![echoes or echos echoes or echos](https://www.briandorey.com/docs/2020-12-19-amazon-echo-dot-gen4-teardown/case-base-1.jpg)
In most cases, this appears in the form of a "bubble" or "ripple" of light that can spread outward as it works its way through clouds of space dust, gas, and more. The resulting light echo that an observer can measure is the visual analog of the sound echo they'd hear if they shouted in an empty symphony hall, with rippling patterns of light reaching the observer at different times. In practice, a light echo can occur from light waves originating in a nova, supernova, or some other bright cosmic event and interacting with the interstellar or even intergalactic medium between the source of light and an observer. Because it moves so quickly, a light echo is only really observable over astronomical distances. A delay from the expected time could mean the light was reflected off some object. Because light moves at a steady rate, it is possible to measure the difference between when light emitted from a source is expected to arrive at a particular location and when light actually arrives. Light, as a wave, propagates in all directions equally and at a constant speed. Get far enough away, and now the extra distance that angled light must travel starts to matter.
![echoes or echos echoes or echos](https://www.pcworld.es/cmsdata/features/3798554/echo-dot-4-review-with-clock_thumb800.jpg)
Even some of the most sensitive light-measuring sensors would be unable to register a difference between the travel times for the two light beams.īut what if, rather than using light to look around our everyday world here on Earth, we instead used it to look out into the deepest reaches of space? The Sun's light takes about eight minutes to reach us here on Earth, and the farther out you go, the longer it takes light to reach us. The laser's light moves so quickly that the infinitesimally slight delay in the angled laser reaching the wall is indistinguishable from the instantaneous transmission to human eyes. Likewise, if you took two laser beams and shot one of them in a straight line so that one hit a far wall and you angled the second one so that it bounced once off the floor and then hit the same point as the first laser, then in theory turning on both laser beams at precisely the same time wouldn't do you much good in seeing which gets to the far wall faster. In our everyday experience, a light echo isn't something we could ever perceive. This speed takes the "echo" of light as it interacts with the world we see and is translated into sight. The light we see bounces off surfaces, through the air, refracted, and reflected, all at the fastest local speed physically possible. When we look out into the cosmos, in a sense, everything we see is an echo.