Editing Faster-than-light (section)

====Hartman effect====
{{Main|Hartman effect}}

The Hartman effect is the tunneling effect through a barrier where the tunneling time tends to a constant for large barriers.<ref>
{{cite journal
|last1=Martinez |first1=J. C.
|last2=Polatdemir |first2=E.
|year=2006
|title=Origin of the Hartman effect
|journal=[[Physics Letters A]]
|volume=351 |issue=1–2 |pages=31–36
|bibcode=2006PhLA..351...31M
|doi=10.1016/j.physleta.2005.10.076
}}</ref><ref>
{{cite journal
|last1=Hartman |first1=T. E.
|year=1962
|title=Tunneling of a Wave Packet
|journal=[[Journal of Applied Physics]]
|volume=33 |issue=12 |pages=3427–3433
|bibcode=1962JAP....33.3427H
|doi=10.1063/1.1702424
}}</ref> This could, for instance, be the gap between two prisms. When the prisms are in contact, the light passes straight through, but when there is a gap, the light is refracted. There is a non-zero probability that the photon will tunnel across the gap rather than follow the refracted path. 

However, it has been claimed that the Hartman effect cannot actually be used to violate relativity by transmitting signals faster than ''c'', also because the tunnelling time "should not be linked to a velocity since evanescent waves do not propagate".<ref>
{{cite journal
|last1=Winful |first1=H. G.
|year=2006
|title=Tunneling time, the Hartman effect, and superluminality: A proposed resolution of an old paradox
|journal=[[Physics Reports]]
|volume=436 |issue=1–2 |pages=1–69
|bibcode=2006PhR...436....1W
|doi=10.1016/j.physrep.2006.09.002
}}</ref> The evanescent waves in the Hartman effect are due to virtual particles and a non-propagating static field, as mentioned in the sections above for gravity and electromagnetism.