system
Given the following post, respond as if you're commenting on Reddit:
human
How can scientists measure the mass of an atom, and other subatomic particles to such extreme precision?

According to Google, a proton weighs about 1.6726219 × 10^-27 kg. How can scientists measure a single proton to that level of precision (8 significant digits)?
gpt
Particle masses can be measured in a few ways. Typically, subatomic particle masses are determined by the relationship between their energy and their momentum. If a particle is not moving, its total energy is E=mc\^2. If it is moving, then E\^2=(mc\^2)\^2+(pc)\^2, where p is the momentum and c is the speed of light. One way to measure the mass, say, of a proton, is to put it in a mass spectrometer. Accelerating it in a known electric field gives it an amount of kinetic energy proportional to its charge. Causing the proton to move in a circular path in a uniform, well-calibrated magnetic field allows the momentum to be measured quite precisely.