I believe the six day creation is only about our earth not the universe
Then you've changed it. It also describes the beginning of light.
I believe the problem is with the big bang theory itself.
Only a problem for one trying to reconcile it with scripture. The skeptic has no need to do that, and hence no such problem.
My understanding is that according to modern claims, dark matter is capable of travelling faster than the speed of light. It can also accelerate time. that suggests surely that the reverse is also true. given the above, why couldnt we use the above as a mechanism for explaining an evolutionary creation that fits inside the literal 6 day creation period of Genesis Chapter 1?
Even if you squeeze the 14 billions years of "creation" into six days, you've still got problems with the order of events in the biblical narrative.
this cannot explain the creation of Man...but it surely can explain the creation of everything else up to Adam?
Then what use is it to an Abrahamist? He's still far from reconciling scripture with the science. Science tells us there were no first pair of humans, so, assuming that your purpose is to bring the two into alignment, if you're forced to call any of the science wrong to preserve a particular religion's creationist narrative, what you end up with is no more valuable than a literalist interpretation of Genesis.
it is not possible to be a Christian and believe Genesis 1-11 is an allegory
That's most Christians in the West if not the world.
Incidentally, no creation myth is an allegory. That's a specific literary from in which a writer substitutes fictional characters and events for nonfictional people and events from history knowing what the fictions stand in for. Gulliver's Travels is a political allegory in which fantastical fictional characters substitute for prominent historical figures like Walpole in the British politics of Swift's era, symbolized by the rope dancer Flimnap. We know what these things stand for as did their author, and they are specific, not place-holders for what is not known as is the case with myths. Like the writers of Genesis, the mythologist has no conception of the actual history of events leading to the existence of the world he finds himself in. He's speculating, and, of course, the guesses are wrong in every creation myth.
But what Abrahamist will call these guesses error? None in my experience. They prefer inaccurate euphemisms like allegory and metaphor. Myths aren't metaphor, either, which also requires the presence of specific literary features to be correctly called that.
They'll tell you that the Viking creation myth, for example, is wrong, not an allegory, but they are loathe to use words like wrong guess and error with their own myths. Nor will they try to find ways to reconcile those myths with natural history. Here's that story if you're interested:
"
Odin, Vili, and Vé killed the giant Ymir. The sons of Bor then ... made the world from him. From his blood they made the sea and the lakes; from his flesh the earth; from his hair the trees; and from his bones the mountains. They made rocks and pebbles from his teeth and jaws and those bones that were broken. Maggots appeared in Ymir's flesh and came to life. By the decree of the gods they acquired human understanding and the appearance of men, although they lived in the earth and in rocks. From Ymir's skull the sons of Bor made the sky ... The sons of Bor flung Ymir's brains into the air, and they became the clouds. Then they took the sparks and burning embers that were flying about after they had been blown out of Muspell, and placed them in the midst of Ginnungagap to give light to heaven above and earth beneath. To the stars they gave appointed places and paths."
This is not an allegory, either - just another incorrect guess from people who didn't know where lightning and thunder came from. They guessed incorrectly about that as well. I'll be that you have no problem with anything I wrote about the Vikings.
Now, if one DOES know where these weather phenomena come from and STILL call it the hammer of Thor, NOW they're using metaphor. What's the difference? He's using a fiction to stand in for a fact known to him, and there is no error. Take away that knowledge, and it becomes a wrong guess again.