einstein

With all this talk of distance and duration being relative depending on the observer’s motion, some may be tempted to ask: So which observer is
“right”? Whose watch shows the “actual” time elapsed? Which length of the rod is “real”? Whose notion of simultaneity is “correct”?
According to the special theory of relativity, all inertial reference frames are equally valid. It is not a question of whether rods actually shrink or
time really slows down; all we know is that observers in different states of motion will measure things differently. And now that we have dispensed
with the ether as “superfluous,” there is no designated “rest” frame of reference that has preference over any other.
One of Einstein’s clearest explanations of what he had wrought was in a letter to his Olympia Academy colleague Solovine:
The theory of relativity can be outlined in a few words. In contrast to the fact, known since ancient times, that movement is perceivable only as
relative movement, physics was based on the notion of absolute movement. The study of light waves had assumed that one state of
movement, that of the light-carrying ether, is distinct from all others. All movements of bodies were supposed to be relative to the light-carrying
ether, which was the incarnation of absolute rest. But after efforts to discover the privileged state of movement of this hypothetical ether through
experiments had failed, it seemed that the problem should be restated. That is what the theory of relativity did. It assumed that there are no
privileged physical states of movement and asked what consequences could be drawn from this.
Einstein’s insight, as he explained it to Solovine, was that we must discard concepts that “have no link with experience,” such as “absolute
simultaneity” and “absolute speed.” 61
It is very important to note, however, that the theory of relativity does not mean that “everything is relative.” It does not mean that everything is
subjective.
Instead, it means that measurements of time, including duration and simultaneity, can be relative, depending on the motion of the observer. So
can the measurements of space, such as distance and length. But there is a union of the two, which we call spacetime, and that remains invariant in
all inertial frames. Likewise, there are things such as the speed of light that remain invariant.
In fact, Einstein briefly considered calling his creation Invariance Theory, but the name never took hold. Max Planck used the term Relativtheorie
in 1906, and by 1907 Einstein, in an exchange with his friend Paul Ehrenfest, was calling it Relativitätstheorie.
One way to understand that Einstein was talking about invariance, rather than declaring everything to be relative, is to think about how far a light
beam would travel in a given period of time. That distance would be the speed of light multiplied by the amount of time it traveled. If we were on a
platform observing this happening on a train speeding by, the elapsed time would appear shorter (time seems to move more slowly on the moving
train), and the distance would appear shorter (rulers seem to be contracted on the moving train). But there is a relationship between the two
quantities—a relationship between the measurements of space and of time—that remains invariant, whatever your frame of reference. 62
A more complex way to understand this is the method used by Hermann Minkowski, Einstein’s former math teacher at the Zurich Polytechnic.
Reflecting on Einstein’s work, Minkowski uttered the expression of amazement that every beleaguered student wants to elicit someday from
condescending professors. “It came as a tremendous surprise, for in his student days Einstein had been a lazy dog,” Minkowski told physicist Max
Born. “He never bothered about mathematics at all.” 63
Minkowski decided to give a formal mathematical structure to the theory. His approach was the same one suggested by the time traveler on the
first page of H. G. Wells’s great novel The Time Machine, published in 1895: “There are really four dimensions, three which we call the three
planes of Space, and a fourth, Time.” Minkowski turned all events into mathematical coordinates in four dimensions, with time as the fourth
dimension. This permitted transformations to occur, but the mathematical relationships between the events remained invariant.
Minkowski dramatically announced his new mathematical approach in a lecture in 1908. “The views of space and time which I wish to lay before
you have sprung from the soil of experimental physics, and therein lies their strength,” he said. “They are radical. Henceforth space by itself, and
time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality.” 64
Einstein, who was still not yet enamored of math, at one point described Minkowski’s work as “superfluous learnedness” and joked, “Since the
mathematicians have grabbed hold of the theory of relativity, I myself no longer understand it.” But he in fact came to admire Minkowski’s handiwork
and wrote a section about it in his popular 1916 book on relativity.
What a wonderful collaboration it could have been! But at the end of 1908, Minkowski was taken to the hospital, fatally stricken with peritonitis.
Legend has it that he declared, “What a pity that I have to die in the age of relativity’s development.” 65
Once again, it’s worth asking why Einstein discovered a new theory and his contemporaries did not. Both Lorentz and Poincaré had already
come up with many of the components of Einstein’s theory. Poincaré even questioned the absolute nature of time.
But neither Lorentz nor Poincaré made the full leap: that there is no need to posit an ether, that there is no absolute rest, that time is relative
based on an observer’s motion, and so is space. Both men, the physicist Kip Thorne says, “were groping toward the same revision of our notions
of space and time as Einstein, but they were groping through a fog of misperceptions foisted on them by Newtonian physics.”
Einstein, by contrast, was able to cast off Newtonian misconceptions. “His conviction that the universe loves simplification and beauty, and his
willingness to be guided by this conviction, even if it meant destroying the foundations of Newtonian physics, led him, with a clarity of thought that
others could not match, to his new description of space and time.” 66
Poincaré never made the connection between the relativity of simultaneity and the relativity of time, and he “drew back when on the brink” of
understanding the full ramifications of his ideas about local time. Why did he hesitate? Despite his interesting insights, he was too much of a
traditionalist in physics to display the rebellious streak in-grained in the unknown patent examiner. 67 “When he came to the decisive step, his nerve
failed him and he clung to old habits of thought and familiar ideas of space and time,” Banesh Hoffmann said of Poincaré. “If this seems surprising,
it is because we underestimate the boldness of Einstein in stating the principle of relativity as an axiom and, by keeping faith with it, changing our
notion of space and time.” 68
A clear explanation of Poincaré’s limitations and Einstein’s boldness comes from one of Einstein’s successors as a theoretical physicist at the
Institute for Advanced Studies in Princeton, Freeman Dyson:
The essential difference between Poincaré and Einstein was that Poincaré was by temperament conservative and Einstein was by
temperament revolutionary. When Poincaré looked for a new theory of electromagnetism, he tried to preserve as much as he could of the old.
He loved the ether and continued to believe in it, even when his own theory showed that it was unobservable. His version of relativity theory was
a patchwork quilt. The new idea of local time, depending on the motion of the observer, was patched onto the old framework of absolute space
and time defined by a rigid and immovable ether. Einstein, on the other hand, saw the old framework as cumbersome and unnecessary and
was delighted to be rid of it. His version of the theory was simpler and more elegant. There was no absolute space and time and there was no
ether. All the complicated explanations of electric and magnetic forces as elastic stresses in the ether could be swept into the dustbin of