Happy Birthday, Einstein: Relativity Faces New Frontier

A century ago this year, a young Swiss physicist who had already revolutionized physics developed a radical new understanding of gravity.

In 1915, Albert Einstein published his general theory of relativity, which described gravity as a fundamental property of space-time. He came up with a set of equations that relate the curvature of space-time to the energy and momentum of the matter and radiation that are present in a particular region.

One hundred years later, Einstein's theory of gravitation has withstood all the tests that scientists could throw at it. But until recently, it wasn't possible to do experiments to probe the theory under extreme conditions to see whether it breaks down. [6 Weird Facts About Gravity]

Now, scientists have the technology to look for evidence that could reveal physics beyond general relativity.

Physicist Albert Einstein stands beside a blackboard with mathematical calculations written across it in 1921.

Martin Behaim

Martin Behaim

Portuguese geographer and navigator

Martin Behaim, Portuguese Martim Behaim, orMartinho De Boémia   (born October 6, 1459, Nürnberg [Germany]—died July 29, 1507, Lisbon [Portugal]), navigator and geographer whose Nürnberg Terrestrial Globe is the earliest globe extant.

Behaim first visited Portugal about 1480 as a merchant in the Flemish trade and, claiming to have been a pupil of the astronomer navigation to King John II. He may have introduced the astrolabe of brass to replace wooden models of this instrument, then used in navigation to ascertain the altitudes of the Sun, Moon, and stars in order to deduce time and latitude. He probably voyaged down the west coast of Africa (1485–86) with Diogo Cão.

Johann Müller (Regiomontanus) at Nürnberg, became an adviser on returning to Nürnberg (1490), Behaim began constructing his globe with the help of the painter Georg Glockendon and finished it in 1492. In view of the extent of Portuguese exploration, his depiction of the world was surprisingly inaccurate and out of date, especially in relation to the west coast of Africa. It is interesting, nevertheless, for the indication it provides of common geographic suppositions on the eve of the discovery of North America. His globe is in the collection of the German National Museum in Nürnberg.