I remember my mum telling me about this while growing up. Let me get this straight, did the prophet physically go into the sky and go to heaven? or was it a spiritual journey.
If it was physical journey someone had to have seen it.
You will see a varying degree of "understandings" on this issue... that logic-defying "miracles" (such as the alleged "Me'raj") seem to appeal to those who are into superstition rather than reality, you will get nowhere with your inquiry.