What does exahertz mean?
An exahertz (symbol EHz) is a unit of frequency equal to one quintillion hertz, or 10¹⁸ cycles per second. It sits near the top of the SI frequency scale, far beyond kilohertz, megahertz, and gigahertz, which describe everyday radio and computing signals. Frequencies measured in exahertz correspond to extremely energetic electromagnetic radiation — gamma rays produced by radioactive decay and cosmic phenomena can reach this range. Because no human-made oscillator comes close to cycling at such rates, the word appears almost exclusively in scientific writing on astrophysics, particle physics, and theoretical limits of electronics. The term combines 'exa-', the SI prefix for 10¹⁸ derived from the Greek 'hex' meaning six, with 'hertz', the unit named after Heinrich Hertz, the nineteenth-century physicist who first demonstrated electromagnetic waves. For general readers, exahertz serves mainly as a marker of just how vast the measurable spectrum of electromagnetic radiation really is.
nounA unit of frequency equal to one quintillion (10¹⁸) hertz, used chiefly in physics and telecommunications to describe extremely high electromagnetic frequencies.
- The SI-derived unit of frequency equal to 10¹⁸ hertz (one quintillion cycles per second).
"Gamma rays occupy the highest end of the electromagnetic spectrum, reaching frequencies of several exahertz."
"Frequencies above the exahertz level fall into the realm of high-energy gamma radiation."
"No current electronic technology can generate signals anywhere near the exahertz scale."
Like hertz and its other SI multiples, exahertz is typically used invariantly in the plural, especially when preceded by a numeral.
"Gamma-ray frequencies can reach several exahertz."
An exahertz is so fast that light itself completes only about three wavelengths per cycle at that frequency — it's the domain of cosmic gamma rays, not anything humans can build.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of exahertz
The word exahertz combines 'exa-', an SI prefix denoting 10¹⁸ adopted in 1975, with 'hertz', the SI unit of frequency introduced in 1960 and named after the German physicist Heinrich Hertz (1857–1894), who first generated and detected electromagnetic waves. The prefix 'exa-' derives ultimately from the Greek 'hex', meaning 'six', reflecting its position as the sixth power of 10³ in the SI series. Cognate forms include other SI-multiple units such as petahertz and zettahertz, as well as Greek-rooted words like hexagon and hexadecimal.
How exahertz is actually used
Exahertz is a technical term confined almost entirely to physics, astronomy, and engineering literature; it is rarely used outside scientific registers. Like other SI multiples of hertz (e.g. kilohertz, gigahertz), its plural is typically left unchanged.
Easily confused with exahertz
A terahertz is 10¹² hertz, whereas an exahertz is vastly larger at 10¹⁸ hertz — a million times greater.
An exabyte measures data storage capacity, while an exahertz measures frequency.