Is string theory pseudoscience? To address this questions, let’s start by understanding what constitutes science and distinguishes it from pseudoscience.

Let’s start by defining science. Science is the intellectual and practical activity encompassing the systematic study of the structure and behavior of the physical and natural world through observation and experiment. The important words in this definition are “observation” and “experiment.” In other words, real science, and scientific theories, requires its hypotheses and associated predictions to be observable and/or be experimentally verified. One example of a solid scientific theory is Einstein’s special theory of relativity. It has withstood over one hundred years of observation and experimental scrutiny. In fact, it is generally held as the “gold standard” that all theories of science should be measured against.

With the above understanding, if I were to propose a new theory that by its inherent nature had at its core hypotheses that we are unable to experimentally verify and yielded predictions we would not be able to observe or measure, I believe many would consider such a theory to be pseudoscience. Pseudoscience is a system of theories, assumptions, and methods erroneously regarded as scientific, but are not verified, or verifiable, by experiment or  observation.

Now let’s examine string theory. String theory is built on the idea that elementary particles are not point-like objects, but are the vibration modes of one-dimensional “string-like” entities of energy. Proponents of string theory generally argue that it offers a theory of gravity and may provide a solution to the problem of reconciling Einstein’s general relativity with quantum mechanics. Therefore, if it were a valid theory, it would represent a leap in the physical sciences. However, there in lies the key question. Is it a valid theory?

Let start with its hypotheses. Can we measure or observe the one-dimensional vibrating strings of energy that form the core hypotheses of string theory? The answer is no, and that is an emphatic no. We cannot measure them with today’s science, and it is unlikely that we will ever be able to measure them. According string theorist the one-dimensional vibrating strings of energy are about equal to the Planck length, which is the smallest length science theorizes to exist. It is equal to 1.616199(97)×10^−35 meters and is defined from three fundamental physical constants, which I won’t to into here for the sake of brevity. The problem is that today’s science is unable to measure anything smaller than 10^-18 meters, which is billions of times larger than a Planck length. Many in the science community do not think we will ever be able to measure a Planck length, regardless of improvements in measurement technology. Therefore, the first significant problem with string theory is that its hypotheses are not verifiable.

Let’s next look at a significant predictions of string theory. In its current form, M-theory (i.e., membrane-theory, the most comprehensive form of string theory), it predicts there are 11 space-time dimensions, in serious disagreement with our senses and the most recent observations using particle accelerators. There is no experimental evidence of additional dimensions beyond the 4 space-time dimensions of Einstein’s general relativity.

There are arguably other issues with string theory, but the above two points, the lack of experimental verification of its hypotheses and its most fundamental prediction of 11 dimensions, serve to make an important point. It fails to pass the definition of science. String theory doesn’t  provide an intellectual and practical activity encompassing the systematic study of the structure and behavior of the physical and natural world through observation and experiment. It is not only unverified, but appears to be unverifiable at its core.

It’s natural to ask, why has string theory gained such a following in the scientific community. First, modern theoretical physics is based on two incompatible theories, Einstein’s theories of relativity and quantum mechanics. As I mentioned in a previous post, some progress has been made to reconcile them, but no progress has been made with regard to a unified theory of gravity. This has caused serious issues in the scientific community and it is only human to seek a theory that offers to resolve the issue. However, in this case, we are taking a theory that is flawed and unverifiable to attempt to reconcile relativity and quantum mechanics, both of which have been widely successful as theories within their specific context. Next, numerous formidable physicists, like Stephen Hawking and Brian Greene, have written best selling books based on string theory. To the average popular science reader, their books are exciting and their standing in the scientific community suggests their books are science fact. How is it possible that Dr. Hawking and Dr. Greene are in such strong support of a questionable theory. I think this has to do with the mathematical elegance of M-theory. It is relatively easy to become enamored with the mathematical formulations and loose sight of the fundamentals. Unfortunately, I think this has happened. Dr. Hawking has gone as far as saying we no longer need a God since we now have M-theory. Opponents rightly ask, where did M-theory come from? I am not going to get into the religious aspects. I only point this out to delineate how deeply some of today’s most respected physicists have embraced string theory.

Where do I stand? Obviously, today’s theoretical physics is based on two incompatible theories, Einstein’s relativity and quantum mechanics. Although, both theories work extremely well in the specific contexts, relativity at the macro level and quantum mechanics at the micro or quantum level (i.e., the level of atoms and subatomic particles), they do not come together to provide cogent theory of gravity. Even though string theory offers a speculative path to resolve the incompatibilities, at its core it appears to be pseudoscience. At best, it is a conjecture, which means it falls into the category of opinion.

I offer this sober warning to those that plan on making a career in science. Before you decide to become a string theorist and spend your career working to understand M-theory mathematics, be sure that you agree with the fundamental hypotheses and predictions of string theory. Don’t fall hopelessly in love with the elegant mathematics. Just because you can publish your theoretical string theory results in respectable scientific journals and participate in professional conferences doesn’t legitimize string theory. Much like a recovering alcoholic, science must admit there is a problem and not grasp at the current fad of string theory. It is better to admit we don’t have a solution than to forward what is likely the most legitimized pseudoscience of modern times, string theory.