May 16, 2017 7:00 AM

Physicists Can't Agree on What Science Even Means Anymore

A nerd fight has broken out over whether cosmic inflation—one of the most widely accepted theories in physics—breaks the rules of testability.

Apologies to Merriam, Webster, and everyone else who has ever assigned themselves the chore of cataloging how English speakers use words, but science is not a noun. I mean, yes, technically it is. 1 But conversationally, most people use ‘science’ like Mark Watney did in The Martian, when he said he would “science the shit” out of the problem of growing food on Mars.

Science the verb is a process of questioning, hypothesizing, experimenting, and—so, so often—being wrong. Again and again and again. Until you get it mostly right. (Because no science [n] is ever complete.) Ideally, the process is democratic: Anybody can science the shit out of anything. In reality, most people “do” science vicariously—by reading about new discoveries and having faith that the discoverers aren’t charlatans. Though it’s not quite faith: We trust them because scientists argue in public.

These arguments happen all the time. Sometimes they last decades. Scientists curse one another out, hold grudges, and stop speaking altogether. But even in the nastiest of arguments, scientists generally tacitly agree that they are all Doing Science. Not Doing Science is an insult, usually reserved for fringe individuals who falsify data or host daytime nutrition shows. In terms of nerd fights, one mainstream scientist accusing another mainstream scientist of Not Doing Science is akin to Kanye West storming Taylor Swift’s 2009 VMA speech to imply that she didn’t deserve Best Female Video.

Recently, a trio of mainstream physicists accused hundreds, perhaps thousands, of other mainstream physicists of Not Doing Science in a very public forum. Their article, published in February’s Scientific American 2, targets the inflationary universe theory, which, during the past 35 years, has come to be what most physicists use to explain the origin (and present state) of the cosmos. By publishing in SciAm, these authors aren’t just asking the vicariously scientific public—you and I—to accept their theory as correct. They are asking us to decide what it means to Do Science.

This whole ordeal goes back to the Big Bang. As in, theory of. It’s not terribly controversial, but it has a few problems. In the early 1980s, physicists were trying to make sense of a particularly vexing one: The Big Bang does not explain why the universe is so flat. Flat, in this sense, doesn’t mean squashed or thin. It means if you zoom really far out and draw a line between any two points, it will be straight—whereas with the Big Bang alone the line would be curved. This is in addition to other observed oddities. For instance, experiments measuring the breadth of the cosmos had shown there was no way the Big Bang was energetic enough to fling the universe so wide, so fast.

Three physicists—Alan Guth of MIT, Andrei Linde of Stanford, and Paul Steinhardt of Princeton—started working on inflation as a potential solution. Their theory posits that a super dense bubble of vacuum energy that super-charged the Big Bang. The universe opened up wide and was essentially a vast, irradiated nothingness, except some regions were ever so slightly more dense than others. These attracted molecules, which formed dust particles, which formed rocks, which attracted gases that got so dense they combusted, wheedled, spun, orbited … you know the rest. 3

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Inflation explained that process so well that it came to dominate mainstream physics. It isn’t a theory, per se—not like the theory of relativity is a theory. It’s more like a thematically connected group of competing hypotheses, what Guth calls an “umbrella.” They share some crucial traits, namely, ripples in the cosmic microwave background radiation. And the hypotheses predict that these traits will conform to certain numerical measurements. Some of these criteria have been met; for instance, in 1998 physicists found proof of dark energy 4, which accounted for 70 percent of the missing matter that inflation had predicted. Confirming other criteria has been more elusive.

For years, scientists have been looking for precise measurements of a type of gravitational radiation left over from the Big Bang. One recent experiment looking used a European Space Agency satellite called Planck. And in 2013, scientists interpreting results from Planck said they fit right into one of the inflationary hypotheses. 5

Eureka? Not according to three other physicists who attended the ESA press conference where the Planck results were announced. They were Avi Loeb, chair of Harvard University’s astronomy department; Anna Ijjas, then a grad student and now a post-doc at Princeton’s Center for Theoretical Science; and Steinhardt, one of the original inflation architects. They felt that the ESA had fit the Planck data to the most convenient inflationary hypothesis. But, crucially, not the simplest. Physics should favor simplicity, and the Planck data actually caused simpler inflationary models to make less sense.

They published a critique of inflation in the journal Physics Letters B—which eventually became the SciAm article—calling out what they saw as errors fitting the Planck data to inflation. They went even further. They pointed out that inflationary energy had never been directly observed, and was therefore hypothetical. Even more vexing to them was the fact that some inflationary models predict the existence of the multiverse, which by definition exists outside this universe’s rules and thus cannot be tested using this universe’s iteration of science.

But inflation’s biggest crime was its flexibility: The authors argue that inflation contains so many hypotheses that you can essentially fit at least one of them around any new data that comes out. In short, inflation can never be disproved. People studying it, therefore, are Not Doing Science.

They had plenty of other, more specific complaints about inflation. You can read about those in SciAm, but they aren’t necessary for you to finish this article. All you need to know is what you probably already suspect: Their accusation dropped like a dollop of potassium in a swimming pool. Four prominent inflationists (Guth, Linde, David Kaiser of MIT, and Yasunori Nomura, the director of UC Berkeley’s Center for Theoretical Physics) wrote a rebuttal defending the science-ness of their theory to the editor of Scientific American. They even went so far as to have it co-signed by nearly 30 other physicists—heavyweights like Stephen Hawking and Rainier Weiss. The original SciAm trio then rebutted the rebuttal with an FAQ about why they are right and the other guys are wrong.

This whole ordeal presents the rest of us with two gifts. The first is nerdy drama—if you really want to get into the details, read this article in UnDark, or this one in The Atlantic.

The second gift is an opportunity to examine what science—the verb, the doing, the process—even is anymore. What these two groups are essentially bickering over is time. To the SciAm trio, inflation has had enough of it. In fact, they say no amount of time would ever give inflationists enough data to confirm one of their hypotheses. More time just gives the inflationists more time to chase their mathematical conjectures onto thinner and thinner limbs. Inflation, they say, is broken. Cut bait, and start looking for some new framework. They even offer their own—the charmingly named Big Bounce.

The pro-inflationists say just need more time. Science takes time. Physics takes a lot of time. These scientists are still working out which hypotheses work, and which don’t. Many theoretical frameworks go through periods like this, in which scientists throw the same data against multiple theories at once, eliminating the bad ones as they go. Usually, it just happens much faster.

All of which is … great. Great because yay, science! But also “great” because it raises the question of how the hell you, the vicariously scientific public, are supposed to decide which pill to swallow. OK, maybe you could go the über-Karl Popper route and side with whoever provides the most empirically grounded research. The downside is that what counts as science will proceed very slowly for you. Or, if you have lots of expendable time and a voracious mind, you can adopt philosophical frameworks like “post-empirical confirmation.” These are just starting points, and both the SciAm trio, and the inflationists are inboard of these respective extremes.

Basically, this is an invitation to think for yourself. Physicists are still figuring all this stuff out—as are most scientists, all the time. You just have to decide how much patience you have for answers … and if the time comes when a theory doesn’t make sense, whether you have the chutzpah to tell several thousand physicists that they aren’t actually doing science.