Professor Brian Keating
The Cosmic Microwave Background [CMB] is made up of photons from the primeval oven that the universe forged the first elements within. So these are the lightest elements, and when they were formed, the left over binding energy of formation was released in a form of heat. That heat propagated throughout the universe for 13.8 billion years, until it arrived at our telescopes. If you’ve used a microwave oven before, you know that microwaves are efficient absorbers of water, and water is very much present in the Earth’s atmosphere.
Often times we would like to go to space. My community has built three satellites, so far, that have been to space to study the CMB, and that’s done at great expense and great risk. It’s almost 100times more expensive if we wanted to put BICEP2 in space than the way we built it at the South Pole.
The atmosphere above the South Pole is very space-like – it’s very desert-like. There are very few water molecules in the atmosphere above the South Pole. We don’t want these photons that are so precious to us, and so few, travelling across the universe, and all of a sudden they smash into a water molecule in our atmosphere. That’s no good. So all of our microwave telescopes need to be built at high elevation, in very cold climates or both.
The results that came from the BICEP2 experiment unfortunately weren’t what you were expecting. Can you explain what happened?
What happened was the BICEP experiment was seeking a signature from the CMB which, if detected, would reveal the presence of inflation – the so-called ‘epoch of ultra-rapid expansion’ that immediately followed the Big Bang. In the first trillionth of a trillionth of a trillionth of a second, it’s hypothesised that the universe underwent this extremely rapid expansion called inflation. If it did, it would solve a number of problems with the Big Bang theory.
To patch those missing bits, the cosmologists of the 1980s and 1990s created a theory called ‘inflation’, which ultimately predicted that the microwave background heat would have a twisting, twirling, swirling pattern, in what’s known as its ‘polarisation’. It became clear to us, and others in the community, that the first people to do this would not only confirm the existence of these waves of gravity that inflation would have caused to resonate in space-time, but also it would be the first pieces of evidence for the quantisation of gravity. This is a goal that eluded even the late, great Albert Einstein and the late, great Stephen Hawking.
How we would do that is complex to describe, but nevertheless the stakes were so high. You could just imagine that something pursued by scientists like Einstein and Hawking is going to be a very, very valuable thing to accomplish. In fact, we were told that the people that could do that would win a Nobel Prize. I think that the impetus for us to pursue this signal was mostly scientific, but there was a part that was caught up in the pursuit of this ultimate accolade that science has to offer, which had been given only twice before in our field. We were going to explain why there was a Big Bang, why there was a universe and perhaps that there is a multiverse. All these things conspired to cause us to want to see this signal.
Unfortunately, as with many aspects of science, when you have a hypothesis made by an authority such as Hawking or Einstein, there’s a tendency to want to try and confirm the hypothesis rather than dispassionately pursuing all different possibilities, or stumbling upon something serendipitously. We were intent on finding this signal, and I think we did great job in trying to convince we hadn’t seen artefacts of the instruments, the atmosphere and our galaxy and Solar System. But we didn’t have enough information at the time to rule out the contributions from the contamination of equally tantalising swirls of microwaves from our galaxy.
That was insufficient in terms of ruling out the hypothesis. We detected something much more prosaic, the emission of dust in the microwave band in our galaxy. That’s [the discovery] that we now believe we made, but we didn’t make a blunder. I always say we didn’t leave the lens cap on the telescope, we didn’t forget to plug in a fibre optic
“I thought that being an astronomer was like being a wizard and you would have to do it for free”
cable and make a huge blunder. It’s the hypothesis, and the claim that we had detected cosmic inflation that was disconfirmed.
Do you think BICEP2 results had much influence on other astronomical announcements since?
Yes. I know for certain it had a tremendous influence on the announcement of the detection of gravitational waves by the LIGO experiment. There’s a book called Gravity’s Kiss [written by Harry Collins], and it describes the inner workings of the LIGO team including emails, correspondences and phone calls – all confidential and redacted information – it’s kind of cloak and dagger.
But, what’s interesting is that they mention BICEP2 dozens of times in their deliberations. Both how to complete the analysis in a way that was dispassionate and agnostic as to the origin of the signal, and also on how to publicise their results.
We [the BICEP2 team] had our press conference the day we made the announcement of the detection of these inflationary gravitational waves but, in the end, our publication was not accepted and peer reviewed until many months after the announcement. So a lot of people took us to task for that. LIGO on the other hand waited until their discovery had been vetted and peer reviewed, and published in physical review letters.
Then there is the EDGES experiment, which is a recent experiment [that detected a signal from a star existing just 180 million years after the Big Bang]. They also had this [the BICEP2 results] in mind, and that they did not want to publish their claims until they had been vetted and peer reviewed and published in an actual journal.
So I know for certain that the BICEP2 episode has become sort of a cautionary tale in some sense, and I think that’s one of the lasting pieces of impact of our experiment. I think the way you release your data has a big impact, the medium is the message as they say, and other groups are learning from our experience.
What do you think will be the next big discovery about the universe?
Well, there are just so many mysteries about the universe. I think some of the things that appeal to me are related – unsurprisingly – to my research.
One is what are the properties of energy and matter throughout the universe? So there’s a particle called a ‘neutrino’, which is one of the 17 elementary particles. They are the fundamental building blocks that cannot be divided into smaller units. We don’t know how much neutrinos weigh, and that’s of great interest to not only cosmologists like me, but particle physicists. You need massive clusters of galaxies to contain the girth that is necessary to have enough of these neutrinos in one place. We hope to do that by using another tool that Einstein invented, called ‘gravitational lensing’. That will be literally refracting the signature of the polarisation in the microwave background, this time at small angular scales.
But what I think is the most interesting question is whether or not we are not only not the centre of our galaxy, or Solar System, but also whether or not our universe is the centre of a ‘multiverse’. There has been a lot of debate about this most recently by many scientific luminaries, and this debate has been really raging and heating up. It really centres on the Copernican principal, as I discuss in my book; can it be extended beyond our universe? Are we just another universe, just like we’re another star or another planet or another galaxy? I think that would be the most fascinating question of all to answer.
Are these the subjects that you are currently studying in the dry conditions of the Atacama Desert in Chile?
Yes, exactly. So I’m the director of what’s known as the Simons Observatory, which is a collaboration of over 200 researchers over all seven continents on Earth. It involves the construction of a large telescope, a six-metre diameter telescope that is roughly 20-times bigger than BICEP, and also many, many BICEP-sized telescopes.
So an array of small telescopes, each the size of BICEP, will look for the gravitational wave signature hypothesised, which originated from the Big Bang inflationary epoch. The very large telescope will look for the gravitational lensing effect that would be indicative not only of the mass of the neutrino, but whether there are other particles even more ghostly present.
This is another alien landscape that is actually more reminiscent of a volcanic planet like Mars where there are these enormous mountains and active volcanoes. It’s quite an astounding location to be in, you have wear an oxygen tank on your back at all times because you’re above half the Earth’s atmospheric pressure that you’d feel at sea level. So you’re wearing protective clothing such as boots, helmets and then you have cannulas in your nose, pumping oxygen into you so that you can actually have some semblance to sanity at high altitude. It’s very difficult, but a very beautiful place to work.
You seem to favour the more extreme working locations, don’t you?
[Laughs] That’s what I get for living in San Diego, you have to work in these forbidden places!