Have you ever imagined how interstellar travel could work? | Ryan Weed | TEDxDanubia


Translator: Reka Lorinczy
Reviewer: TRAN HUONG Before I start talking
about antimatter physics, antimatter rockets,
going to other stars, traveling interstellar, I think it’s important
we ask ourselves a question. That is: Why explore space? We have so many problems here on Earth, we have global warming, hunger, war, why should we spend time, money,
and effort going into space, when we could be spending
that time and effort here on Earth? I could list all
of the technological advances, the medical breakthroughs of over four decades
of human space travel in space, but I think the real question is: Why explore? I think simply the answer is:
It’s in our DNA. We are the descendants of people who were curious
and who explored their environment, and I think we need
to continue doing that. But there’s a problem,
there’s a big problem, and that is that rockets are too slow. In order to demonstrate that, our fastest object
that humans have ever created is the Voyager 1 spacecraft,
and that moves at 15 km/s. That may seem like a fast speed,
but if you want to go to Mars with that, at that speed, it would take
months to get there. If you wanted to go to Pluto – which NASA just did, and they spent a billion dollars
in ten years to get there – it just takes too long. The final example,
really the most important one is: If we want to get to another star, our closest star system Alpha Centauri,
as you see there, is about four light years away,
and that’s 38 million million kilometers. It would take about 30,000 years
at 15 km/s to get there. and, you know,I don’t want
to wait around for that. Luckily, human beings are actually
quite good at developing tools that allow us to explore our environment. In the 1700s, we built very accurate
measurements of time, we built the chronometer
that allows us to travel the seas, and allowed for the Golden Age
of Exploration. In the 1900s, the Wright brothers
developed flight, and really allowed us to master the skies. If you really want to explore
beyond our Solar System, we are going to have
to come up with a new tool. Being an antimatter physicist,
I’m kind of partial to antimatter, but it could be something else, it could be laser propulsion,
laser fusion, or solar cells. Some physicists even think that we can bend space-time
and travel faster than light. But I think antimatter is actually
the nearest term and most realistic. A little bit about antimatter. It was first predicted by Paul Dirac –
up there in the top-right corner. He was actually struggling
with two relatively new concepts, one being special relativity, which describes life
at really high speeds and the speed of light, and quantum mechanics, which describes the Earth
or the world of the very small, atoms and molecules. So he was solving this relativistic
quantum mechanics equation, and he came out with two answers: a positive energy and a negative energy
for these particles. How many times
you’ve been doing your homework, and you come up with a negative answer, and you say: “Chuck that, just look at the positive
energy solutions, because that’s what makes sense.” But Paul Dirac was a genius, and he saw
these negative energy solutions, and he said: “Wait a minute, maybe there’s
a whole new set of particles out there that we haven’t even seen.” Some people thought
he was crazy of course. But it was only three years later that Carl Anderson at CalTech
saw this in his cloud chamber. He saw the track
of a particle going, curving, and it had the same energy
and mass as an electron, but it was curving the wrong way. It should have been curving to the right
if it was an electron. So this is the first experimental
evidence of antimatter or an anti-electron,
which we like to call positrons. So antimatter I like to describe
as mirror matter. If there was an anti-you in a mirror,
it would look exactly like you, except that everything would be flipped. The same is true at the subatomic level. Anti-electrons have
the same mass as electrons, just positive charge rather
than negative charge. That’s why we call them positrons. An interesting characteristic
of antimatter is annihilation. It’s quite unique in that if you have an antimatter particle
and a matter particle, and they get close enough together, they’ll both disappear
and turn into pure energy. Now this is the Universe’s most efficient
means of turning mass into energy, and it’s quite powerful, and that’s what got me interested
in positron physics years ago. What does that mean
in terms of energy density if you had a clump of antimatter? Antimatter has about
90 megajoules per microgram. I know that doesn’t mean much to you, but to put that in more familiar terms, if you had a gram of antimatter,
or an M&M-size piece of antimatter, then you have the same amount of energy
as about 80 kilotons of nuclear weapon, or alternatively about 10 million liters
of liquid natural gas – about a full tanker load. So not only does antimatter
have incredible promises as a fuel for spacecraft, but this has some pretty
significant applications in the future of energy research,
energy production, especially in inertial confinement systems
and pulsed energy delivery. But I’m more interested
in the propulsion side of things, and so is my company. The original concept
of antimatter propulsion, it was actually developed
in the fifties by Eugen Sänger. And what he did was, he said: “What if you had a clump of antimatter,
you took it out in your spacecraft, and then you annihilated it
in the rocket engine nozzle, and you’re able
to direct that energy flow, you’re able to direct those gamma rays
so that you have thrust in one direction.” This was cutting edge at that time, but there were really three problems, one of which was production. You can’t create enough antimatter
to do this, unfortunately. The other is that you
can’t trap the antimatter. Of course, that property of annihilation
which is good for the energy density is really bad for being able to trap it. You need very high strength
magnetic fields, and it just wasn’t feasible,
still isn’t feasible, to trap large amounts of antimatter. The third problem
with the original concept was directing that energy. Gamma rays are much higher
energy than x-rays. Of course, if you go through the TSA
in the airport, they x-ray your bag. X-rays tend to go through everything,
and gamma rays even more so. Reflecting gamma rays is something
that we can’t do right now. So, I started thinking about
these problems in 2011, finishing up my PhD in positron physics. I realized that the real issue,
the limiting factor, was when you went from hot positrons
to cold positrons. Now state of the art in 2011: You had your source of hot positrons,
and what you did, and still do, is to run it through
a solid piece of material. What this does is, it’s very thin, so that most of the positrons
just travel right through, a very small number will actually stop
inside the material. Of course, a large number
of those will hit an electron because our matter
is made of a lot of electrons, and they will lose it. A very small number,
about one out of 1,000, will make it to the surface
and be emitted as a cold positron. So, you have to be able
to create cold positrons in order to work with them. They come out at a million times hotter
than the surface of the Sun, so you have to be able to cool them down. This process was very inefficient, so we started thinking
of new ways to do this. My lab partner and I
discussed this for about a year. We came out with a napkin sketch
of an array moderator. Soon after that we made it
an actual patent, and then asked
for some money from a grant, and we were funded by the Steel Foundation to do the initial proof of concept
on that moderator. This moderator now forms the heart
of all our propulsion concepts, and that little piece up there
is actually very tiny, it is about 3×3 mm, but it’s the source for all
of our antimatter concepts. When you are developing a concept,
you also have to develop a team. So back in 2012, I asked
some friends of mine whom I was working on another
rocket project there in the desert with. I said, “Well, let’s give up
this chemical stuff. Why don’t you guys come help me
build an antimatter rocket?” Who’s going to say no to that? (Laughter) So, we rented a little office, brought in a bunch
of nuclear science equipment. We quickly realized that the landlord
didn’t appreciate that, so we got kicked out of there. In the next year, we moved into
a little more appropriate facility, and then, last year, finally,
we made our way down to a nuclear fallout shelter
with a clean room. This new facility will allow us
to develop some of our concepts and integrate them into a CubeSat,
which is a very small satellite, very easy to launch, very easy
to demonstrate new concepts on. How do we get around those three issues: production, trapping and directing energy? The first two, production and trapping, are got around by having
a very efficient moderator. We use a radioisotope source of positrons
which continuously emits positrons. We run it through
our little tiny moderator, and we can create
a very high-intensity positron beam. The third challenge is directing
the annihilation energy. In order to do that, we transfer the kinetic energy
of the gamma ray into a charged particle via fusion reactions. And now we have a charged particle
that’s high energy rather than a gamma ray. And that’s important because charged particles
like to follow magnetic field lines, as you know from the Aurora Borealis. So, we use magnets like
the one in the bottom right there, to actually direct the energy
and produce thrust. In about two years, we were hoping
to put a demonstrator CubeSat – that little tiny spacecraft – into orbit. Why is this useful? What is it that a really small
spacecraft can do for you? Well, it turns out, that about 4 billion people
on the surface of the Earth don’t have access to Internet. So there’s a lot of companies that want to launch
constellations of small satellites into low Earth orbit. They will create a global network
of broadband Internets, so that anyone can
access that information. I think that would be
an incredible opening door for the Earth. A little bit further down the road, what we want to do,
and what government agencies want to do, and some private companies like SpaceX, they want to send things out to Mars, and our technology
would allow them to do that and cut the transit time significantly. And then, kind of a far-out application
for this, is asteroid mining. I know you’ve probably never heard
of asteroid mining, but it turns out that very small asteroids
in our asteroid belt, metal rich, is worth a lot of money. With chemical rockets,
you can’t just go out there and get it, you need something
like an antimatter system. In terms of extending this technology
into human space travel, that will require, of course,
a lot of work. It turns out that our squishy bodies can only really handle
about 1g acceleration, and even so 1g, 9.8 m/s/s,
is actually pretty high acceleration. NASA took ten years
to get to the Pluto; if we go at 1g, we can get there
in about 3.5 weeks, which isn’t that bad. If we want to go to Alpha Centauri,
the story gets a little different, and we start bringing in
concepts of special relativity. If we want to go out there
at 4.3 light years, at 1g it would take about five years
going at about 85% the speed of light. Once we start getting toward a significant
fraction of the speed of light, we start getting time dilation, which is an interesting phenomenon, but really it’s the thing that allows us
to travel out into the Universe. While five years
has elapsed on the spacecraft, nine years has elapsed on the Earth. It’s getting weird, but still feasible. If we extend this out to Kepler-452b, Kepler-452b is an interesting place
because a lot of people call it Earth 2.0. It’s a little bit bigger than Earth, it’s in the habitable zone of its Sun. A lot of people
want to go there and see – maybe there’s life. I think there is a good chance
that there might be, although it is 1500 light years away. With our 1g spacecraft
we could get there in 12 years on the spacecraft. Unfortunately, 1,500 years
will have passed on Earth. So things are getting a little weirder. If we look at the ultimate
application of this, exploring to the edges of our Universe,
13.5 billion light years away, at 1g we could make it there
in a human lifetime, 30 years. Now, we are going incredibly fast,
towards the speed of light, but the only problem is, that 13.5 billion years would have passed
here on the Earth. What I’m trying to say is that, with the transformative
technology like this, we have to think seriously
about the consequences, and new questions that arise. The first of which is: If we want to really explore beyond
our Solar System into our galaxy, we are going to have to do it ourselves: if we do send a probe or a robot, we will never hear back
from it, essentially. And then the second issue is: If we do want to go out beyond our galaxy, we’re going to essentially
be saying goodbye to this. And you know human beings used
to be a nomadic species, and so one of the questions
I am asking you is: Do we want to become nomads again? Thank you very much. (Applause)

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