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fonix232@fedia.io 2 days agoNot necessarily.
The expansion of the universe here doesn't necessarily mean matter moving faster than light.
Think of the universe as a 3+1 dimensional ballon - specifically, the 3D space we occupy is the 2D surface of the balloon. As you blow air into the ballon, that 2D space expands.
Now, it's a simplistic example mainly because we're three dimensional beings and thus can't easily wrap our heads around a 4D space where one of the surfaces is three dimensional. You run into the same issue as e.g. trying to visualise a tesseract (a four dimensional cube). So a balloon has to do.
And since this expansion of our universe technically happens outside of it, the general laws of physics - such as the speed of light - do not apply.
db0@lemmy.dbzer0.com 1 day ago
That’s what I meant. Since matter isn’t moving at the speed of light, if we assume the universe expansion is due to the movement of its edge objects, then it cannot expand faster than 2c. If the expansion is happening for a different unrelated reason than the edge objects ofc that’s something else
fonix232@fedia.io 1 day ago
Your presumption that there’s an “edge” is at fault here. Consider the surface of the ballon (or rather- a bubble) - it’s continuous, just like our universe. And that’s why it’s hard to explain how a 3D space can expand seemingly without a center point - because said center point is not within the constraints of this 3 dimensional space, just like how the center of a balloon or bubble is not on the two dimensional surface but in the center.
so just like the surface of an expanding bubble, the expansion of our universe doesn’t happen in a plane we can conceptualise easily - it’s a 4 (or possibly more!) dimensional expansion, of which we are just the surface, therefore the expansion appears as if everything literally drifted away from everything - which should be impossible in a 3D space but not when you add a fourth axis.
db0@lemmy.dbzer0.com 1 day ago
I don’t know much about astrophysics, but it seems to me the analogy breaks down. Unlike a balloon, the universe does not move on a medium, so the only way to surmise it’s size is by its edges (i.e. the objects at its farthest edges). So the important thing here is how fast those edges move (the dots, on the balloon) which can never be higher than the speed of light. What am I missing?
fonix232@fedia.io 1 day ago
You're still missing the 2D to 3D translation...
Think in two dimensions. The surface of the balloon is the two dimensions - X and Y axes. The "medium" (the rubber of the balloon) is the fabric of the universe.
The two dimensional space - much like e.g. the surface of the Earth - has no edges. When the balloon expands (on the third dimension, which the surface dwellers are unaware of), all the surface notices is that any two or three or N points have gotten further from each other. The size of this 2D plane thus can be described by a single dimensional number - the circumference of the balloon (aka "how long does it take to get back to the starting point in the 2D space if you go in any direction).
You need to extrapolate this continuous 2D surface on a 3D object to a 3D surface on a 4D object. In a four dimensional space, our universe has a four dimensional volume it consumes - but in 3D, it's effectively infinite (curving into itself, much like the surface of the balloon), but also expanding (everything is being further and further from each other).
To grasp this I'd recommend you read the book Flatland by Edwin Abbott - it's a 140 year old study in the format of a novel, on how beings from an N spatial dimension plane would "see" and interpret a being from an N+1 spatial dimension (in this case, 2D beings, like a square, seeing 3D being, a sphere, intersect with its 2D plane). Mind you it's also a social satire so you'll find a ton of social commentary of the Victorian era Britain, but the core conceptualisation is there - an N spatial dimension being will always have trouble visualising an N+1 dimension.
So again, in our 3 dimensional plane, the universe has no edges, it's infinite, yet expanding. Just like how the surface of a balloon or bubble has no edges, or how the surface of the Earth has no edges - but in a 3D space you can create a bounding box to define its size. Our 3 dimensional universe is essentially the surface of such a 4D bubble, but that fourth dimension is outside of our universe therefore it can't easily be measured directly. Just like how a dot on the surface of the balloon couldn't measure the 3 dimensional space of the balloon, only by inference of the expansion, theorise that it actually exists in a 3 dimensional system but is limited to the 2D surface of said balloon, and infer its mechanics based on the expansion of space between any two points on the surface.