The nature of the center of a black hole is still a topic of active research and speculation in theoretical physics. It is currently not well-understood what exactly lies at the center of a black hole, as the laws of physics, as we know them, break down under the extreme conditions inside a black hole.
However, if we consider the hypothetical scenario where the center of a black hole leads to another universe, we enter the realm of speculative physics and theoretical possibilities. Keep in mind that these ideas are highly speculative and currently unsupported by empirical evidence.
One possibility is the concept of a "wormhole," a speculative structure that connects different regions of space-time or even different universes. In this scenario, the center of a black hole could potentially act as a portal or gateway to another universe through a wormhole. Wormholes are predicted by certain solutions of Einstein's field equations in general relativity but have not been observed or confirmed to exist.
If a black hole's center were indeed a gateway to another universe through a wormhole, crossing into that universe could lead to an entirely different set of physical laws, properties, and dimensions. It is challenging to speculate about the nature of such a universe since our understanding of the laws of physics breaks down at the singularity within a black hole.
However, it's important to note that these ideas remain purely speculative at this point, and there is currently no empirical evidence to support the existence of other universes or the presence of wormholes within black holes. The nature of black hole singularities and the possibilities they hold are subjects of ongoing research and theoretical exploration in physics, particularly in the areas of quantum gravity and string theory.