The Negative Universe

Dandelion(negative)
Dandelion(negative) (Photo credit: tanakawho)

 

If cosmologists are to be believed the Universe came from nothing and is likely to return to nothing. This is odd as there seems to be an awful lot of it! There are between ten to the power 78 and ten to the power 82 atoms in the observable universe, according to some estimates. There’s also a huge amount of energy out there in the universe, and as Einstein said, this is equivalent to matter, according to his famous equation.

Maxwell's Equations
Maxwell’s Equations (Photo credit: DJOtaku)

 

It is likely that the enormous amount of matter and energy that we see out there is balanced by an equivalent amount of “negative” matter and energy somehow. “Negative” is in scare quotes because it may not describe what is actually going on. Anyway, the negative matter and energy may be incorporated into this universe somehow, which means that on average half the universe is this sort of energy. We can’t see it anywhere so far as I know, so it is a bit of a puzzle.

Large Format Doha Panorama Portra 400
Large Format Doha Panorama Portra 400 (Photo credit: Doha Sam)

We can see evidence everywhere for “normal” matter and energy, and we should be able to see evidence of “negative” matter if it is anywhere near us. As I understand it, “negative” matter would behave differently to “normal” in various ways and should be detectable. I’m not sure in what ways it would be different – I can guess that there could be a gravitational attraction between particles of “negative” matter, just as there is between particles of “normal” matter, but there could be a gravitational repulsion between “negative” matter and “normal” matter for example.

Galaxy NGC 720 (NASA, Chandra, 10/22/02)
Galaxy NGC 720 (NASA, Chandra, 10/22/02) (Photo credit: NASA’s Marshall Space Flight Center)

But my ignorance is almost total. I do believe it is true that “negative” matter should be detectable.) Since we can’t see or detect “negative” matter within our locality (ie “the observable universe“) it may be grouped elsewhere in the universe. If so, it may not have any observable effect in our neck of the woods, but inevitable it will have an effect at some time in the astronomical future.

Español: es la misma imagen que aparece en el ...
Español: es la misma imagen que aparece en el articulo en ingles: http://en.wikipedia.org/wiki/Sloan_Great_Wall (Photo credit: Wikipedia)

The reason that I say this is that the universe doesn’t seem to be expanding faster than the speed of light so any effect such as (possibly) gravity which does appear to have a “speed of light” effect will eventually affect our corner of the universe. But the situation is complex, and as the Wikipedia article says,

Due to the non-intuitive nature of the subject and what has been described by some as “careless” choices of wording, certain descriptions of the metric expansion of space and the misconceptions to which such descriptions can lead are an ongoing subject of discussion in the realm of pedagogy and communication of scientific concepts.

In other words, there are many misconceptions and misinterpretations around this topic. However any effect of the possible existence of “negative” matter on our little neck of the universe is likely to be felt a long time in the future, even on a cosmological time scale, I feel. “Negative” matter could have created a negative universe, I guess, which mirrors this universe.

Photo of a printout of the Wikipedia Copyleft ...
Photo of a printout of the Wikipedia Copyleft reflection in mirror, with pen (Photo credit: Wikipedia)

In a negative universe at least one dimension would be reversed but all other dimension would have the same polarity as our universe. If an odd number of dimensions were reversed, would all but one cancel out? I’m not sure but a cursory mathematical examination would indicate that this would not be so, but I lack the time to explore the concept in depth.

Dimensions
Dimensions (Photo credit: Wikipedia)

In our universe things tend to a state of disorder. If one partition of a closed system contains all the matter (in the simplest case, as a gas) and the partition is removed then eventually the matter is eventually dispersed through the whole system. In a negative universe, possibly the opposite would apply – gas dispersed through a system could tend to bunch up in one part of the system. Maxwell’s demon could watch benignly without lifting a finger.

Demonio Maxwell 2
Demonio Maxwell 2 (Photo credit: Wikipedia)

Our view of this is that it is extremely unlikely – would a glass spontaneously rise from the floor, gathering the scattered wine and land on the table complete with wine? Perhaps this is a parochial view, only true in our universe. In some alternate universe, this may be the normality – entropy may tend to decrease, order may tend to increase. Such an entropy twin may simple be the time reversed twin of the original universe. Or the original universe perceived from a time reversed perspective.

The Grand Canyon Time-Zero Project
The Grand Canyon Time-Zero Project (Photo credit: futurowoman)

If the universe sprung out of nothing, then the sum of the universe is zero. Any object has its anti-object. Any event has its anti-event. Maybe the universe has a partner, an anti-universe if you like, or even a mirror universe. Time in our universe runs from the zero moment into the positive future. In a mirror universe would presumably (and debatably) run in the opposite direction from the zero moment and all spacial dimensions would be reversed.

Plus-Reversed,-1960
Plus-Reversed,-1960 (Photo credit: Wikipedia)

This would correspond to a point reflection in time and space, which may or may not be the same as a rotation in time and space. I’m not sure. Some of complexities can be seen in this Wikipedia article on “parity”. In particular some interactions of elementary particles may display chirality, which means that they come in left and right handed versions, like gloves or shoes. All of the above means that if a person were to be point reflected into an anti-universe and all the elementary particles of his body were switched with their anti-particles, there may be no way for the person to tell that the switch had occurred.

different flowers from same plant
different flowers from same plant (Photo credit: ghedo)

Sure, time would be reversed, but so would literally everything else, so a left-handed glove would appear, in the point reflected world, to still be a left-handed glove even though, if we could see the glove it would appear to us, from our point of view to be right-handed. Of course I’ve assumed for much of the above that the reflection that transforms a universe to its anti-universe is a point reflection.

Axial chirality
Axial chirality (Photo credit: Wikipedia)

In mathematical terms that means that all variables are reversed. That is x is replaced by -x, y by -y, z by -z and so on. It may be that the reflection may be in a line and the x dimension stays the same while the others are negated. Or it may be a reflection in a plane (a mirror reflection) where 2 dimensions are unchanged. Or it may be a reflection in a higher number of dimensions.

English: Upper Yosemite fall with reflection
English: Upper Yosemite fall with reflection (Photo credit: Wikipedia)

As you can see, the subject is complex and I’ve not got my head around it (obviously!), but I believe that if we were switched into the anti-universe (including all out particles) it would not look any different from this universe. In fact we would probably find ourselves discussing our anti-universe, which would be our original universe. In fact it would not matter which universe we called “the original” because they both would have come into existence at the same time and there would be no meaning to the term “original”.

A face.. (the original OMG Wall)
A face.. (the original OMG Wall) (Photo credit: eworm)

 

Classification

"Father! Father! / Tell me what ails thee...
“Father! Father! / Tell me what ails thee? / With dismay thou art filling thy child!” (Photo credit: Wikipedia)

Oh, wow, drat and other words of dismay. I haven’t thought of a topic for this week and it is time to write my post. Time to get started.

OK, people seem to like classifying things. This can be so that they can find one item in a large collection of things, or it may be simply a means of bolstering prejudices that they might have. Or any of a myriad number of other reasons.

Garbage Can
Garbage Can (Photo credit: Wikipedia)

When faced with a profusion of things, the human impulse is to classify them. One of the most famous classification systems is that of Carl Linnaeus, whose classification system is used for the not so trivial task of classifying all living things. His system, with modifications is still the basis for biological classification of all organisms.

Digitally improved version of Alexander Roslin...
Digitally improved version of Alexander Roslin’s painting of Carl von Linné. This particular version has had dust and missing specs of paint deleted. (Photo credit: Wikipedia)

When Linnaeus started his classification, it is likely that partial schemes would likely have been in place to classify small groups of organisms, but Linnaeus extended this to all organisms, in an organised way. When someone states that mankind’s scientific name is “Homo Sapiens”, he or she is using the Linnaeus system, at least partially.

“Homo” represents mankind’s Genus, and “Sapiens” is mankind’s  Species, but the species is merely a leaf on the classification tree, which is rooted in the Animalia Kingdom, and descends through Phylum, Class, Order, Family, and Tribe, (which I’m not going to list here) and finally to the Genus and Species.

Darwin's tree of life
Darwin’s tree of life (Photo credit: Wikipedia)

Linnaeus’ system is still in use today, but the emphasis has changed somewhat. When he was doing his work, the classification was based on appearance, and while that is often a good guide to an organism’s place in nature, emphasis has now shifted to the genetic make up of organisms to determine their correct classification.

Agapornis phylogeny
Agapornis phylogeny (Photo credit: Wikipedia)

This has sometimes resulted in whole chunks of the classification tree being moved from one branch to another as knowledge of the genetics of the organisms has come to light. It is obvious that if two organisms have similar genetic make ups, then they must be closely related. Also, it implies that they almost certainly have a common ancestor, and such an ancestor is also fitted into the tree of life and given a species name.

Horned Dinosaur Phylogeny
Horned Dinosaur Phylogeny (Photo credit: Scott Wurzel)

This adds a time dimension to the genetic tree, turning it from a static representation of living organisms into a dynamic picture of all life over all time. The tree of life is evolving.

Another great classification system is the Dewey Decimal Classification system, a proprietary library classification system used to classify books. Every book in a library is assigned a number, which in most cases would not be unique. The number consists of two parts separated by a period (‘.’). Most library users would be aware of the system, and will have used it to locate books.

Spine Books Label show Call Number for Dewey D...
Spine Books Label show Call Number for Dewey Decimal Classification. (Photo credit: Wikipedia)

While the system can classify books in great detail, merely by extending the number after the period to many decimal points, most libraries classify their books in much less detail, using only two or three digits as a suffix. This results in groups of books receiving the same number, with the books in a group sharing a common topic, while differing in detail.

get to know the dewey decimal system
get to know the dewey decimal system (Photo credit: susannaryan)

For instance a particular number may be assigned by the library whose topic might be the geography of the country of Bolivia. (The actual number is 918.4). The library might have only one or two books on the subject of the country of Bolivia, so that number is sufficient to locate any of them.

In the country of Bolivia itself, however, there will almost certainly be many more books on the topic and the Dewey Decimal Classification almost certainly contains more detailed classification numbers which would have to be used in Bolivia libraries to classify the geography books. (I’ve not checked this “factoid” but it is probably true).

Shelf of Books on South America
Shelf of Books on South America (Photo credit: pkdon50)

So the Dewey Decimal Classification system can be hair-splittingly  accurate or broadly general in its application and this flexibility is ideal for libraries. Sometime libraries use a sort of hybrid system, probably driven by the need for a sub-classification where some books have been already more generally classified, where some books are classified as “something.12” and other books are classified as “something.123”. In most cases this inconsistency doesn’t matter.

Topographic map of Bolivia. Created with GMT f...
Topographic map of Bolivia. Created with GMT from public domain GLOBE data. (Photo credit: Wikipedia)

I’ve just realised on writing that, that it may not be inconsistency at all. Instead the “something.123” books may be more specific than the “something.12” books, which would therefore be more general.

An obvious difficulty with the Dewey Decimal Classification system is that there is no cross-reference possible. In the Bolivia example, a book may cover the topic of the geographic causes of distribution of various related Bolivian species of some organism or other. Is this to be classified as biology and be assigned to a class in the 500s (Pure Science), or should it be classified as geography and assigned to a class in the 900s?

English:
English: (Photo credit: Wikipedia)

Nowadays one can do a computer search and come up with a bunch of numbers that fit the topic that is being researched. In the days before computers there were card-based “Topic Catalogs” which would also provide the searcher with a bunch of numbers. The trouble is, many searches would result in multiple numbers, either as a result of a card search or a computer search.  One would then have to go to several locations to decide if the required topic was covered by this Dewey Decimal Classification number or one of the others. I make it sound bad, but really, it wasn’t, and the issue is more a user confusion about what was covered by each topic in the system rather than an issue with the system itself.

Banner for Wikipedia:WikiProject Lists of topics
Banner for Wikipedia:WikiProject Lists of topics (Photo credit: Wikipedia)

A computer search (on Google for example) will provide a list of possible references to a search term, but as anyone has used a computer search is aware, a search term can refer to many topics. A search for the word Socrates gave me a list including a Wikipedia article on the philosopher himself, a list of quotes taken from his work, a biography of the philosopher and a site where his philosophies could be discussed. And that is just the first four items out of an estimated 6 million or so.

Google
Google (Photo credit: warrantedarrest)

Classification of things seems to be a trait of humans. I think that we classify things to simplify things for ourselves, to make it easy to identify threats and possibilities. As such, it is probably an inherited trait possessed by at least the more developed organisms on the planet. However classification can add complexity if one is searching for something, so it is something of a trade off.

google_logo
google_logo (Photo credit: keso)

Ethics and Morals – the Ten Commandments

Ethics and Morals: Timeless and Universal?
Ethics and Morals: Timeless and Universal? (Photo credit: stephenccwu)

I’ve been thinking about ethics and morals over the past week, as preparation of a sort for writing this post. I’m not quite sure what got me started on this topic in the first place though. It would be more accurate to say that it is the basis for ethics and morality is what is interests me.

Religious people don’t have an issue, really, because their religion sets the rules for interactions with others, and any such rule is inviolate because it is supposedly handed to humans by “the powers that be”. The rule base is generally given as the word of god.

Sexta/Viernes/Friday-POSER-Deus - Dios - God
Sexta/Viernes/Friday-POSER-Deus – Dios – God (Photo credit: Caio Basilio)

Laws underscore ethics and morals, as they define what should happen if a person offends against another or the state or establishment. If it is not ethical to steal from another, what should be done? A law defines both the crime and often the punishment.

In the past, when religion had total control of peoples’ lives the religious establishment, the priests or other religious officials generally administered the secular laws and at the same time administered religious matters. In fact there was little difference.

Priest reading
Priest reading (Photo credit: Matthew Almon Roth)

The laws of those times, at least in England and Europe and probably in most of the rest of the world reflected a vengeful deity. The basic ethic was “an eye for an eye and a tooth for a tooth“, with the added spice of an implication of sin.

English: Coat of Arms of His Eminence Jaime Ca...
English: Coat of Arms of His Eminence Jaime Cardinal Sin. (Photo credit: Wikipedia)

Sin is an offence against god, so trumps the mere earthly transgression of the theft or whatever itself, resulting in penalties which would seem far too harsh in this day and age. For instance amputation for theft, deportation, banishment, or death for similar offences was common. Apart from the punishment of the perpetrator, a reason for the severity of the sentences was intended to underline the power of the establishment and to deter others from committing similar crimes.

Ten Commandments
Ten Commandments (Photo credit: glen edelson)

In Christian and Jewish religions there are the Ten Commandments (or Sayings in Judaism). To Christians they are the ten commands of God, and in Judaism they are ten of 613 commandments of God.

Pomegranate heart- corazon de granada
Pomegranate heart- corazon de granada (Photo credit: LifeAsIPictured)

There are three parts to the Ten Commandments.

Firstly, there are four commandments relating to God. From an ethical point of view, if you believed that God was overseeing your life, then you had better do whatever you could to make him happy. A good start is to believe in Him, and then to keep Him happy by worshipping him in appropriate ways.

Detaill of page 130 in section 'Notes to Kent'...
Detaill of page 130 in section ‘Notes to Kent’ of Notes on the churches in the counties of Kent, Sussex, and Surrey The image is a reproduction of a foundation stone of the Plaxtol, ‘abbreviated’ with marks to superficially read ‘This church was built for the worship of God. Anno Domini 1649 (Photo credit: Wikipedia)

Secondly, there is a commandment relating to parents and teachers, in other words, those with authority over one. Again, it makes sense to keep those in authority happy.

Finally, there are five commandments relating to relationships with other people, things such as stealing from them, sleeping with their wife and daughters and so on.

Don't Steal My Coat
Don’t Steal My Coat (Photo credit: Wikipedia)

Outside of the Ten Commandments, it appears that the early Israelites had some ethical beliefs involving animals, as the tale of Balaam’s donkey reveals. Balaam’s donkey complains in a very human way expressing her hurt at Balaam’s treatment of her, and Balaam apologises to her.

Rembrandt's Balaam and his Ass
Rembrandt’s Balaam and his Ass (Photo credit: Wikipedia)

So a religious person has a basis for his assessment of what is right and wrong from the above framework. It was considered right to follow the teachings of the Ten Commandments, and this was reinforced by the society of the time.

Moses with the tablets of the Ten Commandments...
Moses with the tablets of the Ten Commandments, painting by Rembrandt (1659) (Photo credit: Wikipedia)

As with all ethical frameworks, there are times when the framework doesn’t quite seem to fit the situation. When you are starving could it be wrong to steal a loaf of bread, particularly if the bread in question will otherwise go to waste? When your family is starving, could it be wrong to steal to feed them? Obviously if the rules are applied strictly it IS wrong, and often, in the times when religion was paramount, they often were.

Bread Thief
Bread Thief (Photo credit: frankdouwes)

Of course, those who do not have a belief in a deity can still be guided by the Ten Commandments, if they are in fact relevant to them. So let’s have a look at the Ten Commandments from a secular point of view.

Obviously, the four commandments relating to God, don’t apply? Or do they? In dealing with religious people, a non-religious person should be aware of and make allowances for the non-religious person’s belief, so long as they don’t cause a conflict with the non-religious person’s belief. For instance a non-religious person may happily attend a wedding but may object to any attempt to indoctrinate his children with religious beliefs through the child’s schools.

Funny Religious Sticker
Funny Religious Sticker (Photo credit: Amarand Agasi)

An unquestioning following of the fifth commandment may also conflict with a non-religious person’s ethical beliefs. While a non-religious person may accept the authority of the government and of the police, he or she might disagree with the correctness of their actions. Occasionally, though, a non-religious person will disagree with the authorities so much that he or she will rebel against them.

Nobody expects... The Spanish Inquisition!
Nobody expects… The Spanish Inquisition! (Photo credit: Ochre Jelly)

The rest of the commandments deal with relationships with other people, and a non-religious person may well believe that these are ethically correct instructions. They describe how a person might want others to behave towards them, so ethically that is how a person should treat others.

English: Golden Rule, Smithy Brow, Ambleside L...
English: Golden Rule, Smithy Brow, Ambleside Lovely old traditional pub in Ambleside, just across from the main car park. (Photo credit: Wikipedia)

This ethical principle, of “do as you would be done by”, has a long history and is sometimes known as “the Golden Rule“. There is a second part to this principle which “do NOT treat others in a way that you would not like to be treated”. This principle is the basis for the two characters,  Mrs. Doasyouwouldbedoneby and Mrs. Bedonebyasyoudid, from the story “The Water-Babies” by Charles Kingsley.

Cover of "The Water-Babies (Books of Wond...
Cover of The Water-Babies (Books of Wonder)

The Golden Rule seems to be a very good basis for a set of ethical rules. Of course it is too simple to explicitly and accurately cover every eventuality, as the example above of the starving family demonstrates. It also does not make allowance for differences in beliefs, and there are others issues with it, but it can be seen that it is implied in the Ten Commandments.

English: "Mrs. Bedonebyasyoudid." Il...
English: “Mrs. Bedonebyasyoudid.” Illustration for Charles Kingsley’s The Water Babies in charcoal, water, and oil. (New York : Dodd, Mead & Co., 1916), p. 236. (Photo credit: Wikipedia)

The Ten Commandments themselves inherit the issues of the Golden Rule. As given, one should not harm another person, but what if you need to harm someone to save their life? Surgeons do this every day, but one can extend this to the killing of someone. Few people would argue that a policeman who guns down someone on a killing spree, as happens fairly often these days, has acted unethically.

Nevertheless, the Ten Commandments and through them the Golden Rule, provide useful hints and guidelines to good ethical behaviour, even for a non-believer.

Scan of illustration in The water-babies: a fa...
Scan of illustration in The water-babies: a fairy tale for a land-baby (1915) Boston: Houghton Mifflin (Photo credit: Wikipedia)

 

 

Time waits for no man

time travel
time travel (Photo credit: flyzipper)

Time is an odd thing. We say it passes, but it sometimes feels more like we are travelling through. As the old joke goes, we all travel through time – at a rate of one second per second.

While that might bring a smile, it does raise a question about time travel, because if one travels through time, one presumably travels through it at some rate or other, say ten years per minute. The problem with that it is that we are measuring a rate, which is a change of some variable with respect to another, but in this case we are measuring the rate of change of time with respect to time as well.

English: Acceleration as derivative of velocit...
English: Acceleration as derivative of velocity along trajectory (Photo credit: Wikipedia)

The time intervals over which the traveller is passing are measured in the usual way by a clock, but how does the traveller measure his time by? He could carry a clock with him, which he could then use to estimate his progress along the standard time scale. In other words the time traveller would somehow have to carry his own time scale with him which is different to the usual time scale.

Illustration of a light cone, based on Image:L...
Illustration of a light cone, based on Image:Light cone.png (Photo credit: Wikipedia)

Of course, Einstein’s Special Relativity shows that, in a way, we do carry our own time frames around with us, and if we are in motion relative to some other frame then time passes differently the two frames.  Of course, to simply travel in time, we would not want to travel in space, so we can’t use Special Relativity to allow us to use a different time frame, so far as I can see.

Also, we can only travel forward in time by using this loophole. No matter how fast we move relative to someone else, we both move forward in time, so we can’t use Special Relativity to go back in time and kill dear old Grandad.

The Grandfather Paradox
The Grandfather Paradox (Photo credit: Kaptain Kobold)

Einstein’s General Relativity considers that space-time (the conjunction of space and time) possesses curvature, and some theories use this to allow backwards time travel. However these solutions produce “closed time-like curves” which is not so much time travel as a time loop, perhaps like the loop in “Groundhog Day” where Bill Murray’s character repeatedly awakes to the same day.

groundhog day!
groundhog day! (Photo credit: NapaneeGal)

It appears that we need to look further for some way to travel in time. If we can’t use current physics, we will need to consider something more “science fiction” than modern physics. Of course science fiction time travellers don’t seem to explain their travels in more than a cursory way, because, after all, the mechanism is only secondary to the story line.

Time Machine Clockwork
Time Machine Clockwork (Photo credit: Pierre J.)

Two different possible mechanisms spring to mind.

Firstly, one way is to assume a sort of parallel world. A time traveller can enter this parallel world from any point in time and re-enter the standard universe at a different point, earlier or later in time. The traveller travels in time by analogously travelling in space in a world which has its own space-time with one of its space dimensions parallel to the conventional world’s time dimension.

parallel worlds
parallel worlds (Photo credit: aloshbennett)

Secondly, the author can conjecture a viciously curved space-time so that the characters can, at certain locations, move from one part of space-time to another part of time which is either earlier or later in the time dimension. Typically the character will “step sideways” or something to jump between times, either with the help of a machine or maybe not.

HELP ME HELP MYSELF!
HELP ME HELP MYSELF! (Photo credit: eyewashdesign: A. Golden)

One such tale of the second sort is “By His Bootstraps” by Robert A Heinlein, is which the main character passes through a portal to a distant future, only to entangle himself with later (and, relatively, earlier) versions of himself. He encounters a mysterious character who identifies himself as “Diktor”.   I’ll leave it there, as I don’t want to spoil the story for those who haven’t read it yet.

By His Bootstraps
By His Bootstraps (Photo credit: Wikipedia)

An example of the first sort is “The Corridors of Time” by Poul Anderson, where the main character is recruited into a war raging up and down the “corridors of time”.

Most stories, however, don’t specify in more than a cursory way the physics that is supposedly employed by the time traveller.

Train travel
Train travel (Photo credit: Wikipedia)

The effects of time travel are what is explored by these stories. If the traveller goes back in time he or she must interact with the world at the earlier time from when he started. There are time stories in which the traveller changes things so the state of the future time from which he can is changed.

Future World 2012 (Explored)
Future World 2012 (Explored) (Photo credit: Scottwdw)

This is the premise behind the Terminator series of films, where the Cyborg assassin (played by Arnold Schwarzenegger) is sent back in time to kill the mother of John  Connor, the leader of the rebellion against the killer machines. Obviously, in the future from which the Terminator comes, John Connor is born so the Terminator is trying to change the future from which he comes.

The Terminator
The Terminator (Photo credit: Dunechaser)

The obvious paradox here is that the Terminator risks changing the future into one in which he was never created. In which case he would not be able to come back in time to kill Sarah Connor.

The other sort of time travel story treats time as if it were immutable. Any events that happen are eventually shown to have logically been the consequence of the time travel in the first place. For instance, the mysterious stranger on the street turns out to be the time traveller, keeping an eye on the earlier version of himself. All is explained so that the stream of events is logical both from the time sequential point of view and also from the point of view of the traveller. The aforementioned “By His Bootstraps” is a story of this sort.

The Mysterious Stranger
The Mysterious Stranger (Photo credit: Wikipedia)

Is it possible that events in the past could have changed? We would not know it! As far as we would be concerned the past event would have have always happened, since there would be a temporal progression from the past event to our current time. Of course the language is tricky here, as it does not handle such matters as changes to the past.

Einstein's Theory Fights Off Challengers (NASA...
Einstein’s Theory Fights Off Challengers (NASA, Chandra, 04/14/10) (Photo credit: NASA’s Marshall Space Flight Center)

To use the physicists’ favourite analogy of a rubber sheet, if time is considered to be along one dimension of the sheet, and space along the other, then an event which changes the past is like someone pulling a point on the sheet to one side, which affects all the points from both the future and the past of the point which has been moved. But the sheet itself remains intact.

Rubber sheet undergone drying in smoke. Three ...
Rubber sheet undergone drying in smoke. Three versions are there in the picture. 1. Fresh sheet. 2. Little dried in sun light. 3. Dried in smoke. (Photo credit: Wikipedia)

However, I think that this scenario is unlikely. There doesn’t seem (at the present time) any physical mechanism by which time travel could be achieved, and even though it appears that time travel is logically possible (under the sort of scenario as in “By His Bootstraps”) in a deterministic universe, the simplest conclusion is that time travel is most likely unachievable in this universe.

A "jumpgate" of the X Universe, part...
A “jumpgate” of the X Universe, part of a space-travel network. (Photo credit: Wikipedia)