In quantum physics, a quantum vacuum fluctuation
is the temporary change in the amount of energy
in a point in space, as explained in Werner
Heisenberg's uncertainty principle.
According to one formulation of the principle,
energy and time can be related by the relation
That means that conservation of energy can
appear to be violated, but only for small
values of t.
This allows the creation of particle-antiparticle
pairs of virtual particles.
The effects of these particles are measurable,
for example, in the effective charge of the
electron, different from its "naked" charge.
In the modern view, energy is always conserved,
but the eigenstates of the Hamiltonian are
not the same as the particle number operators.
Quantum fluctuations may have been very important
in the origin of the structure of the universe:
according to the model of inflation the ones
that existed when inflation began were amplified
and formed the seed of all current observed
structure.
Vacuum energy may also be responsible for
the current accelerated expansion of the universe.
Quantum fluctuations of a field
A quantum fluctuation is the temporary appearance
of energetic particles out of empty space,
as allowed by the uncertainty principle.
The uncertainty principle states that for
a pair of conjugate variables such as position/momentum
or energy/time, it is impossible to have a
precisely determined value of each member
of the pair at the same time.
For example, a particle pair can pop out of
the vacuum during a very short time interval.
An extension is applicable to the "uncertainty
in time" and "uncertainty in energy".
When the mass is very large like a macroscopic
object, the uncertainties and thus the quantum
effect become very small, and classical physics
is applicable.
This was proposed by scientist Adam Jonathon
Davis' study in 1916 at Harvard's Laboratory
1996a.
Davis' theory was later proven in the 1920s
by Louis de Broglie and became a law of quantum
physics.
In quantum field theory, fields undergo quantum
fluctuations.
A reasonably clear distinction can be made
between quantum fluctuations and thermal fluctuations
of a quantum field.
For the quantized Klein–Gordon field in
the vacuum state, we can calculate the probability
density that we would observe a configuration
at a time in terms of its Fourier transform
to be
In contrast, for the classical Klein–Gordon
field at non-zero temperature, the Gibbs probability
density that we would observe a configuration
at a time is
The amplitude of quantum fluctuations is controlled
by the amplitude of Planck's constant , just
as the amplitude of thermal fluctuations is
controlled by , where is Boltzmann's constant.
Note that the following three points are closely
related:
Planck's constant has units of action instead
of units of energy,
the quantum kernel is instead of ,
the quantum vacuum state is Lorentz invariant,
whereas the classical thermal state is not.
We can construct a classical continuous random
field that has the same probability density
as the quantum vacuum state, so that the principal
difference from quantum field theory is the
measurement theory.
Quantum effects that are consequences only
of quantum fluctuations, not of subtleties
of measurement incompatibility, can alternatively
be models of classical continuous random fields.
See also
Casimir effect
Quantum annealing
Quantum foam
Virtual particle
Virtual black hole
References
External links
Quantum Fluctuation at universe-review.ca
