There is something ancient about campfire ...
After prehistoric humans had learned to light a fire they got light from it... and heat.
When he wanted to see in the darkness of his cave, burning fire gave him light.
When she wanted to feel warm, burning fire gave her heat.
Fire is one of the great discoveries of human race and no other species on Earth knows how to use it or how to light it.
Prehistoric people did not know all the details about the chemistry or nuclear physics involved with burning fires. First evidence we have of controlled fire associated with humans seems to be some 200.000 years old.
There are possibly some modern people, as well, who use fire for all kinds of purposes, like powering a car by burning gasoline or lighting a cigarette but who do not necessarily know how fire gives also them heat and light.
What is Agni?
In most modern Indian languages, the word Agni or its variants mean fire.
What is fire?
What we call fire, is a chemical reaction that involves oxygen.
As an example
1. take a piece of wood that has carbon and hydrogen in it.
2. Add energy to it in the form of heat.
3. At some point the hydrocarbons break up.
3.1. Then oxygen reacts with carbon to form carbon dioxide
3.2. and with hydrogen to form water vapour.
But where does the “fire” – the heat and light come from?
The heated up carbon (and other) atoms rising in the air start throwing off (radiating) electromagnetic energy.
Lower frequencies of EM energy are heat and
higher frequencies EM energy are light.
Niels Bohr said that when electrons in atoms change their energy states, electromagnetic energy is emitted or absorbed.