String Theory For Dummies. Andrew Zimmerman Jones

physicists can then relate to meaningful events in the real world through experiment and other means.

      Science requires both experiment and theory to build explanations of what happens in the world. To paraphrase Einstein, science without theory is lame, while science without experiment is blind.

      

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 shows a specific trace of that particle’s existence. 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 the physics of fundamental particles) 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 building models describing anticipated facts that may be discovered soon. Then they make predictions about the experimental observations that should be obtained. (Of course, phenomenology has a lot more to it, but this is the gist of what you need to know to understand it in relation to string theory.) It’s an intriguing discipline, and one that over the last decades has been focusing on supersymmetry and string theory. When we discuss how to possibly test string theory in Chapter 14, it’s largely the work of phenomenologists that tells scientists what they’re looking for.

      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’s both experimental and theoretical. But what all these approaches have in common is that the scientific results are expressed in the language of science: mathematics.

      The rule of simplicity

      In science, one goal is to propose the fewest “entities” or rules needed to explain how something works. In many ways, the history of science is seen as a progression of simplifying the complex array of natural laws into fewer and fewer fundamental laws.

      

Take Occam’s razor, which is a principle developed in the 14th century by Franciscan friar and logician William of Occam. His “law of parsimony” is basically translated (from Latin) as “Entities must not be multiplied beyond necessity.” (In other words, keep it simple.) Albert Einstein famously stated a similar rule as “Make everything as simple as possible, but not simpler.” Though not a scientific law itself, Occam’s razor tends to guide how scientists formulate their theories.

      In some ways, string theory seems to violate Occam’s razor. For example, in order to be related back to the real world, string theory requires the addition of a lot of odd components that scientists haven’t actually observed yet (extra dimensions, new particles, and other features mentioned in Chapters 10 and 11). However, if these components are indeed necessary, then string theory is in accord with Occam’s razor.

      The role of objectivity in science

      Some people believe that science is purely objective. And, of course, science is objective in the sense that anyone can apply the principles of science in the same way and get the same empirical results in a specific experimental situation. (At least this is how it usually works in physics. Don’t get us started on psychology.) The idea that scientists are themselves inherently objective is a nice thought, but it’s about as true as the notion of pure objectivity in journalism. The debate over string theory demonstrates that the discussion isn’t always purely objective. At its core, the debate is over different opinions about how to view science.

In truth, scientists continually make choices that are subjective, such as which questions to pursue. For example, when string theorist Leonard Susskind met Nobel Prize winner Murray Gell-Mann, Gell-Mann laughed at the very idea of vibrating strings. Two years later, Gell-Mann wanted to hear more about Susskind’s theory.

      In other words, physicists are people. They have mastered a difficult discipline, but that doesn’t make them infallible or immune to pride, passion, or any other human foible. The motivation for their decisions may be financial, aesthetic, personal, or any other reason that influences human decisions.

      The degree to which scientists rely on theory versus experiment in guiding their activities is another subjective choice. Einstein, for example, spoke of the ways in which only the “free inventions of the mind” (pure physical principles, conceived in the mind and aided by the precise application of mathematics) could be used to perceive the deeper truths of nature in ways that pure experiment never could. Of course, had experiments never confirmed his “free inventions,” it’s unlikely that we (or anyone else) would remember his contributions a century later.

Understanding How Scientific Change Is Viewed

      The debates over string theory represent fundamental differences in how to view science. As the first part of this chapter points out, many people have proposed ideas about what the goals of science should be. But over the years, science changes as new ideas are introduced, and it’s in trying to understand the nature of these changes where the meaning of science really comes into question.

      The methods in which scientists adapt old ideas and adopt new ones can also be viewed in different ways, and string theory is all about adapting old ideas and adopting new ones.

      Precision and accuracy: Science as measurement

The transition from early “natural philosophy” to what we now think of as hard science is largely a technological phenomenon that evolved alongside the development of tools that allowed for more precise measurement. The ancient Greeks and Chinese didn’t fail to develop Newton’s theory of gravity because they weren’t inherently intelligent enough. The Greeks are, after all, the same civilization that brought us Socrates, Plato, Aristotle, Euclid, and Archimedes. They were smart enough. What they didn’t have, however, were precise clocks.

      Even if they had been inclined to try to develop the sort of science that would later have taken shape during the Enlightenment a couple of millennia later, their theories wouldn’t have taken shape if they couldn’t properly quantify the measurements of what they were talking about. Without precise clocks, it was difficult to make accurate and exact measurements of the time associated with motion.

      Within the area where they could measure things precisely, these ancient