A: The matter (and energy) in the world is not eternal. Matter and energy can be transformed into each other, which is Einstein's famous mass-energy equation. In other words, mass and energy follow the law of joint conservation. However, in the microscopic situation, there are also cases where mass and energy are not conserved, which has been expounded by the "uncertainty principle" When high-energy protons collide with neutrons, mass and energy are not conserved in a very short time range, which is the moment when gluons are produced and disappeared. Described by the uncertainty principle, it is Δ e Δ t ≥ h/4 π, where h is Planck constant.

B: Besides the common three states of gas, solid and liquid, there is also the fourth state-plasma state and the fifth state-Einstein-Bose condensed state.

C: You can think so, but just like A, you need to extend your concept, because the universe we live in is not only a chemical reaction, but also a large number of nuclear reactions (a microscopic physical change), in which there is mutual transformation of energy and matter.

In addition, the cycle is time-limited, because there are levels of energy, and only high-level energy can be infinitely transformed into low-level energy, and vice versa, work needs to be done! Simply put, the electrical energy and mechanical energy we use will eventually be converted into internal energy, that is, heat energy, because of the second law of thermodynamics. This is also the meaning of the arrow of time. That's what "entropy" upstairs actually means.

An obvious example: when we burn coal to generate electricity, chemical energy is converted into internal energy (the efficiency can be close to 100%), while the thermoelectric conversion efficiency of converting internal energy into electric energy is only about 45%, and more than half of the energy is finally dissipated in the form of waste heat. This also causes the environment to get hot.