5 REAL Possibilities for Interstellar Travel

The future of humanity
is in the stars. If we wanted it badly
enough, interstellar travel could be achievable
in our lifetime. So what would it take
to build a starship? Why don’t we see evidence
of galactic empires? Is our galaxy littered
with the remains of single planet civilizations
as Elon Musk has asked? Is it really so difficult to
colonize other star systems? Recently, there’s been
some pretty wild talk of some crazy ideas for
space travel technologies. We have the non-momentum
conserving Em-Drive, the Wormhole from Interstellar,
and the Alcubierre Warp Drive. That last one is extra cool
and yeah, we’ll get to it. But let me be clear. Humanity’s first
adventure to the stars won’t and shouldn’t wait
for far-off fantastical technologies. Our first starship
would use technologies achievable in our lifetimes. I’m being optimistic
but not unrealistic. Now building a starship
is going to take a huge amount of political
cooperation, money, and single-minded focus. Hell, this thing is so
big we’re going to have to assemble it in space. So for argument’s
sake, let’s say humanity’s future is
at stake, and we just discovered Earth 2.0 in
the Alpha Centauri system. It’s only 4.4 light
years away, but we have to get there before the
Curbles and the impending K1 asteroid that’s on its way. So we have to focus on one
design, our best chance. What do we build? The key is finding
the right balance between speed of the starship
and the amount of time it would take us to develop
the tech to build it. No point in launching
a slow ship in 20 years if the ship we launch in
50 years overtakes it. This balance is
factored into something we call the Wait Calculation,
and we want to get this right. First, option one. Traditional rocket fuel. This is a non-starter, but
just to give you an idea, the fastest manned vehicle
ever was the Apollo 10 rocket, which reached a speed of nearly
25,000 miles per hour, which would get you to Alpha Cen
in nearly 120,000 years. Uh, no. Propellant is the big limiting
challenge with space travel. Conservation of momentum sucks. To learn more, there’s some
very serious rocket science in this episode about farts. The rocket equation tells
us that maximum speed is based on exhaust velocity,
fuel mass, and spacecraft mass. If you want to get to Alpha
Cen in a human lifetime, you need to get to 10%
the speed of light. And to do that with
any liquid rocket fuel, you’d need a fuel tank larger
than the observable universe. Not too efficient. But there are two ways to
achieve high velocities, propel a lot of mass
backwards or propel less mass at much higher speeds. So, yeah. Let’s do the second one. We just want the fuel with
maximum energy density. So direct conversion of
rest mass into energy seems like the way to go. Remember E equals MC squared. The sun does this pretty
well, so let’s build an engine that works like a mini star. I’m talking option two, fusion. In fact why not choose
the most middle option and just explode nukes
behind our starship and surf the blasts. This was a real option
considered for the Orion project by Freeman
Dyson and others in the late ’50s and ’60s. We’re going to assume
modern thermonuclear devices and launch with roughly 3/4 of
our starship’s mass being taken up by 300,000 1 megaton hydrogen
bombs, blast them behind us one by one over about a
month, and we accelerate at 1G to around 10% of
the speed of light. Nice. We get to Alpha Cen
in 44 years, assuming we don’t need to slow
down at the other end. Actually, slowing
down is a huge issue. We need to use half of
our fuel to slow down at the other end,
which unfortunately means we half our speed. So let’s make that 90
years for a one-way trip. This means we’d need three
generations of humans on board that ship and pray that
space babies turn out OK. Still, this tech is
perhaps the most achievable in the shortest time. We already know
how to build bombs. Yay, cold war! Although the 1963 test ban
treaty says no space nukes, maybe we can make an exception
for the future of humanity. There are also some
pretty awesome options to running contained
thermonuclear reactions on board. Fusion rockets,
either pulse blasts like the Daedalus project
or ongoing fusion. You could push to a bit higher
than .1C this way but probably not a lot higher. It’s an awesome option
and may actually happen, but the tech for contained
fusion is only now emerging, and there are many
difficult challenges. It’s rocket science and nuclear
physics, so you know, hard. But fusion turns less than
1% of rest mass into energy. What if we could
get close to 100%? Well, that’s the idea behind
option three, antimatter drives. When matter meets it’s
antimatter counterpart, both particles are
annihilated, liberating most of the rest mass as energy. This is an extremely
efficient fuel. For example, it would only take
around 10 grams of antimatter to fly us to Mars in a month. The big obstacle here is
that harvesting and storing antimatter is
incredibly difficult. We can make in
particle accelerators but it’s slow and
hellishly expensive. We’ve only been able to
do this with small numbers of antiprotons at a
time, not the kilograms we’d need to get to the stars. Assuming we can scale up
production of antiprotons by a factor of say 100
trillion, trillion, then pion rockets
may be a possibility. Annihilate a proton
and an antiproton, and you get charged pions
moving at near light speed. Channeled with magnetic fields,
these pions provide our thrust. That’s something like
50 times more energy per kilogram of fuel than
the best fusion options. Low fuel weight
means our max speed is limited only by how much
antimatter we can make. 0.5C is plausible, meaning a
trip to Alpha Cen would take nine years. It may even be possible to
push 0.8C, which would be nice, because then time dilation
really kicks in, bringing travel time down
to 3.3 years from the astronaut’s perspective. OK, rockets a cool and all. But what if we didn’t have to
carry any propellant at all? What if we could
sail to the stars on a wind made of
light, the light sail? I’m talking about a kilometer
wide sapphire coated sail, riding the beam of a gigantic
space laser blasting the power equivalent of 100
nuclear plants. What the hell, let’s do that. OK, most of the interstellar
thinking for light sails has been about unmanned probes. 10% light speed is
pretty reasonable with modern materials
like a carbon web sail driven by a
microwave beam running on a single nuclear power plant. This is an update to Robert
Forward’s Star Wisp spacecraft, but it should be scalable. If we want to take
actual humans, we’re going to need to
a bigger boat, which means a proper visible light
laser and a larger sail, coated with advanced, reflective
and heat resistant materials like sapphire. This laser is going to have
to be ridiculously large, possibly built on the moon and
powered by massive Helium 3 reactors or in
orbit around the sun powered by vast solar panels. How fast does this thing go? Because we aren’t
carrying any fuel, maximum speed is only limited
by the power and collamation of our laser and the
size of our sail. The longer the effective
range of the beam, the higher the
speed we can reach. 10% light speed or
higher should be doable. These tech issues
need to be factored into the Wait Calculation. And besides these, slowing
down at the other end is a major problem. There are possibilities
for breaking in the stellar wind of
our destination star, although that is tricky. Ultimately, though, the
scalability of the light sail means that speeds even
greater than .1C are possible. OK most awesome option for last,
the Blackhole Drive, in fact, a Schwarzschild Kugelblitz. This is an engine powered
by an artificial black hole and is one of the fastest
options for subluminal travel. This is a black hole made
not from mass but from light. A sufficient energy
density of laser light focused in a small
enough region would bend the fabric of
space time enough to produce a singularity,
the Kugelblitz, German for ball lightning. A black hole of the
right size radiates Hawking radiation like crazy. The smaller the black
hole, the more radiation, and this radiation could
drive our starship. The sweet spot is a black hole
of around 600 billion kilograms or two Empire State
buildings, which would be roughly the
size of a single proton. Such a black hole would
radiate nearly 160 petawatts, which is roughly the
equivalent of 10,000 times the world power consumption. And it would evaporate in
around 3 and 1/2 years. Any smaller and it
evaporates too quickly. Larger and it
radiates too weakly and becomes too massive
to feasibly accelerate the ship and the black hole. Assuming we can catch
most of the radiation, this amount of power
accelerates us to .1C in 20 days and presumably to a significant
fraction of the speed of light in the lifespan
of the black hole. There’s no question that
it ultimately goes faster than the other options. It’s also clearly the coolest
of all the subluminal engines. I mean, even the
Romulans use it. The only drawback is that the
lasers creating the black hole would need to be vastly
more powerful than even the black hole they created. This is a possible yet
very distant technology. OK, so lots of ways
to get to the stars. What’s the fastest? Honestly, if we had to colonize
in the absolute shortest possible time, then it’s
nukes, like the Orion project. We have the tech. We just have to increase
the world’s nuclear arsenal by a factor of 200, which
we shouldn’t do unless it’s a question of extinction. Still, in a super
optimistic estimate, we could have boots on
the ground in 2120 or so. Now fusion engines
are more sustainable, even if the tech is a
minimum of 50 years away. They land us on Alpha Cen in
the latter half of the 2100s, assuming we start now. Pure antimatter
and the Kugelblitz drives, they’re the
starships of the far future. Assuming warp drives
don’t pan out, these are what we’ll
want to actually explore the galaxy with near light
speeds dilating apparent travel time down to human scales. Let’s talk near-term reality. I’m going to come
out and say it. Light sails. We’ll put our first unmanned
probes in the Alpha-Cen system. It’ll take around 45 years
from launch, not slowing down at the other end. And another four and a half
years to get the message that we succeeded. Maybe we could launch a Star
Wisp in less than 30 years. And some kids
watching this video might see this to fruition. Manned light jammers are way
off but totally plausible. Humanity’s first attempts
to land on other worlds might well have us
sailing to the stars. It’s likely between this
and post fusion drives. Either way, pretty epic. Which option are you
most excited about? Let us know in the comments. We hit warp seven next
time on Space Time. Last week we talked about
why the speed of light is really the
speed of causality. You guys had lots of
amazing questions. Andrea Prapone and others asked,
why does the speed of light have to be that specific number,
300,000 kilometers per second? And what would happen to the
universe if it were different? Well, that actual number,
300,000 kilometers per second, just comes from a pretty
arbitrary definition of the length of
kilometers and seconds. Now physicists often choose to
define the speed of light as C equals 1, which we
call natural units. At that point, it
perhaps becomes more interesting to ask why
other fundamental constants of nature have the
values that they do compared to the speed of light. Now that said,
the relative units of the fundamental constants,
the speed of light, the strength of the
fundamental forces, et cetera, are important for
the properties of this universe. And you change them too
much and the universe as we know it doesn’t exist. We’ll talk about that and
more in another episode. Jai Kolra and others ask, what
about quantum entanglement? Shouldn’t we be able to transmit
messages instantly this way? Right. Spooky action at a distance,
as Einstein called it, on the surface does
seem to mess with us. When you collapse
the way function of one entangled particle,
your choice of measurement affects the state of
its entangled partner instantaneously, potentially
over large distances. However, it turns out
that this can’t ever be used to transmit
new information faster than the speed of light,
so causality is preserved. We may do an episode on
this, but in the meantime, Veritasium has as an excellent
one, linked in the description. Ed Stephan asks why
we’re even talking about gravitational waves when
none have ever been observed. Why don’t we get back
to this next week. But in the meantime, in pointing
out the indirect detection of gravitational
waves, Garreth Dean delivers the amazing quote,
“So we haven’t seen a duck, but something’s been quacking
and eating all of our bread sticks.” TheColonel asks,
“Does this now mean I can refer to the speed of
light as total monkey speed?” The answer is yes. And to Tyler Hamilton, all
I have to say is, Yahhhhhh!