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Quantum mechanics dominated most of twentieth century physics. It shook the very foundations on
which classical physics stood. Many people find quantum mechanics non-intuitive, as it goes against
one's notion about the way things work. Einstein, who kept on searching for an alternate theory until his
death, thus did not accept it.
As such, Quantum mechanics allows a very accurate mathematical model of subatomic particle
interactions. It states that every object exists in a particle wave duality wherein every particle has a
frequency and wavelength, properties of waves, and also mass and velocity, properties of particles. The
wavelength of a particle is inversely related to its momentum. Hence particles behave both like waves
and particle.
Another interesting feature is that you cannot predict both the wavelength/frequency and position of an
object at a given time with arbitrary precision. This constitutes the Heisenberg principle which states that
the product of error in particle position and particle wavelength has to be more than or equal to the
Plank’s constant upon wavelength. It was this uncertainty which Einstein resented. "God does not play
dice with the world," he has said.
This uncertainty also brings about certain complexities. Since the position of an electron in an atom
cannot be predicted, it is thus made to constitute an electron cloud that covers the atom with its shape
dependent on the orbit characteristics.
Quantum mechanics is strange because it reduces everything down to probabilities. We can predict how
many electrons in a beam will scatter when moving through a screen with holes in it, but we cannot
predict which electron will scatter in which direction. This is why when a beam of electrons is shot
through two small holes, they end up creating an interference pattern on the other side instead of
making two beams. Even if they are shot one at a time, they create an interference pattern (how can
one electron interfere with itself?). It is very strange, but it shows the wave properties of matter. In
addition, the state of a particle is unknown until it is finally measured or observed. Once measured, the
property observed is based on the probability of the particle being in that state.
It was this interference of a single electron with itself which caused a minority of scientists to come up
with an alternate theory which hypothesized that the electron actually underwent interference with other
electrons which resided in various other states in many other universes parallel to ours. This was
criticized by many physicists and thus has not been adopted.
There is also a finite probability that particles may "tunnel" through or make a quantum leap through
impenetrable barriers. If an electron is placed in a box, it usually does not have enough energy to
penetrate the walls of the box. However, according to quantum theory, the probability wave of the
electron will spread through the box. Depending on the size of the box, you can calculate the probability
that the electron will end up outside the box. Many electronic devices, even the computer you are using
right now, are based on components that allow electrons to tunnel through barriers. However, this also
means that there is a probability for even impossible events to occur too. You can calculate the
probability that you will suddenly disappear and tunnel outside your house. However, the probability is so
small that you would have to wait longer than the lifetime of the entire universe even to see if that could
happen. This probability is based on your wave function. The probability of you staying where you are is
almost infinitely higher than the probability of you being somewhere else.
Many new theories in particle physics have ever since been developed in accordance to quantum
mechanics that explains sub atomic particle interactions. The fundamentals of these interactions are:
- Forces are created by the exchange of discrete packets of energy called quanta. This contrasted
Einstein's geometric picture of forces. When two electrons bump into each other, they repel
because they exchange a packet of energy. The energy of a quantum is in units of Planck's
constant (h = 6.6 x 10-34 J s). In our everyday world, quantum theory is negligible, but the
quantum corrections begin to appear when you enter the subatomic world, accounting for the
strange properties of particles.
- Different forces are caused by the exchange of different quanta. Electromagnetic forces are
caused by the exchange of photons (also known as 'virtual' photon because the exchange of these
cannot be observed). The nuclear strong forces are caused by gluons. Exchange of W and Z
particles and mesons are responsible for the nuclear weak forces. These three forces (excluding
gravity) are unified by the Quantum Theory.
The origins of Quantum mechanics go back to the early 1900's. Max Plank first hypothesized that the
energy of light was proportional to its frequency, since this only seemed to explain the frequency
distribution of a black body. Einstein later developed on the idea to state that light was made up of
packets of energy which could by wholly absorbed or reflected as opposed to a beam of continuous light,
to explain the properties of photoelectric effect. He was awarded the Nobel Prize for physics in 1960 in
recognition of his work on the phenomenon. Little did it seem to him, that this would be the start of a
theory that he would later oppose himself. It was later complete when in 1926, Erwin Schrödinger,
Werner Heisenberg both developed the quantum wave function equation independently.
Work is still underway to integrate the gravitational interactions in the theory that would then explain
every single phenomenon in physics. Existence of a particle whose exchange leads to gravitational
interactions (a graviton) has been speculated.
Source: ThinkQuest
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