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| "Graviffraction" - Einstein's dream |
By:
Charles Douglas Wehner |
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It was in the year between 1904 and 1905 that Albert Einstein
embarked upon three studies that would change the face of
physics. The first was the study of heat. He studied Brownian
Motion - the way in which particles in a colloid jiggle about.
This explained how energy is stored in material as warmth.
Ludwig Boltzmann had discovered the mechanical equivalent of
heat.
The second study took him into the realm of photoelectrics. Max
Planck had discovered that light consists of a kind of "atoms".
The term "atomiki" (indivisibles) had been coined by Democrit of
Smyrna, who stated that only atoms and free space are real. The
term was picked up by Dalton and JJ Thomson as the smallest,
indivisible piece of material. So Planck, in his search for a
new word, introduced the concept of a "quantum" for the smallest
piece of energy. Planck's constant, when multiplied by the
frequency of any particular colour of light, will tell you how
many watt-seconds are the least amount of light of that colour
that are possible.
The third study by Einstein went into the nucleus of the atom,
in the search for an explanation of the riddle of radium. How
can a piece of metal stay warm - seemingly forever? Where is the
energy coming from?
Einstein's second work - on the photoelectric effect - was the
one that brought him the Nobel prize. It related to the puzzle
that light can travel at a huge, but fixed and finite, speed
through free space - and therefore must consist of nothing
solid. Nevertheless, when it collides with something it can
cause that thing to move.
Such calculations are traditionally based upon studies of
momentum - the product of mass and velocity. We know what the
mass is - it is nothing at all, because light is nothing at all.
We also know the speed of light. In a vacuum, it is known as c
(which is about 300 million metres persecond, or 186 thousand
miles per second).
So when we use the MKS system (metres, kilogrammes and seconds),
we multiply zero by three hundred million - and this gives us
the momentum of light. It must surely be nil.
However, when light hits an atom of metal it can throw out an
electron from the metal. This is the photoelectric effect.
Planck goes into some detail about the quantization of energy in
his Nobel prize lecture:
http://nobelprize.org/physics/laureates/1918/planck-lecture.html
So we can say that one quantum of light delivers one single
electron.
The fact that the electron moves means that it has momentum.
That is the product of the mass of the electron and its speed.
So when we divide the momentum by the speed of light, we come up
with the mass of a quantum of light. This is a sensation. Energy
should be weightless, but here we find that it has mass.
Einstein then continued his studies of the movement of the
electron by likening that movement to its behaviour under the
influence of a voltage. It turns out that for each frequency of
light, there is an "electron-volt" rating which describes what
would happen if that light struck an electron. The electron-volt
value can be obtained from Planck's result in Joules
(Watt-seconds) simply by multiplying by a special constant.
His researches showed that the electrons are held in place
inside the atoms by means of known voltages, the work functions.
When light sets them free, the energy of the light in
electron-volts is divided up two ways. The first part of the
voltage if that which is needed to overcome the work function.
The second part is the energy that is left over in the liberated
electron.
This work on the photoelectric effect was so important because
it tied together many loose ends of physics. The spectral lines
of light could now be defined as electron-voltages, and one
could tell exactly where the light originated in the atoms. The
atom was now looked upon as an electrical machine, and one could
predict how metals would behave when used as photocells, for
example. So the whole world of photoelectrics arrived - with
sound-stripe on film and invisible-ray burglar alarms. At the
same time, one could predict the properties of metals in an
electroplating bath (although the photoelectric work-function
was becoming supplemented with the electrochemical
work-function).
Einstein received the 1920 Nobel prize for physics - but it was
delayed for a year. He received the prize itself whilst on board
a ship visiting Japan. His lecture to the Nordic Assembly of
Naturalists was not his acceptance speech, therefore. Already he
is thinking of relativity:
http://nobelprize.org/physics/laureates/1921/press.html
We have entered into a world where matter has mass (weight under
standard gravity), and so also has energy. But are the two kinds
of mass the same?
When we have a lump of material of mass M1, and place it at a
distance D from a second piece of material of mass M2, we get an
attraction between the two.
The law is simple. It is M1 times M2 divided by D and divided
again by D.
That calculation defines the acceleration, or pull, that one
piece of material will exert on the other.
But what of light?
Max Planck had said that the smallest quantum of light is h
times v. Here h is Planck's constant and v is the frequency of
that light.
Einstein now delivered his famous cliché (that E=mc-squared). So
the mass m is E divided by the speed of light and again by the
speed of light.
>From this, we discover that the smallest "mass" of light is h
times v divided by c divided by c.
We have seen that c is an enormous number. When we divided h
times v by c we get a truly tiny quantity of mass. A further
such division makes it ridiculously small. Nevertheless, the
smallest quantum of light is not weightless - it is almost
weightless.
If we want to take a photograph without a lens, we can make a
pinhole camera. A bundle of light-rays will go through the
pinhole to the film, and the sharpest detail on the resulting
image will be only as sharp as the pinhole.
Now we make another camera, with a pinhole half as high and half
as wide. We need to expose the film for four times the time, but
it does indeed become twice as sharp.
Now we make another, with the pinhole four times smaller. At
some point, we get a serious disappointment. The exposures are
getting longer, but the images are not getting any sharper.
What is happening is that the quanta of light, as they pass
through the tiny pinhole, are forced so close together that
their masses interact. Rays of light are pulling rays of light.
This is known as diffraction.
So the rule M1 times M2 divided by D-squared seems to hold for
the mass of energy as well as for the mass of matter.
It was about this time that questions were being asked as to
what would happen in one of the masses - say M1 - was due to
matter, whilst the other - M2 - was due to energy.
Einstein's answer was simple - try it.
As the mass of a quantum of light is so tiny, we need to
counterbalance it with some enormous object if we are to see
some visible effect. Einstein suggested the sun.
The sun is about a hundred-thousand times heavier than the
earth. So it is extremely heavy. If Einstein's prediction were
to come true, a quantum of light of mass M2, skimming past the
sun with its huge mass M1, should be pulled off course.
This would not be gravity, because gravity is something exerted
by matter upon matter.
This would not be diffraction, because diffraction is something
exerted by energy upon energy.
This would be a half-way thing, neither one nor the other. It
would be graviffraction. It would be the gravity of the sun
causing the diffraction of the light.
One has to be careful, because a slight haze of gasses in the
vicinity of the sun may act as a lens - causing refraction
rather than diffraction.
When Einstein predicted the bending of light by the sun, in
1916, scientists waited three years for an eclipse.
Sure enough, as stars and planets on the opposite side of the
solar system tried to drift behind the edge of the sun, the sun
pulled the rays of light off course. The stars stayed visible
due to the curved light path. The prediction had been confirmed.
Charles Douglas Wehner
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