![]() ![]() Its rotation decreases at a rate of about 30 seconds every 10,000 years due to factors such as tidal friction. As it takes the sun one day to rise in the east, set in the west and rise again, a day was almost arbitrarily divided into 24 hours, an hour into 60 minutes and a minute into 60 seconds. The old definition of a second was based on the rotation of Earth. However, a spinning star notwithstanding, these methods are not always entirely accurate. The former relies on the motion of celestial bodies, including Earth, to keep track of time, whether it's the rotation time of a distant spinning star such as a pulsar, the motion of a star across our night sky or the rotation of Earth. There are two main ways of measuring time: dynamic and atomic time. Their results supported Einstein's theory that time fluctuates throughout the universe. In their paper published in 1972 in the journal Science, Hafele and Keating reported that the airborne clocks were about 59 nanoseconds slower than a ground-based atomic clock when traveling east, and 273 nanoseconds faster than the ground-based version when traveling west. Hafele and Richard Keating tested Einstein's theory by flying four cesium atomic clocks on planes around the world, going eastwards and then westwards. Time would speed up and slow down around cosmological bodies with different masses and velocities, and therefore one second on Earth was not the same length of time everywhere in the universe.ĭecades later, Einstein's theory was proven to be true. He postulated that time was more like a river, ebbing and flowing depending on the effects of gravity and space-time. However, in 1905, Albert Einstein asserted that the speed of light doesn't vary, but is a constant, traveling at 186,282 miles per second (299,792 kilometers per second). Every day has roughly 24 hours you don't have one day with 26 and one with 23. This is something that it's easy to think is true. Time must tick from one second to the next, with no difference between the length of any two seconds. By applying this theory, he was able to assume that if the speed of light could vary, then time must be constant. He believed that absolute motion could not be detected, which meant that nothing in the universe had a constant speed, even light. ![]() To Newton, one second on Earth was the same length of time as that same second on Mars, Jupiter or in deep space. In the 17th century, physicist Isaac Newton saw time as an arrow fired from a bow, traveling in a direct, straight line and never deviating from its path. How It Works is the action-packed magazine that's bursting with exciting information about the latest advances in science and technology, featuring everything you need to know about how the world around you - and the universe - works. This article is brought to you by How It Works. ![]()
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