I have come across many times were people think that there isn't going to be much room in Paradise, that if everyone is gathered together on the Day of Judgement- then that is too many people in one place. Even coming across what some Sikhs have stated (not about comparitive religion-but using what they have stated about the next world's room);-
http://www.realsikhism.com/index.php?subaction=showfull&id=1248308791&ucat=7
How do we know we are reborn? We take birth and we do die. Sikhism does believe in the existence of heaven and hell, however, heaven and hell are created to reward and punish, one will then take birth again until one merges in God. According to some religion, the soul either goes to heaven or hell after death and stays there. So, how are people and other animals being born on this Earth? Is God creating new souls?
If He is then no matter how big is heaven or hell it is going to be filled. If you consider a lake as heaven and think of drops of water being added to it as souls, then no matter how big the lake is, if no drops of water is leaving the lake, it is going to be filled some time in future. Our souls just ending in heaven or hell after death and God creating new soul doesn’t make sense. If God creates new souls, then why are children born with disabilities? Souls are born with disabilities because of the bad deeds they committed in their previous life. It is up to God if he sends the soul to hell to make it realize the consequences of its actions or be born and make it realize in its next life.
Allah has created the whole of this Universe, even thinking about this Solar System is vast, so many Earth worlds can fit into Jupiter, and so many between here to the Dwarf Planet Pluto. Then thinking that Allah has created so many solar systems, galaxies, it shouldn't be hard to see that there is so much "space". :D
But even still of course Allah is All-Mighty and he is the Creator of all the heavens and the earths (parallel worlds ie Jinn world). The angels we do not know their numbers, and frankly just at looking at the sizes of some Stars can be a lot to comprehend, here is a nice video (can fast forward to 0:40 seconds);
http://www.youtube.com/watch?v=g4iD-9GSW-0