I've recently read Alastair Reynolds' sci-fi best seller, Redemption Ark, where he explored the concept of manipulating an inertial frame overlaid on the quantum vacuum like many of the other fundamental, underlying fields proposed by quantum field theory.

The method described in the novel was shown to work exceptionally for subluminal travel, wherein a device capable of manipulating the local inertial field would decrease the inertia experienced by particles in the field, thus decreasing the energy required to accelerate them; e.g., manipulating the inertia experienced in the local field by a factor of 0.5 would result in particles requiring 0.25 times the energy needed to accelerate to a given speed had the field been switched off. The upshot was that starships expended less energy by moving less mass, though that missing mass was not at all missing, it was just misrepresented from the norm, seen as having less resistance to changes in motion.

The physics and math behind the effect are, as far as I can tell, imaginary. Here in the real world, from what we have thus far ascertained, inertia is a property of matter and not a property of the local quantum vacuum imposed onto matter.

However, the idea was damned good, and so for my question, I will try to use a slightly modified version of this idea. Please keep in mind that I am not very educated in these matters, I am practiced at regurgitating ideas and concepts I have only flimsy understandings of.

Reynolds imposed guidelines to his inertial dampening effect. Straightforward guestimations at how the manipulation ought to work, given the fantasy science at hand. Should the local inertia be suppressed completely, such that particles in the field experience no inertia, they would become photonic, forced to move at the speed of light. If particles were to experience less than no inertia, they would become tachyonic, forced to travel faster than the speed of light and backward through time. This method seems like a viable approach to convenient, near-light speed travel, however, I believe Reynolds either overlooked an idea or had not and discarded it simply because it doesn't make sense. I hope it is the former because I'm shooting for a similar plausibility.

Try for a moment to imagine that a shift in the inertial "constant" is like a bulge on some film, like the classic presentation we all have seen to portray gravity. The shift may go in any vertical direction, positive or negative, much like the gravity analogy. It is basically analogous. Continue in this moment to imagine that a rising bulge in the film represents a decrease in the inertia experienced by all particles in the local field. In Reynolds' universe, this bulge may rise from units 1 (normal), to 0 (lightspeed), to -n (ludicrous speed), where the value may represent some multiplier of inertia experienced. Reynolds seems to allow this multiplier to be experienced by particles with mass, yet, mass in his system seems to be defined by the inertia they experience, which can be fluctuated. The mass of light, 0, doesn't change proportionally.

In my imaginary system, I propose that photons themselves are subject to this field and that decreasing or increasing the local inertial state has a proportional effect on all particles, tardyonic and photonic, in that field.

Now, if one was in a starship traveling in such a manipulated field, and one was to take a flashlight and shine it down a corridor directly in front of them, one would observe that the speed of light appears to remain consistent with what would be measured should the field be switched off, relative to oneself within the field. The increase is proportional to all particles. To an outside observer, they would observe the speed of the photons emitted from the flashlight within the traveling ship within the field to be traveling a proportion faster/slower than the speed of light.

It is important to note that this proposed field has a gradient-like drop-off whose function yields a range proportional to the distance apart from the origin of the field, like gravity.

That's basically what I had in mind for how it works.

Now, the question. The field certainly does not need to encompass an entire object. Nothing's that perfect. Some parts and pieces of an object can occupy the gradient-like region where the drop-off is significant, down to experiencing the field only nominally. Light, as it enters the significant region of the gradient, would be expected to lose some of its "inertia," increasing in velocity as a result. Based on the accepted answer of this, I know that "nuclear reactions would be much more energetic." (Though, the author of the answer did not elaborate on why that would be the case.) This question is irrelevant to mine anyway. This isn't an increase of the speed of light intrinsically, you see, because, within the field, an observer would observe light moving at what speed it appears to always move at, relatively speaking. So there is no true increase going on here, except in the differential space between the bulk of the field and the outside universe only marginally affected by the field. This is the region of interest to me.

How would energy and matter behave in this region?

Given the differential—objects further from the field feel its effects less than one nearer—perhaps some properties of matter may differ as one traverses the differential. If one soared headlong into such a field, one's head may experience less inertia than one's feet. Given different kinds of gradients, steep (perhaps mere atoms in thickness) to drawn-out (perhaps kilometers), to somewhere in between (meters or less), I want to know how matter would interact with itself and how embarking or disembarking matter and energy (photons) would behave. How would this thing look visually, anyway? That's always an important aspect if one's trying to illustrate something.

Bonus points if you give me an estimate or elaboration on how plausible this all is. That's what I was aiming for, but as I implied, I'm treading "unfamiliar" territory. I don't normally try to design these kinds of systems.


In a universe where inertia is a quantum field overlaid among other quantum fields, and also manipulable, imagine a hill of lowered inertia with some gradient-like drop-off from the peak of the hill. The inertial dampening effects all particles of mass and energy, so that particles entering the region experience less resistance to acceleration. Assume that light is bound to lightspeed by some inertial figure, which can be lowered and raised proportionally to particles surrounding it, such that an observer in any inertial frame always observes a constant speed of light. Across differing frames, however, this is not the case.

How would particles of matter and energy behave in this differential region, should it be steep or drawn-out?

I'm looking for the effects of a molecular bonded object entering the field, say, someone sticking a long pole into it, where the front of the pole experiences less inertia that the end.

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    $\begingroup$ "I'm treading "unfamiliar" territory. I don't normally try to design these kinds of systems." Don't take it personally, but writing reasonable technobabble -- even when asking other people for help -- without long experience reading and watching scifi (like ST:TOS, ST:TNG and ST:VOY) is IMO a disaster waiting to happen. $\endgroup$
    – RonJohn
    Aug 25, 2018 at 2:54
  • $\begingroup$ @RonJohn I think there's a distinction between creating technobabble systems and having exposure to them. I consider myself an avid sci-fi enthusiast (especially for authors like Alastair), and I also happen to own the seasonal dvd collection sets for each of those series you mentioned. It's not that I am unfamiliar with science fiction, I am unfamiliar with creating my own systems. In the past, I used familiar ideas often used by others. $\endgroup$
    – B.fox
    Aug 25, 2018 at 3:03
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    $\begingroup$ If your story is good, people will only care if you bill it as hard science. $\endgroup$
    – RonJohn
    Aug 25, 2018 at 3:26
  • $\begingroup$ TL;DR Variable speed of light is actually a concept in physics, competing with m-theory (except in some cases where m-theory predicts a variable speed of light). This is an area of active research at CERN. $\endgroup$
    – pojo-guy
    Aug 25, 2018 at 10:25
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    $\begingroup$ Inertial mass is due to the Higgs field. Therefore, if it's possible to manipulate the Higgs field, then manipulation of mass and inertia may be possible. Basically the quantum field you are considering is the Higgs field. $\endgroup$
    – a4android
    Aug 25, 2018 at 13:07

4 Answers 4


I'm... honestly having trouble following what you're trying to do here. So I'll attempt to boil it down into a few bullet points just so that I can wrap my head around it and come up with a coherent response. Please correct me if I've missed anything important.

You want to create a region of space (defined by e.g. some gizmo on a spaceship) where:

  • Matter has reduced inertia, so it can accelerated with less force
  • Time runs faster than normal (so that light appears to move unusually fast to an outside observer, but to an observer on the ship it looks fine)

You want to know:

  • How could this possibly work
  • What would happen around the edges of the region, where the effects taper off

For Bullet #1, we need to look to Newton's Second Law of Motion:

$$ F = m \cdot a $$

We want to get more acceleration out of the same force, so we need to reduce the mass somehow. How do we do that? Well, where does mass come from, anyway?

Your first thought might be something to do with the Higgs boson. And indeed, elementary particles, such as electrons and quarks, do indeed get their mass by interacting with the Higgs field. However, for our purposes, mucking with the Higgs field won't actually work.

Why not? Because most of the mass of regular matter comes from protons and neutrons, and most of their mass does not come from the Higgs mechanism. Yes, their component quarks do have Higgs-based masses that contribute to the mass of the nucleon, but most of the mass actually comes from something called the "quantum chromodynamics binding energy" and from Einstein's famous equation:

$$ E = mc^2 $$

As it turns out, hadrons (including protons and neutrons) are a chaotic mess of quarks and gluons constantly popping in and out of existence and zipping around at close to the speed of light. The kinetic energy of the quarks and the energy of the gluons (which, like photons, have energy and momentum but no mass) combined result in around 99% of the mass of the hadron, much in the same way that a massless box with a bunch of massless photons bouncing around inside will have mass determined by the energy of those photons.

So, to reduce the mass of a proton or neutron, we would have to do one of two things:

  • Reduce the QCBE of the nucleon
  • Increase the speed of light

Mucking with the QCBE is a dead end, due to conservation of energy- if you siphon the QCBE out of the nucleons in a chunk of matter, it has to go somewhere, and unless you spray it out of your ship as reaction mass or something, it's still going to contribute to the mass of your ship.

So we're left with futzing with the speed of light. In your question, you wanted your technobabble mass-manipulation technology to have a side effect of increasing the speed of light. Here, I'm proposing that increasing the speed of light would instead be the backbone of the mass-manipulation tech. Funny how that works.

Anyway. How might the speed of light be manipulated? I have no flippin' clue. However, there are some multiverse theories out there that propose that some of the things we take to be fundamental constants in our universe (such as the speed of light) might actually be determined by quantum fields. In eternal inflation scenarios, tiny quantum fluctuations in these fields can be amplified by the inflation and stretched out across entire bubble universe, resulting in universes with different physical constants. In your scenario, maybe your scientists discovered a way to manipulate the speed-of-light field directly.

All right. You've got a gizmo that increases the speed of light in an area around it, cutting the mass of all the hadrons within its area of influence. You've installed one of these devices on your spaceship. What are the repercussions?

First off, you'll be able to travel much faster than you would be able to otherwise. If your engine technology isn't capable of reaching relativistic speeds, then you can use the mass-reduction effect on everything but the engines, reducing the amount of weight they have to lug around.

If, instead, your setting includes the sort of incredibly efficient engines that could take a ship up to relativistic speeds, then you might be better off including the engines in the area of effect. With an increased speed of light, those relativistic effects kick in at higher speeds- so this could actually allow you move faster than the speed of light as measured by an outside observer. Lightspeed manipulation + black hole drive = FTL travel. Which also, I should point out, allows for straight-up time travel, when combined with the right set of moving reference frames. This system also gives a justification for ships needing to get up to relativistic speeds before transitioning to FTL- a requirement I've seen occasionally in science fiction, but always thought was silly. In your system, you have to be going at relativistic speed before you can go FTL because relativistic speed in the immediate vicinity of your ship is FTL for the rest of the universe.

Now, what about the effects on biology? Would your crew members perceive the speed of light as being no different than what it normally is, as requested in the question? My first reaction is yes: all of chemistry (and, by extension, biology) is mediated by the electromagnetic force, which is transmitted by photons. So if the speed of light was increased, then all chemical and biological processes would run at an increased speed... except those that involve moving things around... but since stuff has less mass and will be accelerated more quickly anyway, that might make up for it.

On the other hand, while changing the speed of light will reduce the mass of protons and neutrons, it won't change the mass of electrons (which gain their mass through the Higgs mechanism). Changing the proton-electron mass ratio sounds to me like the sort of thing that could horribly muck up everything we know about how chemistry works. However, remember that I proposed earlier that this technology works by manipulating some quantum field that determines the speed of light. Perhaps similar fields exist for other "fundamental constants", and your scientists have found ways of manipulating those as well. Then, combining and balancing these fields in ways that don't cause people to explode into quark-gluon plasma becomes merely an engineering problem. It would also open the doors for some impressive weapons.

Now, what about the outer edges of the field, where it tapers off? If you're using one of these devices for FTL travel, you probably wouldn't want to move into the area where the local speed of light drops below your speed. As best, you'd be shredded as your molecules get pulled apart faster than the electromagnetic force can pull them back together. At worst, your superluminal atoms create a paradox that destroys the entire universe. What happens will depend on exactly what physical constants are manipulated in what ways, and that in turn depends on your engineers. They'll surely do everything they can to keep the universe- and ship-destroying possibilities from ever occurring. How successful they are depends on you, the author.

What would this thing look like, anyway? For this, we can look to the Principle of Least Time, which states that light will travel from Point A to Point B via the path that gets it to Point B the quickest. Since light travels faster in the vicinity of your technology than it does elsewhere, there are quite a few ways in which a beam of light could detour to travel near your ship and reach its destination faster than it would by traveling in a straight line. Because of this, light will be refracted away from your ship, much in the same way that light is refracted away from the center of a bubble within a block of glass.

An outside observer looking at your ship against a background of distant stars will see the stars appear to be pulled in toward the ship as the ship passes by. It's sort of the opposite of gravitational lensing. In the area immediately around the ship, the observer will see reflections of stars farther from the ship. The stronger the lightspeed-increasing field is, the stronger this effect, and in the limit as the strength increases and the thickness of the tapering zone decreases, the boundary of the field will look more and more like a solid, mirrored ball.

  • $\begingroup$ This is exactly the answer I was looking for. I had no idea QCBE was responsible for the masses of hadrons. It's good to know that without Higgs field manipulation, matter may fly apart, haha. However, I don't think there would be any causal problems with matter or energy exiting the field, well, as far as this imaginary system goes. I'd imagine that the universe would want to agree with me if i say that as matter exited the field, its energy, momentum, speed, etc., are continuously rerepresented by the underlying speed-of-light field. $\endgroup$
    – B.fox
    Aug 25, 2018 at 22:00
  • $\begingroup$ 99%*c* in a 2*c* field equates to 99%*c* in a 1*c* field after having exited the 2*c* field. $\endgroup$
    – B.fox
    Aug 25, 2018 at 22:01
  • $\begingroup$ You mentioned that time travel among certain reference frames is possible. Could you elaborate on that or point me somewhere which details that a little more? I've heard of it before, but it was never really understood. I fail to see how a FTL ship can take off from Earth and wind up returning x years before it left. $\endgroup$
    – B.fox
    Aug 25, 2018 at 22:04
  • $\begingroup$ The best resource I can point to for FTL time travel is this video by PBS Space Time: youtube.com/watch?v=HUMGc8hEkpc It explains the concept far better than I could in a 600-character StackExchange comment. Also, go watch Space Time's videos on quantum mechanics and general relativity- they're really good, and they'll give you a much better understanding of those theories than you'll get anywhere outside of a high-level college course with a whole lotta math. $\endgroup$ Aug 26, 2018 at 1:10

This all sounds like a lot of made up mumbo jumbo with quantum tacked onto it to make it sound sciencey.

Anyways, I can only imagine that the half field would behave in one of two ways. Either within the confines of the transitional field there would be 50% effect relative to the effect within the field, with the region defined by sharp lines similar to thermoclines in water, or it would be some kind of probability field where all particles entered quantum duality, with particles next to the inner field being 99.9...% likely to enter wave state, and, the probability changing slowly across the field until you reach the outer border where particles will always entering particle state 99.9...% of the time. Keep in mind 100% is the original state of any particle or duality, where as a duality with a 50% is represented with 99.9...% chance of being the side of 50% that corresponds to the edge of the field it is on.

Also, do not pass through an inertia changing field, because it will rip your atoms apart kind of like a black hole would. (Edit: Or rather, as each atom passed through it, it would lose the effects granted to it by the inner field and be stuck in space far behind the ship.)

  • $\begingroup$ So, you're basically right when you say that this is all mumbo jumbo with a short quantum thumbnail. When I read your answer, I felt much the same way, except I knew I was misunderstanding due to a lack of knowledge. Perhaps my description of this fantasy system was over-elaborate? Reynolds has this fantastic ability to make complex ideas clear and understandable, perhaps I can locate where exactly in his novel he described the system, and then quote it, seeing as how the two systems are much the same. Otherwise, if that doesn't do it, I believe we reach an impasse. $\endgroup$
    – B.fox
    Aug 25, 2018 at 3:08
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    $\begingroup$ @B.fox No, I mean it sounds like someone who understands quantum physics extrapolated the effects observable on quantum levels to create a bunch of scifi that seems plausible to a layman or the ill informed, but is most likely unachievable. You could call it "slightly more plausible impossible science." $\endgroup$ Aug 25, 2018 at 5:20
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    $\begingroup$ @ClayDeitas Reynolds was a physicist, so he knows how to devise science-fictional concepts with reasonable degrees of scientific plausibility. Reasonable within the requirements of the science-fiction story itself. Calling it "slightly more plausible impossible science" is a fair call. $\endgroup$
    – a4android
    Aug 25, 2018 at 13:33

It is doubtful there there would be any appreciable effect. Special relativity will hold even with light undergoing variations in lightspeed. It's quite likely that Reynolds with his inertial mass varying drive intuited this would be the case. So he left the concept alone. This answer recommends you do the same.

Matter and energy are going to behave very much the same as they do when inertial mass isn't being manipulated to different values.

Lightspeed can already be lowered considerably for photons passing through Bose-Einstein condensates (BECs). That doesn't change how matter and energy behave. Apart from considerations of the extremely low temperatures involved in creating BECs.


From OP:

e.g., manipulating the inertia experienced in the local field by a factor of 0.5 would result in particles requiring 0.25 times the energy needed to accelerate to a given speed had the field been switched off. The upshot was that starships expended less energy by moving less mass

Now let us consider the force on a piece of mass.


Second law: In an inertial reference frame, the vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = ma. (It is assumed here that the mass m is constant – see below.)

If I artificially reduce m on my arm by inserting it into a scifi alternate quantum reference plane but any a remains constant, F exerted on my arm will be different from the adjacent F exerted on my shoulder. That is OK to an extent because I am built for it - I carry things from time to time. As the difference in F between arm and shoulder gets bigger it will stress the connection. If I am carrying something, I can let go. But if it is because of an angry Wookie pulling on my arm, or a quantum intertia field, the F may be too much for the connection between arm and hand to withstand.

Fortunately it would seem that acceleration from gravity is a special case and just as (I recently learned) altering the mass of an object does not alter net acceleration by gravity reducing the reference frame of a thing in orbit should not tear it to pieces with gravitational forces. Other acceleration forces that are not predicated on mass could definitely tear something apart.

And space? In your OP you reduce the inertia of an object. What if you increased it? A lot. This is something to give a boost to the narrative later in the book, Artificially increasing the mass of an object might get it to the point where gravitational effects do matter - the center of orbit between object and nearby large attractor might change. If you really increased inertia a lot by manipulating the local reference frame, the movement of galaxies and even the expansion of space could become relevant. You would seem to be moving very very fast but actually you are not moving at all - everything else is leaving you behind.


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