How do we know that our universe is not contained within a larger entity?
However, the scientific method requires us to provide evidence and reproducibility. So, there are things that we may not be able to determine no matter what we may speculate or dream.
People have speculated that our universe might be part of a larger system of universes. the multuniverse theory.
In 1997 there were three empirical studies that indicated that the rate of the expansion of the universe . These studies used supernovas as a standard candle. All three studies gave the save results, the hypothesis that the rate of expansion should be decreasing was wrong.
The previous scientific consensus was that the universe underwent oscillations between big bangs, and big crushes. The concept of an oscillating universe allowed for the world view of eternal self existent eternal matter and energy.
The supernova studies undermined the belief that our present universe was eternal or self existent. The increasing rate of expansion indicates that not only does our present observable universe have a beginning it will also have an ending it will not recycle. This means that our present universe is an open system there must be something beyond or outside of the present universe.
If the world view of material realism is true then there must be a larger system of matter and energy that our universe is part of. It is not presently possible to obtain empirical evidence of matter or energy outside of our present universe.
Some scientists speculate that our universe is part of a larger entity because another possibility is the existence of supernatural entities to explain the universe being an open system.