But Newtons laws don't work when dealing with speeds close to the speed of light, which is why Einstein had to come up with his general and special theories of relativity.<br /><br />As stated above, the closer you get to c, the more your mass increases and time slows down for you. At c, you would have infinite mass and time would stop for you.<br /><br />Matter cannot be accelerated to the speed of light, because to do so would require infinite energy. Only so called mass-less objects can travel at the speed of light (i.e. photons).<br /><br />But strangely enough, this does not mean that a journey of 5 light years actually takes 5 years at the speed of light! Two phenomena occur when accelerating towards the speed of light - time dilation and length contraction (see the Lorentz transformation for more details).<br /><br />Say we manage to make a spaceship that can accelerate to 0.999c (this would take an immense amount of energy to do, but is still technically possible). Special relativity (specifically the lorentz transformation) tells us that at 0.999c, a journey of 5 light years would only take the spaceship a little under 3 months due to time dilation. And due to length contraction, the distance to the spaceships destination would shrink from 5 light years to 0.22 light years at this speed. Now at 0.999c a journey of 0.22 light years takes a little under 3 months! But of course, this is only relative to the spaceships frame of reference!<br /><br />To an observer watching from an inertial frame of reference, it would still look like the spaceship travelling at 0.999c takes 5.05 years to make the 5 light year journey.<br /><br />This is what throws up the so called "twins paradox". If your twin brother makes that journey, turns round and comes straight back home, to you it would look like the journey took him around 10.1 years. But when he returned he would have aged only a little under 6 months!<br /><br />So, you see, the spaceship doesn't exceed the speed of light and yet <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>