String theory. Who hasn’t heard of it, right? A few weeks ago, a YouTube video about string theory swept through our physics department. The video is called “Bohemian Gravity,” an acapella re-write of “Bohemian Rhapsody” by Queen!
Being a major Queen fan, I had to watch it immediately. And wow, did he do a good job with it! The creator’s name is Timothy Blais. He’s a physics graduate student at McGill University in Montreal, so it’s fairly safe to say he has adequate background to make a video describing the problems of string theory.
I will admit I do not really know what he’s talking about for most of the song, as I haven’t taken any advanced physics classes yet. I am hopeful that, eventually, I will understand everything in the video. For now, I am relying on my limited knowledge of string theory, which mostly comes from various articles found online. String theory suggests that rather than being point-like particles, everything is actually made of one-dimensional entities called “strings.” The particles we think we see are really vibrating loops of string, with each string being either open or closed (two free ends vs. a continuous loop) and vibrating differently in order to make the various particles.
One such theoretical particle predicted by string theory is the graviton. This massless particle would cause a force with the properties of gravity, hence this is why string theory can be considered a theory of quantum gravity. But trying to represent how gravitons would interact with each other causes problems when more than one loop is used in a Feynman diagram, which is simply the title given to a picture depicting how subatomic particles interact. According to the Wiki entry on gravitons, at least two loops “lead to ultraviolet divergences; these are, infinite results that cannot be removed because the quantized general relativity is not renormalizable… That is, the usual ways physicists calculate the probability that a particle will emit or absorb a graviton give nonsensical answers and the theory loses its predictive power.” In this case, the nonsensical answers are described in “Bohemian Gravity” as “infinities will make you cry” because as of right now, string theory is nonrenormalizable.
So while string theory makes so much sense mathematically, and would be a great way to combine gravity and quantum physics into one theory of everything, there really is not any evidence for it to date. Because a theory is actually a concept that has lots and lots of evidence to back it up, string theory should really be called string hypothesis. Some would even argue it doesn’t even reach hypothesis status and is simply a very elegant guess, because in order for it to be a hypothesis, there would have to be some way to test for strings, and we don’t have the technology to do so. Nevertheless, the way I see it, the conclusion is string theory doesn’t have any evidence yet. That in no way means someday someone won’t find any. The most important thing is for scientists to continue following the scientific process and coming to conclusions from evidence they have collected. Breakthroughs in science happen all the time, and none of us knows what tomorrow will bring!