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Depiction of time travel by Kjordand (own work) [CC BY-SA 4.0], via Wikimedia Commons

Back to the Future and Forward to the Past

In his new book Time Travel: A History, James Gleick presents a valuable literary history of the idea of time travel while also highlighting the various paradoxes associated with the topic. Time travel too often can be considered an unserious aspect of physics and the subject only of speculative fiction. By writing this book, Gleick indicates that the paradoxes inherent in the concept should be taken seriously because solving those problems could lead to a more consistent scaffold of understanding for the role of time in theoretical physics. Gleick’s book creates an important history for the concept of time travel and makes the paradoxes clear. The author seems to have written the book in part to bring attention to the topic of time travel in the hopes that other thinkers will take the subject seriously and look for solutions to the paradoxes.

Could an observer be preserved in a current psychological state, and sent into a physical reality of the past or future, and do so without causing any logical paradoxes or violating any laws of physics?

To begin, H.G. Wells still does not get enough credit for his genius. The man single-handedly invented the discipline of World History, pioneered the “invading aliens” genre, and can be fairly credited with introducing the concept of scientific time travel literature. Gleick indicates that the widespread use of trains made humans realize that their relationship to distance differed depending on speed—it was only a matter of thinking about time before someone realized that our relationship to time also differed depending on speed. Gleick writes that Wells did not bother himself much with the physics as “He was just trying to gin up a plausible-sounding plot device for a piece of fantastic storytelling” (p. 4). Yet it is possible to see how the creativity of both Wells and Einstein branched off from the same concepts.

A scientific concept of time travel originated with Wells, but philosophical and poetic musings about time and its effects preceded the great man. Gleick showcases an impressive collection of quotes about time from Tennyson, Poe, and Laplace. The second chapter then highlights “time travel” as a pop-culture phenomenon explored by Mr. Peabody, Mark Twain, and Woody Allen. The point of this discussion appears to be to point out that The Time Machine by H.G. Wells turned time travel into a mechanistic possibility when he moved beyond a concept from his earliest work titled The Sleeper Awakes that featured a man simply sleeping for a long time in a comfortable chair. “Machines improved upon magic armchairs” writes Gleick and “By the last years of the nineteenth century, novel technology was impressing itself upon the culture” (p. 31).

The most interesting section of the book comes when Gleick tries to frame the idea of time and the future itself in the context of the Age of Exploration:

No one bothered with the future in 1516. It was indistinguishable from the present. However, sailors were discovering remote places and strange peoples, so remote places served well for speculating authors spinning fantasies… William Shakespeare, whose imagination seemed limitless, who traveled freely to magical isles and enchanted forests, did not—could not—imagine different times. The past and present are all the same to Shakespeare: mechanical clocks strike the hour in Caesar’s Rome, and Cleopatra plays billiards (p. 35).

The idea of the future as a thing to be strived for should be seen as intertwined with the concept of discovery and the evolution of the scientific method. After crediting Isaac Asimov with developing the idea of “futurism” as a concept denoting the imagining of a speculative time (as if the future was analogous to an island that one sailed to), Gleick then heaps some more importance on a well-known historical cause, that of the printing press. “It began in earnest with the Gutenberg printing press, saving our cultural memory in something visible, tangible, and shareable. It reached critical velocity with the Industrial Revolution and the rise of the machine-looms and mills and furnaces, coal and iron and steam—creating, along with so much else, a sudden nostalgia for the apparently vanishing agrarian way of life” (p. 41).

Was that it? Or was it that humans, in those early years of science and steam, simply did not know just exactly where the boundaries of scientific achievement could be drawn? Just a few decades before Wells, Mary Shelley wrote of using science to raise the dead. Perhaps Frankenstein’s monster and Wells’s Time Machine both stem from an initial period of wonder and naïvete about what might be achieved using science and technology.

The various paradoxes associated with time travel make appearances throughout the narrative, but as in all of his books Gleick has demonstrated a gift for understanding the boundaries of his arguments. He merely presents the paradoxes as philosophical artifacts, but this is where ordinary science can be used to solve the paradoxes.

Grandfather Paradox

Can you go back in time and kill your grandfather, therefore eradicating your own existence? This is the grandfather paradox, and it can be expanded into any “change the past” plot of a science fiction story. Gleick references the philosopher Larry Dwyer, who sees a similar problem with all time travel scenarios:

They all make the same error, according to Dwyer. They imagine that a time traveler could change the past. That cannot happen. Dwyer can live with other difficulties created by time travel: backward causation (effects preceding their causes) and entity multiplication (time travelers and time machines crossing paths with their doubles.) But not this. “Whatever else time travel may entail,” he says, “it does not involve changing the past” (p. 229).

This assumption is always based on the rather squishy premise that time travel would mess up a logical sequence of causations. The solution to the Grandfather Paradox, or “entity multiplication,” has more to do with the travel than with the time. For all of time travel’s many paradoxes, the most basic problem with the concept has been missed. A person traveling back in time would be adding matter to the universe in a way that the Law of Conservation forbids. The matter that makes up a person existed in a different form in the past, so traveling backward in a closed system would be physically impossible. To actually travel backward to an exact past, one would have to unravel one’s own body to do so. A time machine would actually travel back into a past where its component parts existed before being assembled. This would add matter to that universe without actually creating any new matter. To actually travel to the past would be to return to our component parts, eventually star dust.

In other words, you did exist when your grandfather did, just not in a physical shape with a consciousness. To actually travel back to the time of your grandfather, you would need to revert to that state, and would not be capable of altering anything.

Calendar Problem: Future Time Travel

Science fiction hacks have been repeating the old saw that “one can travel into the future just by standing around” for years without actually contemplating what that means. No, you cannot travel into the future by just standing around because the concept of “you” is always in flux. You are moving into the future along with everyone and everything else. Consciousness may be a slippery concept, but it may be thought of as existing in Julian Barbour’s “nows,” which consist of three-second chunks of awareness.

The question is not whether it is possible to travel into the future, but whether or not it is possible to send your current consciousness into a radically different future environment? Is it possible for a nine-year-old boy to travel 30 years into the future as a nine-year-old boy rather than arrive there as a thirtynine- year-old man? That is, could a nineyear- old be sent 30 years into the future to meet his 39-year old self? No, as this would, again, violate the Law of Conservation. Even if the nine-year-old dies somewhere on that continuum, the “stuff” that the nine-year-old is made of will exist in some form in the future, and the molecules that the person is made of cannot exist side-by-side in different formations as this would actually add matter to a closed system.

Multiverses (if this is a paradox)

What if the universe is not a closed system, but an open one that interacts with other universes in a multiverse? This question must be framed by the other time-travel paradoxes. Gleick notes the work of John Hospers here:

Time travel a la Wells is not just impossible, it is logically impossible. It is a contradiction in terms. In an argument that runs for four dense pages, Hospers proves this by power of reason. “How can we be in the 20th century A.D. and the 30th century B.C. at the same time? Here already is one contradiction….it is not logically possible to be in one century of time and in another century of time at the same time.” (p. 222).

Hospers is correct. Even though he does not invoke the Law of Conservation, he comes to the correct conclusion through simple logical analysis. However, since he continues to think of human beings as singular he makes this mistake that Gleick simply records:

Time is simple for Hospers. If you imagine that one day you are in the twentieth century and the next day your time machine carries you back to ancient Egypt, he retorts, “Isn’t there a contradiction here again? For the next day after January 1, 1969, is January 2, 1969. The day after Tuesday is Wednesday (this is analytic—‘Wednesday’ is defined as the day that follows Tuesday)” and so on. And he has one final argument, the last nail in time travel’s logical coffin. The pyramids were built before you were born. You didn’t help. You didn’t even watch. “This is an unchangeable fact,” says Hospers and adds, “You can’t change the past. That is the crucial point: the past happened, and you can’t make what happened not have happened.” (p.223).

We must think of the past as a compilation of particles and waves. You may not have participated in building the pyramids, but the stuff you are made of did exist at the time that the blocks got stacked, and so the physical substance that makes you up did participate, in a small way, in the making of a particular past. Again, you were always here; you just weren’t you.

One proposed workaround here is the multiverse theory. Gleick highlights the work of Hugh Everett III, who developed an adolescent interest in science fiction and studied physics under John Wheeler at Princeton. Gleick sums up Wheeler’s theory:

So what if, he asks—encouraged by Wheeler, who is open as always to the weird and paradoxical—what if every measurement is actually a branching? If a quantum state can be either A or B, then neither possibility is privileged: now there are two copies of the universe, each with its own observers. The world really is a garden of forking paths. Rather than one universe, we have an ensemble of many universes. The cat is definitely alive in one universe. In another the cat is dead. “From the viewpoint of history,” he writes, “all elements of a superposition (all ‘branches’) are ‘actual,’ none any more ‘real’ than the rest.” Protective quotation marks run rampant. For Everett, the word real is thin ice atop a dark pond:

When one is using a theory, one naturally pretends that the constructs of the theory are “real” or “exist.” If the theory is highly successful (i.e., correctly predicts the sense perceptions of the user of the theory), then the confidence in the theory is built up and its constructs tend to be identified with “elements of the real physical world.” This is however a purely psychological matter.

Nonetheless, Everett had a theory, and the theory made a claim: everything that can happen does happen, in one universe or another. (pp. 142–1143).

Everett’s multiverse theory simply reifies the concept of probability. A particle can be described as it exists in one position, but since it could be in an infinite number of other positions, the current position must be compared with all other probabilistic states. This does not mean those states actually exist at any given time. Here’s the confusing part, though, and the part that unlocks a concept of time travel that obeys what we know about physics. Probabilities for the past and the future can exist in any number of nearly infinite states. As Gleick had stated earlier in the book, “Physics is made of mathematics and words, always words and mathematics. Whether the words represent ‘real’ entities is not always a productive question” (p. 112).

Correcting the Paradoxes and Coming to a Time Travel Potentiality

To clear up the paradoxes that Gleick highlights we can begin by looking at a clock and looking at a ruler. A clock is just a ruler bent into a circle; rulers measure distance but what do clocks measure? The best answer is that clocks measure movement. Einstein’s big insight was to see that an observer’s experience of time, like his experience of distance, differs depending upon how fast the observer is moving. Now, if time is the measurement of movement, this would indicate that the absence of movement equals the absence of time.

In quantum calculations, the singularity “before” the Big Bang is expressed as T=0. Pick this equation up and look at it closely and you’ll see that what it really says is that T=Movement, and that zero movement equals zero time. Having said this, we must define what is meant by “time travel.” By time travel, we likely mean that a human observer could be sent, preserved in a current psychological state, into a physical reality of the past or future and do so without causing any logical paradoxes or violating any laws of physics. Is this possible? Yes, it’s possible, but not in a way that validates most science fiction scenarios.

First, we must understand that from our perspective where a particle or wave was three seconds ago and where it will be three seconds from now contain the same probabilities. We are never sure of the past of anything, but if a salt shaker is sitting on the table the odds that it was on the table three seconds ago and the odds that it will be on the table three seconds from now are the same. Those probabilities can change with the arrival of evidence. If I see a salt trail from the counter to the table, that might indicate that the salt shaker was on the counter recently and if someone picks the salt shaker up, that shakes the probabilities, but a docile salt shaker will likely stay in place.

Okay, from this we must understand that the universe does not have a single history, but a series of probable histories that are discerned from using current evidence. As Paul Davies wrote in a 2007 article in New Scientist on “The Flexi-Laws of Physics”:

As Hawking has emphasized, it is a mistake to think there is a single, well-defined cosmic history connecting the big bang to the present state of the universe…. Rather, there will be a multiplicity of possible histories, and which histories are included in the amalgam will depend on what we choose to measure today. “The histories of the universe depend on the precise question asked,” Hawking said in a paper with Thomas Hertog…In other words the existence of life and observers today has an effect on the past. “It leads to a profoundly different view of cosmology, and the relation between cause and effect,” claims Hawking.

Think of right now as a box that connects to other boxes of past probabilities. There are infinite boxes, but only the boxes that include a history that leads to the development of life on the planet, and you as an observer, are lit up. There are several different probabilities that could have led to the universe as we observe it, but we accept only the particular pasts that led to our existence because all others would be illogical. We can discard any past paths that did not lead to the extinction of dinosaurs, because dinosaurs are not here. There are still plenty of paths that could have led to life on the planet, and in the absence of specific evidence, some are equally probable.

Continue thinking about those boxes and this idea can be connected to Relativity Theory. Picture a line with an observer at rest represented at the bottom. His frames of particles and waves (the foundation of all the stuff around him) are divided into relatively small sections. For the purpose of simplicity, let’s imagine a two-year timeline divided into 730 boxes. Now, imagine two larger boxes on top of the timeline that take up the entirety of the timeline (two big boxes on top and 730 small boxes on bottom). The two big boxes represent an observer moving at nearly light speed. The two observers move through their respective boxes and then, meet at the end of the timeline.

Our faster observer only moved through two boxes of particles and waves, while our slower one moved through 730 boxes. They experienced different rates of particle and wave movements, so the observer who moved at nearly light speed only went through two boxes of movement while the slower observer experienced 730 boxes of movement. Once they both revert to the same speed however, the faster observer would be in the future in a more or less preserved state.

What we are talking about here, then, is preserving an observer in a current psychological state while finding a way to move all of the particles and waves around him or her either into a future or past state. This means that time travel is possible to an extent but within certain limits. First of all, to repeat, the Law of Conservation forbids a traveler from moving back to an exact past in a closed system. However, since the laws of physics are reversible, with enough energy it would be possible to reverse particles and waves to a previous state that is probably like the state they were in previously, with the exception that the matter that makes up the traveler would be absent from the past.

This would not create any paradoxes, because this really just puts particles into a probable past state (with the exception of the matter making up the traveler) but in future motion. This is logically sound but physically unlikely (to say the least). Stephen Hawking has always stated that thinking about time travel might be useful even if time travel proves to be ultimately impossible, which, for all practical reasons, it is. However, straightening out these logical paradoxes might lead to a greater understanding of time and space, and for that, those of us with an interest in philosophy should be grateful to James Gleick for giving the topic a serious history. END

About the Author

Dr. Chris Edwards is a frequent contributor to Skeptic and the author of several books.

This article was published on December 28, 2016.


24 responses to “Back to the Future and Forward to the Past”

  1. awc says:

    Last paragraph sums it up. Nice as a thought exercise to help in other areas.

    Most current understanding of physics negates the ability to travel in time to the past for sure. 2nd law, reinnman space-time manifold, wormhole stability requirements in a blink.

    So, it’s all fun for sci-fi but not much else.

  2. Chris Edwards says:

    I always enjoy writing for skeptic because it affords the opportunity to discuss ideas with so many intelligent people. I have read the comments here and thought about them for the last several days. A few points.

    1. Time has to be more than just a philosophical concept because it features in quantum equations and models. The paradoxes traditionally associated with time travel probably indicate that we do not have a clear understanding of what time is. The purpose of solving (or trying to solve) the paradoxes is not to actually say that time travel will one day be possible, but to clarify the role of time in our theoretical models. Stephen Hawking and James Gleick both take time travel seriously and they have done science a real service by doing so. (Besides, Gleick is always a joy to read.)

    2. There is only so much “stuff” in the universe. What we see, over time, are different configurations of that “stuff.” We are all made of stardust. Theoretical models that posit “many universes” run into basic scientific problems as well as philosophical problems. First, someone positing a multiverse would need to explain where all of that new “stuff” came from. Secondly, if we discover “another” universe, doesn’t that make it part of our uni-verse? It’s the same problem with the concept of the supernatural. If someone sees a ghost that means the ghost is made of some material that light can bounce off of and therefore that material can be studied. This takes all of the super out of the supernatural. In the same way, all of the “multi” would be taken out of the multiverse if evidence of it was found. In the last issue of Skeptic I reviewed David Wootton’s brilliant “The Invention of Science.” If there is one lesson to be taken from that book it is this: words matter in science just as much as numbers do.

    3. Time travel might be possible if localized. It is possible to put particles back into previous states using a known source of energy from elsewhere. As an SF concept this could be fun. Localized time travel would be subject to what we know as observers. We could cross-check macro-events to see if the probable past state we put them in corresponds with what we know happened. However, we could not cross-check, say, the atomic arrangement of a corn cob somewhere in Iowa. We would never know if the state that the localized particles and waves are in actually corresponded with a real past state because we just don’t know what the “real” past state was. This is not ethical for real people, or even cats, but this might make for a logically feasible SF novel! We would also need to clarify what we mean by time travel. The best we can do is “time travel to a probable past state where the events can be cross-checked by what we are historically pretty sure of.”

    Thanks for the discussion. I would highly recommend Gleick’s new book. My favorite work of his is still his biography of Richard Feynman.


    • Roy Niles says:

      I think however that scientists who speculate as to how the forces of the universe behave have relied on mathematical “observations” and experiments, rather than on the more difficult system of relying on logical examinations as to how these mathematical systems really work. So that instead of having the conviction that the universe has been constructed mathematically, they might someday (as some already have) come to realise that it’s constructed intelligently using the same trial and error process that biological systems use to predict their immediate futures. I realize this is a hard concept to grasp, but one must also realize that it was logic that developed the mathematics that only humans seem capable of further evolving to be used in our present day sciences, and that this same logic might be better used to understand how and why the universe itself has evolved, rather than having somehow done the highly complicated and self regulating job mathematically.
      In short, logic is a thinking process and mathematical systems cannot think. You might respond that the universe can’t think either, so its logical systems can only have emerged by accident. And that’s the rub, because such an emergence is a logical impossibility, even though quite possible “mathematically.”
      But in the other hand, is it a logical impossibility that the universe can have started (or always existed) by using some sort of reactive “thinking” process to evolve? My answer would be that no, this is more logical than assuming it has come about by using mathematical systems to evolve intelligence!!

    • Jim Davis says:

      Why can’t time just be change? If we eliminate the block universe concept (easy for a layman to do!!) then we just have “now”. I don’t mean entropy but actual physical changes at a molecular level. Would it be possible to assume that each particle only has a “now” and that “now” changes every time the wave function collapses. We wouldn’t be aware of individual particles changing but would only notice the large scale effect of these quantum events. I believe that this could be attributed to the speed of the nerve functions in our brain. (half a millisecond at the fastest) and our reality would reflect all the wave form collapses that took place between the firing of the synapses which changes our current perception of “reality”.

      There would be no actual future since the future, or the flow of time, is simply the changes occurring on the molecular level. There would be no physical past because reality itself changed. The past would only consist of physical or mental recordings of past events. When we observe a distant galaxy we are are observing what was recorded on light waves and not the actual “now” of that galaxy.

      The problem of events occurring at different times to an observer would be due to the speed of light limitation. A human observer can never see reality when it happens because the speed of light would effect the observation even if it’s an extremely small delay at a short distance between the observer and the event (which is actually the accumulation of molecular events between the the time of each observation). The change in reality occurs when a wave collapses into a particle and it doesn’t matter if we are looking at a galaxy billions of light years away. Our observations and the recognition of what we observe in our own brain is what we consider the passage of time. These “observations” would also include our awareness of our own physical self and what we are thinking and doing physically. I’m sure there’s a big hole in this idea but i can’t seem to find it myself.

    • Jim Davis says:

      I just started reading the book “Time Travel : A History” and came across a quote by Ernst Mach in 1883: “It is utterly beyond our power to measure the changes of things by time….Time is an abstraction at which we arrive by means of the changes of things.” This is in line with what I was trying to say above.

      • Roy Niles says:

        That’s very similar to the way I’ve put it – that time is the measure of continuous change. The point is it’s not “time” that dilates, it’s the nature and rate of that change. Special relativity theories didn’t change that.
        Time, then, is a dimension of measurement. But unlike other measurements, it’s also sequential. The ramifications of sequence are yet to be completely thought out. You can slow down change, but we don’t know if we can slow sequential steps.
        The important thing is, however, that we do know we can’t reverse them non-sequentially!!

        • Jim Davis says:

          This discussion may be outside the scope of a book review concerning time travel and why the author believes the that the laws of physics don’t allow time travel in any way hat could be used by humans. I think he made that point very well.

          But Mr. Gleick did spend a lot of time talking about what time might actually be, scientifically, mathematically, logically and philosophically and that is the part I’m trying to get a handle on. There is probably a better forum to talk about this but I don’t know where that is. Quora maybe?

          Roy, your ideas about time being change are similar to what i’ve considered from more of a layman’s POV. I understand the basics of relativity and quantum mechanics. Unfortunately I probably understand just enough to get myself in trouble here.

          The first thing that seems obvious to me is that the idea of time as change, however the mechanism of change is described, that that idea can’t coincide with the block universe concept that seems to arise from Einstein’s relativity. I don’t like the idea of a block universe concept of all past and future time existing at once but it’s not because of free will or ontological reasons. As you (Roy) said above, if time is actually change then there is no actual past or future since the ever changing present. Then our perception of time flowing is just our continually changing perception of the world inside and outside our brain.

          What i am trying to find out now is what exactly is the thing we call change. I understand the basic chemistry explanations of the different states of matter and how they change through interactions at the subatomic level. But why do these reactions, like making iron rust, actually occur. Why is there a reaction between the oxygen in a water molecule and an iron molecule. The easy answer is it’s a scientific law.

          It gets much more complex when you think about consciousness. You see a moving second hand on a clock. Through a series of events starting with the eye that instant image is received by a neuron. In the instant it takes for the synapse to fire the process will be repeated and you will see that the hand has moved. It would seem that this is what gives us the impression of time flowing. Why can’t we think of all these processes in the clock, the eye and the brain just being changes occurring. And if nobody is looking at the clock the changes in the world of matter that cause the second hand to move are still occurring. Why do we need a separate concept of time = t when it seems that everything occurring is a result of change at a subatomic level or even possibly at the quantum level.

  3. John Aalborg says:

    There is no “any given time”. Time does not exist. We are lost in a mental trap which relies on the concept that the present moment is that hesitation in a clock’s tick-tock. Clocks only measure themselves. An atomic clock is measured in the tiniest of chunks, or more precisely, described as a hesitation in “time” AKA “the present”. There is no present. The time we think of in “reality” flows. What we perceive is a stream of almost-instant replays of observations after our marvelous brains have vetted the irrelevancies with quantum spreed. The illusion we think of as “the present” does not exist since we have only the past, which consists only of our memories, and the future which resides only in imagination based on the past. In other words, we do not exist in a material world, and “time travel” is a fun and intriguing subject but a pastime at best. (“pastime” — oh crap”).

    • Roy Niles says:

      Nice, except it’s only the ever changing present that can exist. We remember the non-existent past in the present, and anticipate the yet to exist future in the present.

  4. john byrne says:

    this person talks of violation of the conservation principle of mass/energy.
    This shows a basic misunderstanding. In the instances he cites there would be no such violation.
    The differing arrangements of matter he consider do NOT require any changes in total mass (of the universe).

    When a child is conceived and subsequently born, this does not require any new matter coming into existence.

  5. Jim Garland says:

    Dr. Edward’s assertion that time travel to the past is logically impossible appears based on the assertion that “a person traveling back in time would be adding matter to the universe in a way that the Law of Conservation forbids.” Sorry, but I’m not aware of any such “Law of Conservation,” by which the author appears to mean that the total matter (and presumably its energy equivalent) of the entire universe is conserved over time. On very brief time scales, virtual particles routinely pop in and out of existence, violating the conservation of energy.

    The conservation laws of physics are related to the symmetry properties of the universe, as shown by Emmy Noether in 1915. The conservation of energy results from the time-invariance of physical laws, (conservation of angular momentum from the rotational invariance of the universe, and so forth). However, these conservation laws, valid for finite pieces of the universe, break down when extended to the universe as a whole. General relativity, for example, leaves open the question as to whether conservation of energy applies to the entire universe.

    But even allowing that point, we know that most of the universe consists of dark energy and matter, and it is not at all clear (to me at least), how this huge amount of invisible matter fits into the conservation laws we take for granted in our little visible piece. I personally doubt that time travel is possible, but I also think that a little knowledge is a dangerous thing and one has to be careful not to grasp onto facile arguments that could very well prove to be wrong.

    • Roy Niles says:

      The only thing you can be certain of is, perhaps, uncertainty.

    • Agamemnon says:

      Agreed, there is likely no violation in conservation of energy with time travel. The energy (and matter) comes from the future, subtracted equally from the future as added to the past.

      Actually, in physics, subatomic antimatter particles travel backwards in time (see Feynman diagrams). Antimatter particles have positive mass and energy, but to make sense out of collisions between matter and antimatter the antimatter particles are mathematically represented as traveling backwards in time.

  6. Agamemnon says:

    The grandfather paradox assumes “free-will,” that is, the ability to murder one’s ancestor, through just desiring to do the action, is of a higher level of protection, within the laws of physics, than the consistency of the universe. The grandfather paradox is easily resolved by the more reasonable assumption that the consistency of universe has priority over free-will or any other cause that may result in a time traveler killing his or her ancestor.

    Thus, the grandfather paradox is only a result of people believing they can do anything they want at anytime they may damn want to. There is no basis in physics for this belief.

  7. sittingbytheriver says:

    nice article/review. i read the book a couple weeks back, and really enjoyed it!

  8. Bob Sidethink Pease says:

    It is fun and instructive to think about parallel universes.

    Unfortunately , it is used by some armchair “scientists ”
    to make their collection of astrophysicistal data make their formulas happy.

    So far, if it grinds yer crank , cool.

    There are dangerous folks around who will use this to justify anything whatever . (wife killing e.g.) on the grounds that this is just a bad parallel universe and they can /will
    hop a ride on a better one !!!

    ” aleph null ” infinity easily fits in with these mental hijinks.

    Dr, Sidethink still believes in good ol’ stuff like Karma and responsibility for screwing other people around..

    Dr. Latero Sidethink Hp. D.
    Dobb Stang University

  9. Stephen Nowlin says:

    When deep space astronomers peer into the universe, they don’t see proof of the past as a literal place or dimension to which one might travel — what they see is memory, recorded in light waves. Width is a dimension too, but we don’t talk about traveling there. A video tape of last year’s family vacation is not the past — it is memory. So is a gigabyte of RAM, and so is light. The way we can “travel” to the past is if we find it encoded in a memory medium, and then we travel only as a bystander, a voyeur. Art, photography, video, and now virtual reality technologies, are our time machines.

  10. amoron says:

    Philosophy is indistinguishable from religious belief in terms of the application of skepticism to the fundamental assertions of a claim. Toss in a little science and even skeptics will take you seriously. lol.

    Recent issues: How to live forever. Time Travel. Porn is bad (but this received a special response to affirm porn is indeed, good).

  11. "Tom Curtis" says:

    What does it matter?

  12. Jim Gerrish says:

    Once a person can grasp the concept of space/time as a reality… that is, they are one and the same ( x,y,z, and t), it is obvious there cannot be one without the other and that it is expansion (or inflation) of space/time that creates the illusion of a flow of time from past to future. That also explains why time seems to “travel” in one direction only. We get hung up on the speed of light, when we need to realize that light (and everything else in the universe) travels at the speed of time or the rate at which expansion takes place. The rate of expansion is not uniform throughout the universe, but local to the attraction of mass in each area so we have to add gravity, or mass, to our understanding of space/time. Well, one can’t have mass without energy because they are also one and the same.

    The reality takes all the fun out of science fiction. The reason you can’t go back in time is because you have to simultaneously go back in space – not just in the x,y,z directions, but in the reverse of the expansion that is time. You can slow down your local time by traveling very fast – close to the speed of the expansion of time itself – but that leaves you somewhere else, as well as somewhen else, which isn’t very useful for science fiction story lines.

    • Bob Sidethink Pease says:

      Universe is modeled by a Four dimensional thing-o .
      noted by x,y,z and c*i*t where i = square root of -1

      Recent stuff suggests that having a lot more dimensions and twisty and repeating stuff makes certain guys happy because their “Laws” get obeyed that way.

      A lot of guys like toke-in flights of fancy instead ..

      Dr. S..

  13. Roy Niles says:

    But time is not a “thing” at all, it’s a concept created by the intelligence of humans to make viable predictions for the future based on the measures that can be made in the present of what continuously becomes the unmeasurable past. Nothing is actually “moved” in either the past or the future, all movement (and the continuity of change) is made in the present. And the time of the actual measurement is always now.

    Coming up with the idea that time, for example, is a stubbornly persistent illusion, and basing that on mathematical formulae, rather than on the logic that math was proposed and supposed to serve, is quite possibly ridiculous. Logic (which has never claimed to be as perfect as its math would want it to) wants to tell us that time is nothing except the intelligent efforts of living things to measure change. Telling us as well that the time itself is always now, and the change can logically only go in one sequential direction. Which supposedly does not apply to ‘quantum” energy, which supposedly can move in any changeable direction at any time – mathematically measurable time any case. However, mathematics can’t seem to measure the sequential order of change in more than one direction, and of course neither can the theoretical observer that seems to be necessary for our physical and “quantumly constructed” systems to move in measurable terms at all.
    Hey, the living may require change to live, but the changes don’t seem to require anything resembling living to evolve. Even though they do require energy, a “something” that even Einstein could not adequately explain when it became (to him at least) the most obvious instrument of change.
    And yet even to him, energy seemed to be able to reverse directions. And the time it took was always measureable, assuming a measurer was available.
    And yet again that measurer has never been able to tell anyone that sequences were re-measurable or unmeasurable in reverse. However our human measurers have advised us to stay tuned until the time that sequences can be discovered to be illogical.

    • Stephen Nowlin says:

      I agree with Roy, I think . . .

      Consider of the moment you are in as you read this, and think of the moment about to transpire as you read further. It’s not abstract — we speak of “one minute ago” and “one minute from now” as if they are real physcial dimensions of flowing time — moments we can’t go back to or can’t yet have, even though separated from them by miliseconds. But try to pinpoint the very instant when the future flows through the present and becomes the past in your reading of this paragraph. You can’t do it and science can’t do it. Yet you will agree that this is a linear sequence of words with a beginning and an end (which you could read in either direction if you want). We succumb to the illusion that the reading of the final word in this paragraph is still in the future, and that the reading of the first word in the paragraph is now in the past. Who even knows where the present is, apparently it travels along with your eyes and the reading of each word, and in a moment the present will exist somewhere beyond the exclamation point at the end of this sentence, a punctuation that is currently rushing toward you from the future! Oops, there it went . . .

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