Believe it or not, physicists like to keep it simple. That’s why many scientists, including Albert Einstein, believe that physics can eventually converge on a single, comprehensive paradigm that describes the universe – a theory of everything.
Enter string theory. Very Broadly speaking, string theory is a mathematical framework that replaces point-like particles with one-dimensional “strings” as the fundamental building blocks of matter. It was initially proposed as an explanation of a separate phenomenon, but quickly caught the attention of physicists working to unify quantum mechanics and general relativity – two hugely successful, equally valid theories that notoriously don’t match.
This was followed by two “superstring revolutions”, which saw impressive advances in describing how string theory can capture the complexity of our universe. The excitement over string theory naturally spilled over into popular conversations – science enthusiasts of the 1990s and 2000s, I’m looking at you – producing famous documentaries like PBS’s The Elegant Universe and a stock of popular and academic books.
However, with the turn of the century, the spotlight on string theory appeared to be diminishing. Granted, public opinion is volatile and malleable, and non-academics don’t care, that doesn’t mean the idea is dead. Yet, if Google’s Ngram viewer is any guide, string theory’s influence has wavered over the past decade.
That’s the question we asked physicists for this Geese Asks. What happened to string theory? Clearly, physicists haven’t given up on theories of everything. But is string theory the leading candidate – if it ever was? Or are there better options now? Has its popularity and importance really decreased? If yes, why?
The following responses may have been lightly edited and condensed for clarity.
Daniel Whiteson
Particle physicist, University of California, Irvine, and the ATLAS collaboration at CERN.
String theory is not dead! The main objection is that its predictions are for things on microscopic scales that we cannot yet test, so it has not provided any false predictions. But that doesn’t mean it will never happen. Group theory was a mathematical curiosity for a century, before we discovered that it was necessary to describe particle physics and quantum field theory. I’m not a fan of classifying things as “science” or “not science”, because who knows what stupid curiosity will lead to a discovery?
John H. Schwarz
Theoretical Physicist, California Institute of Technology; Discovered the Green–Schwarz mechanism, which ignited the first superstring revolution in 1984.
the topic came up [around 1984] And has been very active since then. Annual string theory conferences are still going strong and typically have several hundred participants. […] A large part of the theoretical particle physics community is now convinced that we are on the right track to discovering the true unified theory of our universe (and many of the naysayers have repented).
That said, we also realize that there is still much to be understood, and it may take a long time to get experimental evidence to support this theory.
Peter Voight
Mathematician and physicist, Columbia University; author of not even wrong And a blog of the same name.
The idea of string theory as a new fundamental unified theory is long dead. To simplify a bit, it needs ten space-time dimensions, but we only see four, so you have to get rid of six. The simple scenarios that do this don’t look like the real world; Complicated things can throw you almost anything, so don’t anticipate anything.
The last nail in the coffin were the negative results at the LHC about supersymmetry, which is a key part of most scenarios and the only thing with any hope of being observed experimentally. The term “string theory” has come to be used to refer to a vast range of different ideas that have arisen from trying to implement a unified theory. Most “string theorists” now work not on the failed unified theory but on very different topics.
These have led to some important new ideas in mathematics but no new insights into the fundamental physics of our world. In particular, while people study a lot of “quantum gravity”, these are theories that do not explain quantum gravity in our four-dimensional world.
Thomas Van Riet
Theoretical Physicist, University of Leuven in Belgium; Specializing in supergravity, string theory, holography and cosmology.
Yes, [string theory has diminished in popularity]This is because 20 years ago science propagandists and grant writers promised paradise, It never made any sense, We also knew 20 years ago that string theory has a so-called landscape of ground states and therefore has no unique predictions,
But the so-called alternatives cannot compete at all, and it remains a puzzle of sociological dynamics how they were able to frame themselves as alternatives. Let me be clear, it’s great that people study other options. But there is no reason to say that they have achieved a quantum mechanical description of gravity.
People say that without experiment we cannot call one theory better than another. This is almost certainly false. There are a number of consistency checks that are ridiculously difficult to pass. Can you calculate black hole entropy? String theorists were able to calculate it under very ideal conditions and reproduced Hawking’s famous formula for black hole entropy!
This is where science can progress without experimental input and it’s a point that is largely misunderstood by philosophers: in physics we study non-physical things all the time… but that means you create ideal conditions so that you are able to do calculations and test a framework. The game of overcoming mathematical constants in quantum gravity is so strong that it leads the search for theories almost exclusively to strings.
Similarly, string theory may be just a toy model. But that’s cool too! For example, I can look at the Big Bang singularity location in this model and ask myself how does this theory deal with it? This must be answered because it is a mathematically complete theory. So it has to tell you what the beginning of time looks like in this (toy?) model.
carlo rovelli
Theoretical Physicist, Center de Physique Théorique de Luminaire in France; Rovelli is the founder of loop quantum gravity, a rival account to string theory.
Particularly in the last 10 or 5 years, the appeal of string theory has greatly diminished, for the larger physics community. For three reasons. The first is that the theory has indicated that many physical predictions can be verified, such as supersymmetric particles that can be observed [LHC]a negative cosmological constant, the production of mini black holes in particle physics experiments, modifications to Newton’s laws on small scales, etc. None of these predictions have proved correct.
These repeated failures do not completely eliminate the principle, which can always be “adjusted” to take care of the negative outcome. But they have diminished confidence in the theory for most scientists.
The second reason, perhaps even more important, is that the theory attracted much attention in the 1980s and 1990s because it promised to resolve open questions in particle physics. For example, calculating the free parameters of the Standard Model from first principles, understanding why there are three generations of particles, why they are special gauge groups, and so on. The theory never succeeded in this. This failure also undermines the credibility of the string hypothesis.
The third reason is that even after 50 years we still have no clear formulation of string theory. We have a patchwork of related results but no clear overall theory defined by a well-represented set of equations.
hiroshi oguri
Theoretical Physicist, California Institute of Technology; Major contributor to mathematical developments in string theory.
Integrating quantum mechanics with “general” relativity is 25 times more difficult than integrating it with “special” relativity. […] It took physicists 50 years to develop a solid model based on quantum field theory to describe particle physics phenomena (the Standard Model) and 40 years to confirm all of its predictions (Higgs boson discovery).
Therefore, one could argue that it would take 1,250 years to build a realistic model of the universe from string theory and another 1,000 years to verify it experimentally. Now, I don’t think it would actually take that long, but it shows how difficult the problem is. Therefore, I would expect such a unification to yield 25 times more beneficial results and have a 25 times greater impact on a broader range of physics and mathematics.
Currently, string theory is the only promising candidate to achieve unification. No other proposal has had a comparable impact on a wide range of science or mathematical depth. So, in some senses, we theoretical physicists are developing a language for understanding nature.
One thing I want to point out is that, of course, our ultimate goal is to unify general relativity and quantum mechanics and then test it experimentally. I hope there will be a positive test, but if it is rejected, that is also progress in science, so I will accept it.
cameroon wafa
Theoretical Physicist, Harvard University; Wafa received the 2017 Breakthrough Prize in Physics for his work in applying string theory to the study of black holes and the universe.
Puzzles often come in pairs, each serving as a solution to the other! This is what is happening in physics at present. Recent cosmological observations by two groups, DESI and DES, in their data from 2024 and 2025 found evidence that the Standard Model of cosmology, which assumes that the dark sector does not dissipate over time, does not match the data. Currently our string-inspired model is the best model fitting their data!
In a parallel development there are experiments underway in Austria and the US that aim to directly explore the dark dimension [hypothetical extra dimension in string theory]…These experiments are within years of producing their first data.
So it seems that both large-scale cosmological observations and small-scale tabletop experiments are on their way to confirming the predictions of string theory. We may be on the cusp of a major scientific discovery. Within 5 to 10 years we should have a clear picture.