I always have some type of idea or project in my head. A concept for a game, an idea for a story, a design for a website, always something. And in the past, when I've had story ideas, I'd jot them down so as to not forget them. And over time, I've come to realize that there are no original ideas anymore, not even in the realm of science fiction.
One of my ideas came to me when I was reading a physics book and happened across a description of positrons, which apparently travel backwards in time. This gave me the idea that someone might use these particles as a sort of carrier wave, and transmit a signal back in time using them. From this came two story ideas.
The first was a story in which the government takes hold of the project and uses it (amongst other things) to combat crime. One department would simply catalog all crime that took place and transmit it. A second department would receive these transmissions, and act to stop the crimes just before they happened. Thus, the only way to succeed in a crime would be to ensure that no one ever found out about it, which was to be the crux and the plot of the story. Sound similar? Yeah - sound like Minority Report, which was taken from Phillip K. Dick's story that was probably written before I was born.
The second idea I came up with was a tale about a man doing some sort of experiment who ended up receiving transmissions which were originally sent in the distant future. Once he learns to translate these, he learns of the urgency of the transmissions. The people in the future send back information detailing how to successfully freeze someone cryogenically, and people (or people) are essentially sent forward in time to help deal with the problem. The only problem in developing my plot: why would people in the future need anyone from this time? The novel Timescape by Gregory Benford which I'm currently reading was written when I was six years old, and deals with the subject much better than the plot I was working on. It goes back and forth between the two time periods, similarly to how it was done in the movie Frequency. Scientists are sending back information fifty years to prevent ecological disaster. It's entertaining to read a story which was essentially my own idea, even if that idea came decades after the story was published.