I have a question about an expirement that i saw yesturday in my physics class. They were shooting electrons one at a time at a wall on a video. They watched it and it showed a wave pattern on the sheet and it said that even when one electron goes throught it still goes through both slits and so on. Now when they observed it though it behaved like it was solid matter like a marble that made a two slit pattern on the wall. Now why does the observer change the situation for the electron to act so differently. I asked my physics teacher and he said that it required a 400 lvl class and about three weeks. So basically he didnt know. I was wondering if any of you knew why this happened i dont need to understand it right now i just want to know how that happened that the observer changed it. Thankyou tell me if you need it to be clearer.