Niayesh Afshordi, a cosmologist at the Perimeter Institute and the University of Waterloo and (excitingly!) a new FQxI member, has spent the past year with Phil Halper, a Fellow of the Royal Astronomical Society, asking physicists what they actually believe about ten of the most contested questions in physics. They received 1,675 responses, which makes it the largest survey of its kind ever conducted.
Surveys of expert opinion are common in philosophy, where the PhilPapers Survey has charted the state of the discipline twice now. They are however slightly rarer in physics. Halper and Afshordi, who recently co-authored Battle of the Big Bang, have run a smaller version of this before, led by Alice Chen, at a black hole conference in Copenhagen. The new one is around twenty times larger and draws from a much broader pool: the American Physical Society membership and Physics Magazine readers, rather than specialists at a single conference.
The clearest majority from the survey concerned the meaning of the phrase "the Big Bang." 68% of respondents said it should refer to the universe's evolution from a hot, dense state, rather than the literal beginning of time. The Copenhagen survey returned the same figure, which suggests the result isn't an artefact of who happened to respond. Fellow FQxI member Sean Carroll, of Johns Hopkins, joined Afshordi and his Perimeter colleague Ghazal Geshnizjani for a long discussion of the results on Halper's YouTube channel, and treats this finding as a question about words rather than physics. "We use the phrase Big Bang to mean different things," he says, noting that Fred Hoyle's original use of the term simply meant an expanding, cooling universe.
ΛCDM, the standard cosmological model, fell under more scrutiny than one might perhaps think. The most popular pick for dark energy was a time-varying field rather than the cosmological constant the model is built on, possibly reflecting recent DESI results that suggest dark energy evolves over time. Afshordi has weighed in on this with us before. On the FQxI Podcast on dark matter and dark energy last year, he told us he'd sent an email round Perimeter Institute saying "cosmology has changed forever. Einstein invented lambda (Λ), and now it's dead. It took 100 years — but we did it." He featured on the episode with Alice Chen (who ran the earlier survey in Copenhagen with Halper and Afshordi) to discuss the conflicting results about whether dark energy is evolving or a constant, from the DESI and ACT collaborations. It’s a fantastic listen!
Speaking of long reigns coming to an end... string theory, popularly framed since the 1980s as the "only game in town" for quantum gravity, drew only 19% support. Loop quantum gravity and a contingent of physicists who think gravity might not be a quantum phenomenon at all were right behind at 13% and 18% respectively. The cohort of physicists who believed gravity is not quantum surprised the panel. Carroll said the result was "very very different than my experience talking to actual physicists," and Geshnizjani admitted she hadn't realised how many physicists thought gravity wasn't quantum at all.
The Copenhagen interpretation of quantum mechanics came in at 36%. In the YouTube discussion, Halper asks Carroll, whose book Something Deeply Hidden defends many-worlds, whether the various positions should really be called "interpretations" at all. Carroll's answer is no: what we call interpretations of quantum mechanics are distinct scientific theories with different predictions and different ontologies. He had argued earlier in the conversation that quantum mechanics as currently formulated isn't properly defined, and that physicists who don't engage with the problem (saying things like "we don't really have to do any work on this") are "kind of embarrassing." Geshnizjani took a different side: "I am in the shut up and calculate camp," she said, though she added that she admired people who do dig into the foundations.
Although it's often reported in the press that the black hole information paradox has been resolved in favour of information preservation, the survey found that 19% of physicists still side with Stephen Hawking's earlier view that information is lost. Hawking himself famously changed his mind: he conceded a 1997 bet with John Preskill at a conference in Dublin in 2004, handing over a baseball encyclopaedia. His co-signatory Kip Thorne never conceded, and it seems that the wider physics community has also not fully accepted Hawking's specific 2004 argument either.
Halper, in the survey's accompanying press release: "Controversies in physics are decided by data, not votes—but surveys like this are valuable, especially in how scientific thought is communicated to the public. Our results question whether the many opinions attributed to physicists are actually supported by them."
Afshordi has also built an interactive dashboard of the results, which lets you filter responses and see how answers on one question correlate with answers on another. For more from him in his own words, his October 2025 episode of the FQxI Podcast is a good companion piece.