Kurzgesagt – In a Nutshell
Sources – Dark Forest
For the topic of this video we were inspired by the science fiction novel “The Dark Forest” (2008) by Liu Cixin, the second volume of the great trilogy “Remembrance of Earth’s Past”.
- Today, most other species on our planet are so utterly at our mercy that we wipe out a dozen species a day just as an unintentional byproduct of how we like to run things.
A lot of very drastic numbers about extinction rates are floating around on the internet. This is one example:
#United Nations Environment Programme. Secretariat of the Convention on Biological Diversity. Message from Mr. Ahmed Djoghlaf, Executive Secretary, on the occasion of the International Day for Biological Diversity 22 May 2007
https://www.cbd.int/doc/speech/2007/sp-2007-05-22-es-en.pdf
Quote: “Extinction rates are rising by a factor of up to 1,000 above natural rates. Every hour, three species disappear. Every day, up to 150 species are lost. Every year, between 18,000 and 55,000 species become extinct. The cause: human activities.”
Unfortunately, Mr. Djoghlaf made a little mistake: If three species disappear every hour, 72 species would be lost every day. In general, citing a concrete figure for exinction rates is notoriously difficult in general. There are some discussions on the methods and on the “background extinction rate”, i.e. the extinction rate without the human impact, which is hard to determine. Because of this fact, we decided to go with a very conservative number here.
#Fangliang He et al. (2011): Species–area relationships always overestimate extinction rates from habitat loss. Nature, Vol. 473, pp. 368-371
https://www.nature.com/articles/nature09985
Quote: “Despite its importance, estimating extinction rates is still highly uncertain because no proven direct methods or reliable data exist for verifying extinctions. The most widely used indirect method is to estimate extinction rates by reversing the species–area accumulation curve, extrapolating backwards to smaller areas to calculate expected species loss. Estimates of extinction rates based on this method are almost always much higher than those actually observed.”
- The modern world has created conditions that enabled the most peaceful period in human history in modern history, but our nature is still the same.
At least, there is a declining in the absolute number of battle-related war deaths in conflicts between two or more more states since the end of the Second World War:
#Roser, M. (2016): War and Peace. OWID
https://ourworldindata.org/war-and-peace#
Quote: “The absolute number of war deaths has been declining since 1946. In some years in the early post-war era, around half a million people died through direct violence in wars; in contrast, in 2016 the number of all battle-related deaths in conflicts involving at least one state was 87,432.”
- And because of our nature we will likely at some point expand further outwards, into our solar system and eventually other star systems, where resources seem unlimited. There's enough space to keep everyone happy for billions of years. Or is there?
There are an estimated 100-400 billion stars and around 100 billion planets in the Milky Way. These stars and planets might supply energy or other commodities and even an estimated 6 billion planets might be earth-like and thus habitable - for human beings at least.
#NASA (2015): How Many Stars in the Milky Way?
https://asd.gsfc.nasa.gov/blueshift/index.php/2015/07/22/how-many-stars-in-the-milky-way/
Quote: “There are different models for estimating the number of stars in the Milky Way and the answers they give differ depending on what is used as the average mass of a star. The most common answer seems to be that there are 100 billion stars in the Milky Way on the low-end and 400 billion on the high end.”
#Michelle Kunimoto M. and Matthews J.M. (2020): Searching the Entirety of Kepler Data. II. Occurrence Rate Estimates for FGK Stars. The Astronomical Journal, Vol. 159, No. 6
https://iopscience.iop.org/article/10.3847/1538-3881/ab88b0
Quote: “For planets with sizes 0.75–1.5 R⊕ orbiting in a conservatively defined habitable zone (0.99–1.70 au) around G-type stars, we place an upper limit (84.1th percentile) of <0.18 planets per star.”
- If advanced civilization, we or someone else, acquired the technology to travel between the stars, even at a mere 0.1% of the speed of light, it would colonize the entire galaxy in roughly 100 million years. Which is not that long in comparison to the age of our galaxy – in principle any spacefaring civilization should be able to spread rapidly at least over huge sectors of the galaxy.
The Milky Way is estimated to be 10-13.6 billion years old (or 10-13.6 Gyr, 1 Gyr = 1 Gigayear = 1 billion years) which is slightly younger than the universe (13.8 Gyr).
#Sharma S. et al (2019): The K2-HERMES Survey: age and metallicity of the thick disc. Monthly Notices of the Royal Astronomical Society, Volume 490, No. 4, pp. 5335–5352
https://academic.oup.com/mnras/article/490/4/5335/5586605?login=true#176270188
Quote: “Assuming the asteroseismic scaling relations are correct, we estimate the mean age of the thick disc to be about 10 Gyr, in agreement with the traditional idea of an old α-enhanced thick disc.”
#NASA Science Space Place (2019): How old are Galaxies?
https://spaceplace.nasa.gov/galaxies-age/en/
Quote: “Most galaxies are between 10 billion and 13.6 billion years old. Our universe is about 13.8 billion years old, so most galaxies formed when the universe was quite young! Astronomers believe that our own Milky Way galaxy is approximately 13.6 billion years old. The newest galaxy we know of formed only about 500 million years ago.”
- This is amplified by the fact that talking over long distances is extremely hard and takes a long time.
For example, NASA’s 2020 Mars Rover Perseverance’s radio signal, which travels by the speed of light, takes between 5 and 20 minutes back to earth, depending on mars’ distance to earth.
#NASA Science Mars 2020 Mission Perseverance Rover
https://mars.nasa.gov/mars2020/spacecraft/rover/communications/
Quote: “It generally takes about 5 to 20 minutes for a radio signal to travel the distance between Mars and Earth, depending on planet positions.”
- If your opponent is light years away, sending an invasion fleet takes so long that by the time it arrives it might already be hopelessly obsolete. Also there are enough planets in the galaxy, conquering expeditions are a waste of resources.
Travel between stars is much slower than the speed of light, so it takes much longer than simple communication. And during that time, it is unlikely that the technological level of spacecraft will improve. Their capabilities are 'frozen' at the time of departure. It is a real problem if the spacecraft are a military fleet hoping to beat an opponent, as their target will continue to improve their own technology over that period.
If we send an invasion force sufficiently advanced to defeat an alien civilization 50 lightyears away, and it is travelling at 10% of the speed of light, then it might be hopelessly outmatched by the time it arrives.
The alien civilization's level of technology might only get 1% better year on year, but that is enough to make it 144x more advanced by the time the spacecraft arrive.
Here is the calculation for it:
1% better = multiply by 1.01. After 2 years, 1.01 x 1.01 = 1.0201 which is 102.02% or 2.01% better. So, after 50 years, we get 1.01^50 = 1.64463 and after 500 years, 1.01^500 = 144.772. But why 500 years? Because Time = Distance/Speed = 50 lightyears / 0.1 speed of light = 500 years.
- So the ultimate form of planetary annihilation weapon is probably something like a Relativistic Kill Vehicle – a missile shot at a planet at a fraction of the speed of light. For example, a missile the size of a person going 95% the speed of light has as much energy as all nuclear bombs on earth.
Because it travels so close to the speed of light, it packs an incredible amount of energy.
At 95% of the speed of light, each 1 kg of mass has a kinetic energy of 1.98*10^17 joules. A 63 kg projectile would have about 1.25*10^19 joules, which matches the yield of all the nuclear arsenals on Earth as estimated in our “All the Bombs” video:
#Kurzgesagt - In a Nutshell (2019): All the Bombs
https://www.youtube.com/watch?v=JyECrGp-Sw8
You can perform your own relativistic energy calculations using the calculators found here: http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/releng.html
The equation it uses is the following: RKE = Mass * C^2 * ((1/(1 - B^2)^0.5) - 1)
With:
RKE = Relativistic Kinetic Energy
Mass in kg
C = speed of light in m/s
B = the fraction of speed of light the projectile is travelling
- And this is not that absurd of an idea – a civilization only slightly further up the Kardashev scale than we are today would have access to enough energy to send multiple strikes against every planet it suspects of harboring life.
The Kardashev scale, published 1964 by the Russian astronomer Nikolai Semyonovich Kardashev, classifies civilizations regarding to the amount of power they produce. He has defined three levels/types:
Type I: technological level/terrestrial energy consumption in 1964,
Type II: “a civilization capable of harnessing the energy radiated by its own star,”
Type III: “a civilization in possession of energy on the scale of its own galaxy”.
For a lot more on the Kardashev scale, check out our video about it:
#Kurzgesagt - In a Nutshell (2020): What do Alien Civilizations Look Like? The Kardashev Scale
https://www.youtube.com/watch?v=rhFK5_Nx9xY
Or you can find the original paper here:
#Kardashev N.S. (1964): Transmission of information of extraterrestrial civilisations. Soviet Astronomy, Vol. 8, No. 2, pp. 217-221
http://articles.adsabs.harvard.edu/pdf/1964SvA.....8..217K
Quote: “I - technological level close to the level attained on the earth, with energy consumption at ≈4 x 1019 erg/sec.
II - a civilization capable of harnessing the energy radiated by its own star (for example, the stage of successful construction of a “Dyson sphere” [6]); energy consumption at ≈4 x 1033 erg/sec.
III - a civilization in possession of energy on the scale of its own galaxy, with energy consumption a ≈4 x 1044 erg/sec.”
It is difficult to determine just how much energy is needed to reliably wipe out a civilization. The impact of a Relativistic Kill Vehicle with an energy on the same order of magnitude as all the nuclear weapons on Earth, which is 10^20 joules, would be a good estimate. Just to be extra certain, we raise this by a factor 10 to 10^21 Joules. It should be enough to deliver a devastating strike to everybody in a solar system.
10^21 Joules is the equivalent to all the energy produced by humanity on Earth for 1.8 years. Our consumption in 2020 was 556.63 exajoules, which is 5.56*10^20 Joules. It is clearly not possible for our civilization to launch such attacks.
You can find a detailed list of global energy consumption here:
#bp Statistical Review of World Energy 2021
However, a Kardashev Type 1 civilization is described as having access to all the solar energy reaching the Earth, which is 1.74*10^17 watts. That adds up to 5.48*10^24 joules per year.
You can find the detailed calculation here:
#UCAR Center for Science Education (2021): Calculating Planetary Energy Balance & Temperature
https://scied.ucar.edu/earth-system/planetary-energy-balance-temperature-calculate
A 10^21 Joule attack would therefore represent only 0.018% of the total output of a Kardashev Type 1 civilization, the cumulative output of roughly 1.6 hours. A civilization at this scale can wipe out multiple star systems every day without cutting into its energy reserves.
- What makes these kinds of weapons so sinister is how much they favor a first strike, since they would be so fast that it might be impossible to protect yourself effectively against them.
Due to the fact that a warning signal travels with the speed of light, while a “classic” Relativistic Kill Vehicle (RKV) only travels close to the speed of light, a signal would be slightly faster than the rocket.
Assuming a RKV, fired by a civilization 50 light years away, is flying with 99.9% of the speed of light, a signal which could warn us, would reach us just between two to three weeks before an impact. That might be a little short to protect earth from annihilation.
You can try out different scenarios using a simple formula: distance = speed of light * time (s = c * t).
- So at least until we know more, it seems that the best we can do is to fade into the background and listen.
This is what we are doing since many decades, i.g. in the context of many SETI-programms (SETI = Search for Extraterrestrial Intelligence). In general, many SETI-programms are focused on detecting any kind of signal from outer space (called “technosignal” or “technosignature” by some people), like the current “Breakthrought Listen” programm.
#Breakthrought Initiatives (2021): About
https://breakthroughinitiatives.org/about
Quote: “Breakthrough Listen is a $100 million program of astronomical observations and analysis, the most comprehensive ever undertaken in search of evidence of technological civilizations in the Universe. The partners with some of the world’s largest and most advanced telescopes, across five continents, to survey targets including one million nearby stars, the entire galactic plane and 100 nearby galaxies at a wide range of radio and optical frequency bands.”
- The radio signals humanity has transmitted in the last 200 years traveled only a tiny distance and have long decayed into unreadable noise.
In 1901, Guglielmo Marconi confirmed the first transatlantic radio transmission. The radio signal headed up to space and was reflected at the ionosphere, a part of the Earth's upper atmosphere.
#Belrose, J.S. (1995): Fessenden and Marconi: their differing technologies and transatlantic experiments during the first decade of this century. International Conference on 100 Years of Radio, pp. 32-43
https://digital-library.theiet.org/content/conferences/10.1049/cp_19950787
- As for now, the good news is there is actually little we need to do. We just need to be wise and thoughtful about the signals we send out into the galaxy.
In addition to the “step into the background and listen” -approach mentioned above, you can also just go the “shout it out loud” -way (so-called “active SETI”). For this purpose, messages are sent into space that are specially addressed to extraterrestrials. One of the first and probably the best known radio message of that kind is the “Arecibo message”, sent out in 1974. At first sight, it looks like a riddle, but this message contains basic information about humans such as DNA, numbers or our position. It is send to the star cluster M13 about 21,000-25,000 lightyears from earth.
#SETI-Institute (2021): Arecibo Message
https://www.seti.org/seti-institute/project/details/arecibo-message
There is a huge scientific debate about active SETI. In a nutshell, we say “Hello there! Here we are!” to a civilization which is probably hostile to us.
#Musso, P. (2012): The problem of active SETI: An overview. Acta Astronautica, Vol. 78, pp. 43-54
https://www.researchgate.net/publication/256935145_The_problem_of_active_SETI_An_overview
Quote: “The main objection against the idea of transmitting messages from Earth always was, and still is, that, while passive SETI is surely not dangerous for us, active SETI may be, since ETs could be malevolent.”