Earlier this year — and in a discovery that screamed Nobel Prize — Harvard physicists announced that they'd found evidence of gravitational waves in the early universe, potential proof that our universe began with a bang. The claim was duly criticized, but a new analysis may be the most damning yet.
Top image: Planck's Northern (left) and Southern (right) sky projections. Parts of the sky that are clearer of dust are dark blue; the black box in the Southern projection is where BICEP looked. Credit: Planck Collaboration.
This is not the final nail in the coffin for BICEP2, but it's certainly a massive blow. According to a new paper just posted at the arXiv pre-print server, it appears that the galactic dust in the foreground was responsible for all of the signal observed by the BICEP2 team. Ouch.
Natalie Wolchover reports in Quanta Magazine:
Now, scientists have shown that the swirl pattern touted as evidence of primordial gravitational waves — ripples in space and time dating to the universe's explosive birth — could instead all come from magnetically aligned dust. A new analysis of data from the Planck space telescope has concluded that the tiny silicate and carbonate particles spewed into interstellar space by dying stars could account for as much as 100 percent of the signal detected by the BICEP2 telescope and announced to great fanfare this spring.
The Planck analysis is "relatively definitive in that we can't exclude that the entirety of our signal is from dust," said Brian Keating, an astrophysicist at the University of California, San Diego, and a member of the BICEP2 collaboration.
The new dust analysis leaves open the possibility that part of the BICEP2 signal comes from primordial gravitational waves, which are the long-sought fingerprints of a leading Big Bang theory called "inflation." If the universe began with this brief period of exponential expansion, as the cosmologist Alan Guth proposed in 1980, then quantum-size ripples would have stretched into huge, permanent undulations in the fabric of the universe. These gravitational waves would have stamped a swirl pattern, called "B-mode" polarization, in the cosmic microwave background, the oldest light now detectable in the sky.
Indeed, there's still some hope for BICEP2. Results are still expected for a cross correlation and comparison of Planck data and BICEP2 data in the observed regions, along with Planck's own data on the B modes. But it's not looking good.
Much more at Quanta Magazine.