Redefining the SI Second: Optical Clocks and the Future of Timekeeping
For UPSC aspirants – By Suryavanshi IAS
Why Is This Important for UPSC?
This topic connects to:
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GS Paper III – Science and Technology: Developments and their applications
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Prelims – SI Units, Atomic Clocks, GPS, Electromagnetic Radiation
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Essay – Role of Science in Modern Life
Background: Current Definition of the Second
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As per 1967 SI system,
1 second = 9,192,631,770 cycles of radiation from caesium-133 (Cs-133) atom. -
This frequency lies in the microwave range.
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Used globally in GPS, telecom, astronomy, and national time standards.
Why Change Is Needed
| Current Cs Atomic Clocks | New Optical Clocks |
|---|---|
| Microwave frequency (GHz) | Optical frequency (THz) |
| Accuracy: 1 sec / 300 million yrs | 1 sec / 15 billion yrs |
| Used since 1967 | Expected to redefine second by ~2030 |
| Eg: Cs-133 | Eg: Strontium-87, Ytterbium-171, Indium-115 |
Recent Development
What happened?
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World’s biggest test of optical atomic clocks:
10 clocks, 6 countries, 3 continents, 65 scientists.
Locations Involved:
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Germany, France, Italy, Finland, UK, Japan
Technologies Used:
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Fibre optic networks
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GPS with IPPP (Integer Precise Point Positioning)
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Backup clocks during maintenance
Result Highlights:
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38 ratios measured (some for the first time)
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Accuracy achieved: as fine as 4.4 × 10⁻¹⁸
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Minor discrepancies found (e.g., in Italian GPS readings)
Key Concepts for UPSC
| Term | Meaning |
|---|---|
| Atomic Clock | Timekeeping using radiation from atomic transitions |
| Optical Clock | Uses higher-frequency light waves for more precision |
| Hyperfine Transition | Energy jump in atomic electrons, used to define frequency |
| IPPP | GPS technique for extremely precise location/timing |
| Frequency (Hz) | Cycles per second; more cycles = better time resolution |
Q. How are optical atomic clocks redefining the SI second? Discuss their significance.
Intro: Current SI second is based on Cs-133 microwave radiation.
Body: Optical clocks offer 100× precision; used in GPS, astronomy, defence.
Recent Global Test: Coordinated test across 3 continents proved viability.
Significance: Redefining SI unit; improving global timekeeping infrastructure.
Conclusion: A step toward precision-driven technological advancement.
Prelims Practice Q:
Q. Which of the following is true about optical atomic clocks?
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They operate at higher frequencies than caesium clocks.
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They are expected to replace Cs-133 clocks in defining the second.
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They are less accurate than quartz clocks.
Select the correct answer:
A) 1 and 2 ✅
B) 2 and 3
C) 1 and 3
D) All of the above
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