Physicists have spent decades chasing something far too small to ever see.
To explain how extra dimensions could hide right under our noses, physicists point to which ordinary backyard object?
A garden hose From far away a hose looks like a simple line, but up close an ant can crawl around it, just as tiny curled-up dimensions might hide from our view.
String theory was invented to explain what holds atomic nuclei together, and it flopped. Instead of trashing it, physicists aimed it at which famous force?
Gravity The very quirks that made it a bad fit for nuclear physics turned out to make it a promising way to describe gravity with quantum rules.
For years, physicists argued over five rival versions of superstring theory. What did physicist Edward Witten suggest in the mid-1990s?
They were all one theory He proposed that all five were special cases of a single eleven-dimensional theory called M-theory, kicking off a burst of research nicknamed the second superstring revolution.
In one picture of string theory, most particles are strings with their ends stuck to our universe like gum on a sidewalk. Gravity's strings have no ends at all. What shape are they?
Closed loops Because these loops can drift off into a larger hidden space, the idea offers a neat explanation for why gravity is so much weaker than the other forces.
Physicists hoped string theory would explain our one universe. What did it seem to describe instead, frustrating its critics?
Countless possible universes This enormous landscape of possible worlds, plus the lack of a complete definition, has led some physicists to question whether the research is worth continuing.
