Stephen Hawking tends to exaggerate, using hyperbole - exaggerations for emotional effect. In this talk he takes our exponential population growth and extrapolates it forwards to 2600 and predicts that human beings will cover the globe shoulder to shoulder and that our electricity consumption will turn the surface of Earth red hot through the waste heat. Stephen Hawking hasn't taken account of the fact that our exponential growth has stopped. The same number of children were born in 2005 as in 2017 and our population is currently growing due to increasing lifespans, not through exponential growth. The middle of the range estimate is for it to level off at around 11 billion by 2100.. This story is scaring people and that's my motive for debunking it here. 

One of the many news stories about it is here: Stephen Hawking’s latest doomsday prediction: Earth could go to hell by 2600 and the sensationalist press have gone to town on this story

His video is here, starts 5 minutes in.

“This exponential growth cannot continue into the next millennium, By the year 2600, the world’s population would be standing shoulder to shoulder, and the electricity consumption would make the Earth glow red-hot. This is untenable,”

Cue a video of the Earth glowing red hot, it’s atmosphere burning away leaving a dark cinder. Rather bizarrely he shows it lit by a flame below it with flames rising up above it. It starts here

He then goes on to say that this makes it a priority to colonize other planets and star systems.

However, experts on population are agreed that though, as he says correctly, we have been through a process of exponential growth - we no longer are going through it any more - and the world population growth is projected to slow down.

Indeed, the middle of the range projection now has our population level off at 11 billion at around the year 2100 and not grow any further. Lower projections have it level off at ten billion or even start to decline towards the end of the century.

So whatever happens, we aren't headed for Malthusian type exponential growth because we have reached peak child already. In the graph above, the red dotted lines show the upper and lower limits for the 95% prediction interval. The blue lines are for +- 0.5 children per couple average. You can look up the data here, the graphs page for the UN population division.

Though we may not reach peak population this century, and may continue to have some modest growth after 2100,most parts of the world have a good chance of stabilizing before then, especially the more developed countries.

The least developed countries are the ones that would get most population growth. The most rapid growth is in Africa in the projections. You can see a break down for each region of the world here,

Older figures from 2014. Most of the population growth is in Africa by the end of the century by these figures, with everywhere else leveling off by then, the least developed countries are the ones that grow most rapidly, so that's a reflection of the situation in Africa

This is a pattern that’s universal across all the different political groupings and religious beliefs. Muslim countries also are seeing zero growth. The main pattern is that wealthier countries have lower population growth.

The main area of the world with increasing numbers of children now is Africa, because there is so much poverty in Africa, with Nigeria growing so rapidly in population that if it keeps it up, by 2100 it would have a larger population than China. That’s obviously unsustainable. There are education initiatives in Africa to teach people there that having lots of children is not necessarily an advantage. Poor families worldwide tend to have lots of children in order to have a chance of at least some healthy children growing to adulthood.

This may seem counter intuitive as our population is continuing to grow right now, quite rapidly. But all our present day population growth is due to people living longer. The same number of children are born every year, and have done for several years now. Luckily we reached "Peak child" in 2005. The number of children in the world has remained steady for over a decade now.

Many countries are actually seeing a reduction in population, with fewer children than are needed for replacement, as you can see in that diagram above.

I hope those of you who get scared by Stephen Hawking’s frequent doomsday future scenarios can learn from this - that he exaggerates and often makes mistakes too - or at least, leaves out important details - when talking about topics outside his sphere of expertise. This is rather common amongst people who become famous for their expertise and brilliance in some area of science.

Another recent exaggerated Stephen Hawking doomsday is this one: Hawking Says Trump Could Tip Earth To Hot Venus Climate - Is It True? What Can Earth's Climate Tip To? The answer was no, it's not true.

Another one who does this is Michio Kaku - a good scientist in his field but he is rather notorious for making exaggerated and occasionally downright fake predictions of disaster for the world as a whole. In particular, in 2012 he weighed in on the side of those who were saying we were facing a disaster much to the surprise and dismay of other scientists debunking the ridiculous nonsense. He made absurd and outrageous fake claims about the sun that lead other scientists to almost gasp in disbelief. . Michio Kaku - 2012hoax

Stephen Hawking is perhaps not as bad as that but he exaggerates hugely and makes many mistakes when talking about his ideas for ways the world would end.

He has a motive here, perhaps. He is very keen on human spaceflight, and especially, colonizing other planets, including planets around other stars. This speech was done to motivate us to start to make plans to colonize a the nearest star system Proxima Centauri. This is not even remotely practical right now, but he is hoping to set things in motion that will permit it to be colonized in the future.

He is so keen for humans to go into space and leave Earth behind that he says the most absurd things to try to motivate us to do this. He frequently paints very pessimistic pictures about the future of Earth.

But our beautiful Earth is the only place in our solar system where humans can breathe the air, live at comfortable temperatures, and survive without a spacesuit. There is nowhere that’s even a patch on Earth. So, surely it is most important to protect and cherish our Earth. And we can.

We are already doing this. There is no need to send our children to other star systems to deal with our excess population.

For more about this, see: Debunked: Soon we won’t be able to feed everyone because the world population is growing so quickly

It wouldn’t work anyway to go into space as a way to deal with population growth. At some point we have to stop population growth and we might as well do it right now. Though it seems almost as though we have stumbled into a solution to the population growth crisis - still, the important thing is that we have found a way to deal with it.

Let's look a bit closer at this, why interstellar colonization is not a solution to problems of population growth.

WHY EVEN INTERSTELLAR COLONIZATION CAN NEVER SOLVE EXPONENTIAL POPULATION GROWTH

After all what is the point in dashing off to Proxima Centauri if every planet humans colonize is doomed to get filled with humans shoulder to shoulder and glow red hot with the heat? Even if we move from planet to planet every six centuries, before long we’d fill all of the nearby regions of space. Traveling to other stars to deal with population problems is not a viable solution.

To see how this works, let's suppose we set up only ten colonies around nearby stars in the next thousand years, with one new colony on average each century.

So far, fine. Our population has grown only 10 fold in 1000 years. It seems harmless enough doesn’t it? Far slower than doubling every 40 years which would be a roughly 1000 fold increase after 400 years.

Let's suppose that each of those set up another ten in the next thousand years.

(techy note on these calculations: in practice some of them would set up new colonies even before the first thousand years is over, but to simplify the calculation, let's ignore those - the actual numbers would be a bit larger than for our calculation).

So now, after two thousand years, we have a hundred space colonies. So far, fine. Our population has grown only 100 fold in 2000 years. It seems harmless enough doesn’t it?

Now each of those set up another ten colonies, and after three thousand years we have a thousand colonies, and so on. Still there seems no problem. Exponentials are like that. For a long time nothing seems to be happening much. But then, rather suddenly, it gets you.

After only twelve thousand years, we have a trillion colonies. Our galaxy has around 100 billion stars for them to colonize, so we have run out of stars in our galaxy already.

But it's worse than that. Our galaxy is around 100,000 light years in diameter. Unless the colonists have warp drive, or some other form of Faster Than Light (FTL) travel -, then in those twelve thousand years, they can't travel further than 12,000 light years. The limit is 1,200 light years if they travel at a less hazardous speed of a tenth of the speed of light. That's only 1.2% of the diameter of the galaxy.

Clearly our region of the galaxy would get pretty crowded, within 12,000 years, even at this slow rate of a ten fold growth per thousand years.

When you hit an exponential there isn't much you can do except to delay the effects slightly. Even tiny two gram colonists as small as the Etruscan shrews, are no help.

Etruscan Shrew - the smallest known mammal, only 2 grams, much less than a ten thousandth of the mass of an average adult human.

If you think humans can evolve to get as small as this, and evolve this far in the near future too, within a few thousand years, through genetic manipulation, you can add an extra four or five thousand years to the time it would take to run out of matter to make colonists (still assuming a ten fold increase every thousand years).

Even if we go all the way to a science fiction future of. massless colonists, in a civilization with total conversion of matter into energy, and faster than light travel (e.g. warp drive), it only delays the inevitable by thousands of years. Zero rest mass colonists still need energy. Even photons, though they have zero rest mass, still have energy, which has to come from somewhere, for instance, from nuclear fusion or some other form of conversion of matter to energy.

To take this to the limit, suppose we have minimal energy "colonist photons". The lowest energy photons we could fit into our observable universe would be vast ultra ultra low frequency feeble pulses of light with wavelengths of order of the diameter of the observable universe. I'm not saying that it is possible to make such photons, or for a colonist to consist only of a single photon like that. However, any other form of colonist will surely require at least as much energy as this massless minimal energy colonist photon, so this is surely pretty much the ultimate limit of what we could do by way of fitting the maximum possible number of colonists into the observable universe.

Even this does no more than to delay the inevitable by a few more thousand years. Soon, your exponential growth spurt has to stop. As usual, I'll indent the calculations so that they are easy to skip:

Even if you can reduce individual humans to tiny creatures of a few grams like a pigmy shrew, you'll soon run out of matter for all the colonists, The mass of the universe is about 3 x 10^55 grams according to one estimate. If we can reduce the mass of a colonist to one gram, starting with one billion humans (say), and increasing the population ten fold every thousand years, you'd run out of matter in the observable universe to make colonists within 46,000 years. That's just for the mass of the colonists themselves, not taking account of any necessities like food, water, power, life support, air to breathe etc.

You can try a science fiction scenario of massless colonists - could we have "colonists" in the future that have similar mass to a photon somehow? If that was possible, you are still limited because the energy of a photon depends on its wavelength.

The energy of a photon in electron volts is 1.2398/λ where λ is its wavelength in microns. There are about 10^36 electron volts to a kilogram (if you can directly convert matter to energy as an advanced ETI might be able to do). So, now suppose a photon has a wavelength of 93 billion light years (the diameter of the visible universe of 93 billion light years according to one estimate) or around 8.8x10^32 microns. Then its energy will be around 1.4x10^ 33 electron volts (1.2398/(8.8x10^32)).

If we can have massless colonists, each consisting of just one photon, and use the feeblest possible low energy photons, so that each one has a wavelength so vast it spans the entire observable universe , then the total number of colonists we could make from the available matter in the observable universe is at most 3 x 10^55/ (1.4x10^-33) or about 2*10^88

. So, with our assumption of a start population of a billion colonists, multiplying the population by ten every thousand years - then even with warp drive, total conversion of mass to energy, and massless colonists with wavelengths that span the entire observable universe, we run out of matter in our observable universe to make these massless minimal energy single photon colonists within 77,000 years.

So, even if the population increases only ten fold every thousand years, you will run out of matter to make new colonists in the entire observable universe, well before 46,000 years if the colonists have a mass of only one gram each. You run out of matter to make colonists before 77,000 years even if each colonist consists of only a single photon with the least amount of energy compatible with fitting that photon physically into the size of the observable universe and you turn all the matter in the observable universe into these minimal energy single photon colonists.

If the exponential growth is very slow, say, a ten fold increase every million years, the calculation is the same. It's now 77 million years until we get to the single photon colonist end point, even with warp drive and total conversion of matter to energy. Whatever the timescale is for a ten fold increase, just multiply that by 77 and that's the absolute limit of exponential growth within our observable universe. That's going to happen no matter how those colonists evolve and what technology they have, at least so long as they remain within the laws of physics as we understand them today.

I actually see this as a likely solution to "Fermi's paradox" - the puzzle, why our galaxy isn't filled with ETs. It would just take one Extra Terrestrial similar to us to have the capability to travel between stars some time in the last ten billion years or more, and our galaxy should by now be filled with extra terrestrials, shoulder to shoulder, through exponential growth.

This obviously hasn't happened. I think the reason is that just as we practice planetary protection to protect Earth from extra terrestrial microbes returned from other planets, and to protect other planets and moons from Earth microbes, that extra terrestrials, and our future selves, if we have any sense, will practice Galaxy protection.

However that needs a separate article. But I have a long section about it in my "Touch Mars?"

TOUCH MARS? EUROPA? ENCELADUS? OR A TALE OF MISSTEPS?

This must be one of the first books for the general public entirely devoted to planetary protection issues. I was surprised to find very little else, apart from Michael Meltzer's When Biospheres Collide, which is a history of NASA's planetary protection programs, published in 2010, and the technical books written for scientists. That’s the main reason I decided to write a book about it myself, for the general public, available on kindle and also online.

So for more on this suggestion, and more background, see my Touch Mars? Europa? Enceladus?: Or a Tale of Missteps?, on Amazon

It’s also available to read online for free on my website - it’s over 1800 pages, in the kindle book format, with many images. So be patient, as this page has all that in one page and so it takes a while to load: Touch Mars?

The section on galaxy protection is here:

I'm keen on space exploration and humans in space, as you'll find out if you read that book or my other articles here. Totally in support of robotic exploration of Proxima Centauri, and humans in space, and setting up bases, settlements, even a small colony perhaps on the Moon. But I argue that there is no need to colonize anywhere outside of Earth for a "backup" but that instead our hopes are all based around protecting Earth and looking after it. We can do much in space to help with that, out sourcing heavy industry into space, solar power from space, exploration, learning about our solar system, galaxy and universe. But I think protecting Earth has to be our focus, not trying to run away from isssues here to a new supposedly better planet - especially since Earth is so much more habitable for humans than anywhere else in our neighbourhood, probably at lest for many light years in all directions. And I think there is a potential for a future with space colonies, but there's no rush to set them up,. It's not our priority at present and if we approach this without a sense of urgency, to have millions in space as soon as possible, we are much more likely to end up with a stable future in which human activities in space are valuable and useful.

Stories like this really scare young chiuldren who don't know how to evaluate them properly, and many adults also. I frequentlly debunk these stories, see  List of the articles in my Debunking Doomsday blog to date. There are several there from Stephen Hawking. I am sure he can't intend to scare people, but sadly that is one of the effects of his annoncements like this.

Also if you want to help make a difference, you can sign and share these petitions- and do have a look at the comments to get an idea of the scale of the problem. Click “Join Conversation” to see more of them.

And if you need help because you are scared of these stories - well message me of course and comment on any of these posts - and you can also join our Facebook group Doomsday Debunked. See also Seven tips for dealing with doomsday fears

Also, though it’s not so useful for a story like this that is presented “as is” without any comment or criticism even in many of the mainstream papers, you can avoid at least the worst excesses of the sensationalist papers such as the Express with my:

  • Google News Without The Nonsense. You can bookmark that site and use it instead of Google News (or indeed, Apple news too). It’s just the same as Google News, with the sensationalist nonsense fake news filtered out