LIGO is an experiment designed to detect

Question

BlackTom AI · Accepted Answer

Gravitational waves are ripples in spacetime produced by accelerating masses, and LIGO is designed to detect those tiny ripples—especially from violent events like colliding black holes.

1. Relevant knowledge points and concepts
- Gravitational waves: time-varying distortions of spacetime predicted by General Relativity, emitted by asymmetric accelerating mass distributions (e.g., binary mergers).
- LIGO (Laser Interferometer Gravitational-Wave Observatory): a laser interferometer measuring differential changes in arm lengths caused by passing gravitational waves; sensitivity characterized by strain h = ΔL/L.
- Distinction from electromagnetic effects: gravitational redshift and lensing affect light frequency/path, not direct spacetime strain measured by an interferometer.

2. Step-by-step reasoning
- Binary black hole mergers produce large, rapidly changing quadrupole moments → strong gravitational waves.
- A passing wave produces alternating stretches and squeezes of space along perpendicular axes, changing the relative arm lengths of an interferometer.
- LIGO measures the interference pattern of two perpendicular 4 km laser arms to infer ΔL.

3. Calculations / intermediate steps
- Typical detected strain h ~ 10^-21. With L = 4,000 m, ΔL = h·L ≈ 10^-21 × 4×10^3 m = 4×10^-18 m, far smaller than atomic dimensions, requiring LIGO’s extreme sensitivity to detect.

4. Why the correct answer is correct
- The phrasing "gravity waves from colliding black holes" matches gravitational waves from binary black hole mergers—exactly the primary signals LIGO is built to detect (e.g., GW150914).

5. Why other options are incorrect
- Gravitational redshift: a change in photon frequency escaping a gravitational well; measured via spectroscopy, not LIGO.
- Gravitational lensing: bending of light by mass producing multiple images or magnification; an astronomical imaging/photometry phenomenon, not interferometric spacetime strain detection.
- Deflection of starlight by the Sun: a specific lensing effect observed during solar eclipses; again an EM/path effect, not what LIGO measures.

6. Conclusion
Therefore the correct choice is "gravity waves from colliding black holes." This matches the provided answer.

LIGO is an experiment designed to detect单项选择题

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