Answer:
Light can act as a wave or a particle. This is called light wave-particle duality, simply that the light has both the characteristics of fluctuations, but also has the characteristics of particles. Light can propagate forward like a wave, and sometimes show the characteristics of particles.
Metal is not heat resistant and therefore it is not a good heat shield. For example pots are made out of metal because they are good conductors of heat.
Light is said to be the fastest, it is because we have not discovered anything faster than light. If someone discover's something faster than light then that will become the fastest. It is not that we have tried hard enough, it is just that our technology, research and veiw of outer space is limited. Implementing good research and technology requires a lot of money, time and expertise. We have much better things to do than to discover something faster then light because even if it's discovered what can we do with it, with our severe lacking research and technology, it's practically useless and good as updating some newspaper articles. When even light can give us a headache.
Dark matter, antimatter, dark energy and degenerate matter can be said to be different. I'm not sure about the intricasies but all have different energy frequencies and effects. Not sure but please do research about it.
Hope this helps you.