Speed of light, lasers and mass Hopefully this isn't a bad question.  Light travels at the speed it does and nothing else can travel that fast because things have mass, correct?  Or at least correct on an elementary level.  And if lasers, which are light as I understand it, have the ability to destroy other things.  Doesn't that mean light has energy?  But if light has energy shouldn't it have mass?  I thought $E = mc^2$ and $E$ is energy, $m$ is mass. 0 mass times speed of light squared would equal zero energy, right?  It's probably obvious that I'm no physicist but hopefully its also obvious that I enjoy science and physics.
 A: With the first question you are correct. Any "thing" with nonzero mass cannot achieve light speed.  From this equation you can see why
$$m=\frac{m_{0}}{\sqrt{1-\frac{v^2}{c^2}}}$$
where $m_{0}$ is the rest mass of the body (i.e. the mass it has when its speed is zero). As you can see from the equation, when $v=c$, the right hand side will blow up to infinity. And you can't have an infinite mass.  
It's true that photons don't have mass, but that doesn't mean they don't have momentum. The relativistic energy momentum relation states that 
$$E^{2}=p^{2}c^{2}+m^{2}c^{4}$$
Knowing that the mass of the photon is zero, you get the following relation between the energy and momentum
$$E=pc$$ 
I will not bore you with more formulas, but the energy and momentum of the photon depend only on its frequency and wavelength in the following way. 
$$E=h\nu=\frac{hc}{\lambda}$$ 
So, the higher the frequency, the higher the energy of light. You can see this when you play with red, green of violet laser. With a violet laser you can light up a matchstick (having a high frequency) but with a red one you cannot because it has a much smaller frequency. You can read more on wiki.
A: To be simplified.
Mass can be converted from energy. Photon is just the thing that is a pure energy without any mass at all. You can convert photon to mass. But while it is a photon, run in speed of light, it has no mass
The equation E = mc^2 is the conversion, not declaration, it told you that if you convert mass to energy, you will get energy, and if you convert energy to mass, you get mass
A: Wow 'll try and sort this out. Light travels at a velocity that is dictated by a relationship of properties of 'freespace' (empty) called permittivity and permeability. it is the ability to reach and pull for lack of a simplier explaination ... 
Lasers 'cut' because they heat up and either melt or disintegrate complex molecules. Once melted the excess can be air blown away. like a cutting torch, which employs a heat source and a high pressure air source to blow the material out of the way, otherwise it would simply flow and harden when cooled.  ... back to light. Light has mass. It is proportional to its frequency. E=hv is what Planck discovered. it is not much in terms of grams, but it is present. when matter 'absorbs' light it is when a photon's energy is relayed to an electron and the electron accelerates, pushing it into a 'higher' orbit. An interesting point is that neutrinos travel faster than light, not by much but they do. the neutrinos from Supernove 1987A arrived here 3-4 hours before the light did.     
