The US National Institute of Standards and Technology has made its atomic clock presented last year even more precise. Last year it was still a deviation of one second every five billion years, but this has been reduced to once every 15 billion years.
Tweaking such a precision instrument is no mean feat, the organization writes on its site. The clock works by measuring the difference in energy level of the electrons in the nucleus of the element strontium. After the adjustment, the clock is good enough to measure small differences in the passage of time at different altitudes. This difference is due to the difference in gravity and can already be measured with a clock at a difference in height of two centimeters. This effect, gravitational time dilation, is one side of Einstein’s theory of relativity and has been measured before at a greater difference in distance from the center of the Earth. The last time in 2010, researchers succeeded in determining this at a minimum of 33 centimeters.
To make the clock more precise, the researchers placed super-sensitive thermometers in the vacuum chamber of the clock. In this way, errors in measurements and calculations can be corrected better with regard to the heat from the environment, the so-called black radiation. The electric field of black radiation changes the reaction of the atoms to the laser light, so that the measurement will not be precise enough if it is not corrected for.
However, even this precision does not go far enough for the researchers. If the difference in time can be measured even more precisely, ie with a centimeter difference in height, the shape of the earth can be determined even better. One of the researchers even tells the LA Times that if the clock could be made a thousand times more precise, we could hear the ‘symphony of the universe’, for example the change in spacetime when a distant galaxy explodes. Closer to home, this relativistic geodesy is also important in the development of GPS-like navigation systems.
In the clock, a few thousand strontium atoms are held together in a thirty by thirty micrometer column. The column consists of 400 circular regions formed by the lasers. The vibrations of the atoms can thus be measured very precisely by the network of lasers in which they are trapped. The clock is ticking at 430 trillion vibrations per second.
The online version of the paper can be read here.