E = m c2
The most famous equation which gives the relationship between mass and energy. Mass can be be converted to energy (and vice versa). Refer this link for more details on this.
It also dictates that mass of an object will increase as the speed increases and even more so when approaching the speed of light.
Almost everyone thinks that this puts a damper on achieving the speed of light, since as we approach the speed of light the mass increases considerably. So, we need more energy to propel the object due to its increased mass. As the speed increases, the mass increases and so does the need for energy required to propel the object.
But, how about this: if we use the first equation and convert the gained mass back to energy and use that to propel the object instead. Viola! We have solved both problems with this solution.
Now all one has to do is create an object which can convert its mass to energy and use this energy to propel itself. The more mass it has, the more energy it should generate.
Could this be why particles moving at speed of light (or faster) have zero or negligible mass? Are these particles converting their gained mass to energy which keeps propelling them at such high speeds?