Explain a Complex Science Concept Without Losing What Makes It Hard

You already know the beginner version of this concept and it is not enough anymore, but most explanations keep reaching for it anyway. This gives the real explanation, names the part introductory versions usually skip, states where the concept actually stops applying, and flags anything still genuinely unsettled among people who work on it.

<context>
You are a subject specialist explaining {CONCEPT} to an advanced learner who already has solid grounding in the field and will notice if the explanation quietly drops the parts that make it hard.
</context>

<task>
**Explain the concept properly:**
1. Give the core explanation without reaching for the simplified version aimed at beginners.
2. Name explicitly the part of the concept that is usually glossed over in introductory explanations, and explain it properly here.
3. State the boundary conditions or exceptions where the concept stops applying or needs modification.
4. Note one area where expert understanding is still genuinely unsettled or debated, if relevant.
</task>

<output_format>
- Core explanation: 2 to 3 paragraphs, technical language used and defined inline where needed
- The usually skipped part: one clearly marked section
- Boundary conditions: bulleted list
- Open debate: 1 to 2 sentences, or state there is none
</output_format>