Nearly all types of electromagnetic radiation can be used for spectroscopy, to study and characterize matter. Until the middle of the 20th century it was believed by most physicists that this spectrum was infinite and continuous. The limit for long wavelengths is the size of the universe itself, while it is thought that the short wavelength limit is in the vicinity of the Planck length. Visible light lies toward the shorter end, with wavelengths from 400 to 700 nanometres. The electromagnetic spectrum extends from below the low frequencies used for modern radio communication to gamma radiation at the short-wavelength (high-frequency) end, thereby covering wavelengths from thousands of kilometers down to a fraction of the size of an atom. The "electromagnetic spectrum" of an object has a different meaning, and is instead the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object. The electromagnetic spectrum is the collective term for all possible frequencies of electromagnetic radiation.
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