Fermi paradox
Fermi's paradox wonders why, with the age and size of the universe and billions of stars and planets that have existed for billions of years, we have not detected any other alien civilizations. There have been attempts to resolve the Fermi paradox by finding evidence of alien civilizations, along with thoughts that such life could exist without humans knowing.
The physicist Enrico Fermi first asked the question in an informal discussion in 1950. A paper by Michael H. Hart in 1975 made scientists more curious and they began to study the question in more detail. This is why some people call it the Fermi–Hart paradox.[1] Other common names for the same phenomenon are Fermi's question ("Where are they?"), the Fermi Problem, the Great Silence,[2][3][4][5][6] and silentium universi[6][7] (Latin for "the silence of the universe"; the misspelling silencium universi is also common).
Background
[change | change source]Fermi first posed the paradox informally
- The universe is old, there are many stars. In the case that life developing on earth is not exceptional, life outside earth should be common.
- Life is no exception among the planets, our solar system isn't special; therefore, there must be other technologically advanced civilizations in our galaxy.
- The galaxy has a width of about 100,000 light years. In a project, such as Project Icarus, a propulsion has been developed that can reach between 1 and 10 % of the speed of light. With such a propulsion, travelling from one edge to the other (in a straight line, without stopping) takes between one and ten million years. The galaxy is about 10 billion years old. This means that there is enough time to travel this distance, even multiple times.
- If there is or was at least one other civilization in the milky way, there must be some traces left.
The paradox is that no trace of any other civilization outside earth has been found.
Why interstellar communication is difficult
[change | change source]Space is deep
[change | change source]Extraterrestrial life might exist, but humans may not know about it. To send signals across long distances in our galaxy, and the universe, is difficult. This is because the power output needed to project the signal would be very large. Coherent (laser-like) signals travel at the speed of light, but our own galaxy is 100,000 light years across. Alien civilizations may not be able to detect the signal, or they may not understand the communication or the method used to communicate.
Space is dusty
[change | change source]Space is full of dust clouds and magnetic fields, which would disturb or eliminate even a coherent (laser-like) beam of electromagnetic radiation. Thousands of tons of cosmic dust are thought to reach the Earth's surface every year.[8] A signal would face much interference in any long-distance travel across space.
If it is difficult or impossible for us, it may also be difficult for other forms of life. As for other galaxies, the Andromeda galaxy is 2.5 million light years away.[9]
Time
[change | change source]In our Galaxy, the time it takes for signals to travel is very large. Vast eras of time would pass before a reply could be received. There are theories about "worm-holes" in space in which communication could be sent through space more quickly, but these are just theories now. There is still a desire for space travel.[10] Locally in the Solar System, the main goal is to get minerals which are scarce on Earth.[11]
Explanations
[change | change source]There are different explanations to the paradox:
- Earth is a special case, there is no extraterrestrial life
- Colonizing another habitable planet is difficult to impossible. This is mainly due to the large distances. The next star is Proxima Centauri. It is 4.2 light years away. This means that travelling at the speed of light, it takes 4.2 years to reach. The 20 closest stars are between 4.2 and 39 light years away
- Some people think that once a civilization reaches a certain stage of development, it will likely destroy itself.
Related pages
[change | change source]References
[change | change source]- ↑ Wesson, Paul (1990). "Cosmology, extraterrestrial intelligence, and a resolution of the Fermi-Hart paradox". Royal Astronomical Society, Quarterly Journal. 31: 161–170. Bibcode:1990QJRAS..31..161W.
- ↑ Brin, Glen David (1983). "The 'Great Silence': The Controversy Concerning Extraterrestrial Intelligent Life". Quarterly Journal of Royal Astronomical Society. 24: 283–309. Bibcode:1983QJRAS..24..283B.
- ↑ James Annis (1999). "An Astrophysical Explanation for the Great Silence". Journal of the British Interplanetary Society. 52 (1): 19. arXiv:astro-ph/9901322. Bibcode:1999JBIS...52...19A.
- ↑ Hanson, Robin (1998). "The Great Filter – are we almost past it?".
- ↑ Bostrom, Nick (2007). "In Great Silence there is Great Hope" (PDF). Retrieved 2010-09-06.
{{cite journal}}: Cite journal requires|journal=(help) - 1 2 Milan M. Ćirković (2009). "Fermi's Paradox – the last challenge for Copernicanism?". Serbian Astronomical Journal. 178 (178): 1–20. arXiv:0907.3432. Bibcode:2009SerAJ.178....1C. doi:10.2298/SAJ0978001C. S2CID 14038002.
- ↑ Lem, Stanisław (1983). His Master's Voice. Harvest Books. ISBN 0-15-640300-5.
- ↑ Spacecraft measurements of the cosmic dust flux, Herbert A. Zook. doi:10.1007/978-1-4419-8694-8_5
- ↑ Riess, Adam G.; Fliri, Jürgen; Valls-Gabaud, David 2012. Cepheid period-luminosity relations in the near-infrared and the distance to M31 from the Hubble Space Telescope wide field camera 3". The Astrophysical Journal 745 (2): p156.
- ↑ Crawford I.A. 2011. Project Icarus: a review of local interstellar medium properties of relevance for space missions to the nearest stars. Acta Astronautica 68 (7–8): 691–699.
- ↑ Outer Solar System : prospective energy and material resources. Badescu, Viorel,, Zacny, Kris. Cham, Switzerland. 2018-04-28. ISBN 9783319738451
