Big bang is a theory, but fundamental of time is reality.

Article Universal Time

Aside of the questions part related to big-bang (which may or may not be soon falsified by much increased telescope precision from James Webb and follow-up ones to come) it is fully clear, that time is physically indeed the most fundamental entity and such is fully discrete as recently shown by iSpace theory deriving undeniably the existence of the Quantum of time to be 1/6961 iSpaceSecond in new iSpace-IQ unit system (the first able to fully do away with all human artefacts whatsoever) yet able to be in turn lossless convertible into fully MkS/A-SI lab compatible iSpace-Si unit system (keeping the exact arbitrary digit precision results of iSpace theories simpke first order multiplicative exact integer geometric input relations):

Preprint Hubble constant H0 is derived from Newtonian gravitational c...

Preprint iSpace - Quantization of Time in iSpace-IQ Unit-System by 1/...

It is further clear from assumed total dimensionality of 10D = 3D space (as perceived) + 6D subspaces (2x 3D integer LEGO style discrete hence fully quantized) + 1D time (fully discrete likewise as prooven by existence of Quantum of time).

Before one starts to oppose now, that would be incompatible to theory of relativity (either in current or maybe even in a to be modified - corrected, updated form including the missing Doppler effect term as derived 2002 and recently republished by @Lev Verkhovski in his 2022 re-issued preprint in english - it is not as exactly the network style subspace structure of iSpace theory is what allows for geometric compatibility with required space-bending (?) and experimentally confirmed precisely time-delaying nature of both SRT and GR. In other words, also compatible to the not at all unlikely correct model proposed by @Preston Guynn (as posted above).

Dear Mohammed, ''the bigbang (either a myth or not) refers not necessarily to the notion of the beginning of space and niether it refers necessarily to the beginning of time'' otherwise the Planck length and time would not be strictly greater than zero (would be zero instead)... we so far wouldn't even think about the pre-bigbang conditions at a given extent in order to simulate the so-said bigbang itself (it's all about INFORMATION).

Although the most fundamental thing is ''information'', still when evoking the notion of ''information'' there is a simultaneous necessity of the notion of time that has to come into play (time is itself a portion of information, but ''without a mathematical definition of information either in real-time or in imaginary-time'' the notion of information becomes linguistically pure nosense and useless).

Nevertheless, space itself is a portion of information, and still ''without the definition of information in space'' the notion of information holds its sense like it does in your imaginary-time living mind, dear Mohammed... otherwise you wouldn't ask such a great question... hahahahaha... I really enjoyed it.

That said, I personally wouldn't argue against someone who values ​​the fundamental nature of time, especially when he's right (read carefully the very informative work from dear Preston or dear Christian, but if your intellectual capacity does not allow you to do so ''check out my very generic work'').

Article DIRECT PROOF TO THE YANG MILLS EXISTENCE AND MASS GAP (THE U...

As far as our Universe is concerned, its clock started at the moment of its creation. However, if the most credible explanation of its creation (an extension of Dirac's quantum prediction of pair production) is correct, then in some prior Universe, time already existed, and in an infinite number of Universes created by our Universe, each of them will have a brand-new zero for time at the moment of its creation.

However, since the creation of new Universes occurs at only a single point in space-time, and there is no way, even at that point in space, to access that point in space-time after that time has passed, each of the infinity of infinity of Universes is completely unobservable by any other Universes. That is, the Multiverse must exist, but any connection between any two Universes cannot exist. Each occupies a brand-new space-time, completely separate from every other one.

“Time is what keeps everything from happening at once”.

So, the question is: was anything “happening” before the creation of the universe?

Well, we can see as far as the CBR.

All educated guesses past this; we can guess a bit further with the hydrogen to helium ratio, and the smoothness of the CBR.

And that is it.

So, the answer is “do not know, and most likely unknowable”.

The expression " time begins" is a lógica nonsense! It involves circular reasoning!

Dear Mohammed Haimoud,

In the current terminology, time did not start with the Big Bang process, instead there was a period called inflation before the Big Bang during which the universe was expanding exponentially.The rate was so high that any material in that environment would have been reduced to negligible density so effectively it was a hard vacuum. The Big Bang process then converted the energy of the field that had been driving inflation into matter creating the usual hot, dense state with which we are familiar from the CMB. Here are a couple of articles giving some further details:

https://bigthink.com/starts-with-a-bang/when-cosmic-inflation-occurred/

https://bigthink.com/starts-with-a-bang/beginning-big-bang/

Mohammed Haimoud : In an Infinite, Eternal and Ever-changing universe, the question of a "beginning" or "Big Bang" creation of the universe has no meaning! Conventional causality-based physics/mathematics by their nature are limited and are incapable of dealing with the question of Infinity. But infinity is very real; only a dialectical approach can comprehend the Infinite". Please see: http://www.e-journal.org.uk/shape/papers/Special%2064.pdf

That

“Did with the Big Bang, or is it something more fundamental?”, and

“…In the current terminology, time did not start with the Big Bang process, instead there was a period called inflation before the Big Bang during which the universe was expanding exponentially.….”

- are typical, and completely scientifically legitimate, wordings in mainstream physics, where the fundamental phenomenon/notion “Time”, and all other fundamental phenomena/notions, including “Space” and “Matter” – and really so everything in Matter, i.e. , i.e. “particles”, “fundamental Nature forces” – and so “fields”, etc.,

- are fundamentally transcendent/uncertain/irrational. Correspondingly the quotes above are some transcendent, and so really scientifically senseless, passages.

The fundamental phenomena/notions above, and not only, can be, and are, really scientifically defined only in framework of the Shevchenko-Tokarevsky’s really philosophical 2007 “The Information as Absolute” conception, recent version of the basic paper see

https://www.researchgate.net/publication/363645560_The_Information_as_Absolute_-_2022_ed

In the conception it is rigorously proven that there exist nothing else than some informational patterns/systems of the patterns that are elements of the absolutely fundamental and absolutely infinite “Information” Set; the Set exists absolutely objectively, because of it fundamentally – logically - cannot be non-existent, and so exists absolutely eternally, fundamentally having no Beginning and no End.

The phenomenon/notion “Time” is actualized in the Set as the unique universal for all absolutely infinite “number” of the Set’s elements “time dimension”, where every element in the Set, if changes, moves on some “time interval” only in positive direction in this dimension. The dimension, again, has absolutely infinite “length” and fundamentally no any “time beginning” .

Including in some point on the dimension some the Set’s element “Matter” was created, seems indeed on ~13.8 billions of years time interval before now.

More about what are “Matter”, “Time”, “Space”, “Information” [really copy of sections in first link], etc., and what is the really scientifically rationally grounded initial cosmological model of how Matter was created, including what is “inflation epoch” and why Matter practically doesn’t contain antimatter, see

https://www.researchgate.net/publication/367397025_The_Informational_Physical_Model_and_Fundamental_Problems_in_Physics , section “Cosmology”.

Cheers