Answer:
All mass in the Universe was once energy, and energy does not take up space.
Step-by-step explanation:
Everything in the Universe was able to occupy a single point because all mass in the Universe was once energy, and energy does not take up space.
Mass takes up space, but energy does not take up space. Energy can be converted to mass, and mass can be converted to energy.
This was a Study Island Question that I got wrong, so I thought that I would put the right answer for others.