Leap Seconds End in 2027: Let Lunch Hour Be an Illusion

The Lift Line

“That said, there was something mystical about the uncertainty of the most certain measuring devices, the drama of a second gained and lost.” (Editorial, The Indian Express, 20 October 2026)

Why This Editorial Matters for Your Exam

The Indian Express ran an unsigned editorial on 20 October 2026, “Sure, measure time. But let lunch hour be an illusion”, on the decision to stop adding leap seconds to the world’s reference clock. It is short and light in tone, opening with Douglas Adams’s Ford Prefect, but the decision behind it is solid exam material: Resolution 5 of the 28th General Conference on Weights and Measures (CGPM), “On the technical actions needed to ensure the continuity of UTC”.

This page sets out the editorial’s argument, then reads the resolution itself, because the exam will test the resolution, not the wordplay. It also tests two of the editorial’s lines against the record, and traces what the change means for Indian Standard Time (IST), which India’s new IST Rules (see our roundup on the IST Rules) tie to UTC.

UPSC relevance:

• GS Paper 3: science and technology in everyday life; IT and space; time synchronisation for critical infrastructure (transport, energy, telecom, space projects); cybersecurity (time stamps).
• Prelims: UTC, UT1 and TAI; leap seconds; BIPM, CGPM, IERS and ITU; CSIR-NPL and IST.
• Interview: a precise but drifting clock against the Earth’s rotation; who bears the cost of a standard.

In the news: The Indian Express, in its editorial of 20 October 2026, accepts the decision to stop inserting leap seconds into Coordinated Universal Time (UTC). At its meeting in Versailles last week, the CGPM decided that continuous UTC will become effective on 20 May 2027, and that the difference between Earth-rotation time (UT1) and UTC may grow to at most 3,600 seconds (one hour).

The Crux in 60 Words

Clocks keep atomic time; the day follows a slightly irregular Earth. Since 1972, leap seconds have held the two within 0.9 seconds. The CGPM has decided that from 20 May 2027 UTC will run without them, and the gap may grow to one hour. The editorial agrees the shift is sound for computer systems, and mourns a little lost drama.

What the CGPM Decided

For context, the 28th CGPM met at the Palais des Congrès de Versailles from 13 to 15 October 2026 and adopted its resolutions on 15 October 2026. The operative part of Resolution 5 reads:

The CGPM “decides that”: “continuous UTC will become effective on 20 May 2027, the maximum value for the difference |UT1-UTC| will be 3 600 seconds (1 hour), ensuring the long term continuity for UTC for several centuries,”

It then asks the BIPM to “continue to monitor the value of UT1-UTC, its estimated evolution and modelling as determined by the IERS”, to inform the International Committee for Weights and Measures (CIPM) regularly, and to work with the ITU, the International Astronomical Union (IAU), the International Union of Geodesy and Geophysics (IUGG) and the IERS to inform users. The BIPM notes that the official version of the resolution is the French text.

Three points follow from the text:

1. UTC stays. In 2018 the 26th CGPM (Resolution 2) stated that UTC is “the only recommended time scale for international reference and the basis of civil time in most countries”. What ends is the leap-second step, not UTC.
2. The text has no “leap hour”. It sets a ceiling of 3,600 seconds on the gap. It does not say how, or when, a correction will be made if the gap ever approaches that ceiling.
3. The date was brought forward. In 2022 the 27th CGPM (Resolution 4) decided that the maximum value for UT1-UTC “will be increased in, or before, 2035”, to keep UTC continuous “for at least a century”. The statement of the President of the Consultative Committee for Time and Frequency (CCTF), issued at Versailles on the day of adoption, says the CCTF “proposed to accelerate the process”, and as a direct result continuous UTC takes effect on 20 May 2027.

How we got here

The Issue, Decoded

The Analysis

1. The editorial’s case. It opens with Ford Prefect in The Hitchhiker’s Guide to the Galaxy: “Time”, remarked Ford Prefect, “is an illusion. And lunchtime doubly so.” Then it turns serious: getting the “real time” wrong “can have pretty serious consequences”, and for “the physicist and the computer engineer, the difference of even a few fractions of a second can cause problems for experiments and software that the digital world runs on”. Its verdict: “There are sound reasons for the shift: The risk to computer systems is lower.” Its regret: “something mystical about the uncertainty of the most certain measuring devices”. Its comfort: lunchtime “remains an illusion more subject to appetite than the clock”.

2. Why the metrologists acted: the resolution’s own reasons. The editorial gives one reason in a line; the resolution gives several.

• Critical infrastructure. “industrial users and the synchronization needs of national critical infrastructures, for example transportation, energy distribution, telecommunication, and space projects require UTC to be continuous without any future adjustment”. For some applications, a fixed “maximum value for the difference |UT1-UTC|” is needed “to appropriately design the software underlying operational systems”.
• The negative leap second. A CCTF-IERS workshop in March 2025, with experts on Earth rotation, “estimated that the probability of a negative leap second will increase rapidly in the near future, reaching a 30 % probability by 2035”. The resolution adds that “a negative leap second has not previously been applied” and poses “a high risk of causing anomalies and disruption to critical infrastructures that are largely unprepared”, and preparing for one would need financial investment whose amount is “estimated to be similar to their preparations for the millennium bug”. This, the sharpest reason, is absent from the editorial.
• Inconsistent fixes. Global service providers use “different mitigation methods” to avoid time steps, which “leads to inconsistency in timing between different systems”.
• Defection from UTC. A delay “could cause some user organizations to change their reference time scales to, for example, a GNSS time instead of UTC, seriously compromising the concept of international standardization in metrology”.
• More connected devices. The growth of the Internet of Things, smart grids and virtual services “creates an increasing risk of malfunction” with “the insertion of any leap second, especially with a negative one”.

3. Why one hour is tolerable. The resolution’s own reasoning: “in many countries there are differences of more than one hour between local apparent solar time and civil time due to the choice of time zone, and changes of an hour are regularly introduced when daylight-saving time is used”. Those who need Earth-rotation time are not left out: users of UT1 “can find information on the value of the difference UT1-UTC” in GNSS navigation messages and in internet services of the IERS, national metrology institutes and others. Radio time signals get a transition: ITU’s Resolution 655 (Rev. WRC-23), quoted in Resolution 5, resolved to allow dissemination of the larger difference “via radiocommunication system until 2035, but no later than 2040, in cases where existing equipment cannot be replaced earlier”.

4. Check: the “leap hour”. The editorial says the “time lords have decided to grant the world a ‘leap hour’”, and that wayward moments will be collected into one. The resolution does neither. It fixes a one-hour ceiling on the gap and is silent on how or when any correction will be made. A Euronews report on the decision says experts believe “it will still be some time before such a gap would actually require any correction, so the measure is essentially precautionary.” “Leap hour” is the editorial’s phrase, not the CGPM’s.

5. Check: the history and the numbers. The editorial links leap seconds to “1955 and the advent of atomic clocks”. As background, 1955 is when NPL (UK) brought its caesium atomic clock into operation, work that led to the 1967 SI definition of the second. Leap seconds in today’s UTC system date from 1 January 1972: “From 1 January 1972, the seconds of UTC have been exactly the same length as those of TAI”, and “UTC is kept always within 0.9 seconds of UT1 by the insertion of an extra second when necessary” (NPL, UK). The IERS table shows TAI-UTC at 10 seconds on 1 January 1972 and 37 seconds from 1 January 2017: by that count, 27 leap seconds, every one an insertion. There has been none since; IERS Bulletin C, issued in Paris in July 2026, says: “NO leap second will be introduced at the end of December 2026.” The editorial’s figure of 69 countries matches the BIPM’s count of its Member States (“There are currently 69 Member States and 34 Associate States and Economies”); the resolution itself records no vote count.

6. India’s stake. India is a Member State of the BIPM. CSIR-NPL, India’s National Metrology Institute, “maintains India’s national atomic time scale generating IST using an ensemble of atomic clocks and primary frequency standard”, and “IST is continuously kept traceable, within a few nanoseconds” to UTC maintained by the BIPM (PIB, Ministry of Science and Technology). The Legal Metrology (Indian Standard Time) Rules, 2026, introduced in 2026, were notified by the Department of Consumer Affairs on 27 August 2026, published in the Official Gazette on 29 August 2026, and “will come into force 180 days from the date of their publication”, under the slogan “One Nation, One Time”. Secondary time scales run at five Regional Reference Standard Laboratories at Ahmedabad, Bengaluru, Bhubaneswar, Faridabad and Guwahati, set up by CSIR-NPL, ISRO and the Department of Legal Metrology; CSIR-NPL also provides traceability of IST to ISRO for NavIC. The CERT-In Guidelines of 2023 recommend synchronising ICT systems with standard time sources including NPL and NIC. Our analysis: because IST is traceable to UTC, whatever UTC does reaches every system that synchronises to IST; a continuous UTC removes the leap-second step from that chain from 20 May 2027. Resolution 5 decides only the effective date and the one-hour limit; it changes no time zone.

7. The lunar sequel. The same CGPM adopted Resolution 6, “On the definition of an international lunar reference time scale and its traceability to UTC”. It recalls that the IAU in 2024 defined the Lunar Celestial Reference System with its Lunar Coordinate Time (TCL), encourages “space agencies operating pioneering lunar projects to share their practical experience”, and warns that “a proliferation of reference time scales risks ambiguity when exchanging time-tagged data and must be avoided”. It does not itself adopt a lunar time scale. The logic of Resolution 5, one agreed reference rather than many, now extends to the Moon.

Data and Institutions Vault

Prelims-grade facts:

The decision:

• Resolution 5 of the 28th CGPM (2026): “On the technical actions needed to ensure the continuity of UTC”
• Continuous UTC will become effective on 20 May 2027
• Maximum UT1-UTC: 3,600 seconds (1 hour), for continuity of UTC “for several centuries”
• 28th CGPM: Palais des Congrès de Versailles, 13 to 15 October 2026; seven resolutions adopted
• BIPM notes that the official version of Resolution 5 is the French text

The time scales:

• UTC: produced by the BIPM; same rate as TAI; differs from TAI only by an integral number of seconds
• UT1: the time scale describing the angular rotation of the Earth
• 26th CGPM (2018), Resolution 2: UTC the only recommended time scale for international reference
• Old rule: a leap second kept UTC within 0.9 seconds of UT1

The record:

• TAI-UTC: 10 seconds on 1 January 1972; 37 seconds from 1 January 2017 (27 leap seconds, all inserted)
• No negative leap second has ever been applied
• CCTF-IERS workshop, March 2025: 30 per cent probability of a negative leap second by 2035
• IERS Bulletin C: no leap second at the end of December 2026

The institutions:

• BIPM (International Bureau of Weights and Measures): 69 Member States, 34 Associate States and Economies
• Member States are States that have ratified or acceded to the Metre Convention (1875); India is one
• CGPM (General Conference on Weights and Measures): each State has one vote
• IERS (International Earth Rotation and Reference Systems Service): decided leap seconds about 6 months ahead
• ITU Resolution 655 (Rev. WRC-23): radio transition until 2035, no later than 2040

India:

• CSIR-NPL maintains IST, traceable to UTC within a few nanoseconds
• Legal Metrology (IST) Rules, 2026: notified 27 August, gazetted 29 August; come into force 180 days after publication
• Five RRSLs: Ahmedabad, Bengaluru, Bhubaneswar, Faridabad and Guwahati

⚠️ Watch the trap: UTC is not abolished; only the leap-second step ends, from 20 May 2027. The resolution sets a ceiling of one hour on UT1-UTC and does not provide for a “leap hour”. Leap seconds in today’s UTC date from 1 January 1972, not 1955. And 69 is the BIPM’s count of Member States, not a vote tally.

The Debate

Balanced verdict: the editorial is right that the shift is sound, but it undersells the reason (the risk of an untested negative leap second) and overstates the remedy (there is no “leap hour” in the text). The trade is a small, recurring and growing risk to systems today against a slowly widening, capped gap from the Earth’s rotation, with the rule for that distant day still to be written.

How to Think About This

1. Separate the scale from the step. UTC continues as the world’s reference time. What ends from 20 May 2027 is the leap-second step that kept it close to the Earth’s rotation. Write “leap seconds end”, never “UTC abolished”.
2. Separate a ceiling from a correction. “3 600 seconds (1 hour)” is a limit on the gap. Whether that gap is ever closed, and how, is not in Resolution 5. A limit is not a scheduled event.
3. Price the risk for each user. Engineers gain a clock without steps; astronomers and navigators who need Earth-rotation time must apply a correction they already get from GNSS messages and IERS services. Ask who carries the cost of a change in a standard, and whether they have the data to carry it.
4. Follow the chain home. IST is traceable to UTC through CSIR-NPL. A decision in Versailles reaches India’s networks through that chain, which the IST Rules, 2026 are meant to make legal and uniform.

Diagram-in-Words

Read the map top to bottom: two time scales, the old leap-second rule, the reasons for change, the decision of the 28th CGPM, and what the decision leaves open.

Takeaway Box

• Lift line: “there was something mystical about the uncertainty of the most certain measuring devices, the drama of a second gained and lost.”
• The argument: there are “sound reasons for the shift”, since “The risk to computer systems is lower”; lunchtime stays an illusion.
• The decision: CGPM Resolution 5 (2026): continuous UTC from 20 May 2027; UT1-UTC capped at 3,600 seconds (1 hour), continuity “for several centuries”.
• The reasons: critical infrastructure needs continuity; a negative leap second, never applied, at 30 per cent probability by 2035; inconsistent fixes; drift to GNSS time.
• Prelims hooks: UTC, UT1, TAI; 0.9-second rule from 1 January 1972; TAI-UTC 37 seconds from 1 January 2017; BIPM has 69 Member States; ITU transition until 2035, no later than 2040.
• India: CSIR-NPL keeps IST traceable to UTC within a few nanoseconds; IST Rules, 2026 come into force 180 days after publication in the Gazette (29 August 2026).
• Mains keywords: continuous UTC, critical infrastructure, negative leap second, time synchronisation, metrological traceability, international standardisation, One Nation One Time.
• Ethics and Interview: precision against tradition; who bears the cost of changing a global standard.
• Probable question: “Why has the world decided to end leap seconds in UTC? Discuss the implications for critical infrastructure and for India’s standard time.”
• Watch next: 20 May 2027 (continuous UTC); India will host the 61st meeting of the International Committee of Legal Metrology in New Delhi, scheduled for 26 to 28 October 2026; a new definition of the second is to be presented at the 29th CGPM in 2030.

Revision Flowchart

Sources: The Indian Express, editorial, “Sure, measure time. But let lunch hour be an illusion”, 20 October 2026; BIPM, Resolution 5 of the 28th CGPM (2026), “On the technical actions needed to ensure the continuity of UTC”; BIPM, Resolution 6 of the 28th CGPM (2026), lunar reference time scale; BIPM, 28th meeting of the CGPM (2026); BIPM, CGPM 2026: Resolutions adopted; BIPM, Statement by the CCTF President, CGPM 2026; BIPM, Resolution 4 of the 27th CGPM (2022); BIPM, Member States; NPL (UK), “What is a leap second?”; IERS, leap second history table; IERS Bulletin C; PIB, Ministry of Science and Technology, PRID 2306171; CSIR-NPL, Indian Standard Time; PIB, PRID 2324997, International Committee of Legal Metrology meeting; Euronews report on the leap-second decision.

Source: Leap Seconds End in 2027: Let Lunch Hour Be an Illusion — Ujiyari.com | Free UPSC & State PCS Editorial Analysis