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If you've ever watched the show Star Trek, you surely must have wished that you could travel in their wonderful starship, the Enterprise. It can accelerate almost instantly from zero to Impulse Speed, which is about one third of the speed of light. At flat chat, the Enterprise can travel at 2,000 times the speed of light. You could certainly get a close look at a lot of the nearby stars if you could travel at such enormous speeds. Can we ever get to the stars in a human lifetime? Well, the Old Physics says "No", but there's a New Physics on the way that says "Maybe".
Light travels awfully fast - around 300,000 kilometres in one second. Einstein threw a spanner in the works with his Special Theory Of Relativity. He said that nothing can travel faster than the speed of light. As you gradually speed up an object it gets heavier.You then have to apply more energy to make this extra mass go faster. By the time you get up to the speed of light, the object that you're trying to push now has an infinite mass, which is ridiculous!
Now with our present-day science, it seems awfully hard to get to even the nearest stars in a reasonable time. There are three stars in the Alpha Centauri complex, about 4.3 light years away. (A light year is the distance that light travels in one year, and it's a really long way. For example, the planet Neptune is only about 4 light hours from the Sun, but it took the Voyager spacecraft 12 years to get there.)
Suppose you wanted to send the American Space Shuttle to the nearest stars. Suppose that you had a pretty good artificial hibernation process for humans, and you were happy for the journey to take 1,000 years. Well, the fuel needed to get it there in that relatively long period of 1,000 years would be much greater than all of the mass of the Universe - in fact, over 10,000 million million million million million million million million million million times greater than all the mass in the entire known Universe!
So if we're going to get to the stars, we're going to need some radically New Physics to get us there. Some, but definitely not all, physicists think that a New Physics is just around the corner.
It's a bit like the situation that existed a century ago. Back then, there were a few problems in the Land Of Science, but they were too hard to solve and so the physicists just ignored them - they swept them under the carpet. One of these problems was the Age of the Sun. The geologists said that the Earth had to be at least 25 million years old, and probably a lot more. The astronomers knew how big the Sun was. But the best fuel that the physicists could come up with was coal. If the Sun was made entirely from coal, the Sun was big enough to burn for only a million years. How could the Sun keep on burning for the extra 24 million years?
Scientists came up with bizarre theories like the Sun getting extra heat energy from millions of comets that were supposedly continually ramming into it at high speed - but basically, they swept the problem under the cosmic carpet. Early in the 20th century, nuclear energy was discovered, and the problem was solved. But the problem had to be solved with a New Physics, not the Old Physics.
Today, at the end of the 20th century, we're in a similar situation. There are quite a few problems that we sweep under the carpet and ignore, simply because we can't solve them. One of these little problems is the Missing Mass Of The Universe - yes, according to the astronomers, 95% of the Universe is missing. Today, many scientists think that because of this and many other problems, we're heading for another revolution in physics. NASA thinks so too. Over the last few years NASA has quietly organised some extraordinary science. One of them has the seemingly-harmless title of "Breakthrough Propulsion Physics Program". What it's really about is coming up with some short-term or near-term, ways of making the breakthroughs that are needed to be able to travel to the stars and back in a normal human life span.
Last time I was talking about how difficult it is to get to the stars using our current technology. For example, look at the amount of fuel you would need to get something like the Space Shuttle to the nearest stars, the Centauri complex, which is about 4 light years away.
If you're prepared to put up with a fairly slow trip lasting about 1,000 years, and used ordinary rocket fuel, the amount of juice needed is squillions of times bigger than the mass of the entire known Universe! If you use a nuclear fission rocket, you would need about a billion super-tankers of propellant (each weighing about a quarter of a million tonnes). If you use a nuclear fusion rocket, you'd need only about 1,000 super-tankers, but with an antimatter rocket, you'd need only about 10 railway tankers. But in half a century, we have made only one tenth of a billionth of a gram of antimatter - which is only enough to get your fully-loaded family wagon about 15 metres down the driveway before it splutters to a high-tech halt!
But there are a few new methods of space travel, based on the science that does exist today.
Back in the 50s, scientists came up with Project Orion, which is basically strapping nuclear bombs to your butt!
They would explode five nuclear weapons every second, which would push on a giant plate at the back of the spaceship, which would be protected from the spaceship by giant springs.
In 1973, the British Interplanetary Society came up with Project Daedalus.
It was similar to Orion, but instead of five nuclear explosions every second, they wanted to have 250 micro-fusion nuclear explosions every second. They reckoned that they would be able to shove a pay load of a hundred tonnes up to about 12% of the speed of light. This would get you to the Centauri complex in about half a century.
Bussard came up with another way, when he invented the Interstellar Ramjet in 1960.
It didn't carry its own fuel - instead, it would scoop up fuel from the space that it travelled through. It had a funnel out the front, about 2,000 kilometres across. This funnel was not made of solid stuff, but of electromagnetic fields that were generated by an enormous magnetic solenoid. Particles would be trapped by the funnel, fed to the fusion reactor, burnt and thrown out of the back of the Bussard Ramjet.
Robert Forward invented Interstellar Laser Sails.
He reckons "use light, rather than rockets". After all, light can exert a very tiny push on an object. If you have a very powerful light shining on a very large object, the "push" gets reasonably big.
His first plan proposed using a sail 1,000 kilometres across, and shining a 10 million gigawatt laser on it. He reckoned he could send a vehicle weighing 1,000 tonnes to the Centauri complex in just 10 years. The catch was that neat little 10 million gigawatt laser. 10 million gigawatts is 10,000 times more than all of the power used on the Earth today!
So Robert Forward came up with a smaller version of the Interstellar Laser Sail. The new sail is a grid of fine wires weighing only 16 grams, but covering a kilometre. This time, the laser is only 10 gigawatts, which is only one hundredth of all the power generated on the Earth today. The penalty is that the trip would take twice as long (20 years), and the payload would not be 1,000 tonnes, but only 4 grams!
So you can see that we are not going to get to the stars and back in a human lifetime with our present technology. We need to make a big jump. After all, we didn't invent photocopiers by trying to make better carbon paper. We didn't invent steamships by improving sails and rigging.
Instead, we have made various breakthroughs in our technology. We went from the sailing ship, to the steamship, to the propellor plane, then the jet plane, and today we have the rocket. We need to make the breakthrough from the rocket to the next stage.
In a relatively short time, we humans have made it from the Stone Age to the Space Age. Even so, our space travel technology is still pretty primitive. Our robot spacecraft have already left the Solar System, but we humans can barely get to the Moon. With our current technology, getting to the stars and back in a human lifetime is impossible. However, a NASA team has identified three breakthroughs that will get us to the stars. The breakthroughs are (first) to get rid of the need for propellant, (second) to travel much faster, and (third) to harness new sources of energy.
In 1996, Marc Mellis of the NASA's Lewis Research Center created the Breakthrough Propulsion Physics Program. This program has a small floating group of scientists from government, university and industry. Since 1996, they've banged their heads together, and worked out what needs to be done. The first breakthrough the scientists are thinking about is getting rid of, or at least dramatically reducing, the need for propellant. After all, when you drive your car down the road, your wheels grip the road, and your engine turns the wheels. But in space, there's nothing to grip onto. That's why rockets (which go forward by tossing stuff out the back) are the only practical way we have of travelling through space - at least, at the moment. But to get the Space Shuttle to the nearby Centauri stars, in a 1,000-year-journey and using conventional fuels, you need to throw away huge amounts of mass - squillions of times greater than the mass of the entire Universe!
So some scientists are trying to reduce the amount of propellant needed, by fusion, or even anti-matter. This would get our space ship moving rapidly, but still well below the speed of light. But, even so, using anti-matter to accelerate a space ship from zero to half the speed of light, and back to zero, would take 700 times the mass of the space ship. There has to be a better way.
So other scientists are trying to get rid of the propellant entirely. They're thinking about how to manipulate gravity or inertia, or how to interact directly between matter and the spacetime fabric of the universe. Here, they may be able to travel faster than the speed of light!
If we imagine that the fabric of spacetime is a sheet of paper, and our spaceship is a pencil, then Einstein tells us that our pencil (a spaceship) can't move faster than the speed of light - but Einstein doesn't mind one bit that our sheet of paper (the spacetime fabric) can move faster than the speed of light. After all, back in the good old days, just after the Big Bang happened, it's claimed that the fabric of spacetime expanded faster than the speed of light.
So Miguel Alcubierre, a physicist at the University of Wales in Cardiff, worked out (theoretically) how to "warp" spacetime, and travel faster than the speed of light. All you had to do was shrink the fabric of spacetime in front of your spaceship, and at the same time expand it behind your space ship.
Unfortunately Mitchell Pfenning and Larry Ford from Tufts University in Medford in Massachusetts actually worked out the numbers, and found that you could warp only a very tiny section of spacetime (much smaller than an atom), and that the energy needed to do this is around 10 billion times all the energy in the entire Universe - hardly worth it!
Another way to get moving faster than the speed of light is to use a "wormhole". Imagine that you have a two-dimensional sheet of paper with a little black dot at the top right hand corner, and another little black dot in the bottom left hand corner. If you wanted to get from one dot to the other, normally you would have to crawl all the way from one corner of the paper to the other. But suppose that you bend the sheet of paper and bring the two dots in contact with each other. If you knew how to manipulate the Third Dimension, and jump out of the paper and back into it again, you could travel from one dot to the other without having to cross the space in between. Maybe a wormhole could be used to do the same thing, but in our four-dimensional spacetime universe.
Notice that with both the "warping of space" method, and the "wormhole" method, we're no longer throwing propellant out of the back of our spaceship.
To have fair-dinkum space travel (zipping to the stars and back in a human lifetime) we need better technology than we have today. Not only do we need to get rid of most, or all, of the propellant, but we also need to be able to travel much faster, and we need to harness new sources of energy. Let's look at travelling faster. If we travel at 100 kilometres per hour, we can get to the nearby Centauri stars in 50 million years. If we travel at the speed that the Apollo Astronauts used to go to the Moon, it's down to only 900,000 years. And if we travel at the speed of the Voyager II spacecraft, our journey time is 80,000 years. The conclusion is obvious - we have to get up to either some decent fraction of the speed of light, or faster than the speed of light.
The third breakthrough needed for real space travel is some sort of fundamentally new way of generating energy. Nuclear fission, nuclear fusion or even anti-matter simply won't give us enough energy.
But there are other energy sources on the horizon. There's a strange thing called Zero Point Energy. Suppose you make a small hollow metal box, with an internal volume of one cubic centimetre - roughly the volume of the tip of your little finger. Suppose that you remove every particle of matter from inside your little box. All you have left is a vacuum. But this vacuum is not nothing - no, it's made up of a strange sea of particles and anti-particles that wink into existence, and almost instantly, wink out again. Their coming and going creates their strange energy called the Zero Point Energy. This energy is huge - up to 1054 joules in each cubic metre. To put that into Plain English, there's enough Zero Point Energy in the vacuum in our tiny metal box to boil all of the oceans on our planet!
That is the kind of energy level that we need to travel to the stars. And we now know that it's real, not just theory. In 1997, scientists were able to measure, for the first time, the Zero Point Energy pushing two metal plates together.
There is still so much science that we do not know. As far as the physicists are concerned, the natural universe can be explained in terms of the Four Forces. These forces are the Electromagnetic Force (radio, TV, telephones, your Hi-Fi unit, and the like), the Gravity Force (which keeps the planets spinning in their orbits around the Sun, and keeps stuck to the ground), the Weak Nuclear Force (which is responsible for some forms of radioactivity) and the Strong Nuclear Force (which holds the positively charged particles in the core of the atom together).
Of these Four Forces, at the end of the 20th century, we humans can manipulate only one - the Electromagnetic Force. We can measure the waves and the particles that make up the Electromagnetic Force, and we can generate and block the Electromagnetic Force. Today we can use it to talk on a mobile phone to somebody on the other side of the planet, almost instantly.
But 400 years ago we could hardly use the Electromagnetic Force at all. The most sophisticated thing that we could do with the Electromagnetic Force was to cut an orange in half, stick a copper nail into one side of the cut orange and an iron nail into the other side of the cut orange, and touch the two different metals to the wet leg of a frog. The leg of the frog would then jump as the electricity went through it - hardly high-tech at all.
Our knowledge and our ability to use and manipulate the remaining Three Forces of the Universe is not even at that primitive stage, where we were with the Electromagnetic Force 400 years ago. We have a long way to go in our knowledge and our understanding - and somewhere along that pathway, we will uncover the secrets which will get us to the stars.
Now some breakthroughs happen really rapidly. There are only three decades from 1911 (when we first began to understand radioactive decay) to 1942 (when the first working nuclear reactor was built under a gymnasium at Chicago University). It was only in 1997 that the Zero Point Energy was actually measured for the first time. Who knows where we'll be in the next three decades?
Why should we go down this pathway towards getting to the stars? Well, one answer is that it's incredibly cheap, as compared to the annual military budget for the world. Another answer is that we are investing in the future for our children, and for the human race. We are one of the few animals that can see the stars, and the stars are our destiny.
| Standard Model of Particle Physics | |||
| FERMIONS matter constituents | |||
| Ordinary Matter | |||
| Leptons | Quark | ||
| Electron 0.511 |
Electron Neutrino ? |
Up 5 |
Down 8 |
| Exotic matter | |||
| Muon 105.7 |
Muon Neutrino ? |
Charm 1,270 |
Strange 175 |
| Tau 1,784 |
Tau Neutrino ? |
Top 174,000 |
Bottom 4,250 |
| The estimated mass of each particle is shown in the energy equivalent expressed in millions of electron volts. The highly diverse masses are yet to be explained | |||
| Bosons force carriers | |||
| Photons | Gluons | Intermediate Vector Bosons |
Gravitrons |
Matter made of particles with identical mass and spin to particles of ordinary matter, but with opposite charge - for every particle type there is a corresponding antiparticle type. | |||
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Travelling at the Speed of light