Quantum Mechanics is remarkable for two seemingly contradictory reasons. On the one hand, it is so fundamental to our understanding of the workings of our world that it lies at the very heart of most of the technological advances made in the past half century.
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
on which classical physics rests. Principles such as:
1. The old principle of space and time - that physical objects exist separately in space and time in such a way that they are localizable and countable, and the evolution of systems take place in space and time - is no longer true.
2. The principle of causality - that every event has a preceeding cause - is no longer true.
3. The principle of determination, that every later state of a system is uniquely determined by any earlier state - is no longer true.
4. The principle of continuity - that all processes exhibiting a difference between the initial and the final state have to go through every intervening state - is no longer true.
5. The principle of the conservation of energy - that the energy of a closed system can be transformed into various forms but is never gained, lost or destroyed - is no longer true.
Quantum Physics destroyed what many scientists believed to be the perfect picture of Nature; a deterministic clockwork-like laying out of events in time.
BlackBody Radiation Curve
or, how to avoid the
The UltraViolet Catastrophe
The old wave theory of light predicted that the higher the frequency of the radiation (shorter wavelength) emitted from a blackbody, the greater its intensity. This intensity became infinte at ultraviolet frequencies! Yeah sure. . .
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.
The Photoelectric Effect is
demonstrated in a Digital Camera.
A charged-coupled device replaces the age-old film camera. Incident photons of visible light strike the silicon pixel and generate electrons by the
photoelectric effect.
One electron is released from the silicon for every photon striking it.
The electrons are trapped within the pixel because of a positive voltage applied to the electrodes. The number of electrons that are trapped is proportional to the number of photons striking the pixel.
Each pixel in the CCD array accumulates an accurate representation of the light intensity at that point in the picture.
Atoms in a gaseous state will produce Line Spectra. Gas atoms are far apart and minimally interact with each other. If all the gas atoms are the same they will produce the same spectra.
Solids and liquids will produce a Continuous Spectra because the atoms are so closely packed that there is lots of atomic interaction. Almost any photon energy is possible.
Albert Einstein was completely convinced that Quantum Theory was not 'correct'. He said that Quantum theory was incomplete. That nature, God, does not play dice. Einstein fought for 25 years to prove that the universe was not a Quantum universe. His active participation in proving the incompleteness of Quantum Theory led many scientists to add to the mountains of evidence that supported the theory. Einstein did not like the Quantum Entanglement aspect of nor the Statistical nature that was the very foundation of Quantum Theory.
The Great Polaroid Lens Experiment
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?
"I'm sorry that I ever had anything to do with quantum theory," he is said to have lamented to a colleague.
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."
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