An intriguing thread, but I’m going to toss in a POV that differs from the usual. What reasons do we have to believe that a technologically-advanced civilization that has developed interstellar travel would have any better offensive or defensive capabilities than we do? Why do we automatically think, "“Uh-oh. They could destroy us all without lifting a finger or breaking a sweat!”
Let’s say that we figured out how to create and utilize wormholes next year and that we send an exploratory vessel through to some planet with intelligent life. The craft would probably have virtually no defensive capabilities and our offensive capabilities would be typical for this era: propellant-based projectile systems and explosives. I don’t see any reason to believe it unlikely that some nut would take a shot at an alien spacecraft using a hunting rifle and put it out of commission with a couple .308 rounds. Being advanced in one specific technology does not mean being advanced in EVERY technology.
This actually got more traction than I thought it would.
Let me clarify.
This hypothetical craft land in (pick a city, but for argument sake say somewhere in westen Europe)). There is no obvious commication and since we are still around the craft has not attacked or shown hostile intent.
What would the immediate response be from government, the military, media and so on.
Government would try to communicate with the ship.
Illustrate the Pythagorean triangle. Demonstrate base 10 and prime numbers.
Wait for smoke to come out the back.
Probably immediately evacuate the city, have the military cordon off the site and the spacecraft, surround it with all kinds of weapons pointed at it, get a few special-forces and scientist type people to approach the spacecraft, probably all donning hazmat suits.
How many years do you think we are away from traveling to another planet that has intelligent life? We know that it’s not in this solar system. Round numbers. 500 years? A thousand? In all that time do you think we’ll have better weaponry than we do now, or do you think it will be about the same?
I lack confidence in your confidence. Say for example the aliens unintentionally bring a microbe who just loves nitrogen and it quickly discovers that the concentration of nitrogen in our atmosphere is three or four times that of its native environment. Immediately, it begins multiplying very rapidly and consuming or altering the nitrogen in our atmosphere with serious negative effects for life on Earth. It doesn’t have to be a germ that infects us, it just has to be a life form that runs hogwild in our environment and has no natural predators, starving us out. I think rabbits in Australia is a significant and relevant example.
I am inclined to think if they were actually landing a spacecraft to meet with us then their intent is probably peaceful. I mean if they were going to attack us, why would they bother with a meeting? They would probably just attack us outright instead trying to arrange a meeting.
That being said if an honest-by-god extraterrestrial spacecraft appeared in Earth orbit, I think it would trigger a massive panic, resulting in a huge stock market crash and probably people starting to hoard food and other supplies due to people anticipating an alien invasion.
This assumes that the microbes in question are pretty much the same, metabolically, as earth-based microbes. That is highly unlikely. Nothing can live on pure nitrogen - they have to combine it with the other elements, such as (on earth) carbon, hydrogen, and oxygen. The notion that they can live in an atmosphere that is three times higher in nitrogen and have no other adaptations is unlikely in the extreme.
