Implication of an Experiment

Remember Kepler’s laws from my earlier series and how they predicted that planets would have elliptical orbits? Then came Newton and his theory of gravitation, predicting that the orbits shouldn’t be perfectly elliptical because, hey, the planets would exert a pull on each other thereby “distorting” the orbit a bit.

In his book, The Character of Physical Law, Richard Feynman pointed out a very interesting aspect of the laws of physics:
“When a law is right it can be used to find another one… This process has developed into an avalanche of discoveries.”
Feynman used Newton’s laws of gravitation to explain things with 2 examples:
1)      Uranus’ orbit didn’t match the predicted “distortion” from the perfect ellipse for Uranus. Did that mean Newton’s law was wrong? Or, was the law right, in which case it implied the existence of a yet-to-be-discovered planet that was causing the “funny behavior”? It turned out Newton’s law was right; and thus we found the planet, Neptune!
2)     The moons of Jupiter appeared sometimes to get “ahead of time” while at others fall “behind”. Roemer, having confidence in Newton’s laws, felt that the distance from the Earth had something to do with it. He wondered if the cause of ahead/behind measurements was that light took less/more time to get to us on Earth, depending on how far it had to travel. And thus he calculated the velocity of light, thereby also proving that light had a finite speed!

Ok, it’s great when a law is right and leads to other discoveries, but can we be sure that the law was right? What if the observation that doesn’t fit is evidence that the law is wrong? In fact, the deviation of Mercury’s orbit from Newton’s law led people to suspect the existence of another undiscovered planet a la Neptune. But it turned out that this was evidence that Newton’s laws were not right after all. (Mercury’s orbit was one of the first “wins” for Einstein’s theory of relativity).

Today, it’s extremely hard to know when a theory might be wrong. William Poundstone explains why in his book, Labyrinths of Reason:
“Most hypotheses on the edges of current knowledge can be tested only in situations where many “auxiliary” hypotheses are tested as well. Auxiliary hypotheses are background assumptions about how the main hypothesis fits into the general body of knowledge; how microscopes, telescopes and other equipment necessary to test the hypothesis operate; and so on. These auxiliary hypotheses often rule out any quick use of modus tollens (refuting the hypothesis).”

Understanding the implication of an experiment that contradicts a theory is very hard: the theory may be wrong; or there may be something else that we didn’t know about. It’s very hard to know which is the case.

Comments

  1. Ramiah KumarFebruary 28, 2017 at 11:59 AM

    I could appreciate all the points of the blog.

    Your last line, "Understanding the implication of an experiment that contradicts a theory is very hard: the theory may be wrong; or there may be something else that we didn’t know about. It’s very hard to know which is the case" is a good point.

    Fortunately physics is unlike maths, in the sense, observed facts rule, and theories are there only to create a model. It so happens that theories create the illusion "law works perfectly". Actually, the pride can only be, "what realistic model one has built!", but even that laced with, "Hope it lasts".

    One example of the hope demotion (the hope being "a theory can be derailed") is Einstein's EPR paradox challenger. Quantum mechanics won once again and EPR is no longer any paradox. Einstein could not deflate quantum mechanics! See the contrast now, where a theory almost got decimated! There was a time when physicists believed that wave theory of light was absolutely correct, except for one small bit which needed to be tracked - the medium requirement for light transmission. Can you believed it? The experiment that aimed at providing that little bit of "requirement", the Michelson Morley experiment, actually actually uprooted the wave theory of light itself! Luckily for us, that experiment finding gave rise to the theory of relativity for one thing. For another, on the rubble of wave theory of light but not because of it of course but independently, we are fortunate to have the quantum theory. Oddly, it was the same Einstein who solved the quantum dilemma posed by Max Planck by identifying light a particle and paved way for Neils Bohr to come up with a preliminary atom model that once again paved further way to the emergence of full-fledged quantum mechanics.

    I firmly believe that what matters is the underlying truth. It will emerge finally in any case, no matter no matter how many errors happened while searching for it, or, for that matter, how much bewilderment the seekers suffer.

    ReplyDelete

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