Back to aliens.
As per below report, framed in our understanding of conventional physics, the distances across the universe are so vast, that there is no way of storing the fuel on space craft to travel those distances.
The travel would be so long from one habitable planet to another, that even the civilization can disappear before the space craft returns to home planet, as it can take thousands of years for return trip. How much our civilasation evolved and changed in last 2000 years, only?
In that case such travel would be pointless.
On the other hand:
Aliens, (aka UFO), arrive to our planet regularly in hundreds of cases, in fact on daily basis.
If this all is true of UFO regular visiting schedule, then the question is where from do they come from, if it is not from other galaxy, under presumption of time, speed and fuel limitation ?
Inhabiting the earth, but where are they? Oceans?
Inhabiting the earth, but coming from the future? Time travel?
Or do they have a different way of space travel? Stargates? Black holes?
Or do they have a different way of travel, much faster then speed of light, which in our conventional science we consider not possible?
When travelling the speed of light, the mass becomes indefinite.
For bigger mass, you need more fuel.
Is this indication of why all these UFO are small in size? Or they just need "small vehicles" to travel locally?
Something to think about: