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Sunday, January 10, 2016

Philosophers want to know why physicists believe theories they can’t prove

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"It’s often assumed that physics and philosophy are at opposite ends of the academic spectrum." notes Olivia Goldhill, Weekend writer at Quartz.
There's no empirical evidence for string theory. (Discovery channel documentary)

In fact, they’re close—so close that they can overlap, with professors sometimes switching between the two fields as they work to advance our understanding of highly abstract subjects in theoretical physics.

Photo: Richard Dawid
One such professor is Richard Dawid, a philosophy of science researcher at Ludwig Maximilian Universität Munich, who has a PhD in theoretical physics and began his career researching particle physics. He transitioned to philosophy, he tells Quartz, to investigate how physicists can come to believe in certain theories without necessarily having the empirical evidence that proves them.

The criteria for establishing a theory, he discovered, is not in itself subject to scientific enquiry. “They’re considered background assumptions,” says Dawid. “It’s a question that’s driven by physics but it’s a philosophical question.”

Physicists have long relied on a notion advanced by philosopher Karl Popper, that a theory is scientifically valid if it is falsifiable. But in recent years, many serious physicists seem to have abandoned this model. String theory, for example, is one of the most exciting ideas in modern physics. But it’s not testable—so how can physicists be confident that it’s sound?

String theory is at the crux of physics, as it links quantum mechanics with Albert Einstein’s theory of relativity.
The theory argues that subatomic particles are tiny, one-dimensional strings, rather than zero-dimensional points, and are constantly vibrating. It’s thought that at least 10 dimensions are curled up within the strings—but the particles themselves are too small to be detected, let alone these extra dimensions.

“String theory is not a fully developed theory,” Dawid tells Quartz. “Some predictions string theory may give cannot be calculated. It’s not accessible by present-day experiments or experiments in the foreseeable future.
So what can we do with a theory of that kind? We don’t want to live with a theory for 50 years and have no clue whether it’s viable or not.”

The implausibility of testing string theory not just now, but for decades to come, is a new problem for physics. Although Einstein never conducted a single experiment, he put forward his theory in 1915 and, by 1919, experiments found evidence to support one of his key predictions, that a gravitational field causes light to bend.

In cases where empirical evidence is unavailable, Dawid has identified three reasons why people believe in the veracity of the theoretical physics model; none of them are particularly strong by themselves but, in conjunction, he believes that they present strong grounding for trusting an un-provable theory.
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Source: Quartz


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