Yes "I believe" is invalid because your beliefs have no proof to them. There is proof that space exists. There has been proof that it exists for hundreds of years. Where do Meteors come from? How do you explain something falling out of the sky if there is nothing beyond our sky?
And Math is as real as Science as far as your argument is concerned. Math is made of nothing but theories and algorithms that change as often as science does until it cannot be improved upon. Math makes up science as a whole. Since math makes up science since science is fake, so is math.
Yes Science is about questioning accepted truths until they cannot be questioned. When you cannot come up with a valid question, then the theories are proven as facts. You cannot question if space exists. Your only reason for saying it doesn't is "I believe" in which case your beliefs are wrong because it exists, it has extensive proof that it exists as well as phenomenon that happen ever so often out there that effects the planet as a whole.
Space exists. There is no one that questions whether or not it exists with graduate degrees or work is specific fields. You cannot even disprove that it does exist outside of "I believe" so your argument holds no valid points. All you are going to do is blindly disregard everything put in front of you because you don't want to believe it.