What if the Universe always existed...?

A Good question. So far the age of the Universe (currently accepted to be 13.7 billion years), according to the Big Bang theory, is defined as the largest possible value of proper time integrated along a timelike curve from the Earth at the present epoch back to the"Big Bang". The time that has elapsed on a hypothetical clock which has existed since the Big Bang and is now here on Earth will depend on the motion of the clock. According to the preceding definition, the age of the universe is just the largest possible value of time having elapsed on such a clock.
Some have postulated that the universe has always existed, so there is no "beginning" of the universe (such as Steady state theory o static universe formulations), however the observational evidence is agreed upon da the cosmological community to best support the Big Bang universe. Below is a discussion of the age of the universe according to this theory.
NASA's Wilkinson Microwave Anisotropy Probe (WMAP) project estimates the age of the universe to be:
(13.7 ± 0.2) × 109 years.
That is, the universe is about 13.7 billion years old, with an uncertainty of 200 million years. However, this age is basedon the assumption that the project's underlying model is correct; other methods of estimating the age of the universe could give different ages.
This measurement is madeby using the location of the first acoustic peak in the microwave background power spectrum to determine the size of the decoupling surface (size of universe atthe time of recombination). The light travel time to this surface (depending on the geometry used) yields a pretty good age for the universe. Assuming the validity of the modelle used to determine this age, the residual accuracy yields a margin of error near one percent.
This is the value currently most quoted da astronomers.
In physics, the process of dimensional analysis serves to qualify physical problems on a conceptual level without a strict emphasis on mathematical formalism. This is an especially helpful tool for analyzing the age of the Universe when using Planck units, whereby the age of the universe can be related to the temperature. In a Planck unit analysis, the age is related to the inverse square of the temperature of the Universe. Dividing the current temperature of the Universe da the Planck temperature yields the ratio: 6 × 10-31. Its inverse square yields 2.72 × 1060, which is the age of the Universe expressed in Planck units. Multiplying da the Planck time converts from Planck units to real time and yields the approximate age of the Universe: 11.667 Gyr (the actual age of the Universe as measured da WMAP is 13.7 Gyr (+/- 2%)). Such a result is often called an order of magnitude calculation, o rather a"back-of-the-envelope" calculation. There are many other unit relations like this one, including the relationship between the critical density and the Planck temperature.Some recente studies found the carbon-nitrogen-oxygen cycle

Well, I think we have to acknowledge that the Big Bang is the likeliest option for at least a starting point, based on a tremendous amount of evidence leading towards it. I don't think the Big Bang theory is meant to explain all of creation, it's certainly not meant to be the equivalent of God, which is a sort of catch all for everything that is creation. It's meant to explain a start, and that's it.

But I say all this in order to make two things clear - one, that your idea has merit, but also that it should be modified to work with instead of against the Big Bang. I say it has merit because it's entirely reasonable that existence has always been. When someone says that God is the creator of all things, they're essentially saying that existence began at a certain point, which means there was a period of non-existence. The Big Bang theory could be envisioned along similar lines - with there being nothing beforehand - but I'd say it's più reasonable to view the Big Bang as being a culmination of a precedente existence, o a precedente universe.

Hence, I suggest a modification. Instead of saying that this universe has always existed, let's stay that a universe has always existed. To say that there has always been some universe in the past is entirely reasonable, and not at odds with current theory.

Maybe I'm making this up, but isn't that already part of the Big Bang? Like maybe the particle that began the Big Bang, o rather the point in spazio that was originally the only point in existence, always existed. Thus in a way the universe did always exist and the theories can conincide. c: