The Trouble With Time Online Version

8/6/2019 The Trouble With Time Online Version

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What Is Time Travel?

Time travel occurs when there is a discrepancy between thepassage of personal time (such as the time that passes on your watch, or

the time it takes your body to age) and external time (such as measuredby a universal clock, or time as it passes in the outside world).

So, if you sit in a time machine for three minutes of your personal

time, so that you’ve aged three minutes, then step out of the time machine

to find that you are one hundred years in the past, as measured by

external factors like newspapers and the period in history you have

arrived in, then you have time travelled.

Is time travel physically possible?

The simple answer is yes - the more realistic answer is maybe.

Physically possible is one thing, but logically possible is another, andtime travel must be both if it is to ever exist.

ForwardsThere is no question that forwards time travel is possible.

Experiments in time dilation have proven this, and it is something thatyou’ll probably recognise from many movies. A space traveller going

close to the speed of light will return to Earth and find that he has barely

aged at all, but his loved ones have advanced in many more years than

him. This is a form of forwards time travel, and experiments with clockshave confirmed it to be possible.

In Fiction

This is one of the most common mistakes in fiction. People fly all

over the universe at speeds that would cause extreme time dilation, and

yet there is never any discrepancy in their aging compared to those they



leave behind. This is so common that no one will ever question it, so you

could easily get away with ignoring it.

However if you want to be a little more pedantic with your realism,it would be easy to explain away logically. Maybe people travel using

wormholes, which is like taking a short cut with no need for insanespeeds. Or maybe there is a network o f teleportation devices. This could

even help with world building – is there an official network monitored by

whoever is in charge of the universe? If so, is there also an undergroundnetwork of teleportation devices used by people who want to move

around unmonitored?

If you do wish to take time dilation into account, it could also havean interesting effect on your world. Perhaps you wish to move time

forward – this is one way.

The movie Voices of a Distant Star follows the relationship of two

people as time dilation pulls them further apart from each other. It’s a

poignant and sad story, and just one example of how time can pull a story

in unexpected directions.



BackwardsBackwards time travel is a much more

complicated matter, but in terms of physical possibility at least, both the

theories of special relativity and

quantum physics support backwards

time travel.

How Could You Travel Back In Time?

Closed Time-like Curves

Closed time-like curves (CTCs) are one potential means by which

backwards time travel could be achieved. Closed time curves are a

phenomenon where heavy gravity curves space-time so that it loops back upon itself, creating a path that ends in the past.

We are three dimensional beings existing in four dimensional

space-time. Space-time is made up of points that represent things that

happen at specific times and places. Each individual will have a life

made up of a series of these points, all connected so that in space-time

one life will appear to be a long twisting worm. The tip of the worm is

your birth and the end of the worm is your death. Einstein called this line

a worldline and predicted that it can be warped by very strong

gravitational influences, such as a black hole.

This warping can twist the line back upon itself – making it possible to

journey from one point on the line to another that it was not previously

connected to. This means that according to special relativity, closed

time-like curves could naturally exist in the universe, and if we ever findone, we may be able to use it to travel back to the past.



Wormholes

Wormholes are another possibility. They are not just the stuff of movies and books, but rather have a developing scientific framework

behind them. Wormholes involve two entirely different points in space-

time being connected, and research suggests that traversable wormholes

may exist.

What of the Time Machine?The problem that arises with both wormholes and CTCs is how

exactly we would travel through them. As Dave Goldberg explains,

‘travelling through time would be much like travelling through a tunnel in

space—in which case you'd need both an entrance and an exit. As a time

traveller, you can't visit an era unless there's already a time machine when

you get there—an off-ramp.’i

So the problem is not merely inventing a

machine that will safely carry us through the CTC or wormhole, but also

the fact that you won’t be able to travel to any time before it wasinvented. This doesn’t mean time travel isn’t possible – it just limits

when you can go, which is a bit less fun.

In Fiction

In the fiction of time travel methods, you can take science and add

a little imagination to create a solid foundation for time travel in your

story.



Perhaps closed time-like curves require the use of a time machine

to traverse – or perhaps they are simply strange pockets that can sweep

you off to a different place or time. There are many urban legends aboutareas where people simply disappear – the Benuda Triangle being the

most commonly known. CTC’s could be one explanation for this.

In quantum physics there is a theory that suggests the possibility

that pockets of space could exist where time actually moves backwards.If we were to encounter such a pocket, the people living in it would not

even be aware that their sense of time was strange. However, their

history would be our future, and visa versa.

Some questions you could ask when writing a story that includes

wormholes could be:

• Can the wormhole be used for travel to different times,

places or dimensions – or all three?

• Is the wormhole stable? Is it dangerous to travel through?

• What kind of technology is needed to traverse the

wormhole?

• What happens if it closes? People could be trapped on one

side or the other, with no hope of ever finding their way back home.

• Is travel through the wormhole regulated? By whom?



Is Time Travel Logically Possible?Classical physics is deterministic and therefore holds that the past

cannot be changed. The Novikov self-consistency principle supports thisby stating that any event that will cause a paradox or inconsistency in the

past has a zero chance of possibility. That is, if it will cause a paradox or

change the past, it is impossible.ii

Can you change the past?This is one of the most commonly held assumptions about time

travel. If you go back in time and change even the slightest thing, the

butterfly effect will cause a chain reaction that drastically alters the

course of history. The time you originally left will not be the one you

come back to. However, this very concept is the reason the possibility of

time travel remains in dispute.

The reason for this is that if you can change the past, you can

potentially create contradictions that violate the laws of physics – suchcontradictions cannot exist, and therefore, the argument goes, time travel

is not possible.

The Grandfather Paradox

The best example to highlight the problems caused by

contradictions is the Grandfather Paradox. The grandfather paradox says

that if time travel is possible, then it would be possible for a person to go

back in time and kill their own grandfather before he had children. If hedid not have children, then that persons parents would not have been born

and therefore could not have had the child who went back in time to kill

the grandfather. For the person to be alive to go back and kill the

grandfather, he could not have been killed, and yet logically there is noreason he can’t be.

Therefore for time travel to be possible, the grandfather had to

have both been killed and also not been killed. This is a paradox and it is

contradictions like these that potentially forbid time travel.



The Resolution

Some claim that time travel is possible on the basis that the past

cannot be changed. The most persuasive argument for this theory comesfrom David Lewis who in his essay ‘sdklg‘ attempts to resolve theparadoxes involved in time travel. The one relevant to this discussion is

of course the grandfather paradox, and his resolution is widely quoted.

Lewis approaches his resolution by redefining his use of the word ‘can.’

While the time traveller by logical means can kill their grandfather in thesense that they have the ability, skill and opportunity, if you look at a

wider context and the fact that they are a descendant of the grandfather,

they also can’t kill him.

This is much easier to understand when explained as part of a

situation that occurs without time travel. A basketball player can, in the

normal sense of the word, throw the ball through the hoop based on their

training and skills. However, this doesn’t mean they always will. They

might trip, they might misshoot, someone in the crowd might distract

them. So in the wider context, the basketballer can shoot the goal butthere are many factors that could cause him to fail.

Now look back at the time traveller. Even before they go back, theattempt to kill the grandfather has already been made as it occurred in thepast – it has already happened in external time. This is important to

remember. The traveller is not going back to a past from which they

were previously absent – it is the past so they were always a part of it.

The time traveller tried to kill their grandfather, and something stopped

them. The mere fact that they are alive in the present means that they hadalready failed in the past. The failure is pre-existing and thus becomes a

factor as to why the time traveller can’t kill the grandfather.

This overall context contributes to what the time traveller can do.Essentially, the time traveller can kill their grandfather, but they didn’t

due to some coincidence stopping them, and so in actuality they can’t.

Lewis puts forth the proposition that such coincidences will always stop

changes from occurring in the past. Lewis’s theory has recently been

supported by Seth Lloyd, who showed through experiments with photonsthat via the process of postselection, ‘the laws of probability would skew

toward preventing the (paradox) from taking place, so anything that could

go wrong in your attempt to kill your grandfather most likely would

(Clark 2010).’. So quantum mechanics agrees with Lewis.



Backwards CausalityChanging the past is different to causing something in the past to

happen. Causing the past is logically possible.Say you have a photo of your grandmother in a blue sweater. You go

back in time to the day the photo was taken and see that she has a white

sweater laid out on the bed. You accidentally spill juice on the white

sweater, and open the cupboard to find something to replace it, finding a

blue sweater and placing it on the bed. The grandmother finds the bluesweater and wears it instead.

The past has not changed, as the picture always showed her

wearing the blue sweater, however you now know that it was youtravelling to the past that caused her to wear the blue sweater. This is

called backwards causality. It seems strange, but contains no

contradiction and is therefore logically possible.

In Fiction

There are lots of movies and books that get this right, and lots that

don’t. Some that do include:

The Terminator

This gets it right because Rhys issent back to protect Sarah and ensure the

future happens – not change it. The

terminator really cannot win. In some

ways the inability to change the past could

make fiction predictable, however thiswill not be the case in the hands of a

skilled writer. The ending to The

Terminator might be a victory in terms of

Sarah being saved and John beingconceived - but it’s a sad ending

nonetheless.



The plot of 12 Monkeys is consistent when we apply Lewis’s idea

of the distinction between personal and external time. When James is a

boy, he sees a man get shot at an airport, which recurs as a dreamthroughout the movie, and at the end we realise he is witnessing himself

be shot as an older man. It is logically possible he can die at a later stagein his personal time, even if it is earlier in external time that the shooting

occurred. Another consistency is the insistence of the scientists that send

James back that the past cannot be changed. Their goal is to obtain asample of the virus that will help them study it in the future, not change

history by preventing the virus from occurring.

Lewis points out that a key factor in determining the linear natureof personal time is our own memories and sense of personal progression.

In 12 Monkeys time travel has a dangerous effect on the human mind.

The trip completely destabilises James and when faced with psychiatrists

in the past who say he’s crazy, he starts to believe them. The mind has a

tendency to doubt things that don’t seem logical, and 12 Monkeys points

out (in an exaggerated way, as James was already quite unstable) the fact

that our sense of personal continuity is not quite so reliable as Lewis

suggests. James makes the observation that while the past never changes,

we do, so our perception of it does and that’s why it seems different

sometimes.

12 Monkeys inherently understands the complexities of time traveland that the past cannot be changed, and yet plays with our ideas of

perception through James’s unstable mental state. It seems to embody theidea that if time travel existed, the world would be a very strange place

indeed.



The MultiverseMany physicists adhere to the theory that

our universe is just one of many. This theoryavoids the paradoxes incurred in backwards

time travel because the events occur in an

alternative universe where changes cannot

affect the original. The universe branches off

into a new timeline – in the old one yourgrandfather is still alive but you are now absent,

having moved to the new timeline where there

is a dead grandfather and no parallel self – as in

that universe you were never born.

This allows the possibility of changing the past, however the many

worlds theory has its flaws, and when looked at more closely, does not

differ significantly enough in its resolution of the paradoxes to warrant

the theory being a necessity of the possibility of time travel. For more

information see the article Time Travel and the Multiverse at

www.sentientonline.net.

In Fiction

In most fiction, it is safe to assume a single world theory and

therefore to avoid changing the past. If you’d like to use the theory of the

multiverse, however, it would be best to explain it – even a singlesentence can be enough to put things into context and make your story

consistent with scientific principles. There are a few things to keep in

mind though.

• Don’t make things too easy for your characters. Sure they

might be able to change anything they want, but this is bound tohave complications. The Butterfly Effect is a well known

concept where one tiny change can have far reaching

consequences. If characters set such a series of events in

motion, it might not be so easy to fix it. When every littlechange splits off into a new dimension, it might be impossible

to ever get things back to their original state again.

http://www.sentientonline.net/





RetrocausalityRecent experiments in quantum physics suggest that a process

caused retrocausality exists. This involves getting particles to follow aspecific trajectory, then afterwards telling them to take another and

watching as the past seemingly changes, as they then appear in the

destination of the second trajectory instead of the first. This potentially

involves not merely backwards causality, but actually changing the past.

It’s quite hard to get your head around how such a process actuallyworks. I’d recommend reading the original article here:

http://www.newscientist.com/article/mg19125710.900-whats-done-

is-done133-or-is-it.html

Keep in mind though that more experiments are needed beforeserious conclusions are drawn, especially because this theory directly

contradicts the postselection experiments mentioned earlier. But if it is

verified, what will this tell us about our world? Are we one of many after

all?

http://www.newscientist.com/article/mg19125710.900-whats-done-is-done133-or-is-it.html







Causal loopsCausal loops are strange and interesting side effects of time travel.

They are circular patterns that appear to have no beginning, and caninvolve both objects and knowledge.

Knowledge based causal loops can be found in many works of

science fiction. A recent rendering involves Scotty’s equation for

transwarp beaming in the 2009 Star Trek movie. Future Spock visits thepresent Scotty, who is working on the idea but hasn’t cracked it. Spock

gives him the completed equation knowing Scotty was the one who

discovered it, and so Scotty is credited with its invention. This is

consistent, and yet at no point in the timeline did Scotty ever actuallywrite the equation – so where did it come from? This is known as the

Knowledge Paradox, but it is one that while hard to accept, does not

appear to violate either the laws of physics or of logic.

An example of an object being stuck in a causal loop is similar.

Take a diamond that you found in your house under a floorboard. Go

back in time, and place the diamond in the same location under the

floorboard, so that when enough time passes, it’s there for you to find in

the future, to take back into the past. This results in a causal loop. Just

like the time machine blueprints, the diamond has no origin. It didn’tcome from anywhere, just like the knowledge didn’t come from

anywhere or anyone.

In terms of formal logic, this is not a paradox. There is nothing tobe identified in the loop that contradicts any other part of the loop: it’s all

perfectly consistent. While it may seem odd to suppose that information

or objects can spontaneously appear out of nowhere as a result of time

travel, nothing in physics or logic strictly forbids this. Strange as it may

be, it is entirely possible - if time travel is at all.



In Fiction

Futurama’s character Fry realises he is his own grandfather – thisis a causal loop and entirely possible, and a very good example of the fun

you can have with them.



Locating the PresentTime travel involves a person or object travelling forwards or

backwards along a timeline, so that when they reach their destinationthere is a discrepancy between how much of their personal time (for

example, the time that has passed on their watch) has passed, and how

much time has actually passed in the external sequence of events. This

means that in order for it to be possible for people to travel from now to

the future, or the future to now, the future must have already happened –otherwise there would be no future to travel to. But what does this

imply?

It depends on if time is a line, or circular, or something elseentirely, but essentially it gives the impression that if the future has

already passed, indeed extending into a potential infinity, that all times

must exist simultaneously. Otherwise we could not travel between them,

we could not travel to any past if the past ceased to exist once it was done

with. Likewise, we could not travel to the future if it does not yet exist,

and travellers from the future would have no future to come from. Time

would have to be continuous, and therefore, the present as we understand

it either does not exist now, or conversely, exists in every moment

possible from the perspective of personal context, making it almost

redundant.

Therefore, while it is a common assumption that the present is

‘now’ - that this is the point that history has reached as it unfolds - the

possibility of time travel would imply that this is not true. We are but onepart of a timeline that stretches endlessly into the past and present. If

looked at from this perspective, there really is no present outside of

personal time. Are we reliving old events, or stuck in some endless

circular process of existence? If every moment always exists, no moment

we live ever really ends (which corresponds to the idea that time iscircular). Thought about in this way, it is hard to place existence in any

real context.



In Fiction

It is certainly a popular concept in fantasy writing, but the idea of

circular time even has its place in science fiction – where the Big Bang

becomes the Big Crunch in a never ending loop.



In ConclusionTime travel is a complex subject that tends to hurt if you think

about it too much. The reality is both simpler and more complex thanwhat we have seen in movies and books, some of which get it right, most

of which don’t. It involves science, philosophy and horribly complicated

arguments about free will, but things are looking promising.

So it wouldn’t hurt to consider the practical nature of time travel

when it comes to writing fiction – because it never hurts to include a little

science in our stories. It can be inspiring in many ways. For example,

think about this: if time travel was only possible if you lost some degree

of your free will, would it be worth it? Not that the universe cares whatwe think. It’s either possible or it’s not, and when we eventually find out

we’ll have to deal with the consequences, whatever they might be. These

are the sort of issues that can come into play when dealing with time

travel in fiction.



Everyday Travel

Everyday travel times are useful for writers, so as it fits with mytheme of time, I have collected a variety of resources that help calculate

travels times for all different modes of travel.

Travel TimesThis amazingly useful table comes from Fallon Friday on The

Voyager Blog. The original post can be found here:http://voyagerblog.com.au/2008/09/12/fallon-friday-the-realities-of-

travel-time-as-opposed-to-time-travel/

The time it takes to travel 100 miles

(160 km)

Days by horse 2

Days by war horse 3

Days on foot carrying a pack 10

Days on foot across rugged terrain 7Days by wagon 5

Days by oared galley 3

Days by sailed galley 2

http://voyagerblog.com.au/2008/09/12/fallon-friday-the-realities-of-travel-time-as-opposed-to-time-travel/







Horses

Readers can be very touchy about the correct portrayal of horses infiction. Susan F. Craft has put together the very helpful Equestrian

Writer’s Guide, which can be found at

http://www.lrgaf.org/guide/writers-guide.htm. She goes into a wealth of detail, and provides this handy table on travel times.

Gait or Pace

Walk – 3 to 5 mph (four beat movement or gait)

Trot – 8 to 10 mph (two beat movement)Canter – 15 mph (three beat movement)Gallop – 25 to 30 mph (A two-beat stride during which all four legs are

off the ground simultaneously. This is a four-beat movement)

For how long a horse can keep this up for, check out her site.

Do these travel times apply to unicorns too?

That’s probably up to you.

http://www.lrgaf.org/guide/writers-guide.htm





Space TravelThe time it takes to travel

through space depends entirelyon the means of travel – and it issafe to assume that most modes

of travel in science fiction have

yet to be invented. This gives

you a lot of freedom.

However if you’d like to

know how long it takes to travel

through space using existingmethods, Jonathan Oakfrey has provided these calculations on his

website, locat4ed here: http://www.thurb.com/space.htm

He explains how he came to his calculations:

‘I've converted astronomical distances into hypothetical travel times, reckoning that

a car goes at about 100 kph, and the Apollo missions took four days to reach the moon, which

works out to about 4,000 kph. The speed of light (1,079,252,849 kph) is a very long way

beyond anything we can achieve today.’

Journey By car By Apollo Lightspeed

Leave Earth's atmosphere 11 hours 17 minutes -

Earth to Moon 5 months 4 days 1 second

Earth to Mars (at nearest) 63 years 2 years 3 minutes

Earth to Sun 171 years 4 years 8 minutes

Earth to Neptune (at nearest) 4,920 years 123 years 4 hours

Earth to nearest star(Proxima Centauri)

46,000,000 years 1,000,000 years 4 years

Earth to centre of galaxy 300,000,000,000

years

8,000,000,000

years

30,000 years

Earth to Andromeda galaxy don't even think about it 2,000,000years

http://www.thurb.com/space.htm




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