Shoutbox

5000 years would still be stretching it for a race to travel from one inhabited planet to another (in the alien scenario). But considering they can reach relativistic speeds such as 0.8 times the speed of light, they will experience a significant length contraction effect (predicted by Einstein's Theory of Special Relativity which has experimental evidence). Length contraction follows the formula;


This effectively means for example, that if we have a distance of 1000 light years which we need to travel to reach somewhere and we are travelling at 0.8 times the speed of light (ie. 0.8c):
L = 1000 * (1 - (0.8c)^2/(c^2)) ^ 0.5
L = 1000 * (1 - 0.8^2) ^ 0.5
L = 1000 * (1 - 0.64) ^ 0.5
L = 1000 * (0.36) ^ 0.5
L = 1000 * (0.6)
L = 600 light years
This would mean that if we are travelling at 0.8c, it would only take us the time that it would normally take to travel 600 light years in order to actually travel 1000 light years, that is, it would take 60% the time that we would normally predict by; distance divided by velocity; The Wonders of Special Relativity!

Now imagine we are traveling at 0.999999999...9 times the speed of light (since travelling at light speed is physically impossible for any masseous object - discussed later):
L = 1000 * (1 - (0.999999c)^2/(c^2)) ^ 0.5
L = 1000 * (1 - 0.999999999999...) ^ 0.5
L = 1000 * (0.00....1) ^ 0.5
L = 1000 * (0.00..1)
L = just over 0 light years
Therefore if we are travelling at 0.999999999...9 times the speed of light it would take us much much less time to travel 1000 light years (or anywhere essentially)

Now for something hypothetical, what if we are actually travelling at the speed of light (ie. travelling at c)?
L = 1000 * (1 - (c^2)/(c^2)) ^ 0.5
L = 1000 * (1 - 1) ^ 0.5
L = 1000 * 0
L = 0 light years (or 0 distance)
Therefore if we are travelling at the speed of light, we have to travel a distance of zero (ie. it would take 0 seconds, since time = distance / speed) to arrive at any point in the universe. But wait, that would mean that we are everywhere at the same time? Uhoh But dont worry about that, because it turns out that we can never actually reach the speed of light (Sorry to get your hopes up)

Now; Why can't we (or any masseous object ie. an object made up of mass) reach the speed of light?
Firstly, when a force is exerted on a mass, the mass gains Kinetic Energy (KE) which is what makes the object move;
KE = 0.5*mv^2
m is mass
v is velocity
Now, what Einstein's Theory of Special Relativity (which is widely accepted as true and has quite a large amount of experimental evidence nowadays) predicted that as force was applied to an object (ie. as the object gained kinetic energy and began moving faster, since KE = movement energy), a smaller proportion of that gain in kinetic energy was going into the velocity itself, instead, most of it was going into the mass of the object (ie. the faster it got, the less its velocity would increase since the energy was going into mass rather than the velocity). This essentially meant that the faster you get, the 'heavier' or more masseous (greater in mass) you become, and since 'acceleration = mass / force', this means that as the mass increases you would need to provide a larger force to get the object to keep accelerating. This means that the faster an object got, the more force would have to be applied to make it get faster, and as it got faster, the heaver it would get which means you would need to apply yet again more force to get it even faster. When graphed it showed that as the object approached the speed of light (ie. as its velocity got closer to the speed of light), the amount of force necessary to make it accelerate further approached infinite, and as it is obviously impossible to provide an infinite force on an object, it is impossible to actually reach the speed of light.
For that reason, reaching the speed of light is impossible for any object consisiting of mass (ie. any object).
Ok, so howcome when I'm moving in my car I'm not fatter than when im standing on the sidewalk? Well firstly you have to realise that the increase in mass is only noticeable when you are travelling at speeds which are comparable to the speed of light (eg. 10% the speed of light or above), and since the speed of light is  299,792,458 metres per second, or 1,079,252,849 kilometres an hour then you can see that your car (average 60 kilometres an hour) is going no where near that speed. Now the fact is that you actually are fatter (or greater in mass) when you're moving your car, but the amount of mass which you gain is EXTREMELY small and is hence unnoticeable.

Now you may wonder how light travels so fast if nothing else can? Well the fact is that not much is known about the nature of light, no one really understands how it works or what it is made of - so far quantum physicists have noticed that light sometimes behaves as a self-propagating wave of electric and magnetic fields (hence the name electromagnetic radiation) which allows it to travel at the speed of light (since it has no mass), and at other times light behaves as small particles (referred to as photons) - this is known as lights particle-wave duality.
The fact is that the human civilisation's crappy level of science simply doesnt know the answer...