VISUAL ARCHIVE / IMAGE STORY
The Galaxy We See Is Already History
Andromeda reaches our eyes through light emitted about 2.5 million years ago.
Every observation of the Andromeda Galaxy is an archaeological record written in photons. The galaxy we see tonight is separated from whatever may be happening there today by roughly 2.5 million years of light-travel time.
THE OBSERVATION
What we can actually see.
A telescope collects photons after their long journey from M31. That lookback time follows from its distance and the finite speed of light; it is a different issue from what a moving observer calls simultaneous today.
THE ILLUSTRATION
What the artwork imagines.
The luminous galaxy and foreground observer give a journey of photons a human scale. No telescope provides a live picture of a galaxy millions of light-years away.
FROM THE ILLUSTRATED ARTICLE
The story that inspired it.
The Andromeda thought experiment distinguishes the delay of light from the relativity of assigning a distant event to a local present. Andromeda reaches our eyes through light emitted about 2.5 million years ago.
Read There Is No Such Thing as “Right Now” Across the UniverseCHECK THE RECORD
The image interprets the research below. Follow the original work for the measurements and limits behind the scene.
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