Yoga is a science, not a religion. Science demands proof. In the path of yoga, this proof is called samadhi.
Samadhi has been defined as yoga, union with God, a unified state of mind.
Some of the literal meanings of the word samadhi are equanimity, impartial discernment, indifference, joining together, putting in order, setting right, restoring, resolution, completion, union, a whole, conclusion, proof, and acceptance, such as the acceptance of the equivalence of the True nature of all us.
The following two paragraphs are from Swami Kripalu’s book, The Science of Meditation:
The traveler on the path of saranagati (complete surrender) should not bother about the results of penance [tapas]. The achievements and failures of those following the path of saranagati are dependent on God’s will and not on their own efforts. What is the need of grace if achievement depends on effort? What is obtained as a result of effort is known as fruit. Grace is mere grace and is not the result or fruit of action…
…The seeker goes on reaching spiritual attainments one by one, such as asanas [yoga postures], mudras [energy seals], pranayamas [restraint of the life energy], pratyahara [withdrawal of the senses], dharana [concentration], dhyana [meditation], and samadhi [equanimity]. In the beginning the seeker thinks these attainments are trifling*; but only these attainments can give rise to all other [miraculous, superhuman] siddhis [powers]. Yogic scripture even says that nothing worth obtaining is left after attaining these stages of yoga.
There are two stages of samadhi. These two stages have been given different names. Looking at these different names paints a good picture of the two stages, but rather than going into these Sanskrit words and their definitions and descriptions, I will sum things up:
The First Stage of Samadhi:
Separation of the Body and the Mind
In this stage of samadhi, there is always an “object,” something that is perceptible, knowable, and the seed of desire is present. There are four sub-stages of this samadhi that one passes through before the onset of the second stage.
The Second Stage of Samadhi:
Dissolution of the Mind
In this stage, there is no object, no knowable. There is no knower, knowing or known. These three are merged with the Infinite. There is no sense of being conscious of anything—there is nothing there, not even the highly acclaimed Light, nor is there darkness. Again: there is no-thing there. There is no sense of self so there is no viewpoint, no viewing, nothing to view. It is a desireless state, for with its attainment there is nothing left to gain or lose.
This samadhi is impossible to describe. Any words at this point would only serve to confuse and appear to contradict the above statements. The best I can do is to describe it is as an infinite sea of rolling bliss. Period. Still, one might be tempted to use this description for the fourth stage of the first stage of samadhi, the separation of the body and the mind.
So what’s the difference?
If you had only one key for making this distinction you might use this: There is no object.
If there is any consciousness OF anything (object), it isn’t the second stage of samadhi. (It is easier to say what it isn’t than to say what it is.)
In the second stage of samadhi, there is no object and no seed of desire, not a smidgen. It is a fully desireless state of complete, blissful fulfillment. Even when it ends, it isn’t over; it stays with you as you go about the business of living life.
Swami Kripalu’s book, The Science of Meditation, can be downloaded here: http://www.naturalmeditation.net/Design/Kripalu_writings.html
* What I believe is being referred to by the statement, “the seeker thinks these attainments are trifling,” is that in the beginning, the seeker would like nothing more than to go straight to the top without bothering with the intervening stages.