you say, claims based on no mechanism, or a mechanism known to be wrong for other means, require more evidence than claims which don’t contradict conventional wisdom.

  2. While I agree with Bob Park regarding the lack of evidence for carcinogenic cell phones, get a load of this (as Archie Bunker would have said):

    Off course it can. If global warming is anthropogenic, and I feel certain that it is, it should be seen as a demonstration that humans already exert control over the climate. We need only to reverse the sign. Two things can do it: 1) increase efficiency and 2) decrease the number of “warming centers” (i.e. reduce the number of people on Earth). Number 1) should be a crash program, since efficiency pays for itself over time. Human population reduction on the other hand, must be very gradual to retain a voting majority. All subsidies for fecundity, such as tax deductions for dependents, should be eliminated.”

    Number 1 is clear. I’m not sure what he means by number 2. If he is talking about the indirect effects of a high population, sure, no-brainer; those cave men didn’t have to worry about producing too much CO2 since there weren’t that many of them; things are different today. However, that doesn’t seem to be what he means by “warming centers”. Does this guy think The Matrix is real science (i.e. humans produce energy, so harness that as a source of energy)? All energy humans produce (a typical human runs at about 100 watts) comes from the sun.

    Uncle Al posted this fallacy recently on s.p.r and was duly disciplined.

    This seems to be a major fallacy. I’m sure you read about James Randi’s drift to the Dark Side. His retraction was only partial—he was still concerned about “the heat produced”. This shows a huge lack of understanding of the basic principles. Global warming is caused by the greenhouse effect, not by producing too much heat. The amount of heat produced by humans—by their bodies or by their activities—is negligible compared to the amount of heat received from the sun or to the amount of heat released from the Earth as a result of geological processes.

  3. I think Park is talking simply about population when he advocates reducing the number of “warming centers.” I’m sure he’s not talking about Matrix-style science: he’s just making the obvious point that fewer people means less anthropogenic effect of all sorts.

    I really enjoy Bob Park’s columns, but you have to get used to his style: his desire to be pithy and sardonic gets the best of him a lot. (And of course he’s quite capable of being flat-out wrong, like the rest of us.)

    As far as the Eddington quote is concerned, I think the intended audience is key. For people with even a moderately nuanced idea of how science works, I think it makes a valid and important point: the interplay between theory and experiment is more complex than the simple view that theory proposes and experiment decides. But I agree that in some contexts that point is too subtle.

  4. If Park thinks we can exert control over global climate, I don’t understand why he doesn’t mention option 3) put something into the atmosphere that has a net cooling effect. Options include water vapor and sulphur dioxide. For a hundred million dollars or so, I will gladly knock a few degC off the global mean.

  5. “the obvious point that fewer people means less anthropogenic effect of all sorts.”

    That’s true, but it’s also oversimplistic. In fact, every part of the developed world except the United States is already experiencing slowing population growth that will eventually lead to population decline (which is already happening in Japan). Even in the U.S., growth is driven by immigration rather than natural increase. But there are problems in assuming that this alone can solve the problem of anthropogenic effects:

    * Reduced population size does not reduce anthropogenic effects in a one-to-one manner, for the simple reason that smaller families means less sharing of resources than larger ones. If you live in a 2,000 square foot house, it requires the same amount of energy to heat if there are three people in it versus five people. As a result, per capita resource use goes up.

    * While decreasing the overall global population would be a good thing, the reality is that most people don’t live globally, but as citizens of individual countries with semi-autonomous economies. That means maintaining continued economic growth and all the goodies that come out of that (e.g. jobs, taxes for needed government programs, health care and retirement benefits for the increasing number of elderly) is still dependent on replacing the economically nonproductive members of society with newly productive ones. That is why countries like South Korea are desperately attempting to *increase* the birth rate, although history has shown that pro-natal policies are almost always unsuccessful.

    * Related to the above, you can’t simply focus on population while ignoring the vast difference in consumption patterns. Despite the recent growth in emissions in developing countries like China and India (itself largely driven by the production of consumer goods to export to more developed nations), the fact remains that the smaller populations in developed countries still account for a much greater percentage of anthropogenic climate effects than the much larger (and still growing) populations of developing countries. This also complicates the obvious solution to the problem noted in the previous paragraph — immigration. If developed countries open their doors to immigrants from the developing world, those immigrants will see their own resource use climb as they begin to enjoy a first-world lifestyle. At the same time, it’s morally indefensible in my view for the developed world to decide to close its doors to protect its high-consumption lifestyle while condemning two-thirds of humanity to have to scrounge to find even the most basic necessities for survival.

    * So yes, reducing population (which will happen even without taking away child tax credits) is a necessary part of addressing climate change, but it’s not a silver bullet by any means. Unless some geo-engineering solution along the lines proposed by Allen is found, then a solution to global warming will have to address our current patterns of resource use.

  6. It’s a great quote and the idea of mm waves impacting cells just smells funny. Some states (Maine maybe) used to have laws that required signage when a microwave was being used on the premises. I saw such a sign not too long ago so some are still around. Remember those?

    Randi’s recent silliness really made me sad. That guy is one of my all time heroes and to hear the climate contrarians claim a real skeptic like Randi as one of their own is heartbreaking. Allen, your point about geoengineering actually hits the tricky bits right on – who gets their hand on the thermostat if you are going to start putting sulphates in the stratosphere? (Note too that while it would cool the planet, it doesn’t help ocean ocean acidification which is arguably a bigger global change than our changes to the greenhouse effect.)

    More to the point. People read this blog, Ted?

  7. I’m sure the blog has many readers. Some blogs have more comments, but a) that doesn’t necessarily mean more good comments and b) some have way too many comments.

  8. The climate is indeed changing but I believe this is due to the cycle of the sun not man made. How ever I’m not also discounting the fact that man does has an impact on the planet.

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