What would an Alien Race need to Invade Earth?
There are four things we must assume for an alien invasion to be realistic:
1. That there is other life elsewhere in the universe
2. That this life is intelligent
3. That it has a means of getting to Earth
4. That it has a reason to invade Earth
5. That it has the weapons technology to invade Earth
In this article I will examine each of these and assess its possibility or likelihood. If you agree that they are all possible then you must accept that the threat of an alien invasion should not merely be consigned to science fiction.
How likely is it that there is life elsewhere in the universe?
In this galaxy there are more than 10 billion stars, of which our sun is just one. There are more than 10 billion galaxies in the universe, many of which are much, much larger than our own. Many of these stars will have more than one planet, ours has nine. According to modern physics, there are also an infinite number of parallel universes. How likely can it be that Earth is the only planet on which life formed?
Do we know of any other planets where life may have existed?
There is a strong chance that life once existed on Mars. There is evidence of flowing water, the most important perquisite for life, and many scientists believe that bacteria have been found on various meteorites from Mars. If it did exist, that would be two planets with life in just our solar system on which life has evolved - maybe it has done on many thousands of planets elsewhere, in this universe and others. It is also thought that conditions on Saturn's moon, Europa, may be suitable for the evolution of life.
How likely is it that intelligent life has evolved?
Just because there is life on a planet, it does not have to be intelligent. If a meteorite had not wiped out the dinosaurs, mankind would not exist. Life has been evolving on Earth for 4 billion years, of which we have been around for just 1 million (1/4000th of the time), and civilisation just 4000 (1 millionth of the time). Looking at the rest of this site will tell you how many chance events could have extinguished life. However, out of all the universe, surely we cannot be the only intelligent life to evolve?
How likely is it that aliens have a means of getting to Earth?
Even if there is intelligent life elsewhere, it could be billions of light years away. The universe is stupendously large; even one light year is an incredible distance. Light travels at 300,000 kilometres per second. A light year is the distance it can travel in a year, about ten trillion (10,000,000,000,000) kilometres. The nearest star to us, Proxima Centauri, is 4.2 light years away. The whole size of our universe is estimated at one thousand trillion, trillion (1,000,000,000,000,000,000,000,000,000) metres. Journeying across space, even at the impossible speed of light, would take one trillion (1,000,000,000,000) years. Clearly aliens would need to travel faster than light, or interstellar journeys would be impossibly long.
Why is travelling faster than light so difficult?
The trouble is, travelling even at the speed of light is impossible, according to Einstein. Imagine a space ship moves towards you faster than light. The space ship would arrive before the light from its origin reached you, so you would see the space ship arrive before you saw it set off, which is impossible. What happens is that as an object accelerates more energy is required, which increases its mass. This means it requires more energy to accelerate further. Accelerating to the speed of light would require infinite energy, which is impossible.
Is it possible to travel faster than light?
There are several theories as to how faster than light travel (FLT) may be possible.
1. One idea is to use parallel universes. In different universes, there would be different laws of physics, so in some the speed of light barrier would not affect an objects speed. A spacecraft would have to be able to transfer itself into another universe, accelerate past the speed of light for its journey, then return to our universe. There are obvious problems in getting to another universe, and then accelerating to a speed greater than 300,000 km/second.
2. A second idea is called 'folding space'. Imagine space has only two dimensions: length and width, but no height. This would mean it could be drawn on a sheet of paper. Imagine that you could fold this sheet of paper in half. A point on one side of the sheet would then be next to a point on the other. In this way a spacecraft could make itself next to another place, anywhere in the universe.
Clearly, space has three dimensions (length, width and height), so the idea of folding it may seem strange. But from what I've read, the same idea would apply as for two dimensions.
3. A third idea is to alter the speed of light around the spacecraft by using theoretical particles called 'exotic matter'. If the speed of light could be altered, objects could travel at higher speeds without hitting the light speed barrier. This idea could also be used to alter the speed of light at the start and destination points of a spacecraft, an idea more commonly known as a 'wormhole'.
If we do not have this technology, why would aliens?
The simple answer is that although this technology may be hundreds or thousands of years away from development on Earth, other civilisations may be much older. Closer to the centre of the universe, planets would be millions of years older, so life would have had much longer to evolve. As I mentioned before, intelligent life on Earth has only existed for a tiny fraction of its history, and many chance factors could have led to it evolving millions of years earlier. It is extremely unlikely that if extra terrestrial life did exist that it would be at a level of development at all similar to that of Earth.
What reasons would aliens have to invade Earth?
Since on Earth society has become more peaceful as it developed, it is easy to assume that alien civilisations that have developed for thousands of years would not be inclined to go to war. However this easily could not have happened elsewhere, and it is only chance that it did on Earth. Suppose the Nazis had achieved world domination in World War 2, as they easily could have done. If they discovered another civilisation they would not hesitate to destroy it - if they thought other humans had 'impure' blood then what would they think of aliens? So aliens discovering us might simply want to destroy us to racially purify the universe.
A second idea would be that they needed Earth for something, such as resources or living space. There may be very few planet's in the universe that are capable of supporting life, so aliens from an overpopulated, over-polluted world might seize any opportunity to ensure the survival of their species. It may be that their planet was destroyed, or made inhospitable; perhaps in one of the ways suggested on this site. Similarly, if aliens lacked resources essential to them, if they were available on Earth they might see no option other than to invade.
Would aliens be able to defeat Earth?
Despite numerous science-fiction film plots, it is most unlikely that humans could defeat an alien race so advanced that it had faster than light technology. Film plots range from human viruses killing aliens, unlikely since alien invaders could surely think of some sort of protective suit, to humans getting nuclear warheads inside their ship, unlikely since aliens could surely detect us trying. If aliens simply wanted to eradicate humanity, then they could use nuclear weapons or some other technology to kill us without even entering our atmosphere. Nuclear weapons could not be used if they wanted to preserve Earth for themselves, but aliens capable of getting to Earth must surely have some suitable weapon.