Primordial gravitational waves

Scientists have heralded a “whole new era” in physics with the detection of “primordial gravitational waves” – the first tremors of the big bang.


The minuscule ripples in space-time are the last prediction of Albert Einstein’s 1916 general theory of relativity to be verified. Until now, there has only been circumstantial evidence of their existence. The discovery also provides a deep connection between general relativity and quantum mechanics, another central pillar of physics.


It represents a whole new era in cosmology and physics as well.” If the discovery is confirmed, it will almost certainly lead to a Nobel Prize.

The detection comes from the Background Imaging of Cosmic Extragalactic Polarization 2 (Bicep2) experiment – a telescope at the South Pole.


The detection also provides the first direct evidence for a long-held hypothesis called inflation. This states that a fraction of a second after the big bang, the universe was driven to expand hugely. Without this sudden growth spurt, the gravitational waves would not have been amplified enough to be visible.

“Detecting this signal is one of the most important goals in cosmology today.

The primordial gravitational waves were visible because they created a twisting pattern called polarisation in light from the big bang. Polarisation is the direction in which a light wave oscillates. It is invisible to human eyes, which only register brightness and colour. Sunglasses made from polaroid sheets work by blocking out all light waves except those with a specific polarisation.

Light from the big bang has been turned into microwaves by its passage across space. These microwaves were discovered in 1964 and are known as the cosmic microwave background radiation. Bicep2 was designed to measure their polarisation.

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Whereas Bicep2 has only looked at part of the sky visible from the south pole, Planck has mapped the whole sky.

If it confirms the signal and its strength then cosmologists will be presented with an extraordinarily rich seam of data about the conditions immediately after the big bang. “We are going to be able to measure all sorts of subtle details to start pinning down how physics operates in those utterly extreme conditions.

This could reveal the interface between the two great theories of physics:

general relativity and quantum mechanics.

Despite almost a century of effort, the world’s physicists have not been able to show how these theories work together. The primordial gravitational waves that produced the signal seen by Bicep2 were produced in interactions that took place at a trillion times the energies that can be produced in the Large Hadron Collider at Cern.


This is like turning the whole universe into a particle physics experiment.

It could even show them the way to join the two theories together, producing what is sometimes called “the theory of everything”.

“Gravitational waves emitted at the time of the big bang can tell us how the universe came to exist, If these results prove correct, we will have new key information on the very early universe, information that is hard to get from any other source.

“Gravitational waves are a new frontier in astrophysics and cosmology. If today’s findings are accurate then it will further strengthen our understanding of how the universe formed.

The signal detected by Bicep2 is not easy to see because it is masked by distortions caused by the light’s passage through clusters of galaxies, and through dust clouds in the Milky Way. These distortions must be carefully stripped away before the primordial signal can be revealed.

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Some subtle contamination may yet be affecting their data. The only way to know for sure is to have other telescopes and spacecraft see the signal too.

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