I've felt for a long time there's a problem, but it was this rather patronising and condescending article in the Torygraph that got me going. I shouldn't have been surprised - along with "racist Islamo-Euro-phobia" and borderline-paedophilia pictures of hot young totty every time the A-level results come out, the Torygraph deals best in "patronising" and "condescending" - but I'd like to apologise to that Facebook friend for ranting a little bit on her profile. It wasn't about or at her but no-one likes ranting on their virtual doorstep.
Many people get their ideas about time travel from the wonderful film trilogy Back To The Future. I love the films, but sadly its theory of time travel is - just like that Grandfather Paradox - complete gubbins.
Let's take a scenario
Say I go back to the year 1910, kill someone - NOT my grandfather, let's call them Mr. X - then come back to just before I left in the first place. Sound confusing? Let's chronologise that shit!
June 1910 - Time machine appears. Man with strange clothes (Jez) steps out with a gun, shoots Mr. X dead. (Strange man is clearly a bastard.) Strange man (Jez) gets back in time machine, which disappears.
May 2010 - Jez (strange man) invents time machine. Chrome and shit. Looks awesome.
June 2010 - Another time machine appears next to the one Jez just invented. Another Jez steps out, about half an hour older. Jez waves to Jez, Jez waves back at Jez. Universe does not explode.
Jez (original Jez) picks up his gun (no idea where I got it from, I'm not into guns ... maybe I borrowed it from the NRA), gets into time machine (original time machine), sets it to 1910. Time machine disappears. New Jez sits down, has a scone.
...and that's that. There is nothing logically or scientifically impossible in the above sequence. Let's look at some details:
Mr. X never has any children. He doesn't have any children when he is shot in 1910 - maybe he wanted some in the future, but sadly, he is now dead. Mr. X has no descendents because he has been shot dead. There is no paradox with any descendents because he doesn't have any.
Jez meets himself. (Actually, I tell a lie, there is a problem - if the time machine is just a time machine, it would appear and reappear in exactly the same place, unless it had wheels like the Delorean in Back To The Future. Assuming it's not a moving vehicle it would have to teleport as well, or at least be on little wheels.) Back To The Future suggests that if you meet yourself, you could cause the whole universe to explode or melt or something. But aside from the whole "you can't change the past anyway" problem, there is a flaw with the BTTF logic: the human-centric angle! In the BTTF trilogy there is at least one occasion I can remember where Doc and/or Marty meets and interacts with himself/themselves from another time. The way they survive okay and don't blow up the universe (phew!) is by obscuring their identity, so their other self doesn't realise it's them. This suggests the universe actually cares about the conscious mind and awareness of individual human beings, so unless you're counting God or Fate as part of the science here, the concept is bogus.
In the scenario, Jez says hi to Jez, who then goes back and kills someone, comes back to 2010, and says hi to Jez. The event happens twice to Jez, but only once in reality. No worries.
The loop potential
Here's something - what if Jez (are you sick of my name yet? I am) went back in time with the OTHER time machine? The one that just appeared? This creates a loop. Jez didn't need to build a time machine in the first place, because he used the one that came from the past. Obviously this makes it logically impossible, but a loop with no origin/start has been used on a larger scale in many books and movies (e.g. the awesome original vampire series Necroscope by Brian Lumley), so just thought I'd mention :)
Grandson-on-Grandfather action (time porn?)
Let's try replaying the above scenario but different. Let's say Mr. X actually IS Jez's grandfather (Cecil - no really, that was his name), and that Jez tries to shoot him, but something goes wrong and he fails (obviously). Let's also make it 1930 so my grandfather has actually been born. Chronologise!
June 1930 - Time machine appears. Man in strange clothes (Jez) steps out with gun. Jez sees his grandfather Cecil, fires the gun but misses because he's a bad shot (seriously I've only ever fired an air rifle in Scouts, and a laser clay pigeon gun). Tries to fire again but gun misfires and burns his hand or something. Jez realises he is being a twat trying to shoot his own grandfather, gets back in time machine, which disappears.
June 1990 - As a young boy, Jez is told by Cecil how some magic silver box (chrome and shit etc.) appeared and some idiot tried to kill him. (Or not, I mean, it's not important if Jez does or doesn't know, I'm just saying the event was recorded/remembered at the time in 1930.)
June 2010 - Jez invents time machine (chrome blah blah) and for some reason goes batshit mental, deciding to go back and kill his own grandfather. Batshit mental a) because killing people is seriously rude, and b) actually impossible, because his grandfather is still alive in 2010, and so he can't have killed Cecil in 1930.
Okay so I didn't bother with getting Jez back to the present (no scones for attempted murderers) but the above is all you need. Let's think about it:
MAIN POINT: Don't look at it from Jez's point of view. Look at it from reality's point of view.
Okay, if you're watching a film or reading a book and Jez is the lead character and the story follows his life, it goes a) June 2010, Jez invents time machine, THEN b) June 1930, Jez shooting at grandfather. Your attention is focused around Jez being a free agent with all possibilities depending on his actions. Forget that! Eject the idea from your very brain.
It's a red herring. See it from reality's point of view: a) man tries to shoot other man and fails, then b) man invents time machine and gets in. He misses the shot like anyone else misses, and the gun backfires like guns sometimes have done throughout history. There are no special laws of physics, reality or causality that apply only to Jez that do not apply to Cecil, or anyone else there at the time in 1930; Jez is not a special case. Logically it is utterly impossible for Jez to kill his own grandfather, but this doesn't mean his grandfather a) has a magic shield, b) Mother Nature's got his back, c) bullets will bend around him like some 1930s Art Deco version of the Matrix. Jez simply does not kill his grandfather, no more, no less, full stop.
Parallel universes (are you kidding...)
So this is the parallel universes concept comes in. What I find frustrating is that it's not just the writers of BTTF who thought "hey, it's a film, we'll just bypass one bit of logic and BAM! Great story!" - there's actually scientists and clever thinkers who, in order to make killing your own grandfather possible, drag in the many-worlds parallel dimensions rubbish just so it makes sense.
Here's the standard theory on multiple dimensions/universes:
There is an infinite number of universes, one for each possible outcome of every event that could ever have occured. Many sci-fi stories like Sliders and Red Dwarf have just focused on the human events - it's a pretty boring story if the heroes jump into a dimension where there the Milky Way doesn't exist - but the theory accounts for each and every event that could happen to quantum sub-atomic particles. That's a LOT of events (hence the infinite number).
Now I don't much agree with this. I accept the idea that there could be a lot more dimensions that we know about - humans can only sense 3 dimensions (+ time), but there could be lots more. I'm not sure about String Theory - 11 dimensions? Why not 27, or a zillion? - but in general that's fine with me. I just don't really see why there has to be a universe/reality for each and every single quantum event that ever happened. I'm not a quantum physicist, but this is all theoretical, and it sounds far from obvious, let alone likely.
Back to time travel. In order to muck around with the past, the "branches" theory suggests that you can "change" an event in your own history by dimension-jumping to another reality where killing your grandfather actually happened.
This is poor logic and crap judgment. It's like someone tacked on the whole multiple realities thing as an afterthought to make it work. For instance, if the defining feature of this other universe - the only thing that makes it different from my home universe - is that I appear in 1930 and kill my grandfather, how do the sub-atomic particles make it happen? The infinite universes are based on the outcomes of events that can actually happen - whereas it would be absolutely, physically impossible for the particles to change shape into a time machine with me and my memories in it. Not just impossible like time travel is generally impossible, but actually, totally impossible.
I should bring this to a close.
There's a hell of a lot of logical errors in the history of time travel in sci-fi. (And since it hasn't been invented yet, sci-fi is pretty much the only place you ever find time travel.) Even great films like Twelve Monkeys (excellent FAQ here) which generally has the whole time travel stuff nailed (it all wraps up very neatly at the end) make errors with stuff like the radio transmitters in the teeth. Seriously, radio that talks through time? They would've known from the start that he pulls his teeth out and would never have chosen him for the mission. But this is a minor detail just like most errors are minor details. Nooooo problem.
My point - the Grandfather Paradox is junk. It's bunk. It's other words that rhyme with "unk" that mean "loada rubbish". The "branches" theory of time travel, that doesn't stack up either - it simply doesn't hold water.
I'm not really disputing the physics and concept of multiple universes based on quantum mechanics - I don't agree with it, but that's not the discussion here. Besides, most people when thinking about time travel aren't using quantum physics to back up their thought process - they actually think it is just the one universe, the same reality we're all talking about, and that you can muck around with the past like sketches in a sandpit when in actual fact the past has set like concrete.
Sure, I don't worry about it when I watch Back To The Future and Red Dwarf because they're fun and it's not a problem. But next time someone opens their mouth and says "man if I went back in time I'd try not to change anything my granny did so I still get born!", gently remind them that you read a blog and they're talking nonsense. And offer them a scone.