Archive for June, 2010

Planned Obsolescence and Linux — A Real Case

June 30, 2010

Today I had to repair my sister’s PC. After more than 5 years, its internal clock battery ran out and needed to be replaced. Looking at it now, it made me consider: why do most people would want (or need) a computer better than that?

From observation and interview, I found that this how my sister uses her computer: chatting in MSN Messenger, reading emails, web-browsing, social-networking, viewing photos, watching You Tube videos, storing photos from her camera, listening to music, video-chatting with Skype, reading and writing USB sticks and occasionally doing some homework with OpenOffice. To complement that, she could also sporadically use it to watch a DVD.

In the interview, I asked what she thinks about the speed of her computer. She said there is nothing remarkable about it. Compared to my laptop (not one year old), she says it is a little slower. I asked how much, in numbers, and she said: “about 10%”. When I was leaving, she gave me a bonus info: “the slowest is my father’s laptop on Windows”. That is the only computer in house with Windows, it has 1 GB of RAM and a dual processor AMD Turion X2, the first 64 bits in the house, bought in 2007.

Her computer is an AMD Sempron 2200+, with the bizarre RAM count of 640 MB. It dates from 2004 and until today suits all her needs. Some parts were replaced later, and it has an 80GB SATA hard disk, and a 15” LCD wide-screen monitor, but the main internal parts are the same. The cooling fan is hang on green yarn because the old fan was destroyed by dust and the new one is too big to match the screw holes.

As you can see, it can not be considered to be in its best conditions, but it is working very well. Also, I can not say its average failure rate is greater than a new computer, after all, fans are often the first part to be replaced. Fact is, most computers do not get old enough to have its internal parts replaced. These parts do not age fast enough so to age faster than the software they run, what demands the whole computer to be replaced.

This old computer had Microsoft Windows XP installed until 2 years ago, and no new Microsoft product could fit comfortably in it, due its low amount of memory for those days standards. One day it stopped working due to natural Windows worn out, a fact Windows users are familiar with, and believes to be normal, that requires periodical system reinstall. That time I did not reinstall Windows. Instead, I installed Ubuntu 8.04. Since that time, it had no more viruses and the performance did not start to decrease with time. It got through 3 on-line system wide upgrades and is now running Ubuntu 9.10.

As many already knows, Ubuntu is a zero-cost free-as-in-freedom open source and easy to use flavor of GNU/Linux operating system. It came by default with all the software my sister needed to perform the aforementioned tasks, and much more is available on-line. Everything free as in beer, most of them free as in freedom. She can click on every virus and bad site links she wants without getting infected. As long as she does not type her personal info in the bad sites, she is safe.

Then I had, inside home, the best illustration on how Windows and many proprietary software contribute to early obsolescence of computer hardware. None of newer versions of Windows can run in my sister’s computer. Newer Windows uses at least 15 GB of disk, while Ubuntu fits into a CD and installed uses no more than 5 GB, counting the default applications, that includes an office package. This size can increase if install too many programs, but you do not count applications as part of the system, do you?

There are some tasks, like gaming and playing HD movies that do require newer hardware, but that old hardware is perfectly capable of performing any task most of the people need. The only need for a bigger hardware is to run new Windows and its accompanying must-have anti-virus. The tasks people actually perform in their computers are irrelevant to the hardware, compared to the bogus operating systems over it. See, it is not the nature of computers to slowdown over time. They should keep the same speed while the usage pattern of the user is the same. Also, for a set of functionality available in a software, it’s newer versions must perform at least as well for this same set. This means that there is no acceptable reason for newer Excel to need more resources than the older Excel if you will use them in the same way.

The practice to make things seems older without they actually being old is called planned obsolescence, and it is a disgusting practice in view of sustainability, not to mention human quality of life. My sister’s keyboard is horribly dirty. It would take me about 2 hours to clean in completely. Considering a new keyboard costs less than 10 dollars and my specialised work hour may cost more than that, it is more worthy to buy a new keyboard. But I will not do that. I prefer to clean my keyboard, as new ones are only cheap because there are semi-slave workers in China building them for less than 10 dollars a month.


De como a morsa comeu o remador

June 29, 2010

Da pedra do mar
A morsa observa
O marujo a remar
O barco sem vela

Saltando ao mar
Banha a flutuar
Ruma a morsa
Ao barco, afundar

Pobre marinheiro
Triste sina, a sua
Com o barco a guiar
Da morsa se salvar

“Morsa infame e faminta
Mãe maldita a teria”
Bravo marinheiro cansado
À morsa ter esbravejado

Amaldiçoado sois, marinheiro
Pois ao barco a morsa alcançou
Morsa feliz, marinheiro comido
E o barco soçobrou

continua em:
De como o marujo, usando um clipe de papel e uma escova de dentes, abriu caminho pelo buxo da morsa para a sua liberdade

Essa é antiga, uma das primeiras, provavelmente de 2006. Não gosto muito dela, pois é possível notar toda falta de cuidado e inexperiência do pretencioso jovem poeta. De qualquer modo, chega a ser divertida, e registro-a aqui por questões históricas e atendendo a pedidos.

Why I Prefer GPL

June 28, 2010

A few days ago a discussion started on the MSL-TM mailing list about how we choose the license to use on Castaneum, a software project we are developing (at least, we should be developing).

The MSL-TM is a regional group (from Triângulo Mineiro) of people interested in the using and spreading of free software. I like to define free software as any software product that is patrimony of humanity, thus, every human being has the same rights over it. This is my definition, but there are many definitions of it, seen by many different perspective. The definition regarded as the official is the one given by the Free Software Foundation (FSF), the ones who created the term.

Castaneum is a software system aimed to ease control over who uses the computers from university’s library, that we, from MSL-TM, are developing as an effort to remove, or at least lessen, the use of Microsoft Windows in campus, what, I must say, at least 90% is pirated. I heard from the Data Processing Director himself that the university is overwhelmed by Windows viruses, and our highly restrictive firewall is to refrain the spreading of those viruses to the Internet.

I do not know who first choose to license the project under the GNU General Public License (GPL), but I do know that was me who confirmed this choice, when I submitted the first bit of code into the source code repository, and replaced the notice that said we would be using GPL with the license text itself. Some members of the group where not satisfied with the choice, what started the aforementioned discussion.

To summarize the problem (and those who are familiar with free software may be have heard about it), GPL was not free enough. Every written software is property of its author, due to the copyright law, existing in every country I know. For a software to be free, the author must grant some of its rights to everybody who can get the hands on the software, and the ordinary method of doing so is distributing the software under preëxisting free software license. The problem of GPL, a free software license written by the FSF, is that it prevents anyone who gets the software to changes the terms of how it can be distributed. For instance, if I get a software product and create some other software by modifying the original, what is perfectly OK, since it is free, I can only sell my resulting software under the same GPL terms I got the original. It would actually make my new software free, like the one I got. This kind of restriction is ironically called copyleft: while copyright restricts copying, copyleft ensures possibility of copying.

The voices against GPL says that it is a viral license, because every free software that derives something from a GPL’d software must become GPL’d, so it spread like a virus. These people usually prefer licenses like BSD-style and MIT-style. These free software licenses are much smaller and simple than GPL, and have the important distinction of allowing a software distributed under it to be licensed by another person under other license, provided that their little restrictions are met. The big and relevant practical effect is that one (lets say, Apple) may take a free software (lets say, FreeBSD), change it into something else (lets say, MacOS X) and sell it under its own restrictions, disallowing anyone to have the same rights one had when got the original free software. This practice is known as “closing” the software, what is not a very fortunate choice of words.

So far we have: use BSD if you do not mind having your software “closed” and sold by others. Use GPL if you do not want any “restrictive” software product to be derived from your own software. This later is often misinterpreted. Many do think that GPL will refrain others from selling a software, what is very wrong. Anyone can sell GPL’d software, provided that it continues to be GPL’d. The confusion is justifiable since the prevailing business model of software industry requires that, if a software is sold, the buying part is prohibited to copy and redistribute it. Otherwise, it would make no sense selling it at high prices when anyone could get a legal copy from someone who have bought it before. Obviously, GPL’d software is unsuitable to this business model, because it allows the buyer to redistribute the software freely.

BSD and less restrictive licenses are often used in free software projects supported and developed by big corporations, like Google’s Chromium, that is behind Chrome, Apple’s Darwin, that is behind MacOS X. It would allow them to benefit from the free workforce that can develop around a open source project — as described in The Cathedral and the Bazaar book — while giving them the possibility to use it in it’s own non-free products. The term open source can be regarded as the best methodology available on developing free software.

We can put the matter in another perspective: do you believe non-free software is immoral? If so, use GPL, otherwise, use BSD. This question may sound absurd for people outside free and open source community. One may say: “of course it is moral, it is perfectly legal under copyright law”. If so, I may fell tempted to question the morality of this law in regarding of software, and I am not the only one to do so.

I will not get into details on how copyright law got perverted in regard to artistic works, what somehow motivated the creation of Pirate Party and linked Creative Commons and free culture to free software. I will attain to utilitarian software, what every software, besides games, are.

It was a very dirty trick to fit software into the old copyright law, created to protect the rights of artists over their books, plays, paintings and music. The purpose of the law was to give incentive to authors of such artistic and cultural works to create more. Imagine you are a book writer, if anyone could publish your book without paying you anything, you would feel very bad, and would need another job in order to live, so you would write much less than you would if you could earn money by writing.

While the similarities between software and artistic works were taken into consideration when they decided to include software in that law, namely, that they are easy and cheap to copy, but hard and expensive to create, they left outside one difference of most importance. People consume artwork because they want, but consume software because they need.

From an economic point of view, no one systematically order general artwork, like books, from artists, but people do consume them when they are done. On the other hand, people systematically order software from software makers, in a way that is enough to refrain a programmer from starving. Copyright law has little use in this scenario. Actually, most of the small software companies do survive by creating specific programs for specific clients, and selling software in boxes are distant realities.

From a more human point of view, suppose you are a programmer and created a software that is useful for you. Your neighbour asks you to have it, and costs you nothing to give it to him. Would you give? I am pretty sure most of the people would simply give away. Some may say it is part of human nature: if it costs nothing to help, we simply help. Imagine you have a lit candle, and someone besides you have an unlit candle, would you lit his candle for free?

This simple and intuitive concept is reversed in the corporate “software-in-a-box” business model, where already created software, which has cost virtually zero to reproduce, is sold by obscenely high price compared to its reproduction cost. Why is it so? Why our organizations do such things while individuals tend behave in the opposite direction? Everybody knows that corporations do not abide to morals, but instead to profit. While it is permitted by law and by consumers to do immoral lucrative deeds, they will do. And you can hardly imagine how lucrative, compared to the costs, can be to sell a box containing a copy of a software. It is so lucrative that Microsoft employees need to stop playing golf in the corridors when the money for replacing broken windows is over (and I heard this from a Microsoft employee). It makes me wonder: how many times more rich than the second richest man Bill Gates would be if everyone who uses a pirated copy of Microsoft Office paid what is due to him?

This is the reason I prefer GPL over less restrictive licenses, because the only good reason to choose BSD in place of GPL is to endorse a business model I believe to be immoral. But it is idealistic and unpractical to attain too firmly to this resolution. In an ideal world, every software should be free, thus copyright, if existed, should not apply to software. But we have copyright for software, and now days, to believe software should be free is much more weird than to believe software should not be. It can be very difficult to convince someone that free software actually works until he or she sees, with their own eyes, that it works.

Since the development model of free software relies on external contribution from the parties interested in the software, it may be preferable, in some cases, to have the software distributed in less restrictive licenses. A software under BSD license would give some guarantees to a potential contributor, who would not be afraid of investing in it, as the software could be at any time incorporated the his old business model. Even if the contributor has no plans of “closing” the software, he feels much more incline in helping if there is this possibility.

I would say that our economy is not “psychologically” ready to embrace the idea that, once the software is given to people, it can not be brought back into chains.


June 25, 2010

O seu olhar tão profundo
como o mar no fim do mundo
penetra tão fundo na alma
que congela, aquece, acalma

O seu olhar tão sereno
mais ameno que o sonhar
faz amar o coração
e do amar, apaixonar

Olhar profundo, sereno
que cativa, que me espanta
e desfoca o mar e o mundo
e os reflete nesse olhar

Essa é a poesia que eu considero minha obra máxima, datada de primeiro de setembro de 2009, escrita entre as 11:30 e 12:00, mas pensada durante toda a noite precedente, para uma pessoa bem específica. Já deve estar na hora de torná-la pública.

On the Copying of Ideas

June 23, 2010

David Lewis Photo

David Lewis

While revisiting the article “The Paradoxes of Time Travel“, 1975, from David Kellogg Lewis, I noticed — for my surprise — how much my earlier post relates to the introductory ideas of the article. I clearly copied some ideas from him, although I was not fully aware of that while writing. There is a clear relation between the concept of personal time, from Lewis’ article, and the time perception, from my own. Also, the sole motivation for defining the idea of travel to past of future is from that article, where the concept is mentioned, although Lewis classify it as a travel to past.

Judging from now, the classification I presented — mainly the idea of continuous time travel — was deeply influenced by that article. What I did was to generalize the idea of “personal time” to the something more related to Einstein’s relativity, so it would be more close to what I understand of differences in time passing rate (and what I believe most people understand of the subject, if they understand anything at all). Thus, I could, for some kinds of time travel, argue about its physical feasibility.

Anyway, before writing the post, I did not get to the end of Lewis’ article. I told a friend I was thinking on classifying time travels and its paradoxes, and he gave me this article, from a contemporary philosopher. I started reading it, but could not resist the urge of starting my own article, so abandoned it in the middle. There it gets weird, because if I copied so much from him, I should at least have remembered when I read the article again (this time, the whole of it), but instead, the fact surprised me.

Another source of surprise is the idea of cause-effect loop, that I illustrated with a story featuring Jules Verne, and believe to be a pretty much original idea. Poor spirit of mine… don’t I know everything I dare to imagine was already imagined a thousand times before? The same idea was already in that same Lewis’ article, illustrated by the story of a time traveler who told his former self how to build the time machine, but in the part I did not read until after publishing my story.

Sure, my version of it is not very original, but was developed from a Mickey and Goofy comic book I’ve read more than ten years ago, where they travel to past and meet Jules Verne. But I only understood how serious was the matter when I found out about the closed timelike curves, and their potential effect on causality.

Lastly, I want to say that I am writing this because, after finding that Lewis’ article inspired me so much, I felt guilty of not giving proper credit. I also felt really sorry when I found he died in 2001 from health problems, so I can’t bother him with mails telling of my disagreement on his views of time paradoxes.

Time Travel Classification Pocket-Book for Science Fiction

June 21, 2010

On this article, I will try to provide a well-defined classification of time traveling of entities, as seen in fiction and as theorized by physicists and philosophers. To have a good categorization, we need strong definitions on the relevant concepts of time traveling, what will be provided based on what I believe to be the “status quo” on the subject.

Definition: Time

First, we need to define time itself. Time could be seen as an ordered dimension (or set) of cause-effect worlds. I mean with that: the world on a given time is the cause of the world on a later time, and an effect caused by the world on a previous time. You can think it as a film: one film frame is a world at one instant, and the next film frame is the world one instant later, which is a direct consequence of the previous frame. The notion that the cause precedes the consequences is very important here. This definition will suffice for the scope of this article, although it is not entirely true in some hypothetical valid situations on modern physics (I am talking about Closed Timelike Curves, but don’t bother with them for now).

Definition: Entity

Entities are the carriers of the cause-effect chain through time, that influences other entities through the mechanical rules of the world. I am aware that it sounds terribly obscure, and I am not even sure if this definition is complete, but what I mean is that an entity can be anything that exists in the world that can influence other things. A ball, a person, a light ray, an atom, a whale, a glass of water. An entity is what we could call a thing. An entity is what can be a time traveler.

Definition: Time Perception

Now what I think to be the most important definition: the time perception. The time perception is, from the point of view of an entity, the order and the rate that cause-effect are chained “around” itself. For around, I mean what the entity can directly influence and be influenced by, including itself. For a human entity, it is the speed that a person perceives the passage of time, or even better, is the speed the time actually passes for that person. It is a very common mistake to assume that time perception is universal in our reality, like thinking that time passes equally to all entities in the universe. Time does not passes equally to all entities in the universe! If you don’t believe me, consult the nearest physicist.

Definition: Time Travel

Given all those names, what is a time travel? An entity is said to have traveled through time when it went to its own future at its ordinary rate according to its own time perception, but arrived at a point in time dimension that would not be possible by the time perception of an important external reference entity (the Earth, in most cases), had them both shared the same time passage duration and rate. In other words: for a time traveler, time passed just as usual: forward, at regular speed. But by the means of his traveling, he will end up in a different position in time as he would if he had experienced this same time ordinarily on Earth.

Notice that in this definition of time travel, we only consider one-way travels. If you want to visit the future and then get back to the time you belong, it would require from you two time travels: one forwards and one backwards, which are, by nature, different beasts. Specifically, backwards time travels may cause paradoxes, while forwards time travels don’t, and have the same direction of the ordinary time passing rate, what could make it somewhat easier. In some sense, one may think that everything is always traveling towards future, but since we defined the time travel in respect to some external reference, if time is passing equally to everything we consider, then nothing is traveling in time, at least not in the sense defined here.


These were the main terms that must be well understood. Once done, we can dive into classifying time traveling itself. Firstly I want to propose the classification of the travel by continuity of the journey inside the space-time of reality.

Continuous versus Leap

A time travel is continuous if, while traveling, the traveler is in somewhere to be found inside space or somewhen to be found inside history: for instance, it is the case of the famous Twin Paradox, which one twin travels on high-speed through space, and when arrives back at earth, finds that his twin was older than him. Since he was all the time traveling through space and could always be seen from earth, it was a continuous time travel to a future where he found his brother older. On the other hand, we have leap time travels, what is the classical case in fiction, where a dog is placed in a DeLorean and vanishes from reality, to only be found again 5 minutes in future (Back to the Future). Or a war machine is beamed up from a dystopian futuristic world dominated by robots so the next time it would be seen was 45 years in the past (Terminator).

You may have guessed by now that leap time travels are far more common in fiction than the continuous type. It is so because leap travels are much more intuitive and convenient: if I am to travel through time, it is better done instantly, so that I do not have to be anywhen between now and when I want to be. On the other hand, the continuous type is much more technically and theoretically feasible, and fiction targeted to more nerdy audience tend to have more elements of it, like in the movie “Primer”, where the time travelers needed to stay inside the time machine during all the journey, and they would actually be inside it during the time the machine was working. To travel one day to the past, they would need to power on the machine one day before the journey, so the next day, when they get into it and stayed there, the machine would take them to when it was turned on.

Continuous Travel to Future

In the case of continuous time travels, you may have future, past of future and past time travels. Continuous time travel is a mere fact of changing the time perception of the traveler in relation to the reference time perception. In this regard, to send an entity to future, one must make the time perception of that entity slower than the reference. While, in the perception of the entity, one minute have passed, one year have passed in the reference time perception, bringing an entity from past into future. This phenomenon is known as time dilation.

A parody of this time traveling concept can be seen in an episode of The “Powerpuff Girls”, when they raced so fast, making the time slower for them, that when they stopped racing, they where in the future. Accelerating very fast and then de-accelerating back to the initial speed is one method of using time dilation to continuously travel to future. While parodying the physical effect, this same explanation could not be applied to the travel back to past in that same episode, and they only were able to get back home so the episode could have a happy ending.

Continuous Travel to Past of Future

If time perception of a traveler is faster than the reference perception, then he could spend one year in a time machine, get out and find that only one minute have passed in the reference time perception. This is what I called travel to the past of future, because the traveler did not end up in past, but it ended up in a time before he would if he was not traveling.

It seems that there are much more practical issues in using time dilation phenomenon to create this effect than to use it to travel future, although it is not entirely impossible. This kind of time traveling is very well illustrated in “Dragon Ball Z” anime by The Room of Spirit and Time, where one year inside it equals to one day in the outside.

Continuous Travel to Past in the Same Space

The most difficult to understand (and even to think) kind of continuous time travel is the travel to past, where the traveler end up in a time before he started his journey. There is a (maybe a little hard to see) paradox in the “Primer” time machine, where time spent inside it could pass backwards relative to the time outside of it. Imagine you get into the machine to travel past. What would you see? In the moment the machine was powered, would you see yourself undoing what you have done until you have entered the machine? Would you split into two, occupying the same space at the same instant? One for the time going forward and the one for the going backwards? Because, to be able to move into the machine where time passes backwards, your time would need to pass forwards, because the very notion of movement needs time passing forward. It is tricky to even think of this problem, and I can imagine a number of contradictory situations arising from it, both on the entering the machine and exiting from it. The big problem is in the limits, when time passing inverts. There can be no place that at one instant flows one direction and other instant flows another. The time in the machine would be like a one way road, that in the middle of it, the direction inverts, leaving the arriving cars nowhere to go, and leaving no traffic after the inverted part.

Illustration of time as seen as road

What, then, would be a more consistent continuous time travel mechanism that allows travels to past? I will delay this answer until my considerations about leap time travels.

Leap Time Travel

Leap time travels are less physically attainable, at least on non-quantum scale, considering what we currently know about physics. Maybe a fairy can beam you with a magic power and send you through time, but while I try to say one word or two about feasibility, it is not the focus here.

Leap to Future

Suppose you have machine that can instantly send an entity anywhere in space-time. If an entity travels by this mean to future, despite the fact it will no longer exists in reality while it does not arrive to its destination — what itself is bizarre — when it arrives, it will physically behave as it would otherwise, and we would have no further logical problems. If one person disappears to only reappear one year in future, it would walk, talk, tell other how wonderfully he traveled to future, and would influence reality as he always have, with no further consequences.

Leap to Past

The big problem is when someone disappears now and travel to past. Well, past already happened, and already influenced reality so that it would be like it is when then person traveled to past. So what happens if this person kills its former self? It would never be able live to travel past to kill its former self, so it would be alive. Contradiction!

Paradoxes of Traveling to Past

There are three solutions to the travel to past paradox. First: it is impossible to travel past. Well, since this is a time travel discussion, it is fair to discard this solution.

Branching Realities

Second: when the past is altered in a way that would disable the future the traveler knows to happen, the reality is branched, so he would now live in an alternate reality which complies with the new inserted acts of the traveler in the past. This solution is simple, settles the matter, but then arises the question: would the traveler be able to travel back to the reality he left? This fall out of scope of time traveling, into the scope of alternate realities traveling, what may not be so different if this solution to the paradox is to be adopted. Although Marvel stories are not entirely consistent (actually, they are totally inconsistent), it seems that the type of time travel to past the Fantastic Four is often able to perform is the reality branching type.

Self-consistent Realities

The third solution, the most beautiful and astonishing when well orchestrated in science fiction, is the one that estates that reality is self-consistent. If you are able to travel to past, all your actions will inevitably leads to the future you already know. If you think of reality as an system of equations, the travel happens only if there is a solution to the system where there is a travel to the past that leaves the world in a consistent state so that that travel was meant to happen, and the effects caused by a travel led to the travel itself, or at least did not contradicted it. This is the case of time travels as seen in the movie “12 Monkeys” (and by transitivity, in “La Jetée”, which inspired it). Everything though the course of the film leads to what happened in the beginning of it.

The non-contradiction rule have an intimate relationship with Novikov Self-Consistency Principle, created because some solutions to the general relativity equations lead to bizarre things that could be interpreted as time travels to past. At least on this kind of time travel, the principle estates that no contradictory situation could arrive from it.

The biggest problem with this rule has to do with free will. If I want to deliberately kill someone in the past that was alive at my time, somehow I will not succeed, and it may even imply that, if allowing me to travel past will certainly allow me to kill that person, that I may not be able to travel past at all, or only travel with the necessary restriction that would make the present be direct consequence of the past I will be able to influence. This restriction is represented in the “12 Monkeys” movie by the strong stress and mental confusion that were imposed to time travelers, that would influence the travelers to do things they would not do if they were fully aware that they were time travelers.

An amazing effect possible on time travels to past that do not branch reality has to do with causality: what if an effect is its own cause? Suppose I find a sword on a rock. I take the sword and pass on for generations. Then, my grand grandson takes the sword on a travel to past and plant it in the exact same spot I found it, and just leave it there for me to find, then I find it and the story closes. There is no paradox in this story, but where did the sword came from? This situation would break the own definition of time we gave in the beginning of the article. This is the situation depicted in the movie “Predestination” and in one of the time travel situations depicted in movie “Interstellar”.

Swords do rusts, so it is not a very good example. Instead, think that I took a recent edition of the book “Twenty Thousand Leagues Under the Sea”, brought it back to some time it were not written, and gave it to Jules Verne. He takes it, reads it, likes it, and publish it as being his own, so that everybody believes he wrote it, what leads to the reality we know nowdays, so I can take the book back to past, closing the cycle. Who wrote the book? The story just showed up in reality and closed a cycle, it was its own cause. More formal formulations of situations like this, based on general relativity, are called (as I already mentioned), Closed Timelike Curves. It is not a settled matter if closed timelike curves do exists in practice, but what was physically predicted for now is far from allowing a book to travel past.

Continuous Travel Through Space Tunnel

Thus ends the considerations about the paradox and bizarre effects of leap time travels to past. We can now get back to continuous time travels to past. How can it be?

What would somewhat adheres to the definition of continuous time travel is a time tunnel. A time tunnel has two ends and maybe an intermediary space. A more scientifically appealing view would be a wormhole with no intermediate space, and placing your arm inside it would take it to past, as if past was over there, like the next room. The time perception on both ends of the tunnel would be the same to an observer who watched through it, but each end could exist in a different times and space. Observing the other end of the tunnel trough another way besides the tunnel, could reveal that the time perception of one end is different from another, and the difference in time between the two ends is actually increasing, but that would not be observable through the tunnel, since it seamlessly links two different locations of time and space, including their time perception. As a tunnel, it would allow travels in both directions, past and future.

If the branching reality rule applies, the reality is branched at the moment the first entity traverses a tunnel to the past that was not meant to have passed. Since there are zillions of “things” going in every direction in everyplace in space, among light, radiation and all sort of subatomic particle, as long as the tunnel remained open, zillions and zillions of realities would be branching, in a combinatorial explosion of realities and tunnels links between realities. As you can see, the idea of reality branching is not well suited to continuous past time travels. The idea of self consistency seems to be much more appealing in this situation, and it would not be possible to change past through a time tunnel.

A wormhole, that maybe could be used as time tunnel, if somehow they could be created, would look like the one in this video, made by Corvin Zahn:

At first, the wormhole connects just two different places. But if the time of one place is dilated in relation to the other, the time in the ends of the wormhole would also differentiate, turning them time tunnels.

If you find any inconsistency in this article, or any error of any nature, please let me know.