Quantum Physics changed the way we understand Nature. Nature is not as deterministic as we once thought. There are many secret passages that are awaiting discovery.
On the other hand, no one seems to know exactly
what it means!
If only people knew how frustratingly and yet wonderfully un-mundane the quantum world really is, how our familiar and solid reality ultimately rests so tenuously on the unfathomable ghostly reality beneath. No need any longer for tales of Bermuda Triangle or poltergeist activities; quantum phenomena are much stranger.
I must make it clear from the outset that it is not the theory of Quantum Mechanics that is weird or illogical. On the contrary, it is a beautifully accurate and logical mathematical construction that describes Nature superbly well. In fact, without Quantum Mechanics we would not be able to understand the basics of modern chemistry, or electronics, or material science.
Jim Al-Khalili
The year is 1900.
There are problems with some experiments in physics. Scientists are not able to explain Blackbody Radiation. Their inability to find a physical interpretation results in the
Ultraviolet Catastrophe!
Max Planck is forced to create the quantum.
BlackBody
Radiation
Curve
Max Planck does not like this idea.
1) Einstein's photoelectric theory is based on the fact that electrons are ejected from a metal surface with an energy proportional to the frequency of the incident wave.
2) Maxwell's electromagetic theory states that the intensity (amplitude) of the wave is proportional to the energy. These are quite different ideas.
3) According to Planck, the energy of the light quantum is given by E=hv, and so the kinetic energy of the ejected electron is expected to increase with increasing frequency. Increasing the intensity of the incident radiation increases the number of light quanta on the surface, increasing the number, but not the kinetic energies, of the ejected electrons.
4) The fact that increasing the intensity (energy) substanially will not release any electrons at all, unless the frequency of the wave is above the work function is quite problematic for the classical wave theory of light.
5) Photoelectrons are emitted from the surface almost instantaneously, even at low intensities. Classically, we expect the photoelectrons to require some time to absorb the incident radiation before they acquire enough kinetic energy to escape from the metal.
Bohr saw quantum mechanics as a generalization of classical physics although it violates some of the basic ontological principles on which classical physics rests. These principles are:
1) The principle of space and time, i.e., physical objects (systems) exist separately in space and time in such a way that they are localizable and countable, and physical processes (the evolution of systems) take place in space and time. Gone
2) The principle of causality, i.e., every event has a cause. Gone
3) The principle of determination, i.e., every later state of a system is uniquely determined by any earlier state. Gone
4) The principle of continuity, i.e., all processes exhibiting a difference between the initial and the final state have to go through every intervening state. Gone
5) The principle of the conservation of energy, i.e., the energy of a closed system can be transformed into various forms but is never gained, lost or destroyed. Gone
The nature of motion predicted by quantum mechanics is very different from our ordinary experience. At first you will have trouble accepting that the motion of electrons could be so much different than the motion of much heavier objects like baseballs.
Moreover, quantum mechanics does not predict precise trajectories. In fact, knowing the precise position of a particle is generally impossible in quantum mechanics. Instead, quantum mechanics only predicts the relative likelihood that a particle will be found in a variety of locations -- much different from classical mechanics! Despite these differences, the predictions of quantum mechanics coincide with those of classical mechanics for heavy particles, even though they are quite difference for electrons.
Quantum Mechanics
divides the world into two parts, commonly called the [system
and the observer]. Except at specified times the system and
the observer do not interact. An interaction
at those specified times is called a measurement. Quantum
Mechanics predicts all the information that the observer
can possibly obtain about the system. This information can be represented
in different ways. It is often represented in terms of a wave function.
A measurement changes the information an observer
has about the system and therefore changes the wave function of the system.
In quantum theory,
all events are possible (because the initial state of the system is indeterminate),
but some are more likely than others. While the quantum physicist can
say very little about the likelihood of any single event's happening,
quantum physics works as
a science that can make predictions because patterns of probability emerge
in large numbers of events. It is more likely that some events will happen
than others, and over an average of many events, a
given pattern of outcome is predictable. Thus,
to make their science work for them, quantum physicists assign a probability
to each of the possibilities represented in the wave function.
The
Meaning of Quantum Mechanics
Jim Baggot
"We are so used to the notion of a spontaneous transition
that it is, perhaps difficult to see what Einstein got so upset about.
Let me propose the following (very imperfect) analogy. Suppose I lift
an apple 3 meters off the ground and let go. This represents an unstable
situation with respect to the state of the apple lying on the ground,
and so I expect the force of gravity to act immediately on the apple,
causing it to fall. Now imagine that the apple behaves like an excited
electron in an atom. Instead of falling back as soon as the 'exciting'
force is removed, the apple hovers above the ground, falling at some unpredictable
moment that I can calculate only in terms of a probability. Thus, there
may be a high probability that the apple will fall within a very shot
time, but there may also be a distinct, small probability that the apple
will just hover above the ground for several days!
We must be a little careful in our discussion of causality. An excited
electron will fall to a more stable state: it is caused to do so by the
quantum mechanics of the electromagnetic field. However, the exact moment
of the transition appears to be left to chance. In quantum theory, the
direct link between cause and effect appears to be severed."
Physics
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Electron
Microscope
Production
The notion of the observer becoming a part of the observed system is fundamentally new in physics. In quantum physics, the observer is no longer external and neutral, but through the act of measurement he becomes himself a part of observed reality. This marks the end of the neutrality of the experimenter. It also has huge implications on the epistemology of science: certain facts are no longer objectifiable in quantum theory. If in an exact science, such as physics, the outcome of an experiment depends on the view of the observer, then what does this imply for other fields of human knowledge? It would seem that in any faculty of science, there are different interpretations of the same phenomena. More often than occasionally, these interpretations are in conflict with each other. Does this mean that ultimate truth is unknowable?
Implications to HUP
The Principle of Causality
"I'm sorry that I ever had anything to do with quantum theory," he is said to have lamented to a colleague.
