Science requires both theory and experiment to build explanations of what happens in the world. String theory has not yet made the leap from theory to experiment.
In physics, complex mathematical models are built that represent the underlying physical laws that nature follows. These mathematical models are the real theories of physics that physicists can then relate to meaningful events in the real world through experiment and other means.
If physics is built on a foundation of experimental observation, then theoretical physics is the blueprint that explains how those observations fit together. The insights of theory have to move beyond the details of specific observations and connect them in new ways. Ideally, these connections lead to other predictions that are testable by experiment. String theory has not yet made this significant leap from theory to experiment.
A large part of the work in theoretical physics is developing mathematical models — frequently including simplifications that aren’t necessarily realistic — that can be used to predict the results of future experiments. When physicists “observe” a particle, they’re really looking at data that contains a set of numbers that they have interpreted as having certain characteristics.
When they look into the heavens, they receive energy readings that fit certain parameters and explanations. To a physicist, these aren’t “just” numbers; they’re clues to understanding the universe.
High-energy physics (which includes string theory and other physics at high energies) has an intense interplay between theoretical insights and experimental observations. Research papers in this area fall into one of four categories:
Experiment
Lattice (computer simulations)
Phenomenology
Theory
Phenomenology is the study of phenomena (no one ever said physicists were creative when it comes to naming conventions) and relating them within the framework of an existing theory. In other words, scientists focus on taking the existing theory and applying it to the existing facts or build models describing anticipated facts that may be discovered soon. Then they make predictions about what experimental observations should be obtained.
Of course, phenomenology has a lot more to it, but this is the basics of what you need to know to understand it in relation to string theory. It’s an intriguing discipline, and one that has, in recent years, begun to focus on supersymmetry and string theory.
Though scientific research can be conducted with these different methods, there is certainly overlap. Phenomenologists can work on pure theory and can also, of course, prepare a computer simulation. Also, in some ways, a computer simulation can be viewed as a process that is both experimental and theoretical. But what all of these approaches have in common is that the scientific results are expressed in the language of science: mathematics.