Tuesday, 29 January 2013

Faraday and the light!

Another incredible thing I discovered in these two weeks is that the first to propose the light to be an electromagnetic wave was Faraday and not Maxwell!

Faraday is well known for his concept of force line that brought to the modern idea of field, and substituted the Newton idea of force at distance.
Let me do a brute synthesis of the story. When Faraday, yet unknown, started to play with electricity and magnetism, there were a lot of experiments around, the last one by Oersted linking electricity and magnetism, where a current carrying wire was able to deviate (in a quite amazing direction for the period) a compass needle. Faraday (almost) closed the circle, showing with a memorable experiment that a variable magnetic field was able to generate electricity: the born of the electric engine! Thus, electricity and magnetism were able to play each one with the other, somehow exchanging their role.

Then arrived Maxwell, a young genial mathematician, that joined mathematically all these experiment on electricity and magnetism, discovered that the emerging system was not coherent, and invented a new ingredient (the drift current). That's all! Now his theory predicts the existence of a wave composed by a smart combination of electric and magnetic forces and traveling with a speed of 300 000 km/s. The speed of light was recently measured and the value was exactly that! At this point we, physicist, like to joke and let Maxwell pronounce: "Fiat lux, and lux facta fuit".

What is really impressive, is that Faraday, in the absence of the Maxwell formalism, and with an uncomplete experimental framework (as later demonstrated by Maxwell), was able to hypothesize that the light was an electromagnetic field! This is pure genius, no any math, no any logic can interpret this intellectual leap.

A possible, very weak, basis for Faraday idea seems to be a quite complex experiment he made on the effect of magnetism on light polarization.
Et si le temps n'existait pas? Un peu de science subversive by Carlo Rovelli.

Due to a prolonged flue I had the nice "opportunity" to stay two weeks at home in the first half of January, thus I made some readings that deviates from the usual home and work back and forth routine.

Rovelli, twenty years ago, was one of the founders of a particular approach to unify Einstein general relativity and quantum mechanics. For me the booklet is quite intriguing for the rediscovery of the different conceptions of time and space, and in particular to realize we are often driven by a priori conceptual models of which we ignore the force or, worst, we are not even conscious.

Roughly speaking, in Newton age there was a debate on the nature of space and time. Newton made his proposal, of whose limits was himself well aware, and given the incredibly strong explicative and predictive power of his machinery, his ideas dominated human minds for more than three centuries. Newton equations and Newton gravitation law required a fixed spatial background, a kind of box containing all the objects, with an existence in itself, over or better inside which all the events unroll.

Pascal and Leibnitz, each one with some differences, thought that the space do not exists in itself, but it is just the set of relations between the objects. For them, the absolute space cannot exist: of a single object we cannot say if it is moving or at rest, it is meaningless the question itslef given the absence of any reference.
About the time, from an operational point of view, what an experimenter do is to take a physical phenomenon as a reference and compare the phenomenon under study to it. She will use for instance the small pendulum oscillations (as Galileo) or refer to more modern things as the emission or absorption of photons between two specific energetic level of a given atom ("atomic" watches) ... but the essence will be always the same. She also need to set up a well defined system to make the comparison, given that to define simultaneity of events not spatially co-localized will require some sync work, that is (not immediate but) feasible.

Thus, as Newton observed, there's no way to evaluate the absolute time, nevertheless its introduction will far simplify the equations and forced him to use it. What is the simplification? Suppose, for instance, to have five physical measurable things A, B, C, D, E ... (energy, position, velocity, ...). If you can assign to each of them a running label t (as time) you end up with just five temporal functions A(t), B(t), C(t), D(t), E(t). That's all. Otherwise you are forced to make all the comparison of each one to the other, that is A as a function of B, C, D. E, B as a function of C, D, E, ... and so on ... that is twenty-four functions!

Newton ideas had a well-deserved place in our scientific development, he was one the "Great", and his game worked very very well, partly even after Einstein, at least up to now :-).
Why a blog? Because I'm curious and would like to share some ideas, readings, pictures, puzzles, questions (many) and answers (really a few) with curious people. About what? Mainly about science, but not Physics exclusively, ... a lot of Biophysics, Biology and Immunology too will be around, and Math of course. I hope writing will help me to focus the ideas too and the -more than welcome- discussions will improve knowledge for everybody. Physics studies shaped my mind and provided me many instruments to be critic and make sense of what is out there, that is why I entitled this way the blog, but it could be better thought as ... a Bazaar, yes I like it ... it will be a بازار