The Big Little Problem is to characterize the space time continuum from the scale of the Cosmological horizon (The Big) to Plancks length (The Little).

The big little problem can also be characterized in time from the duration of time since the beginning of time (the Big Bang) to an attosecond < (our current ability to parse time) to Planck time.

The Big Little Problem is an open problem.

Physics has characterized elements of the universe in terms of the Standard model. The Standard Model of physics is the theory describing fundamental forces. There are four fundamental forces at work in the universe: the strong force, the weak force, the electromagnetic force (like gravity an infinite-range attractive), and the gravitational force. They work over different ranges and have different strengths. Gravity is the weakest but it has an infinite range.

The Standard model has been refined over time but it has been found incomplete in various ways. Varous other disciplines like cosmology have characterized in various fragmented ways space at various scales and the "rules" that apply in those spaces but there appears to be no integrated view of the space at various scales and the implications of what is possible in those spaces.This has been a function of our lack of tools for measurement. We cannot, by way of example, "see" dark matter

Dark Matter is an inferred missing mass energy in the universe. In the standard lambda-CDM model of cosmology, the mass–energy content of the universe is only 5% ordinary matter.

Particle physicists have been looking inward and astronomers have been looking outward.
The human species lives at the nexus of the Big Little venturing "outward" and "inward" through instrumentation to tap the resources at various scales where the laws of the universe provide different potential resources. What we lack are the necessary tools as well as mental models.

One aspect to the Big Little Problem is the mathematical limits imposed by current computational systems and the seeming intractability of the certain mathematical problems.