world's most accurate clocks are synchronised to a quadrillionth of a second - and it could change how we define time - laser measuring tool

Time may be relative, but physicists insist on accuracy.
While many of us may give home clocks a few minutes of Grace, a group of scientists have successfully synchronized a pair of optical clocks to a few parts per second.
By measuring time precisely, physicists can eventually change the length of a second.
In order to make such accurate measurements, a team led by physicists from the National Institute of Standards and Technology (NIST)
In Colorado, a building fired a laser beam over seven miles into another building (12 km)away.
At any end, they use an optical clock that works in a similar way to a microwave clock, using atoms or ions, the oscillation frequency of these atoms or ions in the optical or visible field is 100,000 higher than the microwave frequency as part of the spectrum.
Using a dedicated laser tool called a frequency comb, they are able to detect regular laser pulses every five nanoseconds-one in 5 billion seconds-as if the clock were ticking.
The two clocks send pulses to each other, and the arrival time is measured at each clock.
The measurements of the group were so tiny that they even considered the swing and air turbulence of the building to consider minor changes that might affect the arrival time of the pulse.
With these differences in mind, they can be subtracted from any difference in the arrival time to synchronize the two to one second.
Once we have measured the difference in clock time, we can speed up or slow down the clock of Site B so that it is consistent with the clock of site A in microseconds, laura Sinclair, a physicist at the National Institute of Science and Technology, explained.
The team wrote in the journal Applied Physics Letters that they reported how they could maintain such accurate accuracy despite the distance.
Sinclair said that 12 km of the turbulent air caused a huge distortion of the laser beam, but the two clocks reached 20 in time.
The physicist added: "How far can we really go?
If one day we want to redefine the second standard so that it is based on the optical standard rather than the microwave standard, we need to be able to connect the best clocks in the world and then distribute the time information.
Earlier this year, German researchers designed a way to measure a second more accurately.
This may mean that the second definition of what is actually going to be changed by an incredible tiny amount --
It's just a fraction of the square of a second.
The change will see the amount of error when estimating the second length reduced from 0.
Secondary Ion for 25 secondsthat is 0.
There are 25 in front of 15 zeros.
Ten times.
Reducing the uncertainty of a second means that physicists will be able to make more accurate estimates of how long an event will take.
In context, this means that such a clock will only lose about 14 billion seconds since the beginning of the universe before 100.