The exact center of the universe is all points. There is no center where the universe is expanding from. All points are expanding from all other points.
My head hurts.
You’re saying that it’s impossible to take a single point on earth, follow that point through space for say, 100 hours, tracing a “line” along the path of that point (taking into account the movement of earth in rotation and also relative to the sun and also taking into account the rotation and movement of the solar system and galaxy), then measuring the length of that “line” to calculate a speed?
Pretty much, yeah.
Sure you can. All you need is a convenient reference frame to measure against. Here’s a nice picture of such a reference frame that’s been in the news these past several weeks.
The thing is, two observers could choose two different reference frames and come to different conclusions. Both would be correct. This is what is meant by no fixed frame of reference, no center of the universe, etc.
Good! That’s a clear sign that you’re beginning to understand the Theory of Relativity.
>well, there’s really no such thing as a “fixed” point in space, right?
>There is no meaningful answer to your question.
>This is what is meant by no fixed frame of reference, no center of the universe, etc.
>Good! That’s a clear sign that you’re beginning to understand the Theory of Relativity.
Or not.
Many of the various relativities including Einsteinian relativity do say that inside a closed box there is no way to sense velocity, and no way to distinguish between acceleration and gravitational attraction. But that’s not the same thing as saying there’s no such thing as a reference frame against which to speak of velocity through the universe.
Look, you get the idea that the universe is expanding, that the further away something is, also statistically the faster it tends to be moving away from you. But you can fit a linear model to that that says that separation velocity is proportional to distance, and speak of how individual objects deviate from that average model. The inertial reference frame for that model is also the reference frame relative to which the very first matter had no bulk velocity. It’s slightly complicated by the fact that the reference frame is expanding, but in the local limit you can treat it as if it weren’t. Whoever mentioned the background microwave radiation was referring to one physical manifestation, one marker, for this reference frame.