So many ways to the stars
Posted by aogMonday, 21 July 2008 at 18:50 TrackBack Ping URL

cjm asks a question that I have seen asked / discussed numerous times elsewhere, which is the feasibility of interstellar travel / colonization. We take this question as a temporally global one, i.e. that such travel is feasible if any plausible descendant civilization of our own could do it.

It seems to be that anyone who is a technophile must come to the same view because to hold a different view requires disbelieving in many other technologies much beloved of the technophiles, any one of which suffices to make interstellar travel feasible. Infeasible interstellar travel requires that not one of these technologies if ever successfully developed. That may turn out to be the case, but it’s not something a technophile should admit.

I will make the assumption that we can build space ships that can go roughly 0.03c, which is achievable with current technology.

Cryo-revivifcation
Bringing someone back from being frozen. If that’s possible, then the long travel times become surmountable.
Strong Artificial Intelligence
An AI would last long enough, or could simply be turned off, for the duration.
Mental Downloading
If human minds can be downloaded in to computational grids, then this is just the strong AI case.
Nigh-Immortality
If human life times become millenial or indefinite, then long travel times are just difficult, not impossible. Note that could be achieved via medical technology (e.g. organ / body creation and transplantation), nano-technology, or genetic engineering.
Self sufficient space colonies
That’s just a multi-generational starship without a motor. And we know how to build the motor.
Industrial anti-matter
This enables much higher speeds for interstellar vessels so that only moderate to no life time extensions are required.

I considered Von Neumann (self-replicating) automata, but I don’t think that’s sufficient of itself, you’d need to put a sentient in system as well which requires one of the other items.

Anything else that should be on the list? It already seems long enough that you’d have to believe in peak humanity to think not consider interstellar travel as quite feasible.

Comments — Formatting by Textile
Harry Eagar Monday, 21 July 2008 at 19:36

Do you require that something recognizably human comes out at the other end?

Hey Skipper Monday, 21 July 2008 at 19:51

You left at least one significant requirement off the list: target acquisition.

I don’t have the time to do the research now, so I will have to run with some hypotheticals.

First, an important fact about our (or any other) galaxy. The inner third, or so, is uninhabitable due to stellar radiation. The outer third is uninhabitable, because stellar density is insufficient to produce rocky planets. Therefore, roughly the middle third correlates to the Goldilocks zone.

So, within the GZ let’s say habitable planets come at one per 1,000 stars. Clearly, casting off for just any old star isn’t stacking the deck for success. The most fundamental problem, more so than any you listed, is picking which star.

There must be a fundamental limit to how far away a (for us) habitable planet can be, and be detectable. If that limit is, say, 50 light years, and there are 500 stars within a fifty-light year radius of earth, then there is only a 50-50 chance of their even being a habitable planet to aim at.

Past that, there are two other problems: changing direction, and stopping once you get where you are going. Both require huge velocity changes, which add to mass, which makes only aggravates all the initial problems.

Annoying Old Guy Monday, 21 July 2008 at 20:26

Mr. Eagar;

Do you require that something recognizably human comes out at the other end?

No. At the time scales implicit here, I find it very unlikely that we’d consider even our own direct descendants as being recognizably human.

Skipper;

I don’t see why rocky planets are required. They can be built out of gas giants if needed.

As for slowing down, that’s implicit in the velocity limits I noted above.

David Cohen Monday, 21 July 2008 at 23:06

Well, I’m skeptical about several of these technologies, but the real scientific problem is a social scientific problem. Why would we bother?

Annoying Old Guy Monday, 21 July 2008 at 23:17

You are committing the unitary fallacy again. Define “we” for me, then I will answer the question.

joe shropshire Tuesday, 22 July 2008 at 00:37

Ah, that’d be the same ‘we’ you just talked about. The body of people who could build such a spaceship, would be the same who would have to make up their minds that they wanted to bad enough, as opposed to all the other difficult but profitable things they might do. You’re committing the ‘everybody as smart as me will naturally think just like me’ fallacy.

Hey Skipper Tuesday, 22 July 2008 at 01:14

I don’t see why rocky planets are required. They can be built out of gas giants if needed.

That is the kind of response that brings every discussion of interstellar exploration to a grinding halt — simply assume the problem away.

Let’s say, for the moment, that building rocky planets out of hydrogen and helium is a non-starter.

Target acquisition alone will bring the whole enterprise to a dead halt.

In the famous words of Sandy Koufax, you can’t hit what you can’t see.

cjm Tuesday, 22 July 2008 at 06:41

the problem i most recently read about is one of fuel and momentum. is there any mass in the great reaches of space to convert into fuel? can momentum carry a ship through these voids?

another even more interesting article posited that the absence of aliens here is a very bad sign for us because it meant that every civilization older than us has perished before it could make the jump. so therefore the closer we come to being able to jump the closer we probably are to whatever fate has befallen other civilizations.

twinle twinkle little star how i wish you weren’t so far

Annoying Old Guy Tuesday, 22 July 2008 at 08:06

The body of people who could build such a spaceship, would be the same who would have to make up their minds that they wanted to bad enough, as opposed to all the other difficult but profitable things they might do.

No, only some subset of the people who could build such a spaceship or afford to buy one, would be the same to decide to go. I am making the assumption that the knowledge to build such a thing was generally available, so that only requirement is for a group to have the will and the resources.

That [build rocky planets] is the kind of response that brings every discussion of interstellar exploration to a grinding halt — simply assume the problem away.

We already know how to do that. One can fuse the hydrogen and helium into rocky materials. Should I assume away that knowledge?

is there any mass in the great reaches of space to convert into fuel? can momentum carry a ship through these voids?

Yes. Yes.

another even more interesting article posited that the absence of aliens here is a very bad sign for us because it meant that every civilization older than us has perished before it could make the jump.

Yes, that’s a concern. But it does presume the (prior) existence of those civilizations. It could turn out to be the case that such a thing is so unlikely that it only happens once per galaxy or per universe.

Let me ask — how does your target acquisition problem prevent success in the mental download, strong AI, and space colony scenarios?

cjm Tuesday, 22 July 2008 at 12:16

slightly OT: is it possible (in the physical sense) to derive energy directly from gravity?

Annoying Old Guy Tuesday, 22 July 2008 at 12:27

Any object moving in a gravity field is converting gravitational potential energy to kinetic energy (or vice versa). There is no way, in current physical theories, to convert from one potential field to another without interacting with mass of some kind. Gravity is not special in that sense.

Annoying Old Guy Tuesday, 22 July 2008 at 12:31

I would also like to note that exo-planet detection is a rapidly improving field. We already know over three hundred nearby stars that have planets, so we have no lack of targets in the local stellar area.

P.S.

stellar density is insufficient to produce rocky planets

Do you have a cite for how stellar density affects planetary formation? Is that based on heavy elements requiring super novas?

within the GZ let’s say habitable planets come at one per 1,000 stars

Please define “habitable”. Do you mean descendants of our civilization can live there, or do you mean unmodified current humans without technology can live there?

cjm Tuesday, 22 July 2008 at 13:12

i was thinking more as a weapon than as a source of propulsion.

re your answer: was that a yes or no?

Harry Eagar Tuesday, 22 July 2008 at 13:15

This seems like a version of the infinite monkeys with typewriters with infinite time proposal. You seem to be asking, given enough time, will humans be able to do anything that does not include a violation of a law of physics?

I’ve no idea, but I’ve been writing about alternative methods of producing power since 1973, and I’m still waiting for the cheap, simple, reliable fuel cell I was told then was just around the corner.

cjm Tuesday, 22 July 2008 at 14:22

by definition, fuel cells are simple and reliable. cheap on the other hand…

the only problem with fuel cells is getting the fuel.

perhaps you are thinking of a device that will catalyze water into its constituent elements?

now that would be interesting

Steven Wood Tuesday, 22 July 2008 at 17:16

Intersting discussion, it does seem somewhat abstract since the technologies required for inter stellar travel are largely just ideas rather than actual techs. Comments such as “I don’t see why rocky planets are required. They can be built out of gas giants if needed.” are somewhat silly though as the current process for turning gas planets into rock ones seeded with heavy elements that could support life are never going to be reproducable by some humans on a space ship, I would agree that a suitable target would need to be indentified first.

cjm Tuesday, 22 July 2008 at 17:49

abstract? we are just trying to decide which prototype to launch first.

Harry Eagar Tuesday, 22 July 2008 at 19:31

As far as I know, the only consumer product using fuel cells is a nail gun, definitely not cheap.

But there are plenty of other applications where simple and reliable fuel cells ought to be a reasonable alternative. I don’t know why it’s not happening but it isn’t.

I think this gedankenexperiment needs to have a time limit, like something sooner than the heat death of the universe.

cjm Tuesday, 22 July 2008 at 21:47

fuel cells are readily available but they have limited applications (they use them in space). given that you have fuel to feed them, you can just as easily run an internal combustion engine powered generator (for less cost). maybe fuel cells have a better conversion rate than engines but they aren’t any kind of solution to our energy needs.

Annoying Old Guy Tuesday, 22 July 2008 at 22:48

My understanding is that fuel cells have maintenance problems. It’s no big deal in something like the Space Shuttle, because once it costs $500M to $800M per flight, swapping out fuel cells is not even noise on the budget. But for consumer items, the battery must last much longer. As cjm points out, cheap matters as much as the other properties.

A time limit? Well, the Sun will go red giant in 4 or 5 billion years, which is much sooner than the heat death of the universe, so we can take that. But it’s not an infinite monkey situation, there are many technophiles that don’t believe we will ever travel or colonize across interstellar distances (e.g., Steve Den Beste, with whom I have argued on precisely this topic). My point is that if you think humans can in time do these other things, you would seemed to be forced to believe in interstellar travel as well.

I don’t expect Skippers objection to make any difference, because by that time we will have colonized the rest of the solar system, and once you’ve done that you have a civilization that has no need of rocky planets, constructible or not.

the current process for turning gas planets into rock ones seeded with heavy elements that could support life are never going to be reproducable by some humans on a space ship

But quite doable by a civilization built by those humans on a space ship. Or perhaps just the space ship — it rather depends on just how advanced and nano-technological our manufacturing capabilities become.

David Cohen Wednesday, 23 July 2008 at 07:35

You still haven’t given a reason why anyone would want to do this (leaving aside the “assume the singularity” problem implicit in what you’ve said).

Annoying Old Guy Wednesday, 23 July 2008 at 09:27

Wealth, power, adventure, knowledge. The same reasons humans have ever colonized distant lands. Given that history, that humans have attempted to colonize basically every where they could travel, I think the burden should be on claiming why that would change once interstellar travel becomes feasible.

cjm Wednesday, 23 July 2008 at 09:33

dc: asks “why”?

answer: Why do birds suddenly appear Every time you are near? Just like me, they long to be Close to you.

Why do stars fall down from the sky Every time you walk by? Just like me, they long to be Close to you.

Harry Eagar Wednesday, 23 July 2008 at 11:27

All those reasons influenced the space rangers who wanted to go to the moon, but what influenced the guys who signed the checks was very earthly power politics, and when that incentive evaporated, the money stopped, too.

Annoying Old Guy Wednesday, 23 July 2008 at 11:42

They were just too early on the economic / technology curve, like the trans-American railroads, where all of the government sponsored ones went bankrupt. Private interests, however, made a success of it.

Similarly, we see private groups like Virgin Galactic and Bigelow Aerospace starting the colonization of low earth orbit. Lunar colonies will appear a few decades after that.

Harry Eagar Wednesday, 23 July 2008 at 16:10

I am not aware that any government-sponsored railroads in the US went bankrupt. I am not aware that there were any government-sponsored railroads, except in Alaska, which has been a big moneymaker, thank you very much.

And I am not aware that any private ones ‘made a success of it.’

In fact, I am not aware of a trans-America railroad in the US, although there is one in Canada.

What are you talking about?

David Cohen Wednesday, 23 July 2008 at 16:29

Wealth, power, adventure, knowledge.

I would argue for each of these — and certainly for wealth and power — the important point is not so much that you can go, but that you can come back and bring stuff back with you. None of your technologies would allow any body to come back, or to bring stuff back with them. Columbus, after all, was trying to get to the West Indies, which he knew existed and had stuff that, if he could get it back to Spain, would make him, his men and Ferdinand and Isabella insanely rich. No one’s going to go to the next star system over without knowing whether it has stuff that would make the round trip worth while, if they could get the stuff back, which they can’t.

It’s possible, of course, that “stuff” for interstellar purposes could be knowledge. That could be brought back, or even sent back by our hypothetical uploaded intelligences. But, again, we have no reason to believe that the destination has any knowledge that is worth money back here. There is knowledge for knowledge’s sake, but I doubt that any body is going to spend their life traveling to another system just to find out what’s there. Marco Pollo learned all about China, but that wasn’t actually useful to him until he returned to Venice and, again, he left knowing that China was there. Even the old standby, religion, which probably prompted more exploration than the four reasons you offer, depends upon the missionary knowing that the heathen is out there.

That leaves adventure. Again, I’m skeptical that any body is going to spend their life traveling to another star solely for adventure — and I don’t really see how sending an AI is adventure. We don’t usually think of JPL as the adventurous side of space exploration. But until it becomes possible for a small number of people to accomplish — that is, after the singularity that I don’t think is going to happen — I don’t see humanity spending years and vast resources on a project undertaken only for adventure.

David Cohen Wednesday, 23 July 2008 at 16:32

On the technical side, you have a habit of treating the intent as the deed. Virgin Galactic and Bigelow Aerospace are not “starting” the colonization of low Earth orbit, except for a very special value of “starting.” Similarly, we don’t know how to make rocks out of gases. We can’t even make the tools necessary to make the tools to do it economically. We have, at best, a theory.

Annoying Old Guy Wednesday, 23 July 2008 at 16:42

I meant trans-continental

The Great Northern was the first transcontinental built without public money and just a few land grants and was one of the few transcontinental railroads not to go bankrupt.

Harry Eagar Wednesday, 23 July 2008 at 18:39

Except that it wasn’t a transcontinental railroad. It connected with other roads that allowed you to cross the continent, but it was not transcontinental, the way the Canadian Pacific is.

Jay Gould spent his entire life trying to create a unified transcontinental line, and while the technology was there, and he operated under no governmental impediments, he couldn’t do it. Nor did anyone else.

Even today, there isn’t an American transcontinental railroad.

It’s a complicated matter, but there are probably good reasons, having to do with traffic hauls, why there isn’t a transcontinental road. Yet powerful men (Gould wasn’t the only one) yearned to put together a transcontinental road in the 19th c. with the same fervor and passion that the space rangers had in the 20th c.

David comes close to my favorite theme about exploration. The trick is not finding stuff. The trick is getting back home alive. Most of the great European explorers ended up in the stewpot, but they had the great success they did because they had a technology — the sailing gun platform — that let them shoot their way out of trouble most of the time. It’s almost certain that the Polynesians covered Cook’s territory before Cook did. But they could colonize only empty places; they could not colonize inhabited territory.

Annoying Old Guy Wednesday, 23 July 2008 at 19:38

the important point is not so much that you can go, but that you can come back and bring stuff back with you.

I would argue that it’s not. The important thing is to possess it and being the ruler of a star system beats being the CEO of a minor company in a developed system. Are you arguing that the colonists of North America all expected to return to England at some point, carrying their wealth and power back with them? Like the Pilgrims did? What if your wealth and power is a plantation or a railroad? How did people plan on getting that back?

Given the technology for interstellar travel, the stuff in other star systems could make one insanely rich without any need to return to one’s original star system.

we have no reason to believe that the destination has any knowledge that is worth money back here

What about the results of experiments in, say, extreme global warming? Stellar engineering? Neutron star exploration? I can think of all sorts of things the knowledge of which would be useful but one would never want to do in an inhabited star system.

religion, which probably prompted more exploration than the four reasons you offer, depends upon the missionary knowing that the heathen is out there

No, it can depend on wanting to escape persecution at home.

until it becomes possible for a small number of people to accomplish

I fully expect it to be come possible for a relatively small number of people to accomplish well before the “singularity”. Again, look at space flight or super computers. The economics of interstellar travel will go the same way.

But they could colonize only empty places; they could not colonize inhabited territory.

And you expect the rest of the galaxy to be inhabited territory?

you have a habit of treating the intent as the deed

No. I don’t ascribe any intent of that sort to those companies. But the East India Tea Company didn’t intend to create the British Empire either. I think you’re committing the error of presuming people accomplish only what they intend. As for starting colonization, we have these companies providing reliable transport, habitation, and profit. What else is required for colonization?

P.S. Gas giants have rocky cores, we could always just extract those.

David Cohen Wednesday, 23 July 2008 at 22:29

What I meant was that you treat the announcement that Virgin Galactic is trying to get a commercial trip to orbit going as the “start” of colonizing near Earth orbit. There’s a long way to go before we’re there.

To put this another way, sailing is a well-established technology, as is flying and nuclear fission power plants, but I’m not holding my breath waiting for small groups of private citizens — or most nation states, for that matter — to build their own nuclear aircraft carrier.

Again, your arguments boil down to, once someone’s done it and we know that it can be done, lots of people will do it. But I still don’t see any rational reason for anyone to go first.

Annoying Old Guy Wednesday, 23 July 2008 at 23:08

Virgin Galatic is partnering with Rutan, which means it’s more than an announcement, it’s backed by built and tested hardware. Bigelow has had a prototype in orbit for years. There’s also the Russian commercial space transport, which takes real money, uses real hardware, and has done real flights. When do you date the start of the conquest of flight, from Kitty Hawk or the DC-3?

once someone’s done it and we know that it can be done, lots of people will do it. But I still don’t see any rational reason for anyone to go first.

But when I give examples of some one going first, you dismiss that as well. I give examples of small groups of private citizens building and testing (not just announcing) space transports and space habitation, and you dismiss too. You sound like a variant of the proof that motion is impossible. There certainly is a long way to go, but every journey starts with a single step. You want to deny anyone would take that first step, and if they do it’s not really a step, and if it is it’s not really the start of the journey.

P.S. Small private groups build super tankers, deep water oil rigs, and floating space launch platforms. But none of those count, because they’re not aircraft carriers? I don’t quite see how that works.

Harry Eagar Thursday, 24 July 2008 at 03:31

No, I don’t expect most of the galaxy to be inhabited, I was going off at a tangent. But you suggest a relevant consideration: ‘How to serve mankind’

Ali Choudhury Thursday, 24 July 2008 at 04:55

What is in interstellar star systems that would make somebody insanely rich?

Annoying Old Guy Thursday, 24 July 2008 at 08:34

Mr. Eagar;

That’s actually the point of my previous post, which is that if there are ETI who plan to “serve man”, nothing we do is going to make any difference, so there’s no point in worrying about it.

Mr Choudhury;

Mass and energy. Raw materials, and plenty of space to build. The same stuff that made the USA insanely rich.

David Cohen Thursday, 24 July 2008 at 09:39

Man, are you jumping around here. My point wasn’t that we won’t colonize near Earth orbit, or even much of the rest of the solar system. I think that we will. My point is that you treat that colonization as a fait accompli just because a bunch of people have said that they’re going to do something that will ultimately be necessary for colonization. I have a lot of respect for Burt Rutan, but all he’s done so far in space is loft a reusable vehicle into (very) low Earth orbit for a brief time. What’s notable about doing what the USSR did 50 years ago is that it is private and relatively cheap. Again, the Russians are carrying space tourists for money, paid up front I’m sure.

The point about the aircraft carrier is precise, and your response helps make my point. The mere fact that something is possible, and will allow for knowledge, power, adventure, etc., isn’t enough for people to go out and do it. Super tankers, deep water oil rigs, and floating space launch platforms are different from aircraft carriers and deep space exploration because there is a calculable return and uncertainty (as opposed to risk) is minimal. Going to another star system is all about uncertainty.

As for immigrants to America, they all knew that America was there and, more or less, what the conditions were. Again, someone has to go first and has to have a reason to go. Also, it’s fairly late in American history before most immigrants didn’t think that they would ultimately go back home. The idea that the 5000 or so people in a generation ship or the AIs in a low mass ship are going to be rich and powerful within their new star system is bizarre. How’s that going to work? (Other than, “Hey, we own a star system. We must be rich and powerful. Please pass the Soylent Green.”)

cjm Thursday, 24 July 2008 at 09:56

perhaps there is an instinctual impulse to move out and keep moving. there is a symetry between the movement of galaxies away from their place of origin, and peoples moving away from their place of origin.

Annoying Old Guy Thursday, 24 July 2008 at 10:40

Mr. Cohen;

How is my about colonizing this star system a bogus “fait accompli” but your claim that we will not one? If the objection is just to the specific starting point, then fine. Branson, Rutan, and Bigelow are completely pointless endeavors guaranteed to fail and disappear from history. What I fail to see is how you can be confident that success will occur in that area without any one being first or succeeding in initial efforts. Won’t your objections here apply just as well to whoever is really the first?

Super tankers, deep water oil rigs, and floating space launch platforms are different from deep space exploration because there is a calculable return and uncertainty (as opposed to risk) is minimal

But aircraft carriers are a difference case because …? Private actors didn’t build ships of the line, but yet they managed to colonize North America. Why doesn’t your argument apply to them?

it’s fairly late in American history before most immigrants didn’t think that they would ultimately go back home

I have to disagree strongly with that. I would say that by the time of Plymouth rock, most immigrants were true immigrants who planned to stay.

The idea that the 5000 or so people in a generation ship or the AIs in a low mass ship are going to be rich and powerful within their new star system is bizarre. How’s that going to work?

The same way the USA became rich. Build industry to use the bountiful natural resources. Here’s a question for you — how much of the wealth in the USA was imported, and how much was built here?

David Cohen Thursday, 24 July 2008 at 11:20

You’re counting colonization of space as something that’s already been done, when in fact it’s something that’s barely been started. I think that it will happen because it satisfies the requirements I’ve set up for investment: there is the probability of satisfactory returns based on information available to us now, but it’s by no means a done deal.

Let’s try this a different way. All large human endeavors not taken on by government have to be approved by financiers. You have to show them how them giving you money now is going to result in your giving them more money later. There’s no way to make deep space exploration look like a paying investment. America, on the other hand, was very much sold as a paying investment. If they hadn’t been able to send stuff back to Europe, the colonies would never have been founded. 5000 people on a generation ship are not going to get rich selling each other stuff and, since they can’t send stuff back, they’re not going to get financing.

Annoying Old Guy Thursday, 24 July 2008 at 13:06

Where am I counting the colonization of space as something that’s already been done? Not if I think it’s “just starting” as in the comments. Not in the original post, which is of the form “if A, then B”. That does not pre-suppose A.

All large human endeavors not taken on by government have to be approved by financiers

We’ve diverged by the end of this sentence. Spruce Goose, Space Ship One, or heck a modern 747 converted for personal use from the point of view of anyone a couple of hundred years ago. Any of the large scale NGO activities (for example, the Gates Foundation has what, $50 billion?).

What financiers do you think paid for the Polynesian colonization of the Pacific? Or the original migration in to North America? Also, for a number of American colonists, the expeditions were paid for by the colonists, not the financiers.

Finally, I don’t see why the 5000 colonists (and their descendants) cannot, over time, get rich selling stuff to each other. How did we on Earth get rich without selling stuff to other star systems? Why won’t that work for the colonists?

Hey Skipper Thursday, 24 July 2008 at 13:30

We already know how [build rocky planets]. One can fuse the hydrogen and helium into rocky materials. Should I assume away that knowledge?

The we know, in outline, how it happens does not mean we know how to do it.

What you should not assume away, although you have done so, is that building rocky planets of sufficient size to retain a breathable atmosphere (or even to walk on) requires gravity attainable only in the presence of stellar masses, and a billion or so years.

Let me ask — how does your target acquisition problem prevent success in the mental download, strong AI, and space colony scenarios?

Presuming we cannot wish away the target acquisition problem, the MD/AI scenario amounts to nothing more than a series of stellar fly-bys until stumbling upon one with a habitable planet (rocky, sufficient gravity, breathable atmosphere, tolerable temperature ongoing vulcanism) — after all, what’s the point of stopping otherwise?

So, strictly speaking, nothing prevents that scenario. However, the results, and the incentive to engage upon it, is very dependent upon whether the density is sufficient to provide anything more than power-ball odd of detecting such a planet.

One cannot wish away the target acquisition problem. Sure, the sphere within which we can detect planets is growing, but it cannot grow without limit. If the rate of habitable planets within the GZ is one in 10,000 stars — a rate I think optimistic, but who knows? — then it is very unlikely that any inhabited planet will ever detect another habitable planet, and four orders of magnitude more unlikely that having found, and gotten to the first, a second will be detected.

Trajectory aggravates the acquisition problem. Let’s say some civilization heads thataway, and hopes for the best. Along the way, they detect a habitable planet, but it is 45 degrees away from velocity.

They will get to wave as it goes by, because there will be no changing direction.

Anyway, MD/AI runs aground — presuming insufficient density and acquisition range — simply because the exercise would be completely pointless. Kind of like burning piles of money: yes, we can, but why?

It defeats the SC scenario completely. Any SC capable of extremely long voyages must be extremely heavy. Heavy equals slow. Also, the inhabitants would have to realize that in order to stand a 50-50 chance of happening upon a habitable planet, they would have to make close passes by 5,000 stars. Since the volume within which the SC could pass is much smaller than the acquisition sphere, for almost all ships, the odds of finding another habitable planet ever are pretty damn small.

Do you have a cite for how stellar density affects planetary formation? Is that based on heavy elements requiring super novas?

No, I read it in a Scientific American article back when it was a reputable publication. I did stumble over a mention of it when looking for (and, oddly, failing to find this side of a subscription shield) stellar densities in Earth’s vicinity.

The reasoning, according to my foggy memory, is that the density of hydrogen is insufficient in the outer regions to produce enough stars large enough to then result in enough supernovae to leave behind enough heavy elements for subsequent planet formation.

Please define “habitable”. Do you mean descendants of our civilization can live there, or do you mean unmodified current humans without technology can live there?

I sort of restricted that above. Habitable means rocky planet with sufficient gravity and tolerable temperatures. Mars would qualify, Venus would not, and gas planets are off the table.

+++

I think it is entirely likely that the habitable planet density is so low that almost no civilizations will be able to acquire a suitable target, and almost none of those that do will find a third, etc.

I also think there is far too much hand waving about accelerating sufficient mass to sufficient speed (and, near as I can tell, you have to carry the mass you are going to use as propellant with you from the start, since acquiring it along the way will cost as much momentum as you can gain from it). Never mind stopping at the other end — note that probes we send to the outer planets are doomed to be flybys.

Consequently, there could easily be thousands of intelligent, thriving, civilizations in our galaxy alone.

All doomed to perpetual isolation.

And that doesn’t even begin to consider the problems David has raised.

cjm Thursday, 24 July 2008 at 13:32

the distant solar system is the egg and travelers to it are the seed — that’s reason enough to do it, and always has been.

Annoying Old Guy Thursday, 24 July 2008 at 14:11

Presuming we cannot wish away the target acquisition problem, the MD/AI scenario amounts to nothing more than a series of stellar fly-bys until stumbling upon one with a habitable planet (rocky, sufficient gravity, breathable atmosphere, tolerable temperature ongoing vulcanism) — after all, what’s the point of stopping otherwise?

Colonizing the star system. I keep repeating this, but you don’t seem to be catching it, that I am utterly unconvinced that what you call a habitable planet is in any way required for colonizing a star system in the MD/AI case. Seriously, why would an AI care about a breathable atmosphere? And in the SC case, your claim is that people who have lived for generations on an artificial habitat suddenly need a habitable planet to survive in another star system. Why? Why not, for instance, live on the space habitat and build more of those?

As for acceleration issues, forgive me if I take the word of professionals who do that sort of calculation for a living over yours. You might also keep in mind that one can always trade off time for acceleration, which is very easy to do for the MD/AI cases.

David Cohen Thursday, 24 July 2008 at 16:29

If you think that any of those examples, including Polynesian expansion, which is the only Earth-bound exploration that even comes close to what we’re talking about, didn’t have to be financially sound ex ante, then you’re wrong. All means need ends to justify them.

Your answer to why we don’t need planets in other solar systems is that we don’t even need planets here, given our colonization of the solar system. You treat colonization as a fait accompli, when we’ve barely begun and certainly haven’t come close to proving that we can colonize anything other than low Earth orbit and, possibly, the Moon.

Annoying Old Guy Thursday, 24 July 2008 at 16:38

If you think that any of those examples, including Polynesian expansion, which is the only Earth-bound exploration that even comes close to what we’re talking about, didn’t have to be financially sound ex ante, then you’re wrong. All means need ends to justify them.

You’re hopping from “financially sound” to “ends”. Do you mean that all ends are economic, then?

I treat colonization of the solar system not as a fait accompli, but as a premise. “If we colonize the solar system, then we’ll expand to other stars”. If I can’t assume a premise for the purposes of discussion, that makes discussion any hypothetical rather difficult. How, then, would you prefer I treat space colonization for the purposes of debating “if we have colonized the solar system, then we’ll expand to other stars”?

cjm Thursday, 24 July 2008 at 19:11

by my count this discussion has gone round the track at least three times. i call a tie.

David Cohen Thursday, 24 July 2008 at 19:18

The only premise you started with is that we could build ships that could go .03 C, or about 20 million miles/hour. I don’t think we can, but I accepted the premise. Basically, going that fast (and slowing down at the other end) would lock us into needing anti-matter and making our ship by sticking rocket engines onto an asteroid to provide reaction mass. The problem then becomes that we couldn’t possibly avoid (or even see) anything in our way and any collision with anything will risk devastating damage, so we also need force fields, which we’ll never have.

5000 people is enough so that you won’t be breeding idiots at the end of the voyage, but not enough to become rich selling each other things.

Finance is the science of whether the ends justify the means.

Annoying Old Guy Thursday, 24 July 2008 at 20:11

No, the 0.03c was my assumption. The development of the listed technologies were my premises. I am mystified as to what you thought those were, if not premises.

Why can’t 5,000 people get rich selling things to each other in the long term? You’re presuming breeding but no population increase?

P.S. I doubled checked on the numbers and you’re half right, as 0.03c depends on perfecting fusion propulsion but does not require anti-matter. Current technology (and I mean things that we have built already) gives about a 1/10th of that, 3 milli-lights, or roughtly 300 years per light year. Freeman Dyson designed a fusion bomb powered Orion style craft he claimed could hit the original 30 milli-light speed.

Peter Burnet Friday, 25 July 2008 at 05:36

Mass and energy. Raw materials, and plenty of space to build.

I dunno, AOG, you might want to work on that prospectus a bit. Is there anyway you can reduce that to gold and spices?

You are greatly exaggerating the exploration-for-exploration’s-sake factor in historical colonization, which is the exception in human history. I think “Here be Dragons” more accurately reflects the default position on the completely unknown. How many science fiction bestsellers feature the eternal quest for joint ventures with aliens in new zinc mines? David is surely right that most of it was financed by people looking, not just for short term wealth, but specific forms of it. Guys like Marco Polo and Columbus didn’t just hold out the promise of “all kinds of neat stuff”. Extraordinary let’s-start-anew exceptions like the Puritans stemmed from a revulsion to, and rejection of, that left behind, not to mention the imperative of avoiding the gallows. (Your 5000 colonists may end up all being moonbats from The Daily Kos, but wow, talk about a much cooler threat than moving to Canada for Hollywood stars terrified of yet another Republican victory!) Even there they knew they could breathe and had a vague idea of where they were going and how they would live. The Jesuits didn’t wander blindly around the new world trying to discover whether there were heathens or not, they knew there were.

Plus what about competition and defence? European explorations and colonizations were races grounded in fears of domination by enemies. How much British, French, Dutch and Portuguese exploration would have occurred without the awe and worry about all that Spanish gold? And in a modern context, would the American public have supported all that fantastically expensive lunar exploration if everyone hadn’t been so freaked out by sputniks?

And if you are right that the pure spirit of adventure and discovery is sufficient to carry us, why is no one trying to colonize the sea-beds? Plenty of crap down there.

Finally, nice try about Polynesia. I’d be the first to admit that if you can hold out the promise of picking fruit languidly under tropical breezes while basking in the attentions of uninhibited supple young maidens, you’re on your way.

Ali Choudhury Friday, 25 July 2008 at 06:21

Don’t we already have limitless energy in the form of nuclear power? By the time we get the tech required for interstellar exploration, we’ll probably be able to nano-engineer all the materials we need. As for space, we’d probably make self-sustaining orbital platforms instead of trying to reach far-too-distant habitable planets.

cjm Friday, 25 July 2008 at 10:52

i can prove aog’s thesis (exploration, always) in two words: second sons.

those at the lower levels of any society are always going to take a chance on a better life elsewhere.

how many people here are living near where they were born? i am in the same county; others?

Annoying Old Guy Friday, 25 July 2008 at 10:57

OK, let’s summarize —

For the cryo-revivification and nigh-immortality scenarios, Skipper’s targeting object to colonization might be valid. We simply don’t know enough about planetary formation to decide. They may require additional technologies (such as controlled fusion) to be viable. For travel, I think it’s still likely there would be visits (if only for some one to be “first”), but without colonization that’s likely to be isolated events. So I’ll mark those as “unproven”.

For the mental download / AI scenarios, I don’t see any valid objections. Such beings would have no need of Skipper-habitable planets and would be quite capable of waiting thousands of years for transit or building stuff in target systems. You can do some very amazing things with very simple technology if you can wait that long.

For the space colonization scenario, it plays out mostly like the MD/AI one.

You are greatly exaggerating the exploration-for-exploration’s-sake factor in historical colonization

I don’t think so. It may be an exception, but the exploration case requires only a minute fringe to take up the challenge. I think you may be underestimating the ennui of nigh-immortality.

But I expect most interstellar travel to be drive by the desire of the travelers to increase their wealth and power by claiming new resources, or the space to conduct activites that would not be permitted in an inhabited star system (such as biological / genetic experimentation).

Industrial anti-matter may be more like the CR/NI scenarios, in that while dramatically reducing travel time, it may not do much for colonization. So you’d see more one off visits, but not necessarily any permanent change without additional technologies.

in a modern context, would the American public have supported all that fantastically expensive lunar exploration if everyone hadn’t been so freaked out by sputniks?

Probably not, but so what? It’s not that expensive lunar exploration that’s going create a permanent expansion in to space. As noted, my model is Branson, Rutan, Bigelow, Paul Allen, John Carmack, not NASA.

Don’t we already have limitless energy in the form of nuclear power? By the time we get the tech required for interstellar exploration, we’ll probably be able to nano-engineer all the materials we need. As for space, we’d probably make self-sustaining orbital platforms instead of trying to reach far-too-distant habitable planets.

No, that’s hardly limitless. Long term we’ll need to go orbital solar or fusion (or both). And if you presume that level of nano-engineering, interstellar colonization looks even more feasible, since you can build just about anything as long as you have mass and energy, both of which are abundant in other star systems. No need to habitable planets. Self sustaining orbital platforms would make wonderful interstellar probes as well.

And that brings me back to what I think is the biggest root of disagreement, which is the view that interstellar colonization means creating duplicates of Earth. You all seem stuck on that, while I think it’s far more likely to be something like Ali’s “self sustaining orbital platforms” transported to another planet of whatever type, the precise nature of the planet being of little significance to the platforms.

cjm Friday, 25 July 2008 at 12:21

depth first search, or recursive exploration.

send out a billion probes and whichever ones get lucky report back (pop the stack) and that’s where you send your platforms. nature has addressed all these issues — god, the ultimate engineer.

David Cohen Friday, 25 July 2008 at 17:40

The problem here is that “report back” means several generations downstream. For those of us who are MD/AI skeptics, or just doubt that we’re going to invest the necessary resources to send a computer to go enjoy itself at our expense, there doesn’t seem to be anything in this for us.

Annoying Old Guy Friday, 25 July 2008 at 18:33

It’s not several generations in the NI/MD/AI scenarios. In the MD case, it’s the MDs who pay for the expedition, not those waiting in the originating star system. I’ll have to think about the AI case. I was presuming that the AIs would be citizens, in which case it’s just the MD case in a different guise. If not, you have to presume that no philanthropic group would ever want to achieve legendary status by being the first to explore (via AI) another star system.

Hey Skipper Friday, 25 July 2008 at 21:21

Now it is time to turn this question on its head.

It is easy to string plausible ballpark numbers together — number of stars in our Galaxy, fraction of those with habitable planets, etc — to come up with some plausible number of intelligent species in our galaxy.

So long as the number is bigger than one, and we aren’t first, then the question becomes:

What key technology/ies did not get developed to prevent that species from having already colonized the galaxy?

++++

I’m with David on the whole MD/AI thing. I think MD is out of the question, and there will be no intelligence that doesn’t occupy a recursive life form.

Annoying Old Guy Friday, 25 July 2008 at 21:32

Because I don’t see any significant show stoppers on the way to colonizing our entire solar system (and apparently neither do you or Mr. Cohen), and thence other stars, my view is that the expected number of tool using sentient species per galaxy is less than one.

cjm Friday, 25 July 2008 at 22:23

wouldn’t “aliens” that arrived here and turned out to be genetic duplicates (astro sapiens?) be proof of a god?

Hey Skipper Saturday, 26 July 2008 at 12:11

cjm:

Since there are so many ways functional DNA can be built — all life on Earth has chosen just one — simply replicating that would be proof enough for me.

AOG:

I don’t think there are any technical show stoppers to colonizing Mars, or maybe some of Saturn and Jupiter’s largest moons.

However, I do think there are at least a couple reasons there could be many sentient species per galaxy, and no colonization.

Presuming MD/AI is either impossible or, as David has noted, makes the whole enterprise pointless, then that leaves the SC scenario, which I think mandates the existence of a habitable planet within acquisition range absolutely essential. Which leads to why I consider target acquisition to be the most fundamental, while also being the most fundamentally limited, capability.

Unfortunately, a viable SC would so heavy that the reaction mass required to accelerate the thing to anything like a sufficient speed would spiral out of control. And that is even before getting to another problem David mentioned above: Hitting something. How long is a mean free path in space? (by mean free path, I mean how far would an SC sized object be able to travel before hitting something big enough to cause crippling damage, which means the MFP is inversely proportional to speed). If that MFP is much shorter than the anticipated distance to a habitable planet, then the enterprise is doomed before weighing anchor.

But that still leaves the question of whether can results in will. If humans master fusion to the point where it can be used to power a space craft, then insufficient energy (hence resources of all kinds) will never be a reason to leave Earth for even Mars, never mind anywhere else.

Nor, considering the demographics that inexorably accompany post-agrarian economies, will population.

There are at least 200E9 stars in our galaxy. Lets say a third of them are in the GZ. And of those, one in 100,000 have life sustaining planets, and of those, one in 100,000 develop sentient life. That still makes for 66 sentient species in the galaxy.

Making one further assumption, all planets capable of sustaining life will life, then the numbers get ugly no matter which way you go. Make the ratio of life sustaining planets 1:10000, then there could be 330 sentient species in the galaxy. Yet one in 10,000 planets capable of sustaining life means something on the order of 300 light years between life sustaining planets (GZ 20,000 to 40,000 light years from the galactic core, average thickness in GZ zone 3,000 light years, 33E9 stars in GZ, 1:10,000 with life sustaining planets).

I’ll bet that is at least an order of magnitude greater greater than fundamental limits on target acquisition will allow.

If the problem is constrained to requiring life sustaining planets — I see at least as many reasons to insist upon as to disregard them — and an SC scenario, then colonizing space may be so close to impossible as to render the distinction without difference.

There could be a hundred, or even thousands, of intelligent species in the Milky Way, all condemned to wondering whether they are the only ones.

Hey Skipper Saturday, 26 July 2008 at 12:24

BTW, here is a link to Galactic Habitable Zone (aka GZ).

Annoying Old Guy Saturday, 26 July 2008 at 12:29

Presuming MD/AI is either impossible or, as David has noted, makes the whole enterprise pointless

Mr. Cohen did not note that, he asserted that. I counter asserted. Naturally, I find my assertion more compelling. Therefore I in no way concede that MD/AI “makes the whole enterprise pointless”. In fact, I think either scenario makes the whole enterprise inevitable.

then that leaves the SC scenario, which I think mandates the existence of a habitable planet within acquisition range absolutely essential.

Because …? You keep harping on this, but you never argue for it, you only assert. You accept the plausiblity of a civilization capable of prospering on Jovian moons, but then claim that, for some completely unstated reason, it would require a Skipper-habitable planet.

P.S. We know Jovians are common, and can resumably presume that therefore Jovian moons are common as well.

Annoying Old Guy Saturday, 26 July 2008 at 12:34

Skipper;

You seem to think I am disregarding the GHZ via ignorance. Not at all. I disregard it because

  1. I am utterly unconvinced as to the necessity of Skipper-habitable planets for interstellar travel or colonization
  2. The science behind the GHZ, as noted up front in the very article you cite, is very conjectural. I actually laughed at the comment that a planet needs to further from the galatic center to avoid “comets and asteroids”, which are stellar phenomenon, not galactic. Although clearly Earth’s distance from the core protected it from such things, right?
Hey Skipper Saturday, 26 July 2008 at 14:27

You seem to think I am disregarding the GHZ via ignorance.

I wasn’t implying ignorance, I thought I remembered you asking for a link to it, which I stumbled over looking for something else. It is worth nothing, tough, that the GHZ is favorable to your argument, and unfavorable to mine.

Mr. Cohen did not note that, he asserted that. I counter asserted.

Inartful phrasing on my part, apologies.

Because …? You keep harping on this, but you never argue [the requirement for a habitable plane], you only assert.

True enough, I have only asserted. My argument is similar to why I think AI will ultimately be impossible: an essential ingredient of intelligence is reproducing life. (Which, I suppose, is only an assertion once removed).

Similarly, the essential ingredient for a SC is mass, and lots of it. So much mass, in fact that there will be no means to even move a SC beyond the gravitational well of the host star, never mind make it to the next one. Additionally, even standing a chance of doing so requires mastering fusion somewhere other than the interior of a star. If it turns out an essential ingredient of fusion is gravity, and lots of it, then what is possible in principle will forever be impossible in fact.

I’m even more skeptical (again with the assertions, I know) of anti-matter.

So, in order for a SC to be a viable solution, it must be capable of a completely self-supported voyage of indeterminate length.

I’m simply calling shenanigans: something big enough to do that will be both hugely expensive and bog slow.

In turn, your that a civilization with all the resources it needs and and whose population worry is far more likely to be of the under- rather than over- variety inevitably undertake such a task itself is an unsubstantiated assertion.

Which is why I turned the question on its head: which is more likely, that despite 33 billion stars (in even the most restricted GHZ case) there is only one sentient species, or that the many hurdles involved mean that the sentient species there are shall forever be separated?

Each of those hurdles is joined by an “and”; all of those hurdles have a probability less than one, and all it takes is one with a probability of zero to put paid to the whole enterprise.

Annoying Old Guy Sunday, 27 July 2008 at 09:26

So much mass, in fact that there will be no means to even move a SC beyond the gravitational well of the host star

“So much air resistance, there will be no means to move faster than the sound barrier”. Hmmm.

But we already know how to build engines to do it, using fission power, it’s simply a matter of scaling up. In the end, it’s purely a matter of energy costs and you all keep telling me we’ll have “unlimited” energy in the future.

your [assertion] that a civilization with all the resources it needs and and whose population worry is far more likely to be of the under- rather than over- variety inevitably undertake such a task itself is an unsubstantiated assertion

You guys are still not reading what I’m writing. That’s the unitary fallacy again. In addition to being stuck on habitable planets, you’re stuck on the idea that any such expedition requires the general approval of an entire civilization. My assertion works as long as there is one group, ever, who decides to do that. You have to assert that not only would the civilization as a whole not do it, but no subgroup ever would either. Yes, in the end it’s dueling assertions, but I think betting that no group of humans would ever do something you consider wasteful and stupid is the wrong way to bet.

P.S. If the civilization is suffering under population, where do they get the people to colonize the local star system?

Peter Burnet Sunday, 27 July 2008 at 10:03

Skipper:

which is more likely, that despite 33 billion stars…

Given the complete lack of evidence either way and the fantastic statistical improbability of both, what sense does it make to talk of likelihood or probability for either?

Hey Skipper Sunday, 27 July 2008 at 16:40

Peter:

Given the complete lack of evidence either way and the fantastic statistical improbability of both …

There is not a complete lack of evidence. The probability is 1 that there is at least one sentient species in the universe. What’s more, should you consider the Neanderthals both intelligent and a separate species, then the chances are 1 that there have been at least two. Porpoises have a larger brain to body mass ratio than humans; they could well be sentient, even if their environment will prevent them ever attaining technology. Looking at the longer term, evolution seems to have at least one kind of arrow: greater brain complexity. Given life and time enough, intelligence, on Earth at least, seems a sure bet.

With at least 33 billion candidate stars — by the most conservative estimate; if the GHZ thesis is wrong, the number could be ten times that — and nothing at all unusual about ours, it seems to me to be singularly unlikely assumption that ours is the only sentient, technology capable species in the galaxy. Or, at the very least, asserting such requires some explaining as to why that should be so.

AOG:

“So much air resistance, there will be no means to move faster than the sound barrier”. Hmmm.

That is not a fair analogy to what I said. More fair would be: “Airline travel will never be economically viable faster than Mach 0.92” I didn’t say we couldn’t put something outside the solar system — after all, that has already been done twice — but that getting something the mass of a SC capable of an indefinite length voyage will either be impossible, or be so slow as the render the enterprise completely pointless.

You say that we already achieve the propulsion required. I don’t agree. The most optimistic specific impulse for a fission motor is less than four orders of magnitude larger than that for existing conventional rockets.

How heavy will such an SC have to be? The mass of 10 aircraft carriers? 100? 1000? No, I haven’t broken out my HP 35s (HP is selling new versions of it, BTW) to do any math. Notionally, though, I don’t see any reason why an SC shouldn’t be six orders of magnitude larger than the pioneer spacecraft. And that is even before getting to that pesky v^2 term in the whole kinetic energy thing. Keeping in mind, of course, that the SC has to more than twice the fuel required to attain terminal velocity.

You guys are still not reading what I’m writing. That’s the unitary fallacy again. In addition to being stuck on habitable planets, you’re stuck on the idea that any such expedition requires the general approval of an entire civilization.

Discarding the MD/AI scenario leaves only SCs. A SC would be so expensive, and the return on investment so delayed (if it is there at all) that I don’t see why one should assume a group large enough to have sufficient resources would find it worth doing.

Yes, I am stuck on habitable (or at least rocky) planets, because I don’t see any reason to go to all the effort to orbit a gas giant when there are plenty of gas giants to be had right here at home.

Heck, even here on Earth there are all kinds of habitable places — most of the Aleutian islands, for starters — that no one goes to the bother to colonize. Too hard, isn’t worth it.

P.S. If the civilization is suffering under population, where do they get the people to colonize the local star system?

I don’t think humans will colonize our own star system. If humans master sufficient technology to make interstellar travel even remotely doable, there will be no wanting for anything. Nor will there be any population pressure. The human population will almost certainly peak within your lifetime, and there is plenty of reason to believe that three hundred years out it will be no more than half its present number.

BTW, all the above still leaves the mean free path problem completely untouched.

Annoying Old Guy Sunday, 27 July 2008 at 19:33

Skipper;

Go look up “ion engine” on that same site. Power that with fission. The fission rockets you cite are useful for high thrust applications, which this would not be. And suppose the SC is 6 orders of magnitude larger than an aircraft carrier. So? I also think that, if we do colonize the solar system (that being the premise of the scenario), SC will, like everything, get absolutely and relatively cheaper. And the group that finds it worth while is the same group that’s on the SC. The real return is access to a much larger set of resources in the other star system.

there are plenty of gas giants to be had right here at home

For now. There used to be endless stretches of land available on Earth as well. Eventually it fills up.

even here on Earth there are all kinds of habitable places — most of the Aleutian islands, for starters — that no one goes to the bother to colonize

Because colonizing such places doesn’t give you access to enormous and valuable resources. Put a few tens of billions of barrels of petroleum deposits under those islands and it would be a very different story.

P.S. The mean free path problem disappears under a certain velocity, because either impact doesn’t hurt or there’s plenty of time to dodge. It’s not clear an SC will exceed that velocity.

Hey Skipper Sunday, 27 July 2008 at 21:05

There used to be endless stretches of land available on Earth as well. Eventually it fills up.

This is a straight question: How much traveling have you done in the US?

There is a reason I ask. West of the Mississippi, population density plummets. I once drove from Boise to Las Vegas, with most of the trip at night. South of Ely, I went for two hours without seeing a man made light of any kind. If you were to travel down that particular meridian, from North Pole to South, the most astonishing thing would be how empty the landscape is. I regularly fly from Indy to Anchorage. Western Canada is empty. In that region, I can probably see (on a clear day) with some detail for 90 miles in any direction (both sides, and aft thanks to the forward motion of the airplane) for a couple hours without seeing any sign of human habitation whatsoever. No roads. No power lines. No towns. Just miles and miles of miles and miles. Once in awhile I end up on the Russian route to Seoul, which puts the airplane east of the Kamchatka peninsula, flying down the western edge of Siberia. It makes western Canada look like a thriving metropolis.

Russia spans 11 time zones, has about half the population of the US, and is depopulating. Australia is empty. New Zealand nearly so.

Alaska has a bunch of oil under its northern coast. There are only enough people to get it out and no more.

Which leads to the next point. Within the next fifty years, the Petroleum Age will end. Unless we are goint to get re-acquainted with Malthus in the worst kind of way, there will be a combination of other-energy supplies and reducing activity-energy intensity to the point where civilization will be able to continue essentially indefinitely.

Simultaneously, the demographic transition will guarantee that an ever greater part of the world will be worried about decreasing population.

Given all the trend lines, I think it is difficult to predict a long term that is troubled by either excess population or insufficient resources.

In other words, in 100 years, there will be no human material need that can’t be completely and indefinitely satisfied here on Earth.

Which means there will be no resource on Mars or Jupiter’s moons that will be worth digging up and transporting to Earth. To put it more bluntly, in the kind of civilization capable of traveling to the stars, what resource would be both enormous and valuable enough to be worth dragging back to Earth? If the Apollo missions had carried nothing but diamonds back to Earth, in monetary terms it still would have been a losing proposition.

So, presuming the MD/AI scenario is a non-starter, how much mass would be required for an SC capable of an indefinite duration voyage.

Then, how fast could the SC go, with the requirement that it be able to stop at the other end, and not be destroyed along the way by the MFP problem, which I suspect is the most restrictive (I must credit David Cohen here. I have never heard it mentioned elsewhere, and didn’t think of it until he broached the problem.)

After that is the sine qua non: How many people, who know they are destined for a foreign shore they shall never reach, will sign up for such a journey? (I’ll ignore for the moment why anyone would put a dime into such a venture.)

Annoying Old Guy Sunday, 27 July 2008 at 21:37

If you want to argue against space colonies, that’s fine, but for this post it’s a premise. And if people exist who are willing to go out for extra-terrestial resources, I see no reason for them to stop at one star system. You could start a post on the subject over at your weblog :-).

You may not see any people, but all of that land is owned. You could not, for instance, just set up a farm, factory, or toxic waste dump.

How many people, who know they are destined for a foreign shore they shall never reach, will sign up for such a journey? (I’ll ignore for the moment why anyone would put a dime into such a venture.)

If you’re going to go on such a journey, why wouldn’t you put all your money in to it? What else would you do with it? You should also consider that the lifestyle on the journey wouldn’t be all that different from life before.

P.S. The collision problem for interstellar flight is noted in many SF stories. Generally via mumbo-jumbo about “meteor lasers” or “repelling fields”, but that’s still an acknowlegement of the problem. Heck, even Star Trek claimed that the grid work you see on the outside of the Enterprise was part of system to deal with the problem. Revelation Space uses lasers and ice armor to handle it. I know Robert Forward addressed it in a more serious way when doing designs for interstellar probes. You don’t see the MFP discussed directly because it’s assumed to be enough smaller than distance to other stars that some kind of collision prevention system is required.

Hey Skipper Monday, 28 July 2008 at 13:52

If you want to argue against space colonies, that’s fine, but for this post it’s a premise.

A premise which is, at least IMHO, very questionable. I could premise a loan application on my winning the lottery, but I shouldn’t be surprised if my banker decided to back my premise with the full faith and credit of his bank.

The recent mortgage schlamozzle notwithstanding.

Kind of reminds me of Red Flag debriefs. The Air-Air guys always had infinite range, 100% PK, instant air re-loadable missiles. Accept their premise as given, and you might as well head for the bar.

And if people exist who are willing to go out for extra-terrestial resources …

Which are, or might plausibly be?

You may not see any people, but all of that land is owned. You could not, for instance, just set up a farm, factory, or toxic waste dump.

That’s as may be. My point is solely that Earth is not suffering from overpopulation now, and will most likely be worrying about its precise opposite long before interstellar travel becomes remotely possible under even the most optimistic premises.

If you’re going to go on such a journey, why wouldn’t you put all your money in to it?

I’m not sure, but I think that is called begging the question, which is this: How many people would sign up for a journey to a foreign shore they are destined to never get remotely close to, never mind reach?

You should also consider that the lifestyle on the journey wouldn’t be all that different from life before.

Huh? I did one of the simpler life activities yesterday: I went for a 30 mile bike ride up a river valley near my house. What plausible SC won’t be so space constrained as to make life nothing other than the Axiom? Take a cruise sometime, and imagine that going on forever.

++++

Humble apologies if I derailed this thread.

Annoying Old Guy Monday, 28 July 2008 at 14:47

I think it rather limits possible discussions if every premise involved has to plausible to everyone participating. The real point was to look at developments that most technophiles presume are inevitable, and see what consequences for interstellar follow.

I did one of the simpler life activities yesterday: I went for a 30 mile bike ride up a river valley near my house. What plausible SC won’t be so space constrained as to make life nothing other than the Axiom?

Irrelevant, since the people on the SC have already accepted that lifestyle. If you are already living on an SC, traveling to another star isn’t going to change your lifestyle much. If you’re already on the Axiom, does it matter if it orbits Jupiter or heads off to Alpha Centauri?

Hey Skipper Tuesday, 29 July 2008 at 14:40

Irrelevant, since the people on the SC have already accepted that lifestyle.

Yes, for the people born onto the SC. But the problem is how do you get people on earth (particularly women), for whom nothing is pushing them off Earth, to sign up for a voyage to a foreign shore none will reach? Even granting the technophiles every bit of their presumptive case, no plausible SC would be anything more than a shallow, constrained simulacrum of Earth.

In the absence of push coming to shove, why would anyone embark on such a voyage?

(And I’m still curious as to what resources there might be in the rest of the solar system so valuable to a society capable of getting them that would be so valuable as to make the effort worth the candle.)

Annoying Old Guy Tuesday, 29 July 2008 at 17:12

Why would you need anyone from Earth? The whole point of an SC is that you’ve got everything you need — the technology, the people, the society, no need of a habitable planet — all set to go. As I noted originally, it’s a multi-generation starship minus the engine. It’s also a particular favorite of the technophiles, making a great premise.

Hey Skipper Tuesday, 29 July 2008 at 17:53

Ok, I guess I am really confused.

Acknowledging the moment that such a thing as an interstellar SC is feasible, then clearly SC’s within the solar system are also feasible.

But that still leaves the question: why would anyone sign up to be on a SC even within the solar system, particularly women?

Regardless of what subsequent generations might be inclined to do, knowing nothing else, getting the first generation on board seems particularly counter intuitive.

Annoying Old Guy Tuesday, 29 July 2008 at 19:53

It’s the other way around

Premise
Space colonies are successful.
Conclusion
Interstellar colonization based on multi-generational ships is feasible.

You may think that space colonies are implausible, but most technophiles are of the opposite opinion and it is those people that I am targeting. To reiterate, I selected this premise precisely because it subsumes basically all of the issues with multi-generational starships and is a common belief among technophiles. The question is, if someone believes in the nigh inevitability of space colonies, for whatever reason or however implausible, could he then reasonably object to the feasibility of interstellar colonization? I am looking for arguments to use against people who already believe one of the premises. In fact, I know people who believe in multiple of them who still dismiss interstellar travel. I think that’s bogus.

If your objection is that none of these are likely to happen, fine. I think you’re wrong, but it’s a defensible position.

BUT — here’s what I was hoping people would dig in to — if you believe that the resolution of the Fermi Paradox is that interstellar travel / colonization is just too hard, what other technologies and achievements must you believe are not possible? Does considering that list cause you to rethink your view on the Fermi Paradox?

Hey Skipper Thursday, 31 July 2008 at 13:03

It’s the other way around.

I meant it the same way as your premise - conclusion: if one accepts the greater problem as solved, then clearly the lesser problem must have been solved along the way.

You may think that space colonies are implausible, but most technophiles are of the opposite opinion and it is those people that I am targeting.

I don’t think they are implausible; quite the opposite. However, while granting that, there is no way an SC capable of an indefinite voyage — a requirement driven by the target acquisition problem — will be anything other than very, very heavy. Which, of course, means slow. So, while I think such an SC plausible, I think a top end more than .003c is out of the question.

if you believe that the resolution of the Fermi Paradox is that interstellar travel / colonization is just too hard, what other technologies and achievements must you believe are not possible?

Since, IMHO, interstellar travel is possible, but at speeds nowhere close to relativistic, the problem isn’t technical, so much as existential. Can and will are two different things.

Right now, we have the technical means to colonize at least the ocean’s continental shelves. Yet we do not.

What is in it for the first generation? They will go, effectively, nowhere. And they will have to endure a a significantly constrained life in order to do so, unless …

… unless the SC is the size of Earth.

We are already on an indefinite voyage SC that is taking a bloody long time to go nowhere in particular. What possible reason could there be to embark upon a shallow simulacrum to do precisely the same thing?

Similarly, solar system tourism might be plausible, but solar system colonization, never. What possible point could there be? (Unnamed resources don’t count).

++++

Another reason for skepticism is what appears to be a pretty ironclad law of diminishing returns in material endeavors (information processing & transmission seem excepted).

150 years ago, the average speed for human terrestrial travel was a walk. Now it is, oh, 60 mph. Where it has been for a several decades, and where it will remain.

Air travel, same. 40 mph 105 years ago, it will never exceed .92M.

Sea travel, same.

I expect space travel to do the same thing. There may be yet a propulsion technologies that will increase specific impulse by 6 orders of magnitude, but that still won’t be enough to overcome diminishing returns leagues shy of speed sufficient to overcome the existential problem.

Clovis Wednesday, 02 October 2013 at 21:34

It is kind of silly to post here so long after the post died away, but I will anyway. My opinion will then be registered for future generations of space travelers :-)

One thing AOG did not consider, and that would solve most of the problems here mentioned, is another kinf of hypothetical futuristic technology: engineering of spacetime.

In principle an advanced enough civilization would be able to build up wormholes and warp-drive spacetimes that would allow such travels in… well, seconds, really.

The recipe is that you need to obtain negative energy densities - something we know how to do in the microscopic world - and grow them up to macroscopic lenghts, in such a controlled way that it changes the topology of the spacetime (in the wormhole case) or creates a “spacetime bubble” (warp-drive spacetime) that can effectively “travel faster than light” - it does not travel faster than light really, in the sense that light rays travelling trhough the bubble are always the fastest thing possible. It looks to travel faster than light when compared to light travelling in regions other than the warp-drive bubble.

Details apart, those solutions are known possible solutions to Einstein’s equations in General Relativity, and the main challenge really rests in creating huge amounts of negative energy densities and controlling it with presently unimaginable precision. (There are many other details that I will ignore here to be brief).

So, cutting to interestellar travel, you would have the following options: with the warpdrive you would be able to travel at velocities greater than any direct-line-without-warp-drive would allow (again, it may look anti-intuitive, but no violation of relativity is involved - we are using relativity in fact all the time to understand it all). Suppose now you arrivied at your destination, e.g. Alpha Centauri, after months or years travelling. If you had also started the creation of your wormhole spacetime back there in earth, and completes it now in your final destination, you will effectively create a spacetime bridge that connects those two points. The next traveller may enter a portal somewhere in Earth and get out in Alpha Centauri, almsot instantaneouly (again, no violation of relativity involved!).

Well, I could expand a lot the explanation to give full details, but I will stop here now. This is the best way I can think of for future space exploration.

Annoying Old Guy Wednesday, 02 October 2013 at 23:20

It’s not clear to me that those physics will work. I was trying to limit it to technologies most people agree will work eventually, precisely to not make my argument depend on disputable advances.

Here’s the question, though — suppose I make such a tunnel. I then move one end of it relativistically around for a while, then bring it back next to the other end. Since the two ends have experienced different amounts of local time (e.g., the twin paradox), do I not have a tunnel that that is a (almost) closed timelike curve?

Clovis Thursday, 03 October 2013 at 08:09

AOG,

Congratulations, you’ve just concluded the same thing that took, to many smart people, a PhD to understand :-)

It is not an almost closed timelike curve, it is really a closed one. IOW, wormholes possibly give rise to time machines. Which, in general relativity, is no big surprise, since we know many other solutions who lead to that too. They are time machines of a restricted sort though (compared to those other solutions), but anyway…

Sincerely, AOG, your scheme of technologies above is really too much restricted for real space exploration. It would, in the best case scenarios, lead to effective colonization only of systems a few dozen years light away, imposing yet decades to exchange of the simplest messages. It is no way to go IMHO.

We need to be bold and imagine how far our theories allow us to go, and I’ve just given you the state of the art of possibilities within the best of our knowledge.

We already do know how to induce negative energy density states even in macroscopic conditions: the space between two almost perfect plates in a Casimir experiment in vaccuum, in principle, has its electromagnetic field in a negative energy state. We do not know how to “extract and mold” this kind of energy, but it is not forbidden by first principles.

We also have strong reasons to believe - although, at this point, no one really knows - that the main component of the Universe, Dark Energy, which is far more abundant than anything else in the Cosmos, is possibly a form of energy behaving like a fluid of negative energy density. Is it a far shot to think of advanced civilizations molding that energy for their own use? Sure, but it is again not forbidden by any physical principle we know of.

All in all, if you ask yourself if any other being could be exploring a Universe so vast, different from what we knew of, say, 40 years ago, the answer is that there are physical principles that indeed allow for it. IMO, it is less of a stretch, for us now, to think of a civilization making use of this in a remote future, than it was for anyone a thousand years ago to imagine Man walking the Moon.

Annoying Old Guy Thursday, 03 October 2013 at 12:05

If you believe that, wouldn’t you also have to believe that we’re basically alone in the Universe? Otherwise, aliens would already be here.

Clovis Thursday, 03 October 2013 at 13:34

AOG,

You assume many things behind this thought.

There is no reason we should assume our evolution has been atypically slower than most other possible civilizations, so it well may be a combination of (i) low rates of success of civilizations to achieve that high technological standards; (ii) typical times for that achievement still higher than typical age of galaxies; (iii) the scales of distance it allows for travel still below galactic distance (or at least local clusters of galaxies). And that need to be combined yet with rate of formation (hence finding) of life in the universe, whose estimatives vary in orders of magnitude.

In short, I think my belief above implies life is not densely distributed, which is not a far stretch anyway.

Annoying Old Guy Thursday, 03 October 2013 at 16:22

There is no reason we should assume our evolution has been atypically slower than most other possible civilizations

Certainly, but there are many stars a billion or two years older than ours. Given similar time scales to sentience, one would expect such civilizations to be a billion or two years ahead of us. Also, our time scale is so large that even tiny percentage differences shift control of the galaxy from one species to another. Even at speeds based on current known technologies, colonizing a galaxy only takes 10-20 megayears.

It’s a good point about inter-galactic travel, but that still puts a limit of roughly one sentient species per galaxy. By “alone” I meant no other sentient species, not lifelessness.

Clovis Thursday, 03 October 2013 at 18:31

AOG,

You are right in your comments, but they are only a tiny part of all things you need to consider in such a calculation.

You may want to read this one to see how people have been doing it in greater detail:

http://www.sciencemag.org/content/303/5654/59.short (The full article is behind a paywall - if you want it, I can email it to you)

If you take the total number of stars that could be candidate for life (any life), within their assumptions, it would be less than 10%. Imagine now a tiny percentage of that being sentient life, divide it by the galaxy distances - you will see that the chance of them hitting us is pretty small.

In a completely different line, you need to take in account that, being those aliens sentients, it means they have their own will. How to account for the possibility that they would want to visit us or make contact?

We have a few dozen tribes here in Brazil, in deep Amazon, with which nowadays we purposedly avoid contact.

Annoying Old Guy Thursday, 03 October 2013 at 20:04

Clovis;

Those calculations are irrelevant. The point is that a single species from a single star could, in 10-20 megayears, using known technology, colonize every habitable planet in the galaxy. Which, naturally, would include ours.

Clovis Friday, 04 October 2013 at 09:05

AOG,

I disagree. There is a lot of unknown technology in your assumptions to conclude that.

That unknowns also lead us to the question of resources. It may well be that, upon achieving the necessary technology, it takes too much resources for them to establish millions and millions of missions to every place they know of. Accounting for that difficulties can easily lead to the time of diffusion to be in the order of 1 Billion years. Which, if you had followed my link, would be near the typical maximum you would expect other stars with life conditions to be older than the sun.

So you argue “look, our scale is so small, and it is easy to find a star 1 billion years older!”, but it is easily the time scale for spreading too, and now if you take account of all the other difficulties in distributions for life formation, it is easy to conclude that the non-presence of ETs is not necessarily a signal of our loneliness.

Annoying Old Guy Friday, 04 October 2013 at 09:31

It may well be that, upon achieving the necessary technology, it takes too much resources for them to establish millions and millions of missions to every place they know of.

But they don’t. The spread is by diffusion, so any particular star system sends out only a few expeditions. Those form colonies, which send out further expeditions. As long as, on average, each colonized star system sends out more than one expedition, you get this result. I don’t see why this would require the time scale to be on the order of 1000 megayears. I have to say that any one addressing this problem by assuming all colonization flights start from the home world and no colony creates daughter colonies is clearly not thinking very clearly about the issue.

But then I can ask about Von Neumann probes. What stops those from covering the galaxy? Skipper doesn’t buy that because he think true artificial intelligence isn’t possible.

Clovis Friday, 04 October 2013 at 10:49

AOG,

Including all the unknowns, and still the fact that a spread by diffusion also means more time needed for each part be reached, i.e. the time for individual colonization and further construction of news missions… all in all, I really do not think that factor 50 over your estimation is that much, with or without Von Neumann probes.

BTW, still on alternative lines, we also do not know if they may be around and just did not want to show themselves explicitly. What makes you so sure I am not an alien? :-)

Annoying Old Guy Friday, 04 October 2013 at 13:23

Clovis;

Because assuming the aliens have spread through the galaxy, especially on your time scale, the odds of them arriving recently enough for humans to exist at that time is, IMHO, vanishingly small. Not impossible, I suppose, but effectively negligible.

Clovis Wednesday, 23 October 2013 at 06:48

BTW, Popular Science has a new piece about one of the technologies I was talking about:

http://www.popsci.com/technology/article/2013-03/faster-light-drive?src=SOC&dom=fb

Post a comment