Some of us still haven't watched this show. Might want to watch the spoilers. If someone as smart as Hawking is a little paranoid about aliens, it makes me feel a little bit better about my own paranoia.
The last episode of that particular show aired in March 2009 and as I remember the rule-of-thumb is that if the show is more than ½ a year old in the country of origin you don't need to 'watch the spoilers' -not even in thread titles.
After reading this I've started to leave glasses of water around the house and have mounted baseball bats on the walls in every room just in case aliens invade...
What if the aliens aren't Christians, and don't mind reboots? The purity of our culture would be destroyed!!!
My thinking is any aliens that contact us are more likely to be benevolent than hostile. To make it to space they would have had to discover nuclear weapons and not destroy their planet with them. They also would have to pour a good deal of resources into non-military space science to first explore their own solar system, then the rest of the galaxy. We barely achieved the first, and can't seem to complete the second.
If they are hostile they wouldn't even need to do that. They could just come down and take what they want. The technology difference would be so extreme we wouldn't have a chance. You saw what a 10-20 year difference in technology did in the Iraq War, imagine a difference of hundreds or thousands of years. If the aliens are hiding it's for our own good.