Dispersion has been evident since FRBs were discovered in 2007. [https://en.wikipedia.org/wiki/Fast_radio_burst https://en.wikipedia.org/wiki/Fast_radio_burst]

Dispersion has been evident since FRBs were discovered in 2007. [https://en.wikipedia.org/wiki/Fast_radio_burst https://en.wikipedia.org/wiki/Fast_radio_burst] "The component frequencies of each burst are delayed by different amounts of time depending on the wavelength. This delay is described by a value referred to as a dispersion measure (DM). This results in a received signal that sweeps rapidly down in frequency, as longer wavelengths are delayed more." [https://en.wikipedia.org/wiki/Dispersion_(optics)#Pulsar_emissions https://en.wikipedia.org/wiki/Dispersion_(optics)#Pulsar_emi...] "dispersion measure (DM) is the column density of free electrons (total electron content) — i.e. the number density of electrons (electrons/cm3) integrated along the path traveled by the photon from the pulsar to the Earth"