With the recent discovery of gravitational waves, we now have a target for probing the very early universe, close to the big bang.  This is because gravitational waves can travel across the universe unimpeded, meaning those created after the big bang are still bouncing around today.  It’s like the big bang was the ringing of a giant bell, and the ringing can still be heard.  But all of our Easter eggs are not in one basket.  There is another way to probe the very early universe, one we haven’t found yet, because it involves particles that are very tiny and...