Alien life and Earth

[Algolei]

Oh? When you visit someone else's home, do you go on a campaign to eradicate all the mice that might live in the walls? When you go out to a park, do you start trying to kill off all the squirrels?

Yes.

Why should visiting aliens try to eradicate anything?

'Cause they're exterminators, too?

 

[Turanil]

In 2006 there will be a new satellite just for searching small exoplanets, those of the kind that could have earth-like conditions. As such, we will know more about what other worlds lie around here. So, could we expect a much more advanced civilization having the means to detect which planets around harbor life, and which of them a technically advanced life? If so, they would know where to send probes.

As to go faster than light, I think in the future (some centuries ahead of now, if all goes well) we will have to think of a much different way to "visit" other planets than go there physically.

Fortunately we have RPGs to dream of that time that we won't see in our life (in all probabilities anyway).

 

[Thornir Alekeg]

I don't buy the idea that we have been visited by aliens. I do believe that we are not the only planet in the universe with life. I think with the number of stars in the galaxy and the number of galaxies in the universe it is highly likely that life exists elsewhere, but the chances of another life form being sufficiently advanced to travel locate our remote little planet are astronomically slim (pun intended) - but like others have said, maybe they have learned things about the laws of the universe that we do not know that make the whole idea of interstellar travel much simpler.

 

[Umbran]

So, could we expect a much more advanced civilization having the means to detect which planets around harbor life, and which of them a technically advanced life? If so, they would know where to send probes.

Problem: barring exotic, faster than light detection, you have a practical problem with lightspeed.

No matter what you are looking at, information only travels at lightspeed. One's ability to deal with a technological civilization, then, depends on the lifetime of that civilization. If the lightspeed round-trip between Earth and the alien civilization is longer than the time our civilization has existed, we'd not have seen any such targetted probes.

That limits us to a sphere perhaps 200 light years across. While there are many stars in that range, there are many, many more outside that range, as the Milky Way is something like 100,000 light years across. Probability is, then that if life in our galaxy isn't incredibly prolific, it only exists outside the sphere in which we could have been detected and responded to.

 

[Dirigible]

No matter what you are looking at, information only travels at lightspeed.

Doesn't gravity work instantly over infinite distances these days?

Err...I'm not being sarcastic. I'm actually asking. I'm not up to date on the latest physics theories.

 

[Algolei]

Doesn't gravity work instantly over infinite distances these days?

Err...I'm not being sarcastic. I'm actually asking. I'm not up to date on the latest physics theories.

Nope! I actually used to wonder that too: "What's the speed of gravity," so to speak. Turns out, somebody actually went and figured it out quite recently!

Let's see how my Google skillz are today....

Shazam! Here it is: http://www.space.com/scienceastronomy/gravity_speed_030107.html
Apparently it's come under criticism since it was published, though.

The first accurate measurement ever taken of the speed with which gravity propagates shows that it is equal to the speed of light, agreeing nicely with the General Theory of Relativity.

You may or may not have ever considered whether gravity has speed. It is of great concern to scientists. Newton thought gravity's force worked instantaneously. Einstein thought it took effect at light speed.

Here's a way to think of the difference:

Though fast, light takes time to travel. If the Sun suddenly disappeared, it would take about 8.3 minutes before daylight on Earth would evaporate. With the Sun gone, gravity would cease to keep Earth in a circular orbit, and it would fly away.

If gravity works instantly, Earth would fly away the moment the Sun disappeared. If gravity works at light speed, Earth's course would not change until 8.3 minutes later.

 

[Dirigible]

Dang. Now I'm gonna have to rewrite all the pseudo-scientific MacGubbinz for my sci fi RPG.

And David Weber will be rotating in his grave.

 

[Dakkareth]

That limits us to a sphere perhaps 200 light years across. While there are many stars in that range, there are many, many more outside that range, as the Milky Way is something like 100,000 light years across. Probability is, then that if life in our galaxy isn't incredibly prolific, it only exists outside the sphere in which we could have been detected and responded to.

Not responded to - granted, if there's no way to avoid the lightspeed problem.

Not detected - I was mentioning the concept of Von Neumann machines, which are essentially self-replicating constructs. Thus you'd send out a few million probes toward the nearest solar systems promising results (and a few others). From there, each one would create many others in its image and send them on their own way based on information newly available from the new point of origin or by a pre-laid plan. Thus it would take a lot of time to cartograph the galaxy, but it could be done, even if the civilization initiating it destroys itself a hundred years after the launch.

 

[Turanil]

In fact reading this thread makes me sad.

I mean: there is a whole incredible bunch of marvels in this galaxy, and because I am not able to move my ass beyond the speed of light, I will never witness any one of them all.

Ah! If "out of body experience" could work (and I could do it)... I would spend my nights traveling the universe...

 

[der_kluge]

I was going to offer this as proof of a previous visit, but skimming the article it seems they have solved this little mystery. Might make a good plot hook for someone, though.


The Coso Artifact
http://www.talkorigins.org/faqs/coso.html