This is a false assumption. The big bang was not an explosion in the usual sense of the word with matter being thrown out from a single event. It is what is described by the universe starting in a hot dense state in an isotropic, homogeneous, and spatially expanding setting.user079622 said:
No, that is not correct.user079622 said:
No, that is not what the Big Bang is.user079622 said:
Because the Big Bang was not an explosion into a pre-existing space.user079622 said:
We can, just not with 100% certainty. Our best current model is that the universe is spatially flat, but there are always finite error bars on real measurements.user079622 said:
All stars/planets in universe lay at same plane as earth? How thick is this plane?PeterDonis said:
That is also false and not what the theory actually says.user079622 said:
Isn't theory in science only validate if can be proofed? Isnt that just one of assumptions?Orodruin said:
Nor what observation says. @user079622 you have a VERY incorrect view of cosmology. I suggest you do some basic reading (NOT pop-science presentations).Orodruin said:
Are we talking about assumptions or proofed theory ?phinds said:
Either way, the view points you have expressed are so far off of reality they are "not even wrong".user079622 said:
That's not what is meant by "flat" in the context of the Universe.user079622 said:
"Flat" in this context does not mean "plane". It means "Euclidean 3-space".user079622 said:
user079622 said:
Theories in science are never "proofed". You compare their predictions with observations, and this can give an increasing level of confidence in the theory, but you can never "proof" it.user079622 said:
user079622 said:
PeterDonis said:
The "flat" picture is of a cylinder, which is not the spatial topology of our universe in our best current model.DaveC426913 said:
Nor what anybody here has said.Orodruin said:
No. There is matter in all directions in all three dimensions.user079622 said:
Yes that make sense. When I look at sky I see stars at all directions.Ibix said:
I don't know what that means.user079622 said:
The question doesn't even make sense. The universe doesn't have a "center".user079622 said:
This shows that you still suffer from the same misconception you had when you started this thread. You have to dispell that misconception if you are to get further.user079622 said:
That's an interesting observation, because the stars you can see are part of the Milky Way galaxy that is disc shaped. It's quite a thick disc, but you get to intergalactic space in a much shorter distance in one direction from another. You are thinking on far too small a scale - it's the galaxies that are more or less uniformly distributed across the sky.user079622 said:
No. In our current models, if you run them backwards the density of matter increases everywhere. There is no single point from which everything came.user079622 said:
And, as @Ibix has pointed out, they are ALL in the (relatively) flat disk of the Milky Way Galaxy. All of the stars you can see with the naked eye are in that disk but basically all of the stars in the Observable Universe are NOT in the Milky Way.user079622 said:
But how can this be physically possible?Ibix said:
Not if it started off as something bigger than a point, as is the case with the Universe. Even the Observable Universe does not shrink to a point if you run time backwards, although it DOES go down to something quite small. I've heard estimates all the way from the size of an atom to the size of a golf ball.user079622 said:
Because this is General Relativity, not Newtonian physics. Your Newtonian intuitions do not work in this domain.user079622 said:
If you assumed that the geometry of spacelike slices of spacetime remained static then you would be correct. Spacetime geometry does not work that way, however.user079622 said:
Obviously that's the problem, hmm. So we are in math world.PeterDonis said:
No - you are interested in bits of physics where we can no longer pretend that Euclidean geometry is an accurate model of the world. That you have an unquestioned belief in the accuracy of Euclidean geometry is part of why you struggle with what we're saying.user079622 said:
Ok so that mean we are still finding what is really happening. So that mean all above members wrote in posts maybe is not 100% correct?Ibix said:
Yeah, they're not the best. There's plenty of diagrams out there. I just hoped to start a discussion for the OP about what curvature is, as opposed to what it's not.PeterDonis said:
Depends what you mean. It's all 100% certain implications of the premises of our models. And our models make extremely accurate predictions of the outcome of experiments that we do. But are they necessarily 100% accurate models of the universe? Almost certainly not - they're just enormously better than anything anyone else has come up with.user079622 said:
Inflation models don't necessarily eliminate the initial singularity.Ibix said:
Newtonian physics is "math world" just as much as GR is. Newtonian physics is just different math, whose predictions are now known to not be as accurate as those of GR.user079622 said:
Depends on what you mean. We don't have good knowledge of what happened before the hot, dense, rapidly expanding state that we call the "Big Bang" (which is not the same thing as the "initial singularity" that appears in some models). We do, however, have good knowledge of the current spatial geometry of the universe--that it is flat to within a very good approximation (i.e., if it is actually curved, the radius of curvature is much, much larger than the radius of our observable universe).user079622 said:
As has already been pointed out, we never can be certain that anything in science is "100% correct".user079622 said:
And, specifically, to the geometry of space.Ibix said:
Ibix said:
More precisely, to the geometry of spacelike hypersurfaces of constant FRW coordinate time (or, equivalently, constant proper time for comoving observers) in the overall FRW spacetime geometry.Jaime Rudas said:
Suppose simply that a current cosmological time state of the universe is unbounded Euclidean 3 space. Then every earlier state, however many doublings of density involved, is also unbounded. The cosmological time exactly zero is not actually part of the model (even in the idealized mathemetical model). Every time later than zero (even e.g. ##1/(((10^{100})^{100})^{100})## seconds after zero) is still an unbounded state. That is just the nature of infinity.user079622 said:
You are misunderstanding what “spatially flat” means. Intuitively it means that the Euclidean geometry works everywhere - the Pythagorean theorem is valid, parallel lines never intersect, the interior angles of a triangle add to 180 degrees, and so forth. The opposite of “flat” is “curved”.user079622 said:
No, not if the fluid extends infinitely in all directions. In such a situation, as the distance between the molecules decreases, the density of the fluid approaches infinity everywhere while at the same time the volume always remains infinite.user079622 said:
