1. Evaluating the Extraterrestrial Hypothesis
Where’s the data?

2. the “extraterrestrial hypothesis?
The belief that we’re not alone – that extraterrestrial life exists.

3. What’s it really based on?
Contrived mathematical probability
Optimism based on assumptions
Conspiracy Theory
Willingness to be deceived

4. Contrived mathematical probability
Drake Equation (1961)
Astronomer and astrophysicist Frank Drake
Founding of SETI

5. Contrived mathematical probability
“The Drake equation leaves much to be desired in terms of what it's supposed to tell us about both the nature and predominance of extraterrestrial life in our Galaxy.” The Drake equation states that:
Source:
Lynette Cook, “The Drake Equation is Obsolete,” Sentient Developments (2007)

6. Contrived mathematical probability

7. Contrived mathematical probability
“The integers that are plugged into this equation are often subject to wide interpretation and can differ significantly from scientist to scientist. Even the slightest change can result in vastly different answers [T]here is often very little consensus among specialists as to what the variables might be. . .
Source:
Lynette Cook, “The Drake Equation is Obsolete,” Sentient Developments (2007)

8. Contrived mathematical probability
. . . Consequently, the Drake formula relies on 'stabs in the dark.' This makes it highly imprecise and unscientific. The margin of error is far beyond what should be considered acceptable or meaningful.”
Source:
Lynette Cook, “The Drake Equation is Obsolete,” Sentient Developments (2007)

9. Contrived mathematical probability
“Another major problem of the Drake Equation is that it does not account for two rather important variables: cosmological developmental phases and time More specifically, it does not take into consideration such factors as the age of the Galaxy,
Source:
Lynette Cook, “The Drake Equation is Obsolete,” Sentient Developments (2007)

10. Contrived mathematical probability
the time at which intelligence first emerged, or the presence of physiochemical variables necessary for the presence of life (such as metallicity required to form planets). The equation assumes a sort of cosmological uniformity rather than a dynamic and ever changing universe. . .
Source:
Lynette Cook, “The Drake Equation is Obsolete,” Sentient Developments (2007)

11. Contrived mathematical probability
. . . the equation asks us to guess the number of Earth-like planets, but it does not ask us when there were Earth- like planets. And intelligence itself may have been present as long as 2 to 4.5 billion years ago.”
Source:
Lynette Cook, “The Drake Equation is Obsolete,” Sentient Developments (2007)

12. Contrived mathematical probability
Recent pessimism:
“These first two variables may be roughly estimated with decades of painstaking astronomical research. Now we are stuck with five truly useless numbers.”
Source:
Tom Hartsfield, “Why the Drake Equation is Useless,” Real Clear Science (2015)

13. Contrived mathematical probability
Source:
Web comic XKCD

14. Optimism based on assumptions
“Princeton University researchers have found that the expectation that life — from bacteria to sentient beings — has or will develop on other planets as on Earth might be based more on optimism than scientific evidence.”
Source:
Princeton University News, April 26, 2012

15. Optimism based on assumptions
“[Researchers] reported in the Proceedings of the National Academy of Sciences that the idea that life has or could arise in an Earth-like environment has only a small amount of supporting evidence, most of it extrapolated from what is known about abiogenesis, or the emergence of life, on early Earth…
Source:
Princeton University News, April 26, 2012

16. Optimism based on assumptions
. . . Instead, their analysis showed that the expectations of life cropping up on exoplanets — those found outside Earth’s solar system — are largely based on the assumption that it would or will happen under the same conditions that allowed life to flourish on this planet. . .
Source:
Princeton University News, April 26, 2012

17. Optimism based on assumptions
. . . In fact, the researchers conclude, the current knowledge about life on other planets suggests that it’s very possible that Earth is a cosmic aberration where life took shape unusually fast. If so, then the chances of the average terrestrial planet hosting life would be low. . .
Source:
Princeton University News, April 26, 2012

18. Optimism based on assumptions
. . . Joshua Winn, an associate professor of physics at the Massachusetts Institute of Technology, said that Turner and Spiegel cast convincing doubt on a prominent basis for expecting extraterrestrial life.” 
Source:
Princeton University News, April 26, 2012

19. Optimism based on assumptions
“Just because life emerged early on Earth does not mean that this is likely to occur on other Earth-like planets.”
Source:
“Extraterrestrial Life Could be Extremely Rare,”

20. Optimism based on assumptions
Peter D. Ward, professor of paleontology at the University of  Washington
  Donald C. Brownlee, professor of Astronomy, University of Washington
member of the National Academy of Sciences and chief scientist of NASA's $166 million Stardust mission
Book summary online

21. Optimism based on assumptions
1. The right chemical elements are too rare in abundance. Modern science suggests that Earth's composition and stability are extraordinarily rare.
Book summary online

22. Optimism based on assumptions
2. Most everywhere else in the Universe, the radiation levels are too high. . . Recent studies show that the cosmos, especially galactic centers, are hotbeds of violence swept by killing waves of X-rays, gamma rays and ionizing radiation.
Book summary online

23. Optimism based on assumptions
3. The rain of killer meteorites is too intense for life ever to have evolved into advanced communities. . . the rate of terrestrial impacts could be as much as 10,000 times higher, but for the presence of Jupiter.
Book summary online

24. Optimism based on assumptions
4. Alien microbes may survive in many places as a kind of cosmic shower scum, they say, but not extraterrestrials civilized enough to be awash in technology.
Book summary online

25. UFO sightings and presumed crashes Government cover-ups
Conspiracy theory
UFO sightings and presumed crashes
Government cover-ups
Anecdotal evidence

26. Even best cases have multiple possible answers besides ETI
Conspiracy theory
Even best cases have multiple possible answers besides ETI
Secret space program
Rogue civilization
Rogue but isolated technology

27. Willingness to be deceived

28. Willingness to be deceived