little green man from outa space
Space propulsion is remarkably easy actually. It's keeping humans alive, healthy and happy as well as shielding off the meteoric iron and radiation.
With our tech we could fly to mars and be reasonably safe but there would have to be a ready made base right there.
This makes it likely our alien friends not just have the tech to fold space and travel infinitely far at infinite speed. But they also have a base here. Now there are millions of places where you can hack a tunnel entrance without peeps finding out.
For example on the moon 10 000 years ago? Or on the north pole? just let it freeze over, this humans wont find a 10 km deep base even if the entrance tunnel is still there. Who are we to think they cant fly straight through the planet? It doesn't seem much harder as straight though a galaxy?
Then given the size of this ball of mud there is quite a lot one could fit inside. Lets say their tunnel is 5 meters height? Maybe it's 5 cm but lets say 5 m. That would allow for 200 floors per kilometer of depth. Say they only build 10 km, that would make their living environment on earth 2000 times as big as ours.
But if their tunnel is only 10 cm in height it could be 100 000 floors on just 10 km. If the aliens are 5 cm in height each floor would be 50x50 = 2500 times as big for them as it would be for us. Making their invisible habitat 100000 X 2500 = 250 000 000 times as big as ours.
You have any idea how much ants live on this planet? You may have the equivalent of a world population in your garden. For as far is human/ant communication goes we have settled for the rather strange conclusion that their language is to complicated for us to understand. There is to much going on to make sense of it. It makes me wonder if the ants feel the same about us. We love to think they are the primates with their genetic labs, indoor gardens and multi-floored mega cities.
5 cm big subterranean aliens would experience our planet 250 000 000 times as large as we do. We humans can fit 10 000 000 000 people on our world and we haven't even got any technology.
There is room for 250 000 000 000 000 000 little grey or green man on this world. At least if their size/tech ratio is as bad as our and that they only build 10 km.
In comparison with our space travelings visiting earth is just as big a project as when we humanoids would visit a different milky way.
Size is very important.
Imagine how big our world would be aliens the size of ants or to aliens a few kilometers in height.
The moon for example could be a space ship. If we look at the research it's much more likely as that it's a ball of mud. A ship that size would allow custom positioning of planets.