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Comment by maeon3 | Hacker News Reader

Given the average lifespan of a human on earth today (around 67), and the average population growth rate (somewhere between 1 and 2%), it causes an acceleration in the number of humans living and being born.

The notion that this growth is unsustainable is scare mongering. 1.5% growth per year is sustainable indefinitely to colonize the galaxy, if we can just keep the resources needed to support that growth flowing. At some point we will need to create a Dyson sphere around the sun to capture most of its energy, and harvest the raw materials in the asteroid belt between mars and Jupiter. As for living space, it will be superstructures orbiting the sun in the habitable zone.

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>The notion that this growth is unsustainable is scare mongering.

Exponential growth makes this statement as wrong as it can be. It may be scaremongering to say it is unsustainable in the short term, but eventually that growth will have to stop, either due to voluntary decision-making on the part of humans everywhere, or due to a scarcity of resources. Or in fact both, given that the scarcity of resources will cause people to decide on reproducing less.

Growth in general is simply not sustainable in the long term. Isaac Asimov once estimated that at "today's" rate of growth (circa 1970), Earth would become a ball of human flesh expanding at the speed of light by 5000AD. Of course its a ridiculous prediction, but it illustrates that between now and then, something must change.

Look at this chart: http://en.wikibooks.org/wiki/File:2nd_Order_Damping_Ratios.s...

Assuming 1 here refers to the maximum "sustainable" population, we'll either oscillate around it, overshoot and come back, or asymptotically approach zero percent growth. There is no such thing as a system with no feedback, which is allowed to grow without bound. It may seem like there are no constraints currently, but they're out there, and eventually we'll hit them.

The world population is not experiencing exponential growth. It's experiencing logistical growth (i.e, following a logistical function rather than an exponential function). We've just been seeing the first half of the curve, which does approximate exponential growth.

But we're starting to see it turn around. In the most developed countries, fertility has dropped to replacement or lower. As the remaining countries develop, their fertility rates are also dropping. It's reasonable to extrapolate from this that at some point in the future, the global fertility rate will be at or below replacement.

The constraints are microeconomic. It's expensive to raise children, especially when you factor in opportunity costs (this part is key to why world population won't stabilize at starvation levels). When you give people birth control, people seem to make a rational economic decision about how many children to have. That provides the feedback mechanism you mentioned.

The developing world has birth control but, in large parts of it (e.g. most of africa), most people aren't using it. This is for economic reasons. In these economies children are your pension fund. There's no RRSP funds or old age security payments. Just children who (hopefully) look after you in your old age. If you have only one or two you will either be an unreasonable burden upon them or simply be abandoned to starve.

The economic support system for seniors in the developed world is currently under a lot of strain too. In countries where pension funds are funded from current taxes the baby-boomer retirement is going to be a tremendous drain on society. The baby-boomer generation should have tucked away a nice huge fund to pay them in retirement as well as support the greater demand on the medical system. Instead, they racked up huge amounts of public debt. Massive amounts of immigration and raising the retirement age have been the stop-gap measure of choice so far, but the developed world's support for senior citizens could easily revert to that of the developing world's without much warning!

So, yes, children are expensive, but for most of history and in large parts of the world today they are a necessary investment for retirement. In only the developed world of the past century have financial pressures favored fewer children, and that could easily change.

fertility rates are dropping worldwide. At some point in the next 30 years, it is expected to fall below replacement level.

Check out this graph comparing fertility rates. China and Iran (!) now have fertility rates below that of the U.S.

http://www.google.com/publicdata/explore?ds=d5bncppjof8f9_&#...

Curiously, rates for Italy and Germany are separated from other developed countries by about .5% http://www.google.com/publicdata/explore?ds=d5bncppjof8f9_&#...

The developing world has birth control but, in large parts of it (e.g. most of africa), most people aren't using it. This is for economic reasons.

I would argue that in many, if not all, of these places this is instad due to poor education, misinformation or religious opposition.

Edit to add: It's also important to distinguish when men have access to birth control and when women have access to it. Fertility rates won't drop until women can control how many children they have.

> But we're starting to see it turn around. In the most developed countries, fertility has dropped to replacement or lower. As the remaining countries develop, their fertility rates are also dropping.

And in the most developed most-developed countries, that has reversed: http://www.nature.com/nature/journal/v460/n7256/abs/nature08...

That makes no sense though. Assuming exponential growth, then it wouldn't grow as a sphere going at the speed of light. The derivative would be a quadratic, not a exponential curve. So if anything that would only approximate the growth for a couple days, at which point exponential would take over. But this presupposes that the humans started on the earth at 5000 AD, where in reality we will have almost certainly taken over venus (aside: Venus is a much more likely target for human colonization than Mars) and probably have several space station states which could easily move at near the speed of light away from the earth.

I can't tell if you're joking or not. Dyson spheres, space mining, superstructures... Currently we have sent a handful of people to a rock orbiting this planet, then gave that up because it was uninteresting. At the moment there is no incentive to send anyone to space because machines can do better that little bit of exploring that is currently being done.

I'd be surprised if in a hundred years there's enough resources or motivation to do any space exploration. To me it seems far more likely that we have spent our fortunes on earthly matters such as wars and the like.

A hundred years ago we'd only just managed to get airborne... If we look at the technological advances of the past hundred years, I think you're being pessimistic.

One wonders if this argument will ever get old. It was being used in exactly this form forty years ago, when aviation (not to mention rocketry) had - perhaps unbenownst to most people at the time - essentially reached the state that it would remain in for the next fifty years, at least. [1] But after forty years on the plateau, it still gets trotted out.

My hypothesis is that this argument will die with the baby boomers, who have a living memory of the day when 2001 really felt like a documentary beamed back from the future, but I could be wrong.

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[1] We had supersonic passenger aircraft and moon rockets in 1972. Then we gave them up, on purpose: They didn't pay their own way.

And I don't want to minimize the hard work of aviation engineers since then: Better avionics, better navigation systems, computerized scheduling, pilotless drones, fly-by-wire... But these are refinements, not fundamental breakthroughs in travel technology.

Sending people to the moon was an incredibly expensive process that gained us nothing. If we are going to spend significant resources on colonizing space it must either be economically viable or at worst a small net cost that can be reasonably subsidized for the long term. So while we are not there yet, there has been fundamental progress on 5 significant technology's for actually developing space since 1972.

Step 1: LEO Scram Jet's which can dramatically increase payload to orbit. http://en.wikipedia.org/wiki/Scramjet

Carbon Nano-tubes, which is the first material that could enable a realistic space tether. http://en.wikipedia.org/wiki/Carbon_nanotube http://en.wikipedia.org/wiki/Tether_propulsion

Step 2: After LEO Ion Thrusters http://en.wikipedia.org/wiki/Ion_thruster which when coupled with high efficiency solar panels enables better delta V than chemical rockets. And makes mining the asteroid belt a reasonable possibility.

Solar Sail's which could enable realistic travel to nearby stars by probes or robots to build infrastructure. http://en.wikipedia.org/wiki/Solar_sail The delta V on slowing down is a major issue if you want to do more than a simple fly by which makes Solar Sail's the best non nuclear option for colonization.

Step 3: Power Fission makes living in space between stars viable. The power requirements for a colonizing the ort cloud and then moving further to the next star(s) only work when you can acquire ridiculous amounts of power, store it for long periods of time, and then tap it on demand. Of the 5 fusion is both the most important and the furthest from fruition but it's still on the path to viability in the next 100 years.

Edit: Fusion not Fission. There is a lot of Fission energy available but not enough to be the basis of infrastructure for the long term when we start trying to build real deltaV aka anywhere close to .01c and beyond.

PS: Voyager 1 was also launched in 1977 which is the first Interstellar craft ever built. Not that it pushes back the end of the 'golden' time period of space travel that far, but it's still outside of the window your thinking about.

Aerospace technology plateaued decades ago. There was a rapid improvement from 1920 to 1970, and since then we aren't any closer to colonizing the solar system than we are today.

You see this pattern all over the place (exponential growth followed by a plateau). Medical technology, for example, as impressive as it is is really only improving at the margins today. In the 40 years between 1970 and 2010, life expectancy at birth for whites has gone up around 5 years. In the 40 years before that, it went up 10 years. In the 40 years before that, it went up almost 20 years.

The speed of light is finite. So, if we where to cover 200 light year radius we would need to expand Pi(200+r)^2 = 1.015 Pi * 200^2 = 1.5 light years in a single year which can't happen.

Put, another way 1.015^10,000 = ~10^64 but there are only ~500 billion stars in our galaxy and that's spread over 100,000 light years.

PS: The milky way only weighs ~4×10^41 kg humanity weighs ~1/2 trillion kg. So at 1.5% growth it takes less than 5,000 years for the projected mass of humanity 10^44kg to be 1,000 times as large as the mass of the milky way.

This is my favourite proposed solution to the Fermi Paradox. I first came across it in Steven Baxter's novel Space -- he explores a few proposed solutions and the speed-of-light-limit-to-growth explanation is the most intriguing.

Put another way: the volume of space we can reach in time t is O(t^3), while the population is O(e^t). Therefore, there is a value of t for which we will overpopulate our light-sphere.

I guess people just can't comprehend the sheer size of the Earth and the massive amount of resources it still has. Just check this graph out: http://www.landartgenerator.org/blagi/archives/127

That's the surface area we need to power EVERYTHING with solar power (which is VERY ineffective at the moment). Add to that wind power (lower in the article), and we're golden for another hundred years.

We don't even need to go to other solar systems (which seems impossible at the moment) - just start colonizing and mining the nearby planets/asteroid field (it's very very hard, but not impossible). Nuclear submarines are a good example of relatively self-sufficient bases/colonies. With time, it's possible to slooowly build something like that in space...

Ya know, with a handful of thorium we wouldn't have to lose all of that shoreline to wind generators...

For sure, I imagine if the technology develops fast enough, the territory needed to generate all of the power we need would be much smaller...

> The notion that this growth is unsustainable is scare mongering.

No. It's stating a very basic and obvious fact to anyone who understands math.

> 1.5% growth per year is sustainable indefinitely to colonize the galaxy, if we can just keep the resources needed to support that growth flowing.

Exponential growth - you don't understand what it means. Dyson spheres are chickenshit when you're trying to sustain exponential growth indefinitely in a three-dimensional universe.

I guess that means at some point the growing number of people born on Earth will have to be shipped to space. I hope there are enough volunteers and space ships.

Meanwhile, I'd also keep in mind this curve, posted earlier on HN: http://en.wikipedia.org/wiki/File:World_population_growth_ra...

"The notion that this growth is unsustainable is scare mongering" AND "if we can just keep the resources needed to support that growth flowing." Sustainability relies on the current technology, natural cycles, and resources (i.e., natural limits). There is no IF.

Sustainability relies on _future_ tech. If we need to know if we can feed 20% more people in 10 years we need to know if we can produce 20% more food in ten years, using what technology is available then. Not what is available today.

And we (and this is what people who keep saying we can't support all those people never take into account) _can count on the extra minds of those 20% to do their uttermost to solve the situation_.

That is what people never take into account.

Meanwhile, farming and food production is one of the least profitable industries to be in... Trust me, when the need comes, there will be a way.

Obviously, the situation is different in poor countries - but just take a look at all the expired food we dump from supermarkets, restaurants, offices and homes - it sure is more than enough to feed a lot of those who are starving... if only we had teleporters...

future tech is not taken into consideration when defining something as currently sustainable. It currently is or it is not sustainable, not "it is sustainable due to inevitable future tech developments".

These solutions are also very expensive. Given the fact that the population growth is at its highest in less developed countries, I think it is a lot more realistic to assume that the population will be "controlled" by killing those least able to defend themselves.

The ethical problems are easily circumvented if you do it indirectly through distribution of resources.

I hope not. Why do you wish for a galactic infestation of humans? Much more attainable is population control here.

Are you kidding? "Set sail and conquer" is our motto, without a challenge we'll die out even without population control :-)

> The notion that this growth is unsustainable is scare mongering.

The notion is more predicated on the absence of science fiction technology.

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