Re: What technologies were developed from Young's light experiment?

You asked 2 complex questions: 
First one:  What technologies were developed directly and indirectly from
Thomas Young's double slit diffraction experiment? I am having difficulty
learning what we got from the results.
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You probably know much of this since you are asking the question, but I
just want to set the stage for other people who migh be reading. For many
years the nature of light was in dispute. Some scientists, including the
very influential Issac Newton, believed it was particles. Other scientists,
led by Huygens, claimed it was made up of waves. So Thomas Young, whose
real job was as a physician, decided he would see if he could get beams of
light to interfere with each other, the way that the wave theory implies
they should. So you already know that he did find an interference pattern,
and that this was very important in convincing people that light was really
wavy. (By the way, it also means that light is a transverse wave. That
means that the waving is side-to-side or up-and-down.))
Good link for Young:  http://en2.wikipedia.org/wiki/Thomas_Young_(scientist)

So what good is that, you ask? Around the same time there was another giant
of science, Michael Faraday, working with crude copper wire and crude
batteries (called voltaic piles in those days). He discovered
electromagnetic induction, which is the ability of a changing magnetic
field to make electricity in a nearby wire. He also demonstrated
electromagnetism, which is the ability of a current in a coil of wire to
make magnetism. So electricity and magnetism were tied together. With the
knowledge that light is wavy, and with the knowledge that electric fields
and magnetic fields are tied together, yet a third guy, James Clerk
Maxwell, put together a beautiful, powerful mathematical description of
light and radio waves, which are all really pretty much the same stuff,
namely waving electric and magnetic fields.
Faraday link: http://www.ibiblio.org/gutenberg/etext98/fdayd10.txt


The scientists of that time, and many still, just want to understand the
world around them. The practical value was not that important to them. It
was the thrill of learning something new about what the world is made of
and how it hangs together. The search goes on, by the way.

So all of that was still theory, and are a bunch of theories good for
anything? In the few years that followed, radiotelegraphy, then radio, then
television were all developed. Is that important enough to impress you? It
all stems from that basic knowledge that light is made of waves. You cannot
make those other advances without that basic knowledge. As Yoda might say,
"Powerful stuff, theory is. Use the Theory, Luke!"

Question 2: Also do the results help the understanding of "QUANTUM
MECHANICS" and if they do does that mean that the technologies we got from
"QUANTUM MECHANICS" are indirectly from the double slit experiment done by
Thomas Young.

I do not really think that the double slit experiment led in any particular
direct path to quantum mechanics. It did turn out that quantum mechanics
predicted that basic particles would behave like waves, but not because of
the double slit experiment. I think that was a big surprise. Physicists
knew a lot about the type of equations that described waves, so they
recognized that the solutions had wavelike features. Because the solutions
to the quantum mechanical equations had a phase, thosee equations predicted
that particle might be able to interfere with each other or themselves. So
the understanding of how waves worked helped the development of quantum
mechanics quite a bit.

A variation of that double slit experiment was done by Davison and Germer
in the early 20th century.  In his Nobel_Lecture
Davison starts his history of how science proceeded toward his results by
starting with Young's experiment. They each did experiments in 1927 that
shot electrons at a crystal. Crystals are very orderly arrangements of
atoms. So the rows of atoms were very much like a bunch of slits, all
arranged next to each other. The electrons bounced off the crystals with a
diffraction pattern. So you could call this the thousand slit experiment.
He was able to show interference in the reflected electrons. This
experiment along with the Bohr description of the atom, the photo-electric
effect, and Plank's theory of blackbody radiation were the experimental
basis and experimental confirmations of quantum mechanics that grew up
between 1905 and 1930. Just as it had been in the early 1800's when Young
and Faraday were active, the early part of the 1900's was an extremely
exciting time in physics.

On the technology part of your second question, I cannot think of a lot of
technologies that directly depend on quantum mechanics. I suppose you could
call nuclear energy and nuclear weapons the main direct consequence of
quantum mechanics. You might also be able to make an argument that the
transistor and all of the computer technology is based on solid state
physics has a lot of quantum mechanical material in it. That seemed to me
to be an weaker, indirect connection. Photonics, or the transmission and
control of signals by light has definitely become important in
communications applications and has a fundamental quantum mechanical basis.
My not particularly well-informed understanding of the development of the
transistor is that the experimenters had been working on the electrical
properties of semiconductors. But let's check. It might be informative to
look at the Nobel speeches by the inventors of the transistor.
They are online at 1956_Physics_Nobel_speeches

   (Please notice in the first couple of pages of Shockley's lecture that
you will find that he thought that asking what technologies we get from
science is much less important than geting new and fundamental ideas.)

Bardeen's lecture gives the best description of transistor's invention: 
Bardeen's_Nobel_Lecture

Sure enough, quantum mechanical ideas, both the hole theory that arose from
Dirac's study of the relativistic wave equation and the photoelectric
effect explained by Einstein, were very important to those researchers'
understanding of the physics of transistor. But I still do not see a direct
line back to Young's explorations of the character of light. Anyway, we are
now talking about the relationship of ideas across 150 years. Scientific
connections get pretty tangled up over a century and a half.

PBS's program:
Transitorized!

I hope that helps a bit. 

David Winsemius