An international team led by Japanese researchers has made a 3D map of 3000 galaxies 13 billion ly from Earth, and found that Einstein's general theory of relativity is still valid.
Their results indicated that even far into the Universe, general relativity is valid, giving further support that the expansion of the Universe could be explained by a
cosmological constant, as proposed by Einstein in his theory of general relativity.
No one has been able to analyze galaxies > 10 billion ly away, but the team managed to break this barrier thanks to the FMOS (Fiber Multi-Object Spectrograph) on the Subaru Telescope, which can analyze galaxies 12.4 - 14.7 billion ly away. The Prime Focus Spectrograph, currently under construction, is expected to be able to study galaxies even further away.