If you measure the redshift and blueshift of every galaxy, you can trace them back to a specific point, which is not centered on us. It might be tempting to ask, "Where is that point?" The answer is that it's relatively close by, only several million light-years away, which is less than 0.1% of the visible Universe's size. However, this isn't the correct way to think about the Big Bang, which is better understood as a moment in time rather than a specific location in space. Here's why.
One of the most challenging concepts for anyone—even professional astrophysicists—to grasp is the nature of the Big Bang and the expanding Universe. At the farthest reaches of what our most powerful telescopes can observe, galaxies are moving away from us so rapidly that the light their stars emitted has been stretched up to twelve times their original wavelength. These stretched light waves are a result of the expanding Universe and appear almost, but not entirely, identical in every direction we observe.
Does the slight difference in redshift between objects in one direction compared to the opposite direction tell us anything about where the Big Bang occurred billions of years ago? After all, we can use redshift to determine when light is moving away from us and blueshift to determine when it's moving towards us. So, if the light from the Big Bang is more redshifted in one direction and more blueshifted in the opposite direction, does that reveal something about our location relative to the "origin point" of the Big Bang?
This approach isn't commonly used in astrophysics, and for good reasons. But we could explore what we'd learn if we did and then discuss why we don't typically think this way.
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