I searched the whole internet but couldn't find anything else than the standard rules/guidelines as to how to use the simple present for future events. I understand that when something is scheduled, e.g. 'The train arrives at 10am,' the simple present is being used. I moved from Germany to California and since I'm here I hear people use the simple present all the time for non-scheduled events in the future or things they think are facts. I'll give you three example sentences I came across in conversations with native speakers:
We were in a furniture store and I sat on a fluffy white seat, the ones that look like huge pillows, and the person I was with said:
'Can you imagine how dirty it gets over time?'
'Can you imagine how dirty it will get over time?'
In another situation, I changed the headlight bulbs of my fiancee's car with her brother and since I'm not really familiar with cars I asked him why I should avoid touching the bulbs and he said:
'The grease from your fingers will burn into the bulb and then it breaks'
'The grease from your fingers will burn into the bulb and then it will break.'
Then, last evening my fiancee had a really bad stomachache and she said:
'I hope it goes away overnight'
'I hope it will go away overnight.'
Is there an exception to the rule here or is it just colloquialism? If so, could someone elaborate on this?