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.

And yet space and time are one. Time and space cannot be defined separately from each other. The time that you experience is a function of the path you take through space. This non-obvious reality is what separates Newtonian physics from modern physics and from the day to day functioning of the technologies that surrund us.

The theory of relativity, proved time and again by experiment, permanently altered our conceptions of both time and space. And through the principle of equivalence Special Relativity defined the relationship between space and 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. These forces all arise from Gauge fields . 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 and yet they increasingly need to look at evidence from both ends of the scales of time, and space.
The human species lives at the nexus of the Big Little venturing "outward" and "inward" through instrumentation at various scales where the laws of the universe provide different potential resources. What we lack are the necessary measurement tools as well as the necessary mental models or framework.

Early in life physics education is replete with artifacts from earlier paradigms that require correction at later stages in the learning process. For example, gravity isn't a force - its the effect of the curvature of space time. Some in the scientific community are attempting to alter the language of physics to modernize it, make it more comprehensible. and accurate. This will take time.

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

One defining feature of space time continium is the proponderance of vacuum space and with the exception of gravity the effective limits of the various force fields. Another is that at scales below the neutrino particles are best thought of as excited states or quant of underlying quantum fields. And yet another is the limits of the "sampling depth of our data".