Appendix to 'The Future is Vast'
My main data source is the long-run estimate by demographers Toshiko Kaneda and Carl Haub (reference below).
From 200,000 BCE until 2020 they calculate that 116,761,402,413 people were born. 7,772,850,162 of these people were alive in 2020.
Of course the error margins around both of these numbers - especially the historical one - are large, which Kaneda and Haub clearly acknowledge. I'm not using their point estimates - neither in the text nor in the chart - because I think that these estimates, down to the individual person, would suggest a wrong sense of precision.
Older estimates of how many people have ever lived were published by Goldberg (1983) and Deevey (1960). They arrived at lower estimates - of 55 billion and 81 billion respectively. Previously it was thought that modern humans emerged only much later and earlier estimates assumed better health conditions, i.e. lower mortality, of people in the distant past.
I believe the more recent work by Kaneda and Haub is the best estimate that is available. But the large uncertainties and the wide range of different estimates that were published in recent decades should be emphasised.
References:
- Toshiko Kaneda and Carl Haub (2021) - How Many People Have Ever Lived on Earth?. Published by the Population Reference Bureau.
- Goldberg (1983) - How many people have ever lived? In Probability in Social Science.
- Deevey (1960) - The Human Population. In Scientific American.
My update of Kaneda and Haub:
Kaneda and Haub published estimates up to mid-2020.
I updated the figures from Kaneda and Haub for mid-2022 by adding the births in the following 2 years. According to the UN there were 139,975,303 births in 2020 and 139,821,086 births in 2021 (these were estimates published before the pandemic and are not precise observations, but the imprecision of these estimates is small relative to the large uncertainties in the other relevant figures).
This means the total number of people ever born up to 2022 is 116,761,402,413 + 139,975,303+139,821,086 = 117,041,198,802 births
According to the UN 7,953,952,577 people are alive in 2022.
People who died between 200,000 BCE and 2022: 116,921,736,195 - 7,953,952,577 = 108,967,783,618 deaths
Share of people alive today among all people ever born: (7,953,952,577 / 117,041,198,802) * 100 = 6.8%
Calculations for drawing the hourglass visualization: Humanity's past and present in grains of sand
Each grain of sand represents 10 million people.
Grains to represent today's population: 7,953,952,577 / 10,000,000 = 795 grains
Grains to represent the dead: 108,967,783,618/ 10,000,000 = 10,897 grains (to not suggest a false sense of certainty around this number I rounded it to 10,900 grains in the visualization).
The scenario shown in the chart on humanity's potential future:
Estimates for the average lifespan of mammalian species: Estimates for the average lifespan of mammalian species range from 0.6 Million years (Barnovsky et al, 2011) to 1.7 million years (Foote and Rap 1996).
As a rough midpoint between these two estimates I follow Toby Ord and use 1 million years.
Remaining length of humanity's existence: As about 200,000 years of history are already behind us we would have close to 800,000 years left.
Size of humanity's population: According to the UN projections, the global population will continue to increase for the rest of this century, but by the end of the century population growth will be close to zero. The UN demographers expect the world population then to be 10.9 billion people. I'm assuming that population growth continues a bit further into the 22nd century and will then stabilize at 11 billion people.
As emphasized throughout the text I am thinking of this as an illustrative scenario that makes it possible to understand the dimensions we are concerned with. It is not a prediction and as with all scenarios about the far distant future, the reality could turn out to be very different; population growth might continue further or the world population could decline.
Life expectancy in the future: The UN demographers project that many countries will have life expectancies higher than 90 years by the end of the century. The world average life expectancy is projected to be 82 years then. If we assume that the rest of the world population can catch up to the healthiest countries in the period after 2100, then an average life expectancy of more than 90 or 100 years is possible (especially for the more distant future, extremely long life expectancies are imaginable).
I assume a life expectancy of 88 years in my projection. This is higher than the projected global average, but lower than the life expectancies projected for the best-off countries. It is certainly a rather conservative estimate if we consider that we could achieve a future in which health continues to improve.
So these are my assumptions for this scenario:
- 800,000 years remaining for our species
- 11,000,000,000 people living at any one time
- 88 years of life expected for the average person
Taking this together, how many children will ever be born after the year 2022?
(800,000 years / 88 years per person) * 11,000,000,000 people =
100,000,000,000,000 people =
100 trillion people will be born in the next 800,000 years
When will the 1000th generation be born?
In the second chart I added this information as an annotation. One has to make several assumptions to estimate this point in time. Here are my assumptions:
In a world in which the population is stable, every 2 people have on average 2 children who live long enough to have children themselves. This would mean that within each 88 year period there will be as many births as there are people.
For simplicity we can assume that one generation is 22 years long (i.e., on average future people have children when they are 22 years old). This is a nice assumption because it means that each generation is a quarter as long as the life length of people in this scenario.
In this world each generation would be a cohort of 11 billion / 4 = 2.75 billion people.
This means that the 1000th generation from today would be born in 22,000 years from today. (This isn't exactly correct because there will be population growth in the next century, i.e. it would take a little longer than 22,000 years.)
In these 1000 generations there will be 2.75 billion * 1000 = 2,750 billion births.
That means the number of births in the next 1000 generations would be 346-times larger than today's world population (2,750 billion / 7.95 billion = 345.9).
How long will it take until as many babies are born as there are people today?
In the second chart I added this information as an annotation.
According to the UN projections there will be 8,036,352,977 children born between 2022 and 2079. This means that there will be as many children born in the next 57 years as there are people alive today.
Humanity's past, present and future in multiples of each other
The future in multiples of all people ever: 100,000,000,000,000 / 117,000,000,000 = 855-times
The future in multiples of the present: 100,000,000,000,000 / 7,953,952,577 = 12,572-times
The past in multiples of the present:
(117,041,198,802 - 7,953,952,577) / 7,953,952,577 = 13.7 = rounded to 14
One trillion in multiples of the present: 1,000,000,000,000 / 7,953,952,577 = 125.724 = rounded to 126 (This is what I use as the number of triangles per row.)
The number of future births over the next 5 billion years in multiples of today's population:
625 quadrillion people would be born in this scenario in the next 5 billion years: 625,000,000,000,000,000 people
People alive in 2022: 7,953,952,577 people
625,000,000,000,000,000 / 7,953,952,577 = 78,577,285
1.5 million years remaining: If Homo sapiens survives as long as Homo erectus
How long has Homo Erectus existed?
Homo erectus is an extinct species of archaic humans. It is among the first recognizable members of the genus Homo. It was also the first human ancestor to spread throughout Eurasia,
Homo erectus survived for at least 1.7 million years. The oldest fossils regarded as Homo Erectus are the Dmanisi specimens from present-day Georgia, dated to 1.8 million years ago (Lordkipanidze et al, 2006). The most recent fossils are from present-day Indonesia, and have been dated to 0.1 million years ago (Yokohama et al., 2008).
How large was humanity's future if we survived as long as Homo erectus?
If we - Homo sapiens - survive as long as Homo erectus we would have 1.5 million years left. Our future would be almost twice as large as shown in the chart in the main text.
Almost 190 trillion children would be born into this world.
This is the calculation:
- 1,500,000 years
- 11,000,000,000 people
- And the average person lives for 88 years
(1,500,000 years / 88 years per person) * 11,000,000,000 people =
187,500,000,000,000 people =
187.5 trillion people would be born in the next 1.5 million years
[Alternatively you could see this by considering that 1,500,000 years is 1.875-times longer than 800,000 years.]
1 billion years: If Homo sapiens survives as long as the earth is habitable
How long will Earth remain habitable? How long will our sun exist?
Astrophysicist Jillian Scudder, Anders Sandberg, and Toby Ord suggest that our planet will remain habitable for roughly a billion years.
- Toby Ord's 'The Precipice', especially footnote 40 in the first chapter.
- Jillian Scudder (2015) - The sun won't die for 5 billion years, so why do humans have only 1 billion years left on Earth?
- Anders Sandberg's text for the BBC: The greatest long-term threats facing humanity. He also explains what will happen when and why.
Based on the scenario above this would be a future in which 125 quadrillion children will be born.
This is the calculation:
- 1,000,000,000 years
- 1,000,000,000 years is 1250-times longer than 800,000 years
- 11,000,000,000 people
- And the average person lives for 88 years
(1,000,000,000 years / 88 years per person) * 11,000,000,000 people =
(1,000,000,000 / 88) * 11,000,000,000 = 125,000,000,000,000,000 people = 125 quadrillion people would be born in this scenario in the next billion years.
A quadrillion is a one followed by 15 zeros (1,000,000,000,000,000).
125 quadrillion is 125 thousand trillion people (According to the short scale).
5 billion years - as long as the sun exists
If humanity survived for as long as the sun exists, 5 billion years.
- 5,000,000,000 years
- 5,000,000,000 years is 6,250-times longer than 800,000 years
- 11,000,000,000 people
- And the average person lives for 88 years
(5,000,000,000 years / 88 years per person) * 11,000,000,000 people =
625,000,000,000,000,000 people =
625 quadrillion people would be born in this scenario in the next 5 billion years.
625 quadrillion is 625 thousand trillion people.
How to imagine 625 quadrillion births?
625 quadrillion relative to 100 trillion
Over the next 5 billion years: 625 quadrillion = 625,000,000,000,000,000
Over the next 800,000 years: 100 trillion = 100,000,000,000,000
625,000,000,000,000,000 / 100,000,000,000,000 = 6,250
Two ways to illustrate this:
- The chart would not fit on one page, but would need 6,250 pages.
- That's a stack that is 62.5 centimeters tall. [If one page is 0.1 mm thick]
- That's a stack of 30 books [If one book is 200 pages. 6250 / 200 = 31.25 books]
- If the chart for the 100 trillion people is 30 cm high, then a chart that shows the future that is 6250-times as long would be 62.5 metres high.
- 6250 * 30 cm = 62.5 metres
625 quadrillion relative to today's population
The ratio between today's world population and the future world population:
625,000,000,000,000,000 / 7,953,952,577 = 78,577,285
The ratio between future people and all people alive today would be 78.6 million to one.
78,577,285 meter are 78,577 kilometer
Making the beach 17 meter wide means it would be 4,622km long (78,577/17). These are 2872 miles.