Why the theories of Einstein, climate change or evolution can never be proved right
Timothy Wotherspoon says the nature of scientific inquiry means that a theory is only as correct as the result of its last experiment – thus ensuring a truly open-minded quest
There have been many headlines over the past week excitedly announcing that scientists at the Laser Interferometer Gravitational-Wave Observatory (Ligo) have detected microscopic undulations in the fabric of space-time caused by gravitational waves sent off from two black holes colliding 1.3 billion light-years from earth. Newspapers around the world reported that the much-anticipated announcement showed that the “100-year journey to prove Einstein’s theory” had finally come to an end. Gravitational waves are predicted by Einstein’s theory of general relativity. Although many predictions have long been observed, gravitational waves had proved elusive.
As a physicist, I am always glad to see public interest in science, but headlines such as “Theory of Einstein’s Proved Right – Again” (Wall Street Journal) give me pause, in no small part because this one appeared three years ago in reference to an entirely different experiment.
Scientific news followers may also recall that, in March 2014, scientists at the Bicep2 telescope near the South Pole reported the detection of gravitational waves in the form of a primordial artefact of the Big Bang. Careful readers may be confused not as to what exactly is general relativity, but how they can be detected for the first time twice in a two-year span and how both of them finally “prove Einstein correct”?
When scientific breakthroughs are announced, the scientific community reacts with both celebration and scepticism. If other scientists can’t reproduce similar outcomes with similar experiments, then something has gone awry. This is what happened to the results announced by the Bicep2 experiment. By early 2015, it was shown that the signal that they detected could not be isolated from the effect of interstellar dust, confounding their findings. The result had to be discarded. Some might find this disappointing, but it demonstrates the greatest power of the scientific method – knowing when you’re wrong.
Einstein’s theory will never be proven correct. No scientific theory ever will be. Anyone who tells you differently does not understand the scientific method. As the late physicist Richard Feynman once eloquently explained, “We can always prove any definite theory wrong. Notice, however, we can never prove it right. Suppose that you invent a good guess, calculate the consequences, discover that every consequence you calculate agrees with experiment. The theory is proved right? No. It is simply not proved wrong.”
A good theory suggests new experiments with outcomes never observed and predicts the results well. General relativity is a great example. Not only does it correctly predict small deviations in Mercury’s orbit, help us peer into black holes and gives us important clues about the history and fate of time and our universe, its predictions allow for global positioning satellites to accurately and precisely fix a location anywhere on the globe, revolutionising the way people make their way across town, and ships’ captains navigate the open sea. It is a better explanation for our cosmos than any other because it accurately predicts the outcomes of more experiences than any other.
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I hope Ligo’s results will withstand the scrutiny of other analyses and further experiments. Assuming it does, what does it prove? It merely shows that the predictions general relativity makes about the way two black holes orbiting each other in a distant galaxy should subtly undulate the earth beneath our feet is consistent with their careful observations.
It is an important distinction to make. The theory of evolution can also never be proved and neither can the theory of climate change. Good scientists who support those theories will change their minds as soon as experiments suggest that those theories are wrong. The same cannot be said for the supporters of religious or political ideologies. If we confuse the meaning of scientific discovery and begin to think that general relativity has been proven true, we not only lose the beauty of that open-mindedness but we create a new cult of science whose members subscribe out of belief instead of scepticism.
Dr Timothy Wotherspoon is a lecturer in the Faculty of Science, University of Hong Kong