'THERE is nothing new to be discovered in physics now, " claimed Lord Kelvin, a hugely respected scientist, in 1900. Five years later, a flurry of scientific papers from an unknown patent office clerk in Bern blew Lord Kelvin's claim out of the water and transformed the way we think about the world.

That clerk was, of course, Albert Einstein, voted Person of the Century by Time magazine in 1999, and widely considered to be one of the most brilliant thinkers of the modern era. This new biography claims to be the first since all of Einstein's papers were made public, and it's clear that Walter Isaacson has done an extraordinary amount of research in building up a picture of Einstein's remarkable and often contradictory life. Isaacson is the former chairman of CNN and managing editor of Time magazine, and while he doesn't have a scientific background he is an acclaimed biographer, and this book reads like a labour of love.

The story of Einstein's life is ripe for telling. Born in 1879 in Germany into a modest Jewish family, he showed an aptitude for physics and engineering at an early age, but his non-conformist attitude, mixed with the anti-Semitism prevalent at the time, meant he didn't follow a conventional academic path, which is how he wound up working in a patent office. In his spare time, Einstein feverishly worked away at scientific problems, and in 1905 he published four papers which revolutionised physics completely, although it would take some time before the scientific establishment recognised and acknowledged that fact.

Among that work was his theory of special relativity, which overturned Newtonian mechanics, stating that time and space were interlinked and not absolutely objectively measurable. At the same time he explained how light interacts with matter in discrete packets (or "quanta") of energy, leading to the development of quantum mechanics. He also provided proof of atomic theory and came up with his most famous equation, E=mc2, which ultimately led to nuclear fission and the atomic bomb.

Einstein's approach to physics was instinctive and inspired. His work in 1905 was not bogged down in complicated mathematics, and mostly sprang from "thought experiments" performed while sitting at his desk. His genius for lateral thinking and his lack of respect for scientific conventions combined to open doors in his thought processes that were closed in the minds of contemporaries.

Isaacson does a good job of describing Einstein's approach, and is a very clear writer when it comes to the scientific bits, but then the beauty of much of Einstein's early work is its simplicity.

Isaacson fares less well when tackling the vastly more complex theory of general relativity, which explains gravity as the distortion of spacetime by matter, published by Einstein a full 10 years after his annus mirabilis.

Einstein never matched these early scientific triumphs, although his fame grew exponentially when many of his theories were proven correct by experiment. With political trouble brewing in 1930s Europe, he emigrated to America, where his exalted status grew by the day.

But as his fame grew, his scientific prowess receded. Much of his later work was spent trying, unsuccessfully, to conjure up a unified theory of gravitation and electromagnetism, as well as picking holes in the very quantum theory he helped create. The essential unpredictability of nature implied by quantum mechanics was a concept Einstein couldn't live with.

This led to his famous remark about God not playing dice, and he wasted a lot of time trying to disprove it, to no avail.

His status as a world-famous celebrity was also in conflict with his outsider status (he was a confirmed internationalist, pacifist and socialist), and he spent a lot of time dabbling in leftfield causes which inevitably brought him into conflict with the establishment.

And then there was his personal life. Einstein does not seem to have been a pleasant man to be married or related to. He gave up his first daughter for adoption without ever seeing her, rejected a son who suffered mental illness and was exceptionally cruel to his first wife.

He later married his own cousin, but that didn't stop him having a string of affairs, and he was generally aloof from his family for his entire life.

Isaacson lets Einstein off the hook a little here, claiming that this detachment was an essential part of what made him such a brilliant scientist and philosopher.

Maybe so, but it's still no excuse, and Isaacson is a little too quick to forgive.

It is a small quibble with what is otherwise a well-balanced, exhaustively researched but still eminently readable biography.

While Einstein may have changed from scientific revolutionary to reactionary during his career, his life remained fascinating and complex to the end, and this book does him justice.