2. 19 www.scifi-art.comwww.scifi-art.com -ejl@scifi-art.org Interstellar Travel Why you can’t get there from here (easily).

3. 19 Goals What is the average distance between stars? How long will interstellar travel take? What is Time Dilation?

4. 19 Average Distances Depends on where. –Spiral arms – 2 pc (7 LY) –Bulge – 0.3 pc (1 LY) –Globular cluster – 0.03 pc (1 Light Month!) M10 – copyright Credner and Kohle

5. 19 How Fast? Voyager 1 (launched 1977) –Fastest made by humanity. –V = 62,000 km/hr (37,000 mph) Current location: –87.5 AU (Pluto = 40 AU) –12 Light Hours Compare model solar system in class to Voyager’s “model speed.” 0.04 miles per year = 0.3 inches per hour!

6. 19 How Long? Time = (distance between stars)/velocity For Voyager 1 in: –Spiral arms = 110,000 years –Bulge = 17,000 yrs –Globular cluster = 1700 yrs M10 – copyright Credner and Kohle

7. 19 Special Relativity Einstein (1905): –Speed of light is a constant. –Impossible to distinguish moving and non-moving frames of reference. Results: –Moving clocks run slow. –Moving meter sticks get short. Our ticket to the stars!

8. 19 Special Relativity 2 Main Postulates: 1. The speed of light is always c. Thou shalt not add your speed to the speed of light!

9. 19 Special Relativity 2. Moving and non- accelerating reference frames are indistinguishable from one another. If it happens at rest, it must happen in (constant) motion. Are you moving, or are you at rest right now? At restConstant velocity

10. 19 Time Dilation Tick! Tock! Tick! Tock! Compare

11. 19 Moving clocks run slow Since: Compare S

12. 19 How slow? Travel to Vega: Distance = 25 LY (7.5 pc) Time = Distance / velocity velocity = 0.999c Time Rest = 25 years Time Moving = 25 years x 0.04 = 1year! Copyright Lynette Cook, used with permission

13. 19 How slow? Travel to Milky Way’s supermassive black hole: Distance = 28,000 LY (8.5 kpc) Time = Distance / velocity velocity = 0.999999c Time Rest = 28 thousand years Time Moving = 28 thousand years x 0.0014 = 40 yrs!

14. 19 Homework #18 Read UFO articles. Come prepared to discuss. Everyone will need to participate in the class discussion for credit.