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 = 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.

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)