Among potential evidence that would further support the Big Bang theory is the cosmic gravitational wave background. Like ripples in a pond, gravitational waves distort the curvature of the spacetime continuum and were first predicted in 1916 by Albert Einstein.
Similar to the Cosmic Microwave Background, a ubiquitous backdrop of gravitational waves permeates space, cosmologists predict. This cosmic gravitational wave background (CGB) should have formed as a result of cosmic inflation, when the universe essentially exploded in size, expanding from smaller than the size of an atom to most of what we see today. All in the time it takes you to blink.
If observed, the cosmic gravitational wave background would be a smoking gun for cosmic inflation and is therefore a popular observing target in cosmology. But gravitational waves are tricky to detect because they do not emit electromagnetic radiation, and the only successful detection so far has been indirect. Most likely, observations of the CGB will also be indirect by observing how they affect light.
In the case of light from the CMB, the oldest and some of the only polarized light in the universe, an interaction with gravitational waves from the CGB will lead to what astrophysicists refer to as B-modes.
|Temperature fluctuations in the CMB measured by the Wilkinson Microwave Anisotropy Probe. Credit: NASA.|
An extensive team of scientists first presented observational evidence of B-modes last July. While the B-mode observations that the team reported proved that B-modes can be measured and detected, their observations were of B-modes created when the direction of a photon's travel is changed due to gravity from a massive object, like galaxy clusters, and not the CGB. Moreover, the July paper's B-modes were about seven orders of magnitude more powerful, and therefore easier to detect, than the B-modes discussed here.
What's more is that recent results suggest B-modes from the CGB are even more difficult to detect than originally thought. The reason stems from a type of perturbation that past researchers have neglected in their calculations, some with the assumption that the effect was negligible. But one scientist shows through a series of complex calculations that the effect leads to CGB B-modes four times less powerful than the already small previously predicted values.
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