Ujil,
How do you know for sure that space has no cause?
Ok. Lets define space again, its three dimensional extension where matter and energy interact. Now, its friday, we having fun after the long week, You and I go to a party together. Music is loud, you are taking shots or may be not, depends if you drink. We having good times, ladies are dancing and so are we. Now we take one more shot and I tell you bro, you are too close ( distance wise) to me and I need some space. Here, space we are talking about the distance. You and I are matters interacting so are stars, galaxies, energies and black holes. What keeps us apart is "space". You and I stand on earth, but earth is just rolling round and round in the space, it does not have a ground to hold ( gravitation force from sun, yes but if it was not there, it would still be rolling through space). The space here we are talking about is the distance between objects a.k.a Space. That distance or space is everywhere through out universe. Nobody has to create or there has to be cause. Now tell me, does there has to be cause to have space/distance between any objects.

How do you know for sure that space was always there?
Again, I am not sure what you think of space. Another example, there is an empty jar. How do you know its empty? Because it does not have nothing. How do you prove there is nothing? "Nothing" is just a name given for the incident when anything is not present. What cause nothing? nothing being there is the cause for nothing. Space is like a distance, in three dimension, where there is nothing, there is space.
Have you experienced by yourself?
Party example comes handy again.

Or do you have any authentic source which proves space has no cause?
When I say there is zero apple on the table, its like asking me to prove "zero apple in the table". First of all, there is not a apple to show you what apple looks like, and zero stands nada, none. So, I cannot prove you there is no apple on the table.

When you claim something, you also need to provide explanations.
Explained enough
You cannot just say space is always there.
Another question arise, why is space always there?
Because its space/ distance/ Dimension where you and I interact, Stars interact, energy interact, forces interact, universe exists.

Why something like empty void (space) wants to exist for itself and forever?
Let me laugh first. Why does nothing exists, why does zero exists. Nothing is just a name given for certain situation, so does zero means, When we say zero apples, where does zero exists. Zero means there is none apple. Its just an analogy. Space is there because its there. Why there is distance between sun and earth, well because they are far in distance, in space.
These are not an easy questions and I am not hoping answers from you because these question cannot be answered through your logical reasoning.
These questions are neither hard, either. Bro, You need to come out of cause and effect phenomena. Space is there because it was always there. Its not a object for you to have cause and effect. Its just a notation for three dimensional directions and time. If we did not call it space, we might call distance, or vacuum or anything.
This is where Vedas starts. Where quantum physics ends, Vedas starts
Ha ha ha. Bro if it was true, then all our courses would be vedas, we would be taught vedas, Nasa would use vedas, Tesla would use veda, So would Newton, So would the world.

Anyways, its nice discussion. Happy friday and enjoy bro. We will talk more.