Daily Archives: September 25, 2009
Not Like a Fox
A very thoughtful, and thought-provoking, chapter from an upcoming book.
If I’d had cancer, people would have rallied around, but because I had schizophrenia, few wanted to know.
They were afraid.
Photon Overlap
To measure ultrafast phenomena, researchers often use repetitive trains of very short laser pulses. For example, they can create two pulse trains from the same source and send them along different paths. To measure the length of the pulses within the trains, they shine both at a “nonlinear” crystal. The crystal produces extra light with double the original frequency when two pulses are present simultaneously. By changing the path followed by one train, perhaps making it a micron or so longer, researchers create a delay of a few femtoseconds. As they increase the extra path length, pulses from the two trains become out of sync, which reduces the crystal’s output and indicates the length of the pulses.
Nothing to do with Dogs
The Poisson/Arago/Fresnel spot, which is a great example of the predictive requirement of science; this one being a binary condition. One implication of the hypothesis is that there will be a spot. Either there isn’t a spot, or there is, and that will or will not falsify the hypothesis.
“If Fresnel’s idea is correct, then the edges of a circular obstruction will act as sources of light waves. Most of these will cancel out and produce a shadow behind the object, as expected. But because the path length from the edge to the middle of the shadow is equal no matter where on the edge you start, the cancellation can’t happen and there has to be a bright spot right in the middle of the shadow. This is self-evidently bogus.”