Three Scientific Revolutions: How They Transformed Our Conceptions of Reality (22 page)

I think it is impossible that a mind free from all preconception can reflect upon the extreme diversity of the phenomena which thus converge to the same result without experiencing a strong impression, and I think that it will henceforth be difficult to defend by rational arguments a hostile attitude to molecular hypotheses.
⁷¹

Einstein's fourth and fifth articles dealing with the “electrodynamics of moving bodies” contain his special theory of relativity that led to the refutation of Newton's affirmation of absolute space and time and toward a definite transition to the third conception of reality. Following Newton's publication of the
Principia
, for two centuries absolute space and time had been regarded as necessary ontological frames of the universe to account for absolute motion and rest. Then in the nineteenth century Maxwell's theory of electromagnetism and the reemergence of the wave theory of light led to the hypothesis that Newton's absolute space was filled with a stationary aether to explain the propagation of electromagnetism and light waves.

But not content with merely positing absolute space and time and the aether, between 1881 and 1929 Albert A. Michelson and Edward W. Morley, both independently and in collaboration, devised a number of tests to indirectly confirm the existence of the aether believed to be at rest in absolute space and thus demonstrate the existence also of absolute motion. The most effective of these tests was Michelson's optical method using his interferometer.

Assuming that the earth's annual revolution through the aether would create an aether drift or wind in the opposite direction, one should be able to demonstrate the existence of the aether, and thus of absolute space, by detecting its effect on the velocity of light. Imagine a circular instrument enumerated like the face of a clock, within which there is placed a light source at 9 o'clock and two reflecting mirrors, one at 12 and one at 3 o'clock, and a light detector at 6 o'clock. There also is a mirror set in the center coated in such a way that it either deflects or transmits the light depending on the angle of interaction of the light and the mirror.
⁷²

According to the experiment, a single beam of light is emitted from the light source at 9 o'clock that splits into two beams, one of which moving horizontally strikes the central mirror and is deflected vertically to the 12 o'clock mirror which then directly reflects it vertically downward
through
the central mirror to the receptor at 6 o'clock. The second beam also moves horizontally but
through
the central mirror to the 3 o'clock mirror that reflects it back to the central mirror that then deflects it to the receptor at 6 o'clock.

As both beams are emitted at the same moment with the same velocity and travel the same distance, but one's trajectory being more vertical and the other's more horizontal, it was predicted that the light beam traveling more in the parallel or vertical direction would, because of the greater aether resistance, be slowed and thus gain an extra 1/25 of a wavelength, which meant that it would return to the detector slightly out of phase. Yet, regardless of how they positioned the interferometer in relation to the to the earth's movement, the two light waves always returned in phase indicating no effect of the aether on their velocity. And so Michelson announced in 1881 that since there was no evidence that an aether drift affected the velocity of light, it can be concluded that it does not exist: “The result of the hypothesis of a stationary aether is thus shown to be incorrect, and the necessary conclusion follows that the hypothesis is erroneous.”
⁷³
When Michelson received the Nobel Prize in physics 1907 he was the first American to do so, but it was not for his aether drift experiment, but for his invention of ingenious optical instruments and other experiments.

Considering the significance of the experiment that constituted one of the “two dark clouds” confronting physics, it is surprising that except for Lord Kelvin, Lord Rayleigh, and Lorentz, its startling and contentious results had little impact at the time. Einstein himself declared that it did not play a “decisive role” in his formulation of the special theory of relativity, despite its demonstrating that the velocity of light remained constant with the implication that there was no absolute motion in relation to the aether existing in absolute space, thus disconfirming the existence of the latter but supporting two of his theses presented in his special theory of relativity. Rather than it being the null results of the Michelson-Morely experiments, Einstein indicated what actually influenced him in a talk given in Kyoto, Japan in December 1922.

I took into consideration Fizeau's experiment and . . . the truth of the Maxwell-Lorentz equation in electrodynamics . . . [that] showed to us [in] the relations of the so-called invariance of the velocity of light that those equations should hold also in the moving frame of reference. This invariance of the velocity of light was, however, in conflict with the rule of addition of velocities we knew of well in mechanics. (p. 139; brackets added)

Given the two “considerations” mentioned in this paper, the invariance of the speed of light and the indistinguishability of moving
inertial
systems because the laws of inertial systems are equivalent, Einstein's rejection of Newton's conception of space and time as absolute frames of the universe follows with stunning simplicity. This is because the presuppositions of their calculations are just the converse of each other. Since in Newtonian mechanics the lengths of measuring rods and the rates of clocks are unaffected by their velocities, two systems in relative motion measuring the velocity of another object must find different dimensions. For example, an automobile that has a velocity of 50 miles per hour as measured by a person a rest on the earth will have a velocity of only 10 miles per hour if measured by a driver traveling at 40 miles per hour in the same direction. This is Galileo's well-known “addition of velocities” principle mentioned by Einstein at the end of the previous quotation.

The anomaly is that though this is true of all other measurements, it is not true of light since anyone, regardless of their velocity, will find the velocity of light to be the same. This can be explained, according to Einstein, if the physical measuring instruments, the rods and clocks, are not as Newton assumed and is true of the relatively slight velocities on the earth, unaffected by their velocities. But for those approaching the velocity of light the measuring rods contract and the clocks slow down in ratio to their velocities thereby explaining the identical determination of the velocity of light irrespective of their different velocities. More explicitly, since
v
= d/t, if the measured distance is greater because of the retraction of the measuring rod and the duration longer because of the slowing of the clocks relative to their velocities, then
v
will increase proportionately to produce the invariant velocity of light. The formula for determining the degree of retraction and retardation is √(1- v
²
/c
²
).
⁷⁴

Another consequence is that as the system approaches the velocity of light mass increases tending to infinity, which is the reason no physical system can attain that velocity and thus light is a limiting velocity. In his second article on special theory, Einstein declared the equivalence of energy and mass as stated in his famous equation
E
=
m
c
²
that superseded Newton's famous equation F = ma at greater velocities, a further transition to a different conception of reality due to the limitations of Newtonian science. It also explains the sun's tremendous source of energy and why its gravitation force is so much greater than any other
solar body
because its mass comprises 98 percent of the mass of the solar system.

While Lorentz's and Einstein's transformation equations correlate the spatial, temporal, and mass measurements from a system at rest to one in uniform motion, German mathematician Herman Minkowski in 1904 devised a formula √{(cT)
²
– R
²
} that gave an identical value for the duration of two events measured by systems in relative uniform motion. As explained by G. J. Whitrow:

If, according to a particular observer, the difference in time between any two events is
T
, this associated spatial interval is
cT
. Then, if
R
is the space-distance between these two events, Minkowski showed that the difference of the squares of
cT
and
R
has the same value for all observers in uniform relative motion. The square root of this quantity is called the
space-time interval
between the two events. Hence although time and three-dimensional space depend on the observer, this new concept of space-time is the same for all observers.
⁷⁵

It is this formula, particularly, that gave rise to the conception of the universe as a four-dimensional continuum of events, three of space and one of time, a central feature of Einstein's general theory of relativity.

However, according to this initial interpretation, because both systems are kinematic (devoid of forces) rather than dynamic due to their being inertial, the modifications attributed to the rods, clocks, and mass in the moving system by the one assumed to be at rest are reciprocal, either system being equal as the reference point. Thus in the special theory the effects are merely apparent rather than actual. Similar to the apparent reduction in size or motion of an object seen from a distance, this effect in the special theory is referred to as the “perspective of velocity.” It is also true that what has been described applies only to electromagnetic phenomena, not to mechanical or acoustical measurements.

In the latter cases the addition of velocities law holds so that the measurements of distant events, their duration, and whether they are simultaneous are relative to the system of reference. But since the velocity of light is constant it is independent of the motion of its source and of any moving detector. In contrast to velocity, the wavelength and frequency
are
affected, but in such a way that their product, which determines their velocity, remains constant. But since information about any distant event requires some causal transmission such as a light signal, no effect can appear before its cause, contrary to science fiction accounts.

As indicated, in contrast to the special theory of relativity, where the relativistic effects were considered apparent because they involve inertial systems devoid of forces, in the general theory where noninertial velocities are considered, the effects are actual. French physicist Paul Langevin's
voyage au boulet
introduced in 1911, known in English as “the twins paradox,” offers a striking illustration. Leaving one twin on the earth with the other boarding a spaceship that accelerates to 1/20,000
^th
less than the speed of light, the twin on the spaceship, owing to the enormous gravitational effect generated by its tremendous acceleration, will have aged two years, while the twin on the earth would have died during the two centuries that had elapsed on the earth.
⁷⁶
More recently these effects have been confirmed in precise experiments using clocks placed in jet aircrafts circling the earth indicating that the lifetimes of radioactive particles were extended by their greater velocities. Presently, the extreme velocities of the subatomic particles in physics have led to their being incorporated into relativistic quantum field theory.

Not satisfied with the restrictions imposed in the special theory by limiting the relative motions to inertial systems, in the general theory published in 1915 Einstein extended his investigations to nonuniform motions involving forces, but with the same intent of extending his explanations to new dimensions while also attaining greater uniformity and simplicity in the laws of nature. In these endeavors he did not utilize empirical experiments but ingenious thought experiments, such as comparing the effects of being in an elevator falling at the same rate as gravity (so that the free fall cancels the effect of gravity) to being suspended in a gravitational free region of outer space to demonstrate their inertial equivalences; or comparing the effect of being in a gravity free elevator in outer space with being pulled upward with the same accelerating force as an elevator on the earth to show their equivalence.

By these thought experiments he intended to demonstrate the equivalence of gravitational and accelerated motions by merely shifting one's frame of reference, similar to mass and energy being equivalent. In another thought experiment he described falling from the roof of a house and releasing objects of different weights as he fell, concluding that since the falling objects were in the same gravitational field they would seem stationary relative to himself regardless of their weights. As he wrote in an unpublished paper in 1907:

The gravitational field has only a relative existence in a way similar to the electric field generated by magnetoelectric induction.
Because for an observer falling freely from the roof of a house there exists
—at least in his immediate surroundings—
no gravitational field.
Indeed, if the observer drops some bodies then these remain relative to him in a state of rest or of uniform motion, independent of their particular chemical or physical nature (in this consideration the air resistance is . . . ignored).

The observer therefore has the right to interpret his state as “at rest.”
⁷⁷

In the same article he refers to this realization that the “gravitational field has only a relative existence” as “the happiest thought of my life. . . .”

As further vindication of this study showing how science has transformed our conceptions of reality, in 1931 he declared this to be true of Maxwell's field theory: