In 1905, our conception of the Universe changed forever when Einstein put forth his special theory of relativity. Prior to Einstein, scientists were able to describe every “point” in the Universe with the use of just four coordinates: three to designate position for each of the three spatial dimensions, plus a time to indicate at which moment any particular event occurred. All of this changed when Einstein had the fundamental realization that every single observer in the Universe, dependent on their motion and location, each had a unique perspective on where and when every event in the Universe would have occurred.
Both space and time, for each observer, was relative. Whenever one observer moves through the Universe relative to another, the observer-in-motion will experience time dilation: where their clocks run slower relative to the observer-at-rest. Based on this, Einstein suggested that we could make use of two clocks to put this to the test: one at the equator, which speeds around the Earth at approximately 1670 km/hr (1038 mph), and one at the Earth’s poles, which is at rest as the Earth rotates about its axis.
In this regard, however, Einstein was wrong: both clocks run at exactly the same rate relative to one another. It wasn’t until 1971 that a proper test could be conducted, and it required a lot more than special relativity to make it so. A “light clock” will appear to run differently for observers moving at different relative speeds, but this is due to the constancy of the speed of light.
Einstein’s law of special relativity governs how these time and distance transformations take place between different observers. However, each individual observer will see time pass at the same rate as long as they remain in their own reference frame: one second-per-second, even though when they bring their clocks together after the experiment, they’ll find that they no longer agree. Back when Einstein first put forth his special theory of relativity, there was a missing element: it didn’t incorporate gravitation into the mix.
He had no idea that proximity to a large gravitational mass could alter the passage of time as well. Owing to the planet’s rotation and the attractive gravitational force of every particle that makes up the Earth, our planet bulges at the equator and gets compressed at the poles. As a result, the Earth’s gravitational pull at the poles is slightly stronger — by about 0.4%, typically — than it is at the equator.
As it turns out, the amount of time dilation due to a point on the equator zipping around the Earth is exactly cancelled by the additional amount of gravitational time dilation that results from the difference in gravity at the Earth’s poles versus the equator. Being deeper in a gravitational field, which the poles are, causes your clock to tick by more slowly, just as moving faster relative to a stationary observer does. If you want to account for the rate at which the passage of time will appear to occur for each and every observer, both the relative motion effects of special relativity and also the relative effects of gravity — i.e., the relative curvature of spacetime between multiple observers — must be taken into account.
Extract — continue reading at the source.
