2. Motivation: Fermi’s ParadoxMotivation: Fermi’s Paradox
If the chances of developing aIf the chances of developing a
technological civilization are 1 in atechnological civilization are 1 in a
million:million:
100,000100,000 civilizationscivilizations in the galaxyin the galaxy
This is an application of theThis is an application of the DrakeDrake
EquationEquation, but, but ignoringignoring thethe LifetimeLifetime
of civilizationsof civilizations
If these are spread over the lifetime of theIf these are spread over the lifetime of the
Galaxy, the time between civilizations is aboutGalaxy, the time between civilizations is about
50,000 years50,000 years
3. Fermi’s ParadoxFermi’s Paradox
With such a long time, a civilization mightWith such a long time, a civilization might
be able to colonize the Galaxy or at leastbe able to colonize the Galaxy or at least
make its presence knownmake its presence known
They could at least send self-replicatingThey could at least send self-replicating
machinesmachines
4. Solutions to Fermi’s ParadoxSolutions to Fermi’s Paradox
There are three solutions to Fermi’sThere are three solutions to Fermi’s
Paradox:Paradox:
1.1. We are aloneWe are alone
2.2. A galactic civilization exists, but it remainsA galactic civilization exists, but it remains
hidden from ushidden from us
3.3. Other civilizations exist, but none haveOther civilizations exist, but none have
colonized the galaxy. Why?colonized the galaxy. Why?
1.1. No interest in doing soNo interest in doing so
2.2. Self-annihilationSelf-annihilation
3.3. Technological difficultiesTechnological difficulties
5. IntroductionIntroduction
In order to travel toIn order to travel to
the stars, colonizethe stars, colonize
other worlds, andother worlds, and
establish anestablish an
Everlasting GalacticEverlasting Galactic
Empire, we will needEmpire, we will need
interstellar travelinterstellar travel
6. Rocket ScienceRocket Science
Current rockets useCurrent rockets use
chemicalchemical fuelsfuels
These can be solids,These can be solids,
liquids, or gasesliquids, or gases
Efficiency of a rocketEfficiency of a rocket
measured with themeasured with the
mass ratiomass ratio ==
Mass with fuel / MassMass with fuel / Mass
without fuelwithout fuel
7. Rocket ScienceRocket Science
To escape the gravityTo escape the gravity
of the Earth need aof the Earth need a
mass ratio of ~39mass ratio of ~39
Single stage rocketsSingle stage rockets
have mass ratios ofhave mass ratios of
~15 or less~15 or less
This is not enough, soThis is not enough, so
we can’t leave thewe can’t leave the
EarthEarth
Or can we?Or can we?
9. Distances to StarsDistances to Stars
The nearest star system (Alpha Centauri)The nearest star system (Alpha Centauri)
is 4 light-years away (40 trillion km)is 4 light-years away (40 trillion km)
At 60mph, this would take… 44 millionAt 60mph, this would take… 44 million
yearsyears
At 17,000mph, this would take just 160,000At 17,000mph, this would take just 160,000
yearsyears
At this speed, it would take aAt this speed, it would take a
billion years to reach the centerbillion years to reach the center
of our Galaxyof our Galaxy
10. What can we do?What can we do?
We need to go faster!We need to go faster!
It’s all a mater of getting higher efficiencyIt’s all a mater of getting higher efficiency
from our fuelfrom our fuel
I can make 0.5
past light speed!
11. Nuclear RocketsNuclear Rockets
Use fission to heatUse fission to heat
hydrogen gas, whichhydrogen gas, which
provides the thrustprovides the thrust
Fuse small pellets ofFuse small pellets of
hydrogen, the energyhydrogen, the energy
released moves itreleased moves it
forwardforward
Set off a nuclearSet off a nuclear
bomb behind youbomb behind you
12. Ion DrivesIon Drives
Shoot out ions from light-weight gasesShoot out ions from light-weight gases
Little thrust, but can work for longer times andLittle thrust, but can work for longer times and
therefore get large velocitiestherefore get large velocities
13. Solar SailsSolar Sails
Use the pressureUse the pressure
from photons of lightfrom photons of light
to push the craftto push the craft
forward- like wind onforward- like wind on
a sail.a sail.
Can also use lasersCan also use lasers
14. Antimatter is like regular matter but withAntimatter is like regular matter but with
opposite chargeopposite charge
When antimatter and matter meet, theyWhen antimatter and matter meet, they
completely annihilate each other producingcompletely annihilate each other producing
energyenergy
Antimatter EnginesAntimatter Engines
15. Like the solar sail, anLike the solar sail, an
interstellar ramjetinterstellar ramjet
carries no fuelcarries no fuel
Take hydrogen fromTake hydrogen from
space and fuse itspace and fuse it
RamjetsRamjets
16. To Infinity, and Beyond!To Infinity, and Beyond!
These newThese new
technologies allowtechnologies allow
light-weight spacelight-weight space
craft to reach verycraft to reach very
high speeds with veryhigh speeds with very
little fuel.little fuel.
In order to go fasterIn order to go faster
we just need to runwe just need to run
the engine for athe engine for a
longer timelonger time
17. But then this guy came along…But then this guy came along…
Image credit: Kevin Hainline
18. A Maximum SpeedA Maximum Speed
The speed of light in aThe speed of light in a
vacuum is always avacuum is always a
constantconstant with respect towith respect to
anyany observer.observer.
This speed, c, isThis speed, c, is
300,000 km/s300,000 km/s
186,000 miles/s186,000 miles/s
1.8 terra furlongs/fortnight1.8 terra furlongs/fortnight
Nothing can travel fasterNothing can travel faster
than lightthan light
19. Special RelativitySpecial Relativity
All motion is relativeAll motion is relative
Many weird effects will happen whenMany weird effects will happen when
special relativity is applied, but I’ll onlyspecial relativity is applied, but I’ll only
mention a few:mention a few:
Moving clocks run slower as seen by aMoving clocks run slower as seen by a
stationary observerstationary observer time dilationtime dilation
Distances are contracted along the directionDistances are contracted along the direction
of motion of a moving objectof motion of a moving object lengthlength
contractioncontraction
20. Special RelativitySpecial Relativity
At 99.99% of c, to go to Vega (25At 99.99% of c, to go to Vega (25
light-years away) and back:light-years away) and back:
Space ship frame: 8 monthsSpace ship frame: 8 months
Earth (stationary) frame: 50 yearsEarth (stationary) frame: 50 years
But light takes 50 years to travelBut light takes 50 years to travel
50 light-years, yet you do this in 850 light-years, yet you do this in 8
months:months:
Length contraction: you travel 0.4Length contraction: you travel 0.4
light-year rather than 25 light-yearlight-year rather than 25 light-year
22. WormholesWormholes
A highly curvedA highly curved
region of space couldregion of space could
intersect anotherintersect another
region of space andregion of space and
form a hole betweenform a hole between
themthem
These wormholes areThese wormholes are
unstable and collapseunstable and collapse
if anything goesif anything goes
through themthrough them
23. The Alternative: Interstellar ArksThe Alternative: Interstellar Arks
Use conventional technology, but be preparedUse conventional technology, but be prepared
to wait a very long timeto wait a very long time
The original travelers will die and new ones willThe original travelers will die and new ones will
be born before reaching the destinationbe born before reaching the destination
Or you could placeOr you could place
everyone in suspendedeveryone in suspended
animation for thousandsanimation for thousands
of yearsof years
A multistage rocket is built of parts, when the fuel runs out in one part it gets ejected. This reduces the mass, which means it is easier to accelerate the remaining stages.
Have been around since 1960s
Used in Deep Space 1 (1998) for 16,246 hours and has consumed about 72 kilograms (continuously for 4800hrs ~ 200days)
The ion propulsion system enabled the spacecraft to close in on the comet Borrelly at a rate of 750,000 miles per day.
It only consumes about 3.5 ounces (100 g) of Xenon per day.
Cosmos 1 (2005) failed to reach orbit [this was a private project]
Doesn’t need to carry fuel
Sails must be very thin (low mass compared to craft)
Small ones have been testing in vacuum chambers and used in some satellites
Approximately 10 grams of antiprotons would be enough fuel to send a manned spacecraft to Mars in one month.
H Fusion: 0.7% of mass to energy
Antimatter: 100% of mass to energy
You cannot tell if you are moving at a constant speed or stationary
In order to move at the speed of light, you would need to apply an infinite amount of energy since the object would be infinitely massive
In these images, physical space is 2D.
The curved space is in an additional dimension that we cannot perceive
The distance through a wormhole is much less than the physical distance
If set up correctly, you could enter one wormhole reach a distant star then get on another wormhole and return to Earth BEFORE you left