The most amazing invention of the 20th century is undoubtedly GPS.
Think about the technology needed to make it work:
- Space flight - putting satellites in orbit around the earth
- Computer - a tiny piece of silicon, relying on quantum mechanics to work, that can do a billion calculations a second.
- Wireless communications - by which pieces of electronics thousands of miles apart can invisibly send information between them
- The theory of relativity - without it the GPS calculations would be way off
And all of this to solve a problem which has affected people for thousands of years, inspiring the development of the compass, astrolabe, much of astronomy, and the development of precise clocks.
If the price of GPS receivers ever drops much lower, and they become much smaller (and both are likely to occur), we will see GPS used in all sorts of devices. For example, your keychain. If you ever lose your keys, you'll be able to go to your computer, type in "where are my keys". It will send a wireless internet signal to the keys, the keys will respond with their GPS data, and the computer will tell you "on the floor of the upstairs bedroom, along the north wall, 2 feet from the window". How cool will that be?