Future Tense
SF is full of stories about alien invaders with curiously limited technology. It's usually just advanced enough to get them from their planet to Earth, but not so advanced that the human characters can't defeat them. Alien invasion stories have other oddities to them, like why there haven't been invasions thousands or millions of years ago, and what, exactly, the invaders are interested in. It's all perfectly acceptable dramatic license, but I wondered if it was possible to explain all of this with a single SF idea. Turns out it is:
Our first assumption is that human beings are the first intelligent lifeform to evolve in the universe. This is consistent with all our observations so far. The second assumption is that in the far future, another intelligent race evolves. The future isn't quite as far away as this, but the universe is noticeably different. Specifically, because of a lack of supernovas the planet the future race evolves on has no uranium or thorium and is tectonically dead. A lack of water is the only thing that stops it being an ocean world. The future race reach a technological level similar to our own, but without nuclear weapons or nuclear power. They can synthesize uranium in particle accelerators, and have a good understanding of nuclear fission. But enough uranium for a single critical mass would be worth more than the whole planet's economy.
Back in the "near" future, human beings have invented a wormhole-based transportation system. Activate two gates simultaneously, and you can step between them even if they're separated by light-years. There's the possibility of nasty side effects, so the two gates are assembled a few meters apart in deep space and switched on.
Back in the far future, the aliens invent a wormhole-based transportation system, assemble two gates, and switch them on...
You're probably ahead of me here. The wormholes connect across time, bringing the two races into contact because they're at roughly equal levels of development. And one race has something worth invading for, once they find out where most of our electric power is generated. Of course it's worth asking why we didn't link up with alien wormholes 1000 years further into their future, when they were far ahead of us. Or why they didn't link up with 3000 AD humanity, when we would be far ahead of them. Perhaps the answer is that neither race survives the war...
Our first assumption is that human beings are the first intelligent lifeform to evolve in the universe. This is consistent with all our observations so far. The second assumption is that in the far future, another intelligent race evolves. The future isn't quite as far away as this, but the universe is noticeably different. Specifically, because of a lack of supernovas the planet the future race evolves on has no uranium or thorium and is tectonically dead. A lack of water is the only thing that stops it being an ocean world. The future race reach a technological level similar to our own, but without nuclear weapons or nuclear power. They can synthesize uranium in particle accelerators, and have a good understanding of nuclear fission. But enough uranium for a single critical mass would be worth more than the whole planet's economy.
Back in the "near" future, human beings have invented a wormhole-based transportation system. Activate two gates simultaneously, and you can step between them even if they're separated by light-years. There's the possibility of nasty side effects, so the two gates are assembled a few meters apart in deep space and switched on.
Back in the far future, the aliens invent a wormhole-based transportation system, assemble two gates, and switch them on...
You're probably ahead of me here. The wormholes connect across time, bringing the two races into contact because they're at roughly equal levels of development. And one race has something worth invading for, once they find out where most of our electric power is generated. Of course it's worth asking why we didn't link up with alien wormholes 1000 years further into their future, when they were far ahead of us. Or why they didn't link up with 3000 AD humanity, when we would be far ahead of them. Perhaps the answer is that neither race survives the war...