Relativity Isn’t Relative
Relativity – the idea that everything is relative,
right? Relative to your perspective, your upbringing, your age, your place and orientation
in space and time? Except that plenty of things – in fact, perhaps most things – aren’t relative. For example, George Washington was the first
president of the United States, World War I happened before the movie Star Wars was
made, this picture shows three apples, and so on. It is true that certain things ARE relative
to one’s perspective – is the apple on your left, or my right? – is 50°F hot or cold?
– is a car fast or slow? big or small? – and that’s precisely what makes these concepts
less interesting to scientists. In physics (and in most science), anything that changes
if you change perspective can’t be a fundamental property of the universe – only things that
are absolute are considered ‘physical’ or ‘real’. And for a long time, physicists thought that
distances in space and intervals of time were absolute, fundamental properties in the universe. The special theory of relativity first described
by Albert Einstein was merely a statement of the realization that we were wrong: distances
in space and time are actually relative – they change depending on how fast you’re moving.
But more importantly, Einstein also described several quantities related to space and time
which *are* absolute: the distance between two events in spacetime, the energy-momentum
of an object, and of course, the speed of light. Similarly, the general theory of relativity
was essentially the recognition that in fact neither the acceleration nor the gravitational
force experienced by an object are absolute quantities. Accelerations can transform into
gravitational fields (and vice versa), depending on your perspective and the path you take
through spacetime. The more fundamental absolute quantity is the *curvature* of spacetime,
which you can think of as a kind of “underlying” or “absolute” gravity. Special and General relativity, are, at their
core, not about what’s relative – they’re about what’s real irrespective of perspective.
If everything were relative, then there could be no science, no laws, no justice – just
opinion. Science exists because it turns out there
*are* absolutes in the universe – truths which are the same regardless of your perspective.
You might even say that science is simply about finding the truths that will still be
true if you remove the scientist. So… goodbye!