1) You could not influence the past in any way. This isn't a rule you have to follow..you are unable to influence the past.
2) You will be completely undetectable by anyone in the past. You have no mass, no ability to influence objects. Like a ghost, just able to see the past unfold.
3) You can travel anywhere in the past, at any speed. You can replay a specific moment over and over again if you like. But you are only able to observe, not touch, influence, or be detectable in any way.
The question is, if you went back 100 years and watched a day in a city go buy...and you repeated that day 1,000 times...would it ever change? No.
Every person would behave exactly the same way every time. Every time, everything would unfold the same way. Every decision would be the same, every action would be the same.
But why wouldn't the day be different every time you went into the past to see that same day unfold? Why would it be the same?
Don't the people you observe have free will? Can't they decide differently than they did before?
The problem is, the past has only one path....and it is going to be the same no matter how you observe it, how many times you go back.
So....what is the difference between the past and the future? You can see the past, but you cannot see the future. The path that the universe took in the past, is knowable.
Why isn't the future knowable just like the past? Because it depends on where we were in the time stream when we decided to go back into our past.
Think about this...if a person in 1,000 years had a time machine and they could observe an incident or event somewhere on Earth in their past...let's say today...our present, their past....would any thing we do today change? No. Remember, we are just part of their past. They have already seen what happened today, tomorrow, the next day. It's just that we have not.
So my question is...if nothing changes in their past, how can we have free will? If we are going to behave a certain way...and behave that same way, no matter how many times a time traveler from our future observes us....how are we actually choosing our own actions and thoughts?