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Time spans an extraordinary range in physics — from the Planck time (5.39 × 10⁻⁴⁴ s, the smallest physically meaningful time interval) to the estimated lifetime of the universe (trillions of years and beyond). This converter covers all major time units from femtoseconds used in ultrafast laser physics to gigayears used in cosmology and stellar evolution.
The second (s) is the SI base unit of time, defined since 1967 by the cesium-133 atom: exactly 9,192,631,770 periods of the radiation corresponding to the hyperfine transition of the ground state of ¹³³Cs. This atomic clock definition provides stability at the level of 10⁻¹⁵ — better than 1 second over 30 million years.
In ultrafast physics, femtosecond (10⁻¹⁵ s) lasers allow snapshots of molecular vibrations (typical period: 10-1000 fs) and chemical bond breaking (100-1000 fs). The attosecond (10⁻¹⁸ s) regime, reached by high-harmonic generation lasers, allows imaging of electron dynamics in atoms — the 2023 Nobel Prize in Physics was awarded for attosecond science. The fastest controlled event is about 43 attoseconds.
In nuclear and particle physics, strongly interacting processes occur on the timescale of 10⁻²³ s (nuclear transit time: fm/c); weak decays range from picoseconds (B mesons, ~1.5 × 10⁻¹² s) to microseconds (muon, 2.2 μs) to minutes (neutron, 10.24 min). Electromagnetic transitions in atoms are nanoseconds to microseconds for allowed transitions.
In cosmology, 1 Gyr = 10⁹ Julian years = 3.156 × 10¹⁶ seconds. The age of the universe is 13.8 Gyr; the Sun formed 4.6 Gyr ago; life appeared on Earth ~3.8 Gyr ago; the proton half-life (if it decays) is > 10³⁴ yr; the estimated time for all stars to die out is ~100 Tyr (10¹⁴ years).
Select the input time unit and enter the value. All conversions pass through seconds. 1 Julian year = 365.25 × 86,400 = 31,557,600 s (exact). 1 Planck time tP = √(ℏG/c⁵) = 5.391247 × 10⁻⁴⁴ s.
Key time scales: Planck time 5.4 × 10⁻⁴⁴ s; nuclear transit time ~10⁻²³ s; atomic transition ~10⁻⁹ s; heartbeat ~1 s; age of universe 4.35 × 10¹⁷ s = 13.8 Gyr. A nanosecond is roughly how long it takes light to travel 30 cm (about 1 foot).
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13.8 Gyr = 4.35 × 10^17 seconds since the Big Bang. The oldest stars in globular clusters are about 13.6 Gyr old, consistent with this age.
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100 femtoseconds = 10^-13 s is the typical time scale for chemical bond breaking and molecular vibrations, accessible by ultrafast pump-probe laser spectroscopy.
The Planck time tP = √(ℏG/c⁵) = 5.391247 × 10⁻⁴⁴ s is the fundamental quantum gravity time scale. Below this time interval, our current physical theories break down — quantum mechanics and general relativity become simultaneously important. It is the time for light to travel one Planck length (1.616 × 10⁻³⁵ m).
The second is defined as exactly 9,192,631,770 periods of the microwave radiation emitted by the hyperfine transition of ground-state cesium-133 atoms at 0 K. Modern optical atomic clocks using strontium or ytterbium are 100-1000 times more stable, achieving fractional uncertainty of 10⁻¹⁸, but the SI second is still defined by cesium pending a future redefinition.
Light travels 29.98 cm (about 1 foot) in 1 nanosecond. This was the basis for Rear Admiral Grace Hopper's famous 'nanosecond' wire demonstrations to explain computer signal propagation delays. Modern computer clock cycles are 0.3-1 ns; RAM access latency is ~10-50 ns; light from a laser pulse can be only a few hundred micrometres long if 1 ns duration.
Free neutron: 611.0 s (10.2 min). Muon: 2.197 × 10⁻⁶ s. Pion (π⁺): 2.603 × 10⁻⁸ s. Kaon (K⁺): 1.238 × 10⁻⁸ s. B meson: ~1.5 × 10⁻¹² s. Z boson: ~2.6 × 10⁻²⁵ s. Higgs boson: ~1.6 × 10⁻²² s. The shorter the lifetime, the broader the energy-mass peak in collider data (via ΔEΔt ≥ ℏ/2).
Formation of Solar System: 4.568 Gyr. Formation of Earth's Moon (giant impact): 4.5 Gyr. Oldest known rocks: 4.0 Gyr. First life (microfossils): 3.7-3.8 Gyr. Snowball Earth: 0.7-0.6 Gyr. Cambrian explosion (complex life): 541 Myr. Dinosaur extinction: 66 Myr. First hominids: 6-7 Myr. Homo sapiens: 300,000 yr. Agriculture: 12,000 yr.
1 attosecond (as) = 10⁻¹⁸ s. The period of visible light is about 1-3 femtoseconds; an attosecond laser pulse is shorter than one optical cycle of visible light. Attosecond science (Nobel Prize 2023: Anne L'Huillier, Pierre Agostini, Ferenc Krausz) enables real-time observation of electron motion in atoms and molecules — ionization happens in tens of attoseconds, electron tunneling in hundreds of attoseconds.
GPS satellites orbit at 20,200 km altitude where time runs faster by 45 μs/day (gravitational blueshift) and slower by 7 μs/day (kinematic redshift from v = 3.87 km/s), netting +38 μs/day relativistic time gain. Without correction, position errors would accumulate at about 10 km/day. GPS clocks are pre-adjusted to run slightly slower on the ground to compensate for this relativistic effect when in orbit.
According to the Big Freeze scenario: ~10¹⁴ yr — last stars die; ~10²⁸ yr — brown dwarfs cool to near absolute zero; ~10³⁷ yr — protons decay (if they do); ~10⁶⁷ yr — black holes of stellar mass evaporate via Hawking radiation; ~10¹⁰⁰ yr — supermassive black holes evaporate; beyond — only cold photons and leptons remain in an expanding, cooling universe.
Carbon-14 has a half-life of 5,730 years = 1.809 × 10¹¹ s. After n half-lives, the fraction remaining is (1/2)^n. Radiocarbon dating is effective for up to ~50,000 years (about 8 half-lives, leaving 1/256 of original ¹⁴C). Older samples use other radioisotopes: K-40/Ar-40 (t½ = 1.25 Gyr) for geological dating, U-235/Pb-207 (t½ = 703.8 Myr) for ancient rocks.
A tropical (solar) year = 365.24219 days = 31,556,926 s — the time for Earth to return to the same position relative to the Sun (equinox to equinox). A sidereal year = 365.25636 days = 31,558,150 s — relative to the fixed stars. A Julian year (used in astronomy) = exactly 365.25 days = 31,557,600 s. The difference arises from the precession of Earth's axis (cycle ~25,772 years).
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