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Exploring Extremely Low Frequency Phenomena

The femtohertz (fHz) is a unit of frequency equal to 10⁻¹⁵ hertz, representing one cycle per 1,000,000,000,000,000 seconds—which is about 31.7 million years. This incredibly low frequency scale is used primarily in astrophysics, cosmology, and geophysics to describe ultra-slow oscillations and waves occurring over vast cosmic timescales.

Frequencies in the femtohertz range are associated with phenomena such as primordial gravitational waves, oscillations in the cosmic microwave background radiation, and long-term magnetic or seismic cycles on Earth. These waves have correspondingly immense wavelengths, stretching over billions of kilometres or even larger cosmic distances.

Because femtohertz frequencies are far beyond everyday human experience, they are mostly relevant for understanding the deep-time evolution of the universe and large-scale cosmic processes. Studying such slow oscillations helps scientists learn about the formation of galaxies, the behavior of space-time, and fundamental physical laws governing the cosmos.

Using femtohertz as a measurement allows researchers to quantify these vast time periods and wavelengths, connecting tiny frequency values with the immense scale of astrophysical phenomena and Earth’s geological history.

The Realm of Extremely Slow Oscillations

The nanohertz (nHz) is a unit of frequency equal to 10⁻⁹ hertz, meaning one cycle occurs every 1 billion seconds—about 31.7 years. This incredibly low frequency is important in fields like astrophysics, cosmology, and geophysics, where slow periodic phenomena unfold over decades to centuries.

Nanohertz frequencies are often associated with gravitational waves produced by supermassive black hole binaries orbiting each other over many years. These ultra-low-frequency waves have immense wavelengths, spanning light-years across space. Pulsar timing arrays, which monitor the precise arrival times of pulsar signals, are used to detect such nanohertz gravitational waves, offering insights into galaxy evolution and cosmic structure.

On Earth, nanohertz frequencies can describe long-term oscillations in the geomagnetic field or climate cycles. Studying these slow frequencies helps scientists understand gradual changes in planetary environments and the universe.

Although nanohertz waves are far below everyday human perception and technological applications, they are critical for unraveling the universe's slowest dynamics. Using nanohertz as a unit helps researchers quantify and analyze these grand-scale processes, linking time scales from decades to cosmic evolution.