Reality → Energy
Energy changes the state of matter and keeps our world moving. Energy occurs in very different forms and is connected with changes in motion as well as with temperature, electromagnetic radiation, and nuclear processes [1] . All energy, maintaining life and civilization on our planet Earth, can be traced back to the nuclear fire in stars. The selected topics shed some light on the fascinating subject of energy.
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There is no easy general definition of energy. Einstein's famous equation of mass/energy equivalence tells us that energy and mass are two aspects of the same thing. Neither energy nor mass can be destroyed or created, but they can change into each other and take on different forms. Regardless of the difficulty to define and explain energy at the fundamental level, energy plays a central role in physics, chemistry, biology, technology, economy, and politics.