> For instance, you send a message back to your collegue to buy a stock yesterday, and you haven't seen him since last Tuesday. So nothing weird would have to h

> For instance, you send a message back to your collegue to buy a stock yesterday, and you haven't seen him since last Tuesday. So nothing weird would have to happen to achieve consistency. Presumably your friend bought the stock, knew not to tell you until tomorrow to give you time to have sent that back to him. If the colleague tried to tell you earlier, something would stop him - because obviously he wasn't able to before you sent the message. I just don’t see how this works in the extremely simple case where you send the message to your past self. Using the colleague just tries to sidestep this. What physically happens if you attempt to send a message to yourself that you don’t remember receiving in your past? Does the system just consistently malfunction? Does it turn out that you had an accident between receiving and sending that caused memory loss?