When considering the existence of the universe and our own existence which, as the cosmological history shows, looks to not matter at all in the existence of the universe, we may wonder how and from what all of this come?
The usual representation of the big bang theory invokes a creation which occurred mysteriously!
This is a hypothesis bound to a theory but the only established fact, is the existence of our mind, and therefore of ourselves, which implies in turn that of the universe, as we are part of it.
It is therefore from this established fact that our analysis must be exerted and not per anthropomorphic examples inspired by our life experience, based on our perception of space and time, as conceived, in this context, as immediate concepts of our mind.
The difficulty arises from the fact that general relativity, the theory ruling the modern cosmology, states that only spacetime, for which our understanding has no experience because its manifestation on our scale is imperceptible, has a physical meaning.
Let us recall that, however, as early as in 1907, Minkowski underlined that in special relativity, space as well as time have no physical reality and are reduced to being only shadows of spacetime which is the only physical reality! 
Elements of Plato’s philosophy: Essentialism
Essence is prior to existence.
Plato defines the essences or ideas which are the intelligible eternal and perfect forms, archetypes, and models of sensitive things which are represented by phenomena in our physical world as their unstable and imperfect images.
The phenomenology of physical entities and the related laws of nature makes sense and are ruled by the ideas.
The allegory of the cave Plato illustrates his arguments by describing a situation where prisoners in a cave only see the shadows, on the wall of this cave, of the outside world.
Can they imagine that these are just shadows of something more complex (ideas) and can they reconstruct them from the shadows or are they have no other choice that to consider those shadows as reality?
If a prisoner claims these shadows are the only reality in existence, is it possible to prove that he is wrong?
In this description, the cave represents the physical world where we live and the shadows are the phenomena that we see. The outside world is the perfect world of ideas.
The paradigm is what exemplifies a rule and can therefore serve as a model. With Plato, it has a pedagogical meaning: the paradigm is the “easy” object on which one is encouraged to train before exerting his sagacity on an object which look like to it but which is more “difficult”.
G. Bachelard  illustrates this by emphasizing that thought is essentially inductive, it reads the complex in the simple, the law in the example.
The notion of existence in philosophy experienced a fundamental boom thanks to Kierkegaard in the 19th century and then, in the 20th century, with Merleau-Ponty and Sartre, depending on where, unlike Plato, existence is prior to essence.
Existence cannot be deduced, it is observed, it is experienced: Sartre: “To exist is simply to be here. The existing ones appear, let themselves be met, but we can never deduce them”. The essence, then, is built in existence.
The success of the Big Bang model, assuming a creation of the universe, proved that claiming that “only the existence of the universe makes sense” is a breaking through hypothesis, not usually accepted.
A creation, in physics, is a singularity and as well as for our mind because one may wonder how something can emerge from nothing? Remember that the quantum vacuum is not nothing. An eternal universe does not solve the solution either, because eternity, which does not allow a point to be unambiguously located, is not also a physical concept.
Theories making the Big Bang emerge from something existing before are only postponing the problem of the existence of what was existing before .
All these hypotheses are based on an external vision of our universe and an external time and space in which it would be located. In fact, in relativity, time and space do not exist, because only spacetime, resulting from Einstein’s equation, exists.
As we have developed in the book, the spacetime defined by general relativity needs nothing other than itself to exist and is able to infer all the phenomenology that we see within the universe where we are and of which we are a part.
Existentialism then appears to be the most appropriate philosophy to describe our relationship with this universe.
 No doubt that he was inspired by Plato’s allegory of the cave.
 This is also true in general relativity.
 In his book « the new scientific spirit »
 A humoristic illustration of this kind of argument is provided by the story of the man who had a leek in its ear on weekdays and a banana on Sunday.