I’ve heard this idea before. Late during the formation of the Earth, there was a period when massive impacts had trailed off enough that there was time enough for the surface to cool between impacts. Given how soon life appeared after the surface cooled for the last time, it seems possible that life appeared several times and then was utterly destroyed when the next giant meteor struck and melted the Earth’s crust again.
Don’t believe you at all here. No blond physicists or scientists daughters or hot random tourists are mentioned, and they are always a part of this kind of operation. Please be more realistic next time.
Thank you to everyone for your interesting and thought provoking posts - particularly **Stranger **(as always).
I started a thread about something similar a while back - creating a probe capable of surviving long enough to function when it reached the next star. The consensus was that it’s extraordinarily difficult for an unmaintained machine to survive so long. Basically, it’s got to switch itself almost off for decades or centuries, switch itself on at the right point, and have not suffered too much damage in the meantime.
I appreciate that the distances are somewhat different, but I believe our greatest achievement so far is Voyager 1, launched 33 years ago, which is reaching the end of the heliosphere (about 10 billion miles). Some way to go yet.
What if it can maintain itself? Some sort of regenerating bio-mechanical construct with redundant AI cores, carrying sufficient raw materials to manufacture any parts that it can’t repair? Essentially, an artificial life form designed to thrive in the vacuum of deep space. It’s not something we can make now, obviously, but in a thousand years? I wouldn’t be surprised.
From where does its energy come?
Bussard ramjet?
I don’t think routine maintenance will take all that much energy, actually. A few gallons of water could probably keep it running for a thousand years.
Collecting charged ions? Tabletop fusion? Diphlebotinum crystals?
If you don’t mind going really slowly (on the order of millennia to cross a light year) then the energy requirements are pretty low. It’s when you want to send a vessel across interstellar space on anything resembling human timeframes that it becomes prohibitive, especially if it is large enough to hold a family of four, a cocksure young pilot, and a nefarious stowaway troublemaker. As already mentioned, keeping any mechanical or sensitive electrical system operating on such timeframes without maintenance is also well and beyond existing technology. The concept that Alessan suggests is essentially Freeman Dyson’s Astrochicken, a biological version of the von Newmann probe, with the idea being that it would be light and cheap (so you can send many for redundancy with the expectation that only a fraction would make it to the destination), robust and self repairing (like organic life), have low energy requirements, and be self-replicating using resources at the destination to build a more sophisticated, matrixed exploratory system. Such technology is certainly in the future, but perhaps not the far far future. It is conceivable that we may have such capability in a few centuries, or even within decades.
Stranger
OK, so as a thought experiment:
If we could keep accelerating something at the same rate as an interplanetary probe, how long would it take to get it to some cool cruising speed, like maybe 0.2c? It’s just a thought experiment, so I’m not considering real life stuff like having to also accelerate the mass of the fuel needed to maintain acceleration. I said “interplanetary,” since I assume that they pull greater g-forces than manned spacecraft.
With a couple of exceptions, interplanetary probes like the Voyager and Cassini–Huygens do not have constant thrust propulsion systems, although they do have course adjustment and reaction control systems (RCS), typically powered by onboard monomethylhydrazine (MMH) as a monopropellant. They are launched into an Earth orbit by a conventional multistage rocket like Delta or Titan, and injected into a interplanetary trajectory (escaping Earth’s sphere of influence) via an upper stage like the Centaur or IUS, and then traveling to their destination via a combination of ballistic low energy Hohman orbits and swingby maneuvers to effect radical changes in direction. The few probes that have used constant or extended duration ion thrust propulsion like Deep Space 1, Hayabusa, and Dawn, have been able to shorten transit times or perform more mission objectives by the use of these systems; however, their thrust levels are minuscule, on the order of millinewtons, and can’t readily be scaled up by making them larger, and while the specific impulse (I[sub]sp[/sub], a measure of efficiency in terms of thrust per expended propellant mass) is very high, typically ~3000 s, the energy efficiency of such systems is low, around ~1% (a lot of energy lost as heat).
However, if you could maintain a constant thrust offering an acceleration of, say 0.1% G, you would reach speeds where relativistic effects predominate in about two months, so as you can see, constant acceleration accumulates kinetic energy quickly. The amount of expended propellant, however, would dwarf the payload itself by several orders of magnitude even using very high specific impulse propulsion.
Stranger
The biggest reason is our federal government. Why do people like William Milton Cooper, John Lear, Philip Schneider all get discredited and forgotten so quickly? How does Bob Lazar go from an expert in physics to a guy selling fireworks with no record of any higher education? The dang guberment. We have already found them on Earth. So theyre just terrestrials.
“Pretty good examination of the moon”? Seriously? How come Nasa releases 1% of the moon’s pictures, and those pictures have a bunch of smudges on them? How come we are prohibited from seeing pics from the other side? Why is the moon in a fixed rotational lock, with the same side facing us at all times? Why are we told that the moon has 1/6 the gravity of earth, but the neutral point btwn the moon and earth has been calculated to show that its actually about 2/3 our gravity? Are there really “graviton” particles? We don’t know anything about our own ocean floors let alone the moon. imo
There’s one in every crowd.
Stranger
Well maybe he’s right. Wells said the aliens were IN the moon, not on the surface. 
Actually at first they decided to get a landing team together and come on over. But since they were going near light speed they quickly started seeing newer and newer tv shows. So they couldn’t watch all the shows and randomly had to pick and choose. All was ok until they saw 10 episodes of Friends back to back. Then they made a u-turn just beyond alpha centari.
The above was about the main mothership. I forgot to tell you about their smaller scout shuttle. It was watching a different channel (PBS, if you must know) and arrived on earth a few years ago. They took human form (actually taking over snatched bodies in the outbacks, like Alaska, where nobody would notice) and mixed into our society, eventually forming what is now known as the tea party. If you look closely into sara palin’s mouth you can actually see the oval in her eyes and split snake tongue.
The reason we would never SEE aliens seems pretty obvious given our current level of technology. we can already make miniature cameras that were the things of science fiction 100 years ago. Imagine what that technology will be like in another 100 years. Well have robot flies eavesdropping on everybody.
Any life form capable of traveling light years would easily have the technology to observe us without ever being detected.
If I remember, our sun is part of the “Third Generation”. However, the idea that we haven’t found extraterrestrials because all of the livable planets formed more or less at the same time is not too far off.
In the first two generations of stars, there was simply not enough heavier elements for life. Almost all barionic matter consisted of helium and hydrogen. Elements up to iron were formed by super sized stars fusing together smaller elements. Elements heavier than iron could only be produced via super novas.
Therefore, life simply couldn’t exist during the first generation of stars because there was nothing other than hydrogen and helium. That generation had to fuse the heavier elements and some of the stars had to become super novas to get heavier elements. Even then, there was probably still not enough until the second generation of stars started dying and turning into super novas.
However, the “third generation” is quite a long time. You’re talking about 5 to 8 billion years, and the first multi-celular life on this planet is a mere few hundred million years old. Mammals only formed maybe 70 million years ago, and we evolved into our current form in just a million or so years. Our civilization is probably no more than 10,000 to 15,000 years old.
We probably won’t find any alien civilization that’s billions of years old, but an advanced alien culture that’s only a million or so years older and more advanced than us could certainly exist.
If there is intelligent alien life, it might not have found us because the universe is really very vast, and finding the few other intelligent life forms is very hard to do. Radio signals from Earth are impossible to separate out from background noise a few dozen light years away. Even now, we found over 500 extra-solar planets not because we can see them, but because we can see their affect upon their host star. It’s why most are super Jupiters and so close to their host stars.
Then again, maybe they don’t want to talk to meat.
Maybe, and maybe not. Doesn’t change your point, though.