In trying to answer this question we must first determine whether beauty is made up of multiple cultural viewpoints that differ from one another, or if there is an inherent standard for beauty that transcends all cultures. For the most part, beauty remains in the eye of the beholder. Just like your sense of humor, different things appeal to different people. Beauty as a cultural standard is subjective and ever changing. This can be seen in the transition from contemporary to modern art, in the differences between eastern and western art styles, and in the changing of fashion over time.

Small side note: Not all art is meant to be beautiful. Art has the dual purpose of catching the eye, but also of conveying a message. This applies very much to the design collective Dada and Marcel Duchamp's piece Fountain (pictured above). The work of Dada was to create art that rejected all that art had previously stood for and to show how the perception of art had changed in previous years. Their goal was less to display the beauty of a factory-made piece of porcelain and more to prove a point that something can become art if it is declared so. This is an interesting discussion on it's own, but not the one I came to make today.
Despite all this, in the end, beauty remains a social constructive, albeit a standard that transcends viewpoints. How then, can two vastly different forms of art, such as a rock song and a piece of Mozart both be considered beautiful? It is here that we can break down some objective standards of beauty, specifically in art forms that have crossed the boundaries of time and culture.
Something to be taken into consideration is the technical difficulty of the piece. In essence, how hard it is to replicate. In this case, difficulty adds value. As humans, intricacy amazes us. This 'awe factor' also points back to God, his creation, and things we cannot understand that inspire our awe.
When we see something we consider beautiful it points us back to God, the true source of beauty. This then allows for an infinite spread of options that beauty can take form in, varying from genre, culture, time period, and medium. Even so, only God can be perfect and truly beautiful. He is Beauty and everything else can only be beautiful in their own capacity. This also means that everything has some intrinsic beauty. God is the Creator of all things and is beautiful; anything that he creates is beautiful in at least some way. Therefore, everything that exists, having some connection to God and His creation, then carries value and a standard of beauty.
It is true, however, that beauty can be distorted and warped. And we must be wary of this. Even so, just be existing, an object has some connection to God and his creation. Therefore, it has even just a smidgen of beauty, inherent just by it's existence. This can be applied to many things, from warped beauty that while dangerous and alluring has some redeemable qualities, to people and places that seem without hope.
By the same token, even if something is beautiful, we don't necessarily have to like it. Bringing us back to our comparison of the difference between classical music and classical rock. We only affirm beauty - we can't assign it. However, society can value certain forms of beauty over another. Therefore, each person may not appreciate certain beautiful things a much as another person. However, that does not diminish their inherent beauty.
Still, with all these differing standards of beauty, what can be considered beautiful? There is a message that I want to get across to each and every one of you reading this; You are beautiful! Yes, you! Have you ever thought about that? Have you ever said to yourself, “Yes, I am beautiful.”? I know it can be hard. Society likes to cram unattainable standards of beauty down our throats sometimes. But the truth is, you are beautiful! You are completely and totally unique - no one is exactly like you. And, most importantly, you are made by God and in His image! How cool is that?
So, the answer to my question is: What is beauty? It’s what each and every one of you are!
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Essay inspired by a discussion from the Upper Room Society.