Basically, we don't know if spacetime is overall flat, or overall curved, nor if it's curved HOW it's curved.
It is the idea that the universe will continue to expand forever. By contrast, the closed theory states that gravity will eventually cause the universe to shrink. (I think) In addition to the above. Essentially it is the theory that the universe has no boundary and is not closed in on itself in any way. The shape of the universe in this case must be either "flat" or "curved" to some extent, but not curved enough to form a cylinder, sphere, ellipsoid or torus.
The key principles of the infinite plane theory suggest that the universe is infinite and flat, with no boundaries or edges. This theory has implications for our understanding of the structure and expansion of the universe, challenging traditional ideas of a finite and curved universe.
In simple terms it is the shape of the universe. Many theories have been put forward for the shape of the universe, but it is generally thought of as being flat, or very slightly curved, but not so curved that it would fold back on itself to form a sphere, cylinder or torus (doughnut shape). This concept of being "flat" requires some unusual thinking because the universe is clearly three dimensional (with a fourth dimension of time) and not a flat two dimensional surface.
Well, honey, a circle is definitely curved. I mean, unless you're living in some alternate universe where circles are straight, then by all means, enlighten me. But in this reality, circles are as curved as a banana on a rollercoaster.
Einstein believed in a finite but unbounded universe, where space-time is curved but does not have any boundaries or edges. This view is consistent with his general theory of relativity, which describes how gravity affects the curvature of space-time.
The flatness problem in cosmology is significant because it raises questions about the geometry and fate of the universe. It refers to the mystery of why the universe appears to be so close to flat, rather than curved, which has implications for the overall structure and expansion of the universe. Understanding this problem is crucial for theories about the evolution and ultimate destiny of the universe.
This is a theoretical model of the universe. A Friedman Universe can have positive, zero or negative curvature. If the curvature is positive then the universe is closed and curved. A light ray going in any direction would make a complete circuit if the universe and return to the starting point. If the universe has zero or negative curvature it is open and unbounded and said to be flat. A light ray would travel in a 'straight' line and not return to its point of origin.
No. You obviously misuderstand the concept of a "curved" universe, probably imagining it like the 2-D surface on a 3-D sphere. This actually isn't too bad of a way to view it, but it has its problems -- caused mainly by taking the mathematical analogy too far. A Friedmann Universe -- ie, one like the one we're now in -- can be mathematically curved but without a surface, and without any other dimension into which this curvature is (well) curving. Even in a universe that was 2-D and closed (ie, a sphere), and its mass was constrained to the surface of a sphere, then no force would be needed to keep that mass on the surface. That mass could no more leave the surface of the sphere then you could walk outside of the three spatial dimensions of our Universe.
a curved seam is a seam that is curved
A curved line is a line that is curved.
A mirror that is curved outward is convex. A mirror that is curved inward is concave.
Curved.