# How was proton determined to be a common component of all atoms?

Based on what I know of the discovery of positive charges, Thompson measured the $e/m$ ratio of various nuclei and their $e/m$ ratio (charge-to-mass ratio) was not constant. People did not know whether they contined a single common positively charged particle charge.

What made them think that? Given different charge-to-mass ratios, why wouldn't one assume multiple types of positive charges in an atom? What motivated people to think that a single common particle could be the cause of their positive charges?

• Hi Shivay, welcome to HSM. I'm not entirely sure what you're asking. Protons are not fundamental particles, but are composed of quarks. – HDE 226868 May 9 '17 at 13:30
• What I mean is that, before quarks were discovered, how could we think of the proton as a fundamental unit of charge? – Shivay Vadhera May 9 '17 at 15:20

Proton did not enjoy the "fundamental" status for very long, and not just because of quarks. For a long time after their first appearance in 1964 quarks were considered speculative entities, and their confinement made protons at least "unbreakable". But many grand unification schemes, starting with the $SU(5)$ one of Georgi-Glashow, predicted proton decay, and experimenters were chasing after it ever since.