Re: [Marxism] Einstein and the Revolution of Physics

[Les Schaffer <schaffer@xxxxxxxxxxxxx>]

Walter Lippmann quoted a Cuban article on Einstein's visit to the island:

> His main discovery was to make public that a particle of matter can become a
> huge amount of energy.


"discovered" in September 1905, by 1910 Einstein had temporarily given
up hope of verifying his prediction. the equivalence of mass and energy
was not confirmed in a careful experimental test until June 1932 by
Cockcroft and Walton. using their newly developed and home-grown 600,000
volt accelerator (attaching such a high voltage system to an *evacuated
tube* was one of their major achievements), they accelerated protons at
Lithium atoms, splitting the latter and producing two alpha particles.
since the weights of the two alpha particles together is less than that
of the heavier Lithium atom, they could calculate the excess energy
released from the Lithium's "excess" mass using e=mc^2, and that matched
with their measurement of the energies of the alphas.

this first nuclear reaction released approximately 14.3  (+/- 2.7)
million electron volts of energy (the modern value is 17.337 +/- 0.007)
. but these alphas will not split other atoms. so the energy yield was
small compared to the fission of uranium that came 7 years later.
uranium releases 200 million electron volts of energy AS WELL AS several
extra neutrons upon fission. the chain-reaction is the real killer. The
German Jew Lise Meitner was the first to put together a working
theoretical model for this process that included a *mechanism* for
conversion of this mass to energy, a story for another day.

of interest historically is the fact that it was not until February of
1932 that the nucleus' constitution was understood. prior to the
discovery of the neutron by Chadwick, the nucleus was presumed to
consist of combinations of protons and electrons. only when this
theoretical error was cleared up could the connection between nuclear
binding energy theories (utilizing e=mc^2) fit so neatly with precise
experimental determination of nuclear masses (Aston's mass spectrograph)
that the whole e=mc^2 and nuclear physics project really get off the
ground.

in the fission of uranium, only 0.09% of the mass of the U atom is
converted into energy. the COMPLETE conversion of particle mass into
energy was not achieved until electron-positron annihilation experiments
were run, i believe first in the early 60's:


http://livefromcern.web.cern.ch/livefromcern/antimatter/history/AM-history02-b.html

positrons are the anti-particle to the electron. the early annihilation
experiments were at low collision energies and produced only photons --
light particles with no (rest) mass, all energy. as colliders became
more sophisticated and powerful, these annihilation experiments came to
reveal whole new classes of sub-atomic particles. now it is believed
quarks can themselves be produced in energetic enough annihilation-type
collisions. in effect, the annihilation mechanism converts matter
briefly into pure energy, where upon that energy can interact with the
(modern) vacuum to produce new and exotic particles.

such matter/anti-matter experiments have themselves a long entangled
history of theory: in 1928 Dirac mixes special relativity and quantum
mechanics in another e=mc^2-like tour de force to predict
anti-particles, along with subsequent experimental discoveries, for
example, observations of anti-particles, annihilation signatures, and so
forth.


moral of the story: the working out of  a (scientific) revolution takes
time. the subsequent effort combines both theoretical and experimental
labor.

postscript:  PET -- positron emission tomography -- is a modern medical
diagnostic technique that depends on these annihilations taking place,
between said positrons, and electrons in the body's tissues.

les schaffer

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