Posts
Part II: The
Philosophical Approach to Time Travel: In other words “Ignoring the Laws of
Physics”
Say “Hi” to Granddad
There are essentially two ways
to deal with this subject, firstly in a general philosophical manner and
secondly in terms of pure physics and what we understand of the laws governing
our actions. While separating between philosophical and physics we will also
further divide between earth based time travel and space-based using elements
such as worm-holes and the associated physics such as Special Relativity. The
problem is that, ignoring the obvious
connection, we could easily descend down a rabbit hole of Carrollian
proportions. This discussion is in and of itself limited by time (the
allocation of it available to the author
without any contained time loops). We will first look at the issue of
time travel ignoring the possibilities as to whether or not it is actually
possible. Once we have made a
determination as to this possibility, we will then look at the actual physical
law and determine how they might support or restrict us. In essence we will
discuss the topic first and then the science (unless unavoidably necessary here
in Part II) will be discussed in Part III.
As mentioned earlier, we will first look at the
philosophical picture. In this scenario we essentially consider a scenario such
as described by Mr. H.G. Wells[1] where a single lone explorer
ventures back in time and then returns to his own time. For the initial
discussion we will concentrate on a single universe model, introducing the
multi-universe or alternative reality scenarios in relation to specific topics.
Essentially we will base the general discussion on an intrepid explorer setting
off through time (as against the pure science approach which Einsteinian
science supports and which takes place on a galactic basis). We will call this “Explorer
Time travel”
Explorer time travel works on the basis that we have
an individual, who through a device of
their own making (or indeed anybody else’s making), is able to transport themselves to a time
not otherwise achievable without their device.
We should perhaps firstly define time travel. There are many
definitions, often suiting specific discussions. For the purpose of this
document time travel is the movement through time at a direction or speed
different to the universe in which the traveller is normally operating. In
essence the time experience of the traveller should be out of synchronisation
relative to an otherwise external observer.
This is essentially the popular version or
Science-fiction approach to the subject and indeed the version which generates
the most discussion. It is where we begin, we'll deal with science-reality in
the next paper. “Eric the Explorer” (no relation to a certain copyrighted
character) is going to be our guinea-pig, experiencing all of the ups and downs
of time travel for our study. Life would be so much more simple, or at least
less complicated for Eric is he did not have to deal with the thorny issue of paradox.
As if life wasn’t already hard enough for Eric, there are a number of
paradoxes to deal with, some of which clash with the others. A basis for much of the discussion is the concept of Causation.
It should be noted at this stage that I will not be dealing with Backwards
Causation, this would prove just a little bit too much of a head-wreck.
Hey Gramps!
In simple terms, events, generally speaking, have causes.
Not only do events have causes but when time travel is involved we have
to consider external and personal time due to some of the paradoxical
situations thrown up. We will look at
some of those paradoxes while avoiding examples or explanations which involve
Time Lords[2] or other such travellers who
have the advantage of being able to use time and space as they wish. The
Grandfather Paradox[3] is perhaps the most famous of
these scenarios. In this paradox our brave Eric is heading back to meet one of
his ancestors (his granddad), but he is on a mission. Eric’s mission is to go
back in time and kill his grandfather before he meets Eric’s Granny (the
applicable one, not the other one.) Can Eric kill his grandfather? Is that even the question? In this scenario
we need to consider that if Eric kills his grandfather, the gentleman in
question will not have met grandmother, and, long story short, Eric would not
be born many years later. Of course if he was never born, he would not be going
back, hence the paradox, or is it? In more detail, the story is as follows,
Eric’s Grandfather died in the year 2000 after a long and eventful life. As
part of this life he met and married dear old granny. Now here is the problem, Granddad
was not a very nice person and through his actions many people suffered over
his long life, Eric included. Still suffering the effects of his grandfather’s
life Eric decides to back in time and assassinate his grandfather, if it works he is already
planning to use the same ability to go back and kill some of the most evil
people in history and in so-doing do the world the same type of favour he is
doing himself and his family. After researching his family tree, Eric learned
that gramps met granny at the harvest fair in their hometown back on July 5th
1940 when he was 19 years old, they courted and married just over two years
later, with the first off-spring introduced to the world about a year later.
(as this is a scenario and not a biography, we will say that this was their
only child, and of course one of Eric’s parents).
Eric is now back enjoying the July 1940 weather, which
if like current July weather (early 21st
century), then “enjoying” might well be generous. However; weather aside, he is
looking for the best way to liquidate his grandfather without implicating
himself or others. Eric decides to put a bomb in his grandfather’s car to
detonate while he is going about his business. Now here is the issue.
Did Eric succeed or not? In the “normal” timeline Eric
went to his grandfather’s funeral back in 2000, with his own father and with
his grandmother also at the funeral. A lot of bodies (living except for the
obvious one). Here is where the causal link comes in. Eric is a direct causal
link with his grandfather. So let’s look at the options.
a) Grandfather is killed in 1940,
preventing him from meeting his would-be future wife.
b) Grandfather survives by chance
c) Grandfather is not allowed to
die by virtue of the “Laws of nature” even if we don’t understand these laws.
d) Timelines are thrown out
completely and all kinds of random events have happened.
This paradox is a little like the old question of “Which
came first, the chicken or the egg?” as children we regard this as a silly non-answerable question, while as
adults once the question is looked at again and properly answered it is clear
that “the egg” is the correct answer (hint: take a long term – evolutionary
view). In this case, our first reaction is to say, “No it cannot happen because
Eric is alive.”
There is also the opposite conundrum, what if Eric
went back in time and introduced his grandparents to each other, causing a type
of predestination, in effect creating the present timeline rather than
disturbing or destroying it.
Looking at the paradox while trying to avoid deploying
the laws of physics. The simple fact is his ancestor survived until 2000
despite Eric’s best efforts so the time travel would seem to have failed. Robin
Le Poidevin[4] maintains that a time
traveller cannot change time and no matter what happens he will not
succeed. A gun misfires or missed,
Granddad bends down at the right time, Eric gets hit by a bus. Essentially the
laws of nature conspire to prevent time travel changing an existing causal
timeline.
The counter argument to this is that Eric did kill his
ancestor, Were is Eric now? Related to this is where there is no causal
relationship. Where a time traveller goes back in time to change an event. Like
the now clichéd “Kill Hitler” scenario. Here the killing of a young Hitler by
an unrelated person with no direct causal connection creates an alternative set
of issues. As there is no causal link,
will nature allow the time line to be changed, if so will it be a
limited change or one which spreads its branches throughout space time? Working
on the premise that it is allowed and Eric shot (or otherwise, killed) Hitler,
where are we now?. Apart from the various other changes to the time line is the
obvious one, Hitler is killed and in so doing, removes the need to go back and
Kill him and so the time travel never takes place. Does this revised time-line
remain in place or does the original time line stress back in some way and so
restore itself?
It would seem that the arguments for not being able to
alter existing timelines and the non-existence cases (either Eric does not
exist or the reason for the time travel no longer exists) have won the day with
no comparable hypothesis being offered to counteract these scenarios, until we
consider alternative realities or universes. There is a school of thought which
says we can deploy the “Many worlds Interpretation”[5] suggesting that all possible
alternative histories are real. Each history is an individual world. When Eric
travels back in time he not only travels back in time but also space, he
travels to a universe where the scenario he is about to live-out is possible,
namely he kills his grandfather (in that reality) and then returns home to his
own time and space. This allows grandfather to be eradicated with the
consequences as imagined, but all in another reality, Eric can go home safely
having killed (one of) his infinite number of grandfathers.
In essence the Grandfather/Ancestor Paradox while not
preventing time travel does seem to put a number of restrictions on one’s ability
to actually time travel; a key restriction being not to alter time lines in any
significant manner. This of course can give birth to an entirely new discussion
on the ramifications of an action into the future, where the causal
relationship alters a future scenario and indeed a scenario off into the
not-as-of-yet achieved future. Having visited and killed/not killed granddad,
what happens if we visit ourselves (let’s not advocate killing ourselves).
The Self Visitation Paradox
Ted Sider[6] describes a scenario
where the traveller travels back to
himself: “I travel back in time and stand in a room with my sitting
10-year-old self. I seem to be both sitting and standing, but how can that be?” Time (no pun intended) for Eric to do
some more travelling. Today is Tuesday (it actually is!) and Eric is heading
off to yesterday at 1.00pm when he was alone waiting for a lunch time pizza
delivery. He was sitting on a bench waiting for his Pizza. Eric now travels
back to yesterday and stands while his other younger and better looking self
sits waiting. It seems he can be both sitting and standing and there are a
number of possible reasons why. One of the more conceptual is Spatial
Location Relativism, this is where the two conditions are relativized to a
spacetime location, personal time or proper time. Proponents of this theory
consider that the locations of the sitting and standing are the essential
pieces of information. Yes Eric is sitting and Standing at the same time so in
essence doing two different actions at the one moment in history (one action
per moment being normal). The important fact is Eric is sitting in one place
and standing in another, at the same time. This approach requires that the time
traveller while fixing to an exact temporal location can have some lee-way in
the spatial location. So visiting yourself is fine as long as you don’t
necessarily inhabit the same spatial coordinates, temporal coordinates fine,
but spatial coordinates are tricky. Given that Eric was able to visit his ancestor
without being restricted to specific spatial coordinates we can assume the same
when visiting ourselves as a possibility.
All reasonably okay here, now
what happens if Eric goes back and rather than sharing time but different space
actually shares time and space. If the sitting and standing Eric are the one
person what happens? Endurantism,
roughly stated, is the view that material objects lack temporal extent and
persist through time by “enduring” – i.e., by being wholly present at
each moment of their existence. Perdurantism is the opposing view that
material objects persist by “perduring” – i.e., by being temporally extended
and having different temporal parts located at different times.[7] This is based on the
terms “endure”and “perdure”[8] If we take the resulting “single” Eric and
call him EricT we might want
to consider the parts of the whole. If
we see Eric1 as the sitting Eric while Eric 2 being the standing Eric. Differing spatial
parts of a person/object might have different characteristics or properties without there being a
contradiction. A spatial part of Eric may be standing while another is sitting.
The fact that may have two heads, four
legs etc. is immaterial. Markosian describes this as “a parallel endurantist
alternative to the perdurantist views”.
Let’s have another look at
these terms. Endurantism or enduring
might best be described as existance as we traditionally regard it. Eric endures through time, always being
himself but changing with time (naturally); he exists at all times (within the
sub-set of life) with his properties changing; while the perdurantist would say
the young and slender Eric and also, say, an older fatter and slightly balder
Eric that is perhaps 10 years older are temporal parts of Eric and that Eric
(or EricT ) is the combination, or aggregate of all his
temporal parts. In other words depending
on our view, the potential paradox of us visiting ourselves can be explained.
Personally I would consider myself an “Endurantist”.
On a basically psychological
level another question needs to be answered. The Brain, does it maintain the
modern Eric’s learnings and memories or does the brain revert back to the
younger state of being? An under
discussed but pertinent argument. If the perdurantist allows for EricT, this must include the brain and subsequent
brain activity. At first blush this may seem an issue but looking to Einstein’s
general relativity we can consider the person travelling as a single system
(biological system) with all the elements travelling at the same velocity and
so not altering. From a paradoxical
perspective the endurantist approach allows for two independently functioning
brains operating in different spatial coordinates. This gets more tricky for EricT who may in
actual fact have two brains, all-be-it not likely to be connected and probably
sufficiently independent to allow for a temporal mutual existence.
Considering the brain and
associated functions, we mentioned
memory earlier, an important discussion point is memory. When Eric travels back in time, will he have
the memories of current Eric or will he revert to the memories of his younger
self, as mentioned earlier there is an argument for him retaining memories in to the
past. Can e say the same for returning
to the future, if the mission is completed, Hitler or granddad dead, will Eric remember the mission when he
returns to the present time. On a simple chronological basis Eric should have
the memories of what he has just experienced, however as the general timeline
is removed can he have a specific set of contextual memories pertinent to his
actions. If this is the case we need also consider that he may remember the facts,
which necessitated the time travelling mission in the first place and in so
doing will Eric retain two sets of
mutually exclusive memories in relation to timeline altered events?
The Eternal Present
It is noticed that the
philosophical discussion essentially centres on our traveller going back in
time and not in to the future. There are a number of possibilities for this.
Some would argue that time (or indeed
space time) is like a river or more accurately a spillage or new spring sprouting
from a well. Consider us at the head of this new stream, this is the present,
we can with great difficulty and energy push ourselves back to a location where
the stream is younger/fresher and then revert to our position at the head of
the stream, however we cannot jump ahead in the stream because it does not
exist yet and so cannot be travelled to. This would essentially reflect the
author’s view.
Eternalists are those who believe that the past, present and future all exist,
while Presentists believe that only
the present, the here-and-now exists. You can see where this is going; if only
the present exists then no travel is possible. We have no issue conceptualising
the past or the future, but does that mean they exist, or do they cease to
exist being replaced by as new condition. This very passage of time rules out
the Nowhere Argument. After all if I, or you only exist for the smallest
quantum of present existance how will you be around to read the end of this
sentence.
So philosophically can we time
travel, well, being a philosophical question the answer is yes and no.
Looking at it logically and not seeing
noticeable chaos examples disjointed non
casual timelines around us (assuming that we would recognise such anomalies) it
is highly unlikely that Wellsian time travel in to the past is pssible.
Of course Einsteinian time
travel gives us General and Special relativity allowing time travel
at the right speed. This as we will see takes great amounts of energy and speed
(of light) with different types of time
travel possible under specific
relativities, but more of that in Part III…
[1] The Time Machine, Wells H.G, 1895
[2] Copyright (probably) British Broadcasting Corporation
[3] René Barjavel, Le Voyageur Imprudent (The Imprudent Traveller),
1943
[4] Travels in Four Dimensions. Oxford: Oxford University Press,
2005
[5] Hugh Everett, 1957
[6] Sider, T. 2001. Four Dimensionalism.
Oxford: Clarendon Press.
[7] Gilmore Cody; Time Travel, Coinciding
Objects and Persistence; Oxford Studies in Metaphysics Vol 3.
No comments:
Post a Comment