We have expansion of the universe, which if we trace back X billion years, leads to one point with essentially infinite mass/energy.
We've seen the result of supernova explosions, and how the matter gets distributed.
How can we trace something back for certain X billion years?
You see, that's the problem. We have measured the speed of light by waves of light, energy a small distance, at the most, to the edge of this solar system. And we calculate that the speed of this light or energy is Y...
How do we measure that the light we receieve from a supernova is 40 light years from the Earth? We recieve the light when we do... How do we know when something was originated for certain? What if there is unknown forces out there that manipulate this energy? Does Gravity affect the photons? Does other photons affect the protons? Does the lack of matter in the universe between solar systems accelerate the speed, but when these light protons hit our suns protons does it slow down the speed? Speed it up? We have only done our tests within our solar system. What happens if we go past the edge of our solar systems do the properties change any? What happens if this light goes across the universe... Do the same rules apply?
The concept I can think of is you have a star in the night, we recieve it's light. To us it got to our eyes now. Now we have someone in the field 300 meters away flashing a flashlight... To my eye, the star and flashlight are the same intensity, got to my eyeball at the same time, but one was originated much later than the other. So how we calculate that the star or supernova is a certain amount of distance away, even though we know the flashlight in the field is 300 meters away.
We don't have anybody on that star to give us a timestamp that wasn't altered by external forces. We apply what we know on Earth in our limited existance and apply that Universally, assuming what we learned on Earth is a constant that equally applies to the Universe. It may not...
Speed of light to me cannot be proven universally. We can't use the speed of light to determine that the galaxy is moving at this speed, or that the universe is 8 billion years old. Because we cannot prove what happens with light across a universe. So doesn't that invalidate the test and anything that uses the speed of light as part of the equation?
Maybe that isn't the best example, but you see where I'm trying to go with this...