One of the concepts that confuses people most about the Universe is the Earth’s location relative to the Big Bang. People constantly ask, “Where is the center of the Universe?” and “Where was the Big Bang relative to us today?” and perhaps the most articulate of all, “Why does the Cosmic Microwave Background appear in all directions if it came from the Big Bang?” We are creatures accustomed to life in a three dimensional universe, and it is extraordinarily difficult to visualize our place in space. It is even harder to visualize that every place in space was once at the center of the Big Bang. (image credit: NASA/WMAP Science Team)
I have to admit that I’m still building my own personal perspective on the Universe, and every once in a while I still have a mental break through. This is hard. A complete understanding can’t come all at once.
But, being a blogger, I’m going to try and get you as far as I can in one posting.
An excellent starting point is, as always, the Cosmic Microwave Background (CMB). This diffuse microwave signal comes from everywhere and lies behind everything. It was formed at the moment the Universe cooled just enough for electrons to combine with atomic nuclei. Prior to that moment, photons couldn’t travel very far without being absorbed by something and then re-emitted with a new color and/or new direction. After that moment, those photons were set free to travel to us today. That moment was called recombination and it occurred roughly 380,000 years after the Big Bang.
Today, 13.7 +/- 0.2 billion years after the Big Bang, we are seeing CMB photons that originated in a sphere of space around the point that would eventually become the place of the Earth. Similarly, photons that originated at the point where the Earth is now located are possibly being observed by aliens at the location where the photons we are seeing originated. Thus, the CMB photons we see are nothing more than a sphere shaped sample of all the photons released during recombination; they are just one small section of the universe. Think of it this way: Imagine the universe as a giant liquid (it is so big we can’t see its edges to define its shape). A scuba diver hovering within the liquid might be able to illuminate the fluid within 10 feet of his head. The fluid beyond the illuminated sphere is still there. It just can never be seen.
Luckily, the universe isn’t a boring liquid, and the light we see isn’t reflecting off any farthest boring visible point. Unfortunately, the photons we see do come from the farthest visible surface of the universe. Luckily, because the universe was a plasma (which behaves loosely like a fluid), any waves propagating through the early universe will be visible to us. Unfortunately, the waves in the early universe have been stretched out to appearing all but flat with the expansion of the universe. Luckily, we have the technology to discern the 1 part in 10,000 remains of the waves.
And what is magical is this: we can use those waves to determine the shape of the universe. If you stand in a room and sing, you will hear your voice come back to you in different ways depending on the shape of the room. At a certain level, it is possible for good forensic scientists to listen to a recording and determine the shape of the room the recording was made within. At a certain level, it is also possible for good cosmologists to determine the shape of the universe based on the waves within the CMB. What we have learned is this: the geometry of the universe is Euclidean. This means parallel lines stay the same distance apart forever. We also know the universe is closed. That means that if a line starts at one point and keeps going for a very very very(!!!) long time, it will eventually get back to where it started, just like a line on the surface of a sphere or a torus.
In fact, a torus is a closed Euclidean shape. Two parallel lines on the surface will always stay the same distance apart and they will eventually circle back to their starting point. It is currently thought that our universe is best visualized as a 4 dimensional hyper-torus.
Here I have to admit, I get the geometry but I can’t actually visualize anything expanding from a singularity – a single point – into a donut.
But this I do understand – I am at the center of the universe. And so are you. And so is everything anyone will ever see with a telescope. At one moment – the first moment – the entire universe was a single point, and that point expanded into everything. Imagine a balloon that when empty is a single point. As you blow it up, the balloon expands. Where on the surface of the balloon is the center of balloon? Everywhere. We are on the surface of a multidimensional universe and every point was at the center. Every point. Even my point and your point.
But there are more issues I have to admit to struggling to comprehend. In the shadowlands at the edge of understanding theorists are looking for evidence of pockets of inflation that went at different rates, or perhaps that simply never stopped expanding. They are looking for evidence of Branes, and probing for variations in gravity.
The CMB is mankind’s first and last best hope for understanding our place in the universe.