__Fermi Paradox__:The

**Fermi paradox**or

**Fermi's paradox**, named after physicist Enrico Fermi, is the apparent contradiction between the lack of evidence and high probability estimates, e.g., those given by the Drake equation, for the existence of extraterrestrial civilizations. The basic points of the argument, made by physicists Enrico Fermi (1901–1954) and Michael H. Hart (born 1932), are:

- There are billions of stars in the galaxy that are similar to the Sun, many of which are billions of years older than Earth.
- With high probability, some of these stars will have Earth-like planets, and if the Earth is typical, some might develop intelligent life.
- Some of these civilizations might develop interstellar travel, a step the Earth is investigating now.
- Even at the slow pace of currently envisioned interstellar travel, the Milky Way galaxy could be completely traversed in a few million years.

https://en.wikipedia.org/wiki/Fermi_paradox

http://waitbutwhy.com/2014/05/fermi-paradox.html

__Simpson's Paradox__:**Simpson's paradox**, or the

**Yule–Simpson effect**, is a paradox in probability and statistics, in which a trend appears in different groups of data but disappears or reverses when these groups are combined. It is sometimes given the impersonal title

**reversal paradox**or

**amalgamation paradox**.

https://en.wikipedia.org/wiki/Simpson%27s_paradox

__Pigeonhole Principle__:In mathematics, the

**pigeonhole principle**states that if

*n*items are put into

*m*containers, with

*n*>

*m*, then at least one container must contain more than one item. This theorem is exemplified in real-life by truisms like "there must be at least two left gloves or two right gloves in a group of three gloves". It is an example of a counting argument, and despite seeming intuitive it can be used to demonstrate possibly unexpected results; for example, that two people in London have the same number of hairs on their head.

https://en.wikipedia.org/wiki/Pigeonhole_principl

**:**

__Birthday Problem__In probability theory, the

**birthday problem**or

**birthday paradox**concerns the probability that, in a set of randomly chosen people, some pair of them will have the same birthday. By the pigeonhole principle, the probability reaches 100% when the number of people reaches 367 (since there are 366 possible birthdays, including February 29). However, 99.9% probability is reached with just 70 people, and 50% probability with 23 people. These conclusions include the assumption that each day of the year (except February 29) is equally probable for a birthday.

https://en.wikipedia.org/wiki/Birthday_problem