DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

Miche–Rundgren theory
the Earth moves through this ether with speed
v, then the travel time for light along the arms
should be aligned along and across the motion
should differ by .5(v/c) 2 ; the “cross stream”
time is shorter. Note that this difference is second
order in the ratio of the velocity to the speed
of light. In the interferometer, this path difference
will lead to a phase difference and an interference
between the two beams of light in the
interferometer. Furthermore, the interferometer
can be turned (Michelson and Morley mounted
theirs on granite and floated it in mercury to facilitate
this) and the interference pattern should
shift as the device is turned. To their amazement,
Michelson and Morley found no such effect,
with an experimental accuracy of about 2
to 3%. Multiple repeat experiments arrived at
the same result. This result was debated for a
very long time. It is now regarded as one of
the fundamental experiments supporting special
relativity.
Miche–Rundgren theory A theory for description
of wave-induced forces on a wall (nonbreaking
waves).
micrometeorite A meteorite less than 1 mm
in diameter. Micrometeorite strikes are a major
source of erosion on the moon, and of the
production of the lunar surface (the regolith).
microstructure Fluctuations on scales at
which entropy is generated by the smoothing
effect of molecular viscosity and diffusivity are
referred to as microstructure. This scale lies typically
below 1mintheocean and lakes; often
structures in CTD profiles (< some dm) resolving
the Kolmogorov or Batchelor scale are generally
called microstructure; see Kolmogorov
scale, Batchelor scale.
microwave background radiation In observational
cosmology, the radiation field at microwave
frequencies with a black body spectrum
corresponding to heat radiation at about 3 K; the
radiation left over from the early period when
the universe was dense and hot, 10 5 years (10 13
sec.) after the Big Bang. Initially the temperature
was so high that ordinary elementary particles
could not exist. Matter emerged from the
Big Bang in the form of a mixture of its sim-
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plest components: protons, neutrons, electrons,
photons, and neutrinos. (Cosmology also considers
still earlier epochs, e.g., inflation; and the
epoch when even protons and neutrons had not
existed because the cosmic matter was a mixture
of quarks.) At first, matter was so hot that no stable
atoms could form and the particles remained
in thermodynamical equilibrium with photons.
However, the universe was cooled because of expansion,
and later, 10 5 years after the Big Bang
and at the temperature ≈ 3000 K, the atomic
nuclei that had come into existence in the meantime
(these were hydrogen [protons], deuterium,
tritium, helium, lithium, beryllium, and boron,
formed in reactions of the protons and neutrons
that were there from the beginning) could capture
the electrons. At this moment, the radiation
was emitted for the last time (this moment
is called last scattering) and it has evolved without
significant contact with matter until now. It
has kept the spectrum of a black body radiation,
but its temperature is constantly decreasing. Exactly
this kind of radiation was detected in 1965,
with the temperature at 2.73 K. Its black-body
spectrum has been verified with a very high precision,
and it comes to us from all directions in
space, with the relative fluctuations of temperature
(T /T ) not exceeding 10 −5 (this result
is obtained after the anisotropies in T caused
by the motion of the Earth on its orbit, of the
sun in the galaxy and of the whole galaxy in
the local group have been subtracted). This discovery
eliminated the steady-state models and
is still the strongest confirmation that the idea
of a Big Bang is correct. The radiation was in
fact detected in 1935 by A. McKellar, through
excitations in the CN-molecules in interstellar
space, but the results were not understood at
that time. The existence of the background radiation
was predicted by George Gamow and
co-workers in 1946–1948 on the basis of theoretical
speculations. Robert Henry Dicke and
James Peebles with co-workers were preparing
an experiment to detect the radiation in 1965,
when it was actually (and accidentally) discovered
by Arno Penzias and Robert W. Wilson in
the course of a quite different experiment, as an
irremovable noise in a microwave antenna.
microwave burst A transient enhancement
of solar radio emission in the mm–cm wave-