Wrong question, she says:
The universe started with a Big Bang and it’s expanded ever since. You probably know this. You probably also know that the universe doesn’t have a center. But where did the big bang happen, if not in the center of the universe? And if the universe expands, doesn’t that mean that matter on the average doesn’t move, contrary to what Einstein said, that absolute rest doesn’t exist? I get these questions a lot. And at the end of this video, you’ll know the answers…
There are two warnings I have to add when it comes to the “Big Bang”. First, I don’t know anybody who actually believes that this singularity is physically real. It probably just means that Einstein’s equations break down and must be replaced by something else. For this reason, physicists use the term “Big Bang” to refer to whatever it is that replaces the singularity to within a Planck time or so. A Planck time is about ten to the minus forty-four seconds.
Second, we don’t actually know that this extrapolation all the way back to the Big Bang is correct because we have no observations dating back to before roughly the creation of atomic nuclei. It could be that Einstein’s equations actually aren’t the right ones for the very early universe. So instead of a Big Bang it could also be that an earlier universe collapsed and then expanded again which is called a Big Bounce. Or there could have been an infinitely long time in which not much happened after which expansion suddenly began. That would also look much like a big bang. We just don’t know which one’s right. The “Big Bang” is just the simplest scenario you get when you naively extrapolate the equations back in time.Sabine Hossenfelder, “Where did the Big Bang happen?” at BackRe(Action)
It would be interesting to know what other physicists think of her approach.
You may also wish to read: The Big Bang: Put simply,the facts are wrong.