In March, astronomers announced that they had found gravitational waves, ripples in cosmic radiation left over from the explosion of Big Bang. The discovery was hailed as “smoking gun” evidence of the universe’s rapid expansion trillionths of a second after the Big Bang almost 14 billion years ago.
Physicists celebrated. In this video from Stanford University, Andrei Linde, one of the founders of cosmic inflation theory, and his wife, physics professor Renata Kallosh, were overcome with joy when they received news of the discovery. Paul Steinhardt, professor of physics at Princeton University, said that the finding immediately changed the field of physics.
“Nobel prizes were predicted and scores of theoretical models spawned. The announcement also influenced decisions about academic appointments and the rejections of papers and grants. It even had a role in governmental planning of large-scale projects,” he wrote yesterday in a column for Nature.
Now it seems astronomers may have celebrated too soon. Two studies, one from Princeton University and one from the Institute for Advanced Study, say that the existing evidence is insufficient
to claim that the gravitational waves have been found..
Einstein first predicted the existence of gravitational waves more than 100 years ago. Major cosmic events, like black holes colliding or the creation of the universe, make waves in spacetime. Those waves continue to spread out like ripples on a pond, traveling at the speed of light.
Finding those primordial waves would further confirm inflation theory, the idea that the universe expanded rapidly, immediately following the Big Bang. Einstein believed that after billions of years, the waves would be too spread out and distorted to find.
But the ripples leave tracks in the “cosmic microwave background” of the universe, a soup of elementary particles leftover from the Big Bang. At BICEP2, a specialized radio telescope in Antarctica, a U.S.-led team of astronomers have been scanning a section of sky looking for specific “twists”, polarizations in the cosmic microwave background. At a press conference at the Harvard Smithsonian Center for Astrophysics this spring, scientists announced they had found a faint twist, the first testable evidence of the primordial waves.
Now studies suggest that twist could be caused by dust in the Milky Way galaxy. Two separate analyses point to recently published data from the Planck satellite, and concluded that the signals picked up by BICEP2 were likely from dust, not the primordial waves.
“Based on what we know right now… we have no evidence for or against gravitational waves,” said Uroš Seljak, an astrophysicist at the University of California, Berkeley, a co-author of one of the latest studies.
These studies raise some interesting points, but they don’t offer conclusive evidence that the polarizations are an exact match to dust either, said Marc Kamionkowski, theoretical physicist at Johns Hopkins University who was not involved in these studies. More information from the Planck satellite about the dust’s “fingerprint” in BICEP2’s region of the sky may determine whether the signal is dust or gravitational waves, he said.
Currently, at least ten different research projects, including CLASS at Johns Hopkins University, ABS and SPIDER at Princeton, NASA Goddard’s PIPER and the Planck satellite, are scanning different regions of the sky looking for gravitational waves.
“I believe that the scrutiny the BICEP2 results have received indicates what an exciting discovery this will be, if confirmed,” Kamionkowski said in an email. “Personally, I am looking forward to the information from Planck and other measurements that will hopefully shed light on whether we really have found a Rosetta Stone from the early Universe, or simply some unexpected interstellar dirt.”