Final answer:
The basic assumption scientists hold about the universe is that it is observable. Possible futures for the universe, discussed by scientists, depend on the amount of mass and dark energy, with current observations suggesting perpetual expansion. Cosmology theories must account for the Big Bang and finite speed of light.
Step-by-step explanation:
The basic assumption scientists hold about the universe is that it is observable (C), which implies that the universe can be studied and understood through observations. While the concept of infinity (A) applies to certain theoretical models, the predictability (B) of the universe is limited to the laws of physics, and there is no consensus that the universe follows a linear path (D).
Discussing the possible futures of the universe, scientists have proposed that it could either expand forever or eventually start to contract, depending on the quantity of mass and the effect of dark energy. Current observations suggest that the universe is expanding at an accelerating rate, indicating that it will likely continue to expand indefinitely. These observations are based on a model of the universe that is isotropic and homogeneous, with the mass density being less than the critical density required to halt the expansion.
Moreover, theories of cosmology must explain fundamental observations such as the Big Bang occurring 13.8 billion years ago and the finite speed of light. Together, these observations and laws describe a universe that is complex, yet displays an underlying order and simplicity that can be understood through physics.