The general theory of relativity conceives of gravity as a result of curved space-time. (Public domain image by NASA.)

If non-science people have heard of one modern theory of physics, it is likely to be that of relativity. In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. Einstein then spent ten years trying to include acceleration in the theory and published his theory of general relativity in 1915. In it, he determined that massive objects cause a distortion in space-time, which is felt as gravity.

One hundred years later, Sarah Howe wrote a sonnet titled “Relativity” for a commission by Britain’s National Poetry Day. It was to be a poem on light. She wrote, paradoxically, about its absence. The poem is about black holes and is dedicated to Stephen Hawking. It begins:

When we wake up brushed by panic in the dark
our pupils grope for the shape of things we know.

That is the light we know in our world of gravity. She is also writing about light at the level of quantum physics where photons behave like particles and also as waves in a mysterious duality. Howe has said of the poem that she was also thinking about how scientist Galileo and poet Milton in their blindness “came to rely on other sorts of eyes.”

Last November was the 100th anniversary of Albert Einstein unveiling the key equations of general relativity, which he did in four lectures at the Prussian Academy of Sciences, and by the end of the month, he had arrived at the ten equations that physicists still use today.

One of his theories was of “spacetime.” Einstein’s theory viewed space and time not as two separate elements, but interwoven. A change in one produces an effect on the other. (His former professor, Hermann Minkowski actually came up with the space-time continuum  but Einstein elaborated on it.

One of the parts of this that you may have heard of is that as the rate of speed goes up, the rate of time must go down and vice versa. For an object moving slowly through space, time is passing quickly and for an object moving at a very high rate of speed, time actually slows down. It is not something that we can observe firsthand, and since we don’t get to travel at anything close to the speed of light, we don’t “go back in time.”

But the theory has been tested many times in experiments sending the most accurate atomic clocks for orbits in rockets, and when they return to Earth the clocks on the rockets are just slightly behind their earthly counterparts.

He also theorized that light curves because gravity pulls at the fabric of spacetime. Einstein thought that curve should be visible during an eclipse, and in 1919, photographs of a solar eclipse proved that the deflection of the sunlight matched Einstein’s prediction.

Isaac Newton had said that gravity was a universal force always pulling on one body on another. We learned that in school and plenty of people know only that about gravity. Einstein argued that there was no “force” of gravity at all.

His concept of space and time is often compared to a stretched fabric or trampoline that can warp and bend because of the presence of massive objects, like our sun. Objects like Earth or us on it move as straight as they can, flowing through curved space-time.

If you are curious about how politics also shaped Einstein’s theory of general relativity, check out this article from