The Extinction of Ether

The Extinction of the Ether

Traditional wave mechanics, derived from waves in water, air
and solids, lead to the natural supposition that there would be a substance
that light propagated through. This substance eventually developed into the
hypothesis of the “‘quasi-rigid’ luminiferous ethername="_ednref1" title="">class=MsoEndnoteReference>[1], the parts of which can carry
out no movements relatively to one another except the small movements of
deformation which correspond to light-waves.” (Einstein, 1920) This special
substance was assumed to exist and mainstream science did not challenge it,
rather science sought to discover the ether’s properties. It was around the
turn of the 20^th century that mainstream science actually began to
question the ether hypothesis. Through the Michelson-Morley Experiment and the
advent of Special Relativity, the luminiferous ether rapidly became extinct.

Michelson-Morley Experiment

The Michelson-Morley Experiment was designed to detect the
rate at which the ether wind blew, not to question its existence. By having
two identical pulses of light traveling perpendicular to each other over an
equal distance, the experimenters expected to discover the direction and
magnitude of the ether wind. Much like one could tell the speed of a river
current by swimming straight across and back if you swim at a known constant
speed. Also, if the direction of the current is in question, you can figure
out both the current speed and direction of the current by having two swimmers
swim on perpendicular paths and figuring out the difference in their times. Figure
1 shows the setup of the experiment.

Figure 1

height=268 src="Phil%20Sci%20Ether%20Paper_files/image001.gif" />

The source is at (S), from which a light beam is emitted
towards a half silvered mirror (a) which is at a 45 degree angle. (a) splits
the beam into two identical parts, reflecting half of the original beam towards
(b) and transmitting half to (c). Both new beams reflect off of the mirrors at
(b) and (c) , respectively, and return to (a) where both beams are split in
half again, with half of both beams heading towards (s) and half going to (d).
At (d) is located an observer. This whole experiment is place on top of a
large turntable.

By taking interference measurements between the two waves
and then rotating the table a few degrees and repeating the measurements, Michelson
and Morley calculated that they could detect an ether wind with a velocity as
little as 1-2 miles per second (Fowler-MM). After completing the experiment, Michelson
Morley could not find any differentiation in the interference measurements, the
“null result”. A result often repeated since, with ever increasing precision.
This null result did not itself lead to a denial of the Ether, due to some keen
explanations from prominent scientists and mathematicians (e.g., Lorentz and
his transform), but rather began the questioning of the Ether’s existence.

Special Relativity

Special Relativity has two primary assumptions: 1.) The laws
of Physics are the same in all frames of reference (the Principle of
Relativity, PR) and 2.) Light travels at c in all frames of reference (the
Light Postulate, LP). The PR is at direct odds with the conception of a “‘quasi-rigid’
luminiferous ether”; as such an ether would define a preferred frame of
reference (an absolute space where absolute velocities and locations are
identifiable). The existence of the ether then turned on the credibility of
Special Relativity. If Special Relativity is the case, then the conception of
the ether is “superfluous inasmuch as the view… will not require an ‘absolutely
stationary space’”. (Einstein, 1905) Special Relativity and its postulates
were supported by various cases; the PR is supported by cases such as Maxwell’s
Asymmetry, the LP is supported by cases like the Pion experiments, and the
whole theory is supported by the Muon cases.

Maxwell’s Asymmetry

Maxwell’s Asymmetry was the idea that absolute velocity
relations to an absolute space (the ether) would matter in how we explain
phenomena. The prevailing view is that Asymmetry should only apply if the
actual phenomena experience an difference (asymmetry) in outcome, but that did
not seem the case. Two examples of Maxwell’s Asymmetry were the speed of light
problem and the magnet/ring problem.

Speed of light problem

Maxwell’s laws led to the calculation of the speed of light,
which appeared (according to the equations) to be an absolute value. If the
speed of light was absolute and the ether did exist, then one would expect the
speed of light to be in reference to the absolute space created by the ether.
If you could travel at the speed of light then an electromagnetic field
traveling in the same direction would have no magnetic component (due to the
relative velocity of the observer and the electromagnetic field being zero),
which brings the contradiction (according to Maxwell’s laws) of an electric
field with no corresponding magnetic field. This questioned the validity of
the notion of absolute velocity and absolute space.

Magnet/Ring problem

The Magnet/Ring problem is the asymmetry caused by two
different laws of Maxwell’s. The two competing laws are in Figure 2. In
Figure 2.A, the magnet is in motion relative to the ring conductor creating an
electric field around the magnet that causes an electric current in the ring. In
Figure 2.B the ring is in equal motion relative to the magnet, but no electric
field is created, though an electromotive force causes an equal current in the
ring.

Figure 2

src="Phil%20Sci%20Ether%20Paper_files/image002.gif" />

It is this asymmetry in
explanation that Einstein cites in the beginning of his 1905 paper. To
Einstein and others, the idea of having two laws describing similar events with
identical outcomes was untenable; there should be one law that describes both
cases. And thus the need for absolute space again was questioned, as the two
cases of Maxwell’s would have different absolute velocities, but the same
outcome. If absolute space doesn’t create a difference in outcome, then it
should be abandoned as meaningless.

Pion (Alvager et. al. 1964)

An alternate explanation for the speed of light being
constant is the conception that c is constant relative to the source or emitter
of the light. If this was the case one would expect that a person traveling
near the speed of light who turned on a flashlight would measure the speed of
the flashlight at c, and a stationary observer would measure the speed of the
light emitted from the flashlight at 2c. However, Alvager’s neutral pion
experiment in 1964, tried out just this arrangement (with the person being
replaced by a neutral pion, and the turning on of the flashlight being replaced
by the decay of the pion releasing photons). Alvager and his team accelerated
a neutral pion to 0.99975 c and after the pion decayed measured the speed of
the light emitted. The speed turned out to be c, thus supporting Einstein’s LP.

Muonclass=MsoEndnoteReference>style='font-size:14.0pt;line-height:200%;font-family:Arial'>[2]

If there was a preferred frame of reference (ether), then
one would expect time and length to be defined by that preferred frame, and
thus standard for all objects in the universe. But from the LP and PR, one can
derive time dilation and length contraction effects, which define time and
length relative to the frame one is in. In 1941, researchers detecting muons
were able to prove time dilation and length contraction effects. At the top of
Mount Washington, muons entering our atmosphere at near the speed of light
(.994c) were detected at a rate of 570 per hour. 6,000 feet below researchers
expected to detect only 35 per hour, due to the calculation of the muons going through
four half-lives in 6 microseconds over the 6,000 feet. However, they detected
400 per hour. The explanation is that the muons experienced a length
contraction of the 6,000 feet into 670 feet, due to their high velocity, and a
time dilation in the expected 6 microseconds to only .67 microseconds. These
effects permit the muons to appear to be living longer to stationary observers,
though in the muons’ frame of reference, they are living just as long as they
would at any speed.

The End of Ether

The Michelson-Morley Experiment and the advent of Special
Relativity defeated the notion of a “‘quasi-rigid’ luminiferous ether”. With
the extinction of the ether hypothesis and the corresponding absolute space, modern
science adopted Special Relativity as the standard explanation of mechanics,
and the luminiferous ether was relegated to science history books. It is
interesting to note that scientists today do generally accept a modification of
the ether idea due to the advent of General Relativity, though it is called “’the
metric’, ‘space’, or ‘vacuum’”. (Wikipedia)

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class=MsoEndnoteReference>style='font-size:10.0pt;line-height:200%;font-family:Arial'>[1]
I speak of “‘quasi-rigid’ luminiferous ether” specifically as Einstein in his
1920 address at the University of Leyden supports a modification of the ether
idea.

Recapitulating,
we may say that according to the general theory of relativity space is endowed
with physical qualities; in this sense, therefore, there exists an ether.
According to the general theory of relativity space without ether is
unthinkable; for in such space there not only would be no propagation of light,
but also no possibility of existence for standards of space and time
(measuring-rods and clocks), nor therefore any space-time intervals in the
physical sense.