The Naked Scientists

The Naked Scientists Forum

Author Topic: If time travel is at all possible...  (Read 9916 times)

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
If time travel is at all possible...
« Reply #25 on: 12/08/2009 09:41:45 »
But, DB, it doesn't hold together and leads to insurmountable logical difficulties. It throws away the concept of causality for example. No backward time travel ideas can be "simply" explained (or even reasonably postulated) because it is probably not possible, at least not to any significant ealier time. It makes for amusing SciFi stories where the physics does not have to be strictly complied with.
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
If time travel is at all possible...
« Reply #26 on: 12/08/2009 10:38:58 »
But we don't know the physics of it.
 

Offline graham.d

  • Neilep Level Member
  • ******
  • Posts: 2208
    • View Profile
If time travel is at all possible...
« Reply #27 on: 12/08/2009 13:13:00 »
IMHO, to avoid causality and logical issues it has to be a parallel universe scenario. I'm afraid I have not studied the details, but, as I understand it, this does not fit with any of the models we have for the universe because of energy considerations. It is true we could try to postulate new physics to encompass what we would like to believe, and there have been arguments to put forward for such a view independent from the idea of time travel, but so far I don't think there have been any that are wholly self consistant.

As a SciFi fan I enjoy all the ideas that come up and can live with suspension of reality, including Dr Who's Tardis, Star Trek's matter tranportation, Faster than light travel, all aliens speaking English and hosts of other extrapolations. But interestingly, and being very nerdish, it annoyed me when Star Trek had the ship in a "geostationary orbit over the North Pole" or when in 2001 (and even in a recent movie) they didn't have low gravity on the moon once inside buildings. I guess its because I dont like something that is even inconsistant with the assumptions made within the self contained fictional scenario. Sad, isn't it :-)
 

Offline LeeE

  • Neilep Level Member
  • ******
  • Posts: 3382
    • View Profile
    • Spatial
If time travel is at all possible...
« Reply #28 on: 12/08/2009 19:38:40 »
I'm a great believer in the simplest explanation being the most likely. The simplest explanation in this case being what I said. It takes but 1 premise - that if you travel back from time B to time A, then from time B's perspective A->B happened the way it did & cannot be altered. Bifurcation & conservation of energy are irrelevant.

The premise that once something has happened it can't be changed doesn't work if time travel is allowable.  The fact that the time traveler didn't exist when time 'A' occurred, but then subsequently must exist there if he is able to travel back to arrive there changes the past and violates the premise.

Conversely, if the past cannot be changed then there is no scope for someone who wasn't already there to arrive there, meaning that time travel is impossible and the premise is redundant.

Actually, there is one way out of this, but it invokes infinite loops, which are even more problematic as you can't establish any start points and end up disappearing up your own fundament; the traveler cannot ever perform the journey for the first time.  If there was a first-time journey, then on that journey there would be no memory of having done so previously, but if the traveler's memory is to be the same on each trip through the loop, because the premise says that nothing must change, he must always remember doing the previous journey, thus precluding a first journey where he didn't.
« Last Edit: 12/08/2009 19:40:36 by LeeE »
 

Offline DoctorBeaver

  • Naked Science Forum GOD!
  • *******
  • Posts: 12656
  • Thanked: 3 times
  • A stitch in time would have confused Einstein.
    • View Profile
If time travel is at all possible...
« Reply #29 on: 12/08/2009 23:52:05 »
But he did exist at time A because he went back to it. He just hadn't been born yet.
 

lyner

  • Guest
If time travel is at all possible...
« Reply #30 on: 12/08/2009 23:56:04 »
? :-\
 

Offline Nizzle

  • Hero Member
  • *****
  • Posts: 964
  • Thanked: 1 times
  • Extropian by choice!
    • View Profile
    • Carnivorous Plants
If time travel is at all possible...
« Reply #31 on: 13/08/2009 10:49:20 »
Doctor Beaver,
IMO: Your thoughts that the past is written in stone and is unchangeable can only be true if the future is also already written in stone and unchangeable.
This is still within the laws of causality, however, mankind does sacrifice free will for it.
« Last Edit: 13/08/2009 10:51:45 by Nizzle »
 

Offline LeeE

  • Neilep Level Member
  • ******
  • Posts: 3382
    • View Profile
    • Spatial
If time travel is at all possible...
« Reply #32 on: 13/08/2009 14:51:24 »
But he did exist at time A because he went back to it. He just hadn't been born yet.

But this doesn't address the first-time issue.  Just as he can't ever make the journey for the first time, he can never be born for the first time, as the sequence of events that occur between time 'A' and time 'B' include his birth and cannot be altered.

Looking at it another way, it's impossible to count the number of times the journey is made because the total would increase with each journey through the loop.  The premise says that nothing can be different though, so the total can't change.
 

The Naked Scientists Forum

If time travel is at all possible...
« Reply #32 on: 13/08/2009 14:51:24 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length