Following Prof. Leonard Susskind's Lectures on Cosmology, we stated that the Universe, as we know it, seems to be electrically neutral, from where we catch some consequences of it.
This simple statement makes sense to me but I also wonder: do we have any big proof or experimental results that support it? e.g., if it wouldn't be the case, we would see electromagnetic fields shifting emission lines due to Zeeman/Stark effect.
Best Answer
To our best knowledge, the observable universe is neutral. All evidence at hand suggests that the number of electrons in the universe is (almost) identical to the number of protons.
If tis was not the case, the electromagnetic force, which is $\sim 10^{39}$ times stronger than the gravitational force, would dominate in the universe. Earth would not follow Kepler's laws, but instead their motion should be derived from Maxwell equations.
Not having observed such behaviour suggests that gravity is in fact the dominant force on the large scale.