if the big bang theory is accepted as 'truth ' surely its no longer a theory?

a scientific theory starts as a hypothesis, a made up plausible answer to a question. the hypothesis is then tested and re-tested. when enough tests are done, and no one can think up a way to disprove it, it becomes a theory. a theory is used as an explanation to a question. and is used as such until it its dis-proven.

a law is a fundamental mechanic that cannot be dis-proven. and is almost always only abstract, such as the laws of physics. where as the theory of relativity is a hypothesis that has been tested and found to work for most things so far, when it is dis-proven or something else sounds better, it will likely be put on a book shelf and forgotten about. a theory cannot become a law, because there is always a chance a theory may be mis-proven. or something else may fit better. a circle peg may fit in a square whole, but the square peg will fit better, type of thing.

a scientific theory starts as a hypothesis, a made up plausible answer to a question. the hypothesis is then tested and re-tested. when enough tests are done, and no one can think up a way to disprove it, it becomes a theory. a theory is used as an explanation to a question. and is used as such until it its dis-proven.

a law is a fundamental mechanic that cannot be dis-proven. and is almost always only abstract, such as the laws of physics. where as the theory of relativity is a hypothesis that has been tested and found to work for most things so far, when it is dis-proven or something else sounds better, it will likely be put on a book shelf and forgotten about. a theory cannot become a law, because there is always a chance a theory may be mis-proven. or something else may fit better. a circle peg may fit in a square whole, but the square peg will fit better, type of thing.

The big bang theory is only accept as the truth in that it is a well established theory and but nothing in science is 100%. So it will remain a theory just like countless other scientific theories.

Scientifically, a theory is a wordy expansion of a scientific law. Scientific laws are short and often expressed mathematically.

That being said, it's not that simple because what a layman calls a theory and what a scientist calls a theory are two different things so even if the big bang theory is later proved false the popular culture and in regular language people will still call it a theory. In truth the original big bang theory has been largely rejected by scientists but the term is so popular it is still used of the modern day standard model of cosmological inflation.

Originally it was believed there was a giant explosion (big bang) that "created" the universe. It was apparent at the time that inertia kept the galaxies etc flying apart. It turned out to everyone's surprise that the rate of inflation was increasing. This led people to wonder what was causing that inflation. To date nobody knows what is causing this expansion but we call it "dark energy". So although the standard model of cosmological inflation is incomplete it is still referred to as the "big bang theory".

The word 'theory' has several different meanings.

It sometimes refers to a tentative idea that may or may not be true. And it sometimes refers to a detailed set of ideas that is universally accepted, for example music theory or number theory,

The expression 'scientific theory' is closer to the second of those meanings; so it does not stop being a theory if it comes to be regarded as certainly true.

The antecedent is false anyway. The big bang theory is still accepted as being the likeliest explanation for how the universe began.

But even a false theory is still a theory; it is only a disproved theory. Like the Ptolemaic idea about Earth being at the center of the whole universe and the planets going around it in deferents and epicycles.

Yes...it's just a theory.

We can observe that the universe is expanding, so what happens if we reverse the expansion? We get to a point where the universe was a single infinitely massive particle. No real explanation is offered, just the mysterious point in space time. This gets to be metaphysics where science and religion collide!

Maybe you need to understand the definition of a scientific theory.

"A common misconception is that scientific theories are rudimentary ideas that will eventually graduate into scientific laws when enough data and evidence have been accumulated. A theory does not change into a scientific law with the accumulation of new or better evidence. A theory will always remain a theory; a law will always remain a law"

From:

https://en.wikipedia.org/wiki/Scientific_theory

please read up on how science works, and what a scientific theory is. i think you may be a little hazy on both points.

all scientific theories are constantly re-examined in the light of new data. if new data are inconsistent with the theory the theory is modified or abandoned.

some theories are so well-established that any inconsistent data would be rejected as experimental error. this is why results are published, and must be reproducible by other researchers.

We do not know if the Big Bang is the process that created the universe itself.

We will need some type of technology to discover the truth about the beginning about the universe.