There is testimony we can acquire, but that is not irrefutable nor scientific.
…how do you know that?
Are you asking how do I know there is testimony we can acquire? Or as you asking why it wouldn’t be irrefutable or scientific?
Yes, your second question.
Because that’s not how science works. With testimony, there is credibility in question. How credible is the witness? and so forth. By its nature, testimony is subject to unprovable scrutiny (that is, scientific scruity, not court-of-law scrutiny) and is not irrefutable.
To refute testimony scientifically is to use the wrong test. The correct test would be “beyond a reasonable doubt” as in a court or some such.
How would there be testimony at the dawn of the universe? Nobody was alive back then. I don’t understand your point.