• Day 11: What If We Put Clocks in Space?

  In 1977, three years before GPS launched, the engineers building the satellites had to make a decision. The clocks they were about to put in orbit were going to run faster than the clocks on the ground. By about 38 microseconds per day. …

• Day 10: The Zero Point

  Three epochs quietly run the world: The Unix epoch. Midnight, January 1, 1970. Almost every computer measures time as seconds since this instant. The GPS epoch. Midnight, January 6, 1980. Every GPS satellite, every navigation chip in every …

• Day 9: A Clock You Can Use to Measure a Mountain

  Yesterday I said cesium was about to be deposed. Today’s the deposition. The successor is the optical lattice clock. It is so precise that, it can detect the altitude difference between two desks in the same office. That last sentence …

• Day 8: 9,192,631,770

  Today’s number is 9,192,631,770. That’s how many times a cesium-133 atom oscillates between two specific energy states in one second. Or, more precisely, it’s how many times we decided a cesium atom does that in one second. The number is …

• Day 7: A Day Is Not 24 Hours

  Last week we talked about what time is, what it might not be, and what your brain does to make you feel it. This week we measure. The obvious place to start is to look up at the sky. Humans did this for several thousand years before they …

• Day 6: Your Brain Is Lying to You About Time

  Yesterday I told you a fly’s now is much shorter than yours and a whale’s is much longer. Today I want to talk about how wide your now actually is, and why none of it is what your brain is showing you. The short answer is that your brain is …

• Day 5: Time Is Not the Same for a Fly

  Try to swat a fly. Even with a flyswatter. You will fail more often than you succeed. You’re not slow. You’re not bad at this. The fly is living in a slower-motion version of the world than you are. The Refresh Rate of Perception Biologists …

• Day 4: Does the Future Already Exist?

  Yesterday I left you with a question, today we are getting stuck in. If the block universe is right, and my death is already sitting in the loaf at coordinates I haven’t reached yet, then in what sense am I choosing anything? It turns out …

• Day 3: Einstein Made Us A Loaf

  When Albert Einstein’s lifelong friend Michele Besso died in March 1955, Einstein wrote a letter to Besso’s family. In it, he wrote one of the most quoted sentences in the philosophy of time: “People like us, who believe in physics, know …

• Day 2: A Philosopher Argued Time Doesn't Exist

  In 1908, a British philosopher named J.M.E. McTaggart published a paper called “The Unreality of Time.” The argument is exactly what it sounds like. He thought he had proven, with logic, that time is an illusion. Not “feels different than …