ore
experiments with it, whether it should be given to the world, or whether
it should be destroyed and never used again."

* * * * *

End of the first page. You look up for a moment, hesitating to turn the
next page. Already you suspect what is coming.

You turn the page.

"I constructed the first time machine a week ago. My calculations had
told me that it would work, but not how it would work. I had expected it
to send an object back in time--it works backward in time only, not
forward--physically unchanged and intact.

"My first experiment showed me my error. I placed a cube of metal in the
machine--it was a miniature of the one you just walked out of--and set
the machine to go backward ten years. I flicked the switch and opened
the door, expecting to find the cube vanished. Instead I found it had
crumbled to powder.

"I put in another cube and sent it two years back. The second cube came
back unchanged, except that it was newer, shinier.

"That gave me the answer. I had been expecting the cubes to go back in
time, and they had done so, but not in the sense I had expected them to.
Those metal cubes had been fabricated about three years previously. I
had sent the first one back years before it had existed in its
fabricated form. Ten years ago it had been ore. The machine returned it
to that state.

"Do you see how our previous theories of time travel have been wrong? We
expected to be able to step into a time machine in, say, 2004, set it
for fifty years back, and then step out in the year 1954 ... but it does
not work that way. The machine does not move in time. Only whatever is
within the machine is affected, and then just with relation to itself
and not to the rest of the Universe.

"I confirmed this with guinea pigs by sending one six weeks old five
weeks back and it came out a baby.

"I need not outline all my experiments here. You will find a record of
them in the desk and you can study it later.

"Do you understand now what has happened to you, Norman?"

* * * * *

You begin to understand. And you begin to sweat.

The _I_ who wrote that letter you are now reading is _you_, yourself at
the age of seventy-five, in this year of 2004. You are that
seventy-five-year-old man, with your body returned to what it had been
fifty years ago, with all the memories of fifty years of living wiped
out.

_You_ invented the time machine.

And be