It has been postulated by some scholars that the Rainbow bridge in Nordic mythology, the one guarded by Heimdallr, may refer to the milky way. However, I have adapted my own personal understanding of it that may or may not lie in the true occult wisdom of the archetypal Bifrost. My studied of Tantric spirituality, and Hindu/Buddhist religion have unearthed the secrets of the chakra system. This itself, rooted in human biology and science. Essentially, the ‘chakras’ are glands found throughout the body, and there are known to be hundreds of them, depending on which physiologist you may ask. In Tantric meditation, there is an entire system based around 7 separate chakras, called the Kundalini. There are more potent stores or ‘wheels’ of revolving life energy, that when tapped into with deep meditation one can raise a serpent lying at the base of the first chakra, and make it ascend to the crown of the head (Sahasrara). In ascetic inner meditation, it is physically possible to control the nervous system, there is how the chakra system works within the self. By focusing solely on one of the 7 glands that form the Kundalini, along the spine, up through the neck and to the crown, the internal energy of the body is refined to one place. The glands, being catalysts to how the body performs and each one fulfilling a certain function. From this I had the idea that the rainbow bridge of Bifrost, made of the same 7 colors of the chakras, leading from earth to the heavens is a cultural variation of the same principle.
The earth or ground in Teutonic religion is called Miðgarðr, and the heavens, Ásgarðr. Heimdall is one of the ‘godhead’ incarnate in Ásgarðr. Human beings dwell at all time on the Earth, but in Tantric ideology, even the profane can rise, with the spirit into a godlike state, divine and sacred. This occurs only in the Sahasrara or the crown chakra the very highest of the hvels. Heimdallr sacrificed one of his senses to Mimir, who holds the secrets of the runes (occult knowledge) in her well. He thus gains awareness of all the worlds, the multi-verse of the cosmology. He becomes as a seer with special abilities, from ‘Teutonic Religion’ by Kveldulf Gundarsson:
“He needs less sleep than a bird; he can see a hundred leagues by night as well as by day, and hear the grass growing in the fields and wool on the sheep. As well as being a warder, he is also a giver of wise and cunning redes”
The redes are advice which are given by ‘higher’ beings, meaning advices taken for the highest self, before coming back to the grounded existence to work weal. The runes themselves may be symbolic of some of the chakras. In the pictured depictions of the 3 realms of being, the serpent (Hindu version being kundalini) rests encircling the middle earth. The axis mundi, Yggdrasil could represent the spine? As physiologists know, it connects the who body, the central axis of all that is. As this is still my theory and I don’t have full knowledge of them, I think it is of worthy study.
Ansuz/Crown chakra/light purple: the esoteric interpretation is one of the Æsir, the higher beings.
Mannaz/Third Eye/violet: this chakra is given the qualities of numinous accord, creativity, and intellect. The Mannaz, meaning mankind. Separate from animal, the vessel of the mind. The Óðr of inspired mental activity.
Galdr/Throat chakra/blue: This may not have an exact runic equal, but could be related to galdrar, the chanting of a rune to fuse the energy of the materialistic body with the cognitive mind.
Wunjo/Heart chakra/green: Both of these are always associated with joy, and feeling. Affection or sensual love coming from the heart.
Sowilo/Solar Plexus/yellow: Esoteric interpretation of the solar energy or lightening. In the Elder Futhark, it stands for the universal will expressed through transitioning of the spiritual ‘hvels’. Hvel = chakra from Sanskrit. It ideographic picture is part of a turning wheel. :ᛋ:
Othala/Navel chakra/orange: Apparently Othala is likened to Midgard, the ‘middle’, and the navel is regarded as the middle by Tantrikas and in Hindu tradition. So there may be something there.
Gebo/Root-sex chakra/red: In Futhark by Edred Thorsson he writes…“Gebo contains the secrets of physically joining two people, in order that they may produce a creative power greater than their sum total” It is a rune of sex magic, that was used in Germanic times, so naturally would be associated with whatever glands are at that point of the body. It is the first source of the ecstasy, where the serpent lays coiled.
A lot of this may be quite far-fetched, for anyone reading this, and for me as well. My intentions as a vitki of the runes is to somehow find the practical within the mythological, and the modern wisdom from esoteric lore. Seeing things from many disciplines, such as a skeptical reductionist perspective, but also a spiritual gnosis is the only way I have been able to come to this theory and make it function in my life. I have read a couple very minimalistic articles about the parallels of the chakras to Bifrost.
The scientist in me says: By thinking of the energy stores located along the cervical spine and head, the nervous system is altered with a conscious effort and releases serotonin and DMT from the pineal gland in the forest, overloading the senses and transcending the material flesh.
The Tantric spiritual/Pagan in me says: Meditating on the essence incarnate at the ground of Miðgarðr;, one travels through the seven layers of Bifrost, discovering the occult symbolism of a special rune at each hvel. The coiled serpent Jǫrmungandr unraveling from earth and finally piercing through the last layer of the human being into one of the Ase (higher being symbolic of godhead) over their life.
In chapter 17 Gylfaginning, High tells Gangleri that the location of Himinbjörg (heaven peak) “stands at the edge where Bifrost reaches heaven.”While describing the god Heimdallr in chapter 27, High says that Heimdallr lives in Himinbjörg by Bifröst. The Hindus regard the mountain as the sacred peak that is the highest the human can go. The mountain as the archetype of a human peak, before ascended to the ‘god’ realm. There are probably other theories and perhaps even some more advanced or ‘proper’ texts written thousands of years ago about this by some Viking shaman, but this is what I got out of it. It is in the end, a tool for understanding ourselves, and we are all trying to make sense of things, because it is our primal need. If by embracing myth, one can more firmly grasp the fundamentals of life by it’s variations of reality, and make it more exciting, then one must take the horns and raise them.
:aferalspirit: 
The problem is in the lore, Bifrost is only three colors
I agree what thoughts on chakras and bifrost is the same. Just Norse humans had different thought on our wheels ( chakras). Different so they could understand in their times. Very interesting topic.