- 4224 - THEORY OF RELATIVITY - defines speed of light? The theory of relativity is simple and elegant. It is also maddeningly nonintuitive. There is one feature of Einstein’s work that takes center stage, and would eventually lead him into a complete reshaping of Newton’s gravity, altering our very conceptions of the fabric of the universe.
------------ 4224 - THEORY OF RELATIVITY - defines speed of light?
- The theory of
relativity is simple and elegant. It is
also maddeningly nonintuitive. There is one feature of Einstein’s work that
takes center stage, and would eventually lead him into a complete reshaping of
Newton’s gravity, altering our very conceptions of the fabric of the universe.
-
- That singular
feature is right there in the name: “relative”. Einstein discovered that what
we once thought immutable was nothing. But to understand how Einstein rewrote
Newton’s insights we first have to rewind the clock back and understand
Newton’s insights.
-
- Once Newton hit
upon his idea for a conception of gravity, a force emanating from and
connecting to all objects, he needed a universe to make his force “universal.
When the Sun reaches out with its gravity and instructs all the planets, even
mighty Jupiter, where to move next, those planets need to know where they are
relative to the Sun. We need to know how far away from the Earth it is so that
it can have the proper rate of acceleration.
-
- Everything in the
universe needs to know where everything else is so that gravity can act with
the appropriate amount of force. Newton
conceived of the cosmos as a vast fixed grid, a series of universal rules and
master clocks, and absolute reference frame from which all other measures could
be taken. This is not meant to be taken
literally. This is all a mathematical
framework that provides the mechanisms for computing gravitational forces, but
the need for that framework is paramount in Newton’s work.
-
- In Newton’s view of
gravity, every gravitational interaction must be computed in regard to that
universal, fixed, absolute frame of reference. The entities of our universe
must know where they are relative to this fixed frame so that gravity can be
the correct strength at the proper times and the proper places.
-
- But James Clerk
Maxwell’s work on electromagnetism flew in the face of this universal frame of
reference. Maxwell’s own genius mathematics said that the speed of light was
the speed of light, always and forever. No matter how fast you were moving, or
in what direction you were moving, whether light was approaching you or
receding, it didn’t matter. Light moved at lightspeed.
-
- If there was some
universal frame of reference, some master clock and absolute ruler, as Newton
suggested, then the speed of light should only be the speed that it is relative
to that absolute frame, because that absolute frame is the benchmark against
which to measure all motion. And so the existence of that absolute frame should
allow you to move astride a beam of light and see it fixed and frozen in place.
-
- Does the universe
have a fixed frame of reference for us to judge all motion against, or are some
things, like the speed of light, immutable and constant, uncaring of our point
of view?
-
- Einstein picked
Maxwell, and Einstein was right. There is no universal frame of reference, no
master clock or absolute ruler. There is no way to judge motion except for the
relative viewpoints of every observer. In other words, this is the relativity
in the theory of relativity: “all motion is relative”.
-
- If Einstein rode
past me on his bicycle, I could only say that he is moving from my perspective.
From his perspective, he could rightly claim that he was fixed still and that I
was the one in motion.
-
- In discarding the
notions of absolute time and space, Einstein did gain something for his effort.
Not all things are relative; there are some constants in the universe. Namely,
the laws of physics. All observers agree on the commonality of the laws of
physics.
-
- Maxwell’s
equations say that the speed of light is a constant. The end. And so it is:
every observer in the universe, regardless of their position or speed or
acceleration, will always view the same speed of light.
-
-
November 16, 2023
- RELATIVITY
- defines speed of light? 4224
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