



The Men’s 100m butterfly final at the Rio 2016 Olympics was remarkable for a few reasons.

Joseph Schooling won Singapore’s first gold medal and a windfall of R10 million for doing so with his Olympic record of 50.39 seconds. He beat his hero Michael Phelps who he met when he was 13. Phelps, as the most successful athlete ever, had to accept silver along with Chad le Clos and Laslo Cseh in the first three way tie at an Olympic swimming event.

Image credit: Google

It prompted some to wonder why they don’t measure the time in thousands of seconds. The reason is remarkable - swimming pools are not built to allow for that level of accuracy!

Competition pools may not be less than 50m but are allowed to be up to 3cm longer. A swimmer could cover a distance greater than 3cm in a less than a 100th of a second. Any race over 50m could have a distance variance of 6cm and still be valid which is why ties in swimming can be expected even if three way ties are still a first.

This illustrates how important for sport a standard set of measures is and the same applies to science, business, construction and just about any industry.

It begins with a second.

One of the first standards humans created was that of time. Arriving at the second after many years and once our means to make mechanical clocks allowed us to determine their length. But mechanical clocks have limitations and so it has been replaced by a more specific and robust definition although it is very likely you did not know about it.

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. Official SI defintion

When you talk about an atomic clock the "atomic" refers to the means the clock uses to measure time - the vibration of the cesium atom.

James May explains below.

So how long is a metre?

It was first derived from a distance unit taken as a fraction of the distance from the pole to the equator running through Paris. A bar of that distance was created in order to measure all other metres against it. That requires a lot of copies to be made and periodically checked to see if it still accurate. Not a great option so it was redefined.

The meter is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. Official SI defintion

That leaves the kilogram.

What bizarre definition might we have for that? We don’t. The kilogram is an actual block of mostly platinum that is used to compare with copies that are distributed around the world and used to check devices' calibration. South Africa has one that is used for Southern Africa. There are plans to change it because scientists know the original kilogram is probably not exactly a kilogram anymore and the thing to replace it may be a special speaker! Watch below for the details.

These units are part of the Metric system created following the French Revolution to use more specific ways to define measurements than the quite arbitrary options from before.

It has been adopted almost everywhere on earth with two notable exceptions: the US and, for some measures, the UK. Liberia and Myanmar also still use both while moving towards a metric system.

It seems odd that the US which welcomed the French ideas of independence and democracy did not like the ideas of the metric system. One reason just after it was introduced was that it placed man ahead of God and imperial units used natural units. This is probably not true as the metric system is decimal based; i.e. it uses 10 as a base, that was chosen for the most part because we happen to have 10 fingers.

Even more remarkable is that the US imperial unit definitions are derived from the metric units, so while the US says the metre is a hard thing to get Americans to adopt, they have no problem using the metre to determine that a foot is 0,3048m. Or watching the Olympics which has most of the events defined in the metric system.

Tom Scott explains why we have an actual kilogram and what we may replace it with.

But before we feel too smug about the foolishness of those in the US or UK, consider that all of us actually are using an older unit for temperature - whether Celsius or Fahrenheit. The standard unit for temperature is Kelvin. It is defined as being 273.16 K at the triple point of water (when it can exist as a solid, liquid and gas) which is equivalent to 0.01 C. The scale is the same as Celsius so 0 K is -273.15 C. A typical summer's day at 25 C should be 298 K, but odds are you would not be keen to do it. You will probably agree that it would be better as you never need to mention a negative temperature which is confusing but your decision to not do it has nothing to do with what is best - it is what you are used to that moves most of us. While the UK, US and both Myanmar and Liberia are working on switching to the metric scale, it will be a tough thing to do if they ever manage it.

On the point of negative temperatures you might smile to know that Celsius’s original scale actually had boiling water at 0 C and freezing at 100, because he was from Sweden and it gets cold there, his original scale would not use negative numbers for below freezing temperature.

Derek Muller explains.

Matt Parker of Brit Lab goes one better at highlighting the strange imperial measurements that were defined for many as the width of three barley corns or four poppyseeds.

This article first appeared on CapeTalk : What a three-way Olympic swimming tie says about our strange measuring system