There isn’t any room,” said Joshua. “You travel back along the line of time and you don’t find the past, but another world, another bracket of consci… - Clifford D. Simak

There isn't any room," said Joshua. "You travel back along the line of time and you don't find the past, but another world, another bracket of consciousness. The earth would be the same, you see, or almost the same. Same trees, same rivers, same hills, but it wouldn't be the world we know. Because it has lived a different life, it has developed differently. The second back of us is not the second back of us at all, but another second, a totally separate sector of time. We live in the same second all the time. We move along within the bracket of that second, that tiny bit of time that has been allotted to our particular world.

What is a bow and arrow?
It is the beginning of the end. It is the winding path that grows to the roaring road of war.
It is a plaything and a weapon and a triumph in human engineering.
It is the first faint stirring of an atom bomb.
It is a symbol of a way of life.

You still could go to some industry or some university or the government and if you could persuade them you had something on the ball — why, then, they might put up the cash after cutting themselves in on just about all of the profits. And, naturally, they'd run the show because it was their money and all you had done was the sweating and the bleeding.

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.