One more time, only you are claiming nothing exited prior to the big bang, the scientific theory does not claim this...
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Expansion of space
Main articles:
Friedmann–Lemaître–Robertson–Walker metric and
Expansion of the universe
The expansion of the Universe was inferred from early twentieth century astronomical observations and is an essential ingredient of the Big Bang theory. Mathematically, general relativity describes
spacetime by a
metric, which determines the distances that separate nearby points. The points, which can be galaxies, stars, or other objects, are specified using a
coordinate chart or "grid" that is laid down over all spacetime. The cosmological principle implies that the metric should be homogeneous and isotropic on large scales, which uniquely singles out the
Friedmann–Lemaître–Robertson–Walker (FLRW) metric. This metric contains a
scale factor, which describes how the size of the universe changes with time. This enables a convenient choice of a
coordinate system to be made, called
comoving coordinates. In this coordinate system, the grid expands along with the universe, and objects that are moving only because of the
expansion of the universe remain at fixed points on the grid. While their
coordinate distance (
comoving distance) remains constant, the
physical distance between two such co-moving points expands proportionally with the scale factor of the universe.
[16]
The Big Bang is not an explosion of
matter moving outward to fill an empty universe.
Instead, space itself expands with time everywhere and increases the physical distances between comoving points. In other words, the Big Bang is not an explosion
in space, but rather an expansion
of space.
[4] Because the FLRW metric assumes a uniform distribution of mass and energy, it applies to our universe only on large scales—local concentrations of matter such as our galaxy do not necessarily expand with the same speed as the whole Universe.
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Quite clearly an inaccuracy I have put in bold . No , people think space itself is expanding when space has no physicality . People also say there is nothing outside of the expansion ,not even space .