Interstellar Travel By: David Rodriguez Astro 5: Life in the Universe Winter 2008

Motivation: Fermi’s Paradox If the chances of developing a technological civilization are 1 in a million: If the chances of developing a technological civilization are 1 in a million: 100,000 civilizations in the galaxy 100,000 civilizations in the galaxy This is an application of the Drake Equation, but ignoring the Lifetime of civilizations This is an application of the Drake Equation, but ignoring the Lifetime of civilizations If these are spread over the lifetime of the Galaxy, the time between civilizations is about 50,000 years

Fermi’s Paradox With such a long time, a civilization might be able to colonize the Galaxy or at least make its presence known With such a long time, a civilization might be able to colonize the Galaxy or at least make its presence known They could at least send self-replicating machines They could at least send self-replicating machines

Solutions to Fermi’s Paradox There are three solutions to Fermi’s Paradox: There are three solutions to Fermi’s Paradox: 1. We are alone 2. A galactic civilization exists, but it remains hidden from us 3. Other civilizations exist, but none have colonized the galaxy. Why? 1. No interest in doing so 2. Self-annihilation 3. Technological difficulties

Introduction In order to travel to the stars, colonize other worlds, and establish an Everlasting Galactic Empire, we will need interstellar travel In order to travel to the stars, colonize other worlds, and establish an Everlasting Galactic Empire, we will need interstellar travel

Rocket Science Current rockets use chemical fuels Current rockets use chemical fuels These can be solids, liquids, or gases These can be solids, liquids, or gases Efficiency of a rocket measured with the mass ratio = Efficiency of a rocket measured with the mass ratio = Mass with fuel / Mass without fuel Mass with fuel / Mass without fuel

Rocket Science To escape the gravity of the Earth need a mass ratio of ~39 To escape the gravity of the Earth need a mass ratio of ~39 Single stage rockets have mass ratios of ~15 or less Single stage rockets have mass ratios of ~15 or less This is not enough, so we can’t leave the Earth This is not enough, so we can’t leave the Earth Or can we? Or can we?

Multistage Rockets

Distances to Stars The nearest star system (Alpha Centauri) is 4 light-years away (40 trillion km) The nearest star system (Alpha Centauri) is 4 light-years away (40 trillion km) At 60mph, this would take… 44 million years At 60mph, this would take… 44 million years At 17,000mph, this would take just 160,000 years At 17,000mph, this would take just 160,000 years At this speed, it would take a billion years to reach the center of our Galaxy

What can we do? We need to go faster! We need to go faster! It’s all a mater of getting higher efficiency from our fuel It’s all a mater of getting higher efficiency from our fuel I can make 0.5 past light speed!

Nuclear Rockets Use fission to heat hydrogen gas, which provides the thrust Use fission to heat hydrogen gas, which provides the thrust Fuse small pellets of hydrogen, the energy released moves it forward Fuse small pellets of hydrogen, the energy released moves it forward Set off a nuclear bomb behind you Set off a nuclear bomb behind you

Ion Drives Shoot out ions from light-weight gases Shoot out ions from light-weight gases Little thrust, but can work for longer times and therefore get large velocities Little thrust, but can work for longer times and therefore get large velocities

Solar Sails Use the pressure from photons of light to push the craft forward- like wind on a sail. Use the pressure from photons of light to push the craft forward- like wind on a sail. Can also use lasers Can also use lasers

Antimatter is like regular matter but with opposite charge Antimatter is like regular matter but with opposite charge When antimatter and matter meet, they completely annihilate each other producing energy When antimatter and matter meet, they completely annihilate each other producing energy Antimatter Engines

Like the solar sail, an interstellar ramjet carries no fuel Like the solar sail, an interstellar ramjet carries no fuel Take hydrogen from space and fuse it Take hydrogen from space and fuse it Ramjets

To Infinity, and Beyond! These new technologies allow light-weight space craft to reach very high speeds with very little fuel. These new technologies allow light-weight space craft to reach very high speeds with very little fuel. In order to go faster we just need to run the engine for a longer time In order to go faster we just need to run the engine for a longer time

But then this guy came along… Image credit: Kevin Hainline

A Maximum Speed The speed of light in a vacuum is always a constant with respect to any observer. The speed of light in a vacuum is always a constant with respect to any observer. This speed, c, is This speed, c, is 300,000 km/s 186,000 miles/s 1.8 terra furlongs/fortnight Nothing can travel faster than light Nothing can travel faster than light

Special Relativity All motion is relative All motion is relative Many weird effects will happen when special relativity is applied, but I’ll only mention a few: Many weird effects will happen when special relativity is applied, but I’ll only mention a few: Moving clocks run slower as seen by a stationary observer  time dilation Moving clocks run slower as seen by a stationary observer  time dilation Distances are contracted along the direction of motion of a moving object  length contraction Distances are contracted along the direction of motion of a moving object  length contraction

Special Relativity At 99.99% of c, to go to Vega (25 light-years away) and back: At 99.99% of c, to go to Vega (25 light-years away) and back: Space ship frame: 8 months Space ship frame: 8 months Earth (stationary) frame: 50 years Earth (stationary) frame: 50 years But light takes 50 years to travel 50 light-years, yet you do this in 8 months: But light takes 50 years to travel 50 light-years, yet you do this in 8 months: Length contraction: you travel 0.4 light-year rather than 25 light-year Length contraction: you travel 0.4 light-year rather than 25 light-year

General Relativity to the Rescue?

Wormholes A highly curved region of space could intersect another region of space and form a hole between them A highly curved region of space could intersect another region of space and form a hole between them These wormholes are unstable and collapse if anything goes through them These wormholes are unstable and collapse if anything goes through them

The Alternative: Interstellar Arks Use conventional technology, but be prepared to wait a very long time Use conventional technology, but be prepared to wait a very long time The original travelers will die and new ones will be born before reaching the destination The original travelers will die and new ones will be born before reaching the destination Or you could place everyone in suspended animation for thousands of years

Questions ?