Update — Mar. 17, 12:00 p.m. ET: The BICEP2 collaboration have detected gravitational waves from the early universe, providing strong evidence for cosmic inflation. The results have been released here along with an FAQ.
Today cosmologists are expected to announce the discovery of gravitational waves.
The Harvard-Smithsonian Centre for Astrophysics announced last week that they would be reporting a “major discovery” today at 12pm EDT (4pm GMT). That’s pretty much all they said, but since then the cosmology rumour mill has been in overdrive about what it could be. Now it seems likely to be the discovery of primordial gravitational waves.
1. Gravitational waves are like ripples in space-time.
After Einstein published his General Theory of Relativity in 1916, scientists started thinking of the universe as being made up of a “fabric of space-time” – kind of like a rubber sheet. Objects in the universe bend this fabric, and more massive objects bend it more. Gravitational waves are thought of as ripples in this fabric. The bigger the object, the bigger the waves it produces.
2. They’re made when two or more really huge objects interact.
Black holes orbiting each other are thought to create gravitational waves, as are merging galaxies. The waves would be really tiny, but they travel through space and time unobstructed, so we should be able to detect them at Earth.
3. Gravitational waves were also made during the big bang.
These “primordial” gravitational waves, if detected, would give us an unprecedented insight into what happened during the big bang itself.
4. The discovery of primordial gravitational waves would provide evidence for inflation in the early universe.
Inflation is a period of rapid expansion that most cosmologists think took place just after the big bang. It came about as a way to explain why the universe is so uniform.
Only inflation would have been able to amplify the gravitational waves created at the inception of the universe into a detectable signal. So if we detect gravitational waves, we can be pretty sure inflation did happen after all.
5. You can find them by measuring stretches in space-time.
Lasers set up to measure the distance between two test masses can detect these tiny stretches in space. But it’s not quite as simple as that. Scientists have to create computer models to show them what to look for in the mass of data they get out of these experiments.
To find primordial waves, cosmologists are scanning the sky at microwave frequencies and looking for tiny variations in how the radiation is oriented.
6. We have never detected gravitational waves directly.
In 1993 the Nobel Prize in Physics was awarded for what was essentially the indirect detection of gravitational waves from two pulsars orbiting each other. But we’re yet to see gravitational waves directly.
7. There are several experiments looking for primordial gravitational waves.
One of them is the BICEP (Background Imaging of Cosmic Extragalactic Polarization) observatory in Antarctica, who are expected to announce their latest results later today. There’s also the South Pole Telescope and PolarBEAR, who will no doubt be looking on with interest.
8. Their discovery will make cosmologists very happy, and almost certainly win someone a Nobel Prize.
Whenever the initial announcement of primordial gravitational waves comes, it will be just be the first chapter of the story. It’ll need to be scrutinised by other teams working in the same area to make sure it really stands up.