The statement that everything in the Universe originated from a single point is a common summary of the Big Bang theory, which describes the early state of the Universe as extremely hot and dense. To address your question regarding how it was possible for everything to occupy a single point, the explanation mainly revolves around the nature of energy, matter, and the laws of physics, especially in the context of the early universe.
The statement that aligns most closely with how everything in the Universe could have occupied a single point is:
"All mass in the Universe was once energy, and energy does not take up space."
According to the principles of relativity, matter and energy are interconvertible (as articulated in Einstein's famous equation E=mc²). During the very early moments of the universe, it was primarily in a state of high-energy density, where traditional concepts of space and all forms of matter (such as atoms, protons, and electrons) were not formed as we understand them today.
In the early Universe, as it expanded from this extremely hot and dense state, energy began to cool and convert into elementary particles, leading to the formation of matter. It is important to note that before the Big Bang, our understanding of the time and physical laws as we know them breaks down, and the concept of "space" as we understand may not apply.
Thus, the idea that all mass was once energy properly captures how everything in the universe could be condensed into a singular point without contradicting the fundamental principles of physics.