Not to be left out here is how I speculate that the universe ends.
It can be speculated that a 4D mega universal entity reached a critical mass at some point in its development and released that energy, previously stored as mass energy, that it had accumulated during its development. This released all of the sub atomic constituents of the entity forming a cloud of high energy particles in 4D space. The movement of the sub atomic particles through 4D space producing disturbances that cause the sub atomic particles to come together to form larger and larger structures.... (until critical mass is reached again repeating the cycle)
Alternatively, if 4D mathematics permits, there may be continuous recycling of matter and energy. When matter reaches the centre of the hypersphere there is nowhere else to go other than back to the outer region of the hypersphere through the centre. This causes the matter to be torn apart and the energy released back into the outer region of the hypersphere.
The centre of the hypersphere is the end of the universe and is the end of subjective time for that universe. All of the matter that has accumulated to form that universe is disintegrated as it is returned to the exterior of the hypersphere either through 3D vector space, as a big bang or along the 4th dimension as continuous recycling.
Both mechanisms can give a continuous cycling and reinvention process. The contraction of the universe being along the 4th dimension, not direct contraction in 3D vector space which is why it is not obvious.
from the Prime Quaternion model.
The hypersphere itself is eternal because it exists in 4 spatial dimensions without time.Only motion along the 4th dimension within the hypersphere gives rise to the subjective experience of time. Relativity only relates to subjective reality not unobservable, material,objective reality, so this structure can be postulated without contradicting Einstein's mathematics.