Right now, no, as Robert Frost says. Nowhere near enough humans to do this. But if you look forward a few thousand years, that's another matter. You would have to import matter, just to create all those extra humans, never mind their food and habitats. That indeed could amount to substantial amounts of matter on planetary scales as we'll see. It would indeed be enough to change the orbits of Earth and other planets - though that would be amongst the least of our worries by then.
First, it's not possible for the population of the Earth, or indeed humans, to continue increasing indefinitely. That's because it's an exponential.
If the population doubled every 100 years (and right now it is more like every 50 years) then every thousand years it increases a thousand fold. So after two thousand years it's increased a million fold, after three thousand, increased a billion fold and so on.
All the mass of our galaxy would be converted into humans, at this rate, within 13,000 years, and all the mass of the entire observable universe in 18,000 years
Also another way to look at it, mass of the Earth around 5.972*10^24 kilograms. The smallest adult humans weigh more than 15 kilograms. So even if we evolve to be really tiny, we'll not manage to make as many as 10^24 humans out of the materials of the Earth even if totally dismantled. We already have more than seven billion.
Given that "multiply by 1000 every 1000 years, then it takes less than 8,000 years, starting with just two people, to convert the entire mass of the Earth into human beings. And so run out of matter. Since we start with over a billion, it will take less than 5,000 years.
That menas that by 5,000 years from now we'd need to convert the entire mass of the Earth into humans in the next 100 years (if continuing to double every century), then twice more in the next 100 years, then four times more in the next 100 years, and so on. Again obviously not sustainable.
Somewhere before 8,000 years from now, it just has to stop no matter what.
Obviously importing materials from the solar system to Earth is not going to help at all. But if we did attempt to do it that way - well by 8,000 years from now, and assuming we don't dismantle the Earth to create more humans, we'd have to at least double the mass of the Earth just to accommodate the mass of the extra humans never mind their habitats.
So at that point, yes, it would have effects on the orbits of other planets - but that would probably be amongst the least of our worries. Maybe we have to dismantle the other planets - if we dismantled Mars, Venus and Mercury and all the asteroids in the asteroid belt, we'd still not have an entire Earth's mass for all those extra humans, and that's just to last out for another century. We'd have started on the outer solar system and maybe the big gas giants already, especially since they would need habitats to live in and food to eat etc. And Jupiter at 317 Earth masses - well by another 900 years, that also would not be enough just for making humans.
Also, the answer obviously isn't to colonize. That just puts off the disaster - by much less than that 13,000 years to convert an entire galaxy of matter into humans. Without faster than light travel we could only explore a tiny fraction of our galaxy, diameter 100,000 light years, in that time. Even if we had FTL, still, we run out of matter in our galaxy long before 13,000 years from now.
At some point we have to stop this exponential growth. Indeed long before probably. By 1,000 years from now, we'd have a thousand times the present population of Earth. Could do that by converting the entire asteroid belt into space habitats. But if it is an exponential, we have to repeat that feat every century, and then thousand years later we have to do that a thousand times per millenium, so will need to create that many new habitats for humans every year. Even that seems unlikely. So doesn't seem likely we can continue like this for 2000 years. Or at the faster doubling rate of every 50 years, then that would happen by 1000 years from now. Never mind making an Earth's mass of humans every century, 8,000 years from now.
So - it's pretty clear that we, and all extra terrestrial intelligences likewise, have to stop exponential growth at some point, just a blink into the future in galactic timescales. (Only out here would be if the ETIs have immensely long lives and are late developers, only able to give birth, say, at age a million years - they could continue exponential growth for billions of years before they hit this issue).
And actually - it might well be that we stop by 2050 - green curve here
Or we might level off at 10,000 around 2100.
There's plenty of hope here, because we have already reached peak child. There are no more children being born this year than there were a couple of years ago. The population continues to grow because of improvements in health and child mortality. Seems a universal rule, for all religions and none, that the wealthier nations have lower birth rates, with the most wealthy ones mainly falling below replacement already. And as nations become more wealthy their average birth rate goes down.
The big unknown is Nigeria. Large population, poor country relatively, high birth rate - it's projected to have a population larger than China if its population growth continues - but that seems incredible, surely it won't continue to grow exponentially for as long as that. The continuing exponential is possible. Peak child could just be a plateau if some country with a high birth rate really takes off for some reason.
But even the "middle of the road" projection now has the population leveling off in the 2100s. And the optimistic projection sees it peaking by 2050. So I think there is reason for optimism there. At any rate, you can predict confidently that it's going to stop some time in the next 8,000 years I think.
Main thing is to make sure it happens peacefully, and not through war and starvation. Right now seems it will happen due to increasing prosperity - which would be best way it can be solved.
I think this is also part of the reason why extra terrestrial intelligences haven't filled the galaxy already. They can't be expanding exponentially. So the big question is - at what point do they stop - how much of the volume of the galaxy or the universe do they occupy before they stop expanding? It's reasonably clear they haven't filled our galaxy, so surely less than the universe, and if galaxy filling, not our galaxy yet.
Is the largest region reasonably fully populated by any ETI one solar system? Is it several solar systems? Hundreds of light years? Are there ETIs that fully occupy entire galaxies (if obviously not ours)?
I think this is part of the explanation for the Fermi paradox myself. The other part would be that self replicating humans or ETs are more dangerous for galactic exploration than self replicating robots (which are much more easily controlled and can be set to not evolve at all). So they'd surely send robots first.
So, you wouldn't want to set off colonies of uncontrolled self replicators, either robotic or human, too far away to be part of your culture and to have intercommunication with them easily. Without FTL, that probably means not much furthr than a few light years and probably safest if they don't travel much beyond your solar system for colonization purposes. Though for exploration without colonization they could go anywhere.
Either that or some other solution, but some way or another they have to find a way to stop this exponential growth peacefully.
Or they will have to be involved in constant warfare, and starvation, which has to halve their population every doubling time, whatever it is. And that doubling time could be very short. If you had uncontrolled colonization - the most prolific colonists would colonize more of the galaxy. So you'd have a strong evolutionary pressure for this special case of uncontrolled expansion into a totally uninhabited area - towards more and more rapid population growth.
For humans that would probably mean child pregnancy, children as young as five - or even younger, giving birth like Lina Medina. Or else, cloning.
One way or another, if nothing was done about it, no foresight into consequences, then the galaxy would probably fill with humans who double in population every five years or less. That then reduces the maximum of 13,000 years for total disaster down to a twentieth of that, less than a thousand years. Within a millenium you'd end up with that situation where half your entire population of humans has to die of starvation, wars, etc, every doubling time, which may be in as short a period as five years or less. Nobody could look at that possibility and see it as a desirable outcome, seems to me - either for us or for any other beings in the galaxy. So civilized beings would surely foresee that and somehow prevent it. The question is how.
I think that any civilization that lets that happen probably can't manage to sustain a space civilization in the first place, because space colonies would be so fragile and easily damaged, that you'd need to have a peaceful, well ordered, and most important, also forward seeing civilization. At present astronauts absolutely have to be rule following,and authority respecting, like people in a submarine, or space diving, or they have no chance of surviving, because conditions there are so dangerous if you do something wrong like make a mistake while donning your spacesuit or while docking the Soyuz TMA. Space is currently a place for people who are happy living in highly regulated conditions.
How that develops in the future, and how that happens is another matter, may be many possible ways to achieve such a civilization, doesn't have to be top down authority for instance. But one way or another it would need to be like that. Can't be a "free for all, most rapidly replicating and most aggressive gets the galaxy" - that's not going to work, and I think any ETI will realize that some time before they think about actually colonizing a galaxy, and that's why they aren't here, if there are ETIs in our galaxy. Maybe they are explorers, but if so, the galaxy - not totally crammed to the brim with ETIs - will still be a big place for them, so then the nearest one could easily be thousands of light years away.
See also my Self Replicating Robots - Safer For Galaxy (and Earth) Than Human Colonists - Is This Why ETs Didn't Colonize Earth?
You can also get it for kindle or to read on other computers in book format also, as Replicating Robots - Safer Than Humans for Earth & Galaxy: Is This Why ETs Haven't Colonized Earth Already, Millions of Years Ago?
I've expanded this answer, and add many things to it, for my blog post as
Why ETs Won't Need To Colonize Or Expand
First, it's not possible for the population of the Earth, or indeed humans, to continue increasing indefinitely. That's because it's an exponential.
If the population doubled every 100 years (and right now it is more like every 50 years) then every thousand years it increases a thousand fold. So after two thousand years it's increased a million fold, after three thousand, increased a billion fold and so on.
All the mass of our galaxy would be converted into humans, at this rate, within 13,000 years, and all the mass of the entire observable universe in 18,000 years
Also another way to look at it, mass of the Earth around 5.972*10^24 kilograms. The smallest adult humans weigh more than 15 kilograms. So even if we evolve to be really tiny, we'll not manage to make as many as 10^24 humans out of the materials of the Earth even if totally dismantled. We already have more than seven billion.
Given that "multiply by 1000 every 1000 years, then it takes less than 8,000 years, starting with just two people, to convert the entire mass of the Earth into human beings. And so run out of matter. Since we start with over a billion, it will take less than 5,000 years.
That menas that by 5,000 years from now we'd need to convert the entire mass of the Earth into humans in the next 100 years (if continuing to double every century), then twice more in the next 100 years, then four times more in the next 100 years, and so on. Again obviously not sustainable.
Somewhere before 8,000 years from now, it just has to stop no matter what.
Obviously importing materials from the solar system to Earth is not going to help at all. But if we did attempt to do it that way - well by 8,000 years from now, and assuming we don't dismantle the Earth to create more humans, we'd have to at least double the mass of the Earth just to accommodate the mass of the extra humans never mind their habitats.
So at that point, yes, it would have effects on the orbits of other planets - but that would probably be amongst the least of our worries. Maybe we have to dismantle the other planets - if we dismantled Mars, Venus and Mercury and all the asteroids in the asteroid belt, we'd still not have an entire Earth's mass for all those extra humans, and that's just to last out for another century. We'd have started on the outer solar system and maybe the big gas giants already, especially since they would need habitats to live in and food to eat etc. And Jupiter at 317 Earth masses - well by another 900 years, that also would not be enough just for making humans.
Also, the answer obviously isn't to colonize. That just puts off the disaster - by much less than that 13,000 years to convert an entire galaxy of matter into humans. Without faster than light travel we could only explore a tiny fraction of our galaxy, diameter 100,000 light years, in that time. Even if we had FTL, still, we run out of matter in our galaxy long before 13,000 years from now.
At some point we have to stop this exponential growth. Indeed long before probably. By 1,000 years from now, we'd have a thousand times the present population of Earth. Could do that by converting the entire asteroid belt into space habitats. But if it is an exponential, we have to repeat that feat every century, and then thousand years later we have to do that a thousand times per millenium, so will need to create that many new habitats for humans every year. Even that seems unlikely. So doesn't seem likely we can continue like this for 2000 years. Or at the faster doubling rate of every 50 years, then that would happen by 1000 years from now. Never mind making an Earth's mass of humans every century, 8,000 years from now.
So - it's pretty clear that we, and all extra terrestrial intelligences likewise, have to stop exponential growth at some point, just a blink into the future in galactic timescales. (Only out here would be if the ETIs have immensely long lives and are late developers, only able to give birth, say, at age a million years - they could continue exponential growth for billions of years before they hit this issue).
And actually - it might well be that we stop by 2050 - green curve here
There's plenty of hope here, because we have already reached peak child. There are no more children being born this year than there were a couple of years ago. The population continues to grow because of improvements in health and child mortality. Seems a universal rule, for all religions and none, that the wealthier nations have lower birth rates, with the most wealthy ones mainly falling below replacement already. And as nations become more wealthy their average birth rate goes down.
The big unknown is Nigeria. Large population, poor country relatively, high birth rate - it's projected to have a population larger than China if its population growth continues - but that seems incredible, surely it won't continue to grow exponentially for as long as that. The continuing exponential is possible. Peak child could just be a plateau if some country with a high birth rate really takes off for some reason.
But even the "middle of the road" projection now has the population leveling off in the 2100s. And the optimistic projection sees it peaking by 2050. So I think there is reason for optimism there. At any rate, you can predict confidently that it's going to stop some time in the next 8,000 years I think.
Main thing is to make sure it happens peacefully, and not through war and starvation. Right now seems it will happen due to increasing prosperity - which would be best way it can be solved.
I think this is also part of the reason why extra terrestrial intelligences haven't filled the galaxy already. They can't be expanding exponentially. So the big question is - at what point do they stop - how much of the volume of the galaxy or the universe do they occupy before they stop expanding? It's reasonably clear they haven't filled our galaxy, so surely less than the universe, and if galaxy filling, not our galaxy yet.
Is the largest region reasonably fully populated by any ETI one solar system? Is it several solar systems? Hundreds of light years? Are there ETIs that fully occupy entire galaxies (if obviously not ours)?
I think this is part of the explanation for the Fermi paradox myself. The other part would be that self replicating humans or ETs are more dangerous for galactic exploration than self replicating robots (which are much more easily controlled and can be set to not evolve at all). So they'd surely send robots first.
So, you wouldn't want to set off colonies of uncontrolled self replicators, either robotic or human, too far away to be part of your culture and to have intercommunication with them easily. Without FTL, that probably means not much furthr than a few light years and probably safest if they don't travel much beyond your solar system for colonization purposes. Though for exploration without colonization they could go anywhere.
Either that or some other solution, but some way or another they have to find a way to stop this exponential growth peacefully.
Or they will have to be involved in constant warfare, and starvation, which has to halve their population every doubling time, whatever it is. And that doubling time could be very short. If you had uncontrolled colonization - the most prolific colonists would colonize more of the galaxy. So you'd have a strong evolutionary pressure for this special case of uncontrolled expansion into a totally uninhabited area - towards more and more rapid population growth.
For humans that would probably mean child pregnancy, children as young as five - or even younger, giving birth like Lina Medina. Or else, cloning.
One way or another, if nothing was done about it, no foresight into consequences, then the galaxy would probably fill with humans who double in population every five years or less. That then reduces the maximum of 13,000 years for total disaster down to a twentieth of that, less than a thousand years. Within a millenium you'd end up with that situation where half your entire population of humans has to die of starvation, wars, etc, every doubling time, which may be in as short a period as five years or less. Nobody could look at that possibility and see it as a desirable outcome, seems to me - either for us or for any other beings in the galaxy. So civilized beings would surely foresee that and somehow prevent it. The question is how.
I think that any civilization that lets that happen probably can't manage to sustain a space civilization in the first place, because space colonies would be so fragile and easily damaged, that you'd need to have a peaceful, well ordered, and most important, also forward seeing civilization. At present astronauts absolutely have to be rule following,and authority respecting, like people in a submarine, or space diving, or they have no chance of surviving, because conditions there are so dangerous if you do something wrong like make a mistake while donning your spacesuit or while docking the Soyuz TMA. Space is currently a place for people who are happy living in highly regulated conditions.
How that develops in the future, and how that happens is another matter, may be many possible ways to achieve such a civilization, doesn't have to be top down authority for instance. But one way or another it would need to be like that. Can't be a "free for all, most rapidly replicating and most aggressive gets the galaxy" - that's not going to work, and I think any ETI will realize that some time before they think about actually colonizing a galaxy, and that's why they aren't here, if there are ETIs in our galaxy. Maybe they are explorers, but if so, the galaxy - not totally crammed to the brim with ETIs - will still be a big place for them, so then the nearest one could easily be thousands of light years away.
See also my Self Replicating Robots - Safer For Galaxy (and Earth) Than Human Colonists - Is This Why ETs Didn't Colonize Earth?
You can also get it for kindle or to read on other computers in book format also, as Replicating Robots - Safer Than Humans for Earth & Galaxy: Is This Why ETs Haven't Colonized Earth Already, Millions of Years Ago?
I've expanded this answer, and add many things to it, for my blog post as
Why ETs Won't Need To Colonize Or Expand
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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