You have it backwards, existence already exists, and there is no evidence of it ceasing to exist, so one can logically and reasonably assume it has always existed in some form or other. However for those who think existence is finite, the onus is on them to prove that existence first came from non-existence....something from absolute nothing.
Actually, the limited of actual stop at the start of the BB's Recombination epoch.
According to the best estimate of the age of the universe, given by NASA and ESA (European Space Agency) with WMAP (Wilkinson Microwave Anisotropy Probe, 2001) and Planck (2009-2013) space telescopes, at 13.798 ± 0.037 billion years ago.
The Recombination epoch is the period is furthest back time we can directly detect and measure, which is 377,000 years after the Big Bang.
This evidence is the Cosmic Microwave Background Radiation or CMBR. It was first detected in 1964 by astronomers Arno Penzias and Robert Wilson at Bell Laboratory, but CMBR was actually theorised and predicted in papers written back in 1948, by Ralph Alpher and Robert Herman.
Since then the COBE (Cosmic Background Explorer, 1989), WMAP and Planck space telescopes have provided images of the CMBR.
CMBR is the earliest light detected. This photons can only be detected by microwave anisotropy. It measure the relic radiation. It is older than the earliest detected quasars.
CMBR can be observed because the universe was no longer opaque at this time (377,000 years after the Big Bang). The Recombination epoch marked the time when electrons bonded with atomic nuclei of hydrogen and helium (ionised) atoms.
Before the Recombination epoch, hydrogen and helium were ionised atoms, meaning it has no electrons, therefore the atoms were all positive charged, and the young universe was in the state of plasma, which made the universe opaque; meaning light cannot move freely.
We currently don't have the technology to detect earlier events of very young universe before the Recombination epoch.
What you have claims cannot be substantiated because we cannot observe anything before the Recombination epoch. We don't know if the universe is eternal or not, we don't know if the universe has a beginning.
Everything before the Recombination epoch and CMBR, are theoretical (mathematical proven) and only hypothetical (still not testable or verifiable).
Creationism and Intelligent Design are not hypothetical or theoretical; no, they are just plain pseudoscience.