The discussion revolves around the concept of the Big Bang and whether its location can be defined by gravitational forces. Participants explore the implications of gravitational interactions, the nature of singularities, and the expansion of the universe, touching on theoretical and conceptual aspects of cosmology.
Participants express multiple competing views regarding the nature of the Big Bang, singularities, and the implications of gravitational forces. The discussion remains unresolved, with no consensus on key points.
Limitations include the dependence on various models of cosmology, the ambiguity surrounding the concept of singularities, and the unresolved nature of certain mathematical interpretations related to density and expansion.
You are implying that there is a center to the expansion of the universe. There is not, so no. I recommend the link in my signature.Ozfer said:So if we summed up all the gravitational force acting on everything (planets stars etc) would the final end point for everything be the location of the big bang? Or does this make no sense due to space bending?
Everything is NOT touching. If it were that would imply a center. I found this very hard to grasp when I started learning this stuff but "the big bang happened everywhere". It did not happen at a point in space but a point in time.Ozfer said:Well that was informative but it still leaves me wondering. In the analogy the pennies never touch, how does that make sense for the big bang singularity where everything is touching?
Ozfer said:So if we summed up all the gravitational force acting on everything (planets stars etc) would the final end point for everything be the location of the big bang? Or does this make no sense due to space bending?
Ozfer said:So what we are saying here is everything existed in a singularity, and everything had something in between it since stuff didn't all touch (not space?), and this stuff in this point could be infinite, and then for some reason it decided to shoot outwards (more space?), but from the stuffs perspective it didn't really shoot outwards? And where was time while all this was happening?
Touching or not (the actual singularity is problematic), the geometry is a closed curve in a higher dimension than can be visualized. So think of lower dimension analogies: which point on the edge of a circle is the center? Which point on the surface of a sphere is the center?Ozfer said:Well that was informative but it still leaves me wondering. In the analogy the pennies never touch, how does that make sense for the big bang singularity where everything is touching?
"Singularity" does not mean what you seem to think it means. It is just a place-holder phrase so that physicists aren't always having to say "the place where the math model breaks down and gives nonphysical results and we don't know WHAT is/was happening".Ozfer said:So what we are saying here is everything existed in a singularity ...
Yes. You cannot use intuition to find a description what happens when you get 'too near' to a singularity. The Laws have to bend when things are compressed into a small enough space. It's analogous to imagining that School Chemistry would still work the same inside a Neutron Star and we would never imagine that - would we?phinds said:"Singularity" does not mean what you seem to think it means. It is just a place-holder phrase so that physicists aren't always having to say "the place where the math model breaks down and gives nonphysical results and we don't know WHAT is/was happening".
It depends on the model. In some cases it refers to a divide by zero error, but if the equation doesn't have the dependent variable in the denominator, you can go all the way to zero without it breaking down. This means that some features may still be capable of being evaluated.phinds said:"Singularity" does not mean what you seem to think it means. It is just a place-holder phrase so that physicists aren't always having to say "the place where the math model breaks down and gives nonphysical results and we don't know WHAT is/was happening".
Interesting. I had not thought of it that way.russ_watters said:Nor does the "singularity" being described as a point require that it is the center of something.
Do you need an example? Directly applicable is two points on a shrinking circle, a common analogy for the universe. Neither point is the "center". As the circle shrinks, the distance between them shrinks, but a "center" never gets established. The distance can go all the way to zero without any errors in some models of the geometry (d=x in particular). At d=0, the points collapse into one point, but that's still fine: a point doesn't have a "center".phinds said:Interesting. I had not thought of it that way.
Helpful. Thanks.russ_watters said:Do you need an example? Directly applicable is two points on a shrinking circle, a common analogy for the universe. Neither point is the "center". As the circle shrinks, the distance between them shrinks, but a "center" never gets established. The distance can go all the way to zero without any errors in some models of the geometry (d=x in particular). At d=0, the points collapse into one point, but that's still fine: a point doesn't have a "center".
Yep, and a good reason to interpret "singularity" as meaning "the place where the math model breaks down and gives nonphysical results and we don't know WHAT is/was happening".What does become problematic is the density, which goes infinite/singularity at d=0.
A singularity is a feature of a model. Something like a boundary where the results do not make sense. It is not a place at all. Certainly not a place where we can be since we build the laws of physics to make sense where we are.Ozfer said:So how do we know we arn't currently in a singularity?
Pretty much none of them. Many of the laws of physics take the form of differential equations that require quantities to be continuous and differentiable to work. Quantities that diverge to infinity as the singularity is approached are not continuous there.Ozfer said:So what laws don't work at the singularity?
Density, as one example. One REASON that the big bang singularity is called a singularity is that the math says that the density goes to infinity, which is not physically meaningful.Ozfer said:Quantities of what? If there is still space, matter, and time it seems like everything should work. If space bends and stuff doesn't touch it seems that solves the density problem.
If you tried to extend the notion of position to the singularity, it would become discontinuous. You could extend time. The singularity could be given a time coordinate. But that does not give you a coordinate system (a "manifold") that extends to include the singularity.Ozfer said:Quantities of what? If there is still space, matter, and time it seems like everything should work. If space bends and stuff doesn't touch it seems that solves the density problem.
If you have two objects traveling around a circle and they collide, you can say they collided at a point and a chosen coordinate system can identify the location of the collision. If instead the circle shrinks to zero diameter, the coordinate system itself disappears when they meet.Ozfer said:Quantities of what? If there is still space, matter, and time it seems like everything should work. If space bends and stuff doesn't touch it seems that solves the density problem.