1.1.2 What is energy?

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Summary:
Matter and energy are two sides of the same coin. One can be transformed into the other: E=mc2.
1.1.2-1  It is said that Einstein was not so concerned with the equation in the form E = mc2. He had the mass, the substance, in the main role, not the energy: m = E / c2. Mass is thus a function of energy. Then the story becomes a little different. In order to "make" 0.6 grams of mass, energy corresponding to an atomic bomb is needed. Imagine then how much energy the universe consists of!

1.1.2-2  So what is "energy"? We use it for nuclear power, kitchen appliances, cars and planes. We cook with heat energy from burning charcoal on the grill. We cycle with energy from muscles that get energy from food through a biological process. The weather is energy. Light and radio waves are energy. Energy is found everywhere in a multitude of different forms, of which "matter", particles, is just one.

1.1.2-3  So what exactly is energy? Nobody knows. The encyclopedia states that energy is the ability to perform work. Steam from the sea surface works its way up to the clouds. Cycling is work. Boiling eggs is work. Blowing up a city is work.

1.1.2-4  Energy is just there. It is a concept that physics has invented with which one can perform calculations. Energy is very visible because it creates movement and transforms things. The amount of energy in the universe is constant, say the laws of physics. It came from The Big Bang and is still here, science says. It just flows outwards and becomes more and more scattered and thinner. This process is called entropy.