No, protons cannot spontaneously turn into neutrons under extreme pressure or any other conditions. Protons and neutrons are fundamental particles that make up the atomic nucleus, and they have different properties.
Protons have a positive charge, while neutrons have no charge. The conversion of a proton into a neutron would require the emission of a positively charged particle, such as a positron, which is the antiparticle of the electron. This process is known as beta-plus decay.
Under certain conditions, such as in certain types of radioactive decay or in high-energy particle interactions, protons can be converted into neutrons through various nuclear reactions. However, these processes typically involve the exchange of other particles, such as the emission or absorption of other particles like positrons or neutrinos.
Extreme pressure alone cannot induce the conversion of protons into neutrons.