A Compass, a Desk and the Speed of Light

Part One · The needle

Hold a compass flat in your hand. Turn your whole body, and the needle still points the same way. Albert Einstein wrote that a compass amazed him when he was four or five years old. He said his father showed it to him. How could a needle act like that, with nothing touching it?

Einstein was born in Ulm, Germany, on March 14, 1879. Years later he wrote a book of notes about his life. In it he said the compass left a deep mark on him. He wrote that he could still remember it, "or at least believe I can remember." Even he was not sure the memory was exact.

Part Two · The desk

Einstein trained in Zurich, Switzerland, to be a physics teacher. He finished his studies. But he could not find a teaching job. In June 1902 he got a different one. It was at the patent office in Bern. A patent is an official paper that says an invention is yours.

A month later he stood at a lectern in room 86. A lectern is a tall desk you stand at. His job was to look at new inventions. He decided if they could get a patent. He called it his "cobbler's trade." One account says it paid well and was easy for his quick mind.

The same account says he split his day in three. Eight hours were for work. Eight were for his own science and other things. Eight were for sleep, but he often wrote instead. In 1905 he was 26. That year he signed four science papers, plus a long report for his doctor's degree.

Part Three · The big ideas

At 16, he wrote, he asked what a beam of light would look like if he raced after it. In his own later account, it would look frozen in place. He called this a paradox, a puzzle that seems to break the rules. He later said it helped lead him to relativity.

In 1905 he wrote a paper that began with two rules. One said that light in empty space always moves at the same speed, whatever moves the lamp. His math then said a clock carried from one place to another falls behind a clock that stayed put. The gap is tiny, but it is there.

He also wrote that light comes in tiny packets. This helps explain what happens when light hits metal. Tiny bits called electrons get knocked loose. Many did not believe it. Yet his Nobel Prize in Physics named the photoelectric effect. It was the 1921 prize. He got it in 1922.

Part Four · The eclipse

In 1915 Einstein finished a new idea about gravity. It said the Sun's gravity should bend starlight that passes close to it. To check, scientists had to photograph stars right next to the Sun. You can only do that in a total eclipse, when the Moon blocks the Sun's glare.

On May 29, 1919, two British teams watched an eclipse. One was on the island of Principe, off West Africa. The other was in Sobral, Brazil. At Principe, thick clouds hid the sky. Only two photos were good enough to use. They were made on glass plates.

The teams checked their photos against pictures of the same stars taken at night. The stars near the Sun had moved a tiny bit. The move fit Einstein's number better than the older theory's. On November 6, 1919, the news was told in London. The next day, it was in the papers.

Part Five · The clocks above you

Now look at your phone. A map app uses GPS. GPS satellites circle about 20,200 kilometers up. Each one has clocks inside. Two of Einstein's ideas pull on those clocks in opposite ways. Speed slows them. Weaker gravity up high speeds them up. In the end they run fast.

It adds up to 38 millionths of a second a day faster than clocks on the ground. That sounds like nothing. But NIST, a US science agency, says that without constant fixes, the satellites' signals would soon be useless. Engineers had to build Einstein's rules into the system.

A compass needs no clocks. It just points. A phone's map is different. It needs clocks that follow his rules. NIST says that in a way, GPS has become the longest-running test of his theories. Every time a blue dot finds you, that test goes on.