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Material World
Application

Timekeeping

Counting a fixed atomic transition to measure time — the application that defines the second, and quietly underwrites navigation and telecommunications.

An atomic clock counts the frequency of a transition between two energy levels in an atom. The value is fixed by physics rather than by manufacture, so two clocks built independently agree — which is what a unit of measurement requires and what no pendulum or quartz oscillator can offer.

Caesium defines the second by international agreement. Rubidium is less accurate and far smaller and cheaper, which is what put atomic timekeeping into telephone networks and navigation satellites rather than leaving it in national laboratories.

Economic significance

Satellite navigation is timekeeping. A receiver works out where it is by comparing when signals from several satellites arrive, and an error of a millionth of a second is an error of some three hundred metres — so every satellite carries atomic clocks and the whole system is a distributed measurement of time rather than of position.

The same dependence runs through telecommunications and financial settlement, where a network that disagrees with itself about the order of events cannot reconcile.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

uses

  • Caesium — element · the second has been defined by a caesium-133 transition since 1967
  • Rubidium — element · less accurate than caesium and small enough to fly, which is what put atomic clocks into satellites and networks
  • Pollucite — mineral · the caesium-133 that defines the second comes from this mineral and essentially nowhere else

Sources

  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Timekeeping back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

  • Timekeeping → uses (the second has been defined by a caesium-133 transition since 1967) → Caesium → is produced by (calcium or barium reducing caesium chloride under vacuum — caesium is too reactive to survive most alternatives) → Metallothermic reduction → takes as input (the cheapest reducing metal and the commonest, and the aluminium in thermite) → Aluminium → is extracted from (via alumina — bauxite is refined by the Bayer process before smelting) → Bauxite → is sourced from (the residue of prolonged tropical weathering, which strips the silica and alkalis out of an aluminosilicate rock and leaves the aluminium behind — basalt is one common parent among several) → Basalt
  • Timekeeping → uses (less accurate than caesium and small enough to fly, which is what put atomic clocks into satellites and networks) → Rubidium → is produced by (reduced from its chloride the same way, and usually as a by-product of the caesium it accompanies in pollucite) → Metallothermic reduction → takes as input (the cheapest reducing metal and the commonest, and the aluminium in thermite) → Aluminium → is extracted from (via alumina — bauxite is refined by the Bayer process before smelting) → Bauxite → is sourced from (the residue of prolonged tropical weathering, which strips the silica and alkalis out of an aluminosilicate rock and leaves the aluminium behind — basalt is one common parent among several) → Basalt
  • Timekeeping → uses (the caesium-133 that defines the second comes from this mineral and essentially nowhere else) → Pollucite
  • Timekeeping → uses (the second has been defined by a caesium-133 transition since 1967) → Caesium → is extracted from (essentially the only commercial source) → Pollucite
  • Timekeeping → uses (less accurate than caesium and small enough to fly, which is what put atomic clocks into satellites and networks) → Rubidium → is extracted from (the main mineral source of rubidium, which substitutes for potassium in the mica) → Lepidolite
  • Timekeeping → uses (the second has been defined by a caesium-133 transition since 1967) → Caesium → is produced by (calcium or barium reducing caesium chloride under vacuum — caesium is too reactive to survive most alternatives) → Metallothermic reduction → takes as input (reserved for halides and the most stubborn oxides, where the cheaper metals will not do the job) → Calcium → is produced by (from molten calcium chloride; there is no smelting route) → Molten salt electrolysis → takes as input (after concentration, as one of the two routes to lithium chloride) → Lepidolite

These are the most distinct paths back. Timekeeping can be traced through others besides.