By Udita Shukla
Recently, researchers at the National Institute of Standards and Technology (NIST), Maryland, USA, created an optical clock using the aluminium atom. The electrons of aluminium switch states over quadrillion time each second, which results in an atomic clock that is up to forty times more accurate than a conventional caesium atomic clocks. Indeed the researchers were able to observe a clear difference in the readings of two optical clocks, which were stationed at a vertical separation of fifty centimetres. Moreover, this effect was also seen at intervals as short as four meters per second.
The science behind atomic clocks
Atomic clocks are essentially based on the natural transitions of electrons among different energy levels in an atom. The length of a unit of time, such as a second, is determined by the total number of complete oscillationsa jump to the higher energy level and back again to the original levelof an atom’s electron. Such a measure is much more stable than any mechanical pendulum as the swinging motion of a pendulum can be easily disturbed by environmental or internal factors.
The new research on atomic clocks has shown that there is a marked difference in the speed of time along the gravitational field. An object that is subjected to a stronger gravitational pull near a source of gravitysuch as the earthalso experiences greater time dilation, and hence, a clock close to a source of gravity runs more slowly. This is what has led to the popular phrase, Time runs faster at your face than at your feet, or, that your head is older than your feet.
This new research clearly demonstrates one of the basic postulates of Einsteins theory of relativity. The Theory of Special Relativity was first published by Albert Einstein in 1905. Among many intriguing predictions, the theory introduced concepts such as time dilation, length contraction, and mass changes. The concept of time dilation states that time runs slower for an object the faster it is moving. While an object at rest moves through time at the full speed with no time dilation, an object that is moving as fast as possiblewhich is the speed of lightceases to move through time. Thus the concepts of motion through space and movement through time are directly linked to Einstein’s theory.
Applications of atomic clocks
Experiments with atomic clocks are already being put to use in the field of navigation. For example, commercial airliners depend on the Global Positioning Services (GPS) satellites which orbit the earth at an altitude of around twenty thousand kilometres. Since the satellites are in continuous motion, the time signal they send must be corrected for deviations of a few nanoseconds, caused by time dilation. GPS satellites are installed with atomic clocks that have an accuracy of a few billionths of a second. These orbiting machines experience a time dilation of about 4 microseconds a day, a number which, when combined with the effects of gravity, climbs up to about 7 microseconds or 7,000 nanoseconds. Without this correction, a GPS unit attempting to plot a gas station to a receiver on earth would send coordinates offset by nearly five miles after only a day in orbit.
On the larger scale, these experimental results may also contribute more to an understanding of fundamental physical theories, such as Einstein’s theories regarding space-time. Research into the effects of time dilation has also added fuel to the active research in time-travel and wormholes. Ongoing research based on the theories of special and general relativity are providing the most impressive examples of how the invisible character of our reality continues to be unveiled for our benefit.
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