  If we use the path integral approach, we can write quantum electrodynamics
(QED) in a way that is manifestly relativistic. However the path integrals are
confined to paths that are on mass-shell. What happens if we extend QED by
computing the path integrals over all paths in energy momentum space, not only
those on mass-shell? We use the requirement of covariance to do this in an
unambiguous way. This gives a QED where the time/energy components appear in a
way that is manifestly parallel to the space/momentum components: we have
dispersion in time, entanglement in time, full equivalence of the Heisenberg
uncertainty principle (HUP) in time to the HUP in space, and so on.
Entanglement in time has the welcome side effect of eliminating the ultraviolet
divergences. We recover standard QED in the long time limit. We predict effects
at scales of attoseconds. With recent developments in attosecond physics and in
quantum computing, these effects should be detectable. Since the predictions
are unambiguous and testable the approach is falsifiable. Falsification would
sharpen our understanding of the role of time in QED. Confirmation would have
significant implications for attosecond physics, quantum computing and
communications, and quantum grav
