Is the Universe Infinite?

A universe is a mysterious place. For millennia, humanity has looked to the skies and wondered just what was out there. It seems that space goes on forever, with black as far as the eye can see. But does it, in fact, go on forever, or is there an outer edge that we simply have not discovered yet? Now get ready, it’s time to ask the question, Is the Universe Infinite?

Is the Universe Infinite

   First, let’s discuss what we mean by infinite. An infinite universe doesn’t necessarily mean that it goes on forever at all times. It can refer to one that is expanding so continually that it never ends, constantly getting larger. Thus, if a universe can expand indefinitely with nothing to stop the expansion, it can be considered infinite.

What we actually observe?

In terms of what we can actually observe,  the observable universe is not infinite. The theory of relativity states that there are certain regions of the universe that we will never be able to see from Earth, where the expansion is faster than the speed of light. We can only see a universe with a radius of roughly 46 billion light years.
   However, it is pretty darn unlikely that the universe ends right where we can no longer observe it. It is even possible that it has no end at all!

Shape of the Universe

Before we can determine whether or not the universe is infinite,  we should first discuss the shape of the universe, as that is quite important in determining its limits.
   Thankfully, while we remain somewhat uncertain, there is more consensus as to the shape of the universe than its finiteness. To understand this, we should first go over the Density Parameter, which is represented with Omega. This is used as a good deal when determining the likely shape of the universe


Density Parameter

   The Density Parameter compares the average density of matter and energy in the universe, to the density at which the universe would only stop expanding after an infinite time. If the average density is higher than the critical density, then the universe will eventually collapse back, and if it’s lower, it will expand infinitely. Some believe that the density parameter is greater than one. In this view, the universe would have a Positive Curvature.
   This universe would be spherical in shape and is referred to as a closed universe. This is because gravity causes the expansion to slow eventually stop, before contracting back to a singularity. Others hold that the universe has a density of less than 1.

Infinite universe

   Here, the universe has negative curvature and would be classified as an open universe. In this case, since the actual density is lower than the critical density, gravity is unable to take over and stop the expansion, so it continues to expand forever. A universe with negative curvature would be infinite, as it would be continuously moving outwards and growing, forming a hyperbolic shape.           
   Finally, the majority of cosmologists subscribe to the view that the universe is flat, with a density parameter of 1. In this view, the universe could very well be infinite. A simply connected flat universe is isotropic and homogenous, meaning it’s the same everywhere. It would have always been infinite, and expansion increases the distance between objects as time goes on.
   Of these three, the flat universe is by far the most commonly held position, because as far as the most scientists are concerned, the density parameter of the universe is 1, or at least very very close to it.
   You can add up all the mass-energy in the universe, average it out, and divide it by the critical energy density. When this is done, using data obtained from the Wilkinson Microwave Anisotropy Probe and the Planck spacecraft, we find a density parameter of 1, plus or minus 0.02. It can also be measured geometrically, looking at angles across the universe, which finds that the density parameter is 1, plus or minus 0.12.
   However, just becuase it seems that the universe seems to be flat, that doesn’t mean that it is necessarily infinite.
   To demonstrate this, imagine the universe as a flat of paper that expands forever. This could be seen as the infinite model, where it can continue to expand infinitely, and has no definite end. However, if we were to imagine folding the paper into a cylinder, then joining the ends of the cylinder, we would have a flat, finite, universe, in a torus or donut shape. The multiple connections of this shape allow it to be finite, and the lack of true edges means that we are able to deal with it mathematically and conceptually.


What’s in Cosmological Terminology?

In cosmological terminology, this universe would be finite, but unbounded. This is not the only way in which our flat universe could be arranged. There are 18 known configurations. For example, it could take the shape of Klein bottles or Mobius strips, were traveling far enough in one direction brings you right back where you started. It’s important that these not have definite edges, as that tends to throw relatively for a loop.
   Unfortunately, however, in our current understanding of physics, there are no laws that predict or restrict the topology. So if we’re trying to decide the topology of the universe, your guess is just about as good as mine.
   And now we return to our question: Is the universe infinite? 
   Sadly, as of now, we just aren’t sure. We’re pretty sure the universe is flat, based on our current understanding of cosmology, but Science has yet to come to a consensus a to what kind of flat universe it is. It could be that it does, in fact, continue to expand for eternity, but it could be a more finite shape, like a torus. 

   We don’t know if the universe will eventually begin to collapse back on itself, or if it will continue to expand forever. As of now, we simply lack the information to come to a definite conclusion, so we will have to wait and see what science will come up with next.
   So, what’s your thought about the infinite universe, let me know in the comments.


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