I must emphasize that although I have a background in physics, by no means do I have expertise in particle physics or string theory. I was a condensed matter physicist, and an experimentalist not a theorist. I do not have any deep understanding of string theory beyond a general background knowledge. What I bring to the table is a bit of awareness of how physics research operates in practice, plus the cynicism that comes with the territory of being an ex-physicist.

String theory was essentially a scientific fad. I’m not going to go into the history, because I have no expertise on that, and the Wikipedia article is frankly opaque. Dr. Collier recently made a more accessible retrospective–although I find the video game irritating, and Dr. Collier is liable to get some things wrong.

The relevant part is that string theory was a fad in scientific research and a fad in popular science. The physicists were overly excited about it, and so was the public. Then there was backlash, which again occurred both among physicists, and in the public. String theory was criticized for failing to make any testable predictions. Peter Woit described the theory as “not even wrong” (and published a book with that title), because a theory could only earn the status of being wrong by making a prediction that was found to be false.

Today, long after all that went down, what I encourage among non-physicist readers is moderation. String theory isn’t exactly a success story, but in the end it’s still legitimate scientific research. Frankly, you probably shouldn’t have any opinion on string theory at all, and it was a mistake for science communicators to have ever encouraged you to have one.

Public opinion on scientific questions

I think it’s important to understand a social reality about science–scientists are trained to take sides. Sure, the scientific ideal is to neutrally adjudicate the evidence, but if you actually want to get paid or get published, you take a side. Specifically, it is a scientist’s job to argue and persuade fellow scientists (and grant providers) of the value of their own novel ideas.

In my opinion, this is the #1 bias in science. When the general public talks about bias among scientists, they think about scientists’ political leanings, or their failures to understand e.g. women’s issues. I’m sorry to say that the biggest bias in science is a lot more petty and self-serving. Scientists’ careers depend on them being able to demonstrate the value of their own contributions. These incentives are the root of the replication crisis as well as incidents of scientific fraud. Jonathan Pruitt didn’t fabricate results because he had a political commitment to some theory of spider behavior, it’s because he had a commitment to his own career success.

So what are the implications on scientific communication to the public? Usually the goal of communicating to the public is to teach what has been well-established in science. However, scientists commonly go beyond that to talk about the “cutting edge”, and are specifically biased towards talking about their own cutting edge. There are a lot of reasons for this. Sometimes, they want to impress upon people that science is an ongoing project (and one that requires public funding). Sometimes raising questions is just a way of intellectually engaging people. Sometimes the audience is mixed, and they’re actually hoping that the relevant experts in the audience will learn about their work. Sometimes it’s just about social status.

Whatever the reason, it can be a bit dangerous. The general public can’t necessarily tell where established science ends and self-advocacy begins. When a scientist talks about a scientific controversy, and tries to pass it off as if they’re totally winning, the general public does not have the tools to be skeptical about it, or even recognize what is happening.

And that’s basically how I see string theory. It was a mistake to communicate it to the public like it was for sure the next big thing. And the public, not knowing better, ate it up. Then the critics came along, and I don’t blame them at all for going to the public, because string theory was already there in the minds of the public, demanding a response. But if you asked me what is the ideal state, I think that the general public should not have any opinion on string theory one way or another.

Let me make a comparison to my field. As a member of the general public, do you have any opinion on the theory of cuprate superconductivity? What do you think is the explanation for the pseudogap observed in such materials? You don’t have an opinion on the subject, because you probably don’t know what a cuprate is, and almost certainly do not understand what a pseudogap is. I published papers about the pseudogap and even I cannot assert an opinion. You shouldn’t have an opinion either. Of what benefit is it to form an opinion on the solutions to a scientific problem that you don’t even understand?

Science communicators have encouraged you to think about and form opinions about string theory. And maybe that was successful at engaging people or whatever, but. If you don’t have the expertise, you know you’re just play-acting, right? You can’t really form a meaningful opinion on string theory.

Falsifiability

I think part of the reason lay people felt entitled to having opinions against string theory, is because the main criticism is on a rhetorical level that they can understand. You might be familiar with falsifiability, which was used by philosopher Karl Popper to address the demarcation problem, i.e. distinguishing science from non-science. The argument is that string theory is unfalsifiable and therefore unscientific, and that’s an argument simple enough for anyone to form an opinion about it.

I’d like to complicate this narrative by talking about how science works in practice. You might be familiar with the scientific method, often taught to kids in flow chart form. You make an observation, form a hypothesis to explain it, test it with an experiment, and draw conclusions. If you think about this for a moment it’s obviously greatly oversimplified. In particular, I observe that science is a collaborative effort. You don’t necessarily go through the whole flow chart personally. You have lots of people who specialize in just one tiny piece of the flow chart, or do stuff that isn’t listed there.

One of the biggest divides in physics is between theory and experiment. Theorists try to come up with explanations for observations, and use math or simulations to understand the implications of a theory. Experimentalists design instruments, perform experiments, and analyze results.

By the way, it’s often explained in popular science that there is a difference between a “hypothesis” (an untested idea) vs a “theory” (a well-tested framework). Often the main purpose is to explain why evolution isn’t “just” a theory, but is actually an extremely well-established and foundational framework. And that’s true about evolution, but it’s just not an accurate description of how “theory” is used by scientists. Scientists use “theory” in multiple ways (including the colloquial “just a theory” sense), but in physics it most frequently refers to the distinction between theory and experiment. So when we talk about string theory or, say, superconductivity theory, that’s what we mean. It’s the distinction between math and concepts vs instruments and observations. It does not typically refer to the distinction between tested and untested–we would never hear the end of arguments about it if that’s what it meant.

The point I’m getting to, is untestable theories are rather common in physics. From the perspective of a theoretical physicist, it’s one of the central challenges. What prediction can you make that is within practical reach of the experimentalists? How do you persuade the experimentalists to actually devote resources to this? Once the result has been found, how do you persuade other scientists that you actually succeeded in confirming/disconfirming your theory?

My experience comes from being on the other side. I’d listen to theorists say, “all you need to do is perform this experiment to test my theory” and we’d tell them that we’d already done that and hadn’t seen anything like that, and they’d tell us we needed to look harder, and we’d explain that we could look a tiny bit harder but there are physical constraints. And then if we do see something or don’t see something, I’m not necessarily convinced, and it certainly doesn’t convince our scientific rivals who have other ideas. And it goes on and on. This is basically the steady state for unresolved problems in physics.

When people talk about a theory being unfalsifiable, it comes off as scandalous. It’s like, don’t these smart people know about falsification, like what we learned in high school? But really, in many scientific controversies, whether theories are testable or not is precisely the subject of the controversy. Each theorist has their own ideas about how to test their theories, and the situation is that other scientists just aren’t buying it.

So the whole thing about string theory being unfalsifiable… that’s never what the problem was. The problem was and is one of magnitude. Critics argue that this theory has been around for decades and decades with so many people in the field, without any testable predictions. I’d bet that every string theorist has an idea or ten about how to test the theory, because they know it’s important, it’s just unclear whether any of these ideas hold any promise whatsoever.

I mean, it sure doesn’t look good for string theory. But I think it’s a mistake to think of it as a Popperian demarcation problem. Contra Popper, untestable theories are a natural problem occurring in the normal course of science. I think particle physics is particularly vulnerable because of its reliance on huge experiments, and the sheer complexity of the theory. And maybe it really is untestable like the critics say.

Either way, string theory does not look like non-science. At worst, it’s science that performed very poorly.

Negative results

Scientific success is by its very nature not entirely up to the scientist. When a scientist has an idea, it is not the scientist who decides whether that idea works out or not; it’s the world that decides. But there are also some ideas that are unpromising from the start. This poses a problem, because a negative result could be a good idea that simply didn’t pan out, or it could reflect negatively on the scientific project. And so we have the file drawer effect, a bias where researchers are less likely to publish negative results than positive results. After all, scientists don’t want to publish something that may reflect poorly on how they spent their grant money, and peer reviewers may not want to see that either.

Although the file drawer effect is usually discussed in the context of statistics-heavy fields like psychology, I have a feeling that it’s much more severe in physics.  People just don’t talk about it, because calling it a file drawer effect implies something going wrong, and yet in physics it feels so justified to bury negative results. The space of unpromising physics ideas is so vast and unstructured, you can’t just test every idea and pretend that you did good work when every result comes back negative. A negative result could mean you’ve disproven a theory, but it’s a lot more likely that there was an experimental problem, or the experiment was not powerful enough, or the theory was never testable by that method.

I’d like to bring this into the context of theoretical physicist. Just as an experimentalist doesn’t know the result until they perform the experiment, a theorist can’t know the predictions until they do the math. Sometimes, an experiment doesn’t play out and the result is negative. And sometimes, a theory doesn’t play out, and no testable predictions pop out of it. An untestable theory is analogous to a negative experimental result. And that can be hard to publish because people have no concept of a file drawer effect in theoretical physics. People think if a theory is untestable it’s just bad.

So the question is, were string theorists unlucky? Or was it just never good to begin with? I really don’t know, I don’t have an opinion.

Personally, I think of scientific research as a bunch of lottery tickets. Very little research does anything valuable, until something does. I’m definitely coming at this from a cynical personal angle, because I came away from my scientific career feeling that I had done nothing of value. I published some novel ideas and made legitimate arguments, but the opposition would not have been persuaded by my work, and it did not go anywhere. Also, the entire field of cuprate superconductivity has virtually no applications, with actual applications using low-temperature superconductors. And that doesn’t mean it was bad to do the work, it just means we didn’t win.

So my take is that string theory is probably not valuable, but that doesn’t make it stand out. To be honest, I do not think string theory would be very valuable even if it were confirmed. Theories like that, they mainly fill the human need for a cosmology, an explanation of the universe. That makes it exciting, and the subject of a great deal of popular science, for better and for worse. But you do not need such a thing to live, and you do not need to have an opinion about it.