Happy 2025! Reflecting on the timeless story of Time

Happy New Year 2025! As I was recently listening to Cyndi Lauper's famous "Time After Time" song, I thought that reflecting on the notion of time as we transition year was a good idea. As always, in this short article series, I'll blend historical, scientific and societal implications on topics that my audience finds interesting or contemporary. This is the first article of this newsletter for 2025. Hopefully, you'll enjoy it. Please feel free to provide any comments or areas you'd like to see covered in future articles.

What is Time?

The numbers you read on your watch? The number of candles you put on one's birthday cake? Einstein's theory of relativity - where time is a "stretchable" concept and not an absolute quantity? A "ruler" summarizing the cosmological evolution of planets and species - including when religions officially emerged?

A more formal definition:

Time is a fundamental dimension in which events occur in a sequential order, allowing for the measurement of durations and the intervals between them. It serves as a framework for understanding the progression from the past through the present and into the future

Some basic facts: we have 365 1/4 days in a year because this is the duration it takes Earth to orbit around the sun. The definition of one second has evolved over the years. It was initially based on the time it takes for Earth to perform a complete rotation (called a solar second or 1/86,400 of a mean solar day of 24 hours, 60 minutes).

You might ask: why 24 hours in a day? It was decided by Egyptians for practical and astronomical reasons (they were using a base-12 number system then). Today's more precise definition involves the cesium-133 atom and the measurement of energy-level transition occurrences. This is called an atomic clock, which GPS satellites embed to provide accurate clock information to receivers - a fundamental aspect of triangulating satellite signals to enable precise localization.

Modern topics around Time

My first genuine appreciation of what Time could even mean was when I was a teenager. We studied fundamental particles in physics and, simultaneously, Egyptian history. Carbon-14 ageing detection, known as radiocarbon dating, seemed like a magical tool—so powerful that it is still used today. This technique enables coarse dating of formerly living materials.

We often talk about fractional seconds - like in sports, where people usually refer to "ms" for milliseconds or 1/1000 of a second. In electronics, people often talk about "ns" for nanoseconds (1/billionths of a second) or 1/10^9, or even "ps" - or picoseconds - which is 1/10^12 of a second. Using laser pulses, scientists can measure time up to the attoseconds or 10^-18 seconds. This can be translated into light travelling 0.3 nanometers - or one billionth of a meter. Measuring time at such a tiny scale is a fundamental component of harnessing the potential of quantum computers.

Atomic clocks can attain attosecond accuracy for several minutes to a few hours, but at the most fundamental level, they can drift over time.

This notion of drift is a well-known issue in computer science. Many protocols and software need to align clocks across computers, for example, to guarantee the proper ordering of data exchanged across networks with different speeds or latency characteristics.

Protocols like IEEE 1588 in time-sensitive networks (TSN) offer sub-millisecond precision, which is often sufficient for most computer applications. They are frequently used in aeronautics, safety-critical energy installation, or even the synchronization or distributed databases (I highly recommend viewing the recent presentation of Amazon AWS CTO Dr Vogels here). Dr Vogels explains that in the absence of clock synchronization, a slew of complex algorithms and inefficient redundant operations impact the cost efficiency of distributed data centres.

It is essential to understand that aligning clocks isn't the same as keeping clocks synchronized. In the military, for example, operations in different time zones are often specified to appear in "Zulu" time or UTC+0. This enables everyone to align in a time zone.

In computer programming, you'll often see a standard function that returns the number of seconds elapsed since January 1, 1970UTC as an absolute measure of time. This, again, is to anchor absolute time reference among computers. Now, how that time reference's measurement evolves is the drift, which you want to keep in check for the desired accuracy. This often means having a master clock reference and compensating for "slave" clocks that may accelerate or slow down time measurement for intrinsic reasons (like the technology used to measure time or the uncertainty of propagating the time to distribute time information on a medium).

Because data processing has latency characteristics (e.g., computers can only process data they receive at a minimum speed), you often don't need attosecond accuracy, but you do need some accuracy to maintain data coherency. For example, if multiple people upgrade a database by adding or deleting entries, the order in which transactions occur is essential to the coherence of the stored information.

The GPS example I mention above is a good, modern example of a use case where end-to-end attosecond accuracy isn't needed to provide accurate localization information, but if GPS satellites had a clock only in the micro-second accuracy range, this could yield a localization accuracy impact in the kilometre range.

Conclusion

If you think about it, time is one of the few metrics the world has aligned—across time and civilisation. Without accurate time measurements, the world as we know it would probably collapse—one more reason to celebrate the new year!

And we shall never forget: time is the only thing money can't buy, so spend it wisely - including with your family.

#time #clock #atomicclock #datacenter #happynewyear #gps

As always, feel free to contact me @ [email protected] if you have comments or questions about this article. Please note that my articles reflect personal opinions on various topics and are always based on publicly available data.

More at www.lohier.com and also my book. You can subscribe to this free bi-weekly newsletter here and access former editions here.