Humans have been keeping time for millennia. It started with sticks in the ground and has advanced to caesium atomic clocks, allowing us to mark the passing of time with increasing accuracy.
Throughout time all clocks have one thing in common – they mark the passage of time by counting regular oscillations. Sun dials, pendulum clocks, and quartz clocks all work by counting periods of oscillations, even if some of them had to be regularly recalibrated against the ‘master clock’ of the earth’s rotation. However, over the centuries we have learnt that the earth’s rotation is not constant – it is gradually slowing down, and it varies with the seasons and fluctuates in unpredictable ways. So how can we make sure that we’re all operating on the same time schedule?
It wasn’t until the invention of the pendulum clock in the 1650s that it was possible to work out the relationship between mean (clock) time and solar time. We now know that solar time is not the same everywhere – even within the same time zone. For example, in the UK Liverpool is 12 minutes behind London.
This didn’t matter very much when travel between towns and cities was slow, but when the railways were invented having different times at different stations caused confusion, near misses and accidents. A new solution was needed.
The Great Western Railway led the way and other railway companies gradually took up ‘railway time’. Eventually times were standardised to Greenwich Mean Time (GMT), developed by John Flamsteed who came up with the formula for converting solar time to mean time, and published a set of conversion tables in the early 1670s.
GMT was adopted as the reference standard for time zones around the globe and the second was formally defined as a fraction (1/86,400) of the mean solar day at the International Meridian Conference, Washington DC, USA in October 1884.
Today, time is marked by International Atomic Time (TAI), using ultra-precise observations of the caesium-133 atom and 340 atomic time clocks in different locations internationally.
Time is fragile
With developments in technology and understanding, the accuracy with which we mark time has increased over the years, and we now have ultra-precise atomic clocks. However, time is more fragile than we think and the faster, more efficient, and more integrated our systems become, the more they rely on these ultra-precise atomic clock timings.
These systems, which include those used for communications, energy, transport, and financial services, are fragile because they are prone to error when it comes to such high levels of precision.
Dr Simon Harwood, Director of Defence and Security, Cranfield University says: “As global data signals have the potential to be jammed and spoofed by criminals and political enemies, access to atomic clocks can become dependent on stable political relations.”
Did you know?
Your computer clock is based on a system clock tick rate and is just a microscopic tuning fork a couple of millimetres long. No two are identical - each will be affected by temperature in different ways and age differently. Typical drift is up to two seconds per day, meaning time stamps are wrong and interactions across networks are based on inaccurate timings.
The relevance of atomic clocks to our everyday lives are contained within Global Positioning System (GPS) satellites. Information determining time to within 100 billionths of a second is shared globally wherever a signal can be received via satellites - making it unnecessary for individual organisations to operate their own atomic clocks.
GPS satellites have been an overwhelming success and over the last couple of decades they have been relied upon for positioning, navigation, and timing (PNT) applications.
“Unfortunately, GPS can be cheaply and easily disrupted by transmitting noise on the same radio-frequency, while the satellites it relies on can malfunction or suffer interference from solar flares. Mobile phones and other wireless communications depend on rigid time standards (an accuracy level of less than one second difference over 3,000 years) to put signals into order, prevent congestion and ensure calls and messages from different operators can be synchronised. The same applies to electricity power grids that have to link energy sources on the same frequency and financial institutions and other businesses need to have a guarantee of the time and date of transactions to the microsecond and the order in which they took place,” adds Dr Harwood.
According to GPS World, a large-scale GPS failure would cause a £1 billion a day economic impact to the UK. The loss of this accurate data would also have severe and life-threatening effects, such as on getting ambulances to patients or getting power to homes around the country.
Technology that can underpin trusted and reliable systems
The UK’s dependence on satellite technologies has been identified by the government as a potential security risk if a satellite were to experience a failure. For instance, in 2016 the decommissioning of a single GPS satellite led to 12 hours of IT and phone system errors globally.
“At Cranfield we are working on a potential solution that seeks to establish technology that can underpin trusted and reliable navigation, communication, and surveillance, as well as timings for traffic management in digital aviation and transport in smart cities,” explains Dr Ivan Petrunin, Lecturer in Digital Signal Processing for Autonomous Systems.
The work builds on existing tech created by UK company Hoptroff and its experience developing Cloud-based backup for the financial services sector. The system is based on a network of mutually resilient cloud-timing hubs, each consisting of three nanosecond-accurate ‘grandmaster’ clocks connected to three different sources. The hubs continuously compare the different sources to ensure that accuracy and source traceability are maintained. To mitigate against satellite communication issues, a backup is supported by a terrestrial location at RISE, the Research Institutes of Sweden.
Building in resilience
Satellite-based technologies are inherently vulnerable, and the accuracy of GPS is not being monitored to the extent needed for resilience. The high vulnerability of GPS to jamming or spoofing, means this lack of monitoring is dangerous. We need to take on the challenge of how national and linked international infrastructures can always depend on time data and that means recognising the problem and investing in new ideas - in particular, being open and alert to emerging innovations coming through from small and micro-enterprises.