In our Universe, in all directions and in all locations, there’s simply more “stuff” that space is full of everywhere we look. On the largest scales of all, the richest galaxy clusters and the sparsest cosmic voids average away, leaving us with a Universe that’s isotropic, homogeneous, and almost perfectly uniform. The oldest light in the Universe, the cosmic microwave background radiation, is a similarly uniform relic left over from the Big Bang itself: a chilly 2.725 K in all directions.
And yet, our view of the Universe is fundamentally limited, as we can only see for around 46 billion light-years in all directions: a limit set by the finite speed of light, the finite age of the Universe, and the amount that the Universe has expanded since the Big Bang. The Universe, to the best that we can tell, may well be infinite in scale. But out there, somewhere beyond the observable Universe, there might yet be a fundamental limit to how far the unobservable universe extends for: a cosmic edge to the extent of the part of the Universe we inhabit.
If someone (even though it isn’t us) were to exist close to that edge, what would they see? That’s what Jason Moorhead wants to know, asking: “Is there a chance there is a galaxy that is close enough to the outside edge of space/time… that someone living in that galaxy could hypothetically see an edge of the current space/time “wall”? When they look in a specific direction, there is no “unobservable universe” and that some sort of boundary of the universe is part of what is observable for them?” It’s not a guarantee that this picture is correct, of course.
But it could be right, and if someone did indeed live close to that edge, what they’d see would be very, very different from the Universe we observe when we look out at it. A visual history of the expanding Universe includes the hot, dense state known as the Big Bang and the growth and formation of structure subsequently. The full suite of data, including the observations of the light elements and the cosmic microwave background, leaves only the Big Bang as a valid explanation for all we see.
As the Universe expands, it also cools, enabling ions, neutral atoms, and eventually molecules, gas clouds, stars, and finally galaxies to form. It’s important to start with the standard picture of our Universe: both theoretically and observationally. From a theoretical perspective, our foundation is threefold.
Combined, these three things inform us that there shouldn’t be any large-scale regions of the Universe that look spectacularly different from any other regions. No direction or location should be particularly cold, empty, hot, or dense. There should be no overall directionality to the Universe, no large-scale, directional magnetic or electric or gravitational fields, and no evidence of the laws of physics to change or evolve with time.
Extract — continue reading at the source.
