The multiverse: it’s a mind boggling, jaw dropping, spine tingling idea. Despite the many physicists who considered them an intriguing possibility, for decades multiple universes were considered the stuff of science fiction – there was simply no way of proving they actually existed. Now, Sri Lankan-born cosmologist Dr. Hiranya Peiris and her colleagues at the University College London, Imperial College London and the Perimeter Institute for Theoretical Physics have designed an observational test that can be used to test the multiverse idea, and they’ve begun applying it to data.
|Dr. Hiranya Peiris|
Could our universe be just one ‘bubble’ universe amid many others in a vast multiverse? The evidence that it is actually possible for a multiverse to exist is mostly theoretical says Hiranya explaining that well tested theories like quantum mechanics (“possibly the best tested physical theory there is”), inflation (“the dominant paradigm for the origin of structure, which has passed every observational test so far”) as well as string theory (“an elegant and compelling theory of quantum gravity”) seem to predict their existence. “It is very hard to wriggle out of these predictions,” she wrote in an email to The Sunday Times.
The multiverse theory was widely considered un-testable. Speculation ran that each alternate universe would have its own entirely alien physical and structural makeup to which our physical laws could not apply. Even if bubble universes existed, we couldn’t dream of moving between them – though they may be born together, they were probably being “hurled apart and space-time is expanding faster than light between them,” Hiranya told the BBC. However, the exciting possibility that there could be a small, rare window of opportunity has fuelled Hiranya’s research and has kept her engaged in the study of the ethereal radiation known as Cosmic Microwave Background data or CMB.
You can see CMB yourself, says Hiranya: about 1% of the snow picked up by an untuned television arises from this radiation, generated when the universe was just 0.01% of its present age. CMB is considered the oldest light in the universe – it’s the left over heat from the Big Bang, formed when the universe was only 380,000 years old. “So, it’s a baby picture of the universe,” says the researcher. In fact, there might be more than one ‘baby’ in these pictures. Some theories hold that if it exists, the multiverse is likely to be expanding at a phenomenal rate; its universes having been pulled apart very soon after they first appeared. Hence any physical contact between them could most likely have occurred only during the period when our own universe was still very much in its infancy.
Hiranya’s team has been scouring the ‘microwave sky’ for signs and they’re relying on a groundbreaking, powerful computer algorithm to help them analyze the data. It was proposed that if ‘bubble universes’ had collided in the distant past, an imprint may have been left on our cosmology. The team believes these imprints might be disc shaped. These “bruises” should be visible in the otherwise smooth pattern of the CMB. In a research paper published in the Physical Review Letters in early August this year the team identified 15 possible candidates of which four were of particular interest.
They’ve generated much excitement with this first observational test of the multiverse, but the current data are not conclusive enough to definitively rule out the possibility that these patterns are due to random chance. “Humans are adept at seeing patterns that are not really there in random data,” says Hiranya. “Our algorithm avoids this in two ways. First, it is fully automated and ‘frozen’ with no free parameters before the operator even looks at the data. It cannot be modified in response to patterns seen in the data. Second, it implements ‘Occam’s razor,’ the idea that a simpler theory should be preferred to a more complex theory unless the latter fits the data much better.”
The data they’ve been working with so far was gathered primarily by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP). Now, the data collected by ESA’s follow-up satellite mission, the Planck space telescope, is expected to up the ante with CMB maps that boast a resolution three times that of the most recent WMAP offering.
Hiranya has spent a significant period of professional life studying WMAP’s data. She’s been involved with the WMAP since the beginning of the project. (Her PhD thesis offered an interpretation of WMAP data). “The first WMAP analysis was ground-breaking in many ways,” she says looking back. “It was the cornerstone of the era of ‘precision cosmology’.” She remembers intense 24 hour work days and many breakthrough moments. “There was a restriction on talking with anyone outside the collaboration which was hard to sustain when we were all bursting with exciting new results,” she says. “Before WMAP, there were many theories for the origin of structure. Afterwards, inflation and very little else was left standing as viable theories.”
With the WMAP spacecraft now in a graveyard orbit, the data from the Planck satellite has begun streaming in. It is way out beyond the orbit of the moon approximately 1.5 million km from the Earth at the L2 Lagrange point of the Earth-Sun system. “Planck will create the highest resolution, highest sensitivity full sky maps of the microwave sky ever made, at several different frequencies,” says Hiranya. A member of the team that will analyze its data, she believes what they find will have a profound impact on cosmology, our understanding of our own Galaxy and the distant extragalactic universe. Unfortunately, we’ll have to wait till 2013. Though Planck’s data collection is slated to finish later this year, it will take till then before it’s cleaned up and ready to be examined in earnest.
As a cosmologist, Hiranya’s research will continue to focus on exploring the origins and evolution of the universe. She says her fascination with the birth of the universe began when she became aware of the massive gaps in our understanding of the physical origin of the Big Bang. (She did her schooling in Sri Lanka, where she credits the Young Astronomers’ Association with kindling her interest in the subject and only moved to the UK with her family when she was sixteen.) “The problem of the origin of structure in our universe is profound; it’s at the cutting edge of theoretical physics and observational cosmology,” she says. Her first research experience with the Galileo PPR team who were then studying temperature maps of Jupiter and its Galilean satellites cemented her fascination. “I learnt first-hand the excitement of seeing something that no human has ever seen before, and the amazing feeling of figuring out something no one had figured out before.”
Today, she lives in London with her partner, an astrophysicist. She expects Planck will keep her busy for years to come. “Cosmology is not an experimental science – it is an observational one. The grand universal experiment has been performed, and we can’t repeat it. Thus, we are like detectives, piecing together clues from the past, because when we look at the distant universe, we see things as they were in the distant past, when the universe was much younger and a simpler place.”
Published in The Sunday Times, Sri Lanka on August 21, 2011. Words by Smriti Daniel.