von Neumann probes.

A von Neumann probe is a self-replicating machine that explores a star's planetary system, then launches copies of itself to other stars, where each new probe makes copies of itself, etc. The idea was proposed by mathematician John von Neumann.

An argument against the existence of advanced extraterrestrial civilizations back in the 80s, echoing Fermi's paradox, was that we'd have been visited by a self-replicating probe by now, or even by several.

What I wonder is: are von Neumann probes even possible?

The logic is elegant. Launch one probe, or a few, let them reproduce and explore the whole galaxy. But think of the technologies involved. If you want to build a probe now, say one to orbit Mars, you can do it because there are large industries that make the things you need, from solar panels to instruments to the rockets to launch it with.

If you go to an undeveloped planet in another star, you're going to have to first find the raw materials to build more probes. While you may be able to find metals like iron and copper and aluminum, and non-metallic elements like carbon and silicon, what about crude oil to make plastics with? granted, you can in theory synthesize hydrocarbons from raw carbon, hydrogen, oxygen and other things, but this just adds tot he complexity.

And then there's environment and energy. Will your processes work in lower or higher gravities? How about zero gravity? How about denser or thinner atmospheres? How about atmospheres with acid contents like Venus'?

What will you use for power? if you have fusion, great! That should work for a very long time, and hydrogen is the most abundant element in the universe. Else, well...

So we're talking about a very big, very heavy, very expensive machine, which won't pay off for at least centuries, likely for much longer. Perhaps no existing civilization can afford one, never mind many.

There is a term for this but I think that the "survival of the fittest" element of evolution causes us to kill ourselves once technology reaches a certain level. The average man with a little preparation can kill hundreds. In 100 years, it may be millions.

Quote: Wizard

There is a term for this but I think that the "survival of the fittest" element of evolution causes us to kill ourselves once technology reaches a certain level. The average man with a little preparation can kill hundreds. In 100 years, it may be millions.

I fail to see any basis for this, seeing as how no civilization we've ever known has destroyed itself. And we also know absolutely nothing about any non-human civilization, starting with whether they even exist :)

One means suggested for von Neumann probes to self-assemble, sort of, is using nano-machines.

Briefly, these are a kind of spin off from the semiconductor industry. The idea is to build machines at the nano-meter scale, or thereabouts, which can assemble structures almost at the molecular level. It's a very popular idea in science fiction, often called "nano" and "nanites." There's an episode where they take over the Enterprise, much to the annoyance of Captain Picard. Thus far, no practical applications have come off it, though these tiny machines have been made experimentally.

Well, if it's possible to make them in such a way that they can access a power source, and contain programming or be controlled externally, and have sensors, and more, I suppose they may work. No need to smelt and refine iron ore, for example, your nanites simply take iron atoms from the ore (somehow). I don't know if this can work with compounds. Chemical bonds can hold on with a great deal of strength (an explosion is pretty much chemical bonds letting loose their energy all at once).

If you think nanites sound like cells, you're right. That's one idea. they wouldn't reproduce by division, like cells do, but they could certainly assemble more nanites as well as von Neumann probe components.

As of now I'd call this notion a very, very, very long shot. Such nano-machines as have been made don't actually do anything other than move around aimlessly, or move their constituent parts.

Quote: Nareed

I fail to see any basis for this

I knew I shouldn't have bothered. Do you expect me to have evidence of civilizations that may have existed on the other side of the galaxy a million years ago?

Insult someone else from now on. I am done.

Quote: Nareed

An argument against the existence of advanced extraterrestrial civilizations back in the 80s, echoing Fermi's paradox, was that we'd have been visited by a self-replicating probe by now, or even by several.

How do you know we haven't? Perhaps they are stealthy.

Quote:

What I wonder is: are von Neumann probes even possible?

Perhaps by the time you could develop that technology, you might have already solved to other ways of exploring about the Universe which is why it is never done.

I also have to wonder why we would necessarily know other civilizations have visited Earth.

US knowing would require several assumptions. For example,

1. That we know all there is to know about all radio frequency spectrums.

2. That others would necessarily communicate on a rf we could detect.

3. That others exist on the same physical scale as we are. They could be minute. They could be enormous. They could be ephemeral. They could have stealth technology beyond our ability to detect.

4. That we are correct in our various understanding of how physics work, most of it theory only. Any number of ways that we could be wrong about things that would radically change the nature of time, existence, space, traveling in space.

5. That other civilizations are anywhere close to where we are in our development. Look at what mankind has learned in just the last 100 years. What about a civilization that has developed 1000 years beyond ours. 10000 years. More. Time frames that are blips on a galaxy existing for billions of years. How would we know they were ever here if they didn't want us to know, assuming a similar geometric progression of their sciences and knowledge?

I think it's a great topic, and we should continue to discuss it. Sorry you got put off it, Wizard.

Quote: Wizard

I knew I shouldn't have bothered. Do you expect me to have evidence of civilizations that may have existed on the other side of the galaxy a million years ago?

Insult someone else from now on. I am done.

I hit that point, too.

I also don't know the term for what you described, but I believe one possible to process is technology gives individual people the ability to kill and destroy more easily and widely, and eventually a small group of the antisocial or the insane has the power to end it all for everyone, so they do.

Quote: rxwine

How do you know we haven't? Perhaps they are stealthy.

If they are, then they've run into us but we haven't run into them :)

Quote:

Perhaps by the time you could develop that technology, you might have already solved to other ways of exploring about the Universe which is why it is never done.

Maybe. But the number one problem in exploring the universe is that it's too damn big. Why, it's as big as the universe! So even if you live forever, can travel anywhere in a femtosecond, and even can be in several places at once, you'd lack the time to explore the entire universe (you may live forever, but the universe probably won't).

If you build self-replicating probes that can do just that, you stand a much better chance.

Quote: Wizard

I knew I shouldn't have bothered. Do you expect me to have evidence of civilizations that may have existed on the other side of the galaxy a million years ago?

Insult someone else from now on. I am done.

I have to ask: what insult?

You made a claim, I said I see no basis for such a claim, adding that we don't know of any extraterrestrial civilizations as yet. I added, too, that no civilization has self-destructed (and I'm adding now: not on purpose, and/or not knowing in advance that a course of action would lead to decline and collapse). I don't see any of this as an insult. Disagreement is not an insult, either.