24 DEC 2013 by ideonexus


However, the subject need not be an esoteric one for a gedankenexperiment to be fruitful. My own favorite is Galileo’s proof that, contrary to Aristotle’s view, objects of different mass fall in a vacuum with the same acceleration. One might think that a real experiment needs to be conducted to test that hypothesis, but Galileo simply asked us to consider a large and a small stone tied together by a very light string. If Aristotle was right, the large stone should speed up the smaller one...
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Gino Segre on the importance and validity of "thought-experiments," using Galileo's disproof of objects falling at different rates as an example.

23 OCT 2013 by ideonexus

 Proof that Objects Fall at the Same Rate

Salv. But, even without further experiment, it is possible to prove clearly, by means of a short and conclusive argument, that a heavier body does not move more rapidly than a lighter one provided both bodies are of the same material and in short such as those mentioned by Aristotle. But tell me, Simplicio, whether you admit that each falling body acquires a definite speed fixed by nature, a velocity which cannot be increased or diminished except by the use of force [violenza] or resistance....
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Galileo's proof is based completely on a thought-experiment, no observation necessary.

27 APR 2013 by ideonexus

 Molyneux's problem

I shall here insert a problem of that very ingenious and studious promoter of real knowledge, the learned and worthy Mr. Molyneux, which he was pleased to send me in a letter some months since; and it is this:- "Suppose a man born blind, and now adult, and taught by his touch to distinguish between a cube and a sphere of the same metal, and nighly of the same bigness, so as to tell, when he felt one and the other, which is the cube, which the sphere. Suppose then the cube and sphere placed on...
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A blind person, familiar with a cube and sphere by touch, is made to see. Without touching the objects, would they be able to distinguish them by sight?

01 JAN 2012 by ideonexus

 Sifting Through Photographs of Our Ancestors to See Evolu...

Find a picture of yourself. Now take a picture of your father and place it on top. Then find a picture of his father, your grandfather. Then place on top of that a picture of your grandfather's father, your great-grandfather. You may not have ever met any of your great-grandfathers. I never met any of mine, but I know that one was a country schoolmaster, one a country doctor, one a forester in British India, and one a lawyer, greedy for cream, who died rock-climbing in old age. Still, even if...
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A great thought-experiment that takes us all the way back to when our ancestor was a fish, but shows us that the neighbors of any ancestor looked identical.