String Theory 12/11/22

Memories with Richard Bleil

He was a physics student and good friend with my office mate.  We were all soon to graduate (he would graduate first, then my office mate, with me in the following semester), and all in theoretical science.  This thesis dealt with string theory.

String theory is outside of my realm of expertise, but the basic concept is that the electrons and nuclei of atoms can be treated as vibrating strings.  There is a strong foundation in this hypothesis in the de Broglie wavelengths, who proved that a given mass in motion has associated with it a certain wavelike characteristic.  This wavelength decreases with mass and increases with velocity, so on the macroscopic scale, such as cars and humans, the wavelike portion of our behavior is negligible.  However, if you get down to the size and velocity of subatomic particles, the amount of wavelike character is not only significant, but it can be measured in the laboratory as well.  Electrons, for example, have a mass like a particle and yet display a diffraction pattern as you would see in light, while light seems to be a wave and yet can exert a pressure (which you can see in a classic well-known toy called a “Crooke’s radiometer”) like particles. 

This wavelike component of subatomic particles is the foundation of Heisenberg’s Uncertainty Principle, which says that we cannot know both position and momentum simultaneously.  The error in Heisenberg’s Principle is so small that it has no impact on classical physics, that is, the physics with which you and I are familiar, but it is significant enough that it explains why subatomic particles cannot, and do not, follow Newtonian (classical) Physics.

This gave rise to Quantum theory and Schrödinger’s equation which deals with probability rather than absolute behaviors.  But that’s not the only theory.  For example, a closely related but different approach to the Heisenberg enigma is known as Density Functional Theory.  A “functional” is a mathematical function that modifies itself as it changes.  In this case, the electrons are treated as a cloud of sorts, with a given density, where “density” refers to the electrons, and negative cloud, in a certain region of space.  The more electrons in that region (called an “orbital”) the higher the charge density (the more negative), but the more negative it becomes, it repels more electrons.  This approach yields very similar results to subatomic behavior as Schrödinger and dovetails nicely.

So why can’t we treat electrons as waves rather than particles?  In a sense, it better explains the concept of “spin” than quantum theory.  I’ve railed against the model spread by authors of textbooks that an electron is a sphere with an axis shoved through it spinning clockwise (spin up) or counterclockwise (spin down) before.  But if electrons are treated as waves, then perhaps “spin up” and “spin down” electrons have their wave phases in sync resulting in constructive interference, while if they’re in the same phase then we have destructive wave interference. 

String theory was more or less at its height when I met this young physicist.  When he told me that his thesis was on string theory, I just had to ask, “of what practical value is string theory?”  His response was “none.”  He was very deadpan and matter-of-fact in his response, so I asked again, “no, seriously, what can it do that quantum cannot.”  He looked at me and said, “nothing.” 

I was stunned.  “So why study it?”  He replied, “well, it’s an interesting intellectual challenge, don’t you think?”

Well, yes, it is.  But why put all of this effort, of many physicists around the world, if it is of no value? 

Currently, I’m working on a project that deals with crime prediction.  If it works, it should be able to reproduce the same crime “heat maps” that criminal statisticians do already.  So the question might come up as to why I’m bothering with such a product if it is already being done?  This is kind of the way that theoretical modeling works, though.  When I complete my programming, the first thing I want to do is see if my model reproduces already established techniques.  This will help build support that my concept is a reasonable approach.  If a model is correct, a newer one should be able to reproduce the results, much as Density Functional Theory reproduces the results of Schrödinger.  But the point of new models is that they can then go on to do more.

Once I can demonstrate that my model reproduces what is already trusted, then I can show how my model can do things that the current approach cannot do, by predicting, in this case, what happens to crime if we make certain changes, such as lighting or bike paths.  Will crime rise, fall, and where will it go?  This is something currently impossible with statistical models.  Density Functional Theory has advantages over Schrödinger in some cases and situations, so both are still in use today. 

String Theory, to the best of my knowledge, does not offer any advantage over Schrödinger or Density Functional Theory.  But that doesn’t mean that it never will.  Right now, as I understand it, it can reproduce what is being found in other models, but, with time, no doubt we’ll find applications where String Theory either works better or makes predictions impossible in the other approaches.  So, yes, it’s an interesting intellectual exercise.

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