Would Any Observer Anywhere Think They're At The Center Of The Universe?


Originally posted at Forbes!

They should! And if their understanding of physics is as advanced as ours, they should subsequently realize that what they see as being the “center” of the Universe is really just the center of the observable universe, which is necessarily centered around them, as the observers.

There are a couple of things in play that allow me to answer this question, and the first is the nature of the observable Universe. The observable Universe is best thought of as a series of spherical shells, centered around our planet, where most of our observing happens (plus or minus a few astronomical units). The amount and number of things that we see in any given direction is limited, fundamentally, by the speed of light. We cannot see things which have not had the time for their light to reach us yet.

In the local Universe, this is not a major constraint, as the time delays that light imposes are relatively manageable. The delays even to communicate with New Horizons, at the very outskirts of our solar system, are only a few hours (it’s a 9 hour round trip from Earth to Pluto and back). From Earth to Mars is a positively rapid 14 minute round trip on average. Within our galaxy, it starts to be a little more noticeable that our vision is a little more delayed getting to us; for instance, our current observations of Eta Carina indicate that that particular star is probably going to explode sometime soon. However, light takes over seven thousand years for it to reach us, so if it had exploded last week, we’d still have 7500 years before we’d be able to notice.

The further out we go, the further behind our vision becomes, lagging more and more dramatically behind “now”. This lag affects light equally as it comes from all directions, so we wind up with spheres of lagged space-time in any possible direction. Because we are the receiving end of all this light, this observable sphere is by definition centered on us. Any other observer at any other position in the Universe should see the same thing; their view of the Universe will be just as limited in scope by the speed of light as our own.

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