# Where does energy come from? On the universal scale, energy is defined in physics as a property of matter. This has been described by Albert Einstein’s famous equation of mass-energy equivalence: E = mc2

In the simplest form, this means that the energy associated with a body at rest is defined by the product of its mass and the square of the speed of light. Energy and mass are therefore different properties of the same thing, known as matter.

In a closed system, energy and mass must always be conserved. For the purposes of this article we will work on the basis that the Universe is a closed system. Therefore we can state that all the matter in the Universe is defined by all the energy and all the mass in the Universe. Using the Big Bang theory of the origin of the Universe, it can be assumed then that all matter was formed at the Big Bang, and thus the Big Bang is the source of all the energy in the Universe.

Energy encountered on earth takes many forms. Some of these forms include:

• Kinetic energy
• Gravitational potential energy
• Electrical potential energy
• Chemical energy
• Light energy
• Sound energy
• Thermal energy
• etc. etc. etc.

Ultimately all of this energy encountered on Earth is derived from the energy contained within and released by the Sun. There are so many different forms of energy that I cannot explain how they can all be traced back to the Sun, but I will use two examples.

• Your device takes electrical energy from the battery within it and creates light energy (images) or sound energy (noises) to complete its function.
• Electrical energy is released from the battery which converts stored chemical energy into electrical energy.
• The stored chemical energy in the battery is converted from electrical energy carried through the mains that you plug your charger into.
• Let’s assume the electrical energy in the mains is converted from a renewable energy source, such as a solar array. The solar array takes light energy and converts it to electrical energy.
• Light energy comes from the Sun. Kinetic energy of a car you are sat in:

• The kinetic energy of the car is generated by converting the rotational energy of the car’s axles into linear motion through friction between the tyre and the road
• The rotational energy of the axle is generated by the movement (and kinetic energy) of a piston in the car engine which is moved by the expansion of gases.
• The expansion of gases is caused by combustion of the petrol in the car’s tank, which is the conversion of chemical energy in the fossil fuel into thermal and kinetic energy in the piston.
• Fossil fuels are formed by the anaerobic decomposition of buried dead organisms at high pressure, and thus the chemical energy in the fossil fuel originally was created by the organism consuming some kind of food (let’s say plant matter)
• The chemical energy stored in the plant was generated via photosynthesis which takes light and thermal energy and converts it to chemical energy
• Light and thermal energy comes from the Sun.

Using this logic, it is possible to work most energy you encounter back to energy input to the Earth by the Sun. The initial energy transfer may have been from the Sun to the Earth very recently (such as at a solar array) but could also be energy from millions of years ago, such is the case with fossil fuels. It could even be energy from the original formation of the Earth 4.5 billion years ago, such as thermal energy trapped in the Earth’s core which maintains life on the planet. But ultimately this logic leads you back to the Sun.

The Sun releases energy as heat and light due to the nuclear fusion that occurs in its core. Nuclear fusion occurs when two atomic nuclei collide at such high speed that they “fuse” together to form a new type of nucleus. This is typically characterised by two hydrogen nuclei combining to form one helium nucleus. When the two nuclei fuse, a large amount of energy is released. In the case of the Sun (and all other stars) this is emitted as both light and thermal energy.

And what was the origin of the Sun and the stars? The Big Bang. Thus all energy ultimately can be traced back to the formation of the Universe at the Big Bang.