Tuesday, November 08, 2005

Grandfather Paradox

What I don't like about Lewis' paper is that he says that time travel can'toccur because you can't change the past. But why do you have to change thepast if you time travel? Isn't it feasible that someone just went to thepast, didn't do anything, didn't breathe, didn't move, but just observed.Then, he went back to the future. He time traveled and nothing changed. Whatdo you guys think?


Blogger mparent said...

But something would HAVE to change by necessity if the past were actually observed. By the mere fact that you are viewing the scene then some photons hit your eye that normally would have passed through that spot. Although this is a small change it is still a change. There is no way to observe the past without interacting with it in some way.
However, just observing should as you suggest should be possible as long as back in time you were actually there observing. If you weren't there observing in the past then your mere presence has caused a change.
The Grandfather Paradox is basically saying that you couldn't kill your grandfather because it would be inconsistent. You would have caused a change that couldn't have happened in the past. if it had then you wouldn't have been around to kill your grandfather in the first place.

2:59 PM  
Blogger Hawaii said...

It is possible to go back in time and "change" things. However, you must allow for pre-destination. Le Poidevin uses the example of WWII and the assassination of AD Ferdinand. If for some reason, the assassin would have missed if a time traveller had not bumped him, then the time traveller MUST travel through time. And he must also "change" the past. It was predestined though.

That's the only reason you can really believe that changing the past is consistent.

8:44 AM  
Blogger frankd23 said...

The actual lewis paper actually goes on to say that time travel can occur as long as your presence doesnt change the future. I saw a show called "Time Lords" and they had an astrophysicist named Igor Novikov on it. He proposed a "force" to prevent you from altering the past in such a way as to change the future. In Novikovs mind, what the hulk proposed would be allowed in time travel. I personally don't like the idea because of what mparent said. I don't think there would be a me back in 1955 just because i travel back there at some point. Its kind of like effect without the cause. The effect is me being back in time, which has already taken place, but the cause, me traveling to the past hasnt happened yet. I think if there is a force preserving the consistency of time, its a force not allowing time travel at all.

11:25 AM  
Blogger mparent said...

The problem with the assassination example is not so much that it must happen but that it is actually what happened. As I said merely being there would cause some changes on a microscopic level. Although we may not notice the changes for many years they would still be there.
I would like to note that I'm not saying that time travel isn't possible. I'm simply saying that it has to be consistent. If I travel from 2005 to 1955 then I had better have been there back in 1955 in actuality. So to sum up: You can't change the past and if you travel back in time you are going to follow the EXACT same sequence of actions that had actually occurred back then.

11:20 AM  
Blogger Nigel said...

This is a question. If time travel were possible, do scientists believe we could ever even approach having the technology capable of sending someone back in time? How would they go about building a "time machine"?

3:17 PM  
Blogger mparent said...

Nigel: I copied your question to a new post because I feel it should be under its own heading.

5:19 AM  
Blogger PVMunchy said...

What if while witnessing a crime, you black out or just can't remember what happened at all? Would this provide an opportunity for you future (or present) self to go back and be in your old body so that you can see what happened? You wouldn't be changing what happened since your original self can't remember anything from that period of time. You would just be observing in your own body and not moving since you are in shock or something. Your future (or present) self could go back to its time and remember what happened and all the details. I think this would get rid of the problem of making any small changes when you travel back.

6:35 AM  
Blogger Kermit said...

If you went back in time but couldn't change anything, does that mean that your mind/soul goes back but your body doesn't? In the witnessing of a crime example, would your consciousness just be transported to your body that was already in the situation? I think that is the only way you could time travel without changing the past physically, although you are now having different thoughts, so i guess it is changing something. there are so many paradoxes that can be associated with time travel (like things happening an infinate number of times, or events without causes) that it seems very unlikely to me that it is possible at all.

8:32 AM  
Blogger stet200 said...

After I have looked at the question that was posed earlier, can you travel back in time physically and not change the past? I think you really cannot. Ok this is what i am thinking, any one feel free to comment. There are 2 points in time, point A and point B. B is the future and A is the past. Ok, so now i am going to travel back to the past. Suppose that A and B are frozen at the point when I am traveling back. Now i am at point A and time is still frozen just at the moment. At that moment there is an unbalance. I would not be at B, the used to be present. Therefore I do not exist in the present. So therefore I would change the present and if you were to return back to the present I would not "exist". I would have died before the present, or something like that, but shortly I would not be a "object" in the present so therefore i would have never gotten to that point in time physically. In other words I do not exist in present anymore and i would never be able to do it ever again. Any one have any thoughts on this?

2:59 PM  

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