Atomic-scale transition
An atomic-scale transition is a rapid change in the energy state of an atom, often occurring in extremely short intervals.
How big is it?
1 fs · time
Time · reference interval
A little perspective
Atomic-scale transition vs Caesium-133 clock transition: duration comparison
One cycle of the caesium-133 clock transition is about 109,000 times the duration of an atomic-scale transition.
ELAPSED TIME
An atomic-scale transition is a rapid change in the energy state of an atom, often occurring in extremely short intervals.
Too small to see at this scale; the bar has not been widened.
The caesium-133 clock transition is the specific change in energy state of a caesium-133 atom that defines the duration of one second in the International System of Units.
Measurements, assumptions & sources +
Atomic-scale transition
Time: 1 fs; reference interval.
A chosen femtosecond process interval; real transitions span many timescales.
Defined examples — our methodology
The marked time is calibrated. Unmeasured illustration details are representative.
Caesium-133 clock transition
One cycle: 108.8 ps; derived.
The SI second is defined from exactly 9,192,631,770 periods of the unperturbed caesium-133 ground-state hyperfine transition. The cycle duration and photon energy here are derived from that exact frequency.
BIPM — The International System of Units
The marked one cycle is calibrated. Unmeasured illustration details are representative.
Use the visual comparison to explore its scale, then check the measurements and sources.
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Why this measurement?
Why we use 1 fs
We compare the duration of an atomic-scale transition. The measurement is labelled reference interval. Check the source notes for its basis.
A chosen femtosecond process interval; real transitions span many timescales.
The picture identifies the subject; the diagram compares the recorded values. How calibrated comparisons work →
Recorded properties
Dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 1 fs | Not recorded | reference interval |
Around this scale
Explore nearby values.
Compare examples with lower, similar and higher values. Each card names the measurement being compared.
Nearest lower valueTime and durationTop quark lifetime5 × 10⁻²⁵ sRepresentative lifetimeThis is the average time a top quark exists before it decays into other particles.Nearest higher valueFundamental physicsCaesium-133 clock transition108.8 psOne cycleThe caesium-133 clock transition is the specific change in energy state of a caesium-133 atom that defines the duration of one second in the International System of Units.Sources and method
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The source records and measurement method remain available for inspection.
There’s always another scale
Follow your curiosity.
TimeBlink of an eye150 msA blink of an eye is the quick closing and opening of the eyelid, usually happening involuntarily.TimeHuman lifetime80 yearsA human lifetime is the span from a person's birth to their death.
TimeAge of Earth4.54 GyrThe age of Earth is the time that has passed since the planet formed from the solar nebula.TimeAge of the universe13.8 GyrThe age of the universe is the time since the Big Bang, marking the beginning of cosmic expansion.Fundamental physicsCaesium-133 clock transition108.8 psThe caesium-133 clock transition is the specific change in energy state of a caesium-133 atom that defines the duration of one second in the International System of Units.TimeTop quark lifetime5 × 10⁻²⁵ sThis is the average time a top quark exists before it decays into other particles.TimeMuon lifetime2.197 µsMuon lifetime is the average time a free muon exists before decaying into other particles, such as an electron and neutrinos.TimeCamera flash1 msA camera flash is a brief, intense burst of light used to illuminate a scene for photography.