Why faster than light travel is inevitably also time travel

I’ve always loved space opera, but when I was growing up, as I learned more about science, I discovered that a lot of the tropes in space opera are problematic.  Space operas, to tell adventure stories among the stars, often have to make compromises.  One of the earliest and most pervasive is FTL (faster than light) travel.

Interestingly, the earliest interstellar space opera stories in the late 1920s largely ignored relativity.  E.E. “Doc” Smith and Edmond Hamilton simply had their adventurers accelerate away at thousands of times the speed of light.  If relativity was mentioned, it was just as a superseded or wrong theory.

But by the early 1930s, authors found a way to seemingly avoid outright ignoring Einstein by simply hand waving technologies that bypassed the laws of physics.  One of the earliest and most enduring was hyperspace, a separate realm that a spaceship could enter to either travel faster than light, or where distances were compressed.  Over the decades, hyperspace came in a wide variety of fashions and with a lot of different names: subspace, u-space, slipstream, etc.

One variant, popularized by Isaac Asimov in his Robot and Foundation series, has hyperspace as a realm where ships jump through it to instantly move light years away.  (I’ll be using this version in an example below.)

There are a wide variety of other FTL technologies that often show up in science fiction.  An interesting example is the ansible, a device that allows instant communication across interstellar distances.  Often the ansible shows up in stories where actual FTL travel is impossible, but an interstellar community is enabled by the instant communications.

I’ve written before that there are lots of problems with all of these ideas.  Generally they’re not based on actual science.  They’re just plot gimmicks to enable the type of stories authors want to tell.  And the few that are somewhat based on science, such as wormholes or Alcubierre drives, involve speculative concepts that haven’t been observed in nature.

But FTL has another issue, one that I only started appreciating a few years ago.  FTL, no matter how you accomplish it, opens the door to time travel.  Most FTL concepts are conceptualized within a Newtonian understanding of the universe.  In that universe, there is an absolute now which exists throughout all of space.  If we imagine a two dimensional diagram with space as the horizontal axis and time as the vertical, then now, or the absolute plane of simultaneity, exists as a flat line throughout the universe.

But that’s not the universe we live in.  We live in a universe governed by special and general relativity (or at least one where those theories are much more predictive than Newton’s laws).  In our universe, there is no single plane of simultaneity, no universal version of now.  In this universe, talking about what is happening “right now” for cosmically distant locations is a meaningless exercise.

Most people are aware that, under special relativity, time flows slower for a traveler at speeds approaching the speed of light.  But not everyone is aware that, from the traveler’s perspective, it’s the rest of the universe that is traveling near the speed of light and experiencing slower time.  How can both see the other as having slower time than themselves?  Because simultaneity is relative.

Image credit: Acdx via Wikipedia

As this image animation shows (which I grabbed from the Wikipedia article on the relativity of simultaneity),  under relativity, whether certain events occur simultaneously is no longer an absolute thing, but a relative one.  If B is stationary, then events A, B, and C all happen simultaneously.  However, if B is moving toward C, B’s plane of simultaneity slopes upward, leaving C in its past.  On the other hand, if B is moving toward A, C is now in its future.  (Note: this never allows information to influence the past because, in normal physics, such information can only travel at the speed of light.)

An important point here is that these effects do not only happen at speeds approaching the speed of light.  They happen with any motion.  However, in normal everyday life, the effect is too small to notice, which is why Newton’s laws work effectively for relatively slow speeds and short distances.

Crucially, the upward or downward slope of simultaneity still happens at slow speeds, but the angle of difference is small, and again we don’t notice.  However, while a small angle of deviation may not be noticeable for everyday distances (say between New York and Sydney), or even for distances within the solar system, when the distances start expanding to thousands, millions, or even billions of light years, then even minute angle deviations grow to significant variances.

So imagine we have a spaceship heading out of the solar system at 1% of c (the speed of light).  Using the Asmovian version of hyperspace, the spaceship jumps to a destination 1000 light years away.

Which plane of simultaneity, which version of now, does the ship’s instant jump happen in?  The plane associated with stationary observers back on Earth?  Or the plane associated with the ship traveling at 1% c?  If it’s the ship’s plane, then when the ship exits hyperspace 1000 light years away, it will do so 18 days in the future of the stationary Earth observers.

That is true if the spaceship’s hyperspace jump is in the direction of its 1% c velocity.  But if the 1000 light  year jump is in the direction opposite the one of it’s velocity, it will arrive 18 days in the stationary observer’s past.

It doesn’t take a whole lot of imagination to see how this technology could be used to travel to arbitrary points in the past or future.  All a ship would need to do is jump in circles either in the direction of their rate of travel or opposite it to travel forward or backward in time.

We encounter exactly the same issue with other versions of FTL, such as warp drives or versions of hyperspace that take time to travel through, it’s just more of gradual than sharp jump in time.

In the case of ansibles, which version of simultaneity are the communications happening over?  The chances that the two correspondents happen to be traveling at the same speeds are nil.  The variances in the speeds of their star’s movement around the galaxy, the orbits of the planets, etc, will all conspire to ensure that their various planes of simultaneity are out of sync with and constantly changing in relation to each other.  An ansible accelerated to relativistic speeds could be used to communicate with the past or future.

Even wormholes would be an issue.  The wormholes in fiction always connect distant points together in the same now, but wormholes are connections between two points in spacetime.  There’s no particular reason it would be limited to some arbitrary version of now.  Indeed, a natural wormhole, like the one in Star Trek Deep Space Nine, would be more likely to open to some distant point in future, long after the heat death of the universe, than somewhere along the Bajoran plane of simultaneity.

We might imagine that if the FTL technology allowed us to choose which plane of simultaneity we moved under, maybe everyone would just agree on some standard, albeit an arbitrary one.  But that only makes the time travel capability more pronounced.  Orson Scott Card made the point years ago that if you’re going to introduce a technology into your fictional universe, you should account for all the ways that technology might be used, or abused.

It’s often said that the absence of tourists from the future probably indicates that time travel is impossible.  Even if future societies have strict taboos against interfering with the past, the idea that such taboos would hold for all societies until the end of time seems unsustainable.  Since FTL is also time travel, the same observation would seem to rule out most forms of it.  (Star gates or wormholes where a destination version has to be built might be the only ones that avoid this issue.)

Unless of course there’s something I’m missing about this?

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81 Responses to Why faster than light travel is inevitably also time travel

  1. Steve Ruis says:

    Well done! Of course, when reading speculative fiction, the last thing we wants is for someone to poke holes in the fascinating bits. But, on the flip side, it seems all too likely that a poorly informed public is likely to believe such fictions are either true or partially true. (Oops!)

    Liked by 1 person

    • That’s true. Often a lot that is commonly accepted as science fiction is actually more fantasy. Of course, fantasy can still be enjoyable. Despite understanding this issue, I still enjoyed Neal Asher’s latest book and many others where the authors either don’t understand or ignore these issues.

      But I also really enjoy the rare gem that does get these things right!

      Liked by 1 person

  2. Very well written. An enjoyable and instructive read for me. You might want to check out my four science fiction novels, The Rational Series (“Why Is Unit 142857 Sad” or “The Tin Man’s Heart”, “The Rats and the Saps”, “Whirlpool”, and “Out of Time”). Click my Amazon author’s page: https://www.amazon.com/Mike-Stone/e/B006VCWBE4.

    Liked by 1 person

  3. Stephen Wysong says:

    So “now” is unquestionably subjective. And I think the relativity of simultaneity can be seen without vast distances involved. Note that “clocks in strong gravity tick slower than clocks in weak gravity. Because gravity is weaker on the ISS than at Earth’s surface, PARCS [a laser-cooled clock] should [does, because PARCS is on the ISS since 2005] accumulate an extra second every 10,000 years compared to clocks ticking on the planet below.”

    (From a 2002 article at https://science.nasa.gov/science-news/science-at-nasa/2002/08apr_atomicclock)

    But … wait a minute Mike! You’re an instrumentalist! What is Time? On what grounds do you believe in Time?

    Liked by 1 person

    • And, of course, there’s the example of the GPS system which has to take GR into account to remain accurate.

      What is time? I have to admit that, other than the obvious answers, I don’t know. It appears to be a dimension along which events and states exist, that processes happen in, and where entropy develops.

      I accept time as a useful concept, an aspect of our understanding of reality. I realize some physicists question its existence, but that doesn’t seem productive to me. I could see it potentially being emergent, but then I think emergent things are just as real as the things they emerge from, at least in the sense of being productive aspects of our models.

      If all else fails, the fact that all my experiences don’t happen together, that they seem separated into some kind of sequence, makes time a useful concept.


      • Stephen Wysong says:

        I took Davies’ About Time off the shelf yesterday. It’s been a few years since I first read it. Thought you’d enjoy comparing your answer to the question “What is Time” with a couple others. It’s an opportunity to see how far we’ve come … 😉

        St. Augustine of Hippo:

        “If no one asks me, I know, but if any Person should require me to tell him, I cannot.”

        The Roman poet-philosopher Lucretius in the first-century:

        “And likewise time cannot itself exist
        But from the flight of things we get a sense of time
        No man, we must confess, feels time itself,
        But only knows of time from flight or rest of things.”

        Apparently we haven’t come very far at all … 😉

        Your last remark reminds me of John Archibald Wheeler’s:

        Time is nature’s way of keeping everything from happening at once.”

        Davies’ book, if you get around to it, is dated in a few places where astronomy and physics have matured since 1995 … gravity wave detection for example, but it’s a great read. The “Prologue” indicates that our belief in flowing time is cultural, but that’s difficult to discern these days since Western perspectives have spread worldwide.


  4. Mike,
    Check me here to see if I’ve got this right.

    It seems to me that before we go directly into FTL travel and science fiction, we should also get into the normal stuff. My understanding has been that the clock for something that is traveling will tick slower than a clock that it’s moving away from. Thus effective time travel when we get to a reasonable percentage of the velocity c. Not only will I age slower on a fast space ship off to some star, but I’ll also age slower coming back and so will return to an Earth that has aged more than I had. And the same could be said if I were simply going around our planet fast enough. Then if I were instead going around our sun but not our planet, it seems to me that I wouldn’t get the full aging tonic of my speed. Here I’d effectively be slowing down dramatically at my furthest and closest arcs in relation to the Earth in general.

    (Here’s an apparent paradox that you might relieve me of: If I were flying around the Earth at a constant radius, then it seems to me that a clock at the center would tick at the same rate as mine does given our constant distance. But it should also tick at the same rate as a surface clock more/less given its constant distance from the center as well. It obviously can’t tick at two different rates, so what gives?)

    Regardless, in all of these standard scenarios there are only clocks that can slow for something with velocity, thus facilitating time travel into the future. There is never time travel into the past as far as I know here.

    So now for your sci-fi hyperspace jump into the past, let me know if I’ve got this right. As normal a fast spaceship will have a slower clock in relation to what its traveling away from, and so will time travel into the future in that regard. But are you saying that the hyperspace jump could nevertheless put the ship in the opposite direction of its travel path, thus facilitating sci-fi time travel into the past?

    Liked by 2 people

    • Eric,
      I think you’ve got the basics right, but possibly except for one. If I were traveling at a substantial portion of c, then from the perspective of someone on Earth, my clock would be moving slower. But from my perspective, the clocks on Earth would be the ones that would be moving slower.

      Also, from the person on Earth’s perspective, the length of my ship would be contracted in the direction of travel. But from my perspective, it would be the length of the Earth and the rest of the universe, in the direction of travel, that appears compressed. This is so because from my point of view, it’s the rest of the universe that is traveling at a high speed.

      This seeming contradiction is resolved when we remember that my plane of simultaneity, essentially my plane of now, is skewed in relation to the plane for someone on Earth. Our versions of now going out into the universe no longer lines up. Something in the person on Earth’s past might be in my future, and vice-versa. (If this doesn’t make sense, take a look again at the image animation in the post. If you listened to the post, you might want to look at it instead.)

      So, the question for the ship making the instant hyperspace jump is, which plane of simultaneity does it take place on? If it happens along ship’s plane, then it will come out of hyperspace in its present, but in the future or past of an observer on Earth. If the hyperspace jump is in the direction opposite to the one ship is moving in, it will come out of the jump in the past of the stationary observer.

      There is no universal now. Special relativity took it away. (Or more accurately, revealed that it was never there.)

      Liked by 1 person

    • Oh, and I stepped over your flying around the Earth scenario because it introduces lots of complexities and I’m too wimpy in my understanding of this stuff to deal with them. 🙂

      Liked by 1 person

    • Mike,
      It’s good to hear that I had the hyperspace jump idea about right. But then this does seem a bit, well… lame. Here velocity causes the past to be present somewhere else from that perspective (which is solid I guess), and then the ship also gets to that past by appearing in the opposite direction of its movement (which seems magic).

      Then regarding the apparent paradox that I’ve noted, hopefully someone else here can straighten this out. I suppose the ship circling above should have angular velocity in relation to its axis, though that shouldn’t effectively be the velocity associated with these relativity effects. And yes circling a clock on the Earth surface at .5c will reflect far less velocity than going away or coming back from it. But unlike for the axis of the orbit this should register some velocity nonetheless.


      • Eric,
        Your comment about the motion and hyperspace jump makes me thing you still might not quite grasp it. Unfortunately, I’m not sure where you don’t grasp it. But the hyperspace jump itself is effectively magic since hyperspace isn’t a scientific concept and no one has any idea how to do an instantaneous jump like that. Nevertheless, it’s a staple of space opera.

        On your paradox, if you were somehow flying around the Earth at relativistic speeds, the same clock relationships I described above would apply. To an observer on the ground, your clock would be moving slower. To you in the ship, the observer’s clock would be slower. Where things get bizarre in that scenario is because you’re flying in a circle, from your perspective, the Earth and universe would be constantly contracting and expanding as your direction of travel changed and the planes of simultaneity would be all over the place.

        It’s worth noting that the energy requirements to do this would be cosmological, and the centrifugal forces would smear you into the sides of the craft. So I guess, technically, your perspective in that scenario would be very brief 🙂

        Liked by 1 person

    • Well if we’re talking magic then it would seem that I do have the hyperspace part about right then Mike. (You know that I’ve got to at least give you a bit of grief for the “fi” part of this hobby. 🙂 )

      Then on my proposed paradox, which I doubt actually is one, in case anyone out there can put this straight for me then I’ll try to state the situation more plainly:

      Imagine clock 1 out in space, as well as clock 2 that’s 1 billion meters away. There is no movement between them and therefore things occur simultaneously from each clock perspective (as in the neutral case of the moving diagram). Now imagine clock 3 that spins around clock 1 it at a speed of .5c such that it always remains exactly 2 billion meters away. As I understand it, even though there will be angular velocity between them, each clock will tick the same and things will occur simultaneously from each perspective since there will be no associated velocity. But now consider the relationship between clocks 2 and 3. There will be velocity between these clocks as their distance fluctuates between 1 and 3 billion meters per orbit. As I understand it the clock in the spinning orbit should tick slower, which we’d see if they were to rendezvous.

      So how can clock 1 tick the same as the other two clocks, if clock 2 and 3 tick differently from each other? Where is my error?


      • I think clock 1 and 3 would still see relativistic effects between them. Yes, the distance is constant, but only because 3 is constantly undergoing insane acceleration to remain in its circular path. Likewise 3 and 2 would also see relativistic effects.

        Which is to say that I think the premise of your question is mistaken. From clock1’s perspective, clock 3 would be moving at 87% of clock 1’s rate. But from clock 3’s perspective, it would be clock 1 moving at 87% of clock 3’s rate.

        Clock 3’s plane of simultaneity would be sloped relative to clock 1 and 2’s, but rotating as it went around its circle. This would mean that for clock 3, clock 2 would be gyrating wildly between its future and past. A wild ride.

        Liked by 1 person

        • Lee Roetcisoender says:

          Both of you have been watching too many science programs. A clock is an instrument which itself is defined by a duration of change. The atomic clock is that reference, it has the SI unit of seconds, 1 second is defined to be exactly 9 192 631 770 oscillations of the isotope Cesium-133. This definition refers to a caesium atom at rest at a temperature of 0 Kelvin. As a practical reference point, the second measured for any atomic clock is also corrected to mean sea level.

          As long as there are no variables which influence the oscillations of the isotope cesium-133 of either clock 1, clock 2, or clock 3, the measurement made by the instruments would be a constant. That measurement is not contingent upon the velocity or position of each clock in relationship to each other regardless of their distance or velocities. It’s bullshit stories like the ones both of you have been duped into believing that turns me off to the church of science… A church by any other name is still a church just the same.


        • Wyrd Smythe says:

          Things get a lot more complicated when rotation is involved, because we’re no longer in the domain of SR. With rotation, you have to use the math of GR, because rotation is acceleration. Clock 3 would experience both SR and GR effects.


          • Lee Roetcisoender says:

            Your first comment is in reference to what is known as “kinematic time dilation”. Your conclusion is incomplete and therefore a misrepresentation of the facts, facts which are gathered by the many, many experiments.

            Your second comments is a non-starter. The only variable which directly affects the oscillation of cesium-133 is referred to as gravitational potential. Both gravitational potential and velocity effects (in the context of kinematic time dilations) are, for example, routinely incorporated into the calculations used for the Global Positioning System.



          • Wyrd Smythe says:

            @Lee: You seem to be agreeing with me, so I’m not sure what you think I have wrong.

            Do you dispute Special Relativity?


          • Ah, thanks. I knew the acceleration part complicated things (which was why I initially tried to evade it), but forgot that acceleration puts us into GR territory.


          • Wyrd Smythe says:

            Considering how many things move in curved paths, GR infects everything. Plus gravity (same thing as acceleration) brings in GR, too.

            It still blows my mind that the center of the Earth is younger than the surface, because clocks tick relatively slower.

            On a big planet, like Jupiter, the effect is even more pronounced, and in the Sun, all the more.

            On a fine scale, spacetime is probably warped like smoke or open water waves… something really complex and chaotic with zillions of small inputs.

            The latest clock, the strontium lattice clock, can detect the GR effect of, IIRC, just centimeters of height difference.


          • So I guess simultaneity is similarly skewed in GR. Meaning that the plane of now for the core of the Earth is different than the plane of now for us on the surface. Of course, your plane of now at a different latitude is different than mine. Reality is absurd.

            Liked by 1 person

          • Wyrd Smythe says:

            Our rotation speeds would differ due to latitude, but we’re at roughly the same point in the gravity well. (Unless one of us lives in Denver. 🙂 )


          • Lee Roetcisoender says:

            @Wyrd.. “It still blows my mind that the center of the Earth is younger than the surface, because clocks tick relatively slower.”

            This statement explains your misrepresentation Wyrd. It’s the same type of misrepresentation that occurs on every science program I’ve ever seen, including NOVA. It’s not your fault dude, but you need to study your own statement and see if you can solve the paradox yourself…

            Here’s a clue: Just because the oscillations of cesium-133 are slower at the center of the earth doesn’t make the center of the earth older. The only thing that model proves is that cesium-133 oscillates slower at the center of the earth then it does on the surface.


          • Wyrd Smythe says:

            @Lee: “Just because the oscillations of cesium-133 are slower at the center of the earth doesn’t make the center of the earth older.”

            Well, no. As I said, it makes it younger.

            If you agree atomic processes are slower due to GR, how it is possible the center of the Earth isn’t younger (by some four years, IIRC, over the nearly five-billion year lifespan)?


          • Lee Roetcisoender says:

            @Wyrd… “If you agree atomic processes are slower due to GR, how it is possible the center of the Earth isn’t younger (by some four years, IIRC, over the nearly five-billion year lifespan)?”

            We have no tools at our disposal with which to make that determination other than conjecture. The point has been made Wyrd, and please don’t deflect; just because atomic processes are slower due to gravitational potential only proves that atomic processes are slower due to gravitational potential, period. Nothing else can be proven utilizing this model. The construct of time is a derivative of human imagination, albeit an ingenious, admirable and useful invention indeed.

            nuff said…


          • Wyrd Smythe says:

            H’okay, if you say so.


    • Mike and Wyrd,
      So beyond all the complex calculations I presume that clock3 ticks slower than the clock1 it spins around given its accelerated mass (rather than ticks the same given no velocity between them as I proposed before). Sounds good. Clocks 1 and 2 still tick the same as each other given that they’re motionless. If clock3 ticks slower still in relation to clock2 because it not only has its accelerated mass, but velocity in relation to clock2, then that would seem paradoxical. Clock3 can’t read slower than clock1 but even more slow still than an equal clock2. So if there is relativistic velocity between clock2 and clock3, perhaps this doesn’t contribute? Any further thoughts about these two motionless clocks that one spins around?


      • Sorry Eric, I’m tapped out. Wyrd might have some additional analyses, but we’ve hit the limit of what I can offer.


      • Wyrd Smythe says:

        What matters is that clock 3 is traveling in the frame shared by clocks 1 and 2. It does not matter that clock 2 is offset. Both clocks 1 and 2 see clock 3 moving in a circular orbit at 0.5c in their shared frame.

        Clock 2 does see clock 3’s relative velocity slow down slightly as it moves away, but it speeds up as it as it moves toward. Overall those cancel.

        On a moment to moment basis, clock 2 would see that slight oscillation whereas clock 1 wouldn’t, but there’s no paradox. You could replicate the effect with sound. A circling siren would have no Doppler shift to someone in the center of the circle, but would to someone near the edge.

        Liked by 1 person

        • So Wyrd, you’re saying that clock3 ticks slower given its accelerated mass than the other two, and those two tick exactly the same given that all three are in a shared reference frame? Thus no paradox? Works for me.

          My follow up question was going to be to ask how a physicist would define such a frame from one that’s not shared. Light cone? Apparently not. I see that Wikipedia covers it, not that it’s simple. Thanks! https://en.m.wikipedia.org/wiki/Frame_of_reference


          • Wyrd Smythe says:

            “So Wyrd, you’re saying that clock3 ticks slower given its accelerated mass than the other two,…”

            Because of its velocity, yes. (Its mass is not relevant here.)

            “…and those two tick exactly the same given that all three are in a shared reference frame?”

            Clocks 1 and 2 share a frame and will keep sync.

            Clock 3 does not share their frame. It’s 0.5c velocity makes it tick 86.6% slower relative to clocks 1 and 2. I don’t know how to calculate the GR effect of the radial acceleration due to the circular orbit, but I assume it would slow the ticks further.

            Clock 3 has a very complicated frame due to that acceleration, parts of which (orientation) are constantly changing. Its dynamics fall under GR, which is a whole other fish kettle.

            “…how a physicist would define such a frame…”

            Its done in terms of velocity and acceleration vectors. If relative velocity is constant, it’s easy to do in 4D Minkowski space; it’s just geometry. Acceleration complicates things. You need tensors to describe curved motion in gravity-warped space. They’re beyond me.

            Liked by 1 person

  5. Lee Roetcisoender says:

    I hate to rain on everybody’s parade, but it’s clear from the comments that everyone has been watching too many science programs and have been duped into believing the outright deception contained within the dogmatism which is intrinsic to the church of science. I’ve watched the same programs on Nova, etc., and it’s all bullshit Time is not a “thing-in-itself”, time is a useful construct and that’s all there is to it. To be concise and succinct: “Time is a unit to measure a duration of change.”

    Liked by 1 person

    • Lee,
      Time being a unit to measure a duration of change is fine. But a model that sees time as absolute isn’t predictive of observations. Those observations force us to view it as something where the rate of change is dependent on where you are and how fast you’re moving.

      If general and special relativity aren’t reality (and I’m always agnostic on that), they are highly predictive of observations. Any new theory will have to account for the same observations.


      • Lee Roetcisoender says:

        You’ve got the tail wagging the dog. Change is the only absolute; and because change is a continuum, what we do is build models to measure a duration of that change. Time is the model which we construct to measure that duration, any duration.

        The rate of change is not another variable in the equation as such, the rate of change is a derivative of that continuum of change. Models in and of themselves are not the problem Mike, what’s problematic is the intrinsic dogmatism which are an inherent feature of those models, including but not limited to general and special relativity. Both are useful for making highly predictive observations, but in the context of the true nature of reality, both are bullshit just like the model of time itself.


        • Lee,
          On the true nature of reality, I can see your point. But the point the post makes only seems reliant on the predictions. (Unless I’m missing something?)

          So I guess the question is, given that time dilation and other Lorentz transformations have been experimentally confirmed a number of times (https://en.wikipedia.org/wiki/Special_relativity#Status ), are you saying that the relativity of simultaneity is not an accurate prediction?


          • Lee Roetcisoender says:

            Time dilation is a model that is only relative to the “instrument” that is used to measure a duration of change, and that instrument is not absolute. The instrument itself is not time, and the instrument does not measure time. The instrument is dependent upon many variables for its own accuracy as an instrument, which simply means that the tick tock of the clock can change depending upon those variables.

            Of course, those variables which affect the measurement instrument must be taken into account in order to make accurate predictions, and those variables are instrumental in making predictions where the constant of the clock changes. None of this has to do with time being a “thing-in-itself” and yes, relativity of simultaneity is an effective tool for making accurate predictions, but that’s all it is, a predictive tool which has nothing to do with the true nature of reality.

            This whole business of time travel, all of which is propagated by the church of science is predicated upon a false paradigm, and that paradigm is that time is a “thing-in-itself”, which it clearly is not…


          • Actually, I think most science is skeptical of time travel, and FTL. Pointing out that they’re linked only reduces the plausibility of FTL.


          • Stephen Wysong says:

            My understanding of “time” in physics is that it’s the temporal dimension of spacetime that, along with the three spatial dimensions yields our 4-dimensional spacetime. We measure distances along the spatial dimensions with a ruler and along the temporal dimension with a clock.

            The upshot of the Relativity of Simultaneity (RoS) after we finish discussing clocks-1, -2 through clock-n is that, for the usual experimental individuals scattered distantly throughout the universe, Alice’s “now” is co-real with a moment in Bob’s “past” and Bob’s “now” is co-real with Charlotte’s “future”, each of which are also co-real with others’ “pasts” and “futures” which, by logical extension, means that all instants of time that we regard as “past” or “future” exist “all at once” in an unchanging and timeless Block Universe.

            If RoS “… is an effective tool for making accurate predictions, but that’s all it is, a predictive tool which has nothing to do with the true nature of reality” then the above “co-reality” predictions would seem to contradict that “nothing to do with … reality” part. Is it impossible for us to know the geometry of our universe?

            There is no “now” or moving, flowing time in the universe or in the laws of physics—now is a feeling that can be correlated with a clock time—it’s not a time. Newton’s assumption that “… absolute, true and mathematical time, of itself, and from its own nature, flows equably without relation to anything external.” was an assumption. I think the growing differences in the earth-bound and GPS-satellite clocks is sufficient proof that his “equably” assumption is false, as does RoS.

            If Alice and Bob are very long-lived with Alice on the ground and Bob orbiting in a GPS satellite and each correlates their subjective “now” with a cesium clock then, after 10,000 or so years couldn’t we say that Alice’s “now” will be correlated with a different clock time than Bob’s “now” (and vice-versa, of course) so that “now” of one is in the “past” of the other?


          • “Is it impossible for us to know the geometry of our universe?”

            I think it’s possible for us to have geometric models that are increasingly accurate, but we can never know if we’ve found the final model. A new observation could always force us to fine tune, or in severe cases, come up with an entirely new model. (Think of the precession of Mercury under Newtonian laws, ultimately resolved with GR.)

            But I’m okay with defining “know” as possession of these predictive models, since that really is the only version of “know ” we ever get.


          • Stephen Wysong says:

            Quite true, we can never never know if we’ve found the final model or the ultimate truth but each generation has the scientific information available to it and must make do with just that and no more. I think it’s noteworthy that newer physics doesn’t replace or obsolete the old—Newtonian mechanics is still with us and still valid, but we’ve learned the limitations of its application. And Relativity physics being repeatedly confirmed for over a century inclines me to believe it won’t be replaced either, but perhaps it will also be found to have quantum level or other limitations of application. Stuckey’s Relational Blockworld physics, however, works the other way around, finding quantum level clarity in Relativity’s block universe, so who knows?

            I think the BU is the only model of the universe that incorporates time though. If you or anyone know of others, I’d like to learn about them. I can’t imagine a flowing time model because it essentially poses a zero length slice of time where the universe exists and change happens, surrounded ahead and behind by non-existence, both future and past, with no suggested or comprehensible mechanism to drive the moving slice of change that’s fundamental to Presentism.

            I’m fascinated by the hints that Einstein left in a handful of quotes as noted in “Breadcrumbs” such as “It is enough for me to contemplate the mystery of conscious life perpetuating itself through all eternity” and I’m quite surprised at the consistent inattention paid thereafter to the consideration of consciousness in the BU. Many physicists have explained the RoS and the BU but Brian Greene is the only one since Einstein to seriously probe the subject in Chapter 5, “The Frozen River” of The Fabric of the Universe—strongly recommended if you haven’t read it.

            Life is short, as they say, and an overarching agnosticism may be logically persuasive and shielded from error but I find it emotionally and scientifically unsatisfying. I’m fascinated by the insights of an “Eternal Unchanging One” that we find throughout history though. And sometimes contemplation of the greatest puzzles has led to some of our most powerful insights, so it seems to me that the stunning contrast between the static and unchanging BU and our ever-present flowing experience may point the way to a fundamental new understanding of reality and the human condition.


          • “I think the BU is the only model of the universe that incorporates time though. If you or anyone know of others, I’d like to learn about them.”

            Not quite sure if I understand what you’re asking for here. I do know that most physics theories incorporate time only in a symmetrical sense, that is, they don’t distinguish what direction things are moving in. The only exceptions appear to be the Second Law of Thermodynamics (entropy) and certain interpretations of quantum mechanics that posit the wave function collapse as an objective event.

            But how could a model of the universe exist that doesn’t incorporate time?

            “Life is short, as they say, and an overarching agnosticism may be logically persuasive and shielded from error but I find it emotionally and scientifically unsatisfying.”

            I can see that. As I noted before, emotionally, I’m a scientific realist. What draws me to science is the quest for truth. I never sit around at night pondering what kind of predictive frameworks can be developed. No. I ponder what is or what might be.

            Yet, intellectually, I think the lessons of the past shouldn’t be ignored. The way I reconcile it is to allow myself to get excited by the ontology, but always with an asterisk for parts that haven’t been tested yet. I think it’s those untested parts where new breakthroughs are hiding, waiting for us to uncover them.

            BTW, I am currently working my way through Greene’s The Fabric of the Universe. I was bothered by the fact that I’d misunderstood the relation between dark energy and gravity, realized that I hadn’t read a basic book covering this stuff since before dark energy was discovered, and recalled how phenomenal of a communicator Greene was. I’m currently in chapter 8.


          • Stephen Wysong says:

            I sketched the essentials of a Presentism, or “flowing time” model above starting with “… a zero length slice of time …”. It’s the best description I can produce of a dynamical Newtonian model of a 3-dimensional universe that includes time as “Absolute, true, and mathematical time, of itself and from its own nature, [that] flows equably without relation to anything external.” I can easily imagine the BU model but not the NU (Newtonian Universe) one. What do you suppose he meant by his reference to “anything external”—to time itself? Beats me, but perhaps you can see what I meant by “model of the universe” with those two examples.

            Good to hear you’re reading Greene’s Fabric …. if you recall, I quoted a few passages from Chapter 5 in “Breadcrumbs” and stated my suspicion that Greene might himself believe in ERL but indicated so only metaphorically. Along with Einstein’s statements, Greene’s Chapter 5 was a significant inspiration for my own ERL thinking.

            As an interesting tidbit, the Einstein quote about “… conscious life perpetuating itself …” appeared in 1931 in the book Living Philosophies from Simon and Schuster, but was reprinted in the Einstein obituary in The New York Times dated April 19, 1955. So we know that Einstein was thinking about his “eternity of life” for at least 25 years. Knowing that newspapers produce obituaries of famous people years in advance of their deaths so they’ll have them on file when the death occurs, I’ve wondered how and why that particular quotation made it into the obituary—it’s the only Einstein quote in the entire obit. Did they ask Einstein to select one? I have several books of Einstein quotations and many of those are noteworthy and appropriate for an obituary. Almost 65 years later though, I’m sure we’ll never know, but is it possible that Einstein chose that in order to draw attention to a Big Hint? In all the ERL-related research I did, no one has ever written about what he might have been referring to. Absolutely no one.

            Just some thoughts …


          • On presentism, I see what you meant now. Given Einstein’s discoveries, I can see the case for now not being an objective concept. Relativity certainly seems to demolish any possibility of a universal now. But does it demolish even a relative version?

            The problem is that there certainly seems to be something different about the current instant. The outside world has causal effects which impinge on our mind. Our current mental state seems like a culmination of all our past experiences. Our knowledge of the past is never as solid as we might imagine, but it seems far more substantial than our predictions of the future. For better or worse, our conscious experience seems to include an inescapable now concept. It also seems hopelessly tangled up with a core self concept.

            I can’t speak to Greene’s belief in the ERL, but I found his descriptions more equivocal than you did. I did think his bread loaf metaphor, where instances of “now” are prospective slices that could be perpendicular to the axis of the loaf, such for a stationary observer, or angled to it as in the case where someone is moving, to be brilliant. Greene repeatedly impresses me with his ability to convey complex concepts.

            Einstein was definitely as much a philosopher as a scientist.


          • Stephen Wysong says:

            As you might recall, Greene notes a Rudolph Carnap conversation with Einstein who was troubled by the “now” business as well: “… the problem of the now worried him seriously. He explained that the experience of the now means something special for man, something essentially different from the past and the future, but that this important difference does not and cannot occur within physics.” Note the phrase used—”the experience of the now.”

            The explanation of the “now” lies within psychology/neuroscience I suppose rather than physics but serious scientific attention to consciousness didn’t exist even in the mid-50s when Einstein died. I discussed the “now” concept in “Breadcrumbs” and, although far from the first to do so, I concluded that “now” is wholly subjective and is a feeling of the immediacy of conscious experience. So “now” is not a time, it’s a feeling, but one that can be correlated with a clock time to produce the common usage of the word “now” that means “this very moment”.

            In the closing paragraphs of Chapter 5, Greene makes the case that all of our conscious moments in the BU are always “illuminated”—always conscious: “… every moment is illuminated, and every moment remains illuminated. Every moment is.” Those moments as they are experienced are all “now’s”. The crucial realization that Greene misses, or at least never mentions, is that we don’t experience individual “now” moments as such—we instead experience all of our conscious moments as fleeting components of a stream/flow of consciousness. Given that idea, instead of seeing moments of consciousness persisting in our worldtubes, we can envision a series of persisting conscious streams “like moving beads on a string.” Therein lies ERL, so Greene comes very close.

            Liked by 1 person

        • Lee Roetcisoender says:

          One final comment Mike:
          Predictive models are not a measure of “truth” by any stretch of the imagination, and the entire premise needs to be revisited. Predictive models are only useful tools; and that useful-ness is contingent upon the objective of that particular predictive model. The most effective predictive model every devised by any institution was during the reign of the Pharaohs, a model which stated that the Pharaoh was a God. Clearly, this model could make predictions with a precision that no scientific model can match. The only distinction between a predictive scientific model and the predictive Egyptian model is a matter of scope…


  6. Brett says:

    Would the wormhole still be a problem if you had to create both ends in the same time close together, before sending off one of them to somewhere else at relativistic speeds?

    That is true if the spaceship’s hyperspace jump is in the direction of its 1% c velocity. But if the 1000 light year jump is in the direction opposite the one of it’s velocity, it will arrive 18 days in the stationary observer’s past.

    I suppose since hyperspace jumps are fictional, you could just handwave it by saying the drive always kicks the spaceship out back into the original plane it entered it from, just displaced in distance.

    Liked by 2 people

    • If you had to create the other end, then it would stop you from traveling to arbitrary points in the past. Although if you accelerated one of the ends to near c in the process of moving it to its destination, it would experience relativistic effects and would, from the standpoint of the other end, now be in the future, and from the remote end, the original would be in the past.

      “you could just handwave it by saying the drive always kicks the spaceship out back into the original plane it entered it from,”

      The problem is that the spaceship is not changing planes in the jump. Its plane before and after the jump are identical. It’s just skewed in relation to the one on the planet it left, and on the planet it’s going to. So which plane is the “original”? The one it had before it left the original planet? The one it had just prior to the jump? Or the one it will have when it reaches the destination planet? None of them agree and whichever one chosen will result in it being at a different time than now according to the other planes.

      The overall issue is that there’s no universal now that the ship can be kicked back to. For anyone who understands that (which admittedly is not most readers), the hand waving won’t work.


  7. paultorek says:

    “a natural wormhole, like the one in Star Trek Deep Space Nine, would be more likely to open to some distant point in future, long after the heat death of the universe”

    That depends on how they get formed. If they were formed only in stellar-rich environments, or black hole collisions, for examples, then no. Or better, our SF authors could follow Brett’s suggestion, and add that all wormholes are engineered, none natural.

    Liked by 1 person

    • From what I’ve read, black holes will be around for about 10100 years, so collisions between might still be a thing for a long time. (Assuming of course that cosmology doesn’t get heavily revised, as seems possible if dark energy is increasing in strength.)


  8. Wyrd Smythe says:

    This reminds me of discussions we had back when I wrote my Special Relativity series! I think the bottom line here is that FTL travel is impossible.

    (Back in my series I posited the possibility of ansibles working if both ends were in the same frame of reference, but a kind soul on the internet set me straight. That can’t work, either.)

    Recent work seems to suggest wormholes are impossible, too. For one thing, it seems they need negative mass, and one belief is that there’s no such thing. (Not everything has a sign.)

    So, what happens to a ship moving at an appreciable fraction of c that jumps into a wormhole? I think it dpends on what the ship’s speed translates to in the wormhole, and how the dynamics of SR and GR behave inside the wormhole.

    One possibility is that entering the wormhole represents a new frame of reference, so the surface of simultaneity would shift to whatever is right in the wormhole. Or it may have no meaning in the wormhole, and meaning only returns once the ship leaves.

    I suspect the ship would be bound by the time of the wormhole mouths, but since we’re talking about something that probably can’t exist, who knows how it behaves.

    Liked by 1 person

  9. Wyrd Smythe says:

    “[F]rom the traveler’s perspective, it’s the rest of the universe that is traveling near the speed of light and experiencing slower time.”

    And the traveler is seeing space contract in the direction of travel. For example, to the muons created high in the atmosphere due to cosmic ray collisions, the Earth’s surface is only meters away because of their speed. Hence they are able to reach the ground before they decay.

    (I did some charts once illustrating the effect. I always meant to post them. Maybe I should.)

    One very pedantic note: In 4D spacetime, we all have a 3D volume of simultaneity.

    I imagine most of us are sitting in a room reading this. You’re at rest relative to the room, and the room (and everything not moving beyond it) is in your volume of simultaneity.

    Something that moves through your volume rapidly enough is “twisted” in spacetime. It’s entire volume is progressively skewed with respect to yours. (It would think the same of you.)

    That’s why the fast train fits in the short tunnel, that skewing of volume. A useful analogy is to hold a ruler lengthwise in front of you. You see the entire length of the ruler. Now turn the ruler so it appears foreshortened. Now it looks shorter to you (of course the ruler is unchanged).

    That’s literally what’s happening with something moving relative to you, but the twist is in 4D spacetime.

    As you say, just walking past someone who’s not moving is enough to make you both have different “now” perspectives of the Andromeda galaxy. (It takes many light years to notice the difference!)

    Liked by 1 person

    • I learned a lot from your relativity series. I definitely recommend it for anyone who’d like a serious primer on special relativity.

      On the ansible, the problem of course is actually getting into the same frame. The relative motions of the respective stars and planets make that effectively impossible. You might be able to attempt a conversation, but depending on the distance involved and differences between the frames, it might not be a very linear one.

      On wormhole possibility, that matches what I’ve heard too. Supposedly they instantly collapse unless you have negative mass to keep them open. The thing I wonder is, just how much negative mass is necessary? And what would be the consequences for anything trying to traverse the wormhole?

      Good question on what happens if a relativistic ship traverses a wormhole. I tend to think it would be the same as normal spacetime, although all the energy involved in keeping the wormhole in place and open might make a major difference at the GR level. Beyond my current level of comprehension.

      “One very pedantic note: In 4D spacetime, we all have a 3D volume of simultaneity.”

      Definitely. But even physicists (such as Brian Greene) use the phrase “plane of simultaneity”, so I feel okay doing it.

      “It takes many light years to notice the difference!”

      Greene uses the example of Chewbacca sitting in his living room 10 billion light years away. If Chewie goes for a walk at 5 mph, his plane of simultaneity relative to us shifts 150 years!

      Of course, for closer distances, like within our galaxy, you need to be moving faster for the effect to be noticeable. But even the relative motions of planets will lead to several seconds or minutes across thousands of light years.


      • Wyrd Smythe says:

        “The relative motions of the respective stars and planets make [getting into the same frame of reference] effectively impossible.”

        That would definitely be a major challenge. My thought at the time was it would involve some zeroing in on the right vector. Maybe the signal got stronger or more coherent as you got closer to exact. It ought to be possible in principle.

        But ansibles — FTL radio — aren’t possible under any circumstance, even in principle, that’s the part I didn’t get. They would also allow time travel (of information). (I’ve been meaning to write an update post; I should get on that.) It takes four parties to demonstrate…

        Imagine A and B in Frame #1, separated by light years, using ansibles to communicate, and C and D in Frame #2, also separated by light years, also in communication with ansibles. Frame #1 and Frame 2 are in relative motion.

        If C passes A, and D passes B, allowing brief message exchange, information can exchanged such that it passes into the past of one of the frames.

        SR, FTL, causality: pick one. 😀

        “The thing I wonder is, just how much negative mass is necessary?”

        😀 I don’t believe in negative mass, so I couldn’t even begin to say!

        (If mass is a ‘something,’ I can see having ‘nothing’ or ‘something,’ but the idea of a “negative” ‘something’ seems incoherent to me. Just because you can put a minus sign in front of ‘something’ doesn’t mean it’s real.)


        • Apparently, related to dark energy, negative pressure is actually a thing. I wonder if you had sufficient negative pressure if that wouldn’t create the repulsive gravity necessary to keep the wormhole open. (I probably just revealed my ignorance at multiple levels.)


  10. J.S. Pailly says:

    In defense of Deep Space Nine, the aliens who lived inside the wormhole did apparently experience time in a different way than the rest of us. I always thought that was a nice nod to the actual science, even if it was only a trivial nod.

    In my own science fiction universe, I always wanted time travel to feature prominently anyway. So I’m sort of taking an “it’s not a bug, it’s a feature” attitude about FTL. FTL technology paved the way for the first time machines.

    Liked by 1 person

    • I only picked on DS9 because it’s well known. But those aliens were a nice touch. And they apparently were the source of Bajoran religion, which was kinda cool.

      For your universe, I like the sound of treating it like a feature instead of just ignoring, as most sci-fi does. The trick is then explaining why people don’t just travel to whatever historical events they want to and make changes. As I recall, you had a mechanism to ensure someone couldn’t mess with their own history.

      Liked by 1 person

  11. Stephen Wysong says:

    I strongly recommend About Time – Einstein’s Unfinished Revolution by physicist Paul Davies from 1995. Most Excellent! Used paperbacks from amazon for a measly five bucks.

    Liked by 1 person

  12. I always viewed the speed of light as moving one quanta of space per one quanta of time. Not knowing the fundamental mechanisms that allow for this change in position, I can imagine space as a checkerboard or honeycomb through which matter is vibrated /jostled a maximum of one cell (space unit) at a time. The wavelength of the vibration (since waves and particles have a level of interchangeable duality) could equal one subatomic particle that conveys a unit of change (not charge) perhaps some neutrino I will call a chronoton particle.

    While faster than light travel does seem impossible to me overall – in the long run, there must be conservation and the speed limit of one unit space per unit of time must apply overall – I am not so sure that chronotons could not be gathered in some version of a “flux capacitor” and allow a ship to use years’ worth of chronotons in mere seconds. Much like damming a river only to release a flood later, I suspect we just might be able to save time in a bottle and then use it up quickly.

    In my early science fiction stories (I have focused on non-fiction topics recently – though my books about prophecies or a POLE SHIFT book are viewed by many as nonsense anyway) a ship could lay dormant, store up chronotons, occasionally re-enter the normal flow of time again to assess their region for danger (from the perspective of their contemporaries outside the ship – they would be appearing from nowhere after a long gap of non-existence) and turn on the flux capacitor/timeshield again to store more chronotons until needed. If, on one of their many reawakenings/re-emergences into normal spacetime – they would detect an enemy fleet approaching – they could intercept it and activate weapons against it millions of times faster than the speed of light – but only because they had stored up unused time already. They can only experience one year per year, but from the perspective of those outside their ship, they might not exist 99.99999% of the year, then use that year in one second.

    Liked by 1 person

    • Your description of quantized space is similar to how I’ve thought it could work. The trick, of course, for physicists is coming up with a mathematics for it that are consistent and that predict or at least match observations.

      Interesting idea on essentially banking time. The thing is, while time is being banked, wouldn’t the people on the ship be in a frozen state? It doesn’t seem like they could decide to pop back into time to see how things are going. Maybe they could decide beforehand how long they’ll be outside. The other thing that pops in my head is that how could the banking mechanism work without time?

      So if I understand correctly, once they’ve banked the time, they could use it to jump over all the distance that would normally take that amount of time to jump? You mentioned bottling it, so presumably you could have thousands of units banking time, then with all that stored in a bottle, a ship could use it all in one large jump.

      Of course, the act of doing that would be equivalent to the hyperspace jump I describe in the post, with all the associated simultaneity issues. But it’s an interesting idea!


      • Banking all the time would cause permanent disappearance. I view it more like a curtain blocking most light or a dimmer switch reducing light output. Store up MOST but not all chronotons – or I agree, you’d never experience any time with which to experience anything else and pop back into normal reality.

        Liked by 1 person

  13. Fizan says:

    Interesting article got my brain juices flowing. I seem to have reached a problem:

    If both the traveler and an observer accelerate away from each other why does the twin-paradox occur i.e. one twin is younger than the other on re-uniting when they moved away and then came back together at high speeds ?

    Liked by 1 person

    • Lee Roetcisoender says:

      It’s only a problem if you buy into the notion of the twin-paradox. The twin-paradox has no more credence than the idea that the center of the earth is younger than the surface, or that a mountain peak is older than both the surface and center of the earth. Reality is not that type of weird, what’s weird are the constructs that we naively buy into.

      Question something, question everything…


    • Thanks Fizan.

      I have to admit that the twin paradox used to have me tied in knots. The secret is to work it out using spacetime diagrams. If you do it right, it always works out. (Google “twin paradox spacetime diagram” for numerous examples.)

      In the absence of that, if the twins accelerate away from each other, then from each of their perspectives, the other’s clock is running slower. However, if they then simultaneously* turn around and start decelerating, they’ll see each other’s clocks “catch up” until they’re back in the same frame.

      *Note that “simultaneously” here would be from the perspective of a stationary third party. From the perspective of each twin, they would have to turn around before the other twin even if they had previously decided to turn at a pre-arranged time, since from their perspective the other twin’s time had slowed down.

      This makes a little more sense if you consider what’s happening if each twin sends a running commentary to the other. From a particular twin’s perspective, the other’s reports slow down as they accelerate, then speed up again as they decelerate, but in their local frame, it’s just how the radio signals arrive. The simultaneity weirdism only arrives as they try to figure out when each report was made based on the travel time of the communication.


  14. Lander7 says:

    You stated — “It doesn’t take a whole lot of imagination to see how this technology could be used to travel to arbitrary points in the past or future.”

    My response — How would anyone ever know? No form of communication could reach back to them and provide evidence of arrival without taking the same amount of time that was displaced getting there. If they return using FTL then very little if any time is lost.

    Liked by 1 person

    • Hey Lander,
      I’m not catching your point. Would you mind elaborating?

      My point was that they could return to their destination earlier than they departed. (With all the associated paradoxes.) But if I’m missing something, I’d love to know it.


      • Lander7 says:

        Let’s break it down:

        The first challenge: If you travel using FTL (18 years difference) how would anyone know you did? They can’t communicate with you?


        • The people at the source couldn’t know when you arrived at the destination. The people at the destination could (assuming anyone is at the destination yet).

          Of course, if you immediately jumped back (without changing your velocity), you’d immediately jump back in space and time to where and when you’d just left.

          However, if before jumping back, you decelerated, reversed course and accelerated toward home, and then jumped, you’d arrive back 36 days after you left.

          But if you do the whole sequence jumping in the direction opposite of your speed both ways, you’d arrive back home 36 days before you’d left.

          (A sci-fi writer, of course, could simply posit that the technology doesn’t allow you jump in a different direction than your actual motion. The crew still has to think about which plane of simultaneity they want to use, but it prevents them going back in time. This won’t work for the Alcubierre drive though.)


          • Lander7 says:

            You stated — “However, if before jumping back, you decelerated, reversed course and accelerated toward home, and then jumped, you’d arrive back 36 days after you left.”

            My response — This would’t prove time travel just a delay in the amount of time needed to return.

            You stated — “But if you do the whole sequence jumping in the direction opposite of your speed both ways, you’d arrive back home 36 days before you’d left.”

            My response — This would not be true since each time you use FTL you move further into the future since time for you is moving increasingly slower (due to mass) while back on Earth it is still moving at the same pace.

            Liked by 1 person

          • Ah, okay, you may not quite understand the plane of simultaneity concept. (Or if you do, then I don’t 🙂 )

            When you are still, the plane of simultaneity is flat relative to other stationary observers. But when you’re traveling, the plane slopes upward in the direction of travel. That means that things in front of you that are in your now, are in the future for a stationary observer.

            But the plane sloping upward in the direction of travel means it slopes downward in the other direction, meaning that something behind you that is in your now is in the past for a stationary observer.

            So if you hyperspace jump in the direction opposite the one you’re traveling in, even if you emerge instantly from your point of view, you’ll emerge in the past as far as a stationary observer is concerned.

            Take another look at the animation in the post, or the wikipedia article. It’s not an easy concept to grasp.

            Liked by 1 person

          • Lander7 says:

            You stated — “Ah, okay, you may not quite understand the plane of simultaneity concept.”

            My response — The concept of simultaneity can’t be applied to FTL since they are not happening within the same frame of reference. This is due solely to the amount of mass applied from FTL.

            To put it another way, the frame of reference is changed do to a stretching of space time from the mass obtained in FTL.

            You don’t need to travel from one location to another to cause this, all you need is mass. The same thing happens to satellites in space, it’s the reason GPS systems have different references to time that need to be corrected between earth and earth orbit.

            Liked by 1 person

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