# Experiments or phenomenon to falsify the existence of monopoles?

This is a related, but opposite question to this one

I have heard about a lot of things regarding elementary and GUT magnetic monopoles, as well the quasiparticle monopoles in spin ice

Since there's like 50 years of non detection of magnetic monopoles, I started to wonder whether monopoles searches have tried to approach the problem from the opposite direction. That is

What physical phenomenon that if observed by experiment, will guarantee that (elementary or GUT) monopoles cannot exist?

I have discussed this problem with my professors today and we arrived at some sort of partial answer in that our current electrodynamic, Standard Model and QED theories have been well tested (particularly for QED which is tested up to the order of $10^{-26}$ from the memory of the discussion) and they all seemed to work fine without monopoles seems to be a sign that monopoles cannot exist, as Maxwell equations with the monopole terms added will result in a host of phenomenon that we never have observed
• You can ask what would happen if we create stronger and stronger magnetic fields. As pointed out in this article: "We argued above that a uniformly magnetized vacuum is stable against spontaneous electron-positron pair production. Nevertheless, at sufficiently high B the vacuum must break down. Magnetic monopoles with mass $m_\eta$ and magnetic charge $\eta$ are spontaneously created when the energy they acquire in falling across a monopole Compton wavelength, $\epsilon\sim\eta B\frac{\hbar}{m_\eta c}$, exceeds their rest energy $m_ηc^2$". – Count Iblis Aug 22 '15 at 4:20