Phase and group velocities of three electrons traveling in slow motion over a distance of 0.4 Ångstroms. The momentum per unit mass (proper velocity) of the middle electron is lightspeed, so that its group velocity is 0.707 c. The top electron has twice the momentum, while the bottom has half. Note that wavelength and phase velocity decrease as the group velocity increases toward c. Coherence widths for high energy electrons, like those used in microscopy, may be orders of magnitude larger than the ones shown here.
{{Information |Description=Phase and group velocities of three electrons traveling in slow motion over a distance of 0.4 Ångstroms. The momentum per unit mass (proper velocity) of the middle electron is lightspeed, so that its group velocity is 0.7