The recent discovery by the LIGO made me wonder about this.

We know that there exists a CMBR, Cosmic Microwave Background Radiation, a blanket of electromagnetic energy covering the universe, made by the Big Bang.

But, the big bang was an explosive event. The huge "shockwave" made by it sent ripples in space time. (Primordial gravitational waves)

Wouldn't these ripples flood the universe creating sort of a Cosmic Gravitational Background Radiation (not exactly radiation)?

If such waves do flood the universe, couldn't a much more sensetive version of LIGO be able to detect this and use it as a contrast to create "gravitational telescopes"?


Yes, there is a predicted cosmic gravitational wave background; an expanding universe is essentially transparent to gravitational waves once they are produced.

There are a number of scenarios in which GWs might be produced - these are listed in the eLISA white paper and include a transition from the inflationary epoch to the hot big bang; but for realistically detectable strain values, an interferometer needs to be sensitive to milli-Hz or lower.

This means that the gravitational waves have extremely long wavelengths and milli-Hz frequencies are masked by seismic activity on Earth. Thus one needs an interferometer with very long arms in space.

Detecting the cosmic gravitational wave background is one of the things the space-based eLISA interferometer may be able to do with its proposed 1 million km arms.

See http://www.ligo.org/science/GW-Stochastic.php

  • $\begingroup$ Do you have any estimate on how long arms would be needed? $\endgroup$ – hyde Feb 13 '16 at 19:48
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    $\begingroup$ @hyde The arms of eLISA are proposed to be 1 million km. $\endgroup$ – ProfRob Feb 13 '16 at 19:52
  • $\begingroup$ How exactly does earth's seismic activity mess around with the interferometer? Is the physical disturbances the cause? Or these vibrations make tiny tiny gravitational waves too? $\endgroup$ – Udit Dey Feb 14 '16 at 12:35
  • $\begingroup$ @UditDey Just the physical vibration of the instrument at low frequencies. $\endgroup$ – ProfRob Feb 14 '16 at 13:01
  • $\begingroup$ @Rob Jeffries So if we could keep the instruments and setup stable enough, we could see the "CGBR" from earth? $\endgroup$ – Udit Dey Feb 16 '16 at 16:02

A review of the underlying theory as of Dec 2019: Primordial backgrounds of relic gravitons by Massimo Giovannini.

The diffuse backgrounds of relic gravitons with frequencies ranging between the aHz band and the GHz region encode the ultimate information on the primeval evolution of the plasma and on the underlying theory of gravity well before the electroweak epoch. While the temperature and polarization anisotropies of the microwave background radiation probe the low-frequency tail of the graviton spectra, during the next score year the pulsar timing arrays and the wide-band interferometers (both terrestrial and hopefully space-borne) will explore a much larger frequency window encompassing the nHz domain and the audio band. The salient theoretical aspects of the relic gravitons are reviewed in a cross-disciplinary perspective touching upon various unsettled questions of particle physics, cosmology and astrophysics.


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