What is "time"? Is it merely a construct of the human imagination, as a result of the way we perceive reality? Or is it tangible, making it an observable facet of reality that can be measured and studied like other elements of our universe?
While such questions remain, there are a lot of things that we have learned about time, and its relationship to thermodynamic laws, gravity, and even how our minds work in relation to the concepts of space and time. Much of this is thanks to the groundbreaking work of Albert Einstein, renowned physicist whose theory of relativity celebrates its centennial this month.
The theory, in its finest summation, helped to simplify our views of physics and the universe by conceptually uniting space and time as a single, unified entity called spacetime.
New York Times described it thusly: "[O]n Nov. 25, 1915, he set down the equation that rules the universe. As compact and mysterious as a Viking rune, it describes space-time as a kind of sagging mattress where matter and energy, like a heavy sleeper, distort the geometry of the cosmos to produce the effect we call gravity, obliging light beams as well as marbles and falling apples to follow curved paths through space."
NASA's Tumbler blog explained how understanding of time in relation to Einstein's predictions helps us today, with everything from smartphones and social media, to GPS units in our cars:
How many of us have used a smartphone to get directions? Or to tag our location on social media? Or to find a recommendation for a nearby restaurant? These activities depend on GPS. GPS uses radio signals from a network of satellites orbiting Earth at an altitude of 20,000 km to pinpoint the location of a GPS receiver. The accuracy of GPS positioning depends on precision in time measurements of billionths of a second. To achieve such timing precision, however, relativity must be taken into account.
Two key predictions, involving the warpage of space and time around a gravitational body such as Earth, as well as how much space and time are pulled along with the rotation of a spinning object (which physicists call "frame-dragging"), were studied with NASA's Gavity Probe B (GP-B) mission, which "used four ultra-precise gyroscopes" to achieve its study of relativity's effects in 2004.
In celebration of the centennial, Science and Technology Facilities Council produced the following video, which provides a short crash-course in general relativity:
The video is narrated, rather appropriately, by actor David Tennant, whose roles have included the tenth incarnation of the time traveling hero Doctor Who, as well as his more recent foray into villainy as "Killgrave", a rendition of the Marvel comics character known as Purple Man featured in the Netflix original series Marvel's Jessica Jones.
Hey, if David Tennant explaining relativity doesn't make studying physics enjoyable for ya, then all hope truly is lost. ;)