A hundred years ago, Auguste Compte, … a great philosopher, said that humans will never be able to visit the stars, that we will never know what stars are made out of, that that's the one thing that science will never ever understand, because they're so far away. And then, just a few years later, scientists took starlight, ran it through a prism, looked at the rainbow coming from the starlight, and said: 'Hydrogen!' Just a few years after this very rational, very reasonable, very scientific prediction was made, that we'll never know what stars are made of.

For more than ten years, my theory was in limbo. Then, finally, in the late 1980s, physicists at Princeton said, 'There's nothing wrong with this theory. It's the only one that works, and we have to open out minds to hyperspace.' We weren't destined to discover this theory for another 100 years because it's so bizarre, so different from everything we'd been doing. We didn't use the normal sequence of discoveries to get to it.
Describing reaction to his superstring theory of hyperspace which mathematically relates the universe's basic forces.

I got a four year scholarship to Harvard, and while I was they they wanted to groom me for work in the Star Wars program designing weapons ignited by hydrogen bombs. I didn't want to do that. I thought about how many scientists had died in World War II.

In fact, it is often stated that of all the theories proposed in this century, the silliest is quantum theory. Some say that the only thing that quantum theory has going for it, in fact, is that it is unquestionably correct.

The strength and weakness of physicists is that we believe in what we can measure. And if we can't measure it, then we say it probably doesn't exist. And that closes us off to an enormous amount of phenomena that we may not be able to measure because they only happened once. For example, the Big Bang. ... That's one reason why they scoffed at higher dimensions for so many years. Now we realize that there's no alternative...

There are 60 sub-atomic particles they've discovered that can explain the thousands of other sub-atomic particles, and the model is too ugly. This is my analogy: it's like taking Scotch tape and taping a giraffe to a mule to a whale to a tiger and saying this is the ultimate theory of particles. ... We have so many particles that Oppenheimer once said you could give a Nobel Prize to the physicist that did not discover a particle that year. We were drowning in sub-atomic particles.
Now we realize that this whole zoo of sub-atomic particles, thousands of them coming out of our accelerators, can be explained by little vibrating strings.