The Shadow Girl by Ray Cummings

I think it advantageous to my narrative now to set down a few scientific facts. The laws, for instance, under which our Time-traveling tower operated. The Indians of 1664 thought the tower was magic. But it was based upon solid science.

The laws of Time and Space -- the true aspect of the Material Universe -- all this is, in our age of 1945, imperfectly understood. So I set down here a few succinct truths. Those of you who care to ponder them may do so. You will find that the scientific aspect of my narrative is much clearer. Those of a different turn of mind may pass over this brief chapter.

The basis of the Material Universe is Energy. Energy we can also call by another name -- Change. Everything exists because it is changing. The living cell feeds itself and grows; multiplies itself; dies and decays; turns to other forms, liquid and gas -- and is not lost, but reconverted. The rocks were gas, then liquid, then solid. The wind and water erodes them -- they break, they powder, they blow away, or wash away as dust, and come again in other forms of other things.

The atoms, the very electrons of all matter in the universe, are breaking down or building up. All changing. All are nothing but manifestations of Energy. And Matter itself? Take a fragment of solid gold -- we find it built of loosely massed molecules, all in movement; and each molecule a group of agitated atoms; and each atom, whirling electrons and a nucleus -- infinitely tiny things to which we give these arbitrary names -- things which in themselves in their essence are nothing at all save Energy!

There is no mass. Nothing of solidity! Whirlpools -- vortexes of nothingness! Of such unsolid stuff you who read this are built. And your home, and your city, and the Earth under you, and all the stars of the Heavens!

At the basis of all this, also, is unceasing change of position. Every tiny fragment of everything is restless -- and every thing, in its entirety, is in motion. We move in space about our tiny Earth. Our Earth whirls us all along; and the Sun sweeps onward, dragging the Earth, itself following some distant Star, which with other Stars is going somewhere. We know all this, now in 1945.

We know, too, that nothing has a continuous existence. Your body, as you now sit reading what you may feel are idle theories, at one instant is existing and at the next is blotted out. And lives again another instant. A changed body, just a little different in every tiny essence of your being from what it was before.

Like a motion picture. There is nothing difficult to grasp in that thought. We see a motion picture as a continuous flow of movement; but we know that in reality the seeming movement is merely a rapid change from one still picture to the next.

So with all our Material Universe. It is as though Time, like a whirling knife-blade, were slashing through us -- blotting us out, letting us live only in the progressive instants between the whirling blades.

"Time" is the factor of all this which we find most unnatural to envisage in its true aspect. I would have you imagine now, what I might term the physical aspect of Time. Consider it, for instance, as an all-pervading etheric fluid. Consider it strewn in a line from the Beginning to the End. Our minds are so limited that we must conceive everything in terms of tangibility -- even the intangible. So I would have you picture Time as a stream of imponderable, invisible fluid. Imagine it in shape so that it could lie in some gigantic pipe -- perfectly straight -- of some inconceivable length. We put the Beginning and the End to bound it.

This Time-fluid, then, you must picture as being at rest -- the one thing of all things which does not move nor change. It lies there -- forever.

But do not forget this pipe-line of Time-fluid in which all this is happening! Let us cling to simple physical analogies. We must imagine, for instance, that the Time-fluid is progressively of different physical character along all its length from its Beginning to its End. Like water in a pipe -- hot at one end, cold at the other, with every gradation of temperature in between. Or, to be just a trifle closer to fact, perhaps, the stream of Time might be imagined as a beam of light -- red at one end and violet at the other -- with every tint and shade merging along the way.

Something then -- like a Thought -- is put into the pipe-line of Time at the Beginning. If you have conceived the fluid of Time as being hot at the Beginning -- then imagine that this foreign, intangible substance which has been placed there is the same temperature. Because of that, let us say, it can remain there. But only for an instant! Because the foreign substance instantly desires to change its character. It desires, let us say, to become a bit cooler. It wants to reexist; to perpetuate itself in changed form.

The fluid of Time at the Beginning will not tolerate anything cooler. Will not tolerate any change at all. So it shifts a changed replica of the restless thing along a bit. An event has occurred. A new thing exists, beside the old thing. Both lie there side by side -- and the difference between their aspects is the change. Also, it is movement.

Not the movement of something tangible as we are wont to conceive it. That is a fallacy; there is no such movement -- nor is there anything of absolute tangibility to move! The aspect of the old thing, compared -- like a motion picture -- to the aspect of the new thing beside it, is what we call movement.

It is also an interval of Time. And that interval -- that pseudo-movement -- that tangible difference between intangible things -- is all that our human senses can perceive. They lie inert in Time. But we are aware of the progressive difference between them. Upon it we have built our conception of Substance, Matter. We are ourselves a part of this ceaseless change -- and to a phantom every other phantom is solid!