---
{
  "path": "/en/open-problems/longitudinal-wave-detection",
  "title": "Free longitudinal-wave detection",
  "category": "Open problems",
  "summary": "Find a response distinguishable from thermal noise, acoustic disturbance and electromagnetic cross-talk.",
  "related": [
    "/theory/space-dynamics/longitudinal-field",
    "/collaborate/how-to-contribute",
    "/ai/build-your-own",
    "/open-problems/space-dynamics/longitudinal-wave-detection"
  ],
  "id": "OP-007-EN",
  "template": "problem",
  "version": "1.1",
  "updated": "2026-09-15",
  "canonical": false,
  "source_tier": "website-guide",
  "depends_on": [],
  "open_problems": [],
  "equations": [],
  "sources": [
    {
      "label": "ASD 建站蓝图与页面模板（用户提供）",
      "kind": "supplied-blueprint"
    }
  ],
  "problem": {
    "expertise": [
      "Experimental physics",
      "Metrology"
    ],
    "difficulty": "High",
    "missing_result": "Derive a response function from perturbation to measurable frequency or length and construct a noise budget.",
    "deliverable": "Source and detector models, transfer function, polarization or direction features, sensitivity and systematics.",
    "current_state": "There is an effective-equation target for a free longitudinal mode; detector coupling and signal strength remain undetermined."
  },
  "theory_status": "OPEN",
  "evidence_status": "UNTESTED",
  "title_en": "Free longitudinal-wave detection",
  "locale": "en",
  "translation_of": "/open-problems/longitudinal-wave-detection",
  "translation_path": "/open-problems/longitudinal-wave-detection",
  "translation_version": "1.1",
  "canonical_url": "https://asd-physics.org/en/open-problems/longitudinal-wave-detection"
}
---

## Why the problem matters
Find a response distinguishable from thermal noise, acoustic disturbance and electromagnetic cross-talk.
## Known structure and progress
There is an effective-equation target for a free longitudinal mode; detector coupling and signal strength remain undetermined.
## Research task
Derive a response function from perturbation to measurable frequency or length and construct a noise budget.
## Deliverables
Source and detector models, transfer function, polarization or direction features, sensitivity and systematics.
## Routes to avoid
Absence of dissipation implies neither absence of geometric spreading nor unlimited penetration or an available communication technology.
## Start collaborating
Download the problem description to recalculate, propose counterexamples or develop models in your own environment. Preserve premises, code, results and failure records.

## Space Dynamics v1.0 handoff
The [formal OP-SD task](/open-problems/space-dynamics/longitudinal-wave-detection) develops this guide's research direction with existing derivations, missing work and reviewable deliverables. The earlier entrance is retained. Current continuum definitions and candidate status follow the [Space Dynamics module](/theory/space-dynamics).