Translator: Reka LorinczyReviewer: TRAN HUONG Before I start talkingabout antimatter physics, antimatter rockets, going to other stars, traveling interstellar, I think it’s importantwe 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 spendingthat time and effort here on Earth? I could list allof the technological advances, the medical breakthroughs of over four decadesof 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 curiousand who explored their environment, and I think we needto 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 objectthat 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 takemonths to get there.
If you wanted to go to Pluto – which NASA just did, and they spent a billion dollarsin 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 yearsat 15 km/s to get there.
and, you know, I don’t wantto wait around for that.
Luckily, human beings are actuallyquite good at developing tools that allow us to explore our environment.
In the 1700s, we built very accuratemeasurements of time, we built the chronometerthat allows us to travel the seas, and allowed for the Golden Ageof Exploration.
In the 1900s, the Wright brothersdeveloped flight, and really allowed us to master the skies.
If you really want to explorebeyond our Solar System, we are going to haveto 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-timeand travel faster than light.
But I think antimatter is actuallythe 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 strugglingwith two relatively new concepts, one being special relativity, which describes lifeat really high speeds and the speed of light, and quantum mechanics, which describes the Earthor the world of the very small, atoms and molecules.
So he was solving this relativisticquantum mechanics equation, and he came out with two answers: a positive energy and a negative energyfor these particles.
How many timesyou've been doing your homework, and you come up with a negative answer, and you say: “Chuck that, just look at the positiveenergy solutions, because that’s what makes sense.
” But Paul Dirac was a genius, and he sawthese negative energy solutions, and he said: “Wait a minute, maybe there’sa whole new set of particles out there that we haven’t even seen.
” Some people thoughthe was crazy of course.
But it was only three years later that Carl Anderson at CalTechsaw this in his cloud chamber.
He saw the trackof a particle going, curving, and it had the same energyand mass as an electron, but it was curving the wrong way.
It should have been curving to the rightif it was an electron.
So this is the first experimentalevidence of antimatter or an anti-electron, which we like to call positrons.
So antimatter I like to describeas 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 havethe same mass as electrons, just positive charge ratherthan negative charge.
That’s why we call them positrons.
An interesting characteristicof antimatter is annihilation.
It’s quite unique in that if you have an antimatter particleand a matter particle, and they get close enough together, they’ll both disappearand turn into pure energy.
Now this is the Universe’s most efficientmeans of turning mass into energy, and it’s quite powerful, and that’s what got me interestedin positron physics years ago.
What does that meanin terms of energy density if you had a clump of antimatter? Antimatter has about90 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 energyas about 80 kilotons of nuclear weapon, or alternatively about 10 million litersof liquid natural gas – about a full tanker load.
So not only does antimatterhave incredible promises as a fuel for spacecraft, but this has some prettysignificant applications in the future of energy research, energy production, especially in inertial confinement systemsand pulsed energy delivery.
But I’m more interestedin the propulsion side of things, and so is my company.
The original conceptof antimatter propulsion, it was actually developedin 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 itin the rocket engine nozzle, and you’re ableto direct that energy flow, you’re able to direct those gamma raysso 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 antimatterto do this, unfortunately.
The other is that youcan’t trap the antimatter.
Of course, that property of annihilationwhich is good for the energy density is really bad for being able to trap it.
You need very high strengthmagnetic fields, and it just wasn’t feasible, still isn't feasible, to trap large amounts of antimatter.
The third problemwith the original concept was directing that energy.
Gamma rays are much higherenergy than x-rays.
Of course, if you go through the TSAin the airport, they x-ray your bag.
X-rays tend to go through everything, and gamma rays even more so.
Reflecting gamma rays is somethingthat we can’t do right now.
So, I started thinking aboutthese 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 positronsto 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 througha solid piece of material.
What this does is, it's very thin, so that most of the positronsjust travel right through, a very small number will actually stopinside the material.
Of course, a large numberof those will hit an electron because our matteris 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 surfaceand be emitted as a cold positron.
So, you have to be ableto create cold positrons in order to work with them.
They come out at a million times hotterthan the surface of the Sun, so you have to be able to cool them down.
This process was very inefficient, so we started thinkingof new ways to do this.
My lab partner and Idiscussed this for about a year.
We came out with a napkin sketchof an array moderator.
Soon after that we made itan actual patent, and then askedfor some money from a grant, and we were funded by the Steel Foundation to do the initial proof of concepton that moderator.
This moderator now forms the heartof all our propulsion concepts, and that little piece up thereis actually very tiny, it is about 3×3 mm, but it’s the source for allof our antimatter concepts.
When you are developing a concept, you also have to develop a team.
So back in 2012, I askedsome friends of mine whom I was working on anotherrocket project there in the desert with.
I said, “Well, let’s give upthis chemical stuff.
Why don't you guys come help mebuild an antimatter rocket?” Who's going to say no to that? (Laughter) So, we rented a little office, brought in a bunchof nuclear science equipment.
We quickly realized that the landlorddidn’t appreciate that, so we got kicked out of there.
In the next year, we moved intoa little more appropriate facility, and then, last year, finally, we made our way down to a nuclear fallout shelterwith a clean room.
This new facility will allow usto develop some of our concepts and integrate them into a CubeSat, which is a very small satellite, very easy to launch, very easyto 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 havinga very efficient moderator.
We use a radioisotope source of positronswhich continuously emits positrons.
We run it throughour little tiny moderator, and we can createa very high-intensity positron beam.
The third challenge is directingthe annihilation energy.
In order to do that, we transfer the kinetic energyof the gamma ray into a charged particle via fusion reactions.
And now we have a charged particlethat's high energy rather than a gamma ray.
And that's important because charged particleslike to follow magnetic field lines, as you know from the Aurora Borealis.
So, we use magnets likethe one in the bottom right there, to actually direct the energyand produce thrust.
In about two years, we were hopingto put a demonstrator CubeSat – that little tiny spacecraft – into orbit.
Why is this useful? What is it that a really smallspacecraft can do for you? Well, it turns out, that about 4 billion peopleon the surface of the Earth don’t have access to Internet.
So there's a lot of companies that want to launchconstellations of small satellites into low Earth orbit.
They will create a global networkof broadband Internets, so that anyone canaccess that information.
I think that would bean 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 technologywould allow them to do that and cut the transit time significantly.
And then, kind of a far-out applicationfor this, is asteroid mining.
I know you've probably never heardof asteroid mining, but it turns out that very small asteroidsin 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 somethinglike an antimatter system.
In terms of extending this technologyinto human space travel, that will require, of course, a lot of work.
It turns out that our squishy bodies can only really handleabout 1g acceleration, and even so 1g, 9.
8 m/s/s, is actually pretty high acceleration.
NASA took ten yearsto get to the Pluto; if we go at 1g, we can get therein 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 inconcepts of special relativity.
If we want to go out thereat 4.
3 light years, at 1g it would take about five yearsgoing at about 85% the speed of light.
Once we start getting toward a significantfraction of the speed of light, we start getting time dilation, which is an interesting phenomenon, but really it’s the thing that allows usto travel out into the Universe.
While five yearshas 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 placebecause a lot of people call it Earth 2.
It’s a little bit bigger than Earth, it’s in the habitable zone of its Sun.
A lot of peoplewant to go there and see – maybe there's life.
I think there is a good chancethat there might be, although it is 1500 light years away.
With our 1g spacecraftwe could get there in 12 years on the spacecraft.
Unfortunately, 1, 500 yearswill have passed on Earth.
So things are getting a little weirder.
If we look at the ultimateapplication of this, exploring to the edges of our Universe, 13.
5 billion light years away, at 1g we could make it therein 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 passedhere on the Earth.
What I’m trying to say is that, with the transformativetechnology like this, we have to think seriouslyabout the consequences, and new questions that arise.
The first of which is: If we want to really explore beyondour 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 backfrom it, essentially.
And then the second issue is: If we do want to go out beyond our galaxy, we're going to essentiallybe saying goodbye to this.
And you know human beings usedto be a nomadic species, and so one of the questionsI am asking you is: Do we want to become nomads again? Thank you very much.