How to Beat The Zombie Apocalypse by Time Travel

 

How to Beat The Zombie Apocalypse by Time Travel

 

Part I

The Zombie

We only have to turn on the TV any night (usually after 9.00pm) to see that the world is being ravaged by various forms of zombies and mutant dead infected people who just won’t lie-down and die. Of course we’ve all been told over the years how to terminate a zombie. Whatever the advice the general method is the same, separate the brain from the rest of the head. This is of course a traditional cure for many types of undeadism; from vampires to zombies and other creatures but is more easily said than done.

All of the advice we receive is usually focused on the tactical situation of defeating an immediate zombie challenge while what we will attempt to do with this paper is look to this danger and how we might overcome it from a strategic level. When we look at plans such as those put forward by the US Army[1] we still see how to deal with the impact of the zombie, indeed the name of the plan says it all, it looks to dealing with “zombie dominance”. Even the CDC[2] (Centers of Disease Control and Prevention), when looking to deal with the zombie treat looks to the emergency situation where the zombies are already with and infecting people.

The greatest challenge with dealing with zombie hordes (the collective noun for a group of zombies), is not the danger of dealing with them one, or more, at a time. This situation is inherently dangerous with usually a far greater chance of permanent death than survival. As with any close quarter battle, you will need to know your enemy, something which is easy enough in this case, in so far as that they will be coming at you trying to eat you, we know they are not going to be planning any big pincer movements or complicated ways of confusing us. Thus far the evolution of the zombie has not repeatedly produced a generation which has learned to think and adapt. This is of course significant because we are dealing with a static enemy and not one which adapts and changes generally.[3] Knowing how our enemy thinks (or more correctly, does not think) helps us to deal with them. Our ability to create and deploy an array of defences and weaponry also improves our chances.

So we are okay there. We should also pick the location of our fights, this is something we can have some influence over, but it is where do not have a place of choice that we can run into difficulty. The biggest challenge is with the horde mentality. Zombies general like to group together and travel in packs.

Evidence gathered to-date indicates that zombies are pack creatures who normally group together to survive and hunt for food. While the grouping together for survival is a useful trait, it is quite annoying to humans who gather in small groups and find themselves outnumbered. Where as a human when in danger will think about running-the-hell away, a zombie will just keep going. It is the attrition caused by such a practice that kills so many humans. We usually realise that as a result of them coming on to us from all sides we are trapped. A further issue is the human practice of “bugger that, I’m taking you all with me” where we do not run away but rather develop a rather stubborn streak which requires us blindly killing any creature we can. While this perhaps a desirable way to fight and defend against other humans it is fairly useless against zombies. We have to shoot, or kill them to stop them; as they do not injure or suffer pain like us, they can keep coming until they are no longer physically able to. All they have to do is infect us.

Infection spread

It is this infection which poses the greatest danger to us as it is normally unheralded and judging from reports to date has a very short incubation time. This short incubation time means we cannot quarantine or separate potential zombie victims, because we simply do not know who is the next victim. We also do not know the “starting Point” or “Ground zero” for the infection. The vectors (infected) are in society and spreading the disease before we know it is there. There are no screening options and when the sick do come looking for medical assistance they usually are close to transition and actually pose a danger to the medical facilities being provided. Such is the speed of transition that a patient sitting in A&E can often be a vector within minutes, removing not only other patients but also the medical staff and the facilities themselves.

The Zombie Research Society[4] staff have looked at the incubation periods of known zombie infection to date. While there is no confirmed set incubation period, an over long asymptomatic incubation period has been ruled out. It is generally understood to be between 4 and 48 hours. The zombie plague is at its most dangerous at the start when it reaches a critical mass as this growth will be quick and likely overwhelm society’s ability to respond. If the disease can be prevented from reaching this level then there is a chance to control and contain it.

To date, the source or ground zero points for vector spread have been epidemic in nature, should an outbreak be pandemic in form then we are likely to face the end of society as we know it. A potential consequence of a non-centred and rapid disease spread is that local emergency treatment and response centres will be overwhelmed before a global response can be put in place. It is the local attrition repeated at various points which will remove society’s ability to remove the risk successfully. The problem is that such a reduction in first response and security efforts will mean that strategically created plans will likely fail because the local resources are not available to implement the necessary plan elements. In essence the short incubation time, coupled with the necessary organisational lag for response will mean that any response effort will be hindered by not only a localised shortage of personnel but also unavailability of emergency resources as a result of them either being damaged or in zombie controlled areas. I say “controlled” but we must acknowledge that the control factor is purely one of us humans not actually having control, it is more a case of resources being outside out immediate range.

When we look at modern diseases, even ones about which we do not know much we can still track the vectors and look to patient zero. Patients are usually cooperative and to a greater or lesser degree coherent, infected zombies are usually anything but cooperative and have no ability to communicate. This reduces the investigative ability to track, trace and eradicate the disease. Two current epidemics give examples of this. The current Middle East Respiratory Syndrome, MERS, (first reported in Saudi Arabia in 2012) is a coronavirus causing acute respiratory illness with high temperatures, cough and shortness of breath, about 30% of confirmed cases have resulted in fatality (permanent fatality). The majority of cases originate in the Arabian Peninsula and have been associated with pilgrimage sites. The source points, vector characteristics (pilgrims or business travellers) and disease factors mean it can be tracked and to an extent controlled. We see something similar with the 2014 outbreak of Ebola in West Africa. Initial reports gave a death-toll of about 50% which is quite low for Ebola, this is currently being revised upwards. However once authorities got a greater grasp of the situation and the necessary external assistance, measures were put in place to contain and control the disease. Initial resistance to medical teams gave an indication of how a less than compliant population can hinder attempts to eradicate the outbreak. In the case of zombies they are down-right belligerent and are likely to have damaged the available medical resources.

Essentially many of the factors we rely on in dealing with “traditional” disease outbreaks such as an ordered society, non-belligerent victims and the ability to control and contain potential vectors where necessary will largely be missing in relation to dealing with the zombie threat.

Zombyism and Feeding

The ability of this disease to spread quickly and directly is perhaps one of the greatest dangers. The desire to feed on medical responders and others also acts as a hindrance. One important aspect of the zombie apocalypse however, which might be of use to us in dealing with it is the need for food. As a general guide uninfected humans can survive about 20 days or so without food and an averagely fit human can last about 3 days without water before things go downhill fast. This is important because it is time related. Where living humans may suffer from lack of food or water we need to look at the impact on zombies.

Looking at food, we can see that this is a rather more complex factor than might be initially thought. The zombie by his (or her) very nature can no longer absorb or digest food as living humans do. The thought is that the necessary minerals are absorbed from liquids with unused solids regurgitated. Most of the essential bodily functions are no longer present so changing utterly the body’s ability to absorb nutrients. This should be a decisive factor in dealing with zombies, but with many viruses, one of the essential dangers of infection is the ability of a virus to alter the nature of its host purely to facilitate the survival of the invading organism. Given the reduced capacity of zombies to not just function but also to efficiently feed we should look at the 20 day rule. In essence one way to control the disease is to limit access to food supplies (i.e. other humans) for at least a month to ensure they no longer have the strength to be a significant danger. This is not an easy option because we will not know if a person is infected until they show external symptoms (which apart from physical ones) only manifest themselves when it is too late. Once outwardly infected they must be isolated and prevented from feeding. A significant school of thought says that once corralled the infected should be eradicated rather than starved. Although there have been isolated cases of cross species feeding it is felt such cases are out of primal urges for food and are usually unsuitable. The absence of multi-species zombieism would also suggest that there is not cross species infection either. It might be presumed that the effect of non-human flesh on zombies might be similar to that of humans, raw flesh or blood of certain types cannot be efficiently used.

Water is another factor, we living humans can last, at most a long-weekend, before declining and dying. Zombies on the other hand do not drink water, nor do they use water for their bodily functions to the extent living humans do so this rule does not apply. The water inherent in the flesh consumed must provide the necessary quantities of moisture needed. While it is possible to isolate and starve zombies it is hard because of the feeding urge which is coupled with the spread vector. Having no lungs breathing and air is not a controllable factor also. In theory zombies can survive in non-air environments such as underwater. Currents, zombie lack of intelligence and various marine predators however limit the effective of water based survival for them. The fact that zombies consume so much blood further indicates the level of transformation. Living humans cannot consume anything other than very small amounts of human blood, (we do not have the necessary enzymes). The altered physicality of zombies means that this is not an issue for them and so they can consume and absorb as much as they need.

It should be noted that there is still much research needed on this area as zombies would seem to directly breaks down and absorb the minerals and nutrients from feeding. Witnesses dealing with zombies have repeatedly reported how the strength of a zombie is often related to how recently they have turned. Conjecture is that the basic strength is inherited from when they were living and the absorption of nutrients contributes to existence. The, as-it-were- life expectancy of a zombie although never properly documented is essentially one of dying from the day created, the absorption of energy from nutrients needs, as with living humans, to equal or exceed the energy expended, otherwise starvation.

It has also been noted that as the energy level of zombies decreases they become more lethargic and essentially go into a low-energy survival mode, this is not quite hibernation and indeed there is no evidence of hibernation experienced to date. Even shorter periods which equate to sleep in humans have been more accurately described as a dormant state rather than sleep. Such behaviour is not unrelated to what we would expect of a virus in its immediate host; the more extreme the environment and the greater the risk to the virus’s existence will often drive it in to a state of animation where it can lay dormant for many years. An example of this is the research being done on the 1918 strain of  influenza.

One hypothesis regarding the zombie’s ability to absorb energy and survive details two aspects firstly expounding from human biology we know we need oxygen and energy to work our limbs and other bodily function. As the zombie’s heart and lungs do not function in any meaningful way it is thought that the nutrient breakdown process (digestion for us humans) is capable of extracting a quantity of oxygen to allow continued motor-function. It would seem to work on a most basic cellular scale transforming the necessary elements to the necessary materials and compounds. As in many other areas of zombie physiology we are hindered by the difficulty in capturing, containing and controlling test specimens. The limited range of movement demonstrated by zombies indicates that the “feeding” and subsequent internal dispersal of nutrients and necessary chemical reactions are not happening to the extent necessary to the zombie to function at a level closer to that of a human.

Having briefly looked at nutrient absorption and muscular action, we should not ignore the role of the brain in the animation of zombies. Just as the heart pumps much needed blood through our bodies and allows us to function, we need to look at what allows “full system operation” within a zombie. The only significant organ left functioning is the brain. When we say functioning we must caution on the level of function available. If we look at the some basic functions we can see how the brain function is impacted by the virus. Perhaps the most obvious and visible characteristics is the ability to communicate. Almost immediately all higher order communications abilities are lost with the victim able to do nothing more than grunt. The lack of oral communication may be a result of one or two factors. Firstly without functioning lungs and air flow through the larynx it is next to impossible for zombies to formulate and speak words. This “eternal silence” is perhaps one of the more nerving aspects of the zombie plague as we witness attackers marching towards us it complete silence. As with many aspects of nature it can be beautiful but also merciless. Nature and aspects such as this virus show us how non-functioning aspects are discarded in favour of allowing the critical characteristics or functions to operate more efficiently and at the same time adapt the immediate (host) environment to a manner which best facilitates external factors such as an invading virus. One theory currently gaining ground is that electrical nerve impulses generated in the brain allow bodily function such as it is. One of the ways this becomes possible is as a result of the attacking virus altering the essential DNA of the host and reducing brain function to merely on of supporting the existence of the virus.

When we think of survival, in human terms, we think of a synergistic strategy of using the resources available to us to survive, viruses often sacrifice the individual [virus] to facilitate the whole, this is done without any obvious swarming. Essentially the body is now an incubation and feeding unit for the virus. The human host has become home to what is no more than an opportunistic parasite altering and feeding from the host in order to survive. The human is the survival method, while the virus controls replication by using the host as a transfer vector to pass on the virus to one vector after another. The human host is reduced to nothing more than a hosting environment.

The limited purpose of the human body to the virus is demonstrated in the restricted abilities, the brain functions to keep the rest of the host functioning and allowing the virus to live and replicate. Although the zombie is seen as a threat and a hunter it must be seen in the context of most other hunters. The significant difference is the zombie does not fear humans and comes from a shared habitat. It is this proximity to the humans they hunt that adds the significant danger. Although humans are caught and killed by many animals it is usually on a direct basis by animals (I am considering mammals only) which are normally shy of humans and live in different food chains. In the modern world human food kills are an opportunistic kill, with zombies the human food kill is a specific target hunting of prey. The human body purely serves to sustain and replicate the virus.

We see also in the movement of zombies how the body adapts to its new function, with all essential brain function capacity dedicated to the virus, nothing but the most rudimentary abilities remain. We see that the legs transport but only at a specific pace, the brain function to assess a certain situation no longer exists and so movement is kept to a basic form. As with many viruses, apparent restrictions are actually advantages to the host. This limited movement conserves energy and brain function allowing the virus to maximise its dominance of the host. Although physically able to catch and kill humans we need to be mindful of the methods used. Appreciating the attack methods of zombies allows us to defend ourselves in the most efficient manner. Zombies catch their prey by trapping in a restricted space or with additional pack members preventing escape from a particular area. Whereas we will fight (as mentioned earlier) the zombie lounges and grabs, the sole purpose of a zombie attack is to sufficiently incapacitate or restrict the human victim just enough to allow for a virus spread through a blood generating injury or exchange of bodily fluids (through non-sexual transmission, as following the general rule of viruses that we mentioned earlier, the human reproductive process is no longer needed as the act of feeding is in-and-of-itself a reproductive act). It takes more of a concerted effort by a human to restrain, defend against or incapacitate a zombie, indeed these very actions are often enough to vector the virus.

The discussion thus far is in relation to direct hand-to-hand or small weapons engagements. It should go without saying that distanced lethal actions are to be recommended. Although no outbreaks thus far have incapacitated the general industrial organisation, we must be prepared for such an event. It is with this in mind that we will not be discussing armed weaponry in the fight other than to discuss the following immediate points.

Firearms are highly specialised tools requiring a certain amount of training but more importantly ammunition. Ammunition like the firearms themselves are restricted and highly specialised items with limited supply. There is a danger in the event of a zombie outbreak that our production or logistics capabilities will be severely compromised and limit out abilities to distribute or replenish supplies. Firearms and such weaponry must be used sparingly. The noise associated with firearms is also a limiting factor as the ever hunting zombies will be attracted to the noise, this of course is fine if you are in a position to safely deal with such a threat, if not; fire and run. The use of firearms will be an initial response item. As the challenge to society increases so in all likely hood will out ability to replenish weaponry stocks diminish. This leave the use of weaponry more suited to the nineteenth century or earlier, swords, knives bows and arrows can all be effective over different ranges. The greater the fighting range the better, because as we mentioned, they only have to infect us, we have to kill them (without infecting ourselves). Where possible avoid close contact but kill at any convenience.

A method of control discussed but not implemented is the use of toxins and poisons on zombies. These have limited impact and are potentially of greater danger to the humans attempting to apply any toxins or poisons. Zombie tissue is already necrotic and short of a chemical reaction dissolving the body parts most materials will have little or no effect. Yes, corrosive chemicals can be used but again to a limited degree only. The danger to humans means that delivery systems need to be restrictive and usually close quartered, this adds greatly to the human danger. Also because zombies do not register pain and function only to feed and replicate the virus, they will continue with any remaining movement of fighting ability until permanently dead, a human will likely retreat once poisons or chemicals are applied to him or her and seek medical assistance. So they do not ingest poisons, toxins and chemicals will only be effective if there is a specific chemical reaction with the zombie tissue (the application of a strong dilution of caustic soda will burn a hole in whoever or whatever organic compound it is applied to, but if the burn in not in a location that will debilitate the zombie then it will continue pain free to hunt or attack its next victim.

As we have mentioned, the primary vector vehicle is touch (wounding, eating etc.) and transmission of bodily fluids such as a blood. To date, despite certain limited anecdotal evidence that the virus may be capable of becoming airborne[5] the overall situation is one of bubonic or physical spread rather than pneumonic or airborne. Where the virus is suspected of becoming pneumonic, it is reported that the virus remain dormant in the human host until such time as the host dies. It is reported that in such cases the corpse is reanimated a short period after death as the virus adapts to the new host environment and begins to take control of the host. In the cases of bubonic transmission we see immediately how higher brain functions such as cognitive abilities, speech, coordinated movement all go, essentially all learned functions are gone and only the reflexive animal movements relating to hunting survive. Speaking of survival it is noted that apart from hunting and replicating there are no survival modes exhibited by the typical zombie, this makes it both easier to remove but also a challenge in so far as it shows no social default social function (other than random hordes) or organisation, thus dispersing any infected population/vectors. In short the use of poisons and toxins and or suitable corrosive chemicals is purely of a localised value and often carries as much danger for the human as the zombie, if not more so, while knowledge of the virus is limited to a certain extent to either laboratory samples or observational analysis. Attempts to study captured zombies have been limited by their constant need to feed and replicate, thus creating an unstable environment for those studying the disease.

We mentioned earlier the ability of viruses to react to cold by turning to a suspended state or hibernation, we should also consider the effect bright light has on them (UV light as we know works well on most viruses (exposed to a surface)) so we might want to consider the effects of weather on the zombie population in relation to two factors, the virus itself and the (formally) human host. We know that severe cold will contain the virus, but not kill it. While it contains a virus it kills humans, so the question is, if there is a population surviving say, sub-zero temperatures can they isolate and remove zombies. The human body cannot physically cope below certain temperatures, it will begin to freeze regardless of its nature. The zombie body should begin to freeze, which if left outside will render the zombie immobile. The limitation here is that the zombie is already dead to as long as it can get mobile it can continue to be a danger; think for example of a zombie shot in the stomach, they can continue with a gaping hole, but remove a leg, they become immobile. The benefit of freezing is the, at least temporary, paralyses, the zombie must be neutralised while still frozen, so limiting danger to the human population.

We can also look to tropical hot weather, this can be a mixed blessing, humid rainforest conditions would most likely allow the virus to thrive (such conditions are most likely the basis for the origins of the virus, before the human manipulation to the present form). That said hot open desert conditions may be good. The climate will again degenerate the physical body and through the use of open spaces protection should be provided; again the ssue here is human survival in a particular climate, it needs to be possible but sufficiently had to limit zombie propagation.

Considering living conditions, a lot of thought must be given to how humans can best live in a manner that protects from zombies. If we look at their mobility we know they can cross flat relatively simple terrain and also travel downhill/stairs (gravity helps), however climbing obstacles or even stairs is somewhat more difficult. Defences which make noise and also require a degree of mobility and agility work well. Traditional defences such as large walls usually work well also, that said, the author is aware of reports that there may be incidences of zombies evolving to climb over each other to get over walls, such evolutionary practices must be stopped and the zombies removed to prevent spread of such innovations.

Cramped living conditions need also to be looked at, as any mutation in a closed space immediately offers danger to all humans present. Living accommodation needs to be designed to allow for the various humans to be closed off from all others, as much for their own protection as any others present. Depending on the nature of the virus and incubation period, communal living may act simply to provide a host reservoir for fresh localised outbreaks, each potential outbreak must be controlled. On more individual basis thought must be given to different solutions to the question of ongoing habitat. The traditional designs of our towns and cities needs to be replaced by an approach which takes account of the new concerns of security, food, communication, maintenance of resources and where possible the production of new. Such social aspects of living in the zombie apocalypse are covered in additional documentation.

What we see is that society has changed and now it is up to those few to come up with a solution, following is a look at one or two of those solutions…

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 5^th 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 21^st 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.

1. a) Grandfather is killed in 1940, preventing him from meeting his would-be future wife.
2. b) Grandfather survives by chance
3. c) Grandfather is not allowed to die by virtue of the “Laws of nature” even if we don’t understand these laws.
4. 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.

^[8] Mark Johnston (1983)

Part III: Time Travel and Relativity – in other words, not ignoring the Laws of Physics
Ed Note:  The original have the necessary formulas but could not be uploaded…
When we think of Time Travel we invariably think of one man; Albert Einstein. He gave us the modern mathematics of time travel and advanced the questions to a level which allowed us to test the hypotheses. He did not however give us Relativity, he did give the world  General Relativity and Special Relativity, both of which we shall detail later. First though, Relativity. To understand the concept of relativity we need to go back in time to 1632 and the Book Dialogue Concerning the Two Chief World systems (Dialogo sopra i due massimi sistemi del mondo). This was the book that eventually had Galileo found “vehemently suspect of heresy”. That however, is another story.
Galileo, by any account, was one of the most significant scientists of his time and probably to his detriment, one of the greatest self-publicists of his time. The book was originally published with the permission of the Roman Inquisition, but his mistake was to alienate former allies in the Jesuits and the Pope himself.
The basic principle upon which Relativity stands is that if an action occurs and two people observe it from different points, the challenge is for them to agree when and where the activity occurred. His principle of relativity states that there is no physical way to tell between a body moving at a constant velocity and a stationary body. We can determine that one body is moving relatively to the others, but it is impossible to determine which of  the objects is moving and which is immobile (without an external reference point).This concept works for all bodies from ships to planets and stars. Galileo explained his principle by the example of two ships.
“Shut yourself up with some friend in the main cabin below decks on some large ship and have with you there some flies, butterflies, and other small flying animals. Have a large bowl of water with some fish in it; hang up a bottle that empties drop by drop into a wide [Note David Eckstein/Samuel Edelstein: This should rather read ‘narrow’ instead of ‘wide’. Think of a bottle with a narrow neck on its top! ] vessel beneath it. With the ship standing still, observe carefully how the little animals fly with equal speed to all sides of the cabin. The fish swim indifferently in all directions; the drops fall into the vessel beneath; and, in throwing something to your friend, you need throw it no more strongly in one direction than another, the distances being equal; jumping with your feet together, you pass equal spaces in every direction. When you have observed all these things carefully (though there is no doubt that when the ship is standing still everything must happen in this way), have the ship proceed with any speed you like, so long as the motion is uniform and not fluctuating this way and that. You will discover not the least change in all the effects named, nor could you tell from any of them whether the ship was moving or standing still. In jumping, you will pass on the floor the same spaces as before, nor will you make larger jumps toward the stern than toward the prow even though the ship is moving quite rapidly, despite the fact that during the time that you are in the air the floor under you will be going in a direction opposite to your jump. In throwing something to your companion, you will need no more force to get it to him whether he is in the direction of the bow or the stern, with yourself situated opposite. The droplets will fall as before into the vessel beneath without dropping toward the stern, although while the drops are in the air the ship runs many spans. The fish in their water will swim toward the front of their bowl with no more effort than toward the back, and will go with equal ease to bait placed anywhere around the edges of the bowl. Finally the butterflies and flies will continue their flights indifferently toward every side, nor will it ever happen that they are concentrated toward the stern, as if tired out from keeping up with the course of the ship, from which they will have been separated during long intervals by keeping themselves in the air.  …“  [05-187f]”
Looking first to the Salvatius Ship, called after the book’s narrator. In short Galileo described how the effects of constant motion (constant velocity)are the same as the effects of stillness, we cannot tell what is motion and what is not. Note, this is constant motion not acceleration which is anoter force to act on a body (ship). With a point of reference (outside) it is impossible to gage which body is moving. We have seen this, for example on a train. While parked at a station with another train sitting on a line next  to you, as one starts to move you cannot tell which one is moving until you have an external reference point to calibrate against what is being observed. Locked in the ship with no view out  and a calm see it will not be possible to determine if the ship is moving  or at rest (acceleration will as mentioned cause additional forces on objects so movement can be determined)
What  we learn from this is that the relative (uniform) motion of the two ships does not impact the laws of motion on the other/either ship. A cannon ball dropped from the top of the main mast on the Salvatius Ship will appear from the other ship (Segredus) to fall in a parabolic course while looking to fall straight down from the Salvatius’ mast.  The same hold true should Segredus be the one dropping cannon ball from the mast of his ship. Now let’s take this to the modern age; in space above (or below, or to the side) Earth are two ships and a joint beach ball. Free from gravity or other forces, the ball does not accelerate in any manner as no force (in any x, y, or z) direction is applied. The motion of the ball is uniform in respect to both ships.
This principle leads on from the principle of inertia, bodies operating on a horizontal plane will not change their velocity as long as no force is applied to them. “The laws of nature  do not permit you to determine if you are stationary, and thus your speed (and that of anything else) always has to be stated as relative to another object”
We are all familiar with the idea of Einstein’s two space ships but is was Galileo who showed us that within a system (ship) the elements, (all having the same velocity) will move relative to each other; not indicating a moving of stationary object. If the ship is totally closed to the world and moving on a calm sea, out sailor, Salvatius will throw the ball up and down catching it each time no differently whether the ship is moving or not.

Inside the ship the ball looks to be moving thus :
Simply up and then down as expected, however if we take one side of the ship and  replace it with a one way mirror  (stay with me) So that Salvatius cannot see out and has no  external; reference We now see the same ball moving in a parabola, as it moves  alone at the steady velocity relative  to the observation point.

The external View: Moving with stead velocity relative to an observation point the same ball going through the same motions will appear to also have a horizontal element to its movement rather than the seemingly purely vertical movement  observed internally.

As we move to the Einsteinian logic we start to think in terms of time and space, but before we can do that we should firm-up on some key factors in relation to relativity, – namely time, space and gravity. For this we will now proceed  to England and Sir Isaac Newton.
Looking from inside the ship the ball goes up straight and down again straight at velocity V1,  over a distance of V2t (t = time).
From outside an observer will see the train move in a direction at velocity V2t. the stationary external obserser will see the ball moving a greater distance along a horizontal plane (the sum of the distance the ball moves within the ship plus the distance of the ship’s travel. The observer sees the ball at velocity V3. The velocity of the ball seen be the external observer can be found using good old fashioned Pythagoras
In essence we are seeing two different views of the one occurrence, both relative a particular  viewing point. If a coordinate system (such as the ship or more modern space ship, essentially a self-contained unit) “A” moves at constant velocity in a straight line with respect to an inertial frame  “B” is also an inertial frame. With two inertial frames moving only uniform to each other and in a straight line, it cannot be determined whether one of the vessels is at rest in space (that is a area with only the two reference vessels and no other external reference point).
The principle is:  “any two observers moving at constant speed and direction with respect to one another will obtain the same results for all mechanical experiments”  In other words, “the mechanical laws of physics are the same for every observer moving uniformly with constant speed in a straight line.
Newton

Having briefly looked at one aspect of Galileo’s contribution in this area of physics and science, we will now look to see how his work influenced those who came after him. Perhaps one of the most significant of those people being Sir Isaac Newton. Like  Galileo, Newton was a man of many talents advancing knowledge of physics; gravity, motion and thermodynamics in particular, the understanding of our place in the stars/universe and even the minting of coins for which he was responsible  at the Royal Mint in the Tower of London. On a somewhat reassuring note we should also remember that despite being one of the greatest minds of his, or any other, generation, he like many others fell victim to the South Sea Bubble.  Having initially invested and made a small fortune, he reinvested and lost a huge fortune.  As with Galileo, we could look to many aspects of Newton’s life, career and relationships (famously bad tempered and difficult to get on with, heavy metal poisoning is suspected) however we will focus on his work in relation to Relativity. As with Galileo, the laws were first published in book form in “Principia Mathematica Philosophiae Naturalis” in 1686, about 50 years after Galileo’s Dialogue. The Principia is still in print and indeed it is easier to find a Latin version than it is to get one in English
Newton’s laws
Newton’s Laws of Motion help us to understand how objects behave when they are standing still, when they are moving, and when forces act upon them. There are three laws of motion.

First Law of Motion
“An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force”.  This law is often called  “the law of inertia”.  Basically what Newton’s First Law is saying is that objects behave predictably. If a ball is sitting on your floor, it isn’t going to start rolling about unless a force acts upon it to cause it to do so. likewise objects in motion do not change their direction unless a force causes them to move from their path.

Second Law of Motion
“The force acting on an object is equal to the mass of that object times its acceleration.” This is written in mathematical form as: F = ma
F is force, m is mass and a is acceleration, Force is understood to be “The Change of momentum with change of time”. Stated also as when a force acts on an object, it will cause the object to accelerate. The larger the mass of the object, the greater the force will need to be to cause it to accelerate .  when a force acts on an object, the object accelerates in the direction of the force. If the mass of the object does not alter, acceleration will increase as the force applied increases; likewise if the force is decreasing/increasing the mass will increase/decrease acceleration respectively. Force is directly proportional to acceleration, while mass is indirectly proportional to acceleration. Using calculus (invented by Newton to support the laws) we find:
F = m(dv/dt)
is the differential change in momentum per unit time, it is a characteristic  of a moving body determined by the product of the body’s mass and velocity. Because acceleration is defined as the instantaneous change in velocity in an instant of time (dv/dt),   giving the equation we first saw above.
F = ma
So far so good, and now for the one everybody can quote:
Third Law of Motion
“For every action there is an equal and opposite reaction”. Applying a force on an object means that the object in question will push back with the exact same force, but in the opposite direction.
The laws of motion form a basis from which we can now look to relativity and how it progressed. Up until the time of Newton and the age of Enlightenment (the ancient Greek view of the world largely still governed.  Aristotle was the reference point for all learning of mechanics (physics). Whereas Aristotle held that the Natural state of matter was stationary (at rest) with respect to the Earth, Newton (and Galileo before him) held the constant state of matter to be one of constant velocity. The Newtonian perspective was that space, motion and time were all absolute and were a uniform inertial frame (just as the boat was for Galileo’s Salvatius)  and that time passed evenly throughout at an eternally fixed and inexorable rate without relation to anything external
It is this linking of time, motion and space that is critical to our understanding and advancement of space-time.  The laws of physics are equal for any observer moving at constant velocity. The constant velocity allows us to have an inertial frame of reference, (when an observer is moving at a constant velocity), providing an environment where the Laws of inertia hold true.
The key to Newton’s laws of Motion  is the Second Law: F = ma , or    a=F/m, the velocity is not the key, but rather the  change of velocity. Due to relativity, every observer moving at the same constant velocity will measure/observe the same forces on  an object as they are from the perspective of acceleration of the object. Following on from the Galilean example, until Salvalius has a deceleration (or acceleration) force applied he will not notice any movement, however as a result of Newton’s first law, as the ship decelerates he will find himself slipping forward  as the forces are applied.  If there is a second ship moving at the same velocity, both will seem not to be moving relative to each other without an external frame of reference. If we were to hang a pendulum in the galley and apply some very powerful sails to alter the velocity by a noticeable acceleration we wound see that the pendulum no longer swings as if it were stable (at constant velocity, even if v=0)    the pendulum will hang at an angle because the  pivot point is being pulled away from the pendulum.
Okay, Newton’s law of motion support the theories of relativity so far, however. One of the important aspects of modern relativity and time travel is light and electromagnetism. Newton of course did much to advance our understanding of the laws of physics and particularly motion ( as well as thermodynamics, but that’s another story) and also light itself with the publication of Opticks in 1704. The finer understanding of the nature and speed of light would come some years later.
Before we jump to everybody’s favourite  Swiss physicist, we should  take a slight diversion or two for some final background. Firstly to the Dutch physicist Hendrik Lorentz.  From what we have seen so far Newtonian mechanics (physics) does not vary in relation to Galilean transformations concerning two inertial frames (at same speed and direction). However this presumes time is a universal concept, with it being the same everywhere from all observers, in other words in line with Special Relativity. The Lorentz transformations show measurements of space/time by two observers are connected, the observers moving at different velocities may measure different distances, elapsed times etc. The Galilean transformations function at relative speeds much smaller than the speed of light.  The Lorentz transformations can be summarised as follows:The frame moves at velocity v, in direction x with respect to the fixed reference frame. The coincide at t=t*=0 (which like the bad soccer game was tied 0-0 at the start) . X* is moving. The Galilean transformation shows coordinates from the fixed frame in terms of its location  in the moving reference frame, which is in line with human intuitive thinking of what we would think it should be like.
This is really theoretical material but it helps on the trip to the final answer.  Looking briefly at the Lorentz transformations we see as follows. The moving primed frame moves with velocity v in the  direction x with respect to the fixed reference frame. The reference frames coincide at t=t’=0. The point x’ is moving with the primed frame.  All as normal so far. The Lorentzian equations for this are: ( the original version has the equations but Blogger would not take them)
This might seem theoretical but in  Minkowski (the mathematical space in which Einstein’s theory  of Special relativity is most conveniently formulated, the ordinary dimensions of  space are joined by a single dimension of time-space, the Lorentz transformations preserve the space-time interval between any two events. They show  the transformations in which the space-time event at the origin is left fixed.  These are important to this essay not just to explain the history of relativity but also to show that as our understanding of it grows so does the complexity of what needs to be considered.
Before we finally arrive with Einstein, we have one last stop and that is with the 19th century Scottish physicist James Clerk Maxwell. Maxwell gave us the theory of electromagnetic radiation, and in so doing linked together electricity, magnetism and light as the same thing essentially. He showed that electrical and magnetic fields travel through space as waves moving at the speed of light. Maxwell postulated that light is undulations in the same medium, that is the cause of electrical and magnetic phenomena.  Doing this, he showed the way to the spectrum of electromagnetic radiation. Defining fields as a tension in the medium, he stated his belief in a new concept – that energies resides in fields as well as bodies. This pointed the way to the application of electromagnetic radiation for such present-day uses as radio, television, radar, microwaves and thermal imaging.
Not forgetting the actual calculations for the speed of light, we will jump back to the 1670’s and Denmark, specifically to the astronomer Ole Rømer. While observing the transit of Jupiter and its moons he calculated the time light takes to travel to earth. His original calculation of 220, 000km/second is about 25% out but gave a method of calculation. It caused some controversy at the time, with opinion being divided, (Huygens and Newton both supporting). James Bradley developed this and confirmed the methodology in 1729 and was only 1000miles per second out.
Even through Einstein’s experiments, the world had still not settled on the speed and nature of light. Maxwell’s waveforms were accepted in time and it was not until the 1980’s that the 17th General Conference of Weights and Measures declared that the speed of light is 299,792,458 meters per second. This may be refined in the future, but the criticality of this measure can be shown in the modern definitions of a meter and even a kilo; both are now determined in relation to light, further reflecting its nature as a constant. It is worth remembering that when Einstein developed the Theory of Special relativity in 1905, he ASSUMED that the speed of light was a constant.

Special Relativity
Having reviewed the history and a little of the nature of relativity  it is about time we looked at the theories of Special and General Relativity. The theory of Special Relativity is based on two postulations, both of which we have covered above to some degree;

• Relativity: The laws of nature are the same in all inertial reference frames
  •    The speed of light in a vacuum is the same in all inertial frames.

These are the two principles which give us such great science-fiction. Special relativity is restricted to objects that are moving at constant speed in a straight line; inertial motion. Einstein’s theory showed that the speed of light is a limit that can be approached but never reached or exceeded  by material objects. It is this idea that gave way to:

E= mc2

In 1905 Einstein published a series of papers covering; photoelectric effect, the proof of atoms, Special Relativity and finally the paper that gave us  The Formula. Originally written as:
m= E/c2 later to become E= mc2 . It shows that mass and energy are the same physical entity, both being able to change into the other, but more on that a little later.

Rather than consider absolute space and time, Einstein used definitions which related to the state of motion of the observer; using the example of an observer on a track and another on the now famous train. Using the existing formula of x* = X – vt (see above) we note the speed of one observer relative to the other. T is the time at which the observed event occurs. The issue here is to consider light in relation to speed.

A ball thrown on a moving train will have a greater speed than a ball thrown with the same force by someone standing on the platform. This is because the speed of the train is added to that of the ball to give its total speed. But this isn’t the case with light. If you measure the speed of the light produced by torches on a moving train and a stationary platform, you will get the same speed – the speed of the train doesn’t matter. When you measure the speed of light it doesn’t matter if you are moving or stationary, or if the source of the light is moving – the speed is always the same: 300,000,000 metres per second.  (Approx).

Here is comes. For the speed of light to  always be the same, something else must change. The measurements of speed and time in this principle depend on how fast you are travelling. As velocity accelerates to the speed of light, relativistic effects on time dilation (clocks running slow) and length contraction become more noticeable.
Using Lorentz  transforms Einstein  developed :

t′ is time as measured by the moving observer
c is the speed of light.
From these, came new  equations the addition of velocities
u and u′ are the speed of any moving object as seen by each observer
v is again the speed of one observer relative to the other.

From this; if a beam of light is projected from the front of the train, moving at the speed of light, an observer on the train will record the speed of the beam as c as per above. However, just as the first observation is in line with the equation, the second observer on a platform will also see the light with speed c, not 2c as might be expected. As we mentioned earlier for light to be constant, the other physical properties must change, the object travelling to light speed becomes shorted along its direction of travel, while time intervals become longer, with time running more slowly for the system as it travels close to the speed of light. The person on the train will measure time and distance (length) as normal, being as they were from his perspective when he set off (the traveller being in the train is part of the system moving at that speed, so the length of the train remains the same for him, as does the rate of passage of time. The observer on the platform, on the other hand will see the train get  smaller. While , eventually when the train stops it will be seen that time has passed more slowly for the train based observer. Comparing clocks, it will seem as the train based observer has jumped from an earlier time to the current platform time. An extended example of this is if observer 1 went on a lap of the solar system in a near light speed vessel and a clock, while observer 2. Waited on Earth with a second clock, both clocks having been synchronised prior to the vessel leaving. After about 5 years passing (from an earth frame of perspective) the vessel returns to earth, observer 2 will see that for him only four years have passed, the times are no longer synchronised.

This can happen by space and time changing relative to the speed of light which stays fixed. If observer 2 was able to watch the vessel as it toured the solar system it wound be noticed that as the vessel got near the speed of light its length  got shorter. And now for the counter intuitive piece – from the equation it is shown that as a body nears the speed of light its mass increases and so it takes more and more energy to increase its speed further, closer to the speed of light. As it nears the speed of light the vessel will become so massive that there will not be sufficient available energy to make it go faster and reach/break the speed of light. As a consequence we learn that nothing with a mass can exceed the speed of light.
This can be shown in equation by:
L0  = proper length
T0,  =  proper time, as measured by an observer on the vessel, , L and T are those values  as measured by a fixed observer.
Looking to  E = mc2 we know that; E = energy, M = mass, C = speed of light and already we can see the relationship between speed, mass and energy.
From this it is starting to look as direct travel in to the future (as viewed by  observers from both frames of reference is not too possible, but  we can see that it is possible to have two bodies move at sufficiently different a speed to facilitate time dilation and what seems like time travel, one observer, relative to the other. This does not even have to from the realms of science fiction

The Hafele and Keating experiments of 1971
Four caesium atomic clocks were flown on regular commercial jets (on scheduled routes) around the world. Two flew east and the other two, west. This would test the theory. Looking at the flight paths for the trips a prediction of the loss/gain of time was made.
Upon return the clocks were compared to the atomic clock at the US Naval Observatory. Those flying east lost 59 +/-10 nanoseconds, while those flying west gained 273 +/- 7 nanoseconds, thus resolving the clock paradox. We can see from looking at special relativity that our options are limited due to the nature of the relationship between energy, mass and the speed of light. What happens when we add gravity in to the mix.

General Relativity
Having given the world special relativity, Einstein went on to develop the theory of General Relativity, which took account of gravity and brought us the understanding that objects of large masscan distort local space and time. This impacts our understanding of the very nature of the space around us.
Our knowledge of gravity tells us that two objects exert a force of attraction on one another. Sir Isaac quantified gravity as part of his study of  Laws of motion. Einstein’s work were largely thought experiments subsequently verified by experiments and observations by persons following. An example of this is the lensing of light around a massive object. How we see gravity is  from the curvature of space time. At its simplest it explains the motion of the planets such as in our solar system, the geometry of space-time dictates how the Earth moves around the Sun.
The Theory has been studied and verified in a number of ways, however we are going to jump to the science of Black holes  and worm holes and how they impact time travel. We know the density of a black hole distorts local time and space but actual time generally?
It might be worth taking a few seconds to determine the difference between a black hole and a wormhole. A wormhole is essentially a tube in space connecting two points (possible black holes or lesser events that sustain a wormhole, in theory if the conditions are correct a vessel could enter  one end and come out the other in a different time and place. A black hole pinches to a point and destroys anything pulled in to it.
For wormholes to be feasible they need to be sufficiently less violent than a black hole and most likely not have an event horizon or point of no return. There are questions about predicting how, or where or when  a vessel might emerge from wormhole. While we have largely accepted and can point to examples of black holes, wormholes are still the subject of our dreams and fantasies.
The theoretical study of wormholes indicates that the first ones close to the big bang, were microscopic and would probably have  grown in time. There is also the question of their stability. It is thought that adding “exotic” matter to the wormholes would stabilse them, however Dr Steven Hawking has suggested this is not possible, it is also thought that adding sufficient “regular” matter might work. As I type this and as you read it, it becomes immediately obvious that however possible it is highly improbable that we could tame or use a wormhole, due to its like unpredictability, size and energy.
General relativity tells us that gravity and acceleration are two names for the same event. In short there is no “force” of gravity. When we see satellites in orbit over the Earth, it is untrue to say they are in a zero gravity environment. They are actually in free-fall within the Earth’s gravitational field. They exhibit the effects of being in their own local inertial frame and so do not register the weight of their own mass. Satellites fall to earth.
In 1949 Kurt Gödel showed that worldliness in closed space-time could curve back on themselves forming a space-time loop, called Closed Timelike Curves (CTCs). An object on a CTC worldline would eventually arrive back where it started,  at the same spacetime position. An older self would appear at one of its own earlier spacetime points.The Physicist Kip Thorne suggested that if one could trap one of the black holes that comprise the mouths of the wormhole it would be conceivable to transport it, preferably at speeds near the speed of light. The moving black hole would age more slowly than the stationary black hole at the other end of the wormhole because of time dilation. Eventually, the two black holes would become unsynchronized and exist in different external times. The natural time traveller could then enter the stationary black hole and emerge from the wormhole some years earlier than when he departed.Of course there are a few issues with black holes and wormholes (especially wormholes) that prevent us from popping back to various times and locations. We have not found a wormhole, even if we did we have no way of getting to them and even if we did we would need to make sure it was not a black hole that would remove us from existence. If we did find it was a wormhole, how do we know where it leads to, somewhere or time in our universe or another perhaps? There is a point known as the Cauchy horizon which is simply the middle of a wormhole or where two inverse or connected black holes meet – if this exists the issue is we know or can surmise nothing about it. Heaven only knows what is there or what could happen.
Of course harping back to the philosophical nature of time travel it is believed that if a CTC or bend in the timespace was used we could not travel back further than date CTC were perceived. The technology needed for such time travel is also far beyond our capabilities today, either to get to a singularity , to map or enter it and even go through it. We also mentioned “exotic” or regular, matter; how do we get such material there is sufficient  quantities and manage the subsequent energy reactions. These however are technicalities. Time travel into the past is allowed by General Relativity.

Conclusion
Can we travel back in time to prevent a zombie apocalypse? Yes and  no. The philosophy of time travel is like most others best answered by taking the economist’s approach “One the one hand…while on the other” looking purely in terms of thought processes, I would have to say that…sorry, the engineer in me is fighting this. It is theoretically and philosophically possible to go back in time. The new question is? What happens then? Do we remember why we went back, how far can we go back, as with the CTC discussion can we only travel back to a fixed boundary point in time. Then we need to consider our physical form when we go back and whether or not we are an adult (presuming we travel as adults) or a child separate to the one in the visited time. Then there is the discussion that we inhabit their physical being or ego and either go along for the ride as a separate entity r control events. So even if we define our physical and mental state on reaching the visit point, we then have to consider the external world, as it were. We need to consider if grandfather will allow us to kill him and then to determine the impact and causal relationship with other events.
If such events were successful, there would then be the consideration of the effects. If the initial reason for the time travel disappeared, what would have been the catalyst  for the time travel have been in the first place. Then there is the multiple universe answer, I have no issue with it, but let’s put t to one side for now. Looking at causality, I cannot help but feel there will be limitations, my concern would be on how those limitations managed to manifest themselves, the very manifestations would suggest links to causality that could be profound (and so possibly unlikely). In theory I am willing to say a form of time travel in to the past is possible but likely to be time and causally restricted.
However I refuse to consider that any kind of Wellsian or basic sci-fi time travel by simple stepping in to a contraption or pressing a button on your wrist-strap. All very entertaining just the same.  This is the point that the laws of physics kick in.  Wellsian time travel is just a non-started. The laws of physics tell us that in terms of the General theory of relativity using wormhole theory and CTCs, all things being equal (such as the wormhole being stable, sufficiently small/weak now to crush whatever enters, having fixed entry and exit points etc.), there does not seem to be anything in the laws of physics to prevent such events. Of course real world limitations make such event highly improbable.
So how does that help us, well however unlikely time travel into a fixed and predetermined point in space and past time may be (Jumping in to a point in the future is not even for discussion!), there is another option. Special relativity. If we can travel in a vessel at a speed sufficiently greater than that of the normal inertial frame  and return to earth at certain times in our chronology we will of course due to time dilation arrive at a time which to us is the future. Now if the world was sufficiently knocked back and depopulated while defeating a past zombie threat to have lost vital, say medical knowledge or abilities, we could consider such options load the necessary cargo on to a ship and travel off at speed  to a pre-determined time point and check if the cargo is needed. Considering that we had the technical ability to do such a thing, it is possible even now, to the mathematics necessary to predict when the ship would arrive back to earth given particular rates of acceleration and deceleration and a specific velocity. We might not be able to prevent a past one, but we might be able to reduce a risk of a new outbreak  in the future…
The next blog will be something a lot lighter and involving a lot less science, possibly…