How to facilitate contact?

1. How to facilitate contact? • Recall the dilemma: direct physical contact with ET or more indirect radio communication.

2. People or Photons? • People have mass and that requires enormous amounts of energy to accelerate. • People have needs (food, water, air, etc) which means more mass to transport! How much mass per person to take? • Space ships travel very slowly • Photons are mass-less and travel at the speed of light!

3. Current spaceship technology • Spacecraft travel at speeds much less than 100,000 km per hour • At this speed, travel to the nearest star would take 46,500 years!

4. Photons • Sending a signal has its own energy challenges • Signal strength drops off as the square of distance.

5. Photons … • Thus for any given signal strength, sending it say one million times further requires (one million)2 times as much energy … that is, one trillion. • This is technically possible (bigger transmitters, shorter messages, etc) but is not cheap. It is cheaper than sending people in spacecraft though.

6. Space Travel • (12) Humans have gone to the Moon • Machines have traveled in our Solar System out to Neptune and en route as we speak to Pluto • As a species we have the urge to explore and colonize.

7. Challenges to travel to the stars • Distances involved are enormous and will take us time to traverse • The energy requirements are equally immense and very difficult to satisfy (even if we are willing to pay the price).

8. Power for the trip • Chemical combustion is our current form of energy in rockets … very inefficient. • Solar power works well near stars but is also inefficient • Nuclear power for both on-board power (to live, etc) as well as thrust is possible with our technology. • Matter and anti-matter … more efficient certainly but also beyond our means at present.

9. Exotic power • Interstellar Ramjets … • Ion propulsion … prototypes already tested. • Warp drive … dilithiunm crystals anyone?

11. Time Dilation • As you travel faster, your own clock (in your frame of reference) slows down from an outside perspective. • Traveling at a significant fraction of the speed of light means you experience a smaller passage of time compared to an Earth based observer

12. Relativity • T = T0 / Sqrt (1 –v2/c2) • where T0 is the time elapsed in the moving frame of reference • where T is the time elapsed in the stationary frame of reference • where v is the speed you are moving relative to the stationary observer.

13. A solution? Perhaps traveling at high speed will allow people to survive interstellar treks.

14. Time dilation example • You and your friend synchronize your watches. • You remain on Earth and your fired ‘flies off’ at 99% the speed of light. • Your friend returns when 1 hour of time has elapsed according to their watch. • You have waited approximately 7 hours for your friend to have returned!

15. One more danger .. • At higher speeds for our spacecraft, the particles in the ISM are now moving at enormous velocities relative to you. • If your spaceship is moving at 99% the speed of light, the kinetic energy of a particle in the ISM will seem like a very energetic bullet and could do serious damage to the spacecraft … shields anyone?!

16. Automated Messengers • Instead of people in spaceships, send automated messengers. • Pioneer and Voyager spacecraft already carry messages from Humanity

17. Von Neuman machines • Build an automated robotic spacecraft and send it to a distant star/planet. • When there, let it mine resources and replicate itself, sending copies of itself to other stars/planets. • In short order, such robots could be everywhere! • So where are they? … the Fermi Paradox (later)