Editing Shapiro time delay (section)

== Shapiro delay of neutrinos and gravitational waves ==
From the nearly simultaneous observations of [[neutrinos]] and [[photons]] from [[SN 1987A]], the Shapiro delay for high-energy neutrinos must be the same as that for photons to within 10%, consistent with recent estimates of the [[neutrino mass]], which imply that those neutrinos were moving at very close to the [[speed of light]]. After the direct detection of [[gravitational waves]] in 2016, the one-way Shapiro delay was calculated by two groups and is about 1800 days. In [[general relativity]] and other metric theories of gravity, though, the Shapiro delay for gravitational waves is expected to be the same as that for light and neutrinos.  However, in theories such as [[tensor–vector–scalar gravity]] and other modified GR theories, which reproduce [[Modified Newtonian dynamics|Milgrom's law]] and avoid the need for [[dark matter]], the Shapiro delay for gravitational waves is much smaller than that for neutrinos or photons.  The observed 1.7-second difference in arrival times seen between gravitational wave and gamma ray arrivals from neutron star merger [[GW170817]] was far less than the estimated Shapiro delay of about 1000 days. This rules out a class of [[modified models of gravity]] that dispense with the need for [[dark matter]].<ref name=Boran2017>{{Cite journal | author=Sibel Boran |display-authors=etal | title=GW170817 Falsifies Dark Matter Emulators | journal=Phys. Rev. D | volume=97 | issue=4 | pages=041501 | arxiv=1710.06168| year=2018 | doi=10.1103/PhysRevD.97.041501 | bibcode=2018PhRvD..97d1501B |s2cid=119468128 }}</ref>