Was there enough time for a planet like earth to exist long before earth?

[SkepticLance]

Sayonara.

Could you inform me on one point, please?

You talk of Dyson bubbles instead of spheres. I assume from that, that we are talking about a very thin wall. If that is true, from whence comes the gravity?

 

Clearly, a ringworld can provide gravity from spinning. A sphere or bubble cannot. I assumed sufficient thickess in the walls for sheer mass to provide gravity. If the walls are thin, how does that work?

 

Incidentally, a thick walled sphere would require enormous mass to be brought in from other stellar systems.

 

Sayonara said :

 

The other function is to provide living space which can be expanded into and added to as and when required.

 

True. However, converting the mass of a stellar system into spinning cylinders will provide even more living space. Unless, of course, you have only enough mass to make a bubble. In that case, refer to query above.

 

I invite you to try living on any given Kuiper Belt object for a week. Your kit bag will include antiseptic cream, 2l bottle of water, packet of tomato seeds, bag of air.

 

Please explain the relevence of this comment.

 

 

but in terms of resources per unit population supported you will be using more matter and energy than you would with a Dyson Bubble.

 

Actually, the opposite is true. A Dyson sphere or bubble cannot trap all the energy emitted. It MUST vent most of it out to space, or else it would become a furnace. A cylinder using fusion power can save energy by generating only what is needed. A star is an uncontrolled source of energy. A fusion generator is under your control. I am, of course, assuming a very advanced technology that can tap all the fuel reserves of a star, and maybe this is pushing our speculation too far. However, I think a Dyson sphere/bubble is a pretty big push already.

 

Because you don't really need to. And even if you continued to build and breed quite rapidly, under those conditions your expansion into the local systems could progress at a very leisurely pace without sacrificing any comfort.

 

Here we are back to matters of motivation. Again, I have to say that you may be right if the number of alien species is small. However, if there are enormous numbers of species, some will be expansionist in motive. That becomes highly probable statistically. Imagine our own species in your scenario, living on a Dyson bubble. Do you really think there would be nobody wanting to shoot off into unknown territory to explore and colonise?

[Sayonara]

Sayonara.

Could you inform me on one point' date=' please?

You talk of Dyson bubbles instead of spheres. I assume from that, that we are talking about a very thin wall. If that is true, from whence comes the gravity?[/quote']

No. I said "A Dyson Bubble is a Dyson Swarm that uses "statite" islands to prevent orbital conflicts".

 

Imagine millions of "islands" orbiting the Sun, in a bubble or shell SHAPE.

 

The solid shell idea is replete with problems, such as the centre of mass difficulty, and the "where the hell is the water and soil coming from then, eh?" problem. Which is why it is considered the most conjectural Dyson scenario.

 

 

Clearly, a ringworld can provide gravity from spinning. A sphere or bubble cannot.

It can, but this is beside the point, because I am not proposing solid shapes.

 

 

Incidentally, a thick walled sphere would require enormous mass to be brought in from other stellar systems.

There is enough mass in the system for a shell of 600Kg/m². Exactly how useful this would be is not an issue since I am discussing the bubble model, which is an extension of Dyson's original swarm model, and not the solid shell that science fiction has turned it into.

 

 

True. However, converting the mass of a stellar system into spinning cylinders will provide even more living space. Unless, of course, you have only enough mass to make a bubble. In that case, refer to query above.

Using the same amount of mass, you will have less land space with cylinders than you would with the islands in the bubble. You also have greater complexity of design, which uses mass.

 

However at this point we are essentially describing the same basic idea.

 

 

Please explain the relevence of this comment.

The mass of most objects in the solar system is only useful if you turn it into something bigger.

 

 

Actually, the opposite is true. A Dyson sphere or bubble cannot trap all the energy emitted.

Well, theoretically it could trap it all, because a race sufficiently advanced enough to build such a contraption might be able to convert the energy into matter, which could even be part of the ongoing construction process.

 

Anyway, you missed my point entirely. O'Neill Cylinders or their equivalent use more matter and energy in construction and maintenance than any given Dyson scenario, assuming equal maximum supported populations.

 

It MUST vent most of it out to space, or else it would become a furnace.

I fail to see how this is bad.

 

 

A cylinder using fusion power can save energy by generating only what is needed.

This introduction of fusion power is somewhat random and spurious. And I fail to see why it can't be exploited by a race that has constructed a Dyson bubble.

 

 

A star is an uncontrolled source of energy.

That is a matter of technological ability. You said yourself a star could be taken apart and used more efficiently, which I read as being quite definitely "controlled".

 

 

A fusion generator is under your control. I am, of course, assuming a very advanced technology that can tap all the fuel reserves of a star, and maybe this is pushing our speculation too far. However, I think a Dyson sphere/bubble is a pretty big push already.

Yes, because you don't know what it is.

 

 

Here we are back to matters of motivation.

Yes, aren't we just? Matters of motivation which, at every turn, you are extrapolating from unsteady assumptions.

 

 

Again, I have to say that you may be right if the number of alien species is small. However, if there are enormous numbers of species, some will be expansionist in motive. That becomes highly probable statistically.

We are back at the numbers gap, which you have not addressed despite it being the crux of the issue.

 

 

Imagine our own species in your scenario, living on a Dyson bubble. Do you really think there would be nobody wanting to shoot off into unknown territory to explore and colonise?

Maybe some, but that doesn't mean they will want to dominate the galaxy. Perhaps we have been so busy building our bubble that we haven't even bothered to develop interstellar technology yet.

 

Life is good here - we have all the energy we can eat, 3 million islands in the network already, and enough resources in the system to build many millions more, a job which the robots are already getting on with.

 

Our race can exist here for the next eight billion years, steadily expanding, and when our star begins to swell we will move to the next one, because we knew it was coming and devised propulsion systems for the entire flotilla.

 

Why bother to go off looking for intense difficulty, when there is so much space?

[SkepticLance]

Sayonara.

You still have not answered the gravity query. If your Dyson bubble is actually made up of quadrillions of small islands in space, like a swarm of asteroids, then they will have insufficient gravity. They could not, for example, hold an atmosphere. It takes a much larger mass to retain air. For example; Earth's moon could hold an atmosphere for about one million years. By then it would have all bled into space, and your swarm of objects would have to be much smaller than the moon, assuming 3 million or more objects from the mass in a stellar system.

 

If your 'bubble' was built, logically, the islands in space would actually be the spinning cylinders I suggested. The people would live inside the cylinders, and sunlight would be collected on the outside. This is just a very minor extension of what I said a long time ago. That humans in space would build lots of habitats/cities to live in. Your Dyson bubble is simply a hell of a lot of those habitats, at one astronomical unit from the sun.

 

If we are, in fact, building spinning cylinders, why not go the one logical step further, and install fusion power plants? Then they would be independent of the need to stay the correct distance from the sun. They could travel to any distance from the sun, or even to other stellar systems.

[Sayonara]

Either technology will do.

 

However if you are travelling to another star system you need a reason why, which (other than the death of the local star) has never been given - only assumed.

 

It's fun going in circles like this.

[Edtharan]

I think the Dyson Swarm (a better and more accurate term than bubble or sphere) would still suffer from instability as individual statlites effect each other. Of course with smaller objects it would be easier to addjust their positions. Therefore it would be posible to stabilise the swarm, but at a cost. The fuel to do so must come from somewhere.

 

Without using any physics breaking technology (sci-fi stuff), we know of no way that a swarm could maintain its positions for long periods of time wihtout having to loose mass (ie rocket engines or ion engines) to do so.

 

the best solution to this that I can come up with is that they produce matter/antimatter from the energy of the sun and use this as rocket fuel to maintain their positions. The "Rockets" would be angled so as to anhilate the matter antimatter outside the habitat (to eliminate any damage to other habitats by stray antimatter) after the thrust is gained from their acceleration. this process is highly innefficient, but it could be maintained as long as sufficent power is available (wether or not they would be able to produce enough matter and antimatter so as to provide enough thrust is another question altogether).

[Sayonara]

The bubble concept is an extension of the swarm concept, with the key difference that solar sails provide the thrust.

[SkepticLance]

Sayonara.

In earlier postings I have suggested two reasons why a species will move away from its sun.

1. The explorer instinct. If it is Earth humans, then we know from observation that this affects a minority of people, but very strongly. There would always be a certain number of people who would fight for the chance to go elsewhere. Some alien species would be similar.

2. Population pressure. If the species involved continues to grow in number (and evolutionary principles suggests that a desire for more than 2 offspring would be a selective advantage), then even a Dyson swarm would eventually be unable to support all of them.

 

And again, I have to say, that if the number of alien species is very large, then at least one will act in just that way.

 

Also, Sayonara, you have not responded to my quibble about gravity. Your Dyson swarm would have to be spinning structures, with the people inside, since there would be too lttle gravity to hold an atmosphere outside.

 

Edtharan, I think you are right in your suggestion that reaction mass would be needed. Correct me if I am wrong, but I cannot see how a solar sail could be used to move inwards towards the sun, which would, in theory, be needed as often as a move outwards.

[swansont]

I actually think that a dyson sphere (or shell or ringworld) would be highly unstable.

 

 

...

 

Second: As I said a circular orbit is unstable' date=' and if you did make a solid ring or sphere then if there is any distrubance to the sphere then one side would get closer and the other side would get further. Gravity would amplify this and the closer side woudl get closer because gravity is stronger and the further side would get further away because the gravity is weaker. This would result in the rapid infall of one side of the sphere into the parent star.

[/quote']

 

Not for a sphere. A sphere is a Gaussian surface, so there is no gravity inside of it due to the sphere (as we have recently discussed in the "hole through the earth" thread). And Newton's third law applies: if the sphere doesn't exert a force on the star, the star does not exert a force on the sphere.

[SkepticLance]

Swansont.

Thanks for that. Belatedly, I realised the same thing, but too late for my posting. That is good information.

 

Thinking about sayonara's swarm...

The swarm MUST be made up of spinning cylinders or similar. Atmosphere could not be kept on the outer side of moonlets or the equivalent of moonlets. Thus, the swarm will end up as cylindrical habitats/cities, or some similar concept. They would not form a sphere as such due to orbital problems. Instead, we would see a whole lot of 'ringworlds', each made up of perhaps a million habitat/cities. The ringworlds would all have to be a slightly different distance from the centre star. Thus, the description of this set up as a bubble or sphere is, in fact, incorrect.

 

If the population continues to grow, eventually even that system will lack capacity for all the individuals. The logical next step is to equip habitats with fusion power plants so they can move further from the central sun, and be independent on stellar power.

 

Having got to that stage, there is nothing to stop them travelling inter-stellar.

[Edtharan]

Edtharan, I think you are right in your suggestion that reaction mass would be needed. Correct me if I am wrong, but I cannot see how a solar sail could be used to move inwards towards the sun, which would, in theory, be needed as often as a move outwards.

Actually a solar sail could be used to move to a closer orbit. It is a bit like a sailboat tacking into the wind.

 

First you would have to use the solar wind to slow down your orbit. This would cause it to decay, bringing you in closer to the star. Then you would have to use it again to speed your self up to stabilise your orbit (as you are closer you need a higher orbital velocity).

 

A solar sail spaceship would not just be going directly away from the star. It would have some angular velocity (ie: it would orbit). By using the sail to adjust this angual velocity, you will be able to control your orbit.

 

But I think for habitats, a solar sail would not be effective. The pressure of the solar wind is small. A habitat would be like a small moon or large asteroid (Think of the Rama space ship in the book "Rendvous with Rama"). A Solar Sail would have to be enormous to have any apreciable effect on a object of that mass.

 

You could build a habitat with thin walls to reduce the weight, but you still have the mass of the population and the walls would still need to be thick enough to stop radiation (both from your star and from cosmic rays too).

 

The explorer instinct. If it is Earth humans, then we know from observation that this affects a minority of people, but very strongly. There would always be a certain number of people who would fight for the chance to go elsewhere. Some alien species would be similar.

I think the exploer instinc would come about with any race that develops technology. To develop technology, a species needs to have curiosity, without this there is no drive to discover new technologies to improve what you have. This curiosity would lead to exploration.

[lucaspa]

I must be very poor at explaining things' date=' since there seems to be a lot of misunderstanding. Let me try again.

 

First, my whole point is that there cannot be, or have been, more than a few technologically advanced alien species in our galaxy. If the total number is less than (say) 100, over the past 2 billion years, then my logic breaks down. However, if the number is large, then probability requires certain outcomes. For example, some of the species will have expanding populations.[/quote']

 

1. We understand quite well. We are just refuting your logic and conclusions.

 

2. We are arguing that it is not inevitable that any of the species will have expanding populations -- at least expanding so that they do interstellar travel at less than lightspeed.

 

For one thing, in order to do interstellar travel at 0.1c, they must have a means of controlling population growth. Which means no expaning population.

 

Second, the rules of economics say that increasing wealth -- which is produced by a technologically advanced civilization -- results in control of population growth.

 

Conclusion: your assertion and assumption that there must be a species with population growth such that it feels compelled to do interstellar travel is invalid.

 

Second : arguing by analogy with Earth life. These intelligences must be enormously varied. On earth we have apes, cetaceans, parrots and crows, cephalopods, carnivores, and elephants - all with quite substantial levels of intelligence. They vary enormously in body form. It seems logical to assume equal variability in psychology. This variability must apply to alien intelligences also. This means, if there are very large numbers of such species, we cannot argue on the basis of psychology.

 

But we can argue on the basis of economics and physics. Those are the same everywhere.

 

Some of the species must, by probability, have the mental attributes for successful expansion. Some will have the mental attributes leading to explosive population growth. Some will have both.

 

So? They are still up against the same economic and physical constraints and, if they don't change, they will die.

 

For instance, if they can't control their population growth, then they will exhaust the resources of their planet before they can even get into space. That may yet happen to humans. Then they go back to a perpetual state of savagery as they fight for scarce resources. Building a generation ship is a huge investment of resources. It requires a lot of spare wealth.

 

See the book The Mote in God's Eye for the consequences of the inability to control population growth and being limited to lightspeed.

 

Third. Travel through the galaxy. According to my Scientific American article, humans will have the ability to travel between stellar systems within 1000 years, at speeds of up to 0.1 to 0.2 c. Since star systems have existed in the Milky Way for 6 to 8 billion years, and IF large numbers of aliens exist and have existed, then the same probability argument strongly suggests that aliens with exploding populations, with the ability to successfully expand would have spread through the galaxy a long time ago.

 

Actually, stars have existed in the Milky way for 10 billion years. But there is another hidden assumption here: the elements available to planets of first generation stars. Our ability is predicated on heavy metals. First generation stars and star systems are metal poor. So they don't have the basic material necessary to make the equipment necessary.

 

Four. Yes, I believe the logical place for most of this population will be in space cities. However, if the population pressure is high enough, they will also colonise every planet they can find.

 

Well, we are arguing that "if". You haven't addressed those arguments against your "if".

 

Remember that, on Earth, the tendency for every successful species is population growth. Very basic and important principles of biological evolution drive every successful species to gain the ability and tendency to grow its population.

 

This is so completely wrong! Successful species are actually in balance with numbers. Population remains constant. It is the competition among the individuals for scarce resources that is the basis for natural selection. Why are there scarce resources? Because more are born than the environment can support. In cases where population is not controlled -- like some deer populations on islands where there are no predators -- then there is a boom and bust cycle. Population rapidly increases until food is exhausted, then 99% of the population starves. And the cycle starts again.

 

Humans are atypical. We have been able, thru technology, to expand resources faster than population. But you notice that this isn't the case everywhere, and lots of people starve today in various parts of the world.

 

So, you are basing your argument on false premises.

 

Five. Leaving remains. Look at what we already have as fossils. Stromatolite fossils (cyanobacteria) from 3.5 billion years ago. Jellyfish leaving impressions in mud from 700 million years ago. Billions of shells, and bones from all ages of life. Almost anything can form a long lived fossil if conditions are right (such as falling in soft mud).

 

Have you read or heard about all the gaps in the fossil record? Yes, we do have fossils from 3.8 billion years ago -- in one small location. Do you think that was the ONLY place life was on earth? But we don't have any fossils from anywhere else, do we?

 

Do we anything like a complete evolutionary sequence from species to species for ALL species on the planet? NO! We have such a sequence for a few of the billions of species on the planet -- more than enough to show evolution happened and to falsify creationism. But not nearly enough to say that the fossil record is anywhere complete.

 

I find it impossible to believe that any alien species could live on Earth and not leave traces. Where is our alien coke bottle?

 

Probably not successfully colonized. After all, if that happened, they'd still be here, wouldn't they? Of course, the colonization could have been unsuccessful. Like so many human colonies down thru the ages. In that case, the coke bottle is buried in sediments under the sea, or under the land, or has degraded. After all, if it fell into a river, grinding against rocks would eventually (in a few thousand years) reduce the bottle to glass dust. And how would we find it?

 

Or even if it was buried, what happens to the bottle when it is compressed as the sediments form sedimentary rock? Fossils are there because they are rock themselves. But a bottle isn't. Does it break? If so, then as the sediments compress, you get that grinding action again.

 

Lots of reasons we haven't found a coke bottle, or anything else, from a visit or failed colony that happened millions of years ago. Many are the same reasons we haven't found fossils of primitive bats.

 

I gave you the reasons before. You ignore them.

 

All you can show is that earth has not been successfully colonized such that the alien species is still here.

 

All this logic falls apart if the number of aliens is small. However, if the number is massive, then at least one species must have come to Earth, colonised, and left traces.

[lucaspa]

Sayonara.

In earlier postings I have suggested two reasons why a species will move away from its sun.

1. The explorer instinct. If it is Earth humans' date=' then we know from observation that this affects a minority of people, but very strongly. There would always be a certain number of people who would fight for the chance to go elsewhere. Some alien species would be similar.[/quote']

 

But you need many more than a small minority. After all, you need to get the wealth necessary to build a generation ship. Not to mention all the R and D to get to the point where you can build a ship. It's a lot of wealth. Humans have a very difficult time getting the wealth together just to get back to the moon.

 

2. Population pressure. If the species involved continues to grow in number (and evolutionary principles suggests that a desire for more than 2 offspring would be a selective advantage), then even a Dyson swarm would eventually be unable to support all of them.

 

Not always. Remember, it is number of surviving offspring. With modern technology, you only need 2 (or 1) to be fairly sure that one grows to adulthood and has kids.

 

And don't forget the wealth necessary to support them. As individuals get wealthier, kids cost more. So, the cost of children is such that a couple can only afford two, if they are to raise them in such that they have a chance to do well and reproduce.

 

And again, I have to say, that if the number of alien species is very large, then at least one will act in just that way.

 

No, that's your assertion. You are saying that, by chance, one will act this way. But we are saying that there are non-chance factors that would squelch the behavior.

 

Edtharan, I think you are right in your suggestion that reaction mass would be needed. Correct me if I am wrong, but I cannot see how a solar sail could be used to move inwards towards the sun, which would, in theory, be needed as often as a move outwards.

 

You use your speed to move toward the sun and use the light from the target sun to brake. You may also be able to tack a solar sail, like you tack a sailboat to move into the wind.

[lucaspa]

I think the Dyson Swarm (a better and more accurate term than bubble or sphere) would still suffer from instability as individual statlites effect each other.

 

There are 2 separate ideas: a Dyson Swarm and a Dyson Sphere or shell. A Dyson Sphere is a hollow sphere at earths orbit, with the inner habitable side facing the sun. You can calculate the amount of living space this provides and it is basically larger than billions of habitable planets.

 

This is NOT Dyson's original concept. The Dyson Swarm is closer to that.

 

http://en.wikipedia.org/wiki/Dyson_sphere

 

Of course with smaller objects it would be easier to addjust their positions. Therefore it would be posible to stabilise the swarm, but at a cost. The fuel to do so must come from somewhere.

 

Without using any physics breaking technology (sci-fi stuff), we know of no way that a swarm could maintain its positions for long periods of time wihtout having to loose mass (ie rocket engines or ion engines) to do so.

 

Not really. What you get is a series of habitats in rings at slightly different angles to the ecliptic and slightly different distances from the sun. See the article. Thus, you don't have interference from one ring to another, but the total effect is to completely block the light from the sun, as well as have an enormous amount of living space.

[SkepticLance]

Edtharan.

Much of your reasoning on the population growth question is based on an "All or Nothing" logic. That is, you suggest that EITHER

- The population growth is totally controlled, so that no expansion is needed

OR

- Population growth is uncontrolled and will expand until disastrous collapse.

 

Now, bear in mind that we are talking about intelligent and technologically advanced beings. An intermediate state can be achieved. If the aliens know thay have to control their numbers, but also have the desire to have more than two offspring per two parents, then a compromise condition can be organised. That is, population control is used with reluctance when needed. Population growth is eagerly embraced when possible. Such a state would render your reasoning invalid.

 

Lucaspa said :

 

After all, you need to get the wealth necessary to build a generation ship. Not to mention all the R and D to get to the point where you can build a ship.

 

We have already got past this point in discussion. I was arguing about what is likely to ahppen AFTER the aliens had achieved a Dyson swarm. The habitat now already exists.

 

And don't forget the wealth necessary to support them. As individuals get wealthier, kids cost more. So, the cost of children is such that a couple can only afford two, if they are to raise them in such that they have a chance to do well and reproduce.

 

This is somewhat unrealistic. You only need to look around you. People do not always decide on numbers of kids by careful logical reasoning. The final numbers are likely to be the result of emotions, not logic. Your faulty logic implies that very wealthy people will have more children. In fact, on average, poor people have more children. If we look at third world nations, and their fertility, you will find it inversely correlates EXACTLY with access to contraception. When people have ready access to contraception, numbers of offspring per couple drop, to western nation levels. Thus, it is not wealth that determines numbers of children.

 

 

You may also be able to tack a solar sail, like you tack a sailboat to move into the wind.

 

That much I know for sure is not true. It is possible that a solar sail may be tacked, but only by a mechanism totally different to a yacht moving through water. I speak as a yachtie. It is only with the use of a keel, centreboard, leeboard or similar that a water yacht can tack. That device is needed to prevent sideways slippage. A solar sail vehicle travels in vacuum, and cannot have a keel or equivalent.

 

Lucaspa said :

 

Actually, stars have existed in the Milky way for 10 billion years. But there is another hidden assumption here: the elements available to planets of first generation stars. Our ability is predicated on heavy metals. First generation stars and star systems are metal poor. So they don't have the basic material necessary to make the equipment necessary.

 

Correct. However, when I talk about 6 to 8 billion year old stars, I am talking only about third generation stellar systems. Roughly 10% of the Milky Way galaxy is third generation stars at least 6 billion years old. Any intelligent species that developed on these systems is likely to have a 2 billion plus head start on Earth.

 

This is so completely wrong! Successful species are actually in balance with numbers. Population remains constant.

 

There is always some population loss, and this is generally quite large. If a population stays at a relatively stable level, it is due to the unbiquitous tendency for the population to grow. In other words, more than two births per pair of parents, to permit compensation for the high death rate. As soon as a species develops to the point where it reduces its own mortality, this drives population growth, which is thus the 'natural' state.

 

Have you read or heard about all the gaps in the fossil record? Yes, we do have fossils from 3.8 billion years ago -- in one small location. Do you think that was the ONLY place life was on earth? But we don't have any fossils from anywhere else, do we?

 

Again, faulty logic. It is true that the numbers of fossils reduce dramatically pre-Cambrian (older than 600 million years). But this is not due to the age of the rocks so much as due to the fact that hard structures were uncommon in living things at that early stage. The oldest 'fossils' are 3.8 billion year old hydrocarbon traces in some Canadian rocks. At that point in the history of Earth life, only very primitive, almost non-life, was likely to exist. Thus no true fossil. The oldest hard fossils are some stromatolite fossils from Western Australia at 3.6 billion years. However, even this is tricky since the hard parts are simply sand grains cemented together over the bacterial colony. Thus, these fossils are controversial. Once living things began forming shells etc, the fossil density dramatically increased. In the 500 to 1000 million age group, a number of fossils have formed from impressions in fine mudstone. eg jellyfish. However, without hard parts, such fossils are rare.

 

Any alien species living on Earth would have left hard structures. Thus, they would have left traces.

[swansont]

Lucaspa said :

And don't forget the wealth necessary to support them. As individuals get wealthier' date=' kids cost more. So, the cost of children is such that a couple can only afford two, if they are to raise them in such that they have a chance to do well and reproduce. [/i']

 

This is somewhat unrealistic. You only need to look around you. People do not always decide on numbers of kids by careful logical reasoning. The final numbers are likely to be the result of emotions, not logic. Your faulty logic implies that very wealthy people will have more children. In fact, on average, poor people have more children. If we look at third world nations, and their fertility, you will find it inversely correlates EXACTLY with access to contraception. When people have ready access to contraception, numbers of offspring per couple drop, to western nation levels. Thus, it is not wealth that determines numbers of children.

 

 

You may also be able to tack a solar sail, like you tack a sailboat to move into the wind.

 

That much I know for sure is not true. It is possible that a solar sail may be tacked, but only by a mechanism totally different to a yacht moving through water. I speak as a yachtie. It is only with the use of a keel, centreboard, leeboard or similar that a water yacht can tack. That device is needed to prevent sideways slippage. A solar sail vehicle travels in vacuum, and cannot have a keel or equivalent.

...

 

Have you read or heard about all the gaps in the fossil record? Yes, we do have fossils from 3.8 billion years ago -- in one small location. Do you think that was the ONLY place life was on earth? But we don't have any fossils from anywhere else, do we?

 

Again, faulty logic. It is true that the numbers of fossils reduce dramatically pre-Cambrian (older than 600 million years). But this is not due to the age of the rocks so much as due to the fact that hard structures were uncommon in living things at that early stage. The oldest 'fossils' are 3.8 billion year old hydrocarbon traces in some Canadian rocks. At that point in the history of Earth life, only very primitive, almost non-life, was likely to exist. Thus no true fossil. The oldest hard fossils are some stromatolite fossils from Western Australia at 3.6 billion years. However, even this is tricky since the hard parts are simply sand grains cemented together over the bacterial colony. Thus, these fossils are controversial. Once living things began forming shells etc, the fossil density dramatically increased. In the 500 to 1000 million age group, a number of fossils have formed from impressions in fine mudstone. eg jellyfish. However, without hard parts, such fossils are rare.

 

Any alien species living on Earth would have left hard structures. Thus, they would have left traces.

 

 

lucaspa's point about children was that reproduction rates correlate inversely with wealth. You were arguing the same thing.

 

A solar sail used near a massive body has the countering force of gravity, which could act like a keel. Radiation pressure isn't the only force on the craft.

 

Your argument about fossils is flawed. You are looking at the total number, but that's not the equivalent of finding a particular one. How many fossils of humans do we have from 4 million years ago? Just a few, and they are only found in certain sections of Africa. How many T-rex fossils are there? A few dozen, and only in North America. How many of these individuals lived over the course of a million years or two or three? What if the alien artifacts, if they existed, were left in an area that has been covered with sediment and/or subducted into the mantle?

[lucaspa]

Edtharan.

Much of your reasoning on the population growth question is based on an "All or Nothing" logic. That is' date=' you suggest that EITHER

- The population growth is totally controlled, so that no expansion is needed

OR

- Population growth is uncontrolled and will expand until disastrous collapse.

 

Now, bear in mind that we are talking about intelligent and technologically advanced beings. An intermediate state can be achieved. If the aliens know thay have to control their numbers, but also have the desire to have more than two offspring per two parents, then a compromise condition can be organised. That is, population control is used with reluctance when needed. Population growth is eagerly embraced when possible. Such a state would render your reasoning invalid.[/quote']

 

No, such a state renders YOUR reasoning invalid. In order to have continuous interstellar expansion, numbers must be uncontrolled. If numbers CAN be controlled, then they will be at the point BEFORE the numbers are such that they have to send excess population off on generation ships.

 

Lucaspa said :

 

After all, you need to get the wealth necessary to build a generation ship. Not to mention all the R and D to get to the point where you can build a ship.

 

We have already got past this point in discussion. I was arguing about what is likely to ahppen AFTER the aliens had achieved a Dyson swarm. The habitat now already exists.

 

Dyson swarm habitats are NOT generation ships. They are habitats in stable orbit around their sun. And such a swarm provides a lot more living space than any new planet around another star. So, if a species has a Dyson swarm, it has no motivation to go colonizing other stars.

 

Generation ships pose different problems. Dyson swarm does not need large amounts of reaction mass -- a generation ship does. A Dyson swarm has cleared out inconvenient debris within the solar system such that they don't have to worry about collisions. A generation ship traveling at 0.1c has to worry about collisions. Even a dust particle at that speed would do enormous harm. So either the ship has to be very massively armored (with an increase in reaction mass needed) or have some way of deflecting interstellar pebbles and dust.

 

And don't forget the wealth necessary to support them. As individuals get wealthier, kids cost more. So, the cost of children is such that a couple can only afford two, if they are to raise them in such that they have a chance to do well and reproduce.

 

This is somewhat unrealistic. You only need to look around you. People do not always decide on numbers of kids by careful logical reasoning. The final numbers are likely to be the result of emotions, not logic. Your faulty logic implies that very wealthy people will have more children. In fact, on average, poor people have more children.

 

Now I know you aren't reading the posts correctly. Look again at what I wrote. I said wealthy individuals have fewer children. Wealth itself is a form of birth control. Why? Because wealthy people can only afford a few children -- each child costs more. Instead of 2 or more kids per room, each kid gets his/her own room, own clothes (not hand-me-downs), own car, private schools, etc. That adds a lot to the cost of each child.

 

Studies done in cultures without birth control still shows an inverse relationship between wealth and number of children. Increase wealth, decrease the number of kids. You said as much.

 

So, in our discussion, you posit an alien species technologically advanced enough to build generation ships. Then you also postulate that such a species would have to do interstellar colonization because of population pressure. But those 2 things are contradictory. Technological advancement means increased wealth. Increased wealth means decreased birth rate. Decreased birth rate means no population pressure. And there goes your motive for interstellar travel.

 

Also, remember that, if you have a generation ship traveling at only 0.1c, then inhabitants of the ship MUST have birth control. So that means the species has birth control at home too. As you noted, access to birth control means drastically decreased birth rates. And there goes your motivation for interstellar travel.

 

The only way you can have population pressure is if there is NO WAY to control birth rate. Like the Moties in Mote in God's Eye. But if that situation prevails, then you have a boom and bust cycle where civilization collapses before it is able to accumulate the spare wealth to build a generation ship.

 

 

However, when I talk about 6 to 8 billion year old stars, I am talking only about third generation stellar systems. Roughly 10% of the Milky Way galaxy is third generation stars at least 6 billion years old.

 

Our sun is 3rd generation. It is only 4.7 billion years old. So, any stars older than 6 billion years are second generation stars and are still deficient in heavy elements. I question your assumption of a 2 billion year head start.

 

There could still be a 60 million year head start. After all, if the asteroid had not hit 65 million years ago, it is possible that one of the dino species would have evolved sentience and tool use. But not a 2 billion year head start.

 

There is always some population loss, and this is generally quite large. If a population stays at a relatively stable level, it is due to the unbiquitous tendency for the population to grow. In other words, more than two births per pair of parents, to permit compensation for the high death rate. As soon as a species develops to the point where it reduces its own mortality, this drives population growth, which is thus the 'natural' state.

 

Population growth is NOT the "natural" state. Population stability is the "natural" state, as scarce resources limit the population. Yes, more individuals are born than the environment can support. But the environment always eliminates the surplus such that population stays constant.

 

In order to "reduce its own mortality", resources have to increase faster than population. This can happen as a population moves into a new geographical area. Humans have increased resources by technology -- particularly farming and herding. But even here there is an ultimate limit due to the finite space on a planet.

 

BUT, as we have seen, if a species is intelligent to have that technology, then we have 2 new factors to limit population growth: economics and technology in the form of birth control.

 

In order to have continuous population growth, you have to postulate a species that cannot choose to limit growth -- whose biology is so weird that they absolutely MUST reproduce. This contradicts your postulate at the beginning of this post: "That is, population control is used with reluctance when needed. Population growth is eagerly embraced when possible."

 

It is true that the numbers of fossils reduce dramatically pre-Cambrian (older than 600 million years). But this is not due to the age of the rocks so much as due to the fact that hard structures were uncommon in living things at that early stage.

 

You missed the point. As you noted, we only have limited areas where pre-Cambrian rock is available. You mention the Canada rocks of 3.8 billion years ago. Where else do we have 3.8 billion year old rock at the surface? NOWHERE. Where else do we have 3.5 billion year old rock at the surface? NOWHERE. So this is why you only have evidence from 2 limited locations.

 

So, what if your coke bottle from colonization were in Michigan? Here is a map of the Michigan area: http://www.earthscape.org/t2/scr01/scr01ac.html

Notice how little of the region is pre-Cambrian. If the aliens were at the site of present-day Milwaukee, no pre-Cambrian rock is exposed: the bottle is still buried.

 

What's worse, much of the rock that is exposed is metamorphic or igneous. The processes that formed this rock would destroy any artifacts that might have been present. This is from Alabama: "The few rocks of that age that do exist have been highly altered through metamorphism and contain no recognizable fossils. " http://www.paleoportal.org/time_space/state.php?name=Alabama

 

See what the site says about Mesozoic rocks: "Most Mesozoic rocks in Alabama are deeply buried beneath younger sediments"

 

Of course, creationist sources have often claimed to have technological artifacts dating long before the evolution of humans. They use the artifacts as evidence against evolution. However, you could easily view them are remaining artifacts of alien visitation or colonization. Why don't you?

 

Any alien species living on Earth would have left hard structures. Thus, they would have left traces.

 

Bats have hard structures -- bones. So where are the fossil bats? Or the fossil woodpeckers? Or many other fossils of vertebrates? They didn't leave traces. WHY?

 

It's not a matter of hard parts. You ignored the points and tried to change it. It's a matter of just how little of the geological record is at the surface for us to find. That's the problem. Your premise is flawed. There have been so many species and groups of species on the planet. Most of them have not left traces. And it's not because they weren't here.

[lucaspa]

If we look at the process of evolution' date=' which should apply to all life in our galaxy, a couple of relevent and probable trends appear.

1. Life, universally, should have a tendency to increase its population.

2. Life, universally, should have mechanisms to ensure geographical dispersal.[/quote']

 

"should have" is not a phrase you can use in science. As it happens, observation says that life does have the ability to increase population. However, observation also shows that many species do not have the mechanisms for geographical dispersal. Corals, for instance, are limited to warm and shallow water. Koala bears are limited to areas where there are eukalyptus trees.

 

If, however, large numbers of such aliens exist, it is seriously probable that a number of them are still driven by those evolutionary trends. These species would increase their numbers and would be expansionist. If they survive long term, they must develop a partial control, and only increase their numbers when conditions permit. I see this as a very likely outcome.

 

Let me get back to Edtharan's point: such expansion as you postulate will end up in war. After all, as number increase on the home planet, you postulate expansion to relieve population pressure.

 

Suppose you do ship off enough to temporarily relieve populatoin pressure (a questionable assumption at sublight speeds). The colony world has a growing population. Eventually they need to ship their population off, so they expand to a new world. And, of course, the home planet is continuing to ship excess population to new colonies. So now you have a sphere of colonized planets such that the inner planets CAN'T ship the population out fast enough past the edge of the sphere. Their population builds up until there is a huge war for the remaining resources or everyone starves. In any case, civilization and population collapses. Now you have a mostly empty planet.

 

So, the inner ring of planets need to ship off excess population. Which is going to be easier, a long way out past the outer ring and hope to find a habitable planet, or the much closer journey to the home planet that is now mostly empty? I say the home planet. Or perhaps the political organization is such to send a battlefleet to a newly settled colony of another planet -- you already know it is habitable.

 

Either way, what you now have is constant war between the planets in the sphere. Either fighting over colonizing the collapsed original home planet and first colonies, or fighting over the new colonies. And the whole civilization collapses and the expansion stops right there.

[SkepticLance]

I am sad to see that this thread is starting to get a bit silly. A lot of arguing is going on about matters that are not relevent to the earlier theme. For example : some of the comments about fossils are just plain ridiculous. It is widely accepted among professional palaeontologists that the reason for minimal fossils before 600 million years ago is lack of hard body parts. Some of the other arguments on this are based on local examples without wide or general application.

 

If aliens had once occupied Earth, it is possible they 'camped overnight' and left no markers. If so, why not a second race, that colonised? Such an occurrence would have left billions of hard remains that would be likely to form fossils. How many coke bottles alone are thrown away each year? To suggest aliens came here and left no traces is ridiculous.

 

Lucaspa mentions corals and koalas. Both have means of dispersal. Look it up. Admittedly koalas method is slow, and inefficient, and not well adapted to Australia after the impact of humans.

 

The question of the effect of population pressure. Again, I wonder if I am not able to communicate. There seems to be a wide divergence in perception on this question. Population pressure causing geographic dispersal does NOT operate on large fractions of the species. It works by influencing very small numbers to get the hell out of there. It is always a small number of pioneers, while the vast majority stays home to face the consequences. Even in Larry Niven's 'motie' books, the only case of a motie emigrating was an individual, while the bulk of moties stayed home and died. This is the way it works in real life. A few pioneers leave, and establish new communities elsewhere. It is NOT an explosion of emigration.

 

Lucaspa says Dyson swarm habitats are not generation ships. Quite the contrary actually. They are IDEAL generation ships. Just a couple of modifications.

 

Lucaspa argues against the 6 billion year time frame. That is not my idea. It came from an item in New Scientist, based on astronomers findings. 10% of our galaxy consists of third generation stars 6 billion years old or more. That is not a matter open to debate. it is a scientifc finding.

 

Swansont points out a problem with my communication of wealth/population growth. Sorry. I was trying to say that, if cost was a limiting factor on numbers of kids, we would expect the very rich to have more kids. Of course, that is not true.

 

I will be going on a month long business trip in a couple of days, and will not be contributing to this (or other) threads during that time.

[Edtharan]

Lucaspa mentions corals and koalas. Both have means of dispersal. Look it up. Admittedly koalas method is slow, and inefficient, and not well adapted to Australia after the impact of humans.

yes, both have means of dispersal, but they also are subject to the effect of population pressure. When corals grow in a reef, they can get too close to eachother. This results in a fight where each coral trys to digest the other (they do this by pushing their intestines out onto the other and digesting them).

 

Also Koalas on Kangeroo Island (IIRC) and a few other places have an expanding population. These Koalas are eating all the available food and are starting to die of starvation. It is only through relocation and culling) schemes performed by humans that they are not completely eating out their food supply. Even with their own ability to relocate, the members near the centre of these ares could not move out to the edge in time before they starved.

[JohnB]

Sceptic, you're not going to the "Fine Foods" show in Melbourne are you?

[swansont]

 

If aliens had once occupied Earth' date=' it is possible they 'camped overnight' and left no markers. If so, why not a second race, that colonised? Such an occurrence would have left billions of hard remains that would be likely to form fossils. How many coke bottles alone are thrown away each year? To suggest aliens came here and left no traces is ridiculous.

[/quote']

 

I don't think that anyone else suggested that, though various scenarios were discussed (aliens didn't make it here; if they did, traces were not preserved). But argument from incredulity doesn't validate your position.

[lucaspa]

I am sad to see that this thread is starting to get a bit silly. A lot of arguing is going on about matters that are not relevent to the earlier theme. For example : some of the comments about fossils are just plain ridiculous. It is widely accepted among professional palaeontologists that the reason for minimal fossils before 600 million years ago is lack of hard body parts. Some of the other arguments on this are based on local examples without wide or general application.

 

Your argument on the presence of alien artifacts rests on the assumption that the geological record is complete. That simply is not true. We don't have a complete fossil record for every species on the planet. Why? Partly because the geological record is not complete.

 

I used pre-Cambrian only to show that we have samples from that period from a very limited geographical area. That applies to every time period in earth's history you care to name. The local examples are just that: examples of a general application. If the aliens had a camp at Milwaukee, we would see artifacts there only if the camp was in a very limited time scale -- the Mississippian. All other time periods are not at the surface. This applies to EVERY square foot of the earth.

 

Again, why no fossils showing an evolutionary history of bats? Because bats don't have an evolutionary history? That would be the conclusion based on your argument: we should have found fossils of bat precursor species. That we have not found those fossils means there were no bat precursor species. See the similarity to your argument: we have not found artifacts or fossils of alien visitors, therefore there were no alien visitors.

 

If aliens had once occupied Earth, it is possible they 'camped overnight' and left no markers. If so, why not a second race, that colonised? Such an occurrence would have left billions of hard remains that would be likely to form fossils. How many coke bottles alone are thrown away each year? To suggest aliens came here and left no traces is ridiculous.

 

You are using "occupied" and "colonized", meaning, in your mind, aliens occupying the entire livable surface of the planet. Even today, look at all the areas that have no coke bottles. All of Antartica, for instance. So, come back 3 billion years from now and the only area of the earth's suface to have rocks dating from now is where Antarctica once was. Would we find evidence of our civilization? No.

 

Also, you have ignored the degradation of coke bottles. It doesn't matter how many are thrown away if they all are ground to dust, does it?

 

Lucaspa mentions corals and koalas. Both have means of dispersal. Look it up. Admittedly koalas method is slow, and inefficient, and not well adapted to Australia after the impact of humans.

 

It's also very limited. That's the point. Eukalyptus is the only food for koalas. So koalas can't go where their food source can't. Corals can't go where the water is too deep or cold. So, dispersal does not = everywhere.

 

Population pressure causing geographic dispersal does NOT operate on large fractions of the species. It works by influencing very small numbers to get the hell out of there. It is always a small number of pioneers, while the vast majority stays home to face the consequences.

 

Haven't been paying attention to the immigration debate, have you? It's not "small numbers" of illegal immigrants we are looking at. Nor was it "small numbers" of Europeans that came to America in the late 1800s.

 

Even in Larry Niven's 'motie' books, the only case of a motie emigrating was an individual, while the bulk of moties stayed home and died. This is the way it works in real life.

 

That's not true. You shouldn't try to fib about the book. There were representatives of each subspecies on the ship -- in frozen sleep. There was only one conscious Motie -- a Mediator.

 

But the story highlights a problem I've been trying to get you to see: ECONOMICS. It took cooperation of most of the Motie planet to produce the mechanism of that emigration: launching lasers and the ship itself. They did so ONLY because all the Motie Masters hoped to get possession of the launching lasers to use for world conquest. And of the thousands and thousands of Cycles, they were only able to get that cooperation once.

 

The problem with slower than light colonization is the economics. So, increasing population pressure soaks up resources -- resources you need to build the colonization ship in the first place. And a colonization effort can't involve just 5-10 explorers. You need at least several hundreds to have a viable colony. Look at what happened at Plymouth. If they had not had a reinfusion of new colonists the 3rd year, the colony was doomed. Too few people to maintain it.

 

For exploration on earth, the economics were in reach. Wooden ships weren't cheap, but they weren't that expensive. Ships used for travel around Europe were adequate -- without modification -- to get across the ocean. That isn't the case with generation ships.

 

We can't afford to build an interstellar generation ship. We have the basic technology if we used the Orion drive. But no nation can afford it and, quite frankly, the taxpayers wouldn't cough up the money. And we have population pressure, don't we?

 

Lucaspa says Dyson swarm habitats are not generation ships. Quite the contrary actually. They are IDEAL generation ships. Just a couple of modifications.

 

LOL! I gave 2 ways that Dyson swarm habitats differ from generation ships and the technical difficulties in making them generation ships. You ignored both and say glibly "just a couple of modifications".

 

But you ignored my major point (you really shouldn't ignore points in a discussion): Once you have Dyson swarm habitats, you have no MOTIVE to go interstellar! In order to live on the habitats without overloading the biosphere, you have a means of controlling the population. So now you have much more living space than any possible habitable planet within your solar system and no population pressure. You have destroyed the motive you say is necessary for interstellar colonization.

 

Since all solar systems are going to be basically the same, there is no economic benefit. Remember, Europe explored and colonized the rest of the world because there were resources -- spices, gold, silver, timber, etc. -- that were either unavailable at home or scarce. There was trade between the home countries and the colonies. But there can be no interstellar trade at speeds of 0.2c or less. Too long for the voyage. So no population pressure and no economic motive.

 

That leaves political/cultural. Some of the initial colonies from Europe were formed for political/cultural reasons. That could still form a motive on Earth for interstellar colonization: some group that feels that its way of life is threatened and wants to go to another planet to preserve it. Raises its own private funds to build a generation ship and leaves.

 

BUT, if you have a Dyson swarm, that motive too disappears: just have your own Dyson ship or ships.

 

Lucaspa argues against the 6 billion year time frame. That is not my idea. It came from an item in New Scientist, based on astronomers findings. 10% of our galaxy consists of third generation stars 6 billion years old or more. That is not a matter open to debate. it is a scientifc finding.

 

Can you remember the article? I've been searching Google for it or references to it and can't find it. Are you sure it didn't say 10% were 6 billion years or younger?

 

Nor can I find an estimate of Population 1 stars by age. I do find that 20% of stars in the galaxy are Population 1, but not a breakdown by age. The oldest Population I stars seem to be about 10 billion years old, but their metal content is about 20% that of Sol. Stars with metal content = Sol's are less than 6 billion years old. http://www.ifa.hawaii.edu/~barnes/ast626_95/pcmw.html

 

I was trying to say that, if cost was a limiting factor on numbers of kids, we would expect the very rich to have more kids.

 

No. Because the wealthier you are the more the kids cost! You are thinking of kids as fixed cost per kid. But it turns out that isn't true. Instead, as family income increases, the cost of each kid increases. As I pointed out, poor families put 2 or more kids per bedroom, use hand-me-down clothes, do not send their kids to private schools, don't buy them cars, etc. All this reduces the per child cost of each kid.

 

BUT, as family income increases, the cost per child increases more than income: 1 child per bedroom, new clothes for each child, private schools cars, etc. All this means that each kid costs more for the rich than for the poor. So the rich can't afford more kids and practice birth control -- even before and in the absence of modern birth control. This seems counter-intuitive to you, but it is well-documented.

 

So, a technologically advanced species is going to have an economic reason to control population growth. When that happens, there goes your motivation for expansion.

[SkepticLance]

JohnB said :

 

Sceptic, you're not going to the "Fine Foods" show in Melbourne are you?

 

Wish I was!. Food is not my profession, but I am an enthusiastic amateur.

 

Lucaspa said :

 

Your argument on the presence of alien artifacts rests on the assumption that the geological record is complete.

 

Of course not! I have a degree in biology and a good understanding of fossilisation and its consequences. Probably only one organism in a trillion or less ended up as a fossil. There are heaps of gaps. What I am saying is that if an alien species is living on Earth, it will inevitably leave vast amounts of materials (garbage) that is non-biodegradable - hence prime candidate for preservation. The vast bulk of that rubbish would never be discovered. However, it is inevitable that at least a few bits and pieces would turn up.

 

Haven't been paying attention to the immigration debate, have you? It's not "small numbers" of illegal immigrants we are looking at. Nor was it "small numbers" of Europeans that came to America in the late 1800s.

 

Everything in this world is relative. My use of the term 'small numbers' was clearly misleading. Sorry. The small size of those numbers is relative to the large size of the numbers left behind. Unless there is something massively traumatic (like the Irish potato famine driving people to America) the percentage of those emigrating is small.

 

That's not true. You shouldn't try to fib about the book. There were representatives of each subspecies on the ship -- in frozen sleep. There was only one conscious Motie -- a Mediator.

 

Sorry again. I meant one ship, of course. It is a while since I read that book.

We should not forget that it is fiction. I do not believe for a moment that a species as immensely capable as the moties could remain trapped on their world as Niven describes it.

 

We can't afford to build an interstellar generation ship. We have the basic technology if we used the Orion drive. But no nation can afford it and, quite frankly, the taxpayers wouldn't cough up the money. And we have population pressure, don't we?

 

Our discussion recently was in relation to a world that already had a Dyson swarm. The economics in that situation are simple. In spite of your assertion that such a habitat is not a generation ship, it would, in fact, be relatively easy to convert. Essentially, all that is needed is an independent energy source such as a fusion generator, and suitable size ion drive engines (or some futuristic equivalent) strapped on. The habitat is already set up for long term survival.

 

Each habitat, for the economic reasons you are so fond of, will be large, and will be independent in terms of food and oxygen generation (assuming they are oxy breathers). If they follow a pattern similar to human, each will have a leader, or small group of leaders. Again, if they are similar to humans, it is inevitable that charismatic leaders will appear from time to time, and some of them, for religious or other reasons, will promise to take their people to a promised land.

 

If they are very dissimilar to humans in terms of motivation, then their actions are quite unpredictable, and they might do almost anything for reasons beyond our grasp.

 

If, over a 2 billion year period, there are very large numbers of such species, then at some stage, this diaspora will occur.

 

If, on the other hand, the species we are discussing, never gets to the stage of building a Dyson swarm, then there is every chance it will build space habitats anyway. When that happens, they will move those habitats to where raw material is available. Their equivalent of asteroid belts, Saturn's rings etc. I have never been terribly convinced by the idea that an advanced species will hang about in the equivalent of Earth orbit to collect energy. With advanced fusion generators, energy is not the limiting factor.

 

Anyway, for extra-stellar travel, all that is need is space habitats/cities. They do not need to be part of a Dyson swarm.

 

Once you have Dyson swarm habitats, you have no MOTIVE to go interstellar!

 

Today, there are more people living in Europe than there was 200 years ago, showing that there was room for more people in Europe, at the time so many were leaving. Yet a lot of people left Europe to go to unknown and potentially hazardous places to live. Motive is more than just; "have I got room to live, and enough bread on my table?" Remember, it is always a small percentage that leaves. It is always the most adventurous and entrepreneurial that do so. Motive comes from those factors, rather than dire need.

 

Swansont said :

 

(aliens didn't make it here; if they did, traces were not preserved)

 

Those are the points, aren't they? However, if aliens are large in number (and remember that Sagan and Drake estimated one million species currently living in our galaxy), and bearing in mind the 2 billion year time frame, it seems impossible to me that they would not make it here. And not just one species. It they did, and did not leave traces, then it must be because they left immediately. And why should they do that? After all, it would take them at least 50 years to get to the next destination, and Earth would be a prime candidate for colonisation.

 

It must be our assumptions at fault. ie. We do not have one million species, or any large number.

[lucaspa]

Lucaspa said :

 

Your argument on the presence of alien artifacts rests on the assumption that the geological record is complete.

 

Of course not! I have a degree in biology and a good understanding of fossilisation and its consequences. Probably only one organism in a trillion or less ended up as a fossil. There are heaps of gaps. What I am saying is that if an alien species is living on Earth' date=' it will inevitably leave vast amounts of materials (garbage) that is non-biodegradable - hence prime candidate for preservation. The vast bulk of that rubbish would never be discovered. However, it is inevitable that at least a few bits and pieces would turn up.[/quote']

 

1. You contradict yourself. If rubbish would turn up, then why not fossils of all those "gaps" in the fossil record. The reasons for the gaps also explain the lack of rubbish. Same reasons to explain the same type of lack of data. As I said, the data does say that an alien species never made a LONG TERM -- billions of years -- colonization of earth. If they had, they would still be here! BUT, it doesn't discount a complete colonization of several million years a billion years ago or a small colongy from 50 million years ago on back \and a visitation (but not colony) anytime in the past.

 

2. There are ways that degrade the rubbish. Fossils persist because they turn to rock. Coke bottles don't. Instead, metals rust and/or melt during metamorphosis, plastics degrade, and glass is ground to dust.

 

3. Of course, if you visit creationists websites, they do post what they claim are artifacts -- what you call "rubbish". Why do you discount them?

 

Haven't been paying attention to the immigration debate, have you? It's not "small numbers" of illegal immigrants we are looking at. Nor was it "small numbers" of Europeans that came to America in the late 1800s.

 

Everything in this world is relative. My use of the term 'small numbers' was clearly misleading. Sorry. The small size of those numbers is relative to the large size of the numbers left behind. Unless there is something massively traumatic (like the Irish potato famine driving people to America) the percentage of those emigrating is small.

 

I do not believe for a moment that a species as immensely capable as the moties could remain trapped on their world as Niven describes it.

 

Niven and Pournelle thought the matter out carefully. They always do. You "do not believe it for a moment" because it goes against what you want to believe. In the biological and physical situation postulated, there is no way for the Moties to get out of their system by sublight. Their population growth means that there aren't spare resources available to build a generation ship. Any Master trying to build one is going to either 1) be conqueored by a neighbor who puts resources into the military instead of a generation ship or 2) the resources are needed to feed and provide the other necessities of the expanding population.

 

The tramline system of faster-than-light is immensely cheaper and it is relatively cheap to build a ship to do that. However, due to the special spacial circumstance in the novel, the Moties couldn't use it (they came out inside a star). But we are discussing a universe where faster-than-light is completely impossible and species are restricted by physics to sublight. In that situation, the economic situation facing the Moties would apply to ANY species unable to control their population.

 

Our discussion recently was in relation to a world that already had a Dyson swarm. The economics in that situation are simple. In spite of your assertion that such a habitat is not a generation ship, it would, in fact, be relatively easy to convert. Essentially, all that is needed is an independent energy source such as a fusion generator, and suitable size ion drive engines (or some futuristic equivalent) strapped on. The habitat is already set up for long term survival.

 

You forgot the modifications to enable it to survive interstellar debris.

 

However, as I pointed out, any species building a Dyson swarm has no motivation for going interstellar. You ignored my extensive discussion of that point.

 

For one thing, it is going to take millions of years to exhaust the available living space offered by the swarm. Just think of the surface area! Those city habitats are going to have, in their volumes, billionsof times the surface area of the earth! For tens or hundreds of millions of years, whenever population gets too high in a ship, just build a new ship and put it into orbit next to them. Only when the entire swarm is such that it fills all available orbits around the sun will the species even begin to feel crowded.

 

Each habitat, for the economic reasons you are so fond of, will be large, and will be independent in terms of food and oxygen generation (assuming they are oxy breathers). If they follow a pattern similar to human, each will have a leader, or small group of leaders. Again, if they are similar to humans, it is inevitable that charismatic leaders will appear from time to time, and some of them, for religious or other reasons, will promise to take their people to a promised land.

 

I see you've just tried to introduce a new motive. Sounds like you are beginning to see the fallacy of the "population growth" argument.

 

However, within the system, they don't have to GO anywhere. Just make a new ship and put it into orbit. In effect, they are already in their "promised land". Your argument only works until all available orbits are taken. Also, notice that you now have the whim of individuals, not an inevitable reason for expansion.

 

Now, also remember, in order to undertake the interstellar trip, they must have population control. Otherwise they will starve or use all the breathable air. Between the stars, there is no source of new air -- no recycling system can be perfect (second law of thermodynamics). So what you have is all you've got. Population growth exhausts those resources and everyone dies. So, in order to even consider an interstellar trip, they have a means of controlling their population.

 

BUT, this means that the time to filling all the orbits in the Dyson swarm gets stretched out even more. Instead of tens of millions of years, it may be billions of years or never. They may never get all the orbits filled.

 

Instead of an inevitable expansion, you are down to another fraction: those species who have such an adventurous spirit that a whole city habitat will decide to invest in the danger, unkowns, and cost of conversion to take one of the city habitats on an interstellar exploration and colonization effort.

 

If, over a 2 billion year period, there are very large numbers of such species, then at some stage, this diaspora will occur.

 

Nope. Not certain at all. After all, over 2 billion years, very few species will have even filled their Dyson swarm orbits.

 

If, on the other hand, the species we are discussing, never gets to the stage of building a Dyson swarm, then there is every chance it will build space habitats anyway. When that happens, they will move those habitats to where raw material is available. Their equivalent of asteroid belts, Saturn's rings etc.

 

Wait a minute. In order to find the materials to build enough ships to have a complete Dyson swarm, you need the raw materials and all the planets in that solar system will go into the effort. The atmospheres for the necessary gasses and the body of the planet for the structure of the ships. In which case the it takes even longer to have population pressure! We are assuming filling a hollow sphere of approximately Earth's orbit. If you expand that volume, then you correspondingly increase the area of living space.

 

Once you have Dyson swarm habitats, you have no MOTIVE to go interstellar!

 

Today, there are more people living in Europe than there was 200 years ago, showing that there was room for more people in Europe, at the time so many were leaving. Yet a lot of people left Europe to go to unknown and potentially hazardous places to live. Motive is more than just; "have I got room to live, and enough bread on my table?" Remember, it is always a small percentage that leaves. It is always the most adventurous and entrepreneurial that do so.

 

So, you have abandoned the motive of population pressure. Now you are talking about economic and adventure motive.

 

Notice that people in Europe aren't emigrating anymore. Why? The economic and political motives are gone. There is enough wealth and political freedom so that people are content where they are. Similarly, people don't emigrate much from the United States. Emigration is from places that are poor and/or have political problems.

 

But, a civilization able to build a Dyson swarm is technologically advanced. This means that everyone is going to have enough wealth. The political aspect is taken care of with people having their own city habitat ships. Don't like the political system you are under? You don't have to build a ship to go to the stars, just build another city habitat. And you can start out small and add on later. A LOT cheaper than building a generation ship.

 

So, this leaves adventure. However, even adventurers had economic motives of greater wealth. Columbus wasn't exploring for the sake of exploring -- he was looking for a new route to the spice islands. How is this achieved by a one-way interstellar colonization trip? You already have wealth at home. If you desire more, there is opportunity there. If you want danger, work on the Jupiter type planets mining material to build new habitats.

 

All in all, any civilization that is capable of building in-system city type habitats has no motive for interstellar colonization. It doesn't even have motive for interstellar exploration. There is nothing out there that would convince people to invest the money in a ship that is never going to come back and realize a profit on the investment.

[SkepticLance]

lucaspa.

You are niggling me because I a suggesting a range of possible motives for going interstellar. We are talking about possible a million species and 2 billion years. There are possibly thousands of different motives for going interstellar. Any of them will do.

 

the data does say that an alien species never made a LONG TERM -- billions of years -- colonization of earth. If they had, they would still be here! BUT, it doesn't discount a complete colonization of several million years

 

For God's sake, lucaspa. If a species was on Earth one million years, it would leave so much garbage that we would be living in their land fills! Yet we have not found a single artifact. And please don't throw crackpots at me. Their hypothetical artifacts would not fool a five year old. Right now, we have NO alien artifacts.

 

Let's forget moties. It is fiction and thus irrelevent to the discussion.

 

Now, also remember, in order to undertake the interstellar trip, they must have population control. Otherwise they will starve or use all the breathable air. Between the stars, there is no source of new air -- no recycling system can be perfect (second law of thermodynamics). So what you have is all you've got. Population growth exhausts those resources and everyone dies. So, in order to even consider an interstellar trip, they have a means of controlling their population.

 

Not so. As pointed out earlier, a trip from Earth to Alpha Centauri at top speed 0.1c and acceleration of 0.01G would take about 50 years. If our hypothetical species doubled its numbers in 50 years without control, it is simple engineering to make the space habitat/city big enough. However, I am suggesting a species that controls its numbers when it must, and multiplies when it can. Are you telling me that such a species is impossible when we talk about a millions species over 2 billion years. I don't think so.