Your right that no one can go back in time and see what it was like but your totally wrong that we can't have any idea about what the universe was like and where it is heading. To deny that is completely ignorant to what we have and are continuing to observe about our universe. Its the same with the earth. We can't go back to the beginning of the earth but we can sure as hell paint some kind of picture about what the early earth looked like based on our current knowledge about geology. There is tons of evidence left around for what the temperature was like in the past what kind of gases were present in the atmosphere.
The same applies to the universe, it can and is being tested. The cosmic microwave backround radiation provides pretty solid evidence that the universe expanded rapidly about 14 billion years ago. We can literally see what the early universe looked like by mapping this radiation because to look deep into space is to literally look into the past.
How can you seriously argue against this overwhelming evidence?
We can also try to simulate some of the conditions of the early universe and see if the experiment evidence matches observations about the universe. That is being done right now at the large hadron collider in geneva. We may quite literally see the laws of nature break down at super high temperatures and pressure, similar conditions to those of the early universe. Its not all just theorizing, theorizing comes first then experiment which proves or denies the theory and then the theory can be thrown out or improved upon.