Are gravitational waves being 'redshifted' away by the cosmological
constant?
>
http://physicsworld.com/cws/article/news/2016/jan/21/are-gravitational-waves-being-redshifted-away-by-the-cosmological-constant
> The theoretical framework underlying gravitational waves may have to
> be revamped to account for dark energy and the acceleration of the
> expansion of the universe. That's the conclusion of researchers in
> the US, who say that while gravitational waves from nearby sources
> will be unaffected, next-generation detectors such as the Laser
> Interferometer Space Antenna (LISA) and the Einstein Telescope –
> which aim to detect gravitational waves from billions of light-years
> away – may fall foul of the expansion of the universe. While such
> telescopes will still detect gravitational waves, the signal detected
> from more distant waves could be fairly different to what is
> currently expected, say the researchers.
>
> Dark energy is best explained by a small but positive value for the
> cosmological constant, which describes the energy density of space.
> It was the famous factor that Albert Einstein discarded from his
> general theory of relativity, when it was found in 1929 that the
> universe was expanding. For the next 69 years, theorists assumed that
> the cosmological constant was equal to zero. However, in 1998, it was
> discovered that the expansion of the universe was accelerating,
> driven by the mysterious dark energy, and the cosmological constant
> was back in the running.
>
> Because the value of the cosmological constant is very small (10–52
> m2), it had been assumed that it would have a negligible effect on
> the mathematical descriptions of gravitational waves. However, Abhay
> Ashtekar and colleagues at the Institute for Gravitation and the
> Cosmos at Penn State University in the US believe that it throws a
> spanner into the works of our current gravitational-wave theories.
>
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