Scope and Excitement of Physics

Physics stays exciting for two reasons that reinforce each other: the astonishing range it covers, and the unpredictable way its biggest discoveries arrive.

Range of scales. Physics is comfortable working at both ends of nature's size and time scale simultaneously:

• Range of mass: from the electron ($\approx 9.11\times10^{-31}$ kg, order $10^{-31}$ kg) to the entire observable universe ($\approx10^{55}$ kg).
• Range of time: from $10^{-22}$ s (roughly the time light takes to cross a nucleus) to $10^{18}$ s (astronomical time scales).

Handling such extremes with the same handful of concepts and laws -- rather than needing a different physics for every scale -- is itself part of what makes the subject powerful.

How discoveries happen. Some discoveries are accidental: magnetism was first noticed by chance, and only later explained theoretically, after which artificial magnets could be manufactured deliberately. Others are theoretical predictions confirmed only much later by experiment -- Einstein's $E=mc^2$ (1905) was not experimentally verified until Cockcroft and Walton's 1932 experiment. Today, theory plus computer simulation is routinely used to hunt for new materials and drugs before anything is built in a lab -- for instance, biocompatible materials for organ replacement are screened using quantum-mechanical predictions before fabrication. …