No proof in science

By June 27, 2017Science

Often in the newspaper you will see it stated that some scientific theory has been proven. That is impossible. Scientific theories cannot be proven, only disproven or shown to be false (i.e. falsified). This applies even to one of the most famous examples; the testing of the predictions of Einstein’s Theory of General Relativity.

Before I go any further, you need to understand the difference between special relativity and general relativity. For Einstein, this relativity business started in 1905 when he published his ‘Special Theory of Relativity’, in which he stated that the speed of light is constant for all inertial (i.e. not accelerating) observers, regardless of the motion of the source. Among other things, it shows that length contracts in the direction of movement, and time slows down for a person travelling at a constant speed relative to an observer. Particle accelerators have determined that the properties of particles moving at near the speed of light are consistent with special relativity and inconsistent with Newtonian mechanics1.

In 1916, Einstein published his theory of General Relativity, which is essentially a theory of gravitation. It generalises Special Relativity and with Newton’s Law of Gravitation, shows that gravity is a geometric property of spacetime. One of the predictions of General Relativity is that of gravitational lensing. Newtonian mechanics also predicted that but at only half the degree (excuse pun) predicted by General Relativity2. This was first tested by Arthur Eddington, Frank Watson Dyson and others, during a total solar eclipse. The eclipse was required so that the normal brightness of the sun did not obscure stars near the same visual line as the sun. Observations were made in Brazil and in Sao Tomé and Principe. The bending of the light from the stars was shown to be in accordance with Einstein’s prediction. At the time, many newspapers and other media around the world stated that Einstein’s theory of general relativity had been proven. This also happened when the theory was tested in Australia in 19223. That it was proven was not correct. A prediction it made turned out to be correct. That is a very different thing. Newton’s ‘laws’ of motion, predicted the movement of most of the planets, but not Mercury. It didn’t ‘behave’ as Newton ‘laws’ said it should4. However, General Relativity explained it perfectly5. As Einstein stated: “No amount of experimentation can ever prove me right; a single experiment can prove me wrong6. If Eddington and others had obtained different results, Einstein’s theory would possibly have been lost in the rubbish bin of defunct theories.

All theories in science are erected to explain some observations or experimental results. Then, to test that theory, more observations are made or experiments carried out. If they are consistent with the theory, then the theory survives. If they are not consistent with the theory, then the theory is either modified (if possible) to explain the new observations, or it is thrown out, and another developed in its place. This new theory is then tested against a new set of observations or experiments, and so on. The longer a theory survives this constant testing, the more reliable it is considered to be. There have been criticisms of General Relativity, but none have been found to be valid. So, it has withstood attacks by all kinds of scientists using all sorts of tests and experiments for just over 100 years.

So, when you hear someone, maybe a journalist, say that a particular scientific theory has been proven, it should be clear they do not know how science works.




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