Bosonic String Theory: The First String Theory
The first string theory has become known as bosonic string theory, and it said that all the particles that physicists have observed are actually the vibration of multidimensional strings. But the theory had consequences that made it unrealistic to use to describe our reality.
A dedicated group of physicists worked on bosonic string theory between 1968 and the early 1970s, when the development of superstring theory (which said the same thing, but fit reality better) supplanted it.
Even though bosonic string theory was flawed and incomplete, string theorists occasionally do mathematical work with this model to test new methods and theories before moving on to the more modern superstring models.
String theory was born in 1968 as an attempt to explain the scattering of particles (specifically hadrons, like protons and neutrons) within a particle accelerator. Originally, it had nothing to do with strings. These early predecessors of string theory were known as dual resonance models.
The initial and final state of particle interactions can be recorded in an array of numbers called an S-matrix. At the time, finding a mathematical structure for this S-matrix was considered to be a significant step toward creating a coherent model of particle physics.
Gabriele Veneziano, a physicist at the CERN particle accelerator laboratory, realized that an existing mathematical formula seemed to explain the mathematical structure of the S-matrix. (Physicist Michio Kaku has stated that Mahiko Suzuki, also at CERN, made the same discovery at the same time, but was persuaded by a mentor not to publish it.)
Veneziano’s explanation has been called the dual resonance model, the Veneziano amplitude, or just the Veneziano model. The dual resonance model was close to the correct result for how hadrons interacted, but not quite correct. At the time Veneziano developed the model, particle accelerators weren’t precise enough to detect the differences between model and reality.
Eventually, it would be shown that the alternative theory of quantum chromodynamics was the correct explanation of hadron behavior.
After the dual resonance model was formed, hundreds of theoretical papers were published in attempts to modify the parameters a bit. This was the way theories were approached in physics; after all, an initial guess at a theory is rarely precisely correct and typically requires subtle tweaks — to see how the theory reacts, how much it can be bent and modified, and so on — so that ultimately it fits with the experimental results.
The dual resonance model would have nothing to do with that sort of tinkering — it simply didn’t allow for any changes that would still enable it to be valid. The mathematical parameters of the theory were too precisely fixed. Attempts to modify the theory in any way quickly led to a collapse of the entire theory.
Like a dagger balanced on its tip, any slight disturbance would send it toppling over. Mathematically, it was locked into a certain set of values. In fact, it has been said by some that the theory had absolutely no adjustable parameters — at least not until it was transformed into an entirely different concept: superstring theory!
This isn’t the way theories are supposed to behave. If you have a theory and modify it so the particle mass, for example, changes a bit, the theory shouldn’t collapse — it should just give you a different result.
When a theory can’t be modified, there are only two possible reasons: either it’s completely wrong or it’s completely right! For several years, dual resonance models looked like they might be completely right, so physicists continued to ponder what they might mean.