Hopefully, we all know by now that our thoughts, beliefs, desires, and emotions can affect our present view of ourselves and the world around us and in doing so, effect the future. But what about the past?  Does what we think now have effect the past?  
    Some studies done in quantum physics indicates that we can.  What we think or believe to be true can change the past.  But don't jump to the conclusion that you can change history by erasing Hitler, or bring someone back from the dead.  The studies seem to indicate that the past can be altered only up until it is first observed.  So when a tape is made of binary beeps indicating heads or tails, if the first person to listen to the tape is told to expect mostly heads, that is what she will hear.  And so will everyone else who listens to the tape after that no matter what they are told to expect.  Once it is observed it can't be changed, according to the scientists.  
    I think that it actually could change again, but it would be impossible today to do so.  What I think would have to happen, is that everyone who observed the results would have to have that memory erased from their mind.  I think if that happened the event would no longer exist, and the next person who listens to the tape will be like a new first.  I could be wrong though.  Some people believe that every thought is recorded and saved in something called the Akashic records.  If they are right, than once something is observed, it could never be erased.