ΜΗΠΩΣ ΕΧΕΙ ΑΠΟΔΕΙΧΘΕΙ ΟΤΙ Η Η ΘΕΩΡΙΑ ΤΩΝ ΧΟΡΔΩΝ ΕΊΝΑΙ ΛΑΝΘΑΣΜΈΝΗ;

 ΜΗΠΩΣ ΕΧΕΙ ΑΠΟΔΕΙΧΘΕΙ ΟΤΙ Η Η ΘΕΩΡΙΑ ΤΩΝ ΧΟΡΔΩΝ ΕΊΝΑΙ ΛΑΝΘΑΣΜΈΝΗ;

Zane Jakobs, B.S./M.S. Aerospace and Aeronautical Engineering, University of Colorado Boulder

No. String Theory can’t be proven wrong yet because it hasn’t really made any quantitative predictions about reality.

In short, there are five different String Theories, all of which exist in at least 9+1 dimensions (the so-called bosonic string theories exist in 26 dimensions). This presented a problem: which, if any, describes reality? That was solved by Edward Witten, who proved that they’re all just different limits of the same 10+1-dimensional theory, which is called M-theory.


Now we have M-theory, but there’s still a big problem with that: we don’t actually know how to use it to make predictions. With, say, quantum electrodynamics, we can say things like “the detector will record two 511MeV

photons,” but we can’t do that with M-theory (yet, at least).

But this is probably not what your teacher meant. See, most quantum field theories don’t have analytic solutions in most or all cases (that is, they don’t have nice, convenient functions as solutions—they have to be approximated). So we use the so-called series expansion to make calculations. This is actually how your calculator computed most trigonometric and exponential functions. As an example, because sin(x)=x−x33!+x55!−x77!+..., if you want to find sin(.356)

, you can just plug it into the above infinite series, taking as many terms as you need to get the requisite precision.

However, lots of times we have a big problem: the infinite series diverges. That is, if you keep adding terms, instead of converging to a finite number, you get infinity. Now, we can usually fix this through a mathematical process called renormalization, which removes the unwanted infinities and gives us nice, finite results.

In order for String Theory to be renormalized, you have to have supersymmetry (if you want to learn more about supersymmetry, read the Wikipedia article—it summarizes it much better than I could). As of now (June 2017), none of our particle physics experiments (most notably the Large Hadron Collider at CERN) have shown any evidence for the existence of supersymmetry.

This in and of itself is not fatal to String Theory. Supersymmetry could still exist, just at a higher energy scale than we can currently access. But not finding it is certainly not good for String Theory. So while it’s not a disproof of String Theory, it most definitely does not help string theorists.

ΑΝΑΔΗΜΟΣΙΕΥΣΗ ΑΠΟ ΤΟ QUORA 21/6/2017