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Many physicists were disheartened at the news that the apparent discovery of gravitational waves from the big bang was likely an error. But a cosmologist from the Perimeter Institute for Theoretical Physics in Waterloo, Ontario felt a bit vindicated.
Neil Turok has been betting all along that primordial gravitational waves—ripples in the fabric of spacetime—would never be seen. Turok expressed little surprise that new results from the Planck satellite observing light from the big bang show that the supposed observation of gravitational waves from the South Pole’s BICEP2 experiment in March was probably contaminated by a haze of dust in our galaxy.
Gravitational waves, if confirmed, would be proof that the baby universe ballooned rapidly just after the big bang in a process called inflation. The idea is popular, but it has some vocal opponents, such as Turok, who helped formulate one of the main alternatives to inflation. Scientific American spoke to Turok about the BICEP2 controversy and how he came to wager with Stephen Hawking against gravitational waves.
[An edited transcript of the conversation follows.]
What does the latest analysis from Planck show?
The Plank paper tells us that the entire BICEP2 signal could be due to dust. This is big news. The only way to distinguish between dust and the kind of signal BICEP2 was looking for is to look in several frequencies. This was a fundamental problem with the BICEP2 claim, because they were only using one frequency. Currently Planck is the only experiment with the capability to look in multiple frequencies. It’s taken them some time to do all the necessary analysis. What they find is that the projected contribution from the dust more than accounts for the BICEP2 measured signal. So what it means is that the simplest explanation of the BICEP2 results is that they were seeing dust.
What does this mean for the idea of inflation, which predicted the gravitational waves?
The theory of inflation has dominated cosmology for 30 years. I have been one of the people pointing out its problems and limitations. In my view, it’s not a convincing explanation for the big bang. One of its problems is it’s very adjustable. It makes very few specific predictions that you could actually go out and check with a measurement.
I’ve been developing a cyclic picture of the universe, according to which the big bang is just the latest in an infinite number of cycles going back into the past. In the cyclic picture there will be big bangs in the future. I developed this theory with Paul Steinhardt. We mostly did so in order to show people there was an alternative to inflation and you didn’t have to believe the party line.
It turns out the cyclic model predicts zero gravitational waves. If gravitational waves are seen they will disprove all the models I’ve developed. I’m also quite happy to see them disproved. I don’t think they are the final answer at all. I also think the cyclic models are too complicated. But these models work every bit as well as inflation in every other respect.
How did you end up making a bet over gravitational waves?
People like Stephen Hawking believe that the simplest inflation models, the most plausible ones, would produce enough gravitational waves that we could detect them. I made a bet with Stephen in 2001 that these gravitational waves would not be there. As soon as the BICEP2 result came out, Stephen told the BBC that he’d won his bet with me. My response was, science requires verification. We never believe the results of one experiment, it needs to be checked. I could see a number of problems with the BICEP2 experiment.
Stephen wrote me an email saying, don’t be a bad loser. He’d lost $100 on the Higgs boson, and had to pay up when it was discovered. He said, you should pay me $200 now because this is much more important. I said, I’m not going to pay because I have very serious doubts. I said, “I bet you the true signal of gravitational waves is less than a quarter of what BICEP2 is claiming.” If it turns out to be even a half of what BICEP2 is claiming, I will pay up.
Do you think you’re going to win?
I’m halfway to winning my bet. Earlier Planck measurements were indicating the level of gravitational waves is less than half of what BICEP2 is claiming. The latest measurements from Planck basically make that very solid. All we need to go is another factor of two down and I win my bet with Stephen. I’m hoping that’ll happen in November because BICEP2 and Planck are working together. BICEP2 is still hoping that when they combine with Planck they will miraculously detect evidence of gravitational waves together. It might happen, they could be lucky, but in my view that’s wishful thinking.
Is all this back and forth about BICEP2 damaging the field, or is this simply the way science is done?
Both. I think a lot of people will take pause at this point and acknowledge there was too much hype about the results, too many claims made, and instead we need to be a little more cautious and scientific and really allow the evidence to be settled.
I think [the BICEP2 researchers] should have said we found a signal that is very interesting, and future experiments will show what it represents. It could be dust, it could be something else. Actually, I advised them to say that. I called them up before the press conference because I’d heard rumors, and advised them to be cautious. Unfortunately they didn’t listen to my advice and they’re probably now wishing they had.
In any case it’s pretty normal for science. The universe puts us right. It’s just mind boggling that we’re able to make these measurements and that they’re telling us something as profound as what happened at the big bang. This would have been termed philosophy not that long ago. Now it’s real science.
What will it mean if there are no primordial gravitational waves?
Finding that your whole picture of the big bang is obscured by dust is a big negative. But so far our observations of the universe are pointing at this marvelously simple picture, and it’s simpler than most of our theories. Our theories are getting more and more arcane and complicated, and the universe is telling us it’s just as simple as it can be. I find that wonderful. It means our theories are in doubt but for the first time there are real clues.