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

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!

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!

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

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.

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.

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).

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.

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

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

Relativity T = T 0 / Sqrt (1 –v 2 /c 2 ) where T 0 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.

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

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!

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?!

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

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)