About the aliens visiting the earth....Yes, they have been here, but..........

[PoindexterOglethorpe]

22. Several points.

I have a son getting his PhD in astronomy, and he's doing exo-planet research. It's not merely a small percentage which have planets, it seems to be the vast majority. Essentially every single star we look at has planets.

We have not yet found a true Earth-like planet, although I'm sure that's a matter of time. Right now we can't quite get a look at the atmospheres, but in time we will.

Anything more than about two and half times the size of the earth is an ice giant or gas giant. That has to do with the physics of planetary formation.

The Universe is around 13 billion years old, give or take. Our own planet is about four and a half billion years old, and it took about a billion years for the first life to appear. Multi-cellular life is less than a billion years old. I'll skip most of the rest, but will go straight to the fact that homo sapiens evolved around 200,000 years ago, fully modern humans from 40 to 60 thousand years ago, and civilization as we know it is about 6,000 years old.

Who knows how long we will last? The pessimists out there think that most technological civilizations will probably destroy themselves before they make it outside of their own solar systems. I simply don't think we have enough evidence to come to any conclusions.

Species have a finite life span. And before you start pointing out that jelly fish have been around a hundred million years, or name some other species that's been around a very long time, those are true anomalies. Species evolve, change, die out. A million years is a good run for most of them.

Which means, the possibility of two intelligent, space-faring species to be around at the same time and to find each other, is vanishingly small.

And, for what it's worth, the Universe is actually young enough that current thinking is that we may well be the first or one of the very first species in our galaxy to evolve intelligence and technology.

Interstellar distances are vaster than most people realize. Here's the example I like to give: our galaxy, Milky Way, which has perhaps 300 billion stars, and Andromeda, which has about a trillion stars, are on a collision course. I know, brace yourself. It'll happen in about 4 or 5 billion years. A while back I asked My Son the Astronomer, when the two galaxies collide, how many stars will actually crash into each other? He replied, "Well, we're not completely sure, but right now the best guess is no more than ten." Think about it. Ten stars out of a combined 1.3 trillion. Of course, he hastened to add, a lot more stars will be gravitationally impacted, but that's not the same.

Most reputable astronomers and physicists are quite certain that FTL travel will never be possible. I know people will airily dismiss that and say we can't begin to know what kind of advances a species even thousands of years ahead of us will achieve. And while in the abstract that's true, I'll repeat myself: reputable astronomers and physicists are quite certain FTL travel will never be possible. There is the possibility that wormholes will turn out to be a reliable way to travel vast differences, but I wouldn't count on it.

Not to mention, long term space travel even within our own solar system may turn out to be more dangerous than we currently understand, given the exposure to radiation involved in very long journeys. Although that may well be solvable. Some kind of relatively thin and lightweight material that effectively blocks radiation probably has a good chance of being invented.

Don't get me wrong. I'd love to be able to travel to distant stars and planets myself. I'm a science fiction fan and love reading such novels. Heck, read the works of Jack McDevitt. He has two different and wonderful series both of which depend on FTL ships for things to happen. But I do get frustrated when people just assume that there really are species out there who've mastered the unmasterable.