I'm surprised at Stephen Hawking for these comments (if the BBC story is an accurate summary).
Aliens raiding our resources? Surely they wouldn't be after any of our heavier elements, such are to be found available in asteroids or moons with much less of a mining problem (due to these bodies being smaller and less geologically active than Earth) and far less of a gravity problem (you don't really need to land and take off from an asteroid, even a large one, you just dock with it). CUrrent thinking is that there are asteroids out there made of enough iron to meet our own needs for decades - one asteroid! What about water? Well there are other watery bodies such as Europa around which again are more accessible and true, there is a surface layer of ice but if you have the energy required to propel yourself between star systems I hardly think melting some ice would be a problem. In any case, the most plausible reason for needing large quantities of water would be for fuel and you're going to get a lot more energy out of it than it would cost you melting it making the advantage of finding it in liquid form negligible. What else have we got? Hydrogen? Just scoop it out of the atmosphere of a gas giant such as Jupiter - don't even need to land. Hydrocarbons (i.e. fossil fuel or methane)? Oil might make energy-sense when you're driving it around on the ground, but it doesn't when you have to fly it up to orbit - i.e. you never see big planes flying oil from Saudi Arabia to the US because it would be grossly inefficient - it gets shipped. There's not much else I can think of. Helium? We're already on the decline of our own stocks and you can pick it up from gas giants. Besides, one use for Helium would be as fuel for fusion reactors and for that you want Helium isotropes which are created by being struck by solar radiation, which of course happens much more on planets and moons that don't have a nice fat magnetosphere protecting them. If you want lots of He3 for your fusion reactors, you go to the moon which is bombarded by solar radiation creating He3, not Earth where the He3 decays over time without being replenished. Anything else? Precious gems?
Grow them yourself in zero gravity - you'll get much better quality that way anyway.
Of course you could propose that some interstellar aliens were just really, really bad planners and said to themselves: "let's just fly in that direction, we're bound to pass a planet rich in liquid water at some point" and that planet happens to be Earth. But Space is big (really big) and I kind of doubt chancers like that would get as far as interstellar travel.
So when you rule out mineral resources, you're left with three things that Earth has that aliens might want: culture, biological research material, location.
Culture isn't something you take, it's something you share. If the aliens want to watch our TV, I pity them (except for Doctor Who of course, which even Aliens would think is great). Absolute worst case scenario in this is that they come down and try to make off with some of our pots and pans and buildings for their space museums. Maybe they'll abduct Bill Bailey. Anyway, more and more of our culture is becoming reproducible media. I don't advocate piracy, but if its the aliens copying all our ebooks, DVDs and music or orbital bombardment, I think we'd let them get away with it.
What else? Biosphere. This, along with Culture, is the big likely one. But much like with Culture, you don't need to destroy it to take it. In fact, there are strong reasons why you wouldn't. If you value our biosphere (which by definition anyone after it does), then you don't destroy it. And it's not like any species or automated system that crosses the distance between star systems is going to need to get the job done in an afternoon. They could spend decades collecting samples. We'd probably even be happy to be their ready-made-on-the-ground collection crew in exchange for the merest droppings of their technology or knowledge of Physics. I'm sure I even know a few people who'd volunteer to go as human representatives and the US would surely give up some of its death row inmates as a goodwill gesture. You could propose a desire on the aliens' parts to experiment with our biosphere, but experiments are something you do with many samples available. You don't vivisect that last remaining tasmanian devil to see how it works.
So last and only viable reason: location. Maybe the aliens are feeling a bit cooped up and want to stretch their tentacles on a planet just the right mass and the right distance from the a star to have liquid water, etc. We can't rule this one out. We can say that any species capable of traversing the interstellar distances would be capable of modifying superficial details of their environment to suit them quite easily though. I.e. if they want warm waters, they can have that on Europa, if they want a biosphere, they could almost certainly seed Mars. The point of that is that for them to want Earth, it would really have to conincide with their preferences to a remarkable degree.
So we have a possibility that aliens might want to colonize which we have reasons why they would not, but we can't rule it out. But raiding us for resources and then moving on as the article says, is a pretty silly idea when you think about it. It was far more of a let-down in the Slytheen stories that they wanted to "melt the Earth to slag and sell it" than it was to have the aliens farting.
Coumbus and the Native Americans is a bad example (as is the British in India, the French in North Africa, US in the Middle East, Spanish in South America, Ethiopia with the rest of Africa and any other examples of more powerful civilisations interacting with less powerful ones). It's a bad example, because in all these cases, the less powerful civilization has something that the more powerful civilization wants. If that's not the case, as it shouldn't be with alien contact, we would instead have much to learn from the aliens. The culture shock to some would be huge, but I think it might do us good to know we stand together as a species in a Universe of other lifeforms, than bickering over our own small world. I personally would love to learn how another intelligent life-form sees the Universe.
Really, the distances between stars are so great, and Space so rich in energy and resources, that the only things we have that each other want are our cultures, our beliefs and our knowledge. And these are trade goods, not finite resources to be plundered. An exchange of ideas makes both sides richer.
And I'm sure the Doctor would agree.
Khadim.
Grow them yourself in zero gravity - you'll get much better quality that way anyway.
