It seemed that Albert Einstein had changed the whole business. In fact, he did not invent the "thought experiment"， but he raised it to high art. Imagine twins, wearing identical (完全相同的) watches; one stays home, while the other rides in a spaceship near the speed of light ... little wonder that from 1919, Einstein was, and remains today, the world's most famous scientist.

　　In his native Germany he became a target (目标；指标) for hatred (仇恨，厌恶) because he was a Jew, a liberal (自由主义者), a humanist, an internationalist. His powerful voice later was widely heard, especially after he moved to the US. Meanwhile, like any famous people, he made bits of legend: that he failed math in school (not true). That he opened a book and found an uncashed $1,500 check he had left as a bookmark (maybe he was absent­minded about everyday affairs)．That he was careless about socks, collars, slippers ... that he couldn't even remember his address: 112 Mercer Street in Princeton, where he finally settled (定居). He died there in 1955. And after the rest of Einstein had been cremated (火化), his brain remained for further research.

　　Thanks to Einstein, we said goodbye to a prior (优先的) universe and a previous (先前的) God. Einstein's God was no clockmaker, but the embodiment (化身) of reason in nature. This God did not control our actions or even sit in judgment on them. Physics is free, and we too are free, in the Einstein universe which is where we live.