Ryan Weed: Have You Ever Imagined How Interstellar Travel Could Work? at TEDxDanubia (Transcript)

Ryan Weed


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.

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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.

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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.

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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.

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