Two galaxies aligned in a way where their gravity acts as a compound lens

Overall reaction and discovery

• Commenters express strong enthusiasm about the first known “Einstein zig‑zag” / double gravitational lens.
• Some discuss how it was found: spotting apparently duplicated sources in survey data, suggesting we might systematically search for more such systems.

Sun as gravitational lens vs galactic lenses

• Several argue for funding a Solar Gravitational Lens (SGL) mission, preferring it over repeat lunar landings.
• Others stress the extreme difficulty: it must go to ~500–650 AU, is effectively single‑target, and cannot be steered sideways practically.
• There’s debate on whether future lower‑cost launch and space manufacturing could make such missions routine; some are optimistic, others warn about resource limits and “low‑hanging fruit” in tech progress.

Cosmology and the Hubble constant

• Commenters highlight that this system combines:
  • Time‑delay cosmography (using different path lengths and delays between lensed images of a variable quasar).
  • Dual source‑plane lensing (two background sources at different distances through the same lens).
• Together, these are expected to constrain the Hubble constant and dark energy equation of state more tightly.
• A lay explanation suggests such systems may also help push observations closer to the earliest observable epochs.

Communication and detectability

• Speculation about using gravitational lenses (or galaxies) as communication amplifiers leads to discussion of:
  • Inverse‑square falloff, noise floors, and background radiation limiting detectability.
  • Focused beams (lasers, powerful radio arrays) vs omnidirectional broadcasts.
• Most see galaxy‑scale lensing for deliberate signaling as implausible due to billion‑year timescales, alignment transience, and unpredictability of civilizations’ existence.

Seeing Earth’s past and “time travel” ideas

• A question about curving light back to see Earth’s past leads to consensus that:
  • Geometry, Earth’s motion, and lack of true focusing make this effectively impossible.
  • Even with black holes, you’d get an extremely faint, unresolved “past Earth,” not a usable image.
• Some mention closed timelike curves theoretically, but only as a pointer, not a practical route.

Nature of gravitational lenses and technical details

• Several clarify that these systems are not “compound lenses” in the everyday optical sense with a single focal point; they produce Einstein rings/arcs and multiple images along a focal line.
• Discussion covers:
  • Symmetry of lensing in principle vs practical irreversibility due to time delays and evolving configurations.
  • Units (jansky/megajansky), astronomy’s CGS conventions, and style notes on SI prefixes.
• One commenter asks whether we’re already at the focal line of other massive lenses; the thread treats this as plausible in principle but leaves details of resolution and practicality unclear.

Timescales, frequency, and perspective

• Galaxy alignments are effectively static on human timescales but temporary over millions of years.
• Analogies to eclipses and the Copernican principle suggest such lenses should be common in the universe, though only a few will be well‑aligned from Earth.
• Several remarks reflect on the immense timescales involved and how small human concerns are in comparison.