Are there specific practices, meditation instructions, intended to identify and realize/experience emptiness? Is this different than realizing non-self, or the emptiness of the self? or the emptiness of other/objects?
So now we go for the Zen view. Or I should say Rinzai view. I want to first pat you on the back. You are absolutely right to say "realize" emptiness. Please do not try to understand it. That's a complete waste of time. I'm not sure if you intended the question this way, but what you are asking for, specifically in your inquiry regarding the emptiness of other things/objects, is nothing less than a request for a full exploration of the path. I will try to be brief as I can. The short answer is that you need to sit and that you need to find a teacher. The long answer follows.
When you first walk into the zendo, your teacher will normally tell you to watch your breath much in the way taught in anapanasati. Here, you begin to develop and collect your mind. As your sitting deepens and your focus improves - and this may happen over the course of months or even years - you will begin to notice one of any number of phenomenon. For some people, it feels like your body is expanding, for others your body may disappear, and for still others, your head may feel like it's twisting. What you experience isn't necessarily as important as that the experiencing is happening. This is your first glimpse of samadhi. In the ten oxherding pictures, this is seeing the ox's tracks for the first time.
Upon seeing the tracks, the next thing that your teacher will do is give you the Mu koan. This practice uses the collected mind you developed with anapanasati and directs it toward an actual experience of emptiness. On every out breath, you will say "muuuuuuuu". As the Pali suttas say, you will follow this for the whole body of the breath with the most important place being the very end of your exhalation right before you inhale. As this practice deepens, you will begin to notice a blankness. This is your first glimpse of emptiness and it usually happens completely by accident. In the ox herding series, this is seeing the ox's butt sticking out from behind a bush. Your next task is to make that experience habitual. This is grabbing the ox's reins. To hold the reins is to generally know where the ox is at all times and how to find him when you need him. With the ox's reins firmly in hand, your next task is to gain mastery over the experience. In essence, you are deepening your command of body, breath, and mind. This is taming and leading the ox. With the ox tame, you may now ride him. This is becoming one with emptiness or one with Mu. As Master Mumon says, here "all the illusory ideas and delusive thoughts accumulated up to the present will be exterminated, and when the time comes, internal and external will be spontaneously united. You will know this, but for yourself only, like a dumb man who has had a dream." At this point, you will be asked to call Mu by your teacher. Your calling of mu will demonstrate how well internal and external are united...how well you, the ox, mu, the body, emptiness, the breath, and mind have all become one thing. Getting to this point can take years.
And with that, your Zen training wheels come off. From here on out, emptiness is no longer a realization. Instead, it becomes a tool that you will use for the remainder of your training. After you answer the Mu koan, you will begin to work through any number of other koans. Zen calls this climbing the mountain of swords that is riddled with the skulls of the fallen. And it can be every bit as daunting as that description implies. Each koan forces you to confront some aspect of yourself - some fear, attachment, belief, etc. - that is keeping you from true enlightenment. But rather than working with these things intellectually as you might in therapy, you approach these karmic impediments from the experience of emptiness. The deeper you go into mu [emptiness], the better the insight you gain, and the more likely you are to unshackle yourself from these obstacles. The entirety of this practice is a dance between the world of form and the world of emptiness. You delve into emptiness in your sitting and you bring it back to the world of form in your probing of the koan you are working with.
Bit by bit, koan by koan, year after year, sesshin after sesshin, the wall between you and enlightenment breaks down. Eventually, it will fall away completely. At the moment of enlightenment, the very separation between the world of form and emptiness dissolves entirely. You will know, just as intimately as the feeling of your butt against the cushion, what the Heart Sutra means when it says that "form is emptiness and emptiness is form". You will directly see the emptiness of all things - of yourself, objects, thought...the entire universe.
And then you get to be the fat old Buddha who gets drunk with the butchers and generally causes a nuisance in the town below. Happy sitting!
Pali Buddhism offers the following instructions for realising emptiness (suññatā):
And what is the emptiness mind-release? There is the case where a monk, having gone into the wilderness, to the root of a tree, or into an empty dwelling, considers thus: 'This is empty of self or of anything pertaining to self.'
And what is empty of a self or of anything pertaining to a self?
The eye is empty of a self or of anything pertaining to a self. Forms... Eye-consciousness... Eye-contact is empty of a self or of anything pertaining to a self.
The ear is empty...
The nose is empty...
The tongue is empty...
The body is empty...
The intellect is empty of a self or of anything pertaining to a self. Mind objects... Intellect-consciousness... Intellect-contact is empty
There is this (mental) dwelling discovered by the Tathagata where, not attending to any themes, he enters & remains in internal emptiness...If...dwelling by means of this dwelling...no covetousness or sadness...will take possession...In this way he is alert there...keeping track of arising & passing away (thus): 'Such is form, such its origination, such its disappearance. Such is feeling... Such is perception... Such are fabrications... Such is consciousness, such its origination, such its disappearance.' As he stays keeping track of arising & passing away with regard to these five aggregates, any conceit that 'I am' with regard to these five aggregates is abandoned...
A monk, not attending to the perception of village, not attending to the perception of human being — attends to the singleness based on the perception of wilderness...not attending to the perception of wilderness — attends to the singleness based on the perception of earth...not attending to the perception of earth — attends to the singleness based on the perception of the dimension of the infinitude of space...not attending to the perception of the dimension of the infinitude of space — attends to the singleness based on the perception of the dimension of the infinitude of consciousness...not attending to the perception of the dimension of the infinitude of consciousness — attends to the singleness based on the perception of the dimension of nothingness...not attending to the perception of the dimension of nothingness — attends to the singleness based on the theme-less concentration of awareness...he discerns that 'Whatever is fabricated & mentally fashioned is inconstant & subject to cessation.' He discerns that 'Whatever disturbances that would exist based on the effluent of sensuality... the effluent of becoming... the effluent of ignorance, are not present. And there is only this modicum of disturbance: that connected with the six sensory spheres, dependent on this very body with life as its condition.' He discerns that 'This mode of perception is empty of the effluent of sensuality, empty of the effluent of (self) becoming, empty of the effluent of ignorance....his entry into emptiness, accords with actuality, is undistorted in meaning, pure — superior & unsurpassed.
In summary, to realise emptiness, as described in MN 121 (above), the mind first be made empty or clear. Then the clear mind can observe everything it observes is empty/vacant/void of any self.
For example, if the mind observes a rock, cloud or tree, it can see clearly there is no 'self'/'ego' in a rock, cloud or tree. When the mind is clear, empty of thoughts & judgments, it can see the breathing & body are the same as a rock, cloud or tree, namely, empty of any self. Observing like this, the breathing will calm & feelings of rapture will arise, which are observed like a rock, cloud or tree, as empty of self. When rapture calms, the mind will be even clearer & all mental phenomena are observed the same as a rock, cloud or tree, as empty of self. This is how to realise emptiness.
To realise not-self & emptiness, the mind must do vipassana.
Through vipassana, by observing carefully with a concentrated mind, we see the Truth of all things. We realize that everything is impermanent. Anything that we are experiencing now is impermanent. Even the things of which we are unaware are impermanent, that is, continually changing and transforming. The single exception is nibbana, the only thing that does not change. Thus, we know the aniccam (impermanence) of everything. Furthermore, the fact of impermanence oppresses and forces us to experience dukkha (unsatisfactoriness)... This state of dukkha can not be endured by anyone; there is no self or soul that can stand up to it. This is anatta. And so we realize aniccam-dukkham-anatta. Together we call them sunnata, voidness of self. Then know tathata, suchness or "just like that." This is the first step of the fourth tetrad. It is called "aniccam-nupassi." Just this one word encompasses the realization of aniccam-dukkham-anatta-sunnata-tathata!
My teacher has a straight forward 4 steps method to learn and realize the Dharma
Listen - Learning the Dharma is frequently described in the scripture to hearing. ("Thus I have heard", "Savaka - one who hears"), essentially coming across teachings whether by paying attention to teachers, reading and so forth.
Contemplate - You reflect on the meanings of the Dharma, slowly making sense of it
Application - You apply the Dharma in your practice and your daily life.
Affirmation - You affirm the truth of the teachings through your practice.
Rinse and repeat as necessary.
With regards to emptiness:
You can study sutras, listen to lectures. But the fundamental break through I had with understanding emptiness in the context of Mahayana came from Nagarjuna famous stanza.
All things arise through causes and conditions.
That I declare as emptiness.
It is also a provisional designation.
It is also the meaning of the Middle Path
This is essentially rephrasing dependent origination
This is because that is
This is not because that is not
Prior to this I could hardly make sense of the Heart Sutra or the Diamond Sutra. But now more often than not feel like very much self evident truth.
And there you have it, this simple concept is all there really is into understanding emptiness. It's not some mystical transcendental experience. It is essentially a rehash of the truths of impermanence and selflessness that is staring at our face everyday. Yet the issue is actually what one do with this realization. It is not that the common person doesn't see impermanence, the common person simply refuse to accept and acknowledge these truths. As I have deepen my practice I start to observe how my friends and family including myself often act in ways that are unenlightened as if we are blind to the truths in front of our face. Our mindless cravings and anger when we don't get what we want. Our selfishness. Our attachments to very impermanent things.
The teaching of emptiness is there to break our attachments to personal views of the world which we construct, even doctrines which are held sacred such as the perfection or infallibility of the Ariyas (Stream Entry, Arahantship). We treat Stream Entry as a magical state where the Stream Entrant no longer have any feelings of doubt, in contrary to what the Buddha have stated from the beginning, that all phenomena are impermanent, and why should doubt and confidence be any different. We treat Arahants as someone who's infallible with no shred of ignorance and other afflictions, someone who attained Nirvana and will never suffer again. Even when the Buddha said that the five aggregates are impermanent, so how can the birth of sankaras be permanently ended? Wisdom is dependently originated, attainment is dependently originated, end of suffering is dependently generated, how can any of them actually be permanently attained or ended? The realizations essentially allow us to see things we ought to have seen before but couldn't due to our ignorance and delusive state of mind.
Ultimately learning the Dharma is to benefit ourselves and others. And maybe just maybe next time we face a difficult situation, we can calmly keep in mind that the situation we are facing is too impermanent and dependently generated, so that we can plant good causes and conditions while being unattached to our troubles and handle them with wisdom.
The most concise answer I have found comes from Nagarjuna:
That which arises dependently we explain as emptiness.
Although this peculiar question seemed got a Mr./Ms. Right to claim the bride/groom, I, however, would like to offer a short answer, sometimes one's patience boiled when reading too much words. Here, my short little trick of how to realize emptiness:
It's both easy and difficult. Easy part is, to understand that the world is mind constructed; the difficult part.... hmmm... is to then walk into a wall and through it, for it's "made of" emptiness :D ~!!
Listening, Studying, Reflection are vital.
Assuming you practice sitting meditation with joyful investigation for ~30min a day, you can probably have a direct insight into emptiness from one of the excellent sutras such as the Diamond Cutter Sutra or the Heart Sutra.
It will take a lot of consistent practice but every step is closer, so in short:
Grow your bodhicitta. Cultivate a deep compassion and weep for the sufferings of all countless sentient beings. Rest in the absolute nature.
Love your teachers
A non-Buddhist answer, perhaps:
My sense of Realization is that it is part of a process of development, or maturation. We simply grow in to it eventually. Glimpses might come earlier, and even be imparted, but then it takes time to stabilize and fully develop the realization, as other answers state.
Seen this way, many approaches will work, as will "no approach" eventually, if the person is so inclined to recognize and value realization. "Seek and ye shall find." Perhaps this is why there can be so many different teachings and schools, all of which worked for someone.
The last stage, I think, is simply letting go. Or, "be let go-ed". As the old Zen story puts it, you release your hold on the cliff edge, only to realize that you were standing on firm ground all along! Ego cannot do this letting go, it arises spontaneously. So maybe the answer to your question is: "One doesn't." Or, "Oneness does" or something silly like that.
Suññatā means more or less not / nonself, i.e., the aggregate and empty as they are not self (they are empty of self, there is no self in it), meditation attainments are empty as they are not self, sense bases are empty as it is not self, the world is empty since it is not self. Anything you call self cannot be absolutely controlled and does not last for ever and the experience always ends misery.
Also the world is made of vibrations and heat hence in this sense the world is empty, as in this answer.
To realise not self you have to do Vipassana to achieve the state of yathā-bhūta-ñāna-dassana. When progressing further in stages of sainthood you will experience Phala Samapatti where all perception and sensation stops. This is also know as empty. Even before this any attainments like Jhana is not self, hence empty. Also higher meditative attainments can be considered empty when there is no roots.
See: (1) Kāma,bhū Sutta 2, (2) Cūla Vedalla Sutta, (3) Mahā Vedalla Sutta, (4) Maha Sunnata Sutta, (5) Cula Sunnata Sutta, (6) The Greater Discourse on Voidness: The “Mahā-Suññatā Sutta” (Majjhima Nikāya No.122) And the Commentary from the Papañcasūdanī
“When a monk has emerged from the attainment of cessation of perception and feeling, houselord,
3 kinds of contacts touch him, that is,
the empty contact,
the signless contact,
the undirected contact.”
This is empty of self or what belongs to self
This, avuso, is the way of explaining by which these states are different in meaning and different in name.
Same in meaning, differing only in name
“And in what way, avuso, are these states same in meaning, differing only in name?”
(1) THE UNSHAKABLE FREEDOM OF MIND THAT IS FREE OF MEASURING
lust is a measure-maker;
hate is a measure-maker;
delusion is a measure-maker.
For a monk whose influxes are destroyed, they are cut off at the root, made like a palm-tree stump, done away with so that they are not subject to further growth.
Avuso, of all the immeasurable freedoms of mind, the unshakable freedom of mind is declared as the foremost. Now, that unshakable freedom of mind is empty of lust, empty of hate, empty of delusion.
(2) THE UNSHAKABLE FREEDOM OF MIND THAT IS FREE OF “THINGS.” Avuso,
lust is a something;
hate is a something;
delusion is a something.
Voidness internally: in himself internally; the meaning is: produced in regard to his own five aggregates. [Commentary to MN 122]
“And which, friend, is the mind-deliverance of voidness? Here, friend, a bhikkhu, gone to the forest or to the root of a tree or to an empty place, considers thus: ’This is void of self or property of a self’. [MN 43]
Of self: void of self, called personality, man, person, and so on. Or property of a self: Void of anything belonging to self called requisite of robes and so forth … . The minddeliverance of voidness belongs to the sense-sphere as to plane, and its object is formations; for it is insight that is here meant by “voidness.” [Commentary to MN 43]
Possessed of full awareness: fully aware through successfully knowing the meditation subject. Externally: in regard to another’s five aggregates. Internally and externally: at one time internally, at another time externally.
This follows Universal Teaching of the Buddhism as preserved in the Pali Canon.