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Posts Tagged ‘experiments’

Rules

In experiments, induction, justificationism on 20/08/2011 at 7:29 am

A philosophical problem has the form: I don’t know my way about. (Ludwig Wittgenstein)

Up until the late 19th century every observation was compatible with Newton’s theory of gravity. All these observations are also compatible with Einstein’s General Theory of Relativity. Two quite different theories were compatible with the same set of observations; therefore, one cannot know they have derived true theories from observations.

Assume we have a long series of numbers. They go on: 2, 4, 8 … What is the next number in the series?

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Change

In experiments, fallibilism on 20/07/2011 at 7:06 am

The problem: if a scientist abandons theory A after deciding that it does not stand up to criticism (say, the theory fails a crucial experiment), the scientist could make the wrong choice. Theory A could very well be true, or be more approximately true (have more verisimilitude), than the replacement theory B.

Why is this a problem?

  1. The crucial experiment could produce a false positive, so that a scientist rejects the theory rather than rejecting the result of the test. Naturally, the scientist’s replacement theory B would have less verisimilitude.
  2.  The crucial experiment produces a true outcome, but theory B is more approximately true than theory A over this small range; however, theory B has overall less verisimilitude than theory A.

This problem applies to any number of crucial experiments: a scientist may abandon a theory with a high degree of objective verisimilitude because he mistakenly thinks it has a low degree of verisimilitude.

The set of preformed crucial experiments will be very small, smaller than all crucial experiments available to the scientist at any one time, which in turn will be very, very small compared to all crucial experiments. This further assumes that the results of the tests are easily decidable.

Think of it this way: the scientist has insufficient reasons, which amount to nothing, after preforming a crucial experiment. Now, just keep adding additional insufficient reasons. What does the scientist have? Nothing.

What have we learned? There cannot be any evidence that anything can raise the objective probability of future success.

Assume that 1 is not an immediate problem. All results of tests are conclusive. The problem still remains, and appears to be far more robust and serious for the scientist than Quine’s problem. Now, how do we deal with 2?

One solution is to tentatively reject A and adopt B. After all, they’re only theories. Truth takes second to coherence, but the rule of operations is the negation of Quine’s holism and goes against Popper’s claim that scientists are interested in increasing verisimilitude in scientific theories. If anything, this best approximates van Fraassen’s position on empirical adequacy.

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Einstein

In experiments on 07/07/2011 at 11:32 am

There are two ways that a theorist goes astray: (1) The devil leads him by the nose with a false hypothesis. (For this he deserves our pity) (2) His arguments are erroneous and sloppy. (For this he deserves a beating). (Einstein, letter to Lorentz, The Collected Papers of Albert Einstein, Princeton University Press, (Princeton, NJ, 1987-2006), volume 8A, p. 88)

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Credible Explanations

In experiments on 19/06/2011 at 10:35 am

Credible explanations grow from the combined testimony of three more or less independent, mutually reinforcing sources — explanatory theory, empirical evidence, and rejection of competing alternative explanations. (Edward Tufte)

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Light

In critical rationalism, experiments on 15/06/2011 at 9:22 pm

As the problem presented itself to us there were three possibilities. There might be no deflection at all; that is, light might not be subject to gravitation. There might be a ‘half-deflection,’ signifying that light was subject to gravitation, as Newton had suggested, and obeyed the simple Newtonian law. Or there might be a ‘full deflection,’ confirming Einstein’s instead of Newton’s law. I remember Dyson explaining all of this to my companion Cottingham, who gathered the main idea that the bigger the deflection, the more exiting it would be. ‘What will it mean if we get double the deflection?’ ‘Then,’ said Dyson, ‘Eddington will go mad, and you will have come home alone. (S. Chandrasekhar, Am. J. Phys. 47, 212 (1979))

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Rutherford

In experiments, fallibilism on 15/06/2011 at 4:01 pm

The famous experiment of Geiger and Marson found that when they shot alpha particles at a very thin sheet of gold foil, a few of the alpha particles – about one in twenty thousand – were reflected by the foil rather than merely deflected. As Rutherford said later:

It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a fifteen-inch shell at a piece of tissue paper and it came back and hit you. (Ernst Rutherford, ‘The Development of the Theory of Atomic Structure’, in Background of Modern Science, edited by J. Needham and W. Pagel, Cambridge University Press, Cambridge, 1938, pp. 61-74.)

This remark of Rutherford’s shows the utterly revolutionary nature of the discovery: no one expected to see alpha particles rebound off gold, and yet it was conceivable. Rutherford realized that the experiment refuted J.J. Thomson’s model of the atom, and he replaced it by his own model of the atom.

This was the beginning of nuclear science.

It also happens to fit exactly within Popper’s method of falsificationism.

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