According to current scientific understanding, protons are considered to be stable particles and do not undergo spontaneous decay. Theoretical models and experiments have placed very stringent lower limits on the proton's lifetime, suggesting that it is at least 10^34 years or more.
The concept of proton decay was proposed as part of the Grand Unified Theories (GUTs), which aim to unify the electromagnetic, weak, and strong nuclear forces into a single framework. In certain GUT models, it is theorized that protons could decay into lighter particles, such as positrons and pions. However, despite extensive experimental searches, no direct evidence of proton decay has been observed so far.
Experiments such as the Super-Kamiokande in Japan and the Sudbury Neutrino Observatory in Canada have set limits on proton decay based on their observations of particles and their interactions. These experiments have not detected any proton decay events within their experimental timeframes, strengthening the belief that protons have extremely long lifetimes.
It's important to note that scientific understanding can evolve over time as new experimental evidence or theoretical advancements emerge. However, protons are considered to be stable particles with lifetimes much longer than the age of the universe.