Wonders of Science: Tick tock goes the clock
by Eric Rasmussen
Spend one hour doing something you enjoy. Then spend an hour standing in line at the Secretary of State’s office waiting for a license plate. Good chance the second hour will feel much longer. Depending on our situation, time passes at different rates for us humans, and amazingly, this relativity holds true for the cosmos.
Albert Einstein shed first light on this universal property, but people have always held a fascination with both time and light.
Ancient Greeks believed light traveled infinitely fast. Then in 1776 astronomer Ole Romer discovered that it abides by a strict speed limit. Through careful observation, he discovered that, on average, a small moon orbited Jupiter once every 42.5 hours. But there was a peculiarity. When Earth and Jupiter were orbiting closest to one another, little moon Io appeared to circle its planet about 22 minutes faster than when Earth and Jupiter were at their greatest separation. https://historyofscience101.files.wordpress.com/2014/01/jupiterconjunction1400x1000.jpg
Io could not be changing its orbital speed, Romer reasoned, so the delay had to come from the extra distance light was traveling to reach Earth. Based on his data and understanding of the solar system, he calculated the speed of light at 492,125,984 mph.
Even though Romer’s number proved lower than the actual 670,616,629 mph we now know light to travel, his discovery, using only rudimentary devices, was incredible.
At certain times, light reflecting from Io must travel farther to reach Earth. Photo credit: https://historyofscience101.files.wordpress.com/2014/01/jupiterconjunction1400x1000.jpg
The scientific community accepted Romer’s speed of light, and considered the rate of time passage to be universal.
Then Einstein came along and threw a wrench in the works. In 1905, he published Special Relativity and demonstrated these two ideas cannot be true. He linked time and space, and drew the conclusion that the faster an object moves through space, the slower time goes by for thatobject—people would theoretically age slower the faster they moved.
Luckily for us, we do not have to take Einstein’s mind-melting theory at his word because an experiment confirmed it.In 1971, scientists used two incredibly precise cesium-beam atomic clocks. One was kept stationary on the ground; the other was placed onboard a commercial airliner flown twice around the world. When the clocks were reunited, they were found to disagree. The clock that had traveled at a fast speed had been ticking slower. https://physicsforme.files.wordpress.com/2012/04/twinparadox-2.jpg
Special relativity shows us that time slows the faster we move. Imagine two identical twin boys. One hops into a rocket and travels at 99 percent the speed of light for 5 years. On arrival back at Earth, he will have aged only 3.5 years. His twin will have aged 5 years!
In 1916, Einstein again shocked the scientific community with his publication of General Relativity. GR demonstrated that gravity is capable of impacting the passage of time. The observed gravitational attraction between masses results from the warping of space and time by those masses.In other words, gravity works to slow down time, and the stronger the gravity, the greater the impact. A clock on Earth will tick slower than one out in space.
In fact, GPS satellite clocks have to be calibrated with general and special relativity in mind, or they become mismatched with clocks on the ground by about 38 microseconds per day. Admittedly, a few microseconds may not sound like much, but a miniscule error in time could mess up miles of locations on Google Maps.
Now that’s a wonder of science!
Eric Rasmussen, BS, M.Ed., obtained his bachelor of science degree at the University of Colorado at Boulder. He majored in ecology and evolutionary biology, and now serves as a Learning Technology Coach at Erie High School and Erie Middle School in the St. Vrain Valley School District, CO.
