Out there in the Universe, there’s so much that we’ve learned and discovered. We know all about the normal matter present in the Universe: the full suite of Standard Model particles and how they interact all throughout cosmic history. We know about the laws that govern reality extremely well, including the fundamental forces and how they behave under a wide variety of cosmic and quantum conditions. We’ve reconstructed most of the history of the Universe in extraordinary detail, and from a variety of different approaches — observationally, theoretically, and experimentally — we’re gathering more and more evidence every day to peel back the curtains that obscure what’s beyond the currently understood frontiers governing reality.

But what lies beyond what we’re already certain about? If we don’t already know, what do the greatest minds who ponder these problems think, and can their intuitions, educated guesses, or even hunches help drive the field forward? In one of the largest surveys of physicists about fundamental physics ever conducted, solicited by Physics magazine in 2025 and published online in 2026, ten big questions about the nature of reality were asked. While anyone can view the results for themselves, it’s worth asking what the survey actually reveals, and whether it can teach us anything meaningful? That’s what Robert Shackleton wants to know, asking if I have:

“…comments on the Afshordi/Halper survey of physicists? Looking forward to reading your take!”

It’s published with a provocative title: “Big Mysteries Survey: Physicists’ Views on Cosmology, Black Holes, Quantum Mechanics, and Quantum Gravity.” Here’s my sure-to-be-unpopular take on it.

This image shows the demographics of the 1675 respondents to a survey on foundational and controversial topics in contemporary physics, conducted by the American Physical Society through their Physics Magazine. Answers are shown in the image.

The first thing worth pointing out is shown above: the pre-survey question of who you are and what you study. This question, arguably, is far more informative than anything else, for the following reasons.

• If you were going to ask a question about astrophysics and/or cosmology, you’d be most interested in what astrophysicists and cosmologists had to say about it, not what the other 88% of survey respondents said.
• If you were going to ask a question about gravity, you’d care what the 9% of gravity researchers said most of all, and not so much what the other 91% of respondents said.
• If you were asking questions about quantum physics or its foundations, you’d want to know what the 18% of respondents who studied it said, not so much what the other 82% said.
• And if you have general questions, you likely want a physicist in general; the survey was, however, open to all, and 30% of all respondents are not self-reported physicists at all.

This tells you that you’re not necessarily getting the expert views of subject matter experts whose expertise is relevant to each question that’s being asked. Instead, you’re getting the aggregate views of 1675 survey respondents, only a fraction of whom have expertise in the area probed by any particular question, and seeing them all together.

As it turns out, if you’re interested, the 10 survey questions are about:

• the Big Bang and the early Universe (two questions),
• dark matter, dark energy, and the expanding Universe (three questions),
• the anthropic principle (one question),
• quantum mechanics and quantum gravity (two questions),
• and black hole interiors and information (two questions).

This is significant, and I’ll explain why.

This animation of the double detonation scenario shows two white dwarfs in close orbit around one another. When material accumulates onto one member, it can cause a surface thermonuclear reaction, which can then propagate around the star until it triggers a core detonation. This scenario could be responsible for up to 100% of observed Type Ia supernovae, while the “classical” picture of accretion onto a white dwarf that then exceeded the Chandrasekhar limit may well be responsible for 0% of Type Ia supernovae.

For me, I’m a lot more interested in what a supernova researcher thinks about the expanding Universe than I am what they think about black hole information, and I’m a lot more interested in what a researcher who works on the foundations of quantum physics thinks about quantum mechanics than I am in what they think about dark matter. So my first thought, before we even get into the questions and the survey results themselves, is that there’s likely to be a whole lot of disagreement in the answers.

Within any given sub-field, most of the researchers within it are aware of the issues and subtleties surrounding the frontiers of that area. If you’re not in that field, you generally aren’t. Misconceptions die hard, and even if you once studied a field and then subsequently learned about advances in that field which have occurred since you last studied it, it’s more likely that the original (mis)information, rather than the more correct, newer information, will emerge from your mind.

Beyond that, none of us has an unlimited toolkit or a fully comprehensive knowledge of the facts; we have the resources and understanding that we possess, and that’s limited. We see that with the very first question in the survey: about the Big Bang.

The first question in a recent 10-question survey of 1675 responses to physics questions is about the nature of the Big Bang, as sorted into five separate options.

Unfortunately, this is not a question about physics itself, but rather about the Big Bang and how people use the term. If you’re in astrophysics and cosmology, you probably spend your time thinking about our actual Universe and what we can conclude/infer based on what we can observe. In that case, the standard definition — i.e., the third option — emerges as the answer, as I’ve written about extensively.

If, however, you work on quantum physics or on the topic of gravity itself, you’re much more likely to not care so much about the hot dense state that corresponds to the hot Big Bang or the early Universe, but rather the question of ultimate initial conditions: questions over the presence and nature of a singularity, initially.

Even though the concept of the Big Bang could have referred to either in the distant past, from say the 1920s through the 1970s, it now has two distinct meanings, depending on who is referring to it. Yes, most people who study things that exist within our physical Universe recognize that the hot Big Bang is an observational fact consistent with our best theories, and that the question over initial conditions and the presence or absence of an initial singularity remain fundamentally unanswered, despite an enormous amount of theoretical work on the topic. It’s not a surprise that there’s a consensus that’s emerged here, as a solid amount of work has gone into busting myths about the Big Bang here in the 21st century, or that there’s a second-best option from people who study the topic from a quantum or general relativity point of view. But this question is the only one asked in the survey that we have any answers about at all.

The second question from a recent 10-question survey of physicists concerns the uniform temperature and spatial flatness representing the initial conditions present during the hot Big Bang, and that remain present ever since. While cosmic inflation is the consensus option, many dissenting, alternative opinions received almost 50% of the votes between all of them.

The second question — about the early Universe — is the only other question (out of 10!) where one option obtained at least 50% of the responses from the survey-takers. The puzzles of cosmic uniformity, where the Universe is observed to have the same temperature everywhere to a precision of 29,999 parts in 30,000, and cosmic flatness, where the expansion rate and the matter-and-energy density must have been balanced to something like 51 significant digits at the start of the hot Big Bang, were pointed out back in the 1970s by Bob Dicke and Jim Peebles.

Why is the Universe this way? Why was it born with a uniform temperature everywhere (the classical horizon problem) and with such perfect spatial flatness everywhere (the flatness problem)? The Big Bang framework, as was understood at the time, offered no explanation or reason. All you could say was, “these are the initial conditions,” and that’s it.

Cosmic inflation was the theory that came along in the early 1980s and solved both of them. The evidence for cosmic inflation having occurred has accumulated substantially in the 45 years since, and it remains the leading solution after all this time: it is the phase that preceded and set up the hot Big Bang. There are many alternatives out there that have garnered a lot of interest, and inflation still remains very poorly understood among non-specialists. Nevertheless, the evidence supporting it is overwhelming, and all of the alternatives face tremendous difficulties in comparison to inflation, while lacking the same predictive power inflation has to explain things like the observed spectrum of scalar (density) fluctuations in the Universe, the presence of super-horizon fluctuations, an upper limit to the maximum temperature of the CMB, and more.

The quantum fluctuations inherent to space, stretched across the Universe during cosmic inflation, gave rise to the density fluctuations imprinted in the cosmic microwave background, which in turn gave rise to the stars, galaxies, and other large-scale structures in the Universe today. This is the best picture we have of how the entire Universe behaves, where inflation precedes and sets up the Big Bang. Unfortunately, we can only access the information contained inside our cosmic horizon, which is all part of the same fraction of one region where inflation ended some 13.8 billion years ago.

This reveals something important: even in the cases where the science is very clear about what the evidence does and doesn’t indicate, it’s a challenge to even get a simple majority of physicists to accept the answer. This is congruent with my own experience:

• as an undergrad, where I had astrophysics professors who didn’t believe the evidence for dark energy, cosmic inflation, or even general relativity,
• as a grad student, where several professors pursued alternative research programs to the mainstream, irrespective of the evidence that contradicted their research directions,
• and as a professor, where very few of my colleagues expressed interest in — but held no shortage of opinions about — specialties other than their own.

Most often, when faced with actual experts in a particular subfield, physicists who lack that expertise themselves are smart enough to not express what I perceive as a deep disrespect for the work and conclusions of those who’ve chosen to work in fields other than their own. But their privately-held beliefs and opinions remain unchanged, and when given the opportunity to share their opinions in a consequence-free manner, no matter how poorly informed, they leap at the opportunity. It isn’t everyone, or even a majority of physicists who are this way, but all it takes is somewhere between 15-25% of them — particularly if they aren’t humble enough to say “I don’t know” when they don’t know — to explain the contrarianism seen in questions such as this.

This bar graph shows the results of the fifth question on a 10-question survey about physics that polled 1675 respondents, concerning the Hubble tension. While we still don’t know the solution, several of the proposed answers here, receiving a substantial number (hundreds) of votes, have legitimately been ruled out.

For example, the fifth question in the survey is shown above: a question over the Hubble tension. At its core, the Hubble tension is a puzzle where different methods of measuring the expansion rate of the Universe, either from an early relic (CMB or BAO studies) that’s imprinted in the Universe, or from a distance ladder (where we start here and look at objects progressively farther away, such as Type Ia supernovae) approach, give fundamentally different and inconsistent answers: 67 km/s/Mpc for the early relic method, and 73 km/s/Mpc for the distance ladder method.

• As you can see, 17% of people blame systematic errors in the supernova data, even though that explanation is definitively ruled out.
• 9% blame systematic errors in the CMB or galaxy survey results, even though many independent teams using independent methods, pipelines, and analysis techniques all get the same answer.
• 22%, the most of any option, blame early dark energy, which is a possible solution, but which has severe constraints on the possibility of its influence explaining the tension fully.

The real problem, however, is one that we face for most of the questions that are part of this survey: we have puzzles, mysteries, and hints as far as what’s going on is concerned, but not enough information to definitively declare an answer. As shown in the two earlier examples, even when we do have enough information to reach a robust conclusion, people outside of that particular field are slow to embrace it.

The X-ray (pink) and overall matter (blue) maps of various colliding galaxy clusters show a clear separation between normal matter and gravitational effects, some of the strongest evidence for dark matter. The X-rays come in two varieties, soft (lower-energy) and hard (higher-energy), where galaxy collisions can create temperatures ranging from several hundreds of thousands of degrees up to ~100 million K. Meanwhile, the fact that the gravitational effects (in blue) are displaced from the location of the mass from the normal matter (pink) shows that dark matter must be present. Without dark matter, these observations (along with many others) cannot be sufficiently explained.

For example, one of the questions asked in the survey is about dark matter, and whether you think dark matter is:

• a low-mass particle like an axion,
• a high-mass particle like a WIMP,
• a non-particle like a primordial black hole,
• non-existent and instead arises from modified gravity,
• non-existent and its inferred presence will someday be accounted for by quantum gravity,

along with other options. Quite frankly, the modified gravity approach is strongly disfavored, the data we have is completely agnostic about the “flavor” of dark matter present in our Universe (but unambiguously supportive of its presence), and so it’s no surprise that people don’t agree on what they think dark matter is: nobody actually knows.

There’s a similar question about dark energy, where the options given are:

• it’s a cosmological constant (the simplest option, and it could be),
• a time-varying scalar field (a more complex option, and it could be),
• blamed on some not-yet understood aspect of gravity, whether quantum or modified gravity (a hand-wavy option, but one that isn’t ruled out),

and of course we’re not going to achieve a consensus here. Nobody knows; all of this is guessing, and the evidence doesn’t strongly point in favor of any one explanation over another.

And that’s the big problem I have with the survey: most of the questions are not about facts, understanding or interpreting the evidence, or drawing conclusions based on the data we’ve acquired. Instead, they’re based on one’s gut feeling about questions that have no clear answer at present for a good reason: lack of discerning information.

If each time a quantum decision were made, our timeline split to allow for two (and only two) possible outcomes, then the number of overall possibilities would increase incredibly rapidly, depending on which combinations of outcomes and what order-of-interactions are allowed. These possibilities cannot all fit within our physical, observable Universe, but the mathematical structure known as a Hilbert space, leveraged in quantum mechanical calculations, can contain them all.

There’s a question about “what sets the values of the fundamental constants,” and of course we have no information at all: only guesses.

There’s a question about what the best idea for quantum gravity is, and again, of course we don’t even know if gravity is quantum in nature, much less which approach is best.

There’s a question about what happens inside of a black hole, where all we have are equations that experience pathological behavior at a singularity.

There’s a question about black hole information, which of course is one of the most famous unsolved paradoxes today.

And, of course, there’s a question that’s equivalent to the greatest argument-starter in physics over the past 100 years: what is your favorite interpretation of quantum mechanics?

People have worked hard to test ideas about determinism in the Universe, and to close as many loopholes as possible in attempts to avoid the fundamental “weirdness” that we see in the quantum Universe. But that fundamental weirdness persists, and can be summed up with just two key points:

• that all quanta appear to propagate in a wave-like fashion,
• but they appear to interact with each other like particles do.

That, to the best of our ability, is what we understand it means to live in a quantum Universe. While there are many interpretations of quantum physics that are consistent with those notions, there have been precious few experiments or observations uncovered that one can make to discern different interpretations from one another. That might make interesting fodder for philosophical debates, but it hasn’t taught us anything about physics, or the nature of reality, that’s different from or inconsistent with Bohr’s original interpretation of quantum physics: the Copenhagen interpretation.

This bar chart shows the results from a survey of 1675 physicists and physics enthusiasts about their favored interpretation of quantum physics. The Copenhagen Interpretation remains the most popular, but there is no clear “favorite” overall.

The core problem is this: surveys and debates are only useful for laying out what is known, evidence-wise, and presenting different ways that one could potentially tell competing ideas apart from one another. The way that one would do this is observationally or experimentally, rather than theoretically or philosophically. The only way we find answers — meaningful, definitive answers — to questions about our physical reality is if we can find a way to interrogate the Universe itself about those issues. The answers to our deepest questions about reality are written on the face of the Universe itself, and until we can figure out how to ask them in a way that compels the Universe to give up its secrets, we simply cannot know.

This was illustrated spectacularly way back in 1920: on April 26, 1920, in particular. On that date, the most famous debate in the history of physics and astronomy occurred: the debate between Harlow Shapley and Heber Curtis over the nature of the spiral nebulae in the sky. Were they objects in the Milky Way itself, like some form of protostar, or were they “island Universes” all unto themselves, far beyond the extent of the Milky Way. Six pieces of evidence were presented, each side got the opportunity to interpret them, and then a panel of jurists voted on which arguments were more compelling and attempted to decide which side won.

Heber Curtis (left) and Harlow Shapley (right) argued their positions on the nature of spiral nebulae, with Curtis arguing for a galactic origin and Shapley arguing for a protostar origin.

Overall, the decision was in favor of Curtis (arguing for the island Universe interpretation) on at least one of the six points, in favor of Shapley (arguing for the protostar interpretation) on multiple points, and that the overall winner was deemed to be inconclusive. That overall decision turned out to be the smart move; three years later, the definitive data arrived from Edwin Hubble’s observations of the spiral nebula seen in Andromeda: demonstrating, from the presence of variable stars discovered within it, its extreme distance far beyond any stars ever seen within the Milky Way. That “proved” the island Universe interpretation to be the correct one, settling the issue not via voting, but with science.

And that’s pretty much what I think about this survey: it might be good for identifying current thoughts about any of these matters — some of which are very good thoughts, but many of which are grossly underinformed — but it isn’t going to be the results of any survey that are going to:

• drive the field forward,
• point the way toward progress,
• or settle any of these controversial issues.

The only way to learn anything meaningful is to obtain definitive data: data that we have in some cases, but that not everyone accepts, understands, or is aware of, and in other cases, data that has yet to arrive, and whose ultimate arrival is not guaranteed.

The best thing, honestly, that one can take away from this survey is just how eager physicists are to express their strongly-held opinions about matters where having one is unjustified on scientific grounds. And the most depressing thing to take away is that even having a correct answer, even with overwhelming evidence supporting it, even if it’s enough to create a consensus within your own sub-field, isn’t enough as far as convincing the majority of physicists outside of your own field goes. From a scientific perspective, surveys about speculative opinions simply don’t have the power to take us anywhere interesting, as far as the prospects of gaining actual knowledge about reality are concerned, at all.

Send in your Ask Ethan questions to startswithabang at gmail dot com!

This article Ask Ethan: What do surveys of physicists actually reveal? is featured on Big Think.

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