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# ASTR 101- Solar System Astronomy - Lab 5 - Life in the Universe

Life in the Universe Experiment A05

· Part A – The Drake Equation

· Part B – The Fermi Paradox

Theory

The abundance and characteristics of planets around other stars has long been a topic of great interest in astronomy. It has direct implications on our understanding of our own planet and solar system. It is also directly linked with the broader philosophical question “are we alone in the universe?” If other stars commonly have planets, this would greatly increase the likelihood of us discovering life elsewhere in the universe.

Planets around other stars proved very elusive to find. In 1995, astronomers had infrared observations of protosolar systems and had detected planets around pulsars. However, no planets around regular stars were known despite the considerable effort that had been exerted to find them. All that we knew about planets came from those in our own solar system.

All of that changed beginning in 1995 when an extrasolar planet was discovered using the radial velocity technique. As of 2014 nearly 1800 extrasolar planets are known, with more being found at an increasing rate. Several large programs are still underway to find more extrasolar planets, including the Kepler space mission. Launched in 2009, Kepler is staring at over 100,000 stars, waiting for a planet to cross in front of one of them.

Procedure

Part A: The Drake Equation

The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy. The equation was written in 1961 by Frank Drake not for purposes of quantifying the number of civilizations but intended as a way to stimulate scientific dialogue at the world's first Search for Extraterrestrial Intelligence (SETI) meeting, in Green Bank, West Virginia. The equation summarizes the main concepts which scientists must contemplate when considering the question of other radio-communicative life. The Drake equation has proved controversial since several of its factors are currently unknown and estimates of their values span a very wide range.

The Drake equation is as follows:

where N is the estimate of the number of civilizations in the Milky Way Galaxy that are currently able to communicate.

1. Look up online, and write down, in your own words, what each variable in the Drake Equation represents:

N : The number of broadcasting civilizations.

R* : Average rate of formation of suitable stars (stars/year) in the Milky Way galaxy

fp : Fraction of stars that form planets

ne : Average number of habitable planets per star

fl : Fraction of habitable planets (ne) where life emerges

fi : Fraction of habitable planets with life where intelligent evolves

fc : Fraction of planets with intelligent life capable of interstellar communication

L : Years a civilization remains detectable

2. Visit the website http://www.pbs.org/lifebeyondearth/listening/drake.html.

This website is a calculator that will estimate the number of intelligible civilizations in the Milky Way. Guess some of the values for the variables in the Drake Equation and use the website to calculate the number of civilizations we can expect to find in the Milky Way.

Number of Civilizations: 1.13

3. Now use the More button after each explanation on the website and use the current best values given there to estimate the number of civilizations.

Current Best Estimates on the Number of Civilizations: 1.13

The Fermi paradox (or Fermi's paradox) is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilization and humanity's lack of contact with, or evidence for, such civilizations. The basic points of the argument, made by physicists Enrico Fermi and Michael H. Hart, are:

· The Sun is a typical star, and relatively young. There are billions of stars in the galaxy that are billions of years older.

· Almost surely, some of these stars will have Earth-like planets. Assuming the Earth is typical, some of these planets may develop intelligent life.

· Some of these civilizations may develop interstellar travel, a technology Earth is investigating even now (such as the 100 Year Starship).

· Even at the slow pace of currently envisioned interstellar travel, the galaxy can be completely colonized in a few tens of millions of years.

According to this line of thinking, the Earth should already have been colonized, or at least visited. But no convincing evidence of this exists. Furthermore, no confirmed signs of intelligence have yet been spotted in our galaxy or elsewhere in the observable universe. Hence Fermi's question, "Where is everybody?"

There are a number of logical arguments to the question “Where is everybody?” Among them are:

1. We are alone. We are the only civilization in the Milky Way or possibly even the Universe.

2. We are the most advanced. There is other life in the galaxy but no advanced civilizations capable of communication.

3. Civilizations come and go throughout the history of the Universe. They spring up but ultimately go extinct for various reasons. (Asteroids, climate change, nuclear war, et…)

4. Civilizations are common, but for various reasons no one has colonized the galaxy. For example, some argue that galactic colonization is too expensive and therefore civilizations would not attempt to do so.

5. Aliens were here in the past or are currently here hiding among us.

6. We are the aliens of a past civilizations.

7. Aliens do not contact us and allow us to develop and evolve naturally (aka - The Zoo Hypothesis).

From the reasons above, or one of your own, state your argument for why we have not made contact with any alien civilizations. Be thorough in your argument, give examples, provide resources, and give facts or number if you can.

Which reason are you choosing? The main reason why we have not been able to make contact with alien civilizations is because they don’t exist. I believe in the creation story where only humans were created and no aliens exists at all.

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