Ether-Cosmos comprises of twenty pieces for piano. The length of each piece is about 1-3 minutes, except the piece no. 18 which is longer than 12 minutes. For Ether-Cosmos No. 8, it is about 1.25 minutes in length. This piece applied music composition approach in the area of rhythm of Elliott Carter, especially in terms of metric modulation or tempo modulation. This approach involves a change of tempo within the music. The metric modulation also relates to note values or duration of notes, proportion of beat, and time signature. Therefore, the techniques of rhythmic organization and arranging tempos within metric modulation concept will be shown in this piece. Accordingly, the composer intends to design this piece with only one theme by arranging its structure as A1-A2-A3 and adding transition between each part until the end. Therefore, the audience can hear and compare the theme of the entire piece whose tempo is changed without feeling the change of tempo in the music.