Test

How to prove a railroad bridge won’t break (illustration)

As the Union Pacific Railroad was being constructed, an elaborate trestle bridge was built across a large canyon in the West. Wanting to test the bridge, the builder loaded a train with enough extra cars and equipment to double its normal payload. The train was then driven to the …

Einstein’s Test of Growing Old (illustration)

None of Einstein’s ideas have so fascinated the public and provoked such controversy among physicists as the so-called “clock paradox.” This paradox is based on the assumption that time passes more slowly for an object in motion than one at rest. Thus, if Einste …