Particle physicists use the energy–time uncertainty relation to estimate the lifetimes of unstable particles produced in high-energy particle accelerators (Chapter 39). Some particles have lifetimes of 10-24 s and shorter—impossible to measure directly. However, physicists can measure particle masses, and they do so for many instances of the same particle to get a distribution of masses. By Einstein’s E = mc2 , that corresponds to a distribution of energies (Fig. 34.16). Measuring the distribution’s width at half its peak (see Fig. 34.16) gives an estimate of the energy uncertainty, and the corresponding ∆t from inequality 34.16 provides the particle’s lifetime.

 

An energy uncertainty of 1 MeV corresponds to a particle lifetime closest to
a. 10^-34 s.
b. 10^-21 s.
c. 10^-9 
s. d. 1μs.