A total solar eclipse helped cement Einstein’s theory of relativity. Today we use the same principles to make the incredibly small corrections in time measurement that allow for accurate GPS positioning.
Global Navigation Satellite Systems and Global Positioning Systems have become integrated into everything that we use in our daily lives – cars, cell phones, pet trackers, drones, etc. However, GPS is only possible because of Einstein’s work with general relativity – but all of his work could have been for nothing if it weren’t for a total solar eclipse in 1919.
Albert Einstein Solar Eclipse Theory
Einstein theorized that mass does not simply generate a gravity force but rather that it warps the theoretical fabric that he called space-time, much like how a weight would warp stretchy fabric laid flat. In Einstein’s mind, what we interpret as gravity here on Earth was just the warping of space-time. But there was really no good way for him to prove it at the time. Einstein was only able to theoretically derive field equations to estimate these warping magnitudes caused by specific amounts of mass like the sun.
How Was the Theory of Relativity Proven?
It was actually Sir Frank Watson Dyson, the Astronomer Royal of Britain, who conceived an experiment that would actually test if space-time existed and how the influence mass influenced it. Einstein theorized that as light from a star passed by the sun, the light would be bent enough that we on earth would actually see the stars right “behind” the sun in a different place than where they actually were. But Einstein could never take a picture of the stars behind the sun because it is impossible to capture the underwhelming dull starlight directly behind the sun… unless, as Sir Frank Watson Dyson proposed, it was during a total solar eclipse! Eureka!
It wasn’t until May 29, 1919 during a total solar eclipse that this could be done. The eclipse spanned from Africa to Brazil, and Sir Dyson and Sir Arthur Eddington spearheaded two twin expeditions to get the proof they need. The expeditions were sent to the Sobral, Brazil and the African island of Principe. There were over a dozen photographs taken of the solar eclipse between the two locations, and all of them were used to confirm Einstein’s theory and his accurate predictions.
Although it looks almost identical to the human eye, the stars that you see around the sun are actually in a different place than what we see and interpret here on earth. This phenomenon is now called gravitational lensing and is, for Einstein, proof that the greatest theory he ever had was actually true. In our physical day-to-day world, gravity actually affects time directly.
From Space Time to Satellite Tech
Since Einstein’s theory was proven, we have continued to see, time and time again, that general relativity is inherently all around us. Modern science has so accurately measured the difference of gravity and its effect on time that if you go to the National Institute of Standards and Technology laboratory and stand 33 cm above your friend for 79 years, you would actually age faster than them by 90 billionths of a second. However, they use a twin pair of aluminum clocks to determine that. Einstein did not have those, but their research proves his theory just the same.
Ultimately, what this means in our modern day is that clocks tick at different paces when exposed to different gravitational field magnitudes. Since GPS satellites fly at an altitude of around 20,000 km from the surface of the earth, they feel a much different gravitational pull than we do, and actually tick faster than the clocks on earth… but not by a lot. When initially launched in 1977, the atomic cesium clocks onboard GPS satellites were actually designed to “tick” 38 µs slower than clocks here on earth so that they matched the same time stamp after becoming subjected to general relativity. This incredibly small correction in time, all predicted by Einstein, is what allows small out-of-the-box GPS modules to tell you your global position within a few centimeters of accuracy.
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Sources:
A Determination of the Deflection of Light by the Sun’s Gravitational Field, from Observations made at the Total Eclipse of May 29, 1919: Sir F. W. Dyson. November 6, 1919. http://rsta.royalsocietypublishing.org/content/roypta/220/571-581/291.full.pdf
Nist Pair of Aluminum Clocks Reveal Einstein’s Relativity at a Personal Scale. September 23, 2010. https://www.nist.gov/news-events/news/2010/09/nist-pair-aluminum-atomic-clocks-reveal-einsteins-relativity-personal-scale