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

[swansont]

It's possible Earth is so toxic to non-Terran life we have been consistently ignored by colonists for the past billion years.

 

 

Or, if they were just exploring, we were visited more than several thousand years ago, and the report says "No technological advances here. Moving on." Or even "Mostly harmless."

[SkepticLance]

Whew!

After all those postings, where do I begin?

Perhaps just a comment or two.

 

First, I was probably wrong at one point in talking of spaceships. It is likely that expansion will be via what we are now calling space cities. Generations in transit matter little for such a structure and such a society.

 

Second, it does not matter too much for space cities, when arriving at another stellar system, whether there are suitable planets or not. They will be able to mine space detritis. There is an enormous amount in our own solar system left over from planet formation, and that is probably true for most stellar systems. Certainly, robot probes sent to Alpha Centauri etc will give us the answer long before any space cities depart.

 

As to aliens doing the same and getting to Earth. I have to keep harping back on the enormous numbers involved. With two billion years to do it, and (according to Sagan and Drake) a million species involved, how is it possible that not one alien species ever got here? It appears beyond belief to me that, if they were here, some time in the past 2 billion years, that they left no traces. Look at the enormous quantity of junk humans have produced. Even the tiniest fraction of that as alien junk would have marked their presense indelibly.

[Sayonara]

Second, it does not matter too much for space cities, when arriving at another stellar system, whether there are suitable planets or not. They will be able to mine space detritis. There is an enormous amount in our own solar system left over from planet formation, and that is probably true for most stellar systems.

Unless you are taking some sort of dimensional shortcut, using FTL technology, or hibernating, I would also expect cities rather than ships for interstellar travel.

 

 

As to aliens doing the same and getting to Earth. I have to keep harping back on the enormous numbers involved. With two billion years to do it, and (according to Sagan and Drake) a million species involved, how is it possible that not one alien species ever got here? It appears beyond belief to me that, if they were here, some time in the past 2 billion years, that they left no traces. Look at the enormous quantity of junk humans have produced. Even the tiniest fraction of that as alien junk would have marked their presense indelibly.

And I will continue to hark back to:

a) They don't necessarily have to have visited every planet in the galaxy, and

b) If they did they would not necessarily leave any traces that persist for vast time periods.

 

I think it is quite likely that a race capable of interstellar travel might know a thing or two about non-intrusive technology, waste reclamation, and ecologically friendly materials. Just the fact that most of their time in space will be spent traversing barren void would seem to suggest a possible predisposition towards making the most of what resources they have.

 

You really really need to consider that an intelligent race which is rapidly running out of planets in an entire galaxy will already have invested considerable planning, development time, and resources putting together a network of artificial biomes around the younger stars (i.e. Dyson Spheres or their equivalent), which would be far more efficient than colonisation and - in sufficient numbers - provide billions of times more land space.

 

Terraforming would become redundant long before the last few thousand planets fell under the colonial flag, and due to the rubbish location of our star system it is not inconceivable that we might always have ended up on the "would be nice..." list, never to be trodden by alien feet.

[swansont]

(according to Sagan and Drake) a million species involved

 

The number you get from the equation depends on the assumptions that go into it, and according to the wiki article Drake's numbers give you an answer of 10. This set (and form of the equation) gives 72. Or six million

[SkepticLance]

Sayonara said :

 

And I will continue to hark back to:

a) They don't necessarily have to have visited every planet in the galaxy, and

b) If they did they would not necessarily leave any traces that persist for vast time periods.

 

I think it is quite likely that a race capable of interstellar travel might know a thing or two about non-intrusive technology, waste reclamation, and ecologically friendly materials.

 

Why would they not visit every planet? Bear in mind that we are talking about potentially a million species, depending on how it is calculated. Also, it is over 2 billion years. Population growth of even one species would be enough to drive them to colonise every system thay can.

 

As to leaving traces, ask yourself why they would bother to cover up? It is always cheaper and easier to leave a mess. This would apply regardless of how advanced the speices was. If they were here 1 to 2 billion years before human evolution, there would be no logical reason to bother. An advanced technology might clean up all the mess that could harm their society. But to clean up so thoroughly that they leave absolutely nothing for us to detect is a bit beyond credulity.

 

Swansont said :

 

The number you get from the equation depends on the assumptions that go into it,

 

Absolutely correct. I am not arguing the validity of the Drake Equation (though at this point in time it is a singularly variable and useless concept), but simply the idea that numerous technologically advanced alien civilisations exist or have existed in the past. The Drake Equation goes as follows

 

Number of advanced alien species = Rate of formation of suitable stars

times Fraction of those stars with planets

times Number of planets in the habitable zone per stellar system

time Fraction of those planets where life develops

times Fraction of life sites where intelligence develops

times Fraction of intelligences where technology develops

times Lifetime of those technically advanced societies.

 

The major weakness of this is that you can put almost any value into some of the variables. In other words, no-one has the faintest idea!

 

My view is simple. Bearing in mind that aliens have had 2 billion years to colonise/explore Earth before humans evolved, and there is no trace of such activity, then it is likely that the total number of such technologically advanced species is very small. Not necessarily zero. Just a small number.

[swansont]

The major weakness of this is that you can put almost any value into some of the variables. In other words' date=' no-one has the faintest idea!

 

My view is simple. Bearing in mind that aliens have had 2 billion years to colonise/explore Earth before humans evolved, and there is no trace of such activity, then it is likely that the total number of such technologically advanced species is very small. Not necessarily zero. Just a small number.[/quote']

 

But the Fermi paradox suffers drom a similar weakness: Many assumptions. You cannot logically conclude that there are few/no intelligent alien species based on no evidence that they've visited us, because a failure of any of the other assumtions to hold also leads to no evidence being available.

[lucaspa]

Whew!

After all those postings' date=' where do I begin?

Perhaps just a comment or two.

 

First, I was probably wrong at one point in talking of spaceships. It is likely that expansion will be via what we are now calling space cities. Generations in transit matter little for such a structure and such a society.[/quote']

 

"City" implies an open space. This isn't going to be true for interstellar travel. You MUST have an enclosed space. Expansion to the "suburbs" is impossible. So is building taller buildings. There is finite space and resources. So yes, generations in transit time matter a great deal! How do you manufacture spares? Remember, no industrial base because there is no room or place to mine new minerals. No shipping of food in from the countryside to THIS city. You grow everything onboard. Also, what do you use for reaction mass? Do you carry it all? Do you use Bussard ramjets? But those only work at near lightspeed; I'm not sure they work at 0.1c. So, do you use the Orion drive? Lightsail? If the latter, trip time is MUCH longer because acceleration is much lower.

 

Second, it does not matter too much for space cities, when arriving at another stellar system, whether there are suitable planets or not. They will be able to mine space detritis. There is an enormous amount in our own solar system left over from planet formation, and that is probably true for most stellar systems. ... It appears beyond belief to me that, if they were here, some time in the past 2 billion years, that they left no traces. Look at the enormous quantity of junk humans have produced.

 

Did you notice that your first point contradicts your second? You say that the spacefaring species living in generation ships has no need to visit habitable planets! So why would there be artifacts on earth if we were visited by a species living in generation ships? They mined the asteroid belt, took some gases from the outer planets, and left. Maybe they stopped off for a little hunting on earth -- hunting T. rex and sauropods would have been exciting, but why try to grow food when your hydoponics gardens are sufficient?

 

As to aliens doing the same and getting to Earth. I have to keep harping back on the enormous numbers involved. With two billion years to do it, and (according to Sagan and Drake) a million species involved, how is it possible that not one alien species ever got here? Even the tiniest fraction of that as alien junk would have marked their presense indelibly.

 

You keep ignoring the points I brought up concerning why such "junk" would not have been found. You need to address those points in a speculative discussion instead of ignoring them. If they just made a stopover, we postulate one or more temporary camps. How large an area does that cover? A square mile per camp? Kinda large, but let's go with that. And they do a 100 camps in different parts of the world -- they are exploring. That's a total of 100 square miles. How many total square miles on the earth? 196,940,400 square miles. So, we are talking a maximum of 1/1,969,404 or about 1 in 2 million. Bad odds for finding the camps. True, land surface is only 30%, but you have to remember that what was land in the past might be sea now. So we can't rule out what is presently sea. For instance, the Black Sea was flooded only about 12,000 years ago. If one of the camps was in the middle of what is today the Black Sea, we wouldn't see it, would we?

 

Now, if the visits were tens of millions of years ago, the camps are buried by sediment or they are eroded. You keep saying that junk would persist. Would it? How long does plastic last? It's pretty nondegradable, but even it has its limits. http://www.azom.com/details.asp?ArticleID=1655#_Plastics,_Not_as

 

Absence of evidence as evidence of absence works only when you can search all the places where evidence might be found. We aren't even close to that in this case.

 

However, I would like to see you address Sayonara's and my economic and birth rate arguments against interstellar exploration in the absence of an FTL drive. You ignore them but never say why they aren't valid.

[lucaspa]

Population growth of even one species would be enough to drive them to colonise every system thay can.

 

Why do you postulate the absolute of population growth?

 

Several studies of humans have shown that, in the absence of modern birth control, birth rate decreases as wealth increases. There are sound economic reasons for this: each child demands more resources as wealth goes up. Therefore a family can support fewer children in the style to which they have become accustomed. So they have fewer kids, even if this means abstinence.

 

If they were here 1 to 2 billion years before human evolution, there would be no logical reason to bother.

 

If you are going to go back 1 to 2 billion years, then you must address the arguments I have put forward for why there are no traces. Starting with what is going to be left after a billion years, and will it even be on the surface. Now, if they actually colonize the planet like you said, then where are they? They'd still be here as the dominant species, wouldn't they?

 

You might want to read the Drako's Tavern series of stories by Larry Niven. In it there used to be a technological civilization on earth 2 billion years ago -- by indigenous anaerobic organisms. The rise of green plants killed the civilization (and species) by oxygen poisoning. What would be left?

 

My view is simple. Bearing in mind that aliens have had 2 billion years to colonise/explore Earth before humans evolved, and there is no trace of such activity, then it is likely that the total number of such technologically advanced species is very small. Not necessarily zero. Just a small number.

 

But our contention is that your view has flawed assumptions. If your assumptions are flawed, then so is "your view", which is the conclusion from the assumptions.

 

Again, "there is no trace of such activity" only counts as evidence if we can really find the traces. There are lots of reasons besides the non-visitation that can account for not having found traces. Your "view" needs to consider them.

[swansont]

That's an excellent point: once you have solved the issue of how to survive multi-generation travel, you've pretty much eliminated the need to colonize planets. You probably wouldn't want to land on the big planets at that point, because of the cost to blast off again — you'd mine the much smaller bodies where the cost/benefit was more favorable.

[Sayonara]

Why would they not visit every planet? Bear in mind that we are talking about potentially a million species, depending on how it is calculated. Also, it is over 2 billion years. Population growth of even one species would be enough to drive them to colonise every system thay can.

The answer to this question was in the post you are replying to:

 

You really really need to consider that an intelligent race which is rapidly running out of planets in an entire galaxy will already have invested considerable planning' date=' development time, and resources putting together a network of artificial biomes around the younger stars (i.e. Dyson Spheres or their equivalent), which would be far more efficient than colonisation and - in sufficient numbers - provide billions of times more land space.

 

Terraforming would become redundant long before the last few thousand planets fell under the colonial flag, and due to the rubbish location of our star system it is not inconceivable that we might always have ended up on the "would be nice..." list, never to be trodden by alien feet.[/quote']

It's all about the economics of effort: cost versus actual returns.

 

If population increase is your driving factor (and you keep insisting it is, so let's go with it), then your limiting commodities are living space and energy resources.

 

Way before the time you are down to only a few thousand empty planets in the galaxy, your population will have volumetric expansion which will have exceeded the available space on those remaining planets before you can reach and colonise them. And what happens afterwards?

 

An intelligent race would be using artificial biomes in orbital shells looooong before they ran out of new planets to colonise.

 

Also bear in mind that although you say "we are talking about potentially a million species", no matter how many species have a share in the galactic population they will all still face the same issue of diminishing living space.

 

 

As to leaving traces, ask yourself why they would bother to cover up?

It's not a matter of covering up, it's a matter of being frugal with what resources you have, and long-term ecological thinking.

 

 

It is always cheaper and easier to leave a mess.

Not necessarily "always", and costs are not always economic in nature.

 

 

But to clean up so thoroughly that they leave absolutely nothing for us to detect is a bit beyond credulity.

As has been stated, there are plenty of reasons we might not have found any traces of a past civilisation. Perhaps they lived on the floor of the ocean. Perhaps the shattering of Pangea dragged their cities into the mantle. Who knows?

[SkepticLance]

I must be very poor at explaining things, 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.

 

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. 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.

 

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.

 

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. And if the number of species is large enough, at least one will suffer that population pressure. 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.

 

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

 

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.

[Sayonara]

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

No, you are not confusing anyone, don't worry. I don't have a problem with most of your postulates. Some of your assumptions are poor though, or I should say "have better alternatives", and this is why I cannot agree with what you conclude from them (just as Lucaspa said earlier).

 

I don't have any particular issues with your last post until:

 

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.

This is not true. Because population is expanding, and the rate of expansion increases as the number of populated planets increases, the benefit to be gained from colonising every planet in the available set will drop as vacant planets in the set run out. This is why species that rapidly multiply in finite habitats often follow the "boom and bust" pattern, driving themselves into a population crash.

 

There will come a point where planetary colonisation becomes inefficient when compared to stationary, artificial biomes (which are the smart way of avoiding the "bust"). After this point the benefit to be gained from colonisation will plummet, and eventually it will be economically stupid.

 

 

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

I am satisifed with the counter-arguments that have already been supplied for this. We have a hard enough time evidencing half the species that we KNOW were 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.

Here you have a large problem, because the point where the number of intelligent races is "small" and the point where the number of alien races is "massive" are highly unlikely to coincide.

 

If small is 10-500 and massive is 500,000-20,000,000, you still have a minimum range of 450,000 species where the colonisation outcomes can only be considered "uncertain".

 

 

By the way, when taking data for your calculations, bear in mind that "speeds of up to 0.2c" means the peak velocity during the trip between two points, not the average velocity for the whole trip. Most actually workable methods of reaching these speeds will require extremely long periods of acceleration and deceleration which will significantly affect the time taken for the journey.

[SkepticLance]

Sayonara said :

 

This is not true. Because population is expanding, and the rate of expansion increases as the number of populated planets increases, the benefit to be gained from colonising every planet in the available set will drop as vacant planets in the set run out. This is why species that rapidly multiply in finite habitats often follow the "boom and bust" pattern, driving themselves into a population crash.

 

To be frank, I don't actually understand this. Perhaps you can re-word? Or are you equating 'benefit' as meaning benefit to the entire species? If you are, the logic breaks down as individuals make decisions based on their own local short term benefit.

 

Boom/bust patterns are characteristic, as you said, of many populations. However, if enough alien species exist, there will be many that get around that problem through the application of intelligence (as humans are doing). In fact, I suspect that species that survive will all find ways to solve that problem.

 

If small is 10-500 and massive is 500,000-20,000,000, you still have a minimum range of 450,000 species where the colonisation outcomes can only be considered "uncertain".

 

Of course, this is the origin of the argument. How much is 'massive'. I am working with the assertion made by Drs Drake and Sagan, of one million alien technological species. If that number is correct, then it becomes a statistical 'certainty' that a certain number will expand through the galaxy.

 

 

By the way, when taking data for your calculations, bear in mind that "speeds of up to 0.2c" means the peak velocity during the trip between two points, not the average velocity for the whole trip. Most actually workable methods of reaching these speeds will require extremely long periods of acceleration and deceleration which will significantly affect the time taken for the journey.

 

That depends on the degree of acceleration. If a space vessel accelerates at one Earth gravity, it would reach a very high fraction of light speed in one year, or 0.1c in about 36 days. If we assume an acceleration of 0.01G, then 0.1c would be achieved in 10 years. Add 10 years deceleration, and we add a total of 10 years to our journey time. For Alpha Centauri, at this acceleration/deceleration, and a top cruising speed of 0.1c, that makes a journey time of 53 years. For a space habitat/hotel/city this would be practical and achievable. In fact, if the space structure was big enough, with a large, independently operating population, journeys of much greater time/distances would be practical.

[swansont]

Boom/bust patterns are characteristic' date=' as you said, of many populations. However, if enough alien species exist, there will be many that get around that problem through the application of intelligence (as humans are doing). In fact, I suspect that species that survive will all find ways to solve that problem.

[/quote']

 

But if they can get around the problem, i.e. achieve a constant population with ease, why would they need to colonize?

[Edtharan]

A civilization with constantly growing populations are going to run into trouble. If the population is growing fast enough then the ability to found new colonies will be outstripped by the growth of the populations.

 

This means that the centre colonies of this civilization will experience overpopulation and the results of this (was over resources as whole planets are plunged into famines, etc). This might even progress to the point where the population can no longer afford to send out colonization attempts.

 

So this creates a situation where any civilization that is going to survive long enough to colonize a larger area of the galaxy will need population controll, or it will repeatedly fall back into war.

 

This will slow, halt, or even reverse the colonization that the civilization is doing. This culd be why we have not had any contact. They all have suffered population growth that exceeds their rate of colonization.

 

Or that they have achieve population stability and no longer need to live on planets.

[SkepticLance]

If we look at the process of evolution, 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.

 

For a species that has evolved a high order of intelligence, these two factors will still apply, and are likely to evolve as behavioural or psychological trends.

 

Of course, intelligence by its nature, is able to overcome and over-ride pure instinct. Thus, technological species should be able to control those two tendencies - at least enough to prevent disaster. However, that does not cause those two drives to disappear.

 

Now, back to my theme. If only a few intelligences exist, possibly they all have may have totally controlled those tendencies and live happily in their own stellar systems at peace.

 

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.

[Sayonara]

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']

Trends which eventually - for all species - are both abruptly terminated by a bewildering array of possible factors.

 

 

For a species that has evolved a high order of intelligence, these two factors will still apply, and are likely to evolve as behavioural or psychological trends.

Of course, intelligence by its nature, is able to overcome and over-ride pure instinct. Thus, technological species should be able to control those two tendencies - at least enough to prevent disaster. However, that does not cause those two drives to disappear.

True, however this does not change the fact that some problems cannot be negotiated away simply by controlling tendencies. Population dynamics and simple ecological principles such as resource partitioning forbid it.

 

 

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.

It doesn't matter how driven they are, they will still hit and exceed the cost:benefit balance point I described earlier.

 

This is really very simple. You cannot support an accelerating rate of population expansion if you only have a finite number of possible sites the population can colonise.

 

The only way around this for an intelligent species is to change strategy, i.e. create new and better sites, and this needs to begin long before the planetary sites run out, otherwise there would be massive and immediate suffering and loss of life, along with resource shortfalls that might endanger relief efforts, exacerbate the death and suffering, and certainly cripple any further expansion.

[SkepticLance]

Sayonara.

Correct me if I am wrong.

Are you someone who believes that the ultimate strategy of a highly advanced species is to build Dyson spheres?

 

You should be aware that such spheres are detectable by astronomers. The heat put out by their suns must be permitted to dissipate, or else they would all die a heat death. The most likely such dissipation is as infra red, which can be picked up by our infra-red telescopes. Apparently, there would be a clear cut spectral signature for such an infra-red source. Thus, we could identify any Dyson spheres anywhere in our stellar neighbourhood.

 

True, we would not do so for any sphere at an exceptional distance from us. However, again harping back to my theme, if the number of alien species is very large, thus meaning many Dyson spheres, we would already have detected them.

[Sayonara]

Not necessarily an entire enclosing sphere (although that would be the ultimate required product if population continued to rise). A ringworld or halo, or connected multiples of the same supporting "islands", would still give hundreds of times more landspace than a couple of habitable planets.

 

On the subject of Dyson Sphere detection, Freeman Dyson himself discussed this idea in his 1959 paper Search for Artificial Stellar Sources of Infra-Red Radiation. The problem is that the Dyson Sphere (or to take it back to the original concept as discussed in the paper, the Dyson Shell) is specifically designed by a given Type II Kardashev Civilisation to harvest the maximum energy possible from a system's star.

 

This produces several key assumptions:

 

1) Even heat energy may be collected and stored to some degree,

2) Excess heat energy may be buffered and vented,

3) Venting is unlikely to be omnidirectional,

4) Venting is unlikely to be continuous.

 

The infra-red signs of a sphere are by no means "clear cut". Add to that the fact that we could be staring right at the infrared traces of a venting sphere and not recognise it as such, and detection suddenly becomes difficult enough that we should not be surprised to have no results yet.

 

SETI has made a couple of attempts to look, and Fermilab started in 2005, but with such a vast expanse of sky to examine and analyse we should expect it to be a while before we find any tell-tale signs, even if the population of spheres is extremely large.

 

However, let's assume that we have scanned the galaxy and there are NO Dyson Spheres. What does this definitely tell us?

 

Well, a Dyson Sphere is just one of the various final products of a Type II Kardashev Civilisation, which may be preparing to become a Type III (your "galactic dominators", using all the energy in the galaxy).

 

The proposed absence of this technology in the galaxy leads to two hypotheses: either they cannot be built, or they are not required to be built.

 

"Cannot be built" can be explained by any number of possibilities:

- The technology is beyond practical efforts,

- No race survives long enough to reach the level of technology required,

- The races that might benefit... are not there.

 

"Not required" breaks down further too:

- Population control in intelligent species precludes energy requirements from reaching Type II,

- There are better and less detectable alternatives, such as an extensible mesh of ringworlds with modular islands,

- Type II is not desirable.

 

 

So even if we assume they are definitely not there, their absence doesn't really tell us anything concrete. Their presence would, but their absence does not.

 

Anyway, this is somewhat moot, because I use the term Dyson Sphere in the sense that Freeman Dyson originally intended it - that of a shell or sphere of independent structures, which would not interfere significantly with heat escaping from the star.

[insane_alien]

i got to agree with sayo on this one. ringworlds and dyson spheres would be far more favourable to an expanding civilization.and besides i'm sure there are far more interesting planets out there. maybe when they start picking up some of our radio broadcasts they might decide to come and investigate.

[Edtharan]

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

 

First an orbit of a plaent is an elipse. Any dyson sphere would have to be in orbit of the partent star, a circular orbit would be unstable because any planet in that solarsystem (not to mention passing stars, etc) would peturb the orb into an elipse.

 

An eliptical orbit would requier the components of the sphere to beable to move relative to one another (this could be solved by flexable joints, but that is not a system that would last for millions of years - the timesacle that a sphere would need to exist for).

 

Second: As I said a circular orbit is unstable, 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.

 

If a civilization had the power to move a sphere so as to keep it in orbit of the star and correst these peturbations, then they would have enough power (or thrust capabilities) to move their entire civilization through space.

 

A situation I think would be more likely is that there would be indipendant "Satalites" in orbit of the star with large solar collectors. These islands would likely be factories of some type and also used in the storage of power (equivalent to batteries - which could be hydrogen for fusion power plants or such).

 

I think a space fareing civilization would not want for power, but a mobile power source. Also if nanotechnology and engineering pans out the way we think it will, then an advanced society would most likely develop some sort of manufacturing similar to it. With it we could take any matter, extract the elements that we need and then recombine them in the form we want. This means that they would not need to visit planets.

 

A steady source of hydrogen that would be fused for power and turned into heavier elements and then a nanofactory would build any device that they wanted.

 

This is not just an arbitary guess on my part. I have based these on a rational suposition:

 

Any Alien species that could develop technology to the point of space travel, must have a certain number of characteristics.

 

First: They must be tool users. It takes tool to build spaceships and spaceships themselves can be seen as tools.

 

Second: They must have logical thought. This is so that they can understand the principles of the world around them. I won't use science, but they would have an equivalent, based on logical thought.

 

Third: They must be curious and have imaginations. Curiosity and Imagination must be a prerequsite for advanceing the quality of tools. If you can't wonder about a better tool, then how can any advancement of that tool come about in a reasonalbe time.

 

These 3 factors will allow a species to develop technology and advance it to a point where they would be capable of intersteller travel. A species with these traits may not develop space travel, but they would be nessesary for that species to do so.

 

This also means that any space traveling species (or even technological species) would have some things in common with us. That bodes well for contact and communication between us.

[insane_alien]

i know that ringworlds and dysonspheres aren't stable. but i was thinking something like the bussard ramjets in the ringworld sequels.if the need for them is great enough then they will build in control systems to keep it stable.

[Sayonara]

First an orbit of a plaent is an elipse. Any dyson sphere would have to be in orbit of the partent star, a circular orbit would be unstable because any planet in that solarsystem (not to mention passing stars, etc) would peturb the orb into an elipse.

The planets in the system would not be a problem, because you have already rendered them assunder and used their materials to build your new giant thingy.

 

However this is not an issue, because the term "Dyson Sphere" is a misnomer. Dyson's paper discussed the possibility of a shell or swarm of energy collecting habitats; essentially what you describe here:

 

A situation I think would be more likely is that there would be indipendant "Satalites" in orbit of the star with large solar collectors. These islands would likely be factories of some type and also used in the storage of power (equivalent to batteries - which could be hydrogen for fusion power plants or such).

 

The solid sphere idea has been popularised through science fiction, and is not a great idea for several reasons, not least of which are those you mentioned. However in the solid sphere's defence, it could quite easily be re-imagined as a spheroid of some sort, with an eliptical circumference, which could be relatively easily accelerated around the central vertical axis as required.

 

The biggest problems I can see with this solid state design are:

 

1) Without artificial assistance, gravitational effects are non-uniform across the inner surface,

 

2) The spheroid shares its centre of mass with... er... the heart of its star. Could you even have "natural" gravity?

[SkepticLance]

I agree with Edtharan that Dyson spheres are not practical. First because they are not stable structures with respect to the central sun. Second, because the enormous effort involved in the building. The amount of energy, time, effort etc is beyond human comprehension. And third, because it is totally unnecessary.

 

The whole rationale of the Dyson sphere (ringword or whatever) is to tap the energy of the central star. Once efficient fusion power is available, this becomes utterly pointless. A Dyson sphere requires a very thick shell in order to have enough mass for gravity. If you have that much material, why not, much more simply, have the mass as hollow cylinders, spinning for gravity, and powered with fusion generators? The total living area for the amount of mass used would be far greater than a Dyson sphere. The use of the mass would be far more efficient.

 

In fact, in terms of efficiency (the number of sentient lives that can be supported per unit mass in a stellar system) it would be far more effective to dismantle the sun - pull it apart and trap the rapidly cooling hydrogen. If a species is capable of building a Dyson sphere, they can dismantle a sun. eg. use enormous magnetic fields to pull the hydrogen into massive flares, which, out in space, are trapped by Bussard type magnetic fields, except powered by fusion generators.

 

After all, if we speculate about the power to create Dyson spheres, we can speculate about what else such a civilisation could do.

 

A planetary system converted into quadrillions of giant spinning cylinders, and a sun dismantled for hydrogen fuel to drive fusion generators, would support far more sentient beings for far longer than a Dyson sphere could. And then, once the species had got that far, why not send those cylinders to all corners of the galaxy to colonise?

 

A sun will fail after, say, ten billion years. The alternative will last as long as the galaxy does.

[Sayonara]

I agree with Edtharan that Dyson spheres are not practical. First because they are not stable structures with respect to the central sun. Second, because the enormous effort involved in the building. The amount of energy, time, effort etc is beyond human comprehension. And third, because it is totally unnecessary.

Yes, but that's if you are talking about solid spheres, which I am not. I am going to switch to the term "Dyson Bubble" to remove all ambiguity. A Dyson Bubble is a Dyson Swarm that uses "statite" islands to prevent orbital conflicts.

 

The whole rationale of the Dyson sphere (ringword or whatever) is to tap the energy of the central star.

Not so. This is one of the two functions. The other function is to provide living space which can be expanded into and added to as and when required.

 

A moderately populated Dyson Bubble requires only about as much mass as one of the larger asteroids in this system (so it is very easily expanded because there is plenty of raw material laying about the place), and represents living space for billions of people, which in turn represents a resource saving of many millions of your city vessels (which would be something along the lines of the O'Neill Cylinder) along with a time saving of their combined journey and colonisation stopover times, and without the massive risks of rapid changes in birth or mortality rates, encounters with unexpected phenomena, etc.

 

Once efficient fusion power is available, this becomes utterly pointless. A Dyson sphere requires a very thick shell in order to have enough mass for gravity. If you have that much material, why not, much more simply, have the mass as hollow cylinders, spinning for gravity, and powered with fusion generators?

Problems for solid spheres, not bubbles.

 

The total living area for the amount of mass used would be far greater than a Dyson sphere. The use of the mass would be far more efficient.

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.

 

In fact, in terms of efficiency (the number of sentient lives that can be supported per unit mass in a stellar system) it would be far more effective to dismantle the sun - pull it apart and trap the rapidly cooling hydrogen.

You would already need your artificial living space and alternative energy sources in place before you did this.

 

If a species is capable of building a Dyson sphere, they can dismantle a sun. eg. use enormous magnetic fields to pull the hydrogen into massive flares, which, out in space, are trapped by Bussard type magnetic fields, except powered by fusion generators.

Possible yes, but you are forgetting that effectively limitless energy and solar engineering means you don't really have to colonise anything.

 

A planetary system converted into quadrillions of giant spinning cylinders, and a sun dismantled for hydrogen fuel to drive fusion generators, would support far more sentient beings for far longer than a Dyson sphere could.

But less efficiently. O'Neill cylinders are all very well if you are transporting a large but stable population somewhere nicer over a long period of time, but in terms of resources per unit population supported you will be using more matter and energy than you would with a Dyson Bubble.

 

And then, once the species had got that far, why not send those cylinders to all corners of the galaxy to colonise?

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.

 

A sun will fail after, say, ten billion years. The alternative will last as long as the galaxy does.

That's a separate issue entirely, and will affect both colonists AND sit-at-homes.

 

 

I think it might be helpful to remind you at this point that I am not making an argument for many or few intelligent species, or for previous intelligent species colonising or failing to colonise the galaxy.

 

What I am trying to highlight is that the information we have is insufficient to allow confident conclusions to be drawn from our conjectures.