The emptiness of phenomena is a concept that goes beyond the Mahayana and is also found in Indian spiritual systems.
According to tradition, Buddha Gautama mentions the emptiness of all things already in the Samyutta Nikaya 35.85, which rather meant the 'Small emptiness in the area of Prakriti', and in the Majjhima Nikaya - 121: Culasuññata Sutta, that speaks of a highest degree of emptiness.
Today's conception of emptiness was further elaborated in the teachings of Nagarjuna, who defended it in Sūnyatāsaptati and tried to reconcile it with Buddha's teachings. Nagarjuna represented the universal emptiness of indwelling self-nature (svabhāva-śūnyatā).
Asanga saw in everything as phenomens of consciousness(vijnana, Yogacara). The hgher amalavijñāna ("immaculate consciousness") is considered by some Yogācāra schools as a ninth level of consciousness. This "pure consciousness is identified with the nature of reality (parinispanna) or suchness.
The emptiness, however, is not entirely empty. It can create things, and it is permeated with the highest wisdom and the Buddha-nature, and it in some linages it is also seen as the highest aspect of the Trikaya.
The doctrine of "emptiness" (as shunyata, Chin kung / suunyaa) as the irrationality of all things and the only reality is in the center of the Madhyamaka philosophy elaborated by Nagarjuna: The concept of "emptiness" does not mean that things do not exist, but that they exist only in complete dependence in causality. 
The Madhyamaka argument that beyond the highest Samadhi there is only emptiness is however subjective and therefore little conclusive, and has also been criticized by Kashmiri Shivaism.
The Yogacara, on the other hand, formulatet the emptiness more positively with Tathagatagharba, suchness (tathata), thatness (tattva), and Dharmadhatu.
The tibetan Shentong (Wyl.gzhan stong, zhäntong or zhentong, 'other emptiness', extrinsic emptiness) sees the emptiness as a substratum or essence behind the reality of phenomenon, inherently present and 'empty of other', empty of all qualities except its inherent existence. It thus approaches the Yogacara concept of the Buddhanatur.
Lama Anagarika Govinda commented, "Sunyata is the emptiness of all conceptual determinations, the recognition of a higher, inexpressible, indefinable reality that can only be experienced in the state of complete enlightenment.
In the Mahaparinirvana Sutra, the emptiness in the highest sense is the Paramartha-Sunyata, which takes up all opposites and unites them.Mahaprajnaparamita Sutra
The Mahaprajnaparamita-sutra describes 18 forms of emptiness (shunyata, Pali sunnata) 
In general two forms of meditation on emptiness are distinguished:
Space-related meditation must come first, for without the realization of the complete absence of the indwelling existence the illusion-like perception or the understanding will not take placen(Dalai Lama).
Emanations of Sunyata
Those who regard the tantric Yamantaka as Vajra - Bhairava, who is regarded as the direct emanation of the Sunyata, sees that this great emptiness is the equivalent of the static aspect (Bhairava) of Shiva in the Trimurti, above which regarding the Bahvricha Upanishad still higher powers exist - with the Ishvara as essence (and above him Sadashiva).
Already the Nasadiya Sukta of the Rigveda speaks of a non-nothingness as the beginning of creation.
An emptiness in the Tapa-Loka is penetrated from the Hindu viewpoint by the Omkara-Shabda of the Ishvara, the basis of existence of the Trimurti.
The Varaha Upanishade says in chapter 4.18: Like an empty pot in the Akasa (space), emptiness rules both inside and outside;
In the Devi Upanishad is to read I am the Shoonya and beyond the Shoonya.
What appears to the disciple as emptiness, when all impulses in consiousness have ceased to be, is not really emptiness but avyakta (unmanifest). But he must also pass through the void; (Swami Paramananda in : Concentration and Meditation 
Hinduism knows another mental little emptiness 'Sunyata' in the area of the Anthakarana (Manas - Ahamkara - Buddhi) of Prakriti.
Sivas's Akasha-aspect is bhairava. Vajra-bhairava is the first emanation of the buddhist emptyness, which seems to be equivalent to the akasha of the trimurti.
In addition, there is something similar with the Akasha in yoga, which is attributed to the quality of space and sound 
1. Chid Akasha (also Chidakasha, Sanskrit: cidākāśa m.) or 'consciousness (Chit) - space (Akasha)': the consciousness space perceived in the area of the head.
2. Bhrumadhya Akasha(Sanskrit. bhrūmadhyākāśa) or mahāśūnya : The empty space in the Eyebrow center (Ajna).
3. Vishuddhi Akasha (Sanskrit viśuddhyākāśa) : The empty space (Akasha) in the throat center. In the Hatha Pradipika (Kap. 4.71) t he synonym atishunya is used for this.
4. Hrid Akasha (Sanskrit: hṛdākāśa) : The empty space (Akasha) in the heart (Hrid). In the Hatha Pradipika the synonymous Shunya is used (chapter 4.71)
In Taoism there is a similar term Wújí , which can also be translated literally with 'cosmos' and 'empty space'.Radhasoami
In the Radhasoami there is such a void Maha Sunna (Bhavsaagar, the terrible 'Tibar Khand')  on similarly high planes as the Tapoloka, but there are further higher planes there.
In the Kabbalah exists a similar emptiness as 'Belima' (What-less) together with 'Reschit'.  (See : Ayin and Yesh)
In Greek mysticism, as well as among the orphans, the chaos (gaping space, yawning emptiness) was often regarded as the primal state of the world.
The chaos is also looked at as a God who filled the space between heaven and earth and created the first beings Gaia, Tartaros, Uranos, Nyx and Erebos.
Hesiod, for example, wrote the following: Truly, the chaos and first later the earth was formed (verse 116). In this myth, chaos is similar to nothingness and emptiness.
In ancient Egypt, Niau and Niaut (the negation, the nothingness) symbolized a similar emptiness.
In Shivaism, emptiness  emerges with the extinction of knowledge. In Vira - Shivaism, emptiness is seen as the true unity and identity of Siva (Linga) and soul (anga).
In the Spanda doctrine of kashmirian Shivaism, a distinction is made between 'nirmesa' (secrecy of essential nature) and 'unmesa' (phenomenon of the world as distinct from Shiva). 
The Shiva Samhita mentions a emptyness - contemplation in chapter 6.6.47 with the aim of Chid Akasa and further in chapter 6.10.161.
The Madhyadhama (central channel) is also referred to as sunya or sunyatisunya (absolute emptiness) in Kashmiri Shivaism.
The Vijnanabhairava contains the expression sunya et al. In verses 39, 40, 45, 48, and 122, and teaches dharanas about it. The word sunya appearing in verse 42 of the Vijnanabhairava was interpreted as unmana by Sivopadhyaya. In verse 61 Madhya was interpreted by Sivopadhyaya as sunya.
The Shiva Sutra mentions emptiness as well.
Ksemaraja interpreted sunya in his commentary on the Svacchanda Tantra VI, 57, which in chapter IV.288-290 teaches six gradual contemplations of emptiness upt to Paramashiva, as Maya and sunyatisunya as Mahamaya, which runs here as far as Paramshiva. .
The most common interpretation is that of Sivopadhyaya in his commentary on the verse 127 of the Vijnanabhairava: What is free from all carriers, whether from external existing such as glass or flowers, or internal existences such as joy, pain, or thought, which is free from all tattvas or constitutive principles, of traces of Kleshas, that is sunya
(The concept of an ultimate emptiness without characteristics does not yet answer the question as to why nothing really exists. )
Even from the point of view of modern science, all forms are rather empty:
The atom  consists of a very tiny atomic nucleus with an electron shell which determines its size and shape. The rest of the spherical atom is empty and is interspersed with electric and magnetic fields and gravitational fields (and, of course, with much smaller very short-lived nuclear particles than the neutrons of the nucleus). Even if the electron is described as a negative pole today with a probability function, it moves at certain stable energies around the nucleus.
The smaller hindu sunyata emptiness in the area of Prakriti corresponds to this material emptiness - but on a somewhat higher plane.