A tone cluster is a musical chord comprising at least three adjacent tones in a scale. Prototypical tone clusters are based on the chromatic scale and are separated by semitones. For instance, three adjacent piano keys (such as C, C♯, and D) struck simultaneously produce a tone cluster. Variants of the tone cluster include chords comprising adjacent tones separated diatonically, pentatonically, or microtonally….In standard Western classical music practice, all tone clusters are classifiable as secundal chords—that is, they are constructed from minor seconds (intervals of one semitone), major seconds (intervals of two semitones), or, in the case of certain pentatonic clusters, augmented seconds (intervals of three semitones). Stacks of adjacent microtonal pitches also constitute tone clusters.
Note that you can have tone clusters and still have a tonic center (in other words, tone clusters does not necessarily mean atonality).
Is this really music?
Musicologist Jean-Jacques Nattiez considers the difference between noise and music nebulous, explaining that “The border between music and noise is always culturally defined—which implies that, even within a single society, this border does not always pass through the same place; in short, there is rarely a consensus … By all accounts there is no single and intercultural universal concept defining what music might be” (Nattiez 1990, 48, 55)….An often-cited definition of music is that it is “organized sound”, a term originally coined by modernist composer Edgard Varèse (Goldman 1961, 133) in reference to his own musical aesthetic. Varèse’s concept of music as “organized sound” fits into his vision of “sound as living matter” and of “musical space as open rather than bounded” (Chou 1966a, 1–4). He conceived the elements of his music in terms of “sound-masses”, likening their organization to the natural phenomenon of crystallization (Chou 1966b, 157). Varèse thought that “to stubbornly conditioned ears, anything new in music has always been called noise“, and he posed the question, “what is music but organized noises?” (Varèse and Chou 1966, 18)…Italian composer Luciano Berio: “Music is everything that one listens to with the intention of listening to music” (Berio, Dalmonte, and Varga 1985, 19). This approach permits the boundary between music and noise to change over time as the conventions of musical interpretation evolve within a culture, to be different in different cultures at any given moment, and to vary from person to person according to their experience and proclivities. It is further consistent with the subjective reality that even what would commonly be considered music is experienced as nonmusic if the mind is concentrating on other matters and thus not perceiving the sound’s essence as music (Clifton 1983, 9).
Oh look, a digression 😉 https://en.wikipedia.org/wiki/Zoomusicology
Sonorism is rooted in the nationalistic movement of the 1920s called “Polish colourism”, whose best-known exponent is Karol Szymanowski. Sonorism as such was developed in the 1950s and 1960s as a means of gaining freedom from strict serialism, particularly by Krzysztof Penderecki, but also in a number of compositions by Grażyna Bacewicz, Henryk Górecki, Kazimierz Serocki, Wojciech Kilar, Witold Szalonek, Witold Rudziński, Zbigniew Bujarski, Zbigniew Penherski, and Zygmunt Krauze, amongst others (Granat 2008; Rappoport-Gelfand 1991, 68–69).
He was largely unknown outside Poland until the mid-to late 1980s, and his fame arrived in the 1990s. In 1992, 15 years after it was composed, a recording of his Third Symphony, Symphony of Sorrowful Songs—recorded with sopranoDawn Upshaw and released to commemorate the memory of those lost during the Holocaust—became a worldwide commercial and critical success, selling more than a million copies and vastly exceeding the typical lifetime sales of a recording of symphonic music by a 20th-century composer. As surprised as anyone at its popularity, Górecki said, “Perhaps people find something they need in this piece of music […] somehow I hit the right note, something they were missing. Something somewhere had been lost to them. I feel that I instinctively knew what they needed.”[13
Since Górecki’s move away from serialism and dissonance in the 1970s, he is frequently compared to composers such as Arvo Pärt, John Tavener and Giya Kancheli. The term holy minimalism is often used to group these composers, due to their shared simplified approach to texture, tonality and melody, in works often reflecting deeply held religious beliefs. However, none of these composers has admitted to common influences. His modernist techniques are also compared to Igor Stravinsky, Béla Bartók, Paul Hindemith and Dmitri Shostakovich.