Ask any physicist to name the top two theories of the 20th century, and you’ll almost always get the same automatic answer: Einstein’s relativity and quantum mechanics. But lately a few 21st century thinkers have hinted that maybe the third-place theory should move up a notch. In the wake of the computer revolution, information theory might deserve to displace relativity in the rankings.
That revisionist perspective reflects a late 20th century twist in the story of that century’s theories: the surreptitious merger of quantum theory with information science. Their origins had been entirely independent. Quantum mechanics arose in the 1920s as the math for describing the odd behavior of atoms and electrons; information theory came along two decades later, as formulas for quantifying communication over telephone lines. For decades the two theories led separate lives in fields of study far removed from one another. While physicists expended their intellectual energy on uniting quantum mechanics with relativity (a quest that continues, still without success), information scientists graduated from telephones to computers with only occasional concern for quanta. But then in the 1980s and ’90s, quantum and information science met, married and produced offspring — specifically, the intellectual enterprise known today as quantum information theory.
Initially, quantum information snared the attention of physics fans for its possible uses in sending secret codes and creating superfast computers. Those and other potential quantum technologies continue to occupy scientists’ time at research centers around the world, from Canada to Austria to Singapore. But theorists pursuing quantum information’s secrets are more motivated by the quest to acquire a deeper understanding of physical reality, and perhaps to grasp more fully the nature of quantum mechanics itself.