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the observer) stretch our credulity, but with an open mind and a faith in
classical logic and experiment, they can be accommodated.
Newton meets Schrödinger and Heisenberg
On the other hand, the concepts of QM are so strange that even a genius such
as Einstein could not accept them. Why do we see so little evidence of these
weird quantum phenomena, except in the world of atoms and fundamental
particles?
Since its earliest days, it has been realised that QM should transition
smoothly into classical mechanics as one moves from the microscopic world
of fundamental particles and atoms to the macroscopic world of everyday
objects. This was recognised by Nils Bohr and is given the name of Bohr’s
Correspondence Principle.
Bohr showed how for macroscopic systems, the energies involved in the
interactions of their components are much larger than the energies of individual quantum transitions, and in this case the quantum results reduced to
those expected from classical mechanics. In addition, macroscopic bodies are
comprised of many smaller particles interacting with each other. The wave
functions of these smaller particles are continually being jumbled together as
the particles move about and swap energies. The resultant composite wave
function for the macroscopic body is therefore “decoherent”, which means
that it does not produce interference effects. When we walk through a narrow
doorway, we have no chance of being diffracted away from our normal path,
as a quantum particle would be, passing through a narrow slit.
This all sounds well and good. However, not everybody at the time was
convinced by Bohr’s arguments, and the controversy is still alive. There are
some simple quantum systems, e.g. a particle confined in a box, that do not
pass smoothly from a quantum mechanical to a classical description as the
energy of the particle increases [5]. Nobel Laureates, Albert Einstein and Max
Born, disagreed strongly on this issue, leading to Born dismissing Einstein’s
obduracy to be the result of his old age, a blow below the belt if ever there
was one.
As we have seen in Chap. 5, Schrödinger’s qualms about the QM-Classical
interface led him to formulate the Schrödinger’s Cat thought experiment to
emphasise the problem. It may seem rather ridiculous to consider a cat as
being in a superposition of states, one in which it is alive and one in which it
is dead. However, what if the cat is replaced by a virus? These are considered
by many to be living creatures.
R. Barrett and P. P. Delsanto
the observer) stretch our credulity, but with an open mind and a faith in
classical logic and experiment, they can be accommodated.
Newton meets Schrödinger and Heisenberg
On the other hand, the concepts of QM are so strange that even a genius such
as Einstein could not accept them. Why do we see so little evidence of these
weird quantum phenomena, except in the world of atoms and fundamental
particles?
Since its earliest days, it has been realised that QM should transition
smoothly into classical mechanics as one moves from the microscopic world
of fundamental particles and atoms to the macroscopic world of everyday
objects. This was recognised by Nils Bohr and is given the name of Bohr’s
Correspondence Principle.
Bohr showed how for macroscopic systems, the energies involved in the
interactions of their components are much larger than the energies of individual quantum transitions, and in this case the quantum results reduced to
those expected from classical mechanics. In addition, macroscopic bodies are
comprised of many smaller particles interacting with each other. The wave
functions of these smaller particles are continually being jumbled together as
the particles move about and swap energies. The resultant composite wave
function for the macroscopic body is therefore “decoherent”, which means
that it does not produce interference effects. When we walk through a narrow
doorway, we have no chance of being diffracted away from our normal path,
as a quantum particle would be, passing through a narrow slit.
This all sounds well and good. However, not everybody at the time was
convinced by Bohr’s arguments, and the controversy is still alive. There are
some simple quantum systems, e.g. a particle confined in a box, that do not
pass smoothly from a quantum mechanical to a classical description as the
energy of the particle increases [5]. Nobel Laureates, Albert Einstein and Max
Born, disagreed strongly on this issue, leading to Born dismissing Einstein’s
obduracy to be the result of his old age, a blow below the belt if ever there
was one.
As we have seen in Chap. 5, Schrödinger’s qualms about the QM-Classical
interface led him to formulate the Schrödinger’s Cat thought experiment to
emphasise the problem. It may seem rather ridiculous to consider a cat as
being in a superposition of states, one in which it is alive and one in which it
is dead. However, what if the cat is replaced by a virus? These are considered
by many to be living creatures.