I'm no scientist, but I don't think there ever was a 'nothing' in its purest form. Every single particle that ever existed, still exists today. It just changes states of existence, combines with other particles, elements and compounds. According to the commonly accepted expanding universe theory, those particles or matter as we know it, is in the constant state of expansion though. Which supports the big bang theory and basically means that these particles existed in much higher concentration at some point in the past, but are getting diluted by the endless void of space as the time goes by. Same with energy. It never disappears into thin air, rather transforms into different kinds of energy. For example, an object suspended in the air above ground possesses potential energy, once let go, left to the forces of gravity it sets in motion. Potential energy converts into kinetic energy at this point. When this object falls to the ground and comes to a stop, a portion of that energy is passed on to objects being impacted, and as a result move out of the way and other portion converts into heat energy. Thats why meteors rarely make it to earth. Constant collisions with air molecules create friction and a lot of heat as a result. That is what makes meteors burn up before they hit the ground. A common phenomenon referred to as a 'shooting star'.