Charles Bennett considers new discoveries in cosmology in the Isaac Newton Lecture

13 November 2017

Experiments to probe the cosmic microwave background (CMB) have shown an amazingly close fit with the standard model of cosmology, but enough uncertainties remain to suggest that we could be on the verge of discovering new physics, Professor Charles L Bennett said in this year’s Isaac Newton Lecture.

Charles Bennett considers new discoveries in cosmology in the Isaac Newton Lecture

Giving the lecture at the IOP’s London centre on 8 November as the winner of the Institute’s 2017 Isaac Newton Medal and Prize – its international medal and most prestigious prize – he said: “We have learned a lot about our universe. We have come a very long way – amazingly so – in the last 25 years and the Lambda Cold Dark Matter (ΛCDM) model is impressively successful, but what is it that we don’t know?”

Professor Bennett won the IOP’s prize for his leadership of the Wilkinson Microwave Anisotropy Probe (WMAP) – a satellite experiment to make extremely precise measurements of the CMB, which provided evidence for dark energy, the nature of dark matter and serious tests for inflation in the early universe. It followed on from the Cosmic Background Explorer (COBE), in which he had a critical role in the Differential Microwave Radiometer project.

COBE confirmed that there was a hot, dense, early universe, discovered temperature fluctuations across the sky and allowed estimates of the cosmic neutrino density, he said. “We proposed the WMAP mission to follow that up with greater sensitivity and precision,” he explained

Charles Bennett considers new discoveries in cosmology in the Isaac Newton Lecture

The ΛCDM model – the standard model of cosmology – is based on six parameters, including the physical density of baryonic (normal) matter and of cold dark matter, and the age of the universe. The data from WMAP shrank the former uncertainty in these six taken together by a factor of 68,000. “The six-parameter ΛCDM model didn’t break,” he said, and Science Magazine had named this its Breakthrough of the Year in 2003.

The Planck mission a decade later produced results that initially looked consistent with the WMAP data, but on closer investigation they were found to be off each other by a factor of six standard deviations – a figure that was not acceptable, he said. “Is this the result of underestimating uncertainties or is there new physics that we haven’t discovered yet?” he said. “We used to have cosmic convergence but I don’t feel that we have that anymore.”

He is now working on the Cosmology Large Angular Surveyor (CLASS), which is led by Johns Hopkins University in collaboration with NASA and other institutions around the world. Its principal aim is to detect and characterise a pattern of polarisation that is expected to be imprinted on the CMB by gravitational waves arising from inflation in the early universe.

Being interviewed in front of the audience after the lecture by the IOP’s chief executive Professor Paul Hardaker, he said: “I have studied the CMB for my whole career and I’m always amazed at how much progress has been made. Things that we thought would be impossible we now do routinely.”

Charles Bennett considers new discoveries in cosmology in the Isaac Newton Lecture

Asked about what sparked his fascination with science, he recalled being given a telescope by his grandmother and developing an interest in technical matters after working in a television and radio repair shop as a teenager. Later, as a PhD student, he heard a talk on the CMB by Professor Rainer Weiss (who has just shared in the Nobel Prize in Physics) at the Massachusetts Institute of Technology, and asked how he could be involved. This eventually led to him working on COBE.

He described how the COBE project nearly came to an end before it launched, as it was due to be taken on the space shuttle that was grounded after the Challenger disaster, when all other NASA launches were also put on hold. However, the team persuaded NASA that their project could be delivered in around two years and they met the “enormous challenge” of halving the weight of the equipment for launch on another vehicle, he said.

Taking questions from the audience, he said that he was far from content with the disagreements in the data from different missions. “I am not relaxed about it but I am puzzled about it. We need to figure out what’s going on,” he said.

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