How Many People Can An Earth-like World Support At Max?

[Spacescifi]

So I fully intend to use both mortal and biologically (can't die of old age) immortal space faring races in my scifi.

That said...I was wondering about the max population of an Earth-like world with immortals.

Like if no one died but people where shipped out to colonize space on the regular, what is the max Earth population of residents who can just stay?

My thoughts: Large oceans like ours could actually be habital if they built a bunch of floating cities across the oceans.

To get even more crazier hey could make a bunch of floating cities too like this:

 

 

Your thoughts?

Edited January 2, 2021 by Spacescifi

[kerbiloid]

A billion or two.

[razark]

The capacity of Earth seems to be around one billion.

We can get above that for brief periods of time but it requires using up resources that we don't have sufficient reserves of.  Once those run out, you end up with a mass die-off.

 

Of course, if you're shipping any significant mass of beings off-world, the resources for doing so are going to run out even faster, and will make survival, much less continued off-worlding, a pipe dream for those left behind.

 

 

39 minutes ago, Spacescifi said:

Large oceans like ours could actually be habital if they built a bunch of floating cities across the oceans.

"Pave the oceans" doesn't seem to have a long-term benefit to the oceans and the species that live in them.

40 minutes ago, Spacescifi said:

To get even more crazier hey could make a bunch of floating cities too like this:

Sounds great. 

So, what happens to the cropland that exists in the perpetual shadow of the floating cities?

Edited January 2, 2021 by razark

[Piscator]

The answer to this question seems to mainly depend on the available technology. If you have closed-loop life support systems at your disposal (which seems like a reasonal thing to have if you're shipping people around between stars) the capacity of a planet is only limited by your capability to build autonomous habitats. This wouldn't leave the planet exactly national park worthy though.

By the way, is there a reason why you're race can't use birth control, that is, only get enough children to replace accidential deaths?  Managing population growth this way is always easier than sending people off to space colonies.

[DDE]

Countless trillions. The only real limit is energy production.

[Scotius]

I suggest you read Larry Niven's RingWorld series.

His race of Puppeteers dealt with overcrowding by turning their homeworld into one giant city of extremely tall buildings, turning four planets into agricultural worlds... and draconian birth control.

Barrring that, you could also dig underground, leaving the surface for food production.

[magnemoe]

2 hours ago, razark said:

The capacity of Earth seems to be around one billion.

We can get above that for brief periods of time but it requires using up resources that we don't have sufficient reserves of.  Once those run out, you end up with a mass die-off.

Of course, if you're shipping any significant mass of beings off-world, the resources for doing so are going to run out even faster, and will make survival, much less continued off-worlding, a pipe dream for those left behind.

"Pave the oceans" doesn't seem to have a long-term benefit to the oceans and the species that live in them.

Sounds great. 

So, what happens to the cropland that exists in the perpetual shadow of the floating cities?

Its an  technology question, without agriculture its around 10 millions. With current technology 10-20 billions depending on standard of living. 
With lab grown meat, vertical farming, good recycling, good energy sources and a bit import its just waste heat limited.
Humans don't take up much space even in not very dense cities, that take up land is farmland. 

You will not get something like Trantor or Corision,  as they will get too hot, you will get much larger and also denser cities than today however.
The puppeteers planet has the same issue and they talk about the heat problem a lot however an planet city would have even larger heat issues than in the book. 

[kerbiloid]

3 hours ago, Piscator said:

If you have closed-loop life support systems at your disposal (which seems like a reasonal thing to have if you're shipping people around between stars) the capacity of a planet is only limited by your capability to build autonomous habitats.

By the heat sink capacity.

Even with a close-loop system you need energy for every process.
So, you need to take away the waste heat.

Once your waste heat gets compared to the solar income, the planet becomes a new Venus.

So, actually you are always limited with the solar income, no matter how great are the biosystems and the power plants.
You can just redistribute and optimize the solar energy and add some tiny energy from fusion reactors where you need it to be concentrated. Say, for the 3d-industry.

1 hour ago, DDE said:

only real limit

And the ultimate one.

1 hour ago, Scotius said:

His race of Puppeteers dealt with overcrowding by turning their homeworld into one giant city of extremely tall buildings, turning four planets into agricultural worlds... and draconian birth control.

Do you still believe the Puppeteers? These paranoidal liars will tell and show anything but truth about their planet.

The room itself is not a problem.

***
Upd.
A space elevatorcan solve the problem to some extent.
Lift the excessive humans up and tell to others that you've sent them to space. 
Technically, it's a truth, after all.

As the way down is not necessary, it can be a fountain.

Edited January 2, 2021 by kerbiloid

[Scotius]

If you're already going so far... why waste perfectly good biomass?

And now we are in Soylent Green territory

[Spacescifi]

4 hours ago, Piscator said:

The answer to this question seems to mainly depend on the available technology. If you have closed-loop life support systems at your disposal (which seems like a reasonal thing to have if you're shipping people around between stars) the capacity of a planet is only limited by your capability to build autonomous habitats. This wouldn't leave the planet exactly national park worthy though.

By the way, is there a reason why you're race can't use birth control, that is, only get enough children to replace accidential deaths?  Managing population growth this way is always easier than sending people off to space colonies.

 

They have nearly closed loop power production for their starships, which need recarging of their propulsion system via a natural resource which is found in random solar systems across the galaxy. Usually one out of every fifty solar systems. Their home system is one. Local moon has the highest concentration, easily mined from the surface.

As for birth control...they have greater self control than we do, and yet they are not emotionless Vulcans. If one does not eat food for a few days then although they may have relations...their body's reproductive capacity will be sterile until they start eating again for the same amount of time. It only has to take place for one partner, as the other could be normal, eating everyday.

Space colonization is primarily for those who decide to have kids. There are those on the homeworld who do not have children at all. It just means a lot of  people fasting on the regular and that normal eating of food is the time they must avoid sex if they don't want a baby.

Edited January 2, 2021 by Spacescifi

[kerbiloid]

Enough large civilisation of immortals with unlimited breeding will sooner or later form a star with the individuals' self-gravity.

[magnemoe]

7 hours ago, Spacescifi said:

 

They have nearly closed loop power production for their starships, which need recarging of their propulsion system via a natural resource which is found in random solar systems across the galaxy. Usually one out of every fifty solar systems. Their home system is one. Local moon has the highest concentration, easily mined from the surface.

As for birth control...they have greater self control than we do, and yet they are not emotionless Vulcans. If one does not eat food for a few days then although they may have relations...their body's reproductive capacity will be sterile until they start eating again for the same amount of time. It only has to take place for one partner, as the other could be normal, eating everyday.

Space colonization is primarily for those who decide to have kids. There are those on the homeworld who do not have children at all. It just means a lot of  people fasting on the regular and that normal eating of food is the time they must avoid sex if they don't want a baby.

The natural  birth control is nice but you could just use something saver and easier to use like an pill, an implant or something, 2-3 layers you probably want an default off and an cooldown for turning it on for both sexes and perhaps an second layer of defense. 

Now for humans in all kind of close to first world level countries reproduction rate is below replacement rate. Independent on culture or religion. 
If you do low tech agriculture kids are cheap field hands at least short term. 
If you live in an first world city and tries to keep up with the Jones kids are very expensive. 
But this might well change again, radical life extension, much more wealth and stuff like robot servants and artificial wombs. "The grand kids has grown up, should we not have a kid or two? Same procedure as last century James? Yes its an tradition now, I'm getting lots of adds for baby stuff" 
Not this paragraph is for humans. The above would hold true for pretty much any technological civilizations. 

The later one might also be an great late filter we dodged simply because social status is more important than lots of kids  
Think about that one then you go to bed: Your friendly nightmare fuel station attendant 

 

[Spacescifi]

1 hour ago, magnemoe said:

The natural  birth control is nice but you could just use something saver and easier to use like an pill, an implant or something, 2-3 layers you probably want an default off and an cooldown for turning it on for both sexes and perhaps an second layer of defense. 

Now for humans in all kind of close to first world level countries reproduction rate is below replacement rate. Independent on culture or religion. 
If you do low tech agriculture kids are cheap field hands at least short term. 
If you live in an first world city and tries to keep up with the Jones kids are very expensive. 
But this might well change again, radical life extension, much more wealth and stuff like robot servants and artificial wombs. "The grand kids has grown up, should we not have a kid or two? Same procedure as last century James? Yes its an tradition now, I'm getting lots of adds for baby stuff" 
Not this paragraph is for humans. The above would hold true for pretty much any technological civilizations. 

The later one might also be an great late filter we dodged simply because social status is more important than lots of kids  
Think about that one then you go to bed: Your friendly nightmare fuel station attendant 

 

 

Wow...you could make a funny comedic scifi writer with lines like that!

Late great filter? What does having children have to do with that?

Keeping up with the Jones kids? Yeah I suppose that would always be a factor, since even lower creatures (animals) compete to be the best at what they do, there is no reason to think immortals won't.

Which also means experts in many fields of endeavor will be numerous.

I am not sure the concept of immortality has been explored adequately beyond the 'keeping the mortal status quo because is immortality is bad' trope.

I find immortality as a concept fascinating in part because it is barely trodden ground.

Such a race would be a bit more in mind and behavior than the modern nation state acting civilizations we see in SW or ST.

Edited January 2, 2021 by Spacescifi

[kerbiloid]

If these immortals still need to eat, it's a rather bad trope.

[Spacescifi]

21 minutes ago, kerbiloid said:

If these immortals still need to eat, it's a rather bad trope.

 

All living things known eat to survive...that is less trope and more just known.

[kerbiloid]

So, they are limited by agriculture, i.e. firstly by water and sun. Also, fertilizers.

Edited January 3, 2021 by kerbiloid

[Serenity]

It pains to me to see the idea we have to use birth control or a different system to control population.

Our main drive is to expand so our top priority should be how to achieve that most effectively, not limit it and destroy ourselves.

If we can't figure out a way to support exponential numbers of populations then eventually we will vanish even if we somehow control the numbers.

I feel its almost a certainty when someone or something believes there is enough of something then its a matter of time before he no longer wants it/needs it .

Edited January 3, 2021 by Boyster

[kerbiloid]

34 minutes ago, Boyster said:

It pains to me to see the idea we have to use birth control or a different system to control population.

Currently it looks like that rather than in futuristic thrillers of 1980s, in a developed urbanized culture not a birth control is needed, but vice versa, a motivation is hard to invent.

Edited January 3, 2021 by kerbiloid

[Serenity]

13 minutes ago, kerbiloid said:

Currently it looks like that rather than in futuristic thrillers of 1980s, in a developed urbanized culture not a birth control is needed, but vice versa, a motivation is hard to invent.

Maybe but since the motivation is mainly biological it would take some major tampering with our body to alter that.

Our motivation comes from many things but lets face it, the primary objective is to reproduce and our minds can work around of this but in the end they get overpowered.

[Spacescifi]

1 hour ago, Boyster said:

Maybe but since the motivation is mainly biological it would take some major tampering with our body to alter that.

Our motivation comes from many things but lets face it, the primary objective is to reproduce and our minds can work around of this but in the end they get overpowered.

 

I tailor make my scifi aliens to do what humans cannot EXACTLY for this reason...to fit the setting.

I also think changing the 'face' of every alien race I create but subjecting them to all the limits of IRL humanity to be....restrictive and unnecessary.

This IS fiction so let creativity fly I say.

Within acceptable limits I accept anyway...like I am not going into pure fantasy superhero tropes.

Edited January 3, 2021 by Spacescifi

[Serenity]

1 hour ago, Spacescifi said:

I tailor make my scifi aliens to do what humans cannot EXACTLY for this reason...to fit the setting.

I also think changing the 'face' of every alien race I create but subjecting them to all the limits of IRL humanity to be....restrictive and unnecessary.

This IS fiction so let creativity fly I say.

Within acceptable limits I accept anyway...like I am not going into pure fantasy superhero tropes.

I accept that only if you create a sci fi motivational drive of the same magnitude.

For example a mortal enemy or a mystic/higher purpose etc.

[Vanamonde]

As others have noted, this question can only be answered if the question specifies the technology available. Many experts were predicting mass starvation by the 1970s, but better fertilizers, pest control measures, and more productive breeds of crops dramatically increased production and easily averted a crisis. 

[magnemoe]

20 hours ago, Spacescifi said:

 

Wow...you could make a funny comedic scifi writer with lines like that!

Late great filter? What does having children have to do with that?

Keeping up with the Jones kids? Yeah I suppose that would always be a factor, since even lower creatures (animals) compete to be the best at what they do, there is no reason to think immortals won't.

Which also means experts in many fields of endeavor will be numerous.

I am not sure the concept of immortality has been explored adequately beyond the 'keeping the mortal status quo because is immortality is bad' trope.

I find immortality as a concept fascinating in part because it is barely trodden ground.

Such a race would be a bit more in mind and behavior than the modern nation state acting civilizations we see in SW or ST.

Great late filter: if the drive to have more kids is strong enough you wold get the 70's overpopulation scenario. 
Easy to imagine aliens running into this trap. 

And yes the other reasons why most today don't have lots of kids is because they don't die, but also its expensive. 

Else I agree with you with radical life extension you will get population issues even with pretty low birth rates say a couple have one kid every century and average lifespan is some thousand years, limited by accidents. 
This will be rather slow but it will still be exponential. 
People who live thousands of years will think more long term, but again grand kids got they own kids so you want another baby. 

I would not go interstellar import as tech level is too high, more than enough resources in the solar system, if needed make it an multi sun system but endgame of an solar system civilization is  K2. 
And the obvious long term solution here is an dyson swarm.

However its good reasons to stay on the planet, most work involves other people and light speed lag is an issue communicating and while its an very strong space industry and you are in practice K1 only some million people live in space and most of it in lower orbit. 
Culture strengthen this you want to talk to your clients and teams, online gaming and vr is very lag sensitive. 
Not that you need open spaces, that is easier to make by spamming space habitats. 
 

[kerbiloid]

1 hour ago, Vanamonde said:

more productive breeds of crops dramatically increased production

Not so dramatically

Spoiler

and the water from greatest rivers is almost over.

[magnemoe]

27 minutes ago, kerbiloid said:

Not so dramatically

  Hide contents

and the water from greatest rivers is almost over.

An 100% increase over 60 years, yes its very low compared to computers, now compare to 1950 power plants  
Amazon, the Nile, Yangtze and Mississippi kind of reach the oceans. I say the ground water is the secondary issue as people pump out so much the land sink or they run out of fresh water. 
Primary is that fresh water is just salt water+energy or most problems can be solved with enough energy. 

All who is kind of irrelevant as halfway we in the same time went from subsidiary farming  to industrial farming with collective farms as an speed bump. 
Compare price to stock food like rice. wheat or potato the last 60 years and price has gone down. 
Now you do more genetic on your food than yourself. 
Again there are the huge famines in the horrible year of 2020 or the last 10 ones. 
150 years ago famines was regular in western Europe outside of wars and communism was not popular yet.