What happened after the Big Bang? If scientists are right, the answer lies in the ticking of primordial clocks.
Since the discovery that our Universe is expanding, cosmologists have put forward ideas about how the Universe began. Was there a Big Crunch before the Big Bang? Did the Universe expand quickly or slowly?
“Imagine you took the frames of a movie and stacked them all randomly on top of each other. If those frames aren’t labeled with a time, you can’t put them in order,” says Xingang Chen of the Harvard-Smithsonian Center for Astrophysics (CfA) and the University of Texas at Dallas. “Did the primordial universe crunch or bang? If you don’t know whether the movie is running forward or in reverse, you can’t tell the difference.”
Because the beginning of the cosmos isn’t viewable by even our most powerful telescopes, it’s been impossible to prove which theory is correct, but a new paper published in the Journal of Cosmology and Astroparticle Physics seeks answers in the massive particle signatures found in the afterglow of the Big Bang, called the cosmic microwave background (CMB).
Fluctuations from the particles on the CMB, which existed for just a fraction of a second after the Big Bang, may contain time stamps of the early Universe.
Until now, distinguishing between different expansion scenarios involved searching for traces of gravitational waves in the CMB. These theoretical studies give clues to the spatial variations in the primordial Universe, but lack information on the passage of time.
The research of Xingang Chen, Yi Wang, and Mohammad Hossein Namjoo suggests a different method. "Here we are proposing a new approach that could allow us to directly reveal the evolutionary history of the primordial universe from astrophysical signals,” says Chen.
"Ticks of these primordial standard clocks would create corresponding wiggles in measurements of the cosmic microwave background, whose pattern is unique for each scenario," says study co-author Yi Wang.
According to Chen, Wang and Namjoo’s research, subatomic heavy particles like those found on the CMB will oscillate back and forth in a universal and standard way. These oscillations would act as clock ticks, providing a way to measure the passage of time at the beginning of the Universe.
“From observing the oscillation of the massive particles, we are able to reconstruct when fluctuations are created in the primordial universe,” notes Wang. “Soon, we may be able to verify the evolutionary history towards how our universe was created, which has remained a myth for so long.”
Current data isn’t accurate enough to spot such small variations, but ongoing projects like BICEP3, which uses an unprecedented total of 2,560 detectors to study the CMB, may soon become powerful enough to provide precise measurements that scientists can use to solve the mystery of what happened after the Big Bang.