In many movies, TV series and science fictions, our descendants travel throughout the stars and galaxies as frequently as we travel around the earth by planes. In these stories the fly their space craft’s near the speed of light, or they might use Wormholes as a short cut. Sometimes they travel interstellar distances within few hours! Will the future advancement of science and technology allow all of this stuff to be happened? To answer all these questions we have to consider some modern understandings of physics.
As interstellar distances are measured in light years, to travel such distances within the lifetime of a person, it is essential to travel near the speed of light.(it is impossible to travel at or more than the speed of light as it violates the postulates of the theory of relativity). In order to achieve a speed of few percent of the speed of light an enormous amount of energy is needed. The energy that it would consume to speed up a ship that of the size of a space shuttle to a speed of 0.5c is nearly 1000 times the total annual energy use of the world today. Clearly it would need new types of energy sources in order to make the interstellar travel a reality.
Nuclear fusion would be a favorable source of energy. Although the technology today is not sufficient to carry out the fusion reactions in a controlled environment, we can keep hopes on the future technology to do so. Then faster space ships will not be a fiction.
Some scientists have proposed a way of achieving a speed that carries the ship to the nearest star within a century. That is by using nuclear explosions to ‘push’ the ship forward. Continuous nuclear explosions that take place behind the ship will generate a radiation pressure on the pusher plates at the back of the ship. In this case thousands of small nuclear bombs should be detonated, and the mass of the fuel will increase the mass of the ship making it harder to accelerate. One alternative is to reduce the mass of the fuel is to collect it from the interstellar medium. Although the density of the ISM is very low sufficiently large ‘scoop’ would be able to collect reasonable amount of Hydrogen as the nuclear fuel.
When focusing on completely theoretical methods that have being proposed to travel across the stars, wormholes have a special place among both scientists and writers. But it would be impossible to predict what will happen to the space ship or the crew, inside the wormhole, as the worm hole is a result of space-time discontinuity and the ship itself is a part of the space-time.
In conclusion we can see although there are enormous obstacles to achieve interstellar travel, there is no reason to think it is impossible. If we continue to seek out the mysteries of the universe, one day our descendants will make journeys to the stars.
References: The Cosmic Perspective (Bennett,Donahue,Schneider,Voit)
(This is the summary of what we discussed at our second session)