How can the universe be endless?

What is know as "Einstein's Forgotten Model of the Universe" is worth looking up. In a 1931 paper he described a universe that expands after the Big Bang and then contracts-- called the Big Crunch.

Maybe an oscillating universe? Much like the Hindu cosmological cycle?

For details check out this paper:

https://tutor.hix.ai

The idea of an endless universe is based on the concept of spatial infinity, which holds that the universe has no boundaries or edges. Some cosmological models, like the idea of an expanding universe or a universe with a toroidal (doughnut-shaped) topology, support this idea; however, our knowledge of the universe is still limited, and scientists are still working to determine its true nature.

The concept of the universe being endless, or infinite, is based on current scientific understanding and theoretical models in cosmology. According to the theory of cosmic inflation, the universe underwent a rapid expansion in the early moments after the Big Bang, and this expansion may have continued indefinitely in some regions, leading to an infinite universe.

Additionally, observations from cosmological studies, such as the cosmic microwave background radiation and the large-scale structure of the universe, suggest that the universe is spatially flat or nearly flat on very large scales, which is consistent with the idea of an infinite universe.

Furthermore, some theories in theoretical physics, such as certain versions of string theory or the multiverse hypothesis, propose the existence of multiple universes or dimensions beyond our observable universe, some of which may also be infinite in extent.

It's important to note that while the concept of an endless universe is supported by scientific theories and observations, our understanding of the universe is still evolving, and there are ongoing debates and research in cosmology to further explore its nature and structure.