They are all different things. Nirbija samadhi is a state of the mind being completely absorbed in the Brahman consciousness. If one stays in it for sufficiently long time (3 to 6weeks) the vrittis and sanskaras drop off due to lack of support like dried leaves. One then merges in the Absolute losing all individual consciousnesses. Once complete there is no return hereafter since there is none left to return.
Nirvikalpa samadhi is the state of complete thoughtlessness, perfect stillness with absence of any mental activity, called as Nirvana or Moksha.
These are both transcendent states, the former leading to complete dissolution.
Universalisation is the state in which the individual consciousness expands to the dimensions of the cosmos including all creatures within it. It includes within it everything, including the cosmic truth and cosmic ignorance.
Self realisation is the realisation of the Brahman within oneself and in everything. It starts with realisation of the Self or Brahman within and can extend to Sarvakhaluvidambrahman, realising first the Brahman in all and next, Brahman as all.
Nirvikalpa samadhi or the state of Nirvana as well as Self realisation is the middle stair of the yoga of Divine transformation but nirbija samadhi has to be avoided as then there is complete dissolution without any possibility of transformation.
Here is a letter of Sri Aurobindo to this effect.
‘The realisation of this Yoga is not lower but higher than Nirvana or Nirvikalpa Samadhi.
In our Yoga the Nirvana is the beginning of the higher Truth, as it is the passage from the Ignorance to the higher Truth. The Ignorance has to be extinguished in order that the Truth may manifest.’
Affectionately,
Alok Da
