In my previous post, I talked about aliens landing on our planet and that we will be toast if they did.
But why would they land?
All alien movies show alien ships making landfall. The aliens get up close and personal just so Hollywood can treat us to some office jockeys, suddenly turned urban warriors, going pew pew with a rifle against tentacled alien murder-bots.
See here's the thing. We have long known that the best way to kill something is to stay out of range of that thing you are trying to kill so it doesn't try to kill you back. That is why we invented bows and guns and artillery and bombs that we drop from the sky. If we understand this, I am positive that an alien civilization with millions of years of evolution under its belt will also understand this.
And they will stay out of range.
In my previous post, the wooden ships of the Spanish Armada get destroyed by Hellfire missiles of a modern navy in a hypothetical battle. The Hellfire missiles travel over the horizon from seven miles away, and the Spanish do not see the enemy. Aliens landing on Earth is like the modern navy deciding that the best way to destory the Spanish fleet, instead, will be to board them, cutlass in teeth, and engage in hand to hand combat. No sane admiral would entertain that thought.
Apply that to the aliens. An equivalence may be that they will park their starships in the vicinity of Alpha Centauri, which is 4 light years away and well out of reach of humans. Hell, even the Oort Cloud will work nicely. And they will deliver whatever civilization-ending superweapons they have, from there.
Easy breezy.
But that's not all, folks. Let's talk about weapon delivery.
We just got done assuming that alien weaponry will be delivered, ballistic missile style, from deep space. Three-dimensional space, to be exact.
Why?
An alien tech could conceivably deliver weapons through four-dimensional space, and we would have exactly zero ways to detect or stop said weapons.
No, I am not high. Stay with me. We know that higher spatial dimensions are possible. We can do the math and it checks out. But we cannot influence anything beyond three dimesions; we don't have the tech. But an alien civ could have the tech.
Here's how it would work. Let me explain with an example. Take a piece of paper and draw a stick figure on it. Now imagine that this stick figure can only crawl around on the surface of that paper. It cannot rise up out of that paper. It's vision and movement goes only up/down/left/right on that piece of paper. And boom! you have just created a 2D being. A Flatlander.
You, as a 3D being, have immense power over Flatlander. If you wanted to destroy Flatlander, you have a number of unstoppable ways to do it. You could cut through the paper with a pair of scissors, and Flatlander would not see or feel the prongs until it was torn in half. You could bring down a hammer on its smarmy face. You could drop a bunch of acid on its torso. You get the idea.
Having access to a higher dimension is a game-breaking advantage.
An alien with access to 4D will have exactly the same advantage over our 3D selves that we have over Flatlander. We will be powerless to stop alien weapons delivered over 4D because we will only feel those weapons nanoseconds before vaporization.
Glad I could brighten your day. Laters.
Postscript: I cheated a bit when I said Flatlander has no way to detect you. It does. Your 3D self casts a 2D shadow on the paper and this is what Flatlander sees. A fat lot of good it does since you cannot interact with or harm a shadow, but still, detection is possible. Similarly, we would indeed see huge 3D shadows (yep, 3D shadows) of 4D weapons hurtling down on us.
But...if the aliens wanted to take even this little bit of...ummm...satisfaction away from us, they could.
What would you do if you wanted to prevent Flatlander from detecting you? You could simply increase the ambient light in 3D space so that you cast little or no shadow on Flatland. Movie sets and photo studios do it all the time.
In the same way, the aliens could increase the ambient light in 4D space, and then, the only hint we would have of our imminent destruction would be, ironically, what we would think of as, a really bright sunny day.