Updated: May 28, 2020
The main science behind Kundalini is simple … Our bodies are made of 4 main elements (oxygen, carbon, hydrogen, and nitrogen) which amount to over 95% of a human body, plus small amounts of Calcium, Phosphorus, Potassium, sulfur, etc. All this elements of the body are borrowed by a soul from the planet in order to get an instrument (a body) to experiment life around and gather experiences.
When the body is worn out after 70-80 years of life the soul discards the body (death) and leaves for another life, taking with him the experiences/lessons gathered to the next life.
In order to maintain the body for so long one needs lots of energy to sustain life, energy that comes partially through eating and drinking, but also more important directly from the planet through the energy she emits to all that lives on Her body including humans. The channel for this type of life-sustaining energy is through our feet soles and upwards through the feet where they join in C1 (chakra 1, root chakra) and feed the reservoir of energy there. This energy lifeline between the planet and human bodies has to work permanently and without fail or death occurs quickly. This root-energy in C1 is what yoga calls kundalini, which in fact is the life energy from Mother Earth that keeps all our bodies alive. Our kundalini in C1 is actually a very small part of Earth’s life-energy that mirrors Mother Earth in our bodies, a projection of Her in our bodies.
In an ideal case the kundalini energy goes up the spine through all chakras (increasing its vibration along the way) without obstacles and feeding the body organs around, and arriving in C7 (crown chakra) unites with cosmos energy that comes from above. Of course that this doesn’t happen in the ordinary 3D human bodies where chakras are clogged and kundalini can’t go up. Things are actually a bit more complicated since there are two different energy circuits in parallel, first the kundalini circuit that goes up the spine, and there is a second circuit of energy that comes from the sun and cosmic energy through C7 and goes down to C1 through a parallel circuit than through the chakras, but I wanted to keep the discussion limited to the question.
The result means actually that Mother Earth’s energy goes up the spine and eventually merge with the sun and cosmic energy in C7, hence our body becomes ideally a physical conduit for Earth’s energy that merges with the higher cosmic energies throughout our body. For this to happen one has to become “enlightened”, that is maintain his chakras open and clean of any 3D energies that clog the chakras like fears, worries, anxiety, agitation, envy etc; only then one can be united with the rest of Creation.
The ancient Hindu religious term for Earth’s energy was “kundalini Shakti”, and told in sacred texts that it’s destined to rise through shushumna channel until it unites with god Shiva in 6th chakra (representing actually the cosmic energy) is exactly what I explained you above in modern terms.
A true spiritual will work all his life to unclog his chakras and make kundalini find its way up.