Steinhardt has written articles like this for Scientific American before. But a particular line in the most recent article’s conclusion set people off: “…Inflationary cosmology, as we currently understand it, cannot be evaluated using the scientific method.” In other words, Steinhardt argues, the dominant theory for the formation of our universe isn’t testable, and thus, not real science.
Inflation proposer and MIT professor Guth penned the response with physicists David Kaiser (MIT), Andrei Linde (Stanford), and Yasunori Nomura (UC Berkeley), then gathered famous signatories from across the physics world. The four disagreed with many of the statements in the Scientific American article, but “We were particularly in strong disagreement with the statements they made about the testability of inflation which we thought were completely without justification,” Guth told Gizmodo. “We thought it was about time someone answered those objections.”
The response letter, also published in Scientific American, sums up the physicists’ complaints. Inflation isn’t just one theory but many models, and no one thinks that all of these models are correct, it says. Some models have been ruled out, others haven’t. Some of them have made correct predictions, like the average mass density of the universe, for example. The models have gotten more accurate over time with the help of more mathematical theories and observation. But the letter’s main point is that while inflationary models have become the predominant way to explain the universe, they’re still testable science, and could be disproven if the right evidence turned up.
When I called some of the signatories, they felt conflicted about the initial article, the response letter, or both. Renata Kallosh, a Stanford theoretical physicist, told Gizmodo in an email that she’d reviewed some of Steinhardt’s papers, and they contained errors. MIT theoretical physicist and Nobel laureate Frank Wilczek told Gizmodo that the initial article was “very biased,” a selective interpretation of inflation that bordered on slander. “It’s kind of outrageous,” he said. But still, he said he “was uncomfortable with the idea bringing some massive hammer of dissent down,” and thought the new letter was possibly overkill.
That’s because the signers of the response letter—even Guth—agree that inflation isn’t an established truth yet. “The model of inflation is incredibly unsatisfying,” Lisa Randall, Harvard University physicist, told Gizmodo. “It’s very hard to define exactly what is meant by inflation, and that is somewhat the source of disagreement here.” Sean Carroll, theoretical physicist at Caltech, pointed me towards his blog, where he summed his (and my) opinions up:
We judge theories by what predictions they make that we can test, not the ones they make…