1 / 30

Week 13: Discovering SETI

Week 13: Discovering SETI. The Drake List Intelligence SETI. The Drake List (aka “the Drake Equation”). Simplified math can often derive sophisticated results. Example: How many undergraduates are at Harvard? How many candidate undergraduates apply per year? ~ 24,000

ataret
Download Presentation

Week 13: Discovering SETI

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Week 13: Discovering SETI The Drake List Intelligence SETI

  2. The Drake List (aka “the Drake Equation”) Simplified math can often derive sophisticated results. Example: How many undergraduates are at Harvard? How many candidate undergraduates apply per year? ~ 24,000 How many of these candidates are accepted? ~ 7% How long do students typically stay? ~ 4 years 24,000 applicants/year × 0.07 acceptances/applicant × 4 years = 6720 students

  3. The Drake List (aka “the Drake Equation”) An interesting exercise from 1961 that helps, in concept: — Calculate the number of advanced civilizations in the galaxy; — Calculate the distance to the nearest extraterrestrial civilization. In practice, it mostly… — Encourages other sciences to dismiss astrobiology as fluff! Three important considerations are included in this equation: How rapidly candidate stars are being formed; How many of these candidate stars could give rise to actual civilizations; How long the civilizations persist. (Yes, just like the Harvard calculation.)

  4. Input factors for the Drake list How many civilizations are in the galaxy? What is the rate at which stars form? (R*, stars/year) What fraction of stars have adequate life-spans? (FT) What fraction of stars could have habitable planets? (FP) How many habitable planets occur around each star? (NP) What fraction of habitable planets develop life? (FL) What fraction of planets with life-forms develop intelligent life-forms? (FInt) What fraction of intelligent life-forms develop civilizations capable of interstellar communication? (FComm) How long does each planet typically maintain such civilizations? (L)

  5. Constructing the Drake equation What is the rate at which stars form? Galactic star formation is a subject of considerable research efforts around the world. Details differ, but to a general order of magnitude, scientists feel that about 10-20 new stars reach the main sequence each year.R*=10-20 stars/year

  6. Constructing the Drake equation What fraction of stars have adequate lifespans?Ruling out O, B, A, and F stars leaves about 97% of all stars.FT = 0.97 Formation rate of suitable stars = R* × FT

  7. Constructing the Drake equation What fraction of stars might have habitable planets?FP = ?? (~0 for the rare Earth hypothesis) Kepler results suggest FP = 1.4-2.7% for sunlike stars Formation rate of habitable star systems= (R* × FT) × FP

  8. Constructing the Drake equation How many habitable planets occur around each star?For the Sun, NP = 1-2. It will be several years before we can have reasonable information about other star systems. Should we follow the Rare Earth Hypothesis, or the Copernican Principle?Since the majority of stars formed are K and M stars with tiny habitable zones, might we infer that there should be room for very few planets in the habitable zone?Formation rate of habitable planets = (R* × FT) × FP × NP This is similar to your book’s term “NHP”, which is the total number of habitable planets currently formed.

  9. Constructing the Drake equation What fraction of planets develop life?How difficult is it for life to develop? Are the conditions so specific that life almost never develops?Note that life developed relatively soon after the planet became habitable (after the cessation of the late heavy bombardment). This suggests that life develops rapidly, i.e., relatively easily.Furthermore, the chemical ingredients of life are widespread through the universe, and readily synthesized into more advanced compounds, as demonstrated by the Miller-Urey experiment.FLife = 1.0? Formation rate of planets with life = (R* × FT× FP × NP) × FLife

  10. Constructing the Drake equation What fraction of planets develop intelligent life-forms?Treating the Cenozoic era (post K-T boundary) primates as one lineage, we might wish to include cetaceans (whales and dolphins) in the ranks of intelligent life. So, on our planet, we know intelligent life developed not once, but twice. This suggests that intelligence occurs relatively frequently?FInt = ? Formation rate of planets with intelligent life = (R* × FT× FP × NP× FLife ) × FInt

  11. Constructing the Drake equation What fraction of intelligent life-forms develop civilizations capable of interstellar communication?Is such a step possible for fully aquatic organisms? If not, should cetaceans be removed from the list?FComm = ? Formation rate of planets with technological civilizations = (R* × FT× FP × NP× FLife) × (FInt × Fcomm)

  12. Constructing the Drake equation How long does each civilization persist?Perhaps the most variable and unknown of all the components of the Drake List of parameters.If advanced species go extinct because they self-destruct, or because of the environment, this results in a decrease in the overall number of species in the galaxy at any time.Vertebrate species typically survive for about 2 million yearsL=2×106 yrIf advanced species overcome the obstacles to survival imposed upon them by their environments, survival time is the age of the galaxy: L=109 yr

  13. The Drake equation N.B. See “Cosmic Calculation 12.1” to see how to convert N to the distance to our nearest neighbor! Lets use the equation to determine the number of advanced, communicating civilizations in the galaxy: N = R* FT FP NP FLife FInt FCommL R*  star formation rate FT  stars with adequate life spans FP  stars with planets NP  # of planets per system FLife  planets that develop life FInt  planets that develop intelligent life FComm  planets with interstellar communications L  survival lifetimes — Or, as in your book— N = (R* FT FP NP ×L) × (FLife) × (FInt FComm)) = NHP × FLife × FCiv × FNow Alas, N is what you want it to be! We are no closer to having N, than we were when Drake developed the equation in 1961!

  14. FInt: Intelligence in the galaxy Intelligence is important enough of a concept for us to examine this more closely. First, how do we measure intelligence? “IQ” (intelligence quotient) was originally defined as a fraction, i.e., a person’s “mental age” divided by their chronological age, times 100. Now standardized IQ tests are created, with a difficulty level so that on average people score 100, and 1σ = 15 points. Therefore, 67% of people have an IQ of 85-115 points. IQ tests are controversial, and may reflect cultural biases such as social status, education, health care, etc.

  15. FInt: Intelligence in the galaxy IQ tests cannot be given to other species, so we use “Encephalization quotient” (EQ) instead. It is the average ratio of brain mass to body mass. In general, bigger bodies require bigger brains to run them. But some organisms have a larger-than-necessary brains. They are the smarty-pants organisms that would contribute to FInt.

  16. FInt: Intelligence in the galaxy If we think that intelligence is a common adaptation by life forms in our galaxy, it must have an evolutionary reason to develop. Hypothesis Intelligence has an evolutionary advantage. Predictions We should observe intelligence being favored by evolutionary selection pressures; We should see the evolution of other intelligent species (i.e., intelligence is a strategy appearing multiple times, in convergent evolutionary pathways; We should see that intelligent species have a competitive advantage over non-intelligent species.

  17. Intelligence as a strategy for survival Do we see intelligent species evolving often? There are not many smart animals. That doesn’t necessarily mean that intelligence is not an advantageous adaptation—rather it just might simply be limited in application. If you are a grass-eating herd animal, you don’t have to be smart. You just have to be able to eat, and evade predators long enough to reproduce. There are some surprisingly smart animals, such as corvids (i.e., crows and ravens). However, intelligence seems to be a relatively uncommon evolutionary approach. Is intelligence rare and unlikely?

  18. Intelligence as a strategy for survival What factors favor intelligence? While we do see a few cases in which the EQ of animal lineages have increased in time, it seems to be a relatively uncommon evolutionary approach. Cetacean encephalization (EQ=2-5) seems to have been associated with the development of sonar in toothed whales. Similarly, human encephalization (EQ=7) may have been associated with the development of verbal language.

  19. Intelligence as a strategy for survival Why our large brains? Taipans are astonishingly venomous, with neurotoxins and other toxic agents. A single bite injects enough venom to easily kill a human several times over. Why did taipans evolve such a toxic bite in a land without very large mammals? Similarly, humans seem to be far smarter than is needed from an evolutionary perspective. Was it highly fortuitous humans just managed to evolve such an unnecessarily large EQ?

  20. SETI—what is being sought? Local communication signals used by aliens?Probably very weak, nearly undetectable signals. Note that in human civilization, our TV broadcasts have switched from 30MW stations to 20W satellite direct-to-TV transmissions. We are going into stealth mode. Communication between worlds?Probably weak for communications between nearby planets—only distant planets would have strong communication signals. Communications between distant planets would probably be highly directional, and unlikely to be detected. Intentional signal beacons.This third type of signal is what would be most likely to be observed and understood, as it would be designed for our detecting it. Optical or radio?SETI has traditionally been conducted in radio wavelengths. Recently, some SETI work has been conducted in optical wavelengths, i.e., seeking flashes of laser light. An advantage is that there could be no interference from terrestrial sources. A gregarious civilization would be visible with our naked eyes!

  21. SETI experiments: first attempts 1899 Nikola Tesla (who developed AC) thought he detected alien broadcasts but these were later found to be whistlers (caused by lightning) and possibly Jupiter’s magnetosphere in 1899. “The thought flashed through my mind that the disturbances I had observed might be due to intelligent control…. The feeling is constantly growing on me that I had been the first to hear the greeting of one planet to another.” GuglielmoMarconi (developed the radio telegraph) detected similar false signals. 1924 The US army tried to detect aliens during a close approach to Mars.

  22. Green Bank, 1960: Frank Drake used the 26m radio scope in Green Bank, West Virginia, to look for 1420 MHz signals in two star systems. This was called Project Ozma. Continued in 1970s with “project Ozpa” and “Ozma II.” Ohio State University, 1973-1998:The “Big Ear” detected something on 15 August 1977, “6EQUJ5”, the “WOW signal,” which lasted 37 seconds and rated 30 sigma.37 seconds was an integration time, and it was missing on a return scan, only several minutes later.RA= 19h 25m 31s ± 10s or 19h 28m 22s ± 10s,Declination= −26°57′ ± 20′ ; Sagittarius SETI experiments: early years

  23. Two NASA searches began in 1992: Arecibo, 1992: This 300m telescope started to look for radio transmissions. Goldstone Deep Space Complex, CA, 1992:A 34m telescope in the Mojave desert begins simultaneous search.Less than 12 months later, NASA’s work was killed by Sen. Richard Bryan (NV). SETI experiments: NASA

  24. SETI institute, founded 1984:Continues to search at various telescopes, including the Parks 64m, Greenbank, VA, etc.The Allen Array in Hat Creek (N California) has 42 antennae, and an ultimate construction target of 350 antennae. SETI@home, 1999: A “distributed computing project,” with 5 million users, the world’s largest extended supercomputer. Current SETI projects

  25. What if SETI ever became successful? What would we do if we were successful? Protocols in the “Declaration of Principles Concerning Activities Following the Detection of Extraterrestrial Intelligence” are recommended. In summary: Verify it cannot be explained by conventional means. Tell your funding agencies (so they can avoid embarrassment).Governments should be informed. (Note: just “should”.) Announce the news to all scientists, including many scientific organizations and the UN. Go public. All data is made public. Seek verification of the detection by further study. Seek international agreement to protect the signal from terrestrial pollution. Plans to send a response would be studied carefully, after appropriate international consultations. Will these guidelines be followed by publication hungry scientists?

  26. CETI (note the C instead of the S) SETI (Search for extraterrestrial intelligences)—passive. CETI (Communication with extraterrestrial intelligence)—active. CETI is by its nature potentially much more dangerous. Unfortunately, many of these are science-lite PR stunts. Ex: In 2008, on its 40th anniversary, an mp3 file of the Beatles song, “Across the Universe” was beamed to Polaris (433 LY) by NASA. Some cautious scientists advise that it would be far wiser for us to quietly listen in to possible conversations, instead of bursting in, yelling at the top of our lungs.

  27. CETI 1974: “Arecibo Broadcast.” A 3-minute signal was sent towards M13, a globular cluster of a few×105 stars. If it were intecepted intact and properly decoded, it could resolve to a 23×73 pixel graphic. Lucky inhabitants will get this signal from Drake, Sagan, and others in 21,000 years.

  28. Results from CETI After a 2001 transmission, a prank “response” was carved into a wheat field by a group of crop circle aficionados…

  29. Alexander Zaitsev, Chief Scientist at the Russian Academy of Sciences’ Institute of Radio Engineering and Electronics (Evpatoriya, Eukraine) is continuing to use instrumentation to blast powerful signals to stars like Gliese 581, which has several planets. 1999: Cosmic Call 1—to four nearby stars. Mathematically more robust than the Arecibo broadcast (it was less prone to degradation if individual pixels are lost), it was marred by the inclusion of names and addresses of 2000 donors to the program. 2001: Teenage Message—to six nearby sunlike stars. 2003: Cosmic Call 2—to five nearby stars. 2008: A Message from Earth—to the single star, Gliese 581. To arrive in 2029. 2009: Canberra Australia joins the silliness with “Hello from Earth”, a stunt broadcast to Gliese 581, with little or no science behind it. Further attempts at active CETI

  30. Concerns about CETI Remember item #8 in the protocol for detecting alien broadcasts? “8) Plans to send a response would be studied carefully, after appropriate international consultations.” During a scientific meeting in 2007, this was modified by deleting the phrase involving “after appropriate international consultations” “8) Plans to send a response would be studied carefully.” This has no teeth. Various senior scientists at the leading international SETI study group have recently resigned in disgust and protest. Who are these few scientists to speak for all of humanity? Should scientists be doing the talking, or should diplomats be involved? This may seem funny today, but will it be funny tomorrow?

More Related