The evidence for universal existence is existence, it is real do you not agree, otoh, there is no direct evidence of the existence coming from non-existence.
Well, the big bang cosmology don't propose "nothingness", nor "nonexistence", so your claim regarding to BB would be strawman.
During the 1920s, 3 theoretical physicists came up with very similar models of the hypothesis on expanding universe cosmology, because Edwin Hubble discovered in 1919, there were more galaxies than the Milky Way, and that the universe was larger than the Milky Way.
These 3 physicists were
- Alexander Friedmann (1922)
- Howard Percy Robertson (1924-1925)
- Georges Lemaître (1927)
They have similar concept, because each have modified Albert Einstein’s field equations for General Relativity (1915), by adding a metric that provide the exact solution to the explain, mathematically, the universe “expanding”. As the equations were modified for expanding universe model, it was renamed the
Friedmann equations, while the metric itself was known today as the
FLRW metric (which stands for Friedmann-Lemaître-Robertson-Walker metric; “Walker” being Arthur Geoffrey Walker had worked on the metric with Robertson in 1936).
Robertson and Lemaître have (independently) proposed, that the “expanding” universe could be inferred with distant objects (eg distant galaxies) were moving away were observed from the observer and from each other, by observing of the light’s wavelengths were shifting towards the red in the electromagnetic spectrum, hence its known as the
Redshift. It was Edwin Hubble who observed the redshift in 1929, through the Hooker Telescope at Mount Wilson Observatory.
The Redshift together with the Friedmann equations (plus the FLRW metric) became known as the
Hubble’s Law, the first observational evidence for the expanding universe model.
Georges Lemaître wrote the Hypothesis of the Primeval Atom, which described the universe was much smaller and denser than it is today, however he described the earliest initial state of the universe being colder, near absolute zero, as ball of cold perfect liquid, hence it became known later as the Cold Big Bang.
However in 1948, another party of 3 theoretical physicists have build upon and modified the expanding universe model:
- George Gamow, a former student of Alexander Friedmann
- Ralph Alpher, a former student of Gamow
- Robert Herman
Gamow with Alpher proposed that the universe was indeed smaller and denser in the beginning, but proposed it was infinitely hot and infinitely dense at the beginning, hence describing the Hot Big Bang (HBB) model.
The Hot Big Bang model have also included Gamow & Alpher proposal that the “atoms” (eg hydrogen, deuterium, helium & lithium) were formed during the Primordial Nucleosynthesis or the Big Bang Nucleosynthesis.
Alpher with Herman proposed the Cosmic Microwave Background Radiation (CMBR), occurring after the last scattering of photons during Recombination Epoch (378,000 years after the Big Bang).
The points in all this, Ben, about the Big Bang history lesson, is not only about the universe expanding, but it was also about the
origin of atoms, and this origin didn’t form nothing.
Plus, if the universe was very hot and very DENSE at the beginning, then there must be “something” already there. You cannot have “density” with nothingness.
This is way, I find you are falsely proposing nothingness or nonexistent in the Big Bang theory. The theory proposed no such things.