Einstein’s Principle of Equivalence verified in quasars for the first time

Artist impression of a quasar. Credit: ESO/M. Kornmesser
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Ratio between the measured and predicted gravitational redshifts vs. cosmological redshift, zcosm. Main panel: data from the present work. Superior inset: Solar System and Milky Way data from the literature. Inferior inset: galaxy cluster data from the literature (see Figure 1 of the paper).

We perform a new test of Einstein's Equivalence Principle which, for the first time, extends to very early cosmological epochs (we have studied its validity in 80% of the history of the Universe). The Einstein Equivalence Principle is essential for generalizing physical laws in the presence of gravity. Our test of the Equivalence Principle is based on one of Einstein's classical predictions: the gravitational redshift of photons. This test has been accurately put into practice in our Solar System and in some stars in our Galaxy (e.g. Sirius B). However, so far it has not been applied to

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Artistic representation of the Sun, the Earth and the Moon (not to scale) with the space-time curvature of Einstein's General Relativity over the spectrum of sunlight reflected from the Moon (in colors from blue to red). The spectrum is taken with the HARPS instrument and calibrated with the LFC. Credit: Gabriel Pérez Díaz, SMM (IAC).

An international team of researchers led by the Instituto de Astrofísica de Canarias (IAC) has measured, with unprecedented accuracy, the gravitational redshift of the Sun, a change in frequency of the lines in the solar spectrum which is produced when the light escapes from the gravitational field of the Sun on its way to Earth. This work, which verifies one of the predictions of Einstein’s General Relativity, is to be published in the journal Astronomy & Astrophysics.

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