1. Drake Equation Lecture Thirty-Three, April 23, 2003

2. Project Due Friday April 25. Due Friday April 25. Discuss as much of the science from class as possible. Discuss as much of the science from class as possible. If your project is in electronic form you can turn in a disk or email it. If your project is in electronic form you can turn in a disk or email it. However, also turn in a hard copy! However, also turn in a hard copy! Everyone should turn in a paper copy. Everyone should turn in a paper copy.

3. SETI: Message in a Cosmic Bottle How to send or receive a radio beacon? How to send or receive a radio beacon? Want signal to look “unnatural” and stand out above background of natural radio noise in Galaxy. Want signal to look “unnatural” and stand out above background of natural radio noise in Galaxy. Broad frequency region around a few GHZ (few times 10 9 cycles per second). This is in the microwave region (high frequency radio) of the spectrum. Here natural noise is relatively small. Broad frequency region around a few GHZ (few times 10 9 cycles per second). This is in the microwave region (high frequency radio) of the spectrum. Here natural noise is relatively small. Radio communication over interstellar distances is feasible with present technology! Radio communication over interstellar distances is feasible with present technology!

4. Is anyone there? Intelligence is ability to use radios. Intelligence is ability to use radios. Important differences searching for intelligent compared to primitive life! Important differences searching for intelligent compared to primitive life! How many civilizations are there in the galaxy that might try to call us? How many civilizations are there in the galaxy that might try to call us? The Drake equation is away to discuss our ignorance of this fundamental question. The Drake equation is away to discuss our ignorance of this fundamental question.

5. Drake Eq. Is there likely to be anyone trying to send radio signals? Is SETI likely to succeed? Is there likely to be anyone trying to send radio signals? Is SETI likely to succeed? Assumes a steady state: rate of new civilizations is nearly equal to rate of their death. Assumes a steady state: rate of new civilizations is nearly equal to rate of their death. “Writes one number, that we do not know, as the product of seven numbers, that we do not know.” “Writes one number, that we do not know, as the product of seven numbers, that we do not know.”

6. Drake Equation N c =R s f p n f l f i f c L N c =R s f p n f l f i f c L R s =rate of (suitable) star formation R s =rate of (suitable) star formation f p =fraction of stars with planets f p =fraction of stars with planets n=number of “Earthlike” planets per solar system n=number of “Earthlike” planets per solar system f l =fraction of “Earths” with life f l =fraction of “Earths” with life f i =fraction that is intelligent f i =fraction that is intelligent f c =fraction that develops a civilization f c =fraction that develops a civilization L=lifetime of civilization L=lifetime of civilization

7. Drake Equation N s = A ¢ B ¢ C A = Astronomy = R s ¢ f p ¢ n B = Biology = f l ¢ f i C = Civilization = f c ¢ L

8. Astronomy factors R s, f p, n R s =# of suitable stars born each year in galaxy. R s =# of suitable stars born each year in galaxy. If suitable stars mean sun like. R s ¼ 2 (Probably want single stars not binary) If suitable stars mean sun like. R s ¼ 2 (Probably want single stars not binary) f p = fraction of stars with planets. We are measuring f p as we find planets. f p > 0.1 f p = fraction of stars with planets. We are measuring f p as we find planets. f p > 0.1 n=# of earths per solar system. We will start to measure this with Terrestrial Planet Finder or similar spacecraft in near future. Now we have no reason to assume n is small. Note, how much like earth do we require?? n=# of earths per solar system. We will start to measure this with Terrestrial Planet Finder or similar spacecraft in near future. Now we have no reason to assume n is small. Note, how much like earth do we require??

9. Astronomy Factors So far R s, f p and n are straight forward factors from astronomy that we either know or will soon at least partially measure. So far R s, f p and n are straight forward factors from astronomy that we either know or will soon at least partially measure. Therefore these factors are not very controversial and probably not very small. Therefore these factors are not very controversial and probably not very small. Thus these factors do not dampen enthusiasm for SETI. Thus these factors do not dampen enthusiasm for SETI.

10. Biology Factors f l, f i Fraction of earths that develop life f l. Fraction of earths that develop life f l. Some requirements for life: Some requirements for life: –Elements such as H, C, N, O… –Liquid H_2O –Energy source (chemical or star light…) –Primitive organic compounds such as amino acids. –Time to allow chemical reactions to increase the complexity of molecules.

11. f l may be large We assume f l may be large because life started relatively quickly on earth. We assume f l may be large because life started relatively quickly on earth. Simple organic compounds may be common. (Remember Miller exp.) Simple organic compounds may be common. (Remember Miller exp.) However, there is a lot we don’t know about the origin of earth life. However, there is a lot we don’t know about the origin of earth life. Finding life on Mars or elsewhere would strongly suggest that f l is large. Finding life on Mars or elsewhere would strongly suggest that f l is large.

12. Origin of Intelligence

13. f i = fraction of life that develops intelligence Intelligence may provide evolutionary advantage. Intelligence may provide evolutionary advantage. However brain needs massive resources. Evolution will not favor intelligence unless advantages are very large. However brain needs massive resources. Evolution will not favor intelligence unless advantages are very large. Low level intelligence needed for vision, mobility, eye-limb coordination… Low level intelligence needed for vision, mobility, eye-limb coordination… How large is the leap from this to humans? How large is the leap from this to humans? How long does intelligence need to evolve? How long does intelligence need to evolve?

14. Fraction that develops Civilization What is civilization? Working together? Using technology? … What is civilization? Working together? Using technology? … Do army ants or bees have a civilization? Do army ants or bees have a civilization? What role does civilization play in evolution? What role does civilization play in evolution? Here civilization means technology and radios. Here civilization means technology and radios.

15. Lifetime of Civilization Many civilizations on earth come and go: Egypt, Greece, Rome,… Many civilizations on earth come and go: Egypt, Greece, Rome,… We face many man made and natural dangers. We face many man made and natural dangers. Vast majority of species that every lived on earth are now extinct. Vast majority of species that every lived on earth are now extinct.

16. Total Extinction How close have we ever come to the total extinction of all life on earth? How close have we ever come to the total extinction of all life on earth? A very large impact could kill all life. A very large impact could kill all life. –It would have to be so large that the heat boiled away all the oceans and filled the atmosphere with molten rock! –Perhaps this happened very early on and life had to start more than once. –We don’t think there has been this large an impact since.

17. Snowball Earth We have evidence that about 700 million years ago earth was covered in a global and very deep ice age. We have evidence that about 700 million years ago earth was covered in a global and very deep ice age. Originally it was thought such an ice age would be disastrous with no way out. Originally it was thought such an ice age would be disastrous with no way out. –Snow and ice reflect sun’s heat and this would keep earth cold with no way to melt the ice. –Apparently there is a way out.

18. CO 2 Cycle Controls Temp. Volcanoes continue to put CO_2 into atmosphere even in ice world. Volcanoes continue to put CO_2 into atmosphere even in ice world. However, ice covers rock. Thus no way to capture CO 2 back into the rock to make new carbonates. However, ice covers rock. Thus no way to capture CO 2 back into the rock to make new carbonates. Greenhouse CO 2 continues to build up in atmosphere. This finally melts ice and converts earth from frozen to very warm. Greenhouse CO 2 continues to build up in atmosphere. This finally melts ice and converts earth from frozen to very warm. With ice gone, eventually high CO 2 in atmosphere recaptured into rocks. With ice gone, eventually high CO 2 in atmosphere recaptured into rocks.

19. Snowball earth and life Ice killed much life. However, some small pockets survived perhaps in volcanically heated pools. Ice killed much life. However, some small pockets survived perhaps in volcanically heated pools. This was before life had evolved hard parts (such as bones) that left clear fossils. This was before life had evolved hard parts (such as bones) that left clear fossils. Great explosion of life with great increase in complexity and diversity occurred just after the snowball. Great explosion of life with great increase in complexity and diversity occurred just after the snowball.

20. Space colonization and Lifetime If we colonize Mars say this might protect some life against many dangers such as a single large impact or a disease. If we colonize Mars say this might protect some life against many dangers such as a single large impact or a disease. Still depend on the same sun so the sun going red giant will kill both earth and mars. Still depend on the same sun so the sun going red giant will kill both earth and mars. Colonizing other stars may prevent total extinction of humans and increase L. Colonizing other stars may prevent total extinction of humans and increase L.

21. Number in Galaxy Provides an estimate of distance between civilizations thus how far one must communicate. Provides an estimate of distance between civilizations thus how far one must communicate. Represent galaxy as a disk about 50000 Lt-years in radius. Represent galaxy as a disk about 50000 Lt-years in radius. Area of galaxy=  R 2 = 7.85e9 (Lt-Y) 2. Area of galaxy=  R 2 = 7.85e9 (Lt-Y) 2. Density of civilizations  =N/A Density of civilizations  =N/A

22. Example N=10^6  =1e6/7.85e9 = 1.3e-4 civilizations per square Lt-Y.  =1e6/7.85e9 = 1.3e-4 civilizations per square Lt-Y. Average distance to next civilization L Average distance to next civilization L  ¼ 1/L 2 assume uniform grid of civilizations each L apart.  ¼ 1/L 2 assume uniform grid of civilizations each L apart. Or L ¼ [1/  ] 1/2. Or L ¼ [1/  ] 1/2. L ¼ 90 Lt-Years. L ¼ 90 Lt-Years.

23. What makes Earth Special? Is this a physics/ astronomy question? Or a biological question? Or a religious /philosophical question? What are some of the physics that goes into Earth having a stable climate for five billion years?

24. Are We Alone? Yes! Yes! But how can that be. All those worlds, all those Suns in all those Galaxies. But how can that be. All those worlds, all those Suns in all those Galaxies. Why only us? Why only us? How could the Universe be so big and so so lonely? How could the Universe be so big and so so lonely? What is our destiny? If we kill ourselves, what has it all been for? What is our destiny? If we kill ourselves, what has it all been for? All those worlds we can not detect. What are they for? All those worlds we can not detect. What are they for? “It would be a great waste of space”. “It would be a great waste of space”.

25. We are not alone! The Universe may team with intelligent life! The Universe may team with intelligent life! Man has been here for only a few million years. Less then one one thousandth the age of the Universe. It is very likely that other intelligences are much older and wiser then we. Man has been here for only a few million years. Less then one one thousandth the age of the Universe. It is very likely that other intelligences are much older and wiser then we. We are but an insignificant new comer in a vast crowd. We are but an insignificant new comer in a vast crowd. –What do we matter? –What will the older and wiser races do with us?

26. Either Way it’s Scary How can we be so utterly alone! How can we be so utterly alone! Or Or How can we be so insignificant. Just one among so many countless millions. How can we be so insignificant. Just one among so many countless millions.

27. Primitive Life Primitive life may be common in the Universe. Primitive life may be common in the Universe. –Organic compounds may be easy to make, [Review Miller Exp.], and they may be common [Amino acids found in meteorites, spectral lines from some compounds found in space and in the atmosphere of Titan…]. –Life appears to have started quickly on Earth. [What happened quickly may be highly probable to happen elsewhere.] Life is extraordinarily complicated. We don’t understand very much about how it got started on Earth. Life is extraordinarily complicated. We don’t understand very much about how it got started on Earth.