First as a side note, I was always greatly amused by the "grand father" paradox which assumes that time travellers have this pressing need to whack their parents/grand parents (presumably they dont need to travel in time to achieve this unless these relatives are already dead in which case travelling in time to kill them seems a bit of ... overkill .... /ttiforum/images/graemlins/smile.gif).
But more seriously, I assume, that before human beings are able to travel in time (if ever) we would be able to send inanimated objects (since that is usually less complex) and before that some kind of signals (i.e information.. that is the least complex). Thats exactly the way we currently go about exploring space... first we send signals (and analyze those we receive), then probes/satellites and last of all humans (still waiting for someone to set foot on Mars).
This introduces the following potential paradox on which I would appreciate your comments.
So Bob and Bill have some kind of Apparatus allowing them to send information back in time. Bob and Bill are sitting in Bob's living room on Monday 10:00 and declare the following:
"On Wednesday at 11:00 we will send to ourselves a message including a timestamp of when it was sent that will reach us in this room at 10:05 today"
What happens at 10:05 on Monday ?
One of 3 things :
A. Bob and Bill do not receive a message
Then the Apparatus does not work as presumably if it did, they could at any day/time of their choice send a message back to Monday 10:05.
B. Bob and Bill do receive a message bearing the timestamp "Wednesday 11:00"
This introduces some interesting questions. First it would mean that simply stating an intent (I will send myself a message) immediately produces an effect (the message is received).
Second many things could happen by Wednesday (Bob and Bill forget to send the message, Bob and Bill are late sending the message, Bob and Bill meet an untimely death - so what then of the timestamp etc...) preventing or delaying the sending of the message. What happens then ? Does the message received on Monday "dematerialize" by Wednesday 11:00 if not sent by then ?
C. Bob and Bill do receive a message but its contents are somewhat or even enterily different from what they stated on Monday.
This example can be made more tricky .. Say Bob and Bill state
"On Wednesday at 11:00 we will send to ourselves a message including a timestamp of when it was sent that will reach us in this room at 10:05 today. The message we will send on Wednesday will contain none of the words included in the message we receive 5 minutes from now"
Or
"On Wednesday at 11:00 we will send to ourselves a message including a timestamp of when it was sent that should have reached us =but did not= in this room at 9:55 today. The message we will send on Wednesday will contain none of the words included in the message we receive"
You can imagine many other variations of this. Basically these paradoxes are based on the premise that you use the knowledge that you CAN send information back in time to plan some actions in the future which would affect your current present or past.
But more seriously, I assume, that before human beings are able to travel in time (if ever) we would be able to send inanimated objects (since that is usually less complex) and before that some kind of signals (i.e information.. that is the least complex). Thats exactly the way we currently go about exploring space... first we send signals (and analyze those we receive), then probes/satellites and last of all humans (still waiting for someone to set foot on Mars).
This introduces the following potential paradox on which I would appreciate your comments.
So Bob and Bill have some kind of Apparatus allowing them to send information back in time. Bob and Bill are sitting in Bob's living room on Monday 10:00 and declare the following:
"On Wednesday at 11:00 we will send to ourselves a message including a timestamp of when it was sent that will reach us in this room at 10:05 today"
What happens at 10:05 on Monday ?
One of 3 things :
A. Bob and Bill do not receive a message
Then the Apparatus does not work as presumably if it did, they could at any day/time of their choice send a message back to Monday 10:05.
B. Bob and Bill do receive a message bearing the timestamp "Wednesday 11:00"
This introduces some interesting questions. First it would mean that simply stating an intent (I will send myself a message) immediately produces an effect (the message is received).
Second many things could happen by Wednesday (Bob and Bill forget to send the message, Bob and Bill are late sending the message, Bob and Bill meet an untimely death - so what then of the timestamp etc...) preventing or delaying the sending of the message. What happens then ? Does the message received on Monday "dematerialize" by Wednesday 11:00 if not sent by then ?
C. Bob and Bill do receive a message but its contents are somewhat or even enterily different from what they stated on Monday.
This example can be made more tricky .. Say Bob and Bill state
"On Wednesday at 11:00 we will send to ourselves a message including a timestamp of when it was sent that will reach us in this room at 10:05 today. The message we will send on Wednesday will contain none of the words included in the message we receive 5 minutes from now"
Or
"On Wednesday at 11:00 we will send to ourselves a message including a timestamp of when it was sent that should have reached us =but did not= in this room at 9:55 today. The message we will send on Wednesday will contain none of the words included in the message we receive"
You can imagine many other variations of this. Basically these paradoxes are based on the premise that you use the knowledge that you CAN send information back in time to plan some actions in the future which would affect your current present or past.