Simak Clifford. Ring Around the Sun

There was no time, Hezekiah had said. No such thing as time in the terms of normal human thought. Time was bracketed and each of its brackets contained a single phase of a universe so vastly beyond human comprehension that it brought a man up short against the impossibility of envisioning it.
And time itself? Time was a never-ending medium that stretched into the future and the past — except there was no future and no past, but an infinite number of brackets, extending either way, each bracket enclosing its single phase of the Universe.
Back on Man's original Earth, there had been speculation on travelling in time, of going back into yesterday or forward into tomorrow. And now he knew that you could not do it, that the same instant of time remained forever within each bracket, that Man's Earth had ridden the same bubble of the single instant from the time of its genesis and that it would die and come to nothing within that self-same instant.
You could travel in time, of course, but there would be no yesterday and no tomorrow. But if you held a certain time sense you could break from one bracket to another, and when you did you would not find yesterday or tomorrow, but another world.
There was a world of mutants, men and women who were more than normal men and women, persons who had certain human talents and certain human understandings which the normal men and women of the world had never known, or having known, could not utilize in their entirety, unable to use intelligently all the mighty powers which lay dormant in their brains.
The people finally know.
They've been told about the mutants.
And they hated the mutants.
Of course, they hated them.
They hated them because the existence of the mutants makes them second-class humans, because they are Neanderthalers suddenly invaded by a bow and arrow people.