I heard from another post that the microwave oven background radiation from the dawn of the universe can be used as a vantage point on the universe, but since it is everywhere how can it be used as a point of view from which to look “down” on the whole universe?
Microwave ovens have nothing to do with the Cosmic Microwave Background radiation.
The CMB is essentially an ‘echo’ of the Big Bang and as such is about as far back in time that we can look and get information (IIRC the CMB represents something like 300,000 years post Big Bang but don’t hold me to that). The background radiation is not even but shows irregularities. What we are seeing is the ‘surface of last scattering’. Before that the Universe was opaque so we can’t peer into what was going on. Still, by looking at the CMB and looking at what is around us today scientists can start drawing conclusions about how the Universe evolved.
Mainly because it’s what’s left over of the big bang. The universe started out very small and very hot, billions of degrees. It’s been expanding and cooling for the past 15 or so billion years, and this 3 degree kelvin radiation is what’s left of that heat. Take what you know about it, and plot it backwards through time and you gain a pretty good understanding of the early universe.
The Cosmic Microwave Background (CMB) does not define a specific point in the universe, but it does define a reference frame so you can measure velocities against the CMB frame. The reason is Doppler shift; if you are moving relative to the CMB frame, the CMB will appear blueshifted on one part of the sky and redshifted on the opposite side.