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  • 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!

Relativity - the idea that everything is relative, right?

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B1 中級

相対性は相対性ではない (Relativity Isn't Relative)

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    林宜悉 に公開 2021 年 01 月 14 日
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