Relativity in five minutes: Einstein’s bullet points

Oscar-winner Geoffrey Rush plays Albert Einstein in National Geographic’s Genius. The new series was produced by Ron Howard and Brian Grazer. It is based on the Walter Isaacson book Einstein: His Life and Universe. (Dusan Martincek)

There’s a new National Geographic series called Genius, which depicts the life of Albert Einstein. I’m hoping viewers will come away with some basic understanding of Einstein’s ideas. It’s desperately needed, because the public is largely clueless about the wonderful relativity theories. Meanwhile, if you have five minutes right now, I’ll summarize the most important takeaways from one of history’s most important science developments.

There were actually two: two separate developments. Albert Einstein’s initial breakthrough was his 1905 Special Theory of Relativity, whose ideas were mostly evolutionary rather than revolutionary. It built upon revelations from physicists like Hendrik Lorentz and George Fitzgerald, and explained the bewildering 19th-century discovery that light has a constant speed. It used simple math that even I could easily teach to my college students in the 1990s. But Einstein’s 1916 general relativity theory seemingly came from outer space. It had very little precedent and was truly an act of genius. Its math was complex, and utilized “field equations” that even NASA avoids whenever possible. A few years later it was said that only five people in the world understood General Relativity.


Special relativity clarified the concept of reference frames – meaning, the laws of physics work just as well from a moving platform as from a stationary one, but observers in each see different things happening; two events occurring sequentially in one situation might appear simultaneous in the other. And observers in each might disagree in their measurements of length and the passage of time, but would always agree when it came to light, which is always observed to have a constant speed. It established that matter and energy are two faces of the same phenomenon, so that a baseball is merely a sphere of concentrated energy. His famous equation E = mc², derived from the well-known kinetic energy formula E= ½mv² combined with the Lorentz transformation equation, showed how energy and matter convert to each other. This was the basis for the atomic bombs created 40 years later. It’s actually better not to say that mass can convert to energy; rather, mass is energy.

By contrast, general relativity largely dealt with motion. Einstein showed that gravity, rather than being a force, is identical to acceleration, and results from a warping of empty space produced by nearby massive objects. (Thus, the feeling you get when standing on a sidewalk is not that Earth’s gravity is pulling on your feet, but that your body is being accelerated downward by the curved spacetime created by Earth’s mass.) Thus, a planet orbiting the Sun is merely falling in a straight path through the curved space caused by the Sun’s mass.

Einstein also introduced the concept of space-time, a mathematical construct (not an actual physical entity) that explains how objects move. One takeaway from this is that if we regard time and space as distinct from each other, we run into problems because each is illusory in and of itself. In reality, said Einstein, traveling faster through space always results in traveling at a slower rate through time. Thus, another aspect of general relativity is length contraction and time dilation. This means that distances in space shrink as you move faster, while at the same time anyone observing you sees your time slowing down.

These were mind-bending ideas. But were they true? British physicist Arthur Eddington realized that general relativity could be proven or disproven during a total solar eclipse. So, expeditions were dispatched during the eclipse of May 29, 1919, when the Sun was embedded in a star cluster in Taurus. Careful measurements showed that the stars nearest the Sun shifted position, proving that warped space-time had caused their light to arrive here by taking a slightly different path.

Hopefully, all this is of some help in grasping the basics of Einstein’s genius.