Is the universe confined by its own matter, mass and temperature?
There is no “outside”, the universe contains all space there is. No matter how far you look, you will just see more of the same – stars, galaxies, nebulae, etc. The space goes on forever, but is actually not infinite but curved on itself in a higher dimension. There is nowhere else for matter to “leak”, any possible location is already part of the universe. P.S. Keep in mind that space isn’t just some “nothingness” in which everything else is located. Space (or more precisely space-time) is the fabric of the universe which can be stretched or distorted, and it is never truly empty. Space, according to quantum mechanics, is the lowest state of energy. And from Einstein’s famous equation we know that energy and matter are basically two manifestations of the same thing. This means that space, matter and energy are all part of the fabric of the universe, unseparable from each other. You can’t have space without energy, and energy can “materialise” into matter (and back). It’s actually one
