But nobody really regards these as ‘fundamental’ forces. For example, the two-neutrino exchange force is a known phenomenon whereas neutrinos in isolation feel nothing but the weak force. Scientists found that right after the Big Bang, electromagnetism and the weak force were fused into the electroweak force. The mathematical symmetry governing Einstein’s equations can’t be easily put in the same class as the symmetries of the other fundamental forces. So taken together, it is all right to say there are four fundamental forces in everyday speech.

Source: The Hindu November 15, 2023 18:52 UTC