Thursday, September 29, 2016

Dark matter or a new theory

Urbain Le Verrier
Science studies facts and tries to explain why they occur. Scientific theories are the more credible, the more facts they explain or predict. A single fact in opposition to a theory, or a single unconfirmed prediction, is enough to make us consider revising the theory. With the scientific method, theories are never final and facts must always take precedence.
We have a classic historical example in the theory of universal gravitation, which allowed Newton to explain events like the fall of bodies and the movement of planets and satellites. Its first achievement, by Newton himself, was the mathematical deduction of Kepler’s three experimental laws, obtained empirically from the observation of the orbits of the planets. But the greatest success of the theory was a correct prediction when discrepancies were detected between the orbit of Uranus deduced from the theory and the observed orbit. When something like this happens, the problem can be solved in two ways:

·      Either the theory is not correct and needs to be modified.
·      Or there is some unknown fact that, keeping the theory intact, explains the discrepancy.
In 1845, the French astronomer Le Verrier thought that the problem would be solved if there were an unknown planet beyond Uranus. On 23 September 1846, the German astronomer Galle discovered the planet, which was called Neptune. The success of this prediction became scientific news of the first order, an apparently final slap on the back for Newton’s theory of gravitation.
In 1855, Le Verrier transferred his attention to Mercury’s orbit, which also had discrepancies with the predictions of Newton’s theory, and used the same procedure he had applied with spectacular success ten years earlier. The discrepancies could be explained if there were an unknown planet between Mercury and the Sun. Le Verrier was so sure that this planet would be discovered, that he even gave it a name: Vulcan.
Leonard Nimoy as Mr. Spock
During 60 years, the astronomers searched in vain for the mysterious and elusive planet Vulcan. In this case, the solution of the problem was the other one: the theory must be modified. In 1915 Einstein published the general theory of relativity, which corrected Newton’s theory and explained, among other things, the discrepancies in the orbit of Mercury. The planet Vulcan only persists today in the TV series Star Trek, where the big-eared Mr. Spock is said to have been born in the planet that never existed.
We are facing now a similar situation: Einstein’s theory does not explain the movement of stars in galaxies. Faced with this problem, as always, there are two possibilities:
·      Either something undiscovered (we call it dark matter) explains the discrepancy.
·      Or the theory must be modified: perhaps general relativity cannot be applied to galaxies without some corrections.
For over two decades, astronomers have tried to save the theory by proposing the existence of dark matter, whose presence (five times more massive than ordinary matter) would explain the discrepancies. But even though it is being sought tirelessly, dark matter has not yet been detected. Is it time to think about changing the theory? Do we need a new Einstein?
Gary Bernstein
In an interview published on August 20, 2016 in a Spanish newspaper, astrophysicist Gary Bernstein, one of the defenders of the existence of dark matter, explains the alternative in these words:
What are the footprints of dark matter?
We observe galaxies moving faster than they should, unless they contain much more matter than we can show.
What if something else were speeding them up?
Some believe that the law of gravity fails in those galaxies.
Is this a serious thought?
Newton just took measures in the solar system. The galaxies are a trillion times larger... perhaps Newton’s laws are not applicable to them.
Is that scientific?
Shall we accept that what we can experiment and prove will never explain the whole universe? ... Either the law of gravity is wrong, or there are particles beyond what we can see, touch or experiment with.

Notice the interviewer’s surprise. He thinks that suspecting that Newton’s laws may not be correct is unscientific. Perhaps he believes that being scientists means never doubting of the truth of our theories. Unfortunately, many scientists also fall into this mistake.

Manuel Alfonseca

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