Everything is a form of energy. ~ Nisargadatta Maharaj
The ancient Greeks assumed existence to be eternal, comprising infinite space; so did Einstein for a time.
Others considered cosmogony. Among them was Chinese philosopher Lao Tzu 2,500 years ago, English theologian Robert Grosseteste in the 13th century, and modern astrophysicists. All propose that the universe emerged from a figurative pinprick of energy which contained within all that the cosmos was ever going to contain. According to this expansive story, energy from an originating singularity began to spread, and in doing so, somehow diversified, both in frequency and capability. The energetic diffusion was into nothingness: spacetime itself being packaged as part of cosmic energy.
From our perch in the cosmos, the farthest we can detect is 46.5 billion light years away. As light speed delimits cosmological distance, and Earth is unlikely to be in the center of the cosmos, our universe may be over 100 billion years old. (This extensive astronomical duration contrasts with the now-conventional cosmogonic fiction of a much more recent origination followed by an instantaneous supraluminal expansion (cosmic inflation).)
Like butter spread thin on toast, as the universe expanded, local energy intensity lessened. After an indeterminate duration, the spatial concentration of energy formed localized patterns from which substance descended. Matter was born; or so it seems.