Any vehicle that can cross interstellar space in a reasonable time also has enough energy to destroy a planet, simply by crashing into it.
So any alien race that can travel here could also drone strike earth and kill us all before we even saw it coming.
In fact, this makes it a prudent move to pre-emptively kill any civilization you notice, cause you can’t ever know if they would do it to you, before it’s too late. It’s the principle of Mutually Assured Destruction, without the Mutual part.As for diseases, we’d have to meet them in completely closed-off chambers.
And even then, it’s possible that they emit strong x-rays to scan their surroundings, giving us radiation poisoning.
Or they use 200dB sonar, deafening us. Or the other way around, their bodies rapidly oxidize in an oxygen-rich environment.On the other hand, they might be sensible enough to have banned nukes, so our weapons would be more powerful than theirs.
Also, it seems unlikely to me that life that evolved totally separately from us would be biologically similar enough for our diseases to transfer between us
Probably fungus could end up feasting on them like they are moving piles of organic material.
We almost certainly can’t catch a disease from them in the same way we can’t catch most animal and plant diseases. Each virus and bacterium relies on certain aspects of the host to survive and reproduce.
Fungal infections are more possible, because fungi just feed on decomposing organic matter. As long as they’re carbon-based, they’re probably edible. Same for parasites: as long as they’re made of meat, they’re edible. (Barring any strange chemical composition, like if for some reason they carry large amounts of what we would consider toxic metals.)
Yes to the first assumption - with a caveat. To cross the width of space, their technology must be far ahead of ours. Imagine a modern army fighting one from the 18th century, and you could imagine what a tank, a machinegun, modern artillery or whatever other aspects would do.
BUT: There is also the point that we would fight locally, while they would need quite long-winded logistics. OK, they could mine asteroids, and if they have all the means of production, we would be f-ed.
Regarding the disease, well, any disease needs a host, and it is formed by evolution over millions of years to work on that host platform. Just imagine the aliens have a different interpretation of DNA, maybe for pairs forming a codon instead of three, or just different encodings of amino acids for their codons, and nothing would work. And that would assume that they are similar enough to actually have DNA.
What they could do, though, if they are technologically far ahead, they could probably synthesize a virus that is basically made to kill us off the planet before we know it.
So better not piss off any aliens that made their way to us… Gray lives matter!
There’s an interesting caveat, looking at recent war history ……
War technology has always been a “battle” between offensive technology and defensive. However in recent years, offensive dominates. We may have reached the limits of physical materials such that there is no defense. Certainly a lot of todays fighting requires stopping the attack or making it miss, rather than trying to survive it.
There’s no reason to expect that shields can exist, so it’s quite possible we can hurt the aliens and their advantages are standoff and intelligent weapons, reconnaissance, targeting. Looking at recent wars, would we be like Iraq, appearing similar in destructive ability but overwhelmed, or more like Ukraine, appearing to have no chance but successfully fighting back? Ukraine’s advantage is partly economic: using cheap drones to destroy expensive or nonreplaceable tech. Imagine the Aliens as Russia, with all the apparent advantages in size, tech, experience …… but they only have the weapons they came with and we can at least sting them, we can make them spend irreplaceable weapons on our much cheaper technology
Or think of Stargate SG-1. Humans technology was primitive, but the weapons could still kill. A combination of unwieldy political structure of the aliens and clever application of force managed to minimize the impact of the technology advantages. Then of course making the right friends enabled those humans to leapfrog ahead
