Astro2110 – The Solar System

The Universe is expanding, and at an ever accelerating rate. What does this mean, though? If we consider the Big Bang theory, then all that ever did, currently does, or ever will exist in our Universe (physical or otherwise) was all held within an infinitesimally small point at the start of existence. So, with the expansion of this point into everything we know today, how can it still be expanding? As we know from the principle of mass conservation, mass can neither be created nor destroyed. In regards to the expansion of the Universe, though, we run into a bit of an interesting notion. For expansion to happen with only the matter that’s been here since the Big Bang implies that what is here now is being stretched, so to speak. This is similar, if we consider for a moment, a balloon; the physical makeup of the balloon never changes, but as air is blown into it (dark energy in the case of the Universe), that which was already present begins to stretch until the balloon cannot store anymore energy and simply burst. Thinking of the Universe, it’s hard to imagine that scenario happening since no physical matter, as we can tell, is being stretched. What has been noted, though, is that galaxies are moving apart from one another at an increasing rate and this is the prevailing evidence on why the Universe is still expanding. A possible explanation is that the fabric of space-time itself is stretching or potentially dark matter since we can’t see either of them. This would explain why we are not noting changes in observable matter stretching, but even so I feel that we would observe changes, if even minute, in gravitational fields that we observe.

Will the expansion last forever, though, is the large question at hand. Perhaps we already know what will happen if we take a moment to consider the life of a star; fusion at the core (adding energy), red giant (expansion), supernova (burst), and black hole (big crunch). The phase we’re in now is similar to that of the red giant phase since we are expanding and cooling down. Following this line of thought, we are approaching the point at which our Universe will begin to have a gravitational collapse. At that time, our Universe will probably burst out in the most magnificent explosion possible in our realm only to create the densest singularity point possible. This will absorb every bit of matter into itself until it is time for it all to explode outward once again, in an endless cycle.

When one looks at the great expanse of the Universe, they will see a mix of moons, planets, stars, and galaxies, but what about all of the open “space” in between these celestial bodies? Most are familiar with the fabric of space-time, which is best described by general relativity, as it illustrates in a logical fashion how gravity affects bodies and their movements through the Universe. However, what is mostly considered is actual matter which only accounts for roughly 5% of the Universe; what we should be looking to is dark matter when considering the curvature of space-time since it accounts for approximately 85% of the Universe (with the rest being accounted for by dark energy). Dark matter is a type of matter that cannot be seen, but that we know is there due to the gravitational effects it has on visible matter. When we look at how empty the Universe looks, it helps to have something to fill the void, so to speak. Also, as we’ve noted before with black holes, just because something is naked to the human eye doesn’t mean that it’s not there. I feel that a good analogy when considering matter versus dark matter is akin to looking at a piece of cotton candy; what we can see is the thin wisps of colored sugar, but the primary ingredient is air which we cannot see.

In considering dark matter as being uniform across the expanse of the Universe, it sheds some light on why we can still feel the effects of gravity and the curvature of the space-time fabric even in the “empty” zones between planets and even between galaxies. Currently, we have no way of proving the existence of dark matter except through theoretical equations. It may, unfortunately, be one of the great mysteries of the Universe that we may never have a chance to fully explore.