Search for Life in the Universe

1. Search for Life in the Universe Part 1 - Interstellar Travel

2. Skyline Staff Meeting AST 248, Fall 2005

3. Outline • Challenges of Interstellar Travel • Distance • Speed • Energy • “Conventional” Interstellar Spacecraft • Chemical Rockets • Nuclear Rockets • Ions, Sunlight, and Lasers • Interstellar Arks • Relativistic Travel • Time Dilation • Antimatter and Ramjets • Hyperspace and Wormholes

4. Distance • Pioneer 10 example: • Jupiter: 21 months • Alpha Centauri (not aimed there): 115,000 yr • Nearest star to trajectory: 3.3 ly in 2 myr • Messages: • Where we are: positions relative to pulsars • Who we are: simple pictures • Our culture: music samples

6. Speed • Speed of light • Special theory of relativity (1905): speed of light is the ultimate speed that cannot be exceeded • Nearest stars 4.4 ly • Minimum roundtrip travel time is 8.8 yr • Time dilation • Simultaneity is not universal • Allows enormous reduction in travel time for the traveler, but not for the folks back home

7. Energy • Velocity for interstellar travel • Escape velocity from Earth: 11 km/s • Travel velocity, say 0.1c = 30,000 km/s, dominates energy requirement • ~ 100 x world annual energy consumption • Add cost of provisions

8. Chemical Rockets • Newton’s Third Law • To every action there is an equal and opposite reaction • Shoot mass out of the back  propel forward • Mass ratio • Escape from Earth: 39 • Best single-stage rocket: < 15 • Multi-staged rockets • Necessary, and used, to leave Earth, or even for intercontinental ballistic missiles • Interstellar travel: impractical, hundreds to thousands of stages required

9. Nuclear Rockets • Method • Advantage: higher energy/mass ratio of nuclear reactions • Disadvantage: controlled use, especially fusion • Maximum speed: ~ 0.1c, i.e., minimum travel time of decades • Project Rover • Fission rocket • Achieve speeds 23 times chemical rockets • Application: manned mission to Mars, since abandoned • Project Orion • Explode H bombs behind the spaceship and let the shock waves propel the spaceship • Too expensive, also violates ban on nuclear explosions in space • Project Daedalus • Use pellets of 2H and 3He, ignited by an electron beam from the spacecraft

12. Ions, Sunlight, and Lasers • Ions • Same as a TV ion gun, but ions released into space • NASA tested a low-power version, Deep Space 1 • Sunlight • Radiation pressure on large solar sails • Need sails hundreds of kilometers wide • Bulk of acceleration near the Sun • Lasers • Laser on Earth: continual acceleration • Mirror size: hundreds of kilometers • Power needed: >1,000 x total Earth production • Travel relies on continuation of project • Slow down and then return: propellant on board heated by laser?

15. Interstellar Arks • Ideas • Hibernation: long sleep • Long life: slow down aging • Multi-generational: accept many generations • Hibernation • How do we put people to sleep? • How do we wake them up? • Long life: • Pure speculation • Robotic mission would be simpler • Multi-generational: • Perseverance in the mission and/or infighting • Loss of expertise

16. Time Dilation

17. Antimatter and Ramjets • Antimatter • Exists: all matter has antimatter • Matterantimatter annihilation: all rest mass released as  rays, cf., < 0.8% in nuclear reactions • Problem: controlled storage • Ramjets • Collect H from the interstellar medium and fuse it • Need scoops hundreds of kilometer wide • Danger of high speed • Collisions with dust particles cause enormous damage • Need heavy shielding

18. Hyperspace and Wormholes • Hyperspace • General theory of relativity (1916): space is warped by gravity • Detailed experimental tests in weak gravity: • Solar system • Binary pulsar • Black holes: stellar (~10 MSun) and galactic (~106109MSun) shown to exist • Wormholes • Rotating black holes connect to another flat space • Other flat space may connect to ours somewhere, but may not • We will know only after we go through the wormhole • Stellar black holes: have too strong a tidal force, which would rip us apart • Massive black holes: only known in galactic nuclei, have to get there

21. Inventing Alien Life forms • This activity is from the Univ. of Washingtonhttp://www.astro.washington.edu/labs/clearinghouse/activities/aliens.html • Take one dice for each group of 2 students and try the evolution experiment to create your own alien. The rolling of the dice reproduces the random elements in evolution. • When you have finished, draw a picture of your alien and give it a a name

22. Inventing Alien Life forms • Write a paragraph that has the following information: • Describe the environment your creature needs to survive. • Where in our solar system would you be most likely to find such a creature? • What sort of food source might your creature need? • Is your creature alone in its environment? If not, how does it coexist with other species?