Inspired by this article, which refers to two other articles. (article 1) (article 2)

These articles suggest that the permittivity of free space ($\epsilon_0$) might be adjustable by changing the density of virtual particles in a volume of space.

The speed of light is : $c = {1 \over {\sqrt{\epsilon_0 \mu_0}}}$.

$\epsilon_0$ isn't required to hit any exotic values to create an appreciable increase in $c$. A simple $1 \over {100}$ reduction of $\epsilon_0$ would obtain a new $c_n = 10 c_0$

I'd like a hard-science (TRL 1) sanity check of this approach to an FTL engine:

  • Emitters around the bow and sides of the vessel produce colliding ion streams with sufficient collision energy to create Higgs bosons.
  • The Higgs fluctuations reduce the coupling between charge and mass, "de-massing" (reference) even virtual particles
  • The "de-massed" virtual particles keep their kinetic energy ($KE = {1 \over 2} m v^2$), meaning their velocity would increase. Reducing the virtual particles in the Higgs-illuminated volume.
  • Per original article, the reduction of virtual particles in the volume outside of the ship creates a region of "superpermittivity" (better permittivity than $\epsilon_0$) outside the vessel.
  • This field remains ahead of and around the ship much like a sonic shockwave.
  • The vessel and all the local space with it, travel behind the shockwave using ordinary rocket propulsion at ordinary sub-light speeds, but enjoying both an effective mass decrease ($m_n = m_0 {{c_0^2} \over {c_n^2}}$) and access to absolute velocities higher than $c$ without violating any causality, because the ship never exceeds the speed of light locally.

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Does this approach work?

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    $\begingroup$ There are some very smart random internet people hanging out here from time to time. $\endgroup$ Nov 19, 2020 at 0:35
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    $\begingroup$ "Without violating any causality, because the ship never exceeds the speed of light locally": that's not how it works. It doesn't matter how the ship travels faster than light from point A to point B; all it matters is that it travels faster than light from point A to point B. (When I was young and reading such things virtual particles were not real physical objects, but rather just convenient mathematical artifacts occurring in calculation. There is no "density of virtual particles" to change. Has anybody ever devised an experiment showing that virtual particles have physical existence?) $\endgroup$
    – AlexP
    Nov 19, 2020 at 1:08
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    $\begingroup$ @ksbes, Alcubierre himself points out that any method of traveling faster than light, including his drive, could in principle be used to travel in time and therefore violate causality. He believes in the chronology protection conjecture as a way around it, which has nothing to do with his particular proposed method of FTL. $\endgroup$ Nov 19, 2020 at 17:43
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    $\begingroup$ if you can get a message from A to B faster than a beam of light can get there, you can break causality. it doesn't matter at all how you get it there. $\endgroup$
    – ths
    Nov 19, 2020 at 17:43
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    $\begingroup$ It's too complicated for a full answer in the time I have. But the constants like speed of light MAY be determined by freezing-in of spontaneous symmetry breaking. There may be domains where the constants are different, producing boundary regions with very strange conditions. In this domain the speed of light is one value, and in that domain another. However, this is probably not useful for travel, because you have to go to the domain with the value you want, and it is cosmic distance away. $\endgroup$
    – puppetsock
    Nov 19, 2020 at 20:13

3 Answers 3


As others pointed out, the premise to your FTL engine arises from a misunderstanding of the article and under the hard-science constraints would not be feasible. You are correct in that the article is proposing that the permittivity and permeability of free space arise from virtual particles. However, it appear there is a misunderstanding of the meaning and implications of virtual particles.

Virtual Particles and Quantum Field Theory

Virtual particles arise as mathematical artifacts which "build", so to speak, an interaction. By summing up the various terms produced by virtual particle - particle interactions (whose quantities are determined by the likelihood of the virtual interaction), an interaction can be described at the chosen level within a perturbation expansion.

To formulate a perturbative expansion within quantum field theory, an energy scale (soft over hard) needs to be identified. This places restriction on the energy range over which the theory is applied to ensure a finite number of interactions at each level of the expansion, which is important for convergence. The particles in the interaction are cast as excited states of an underlying fundamental field which allows for the application of perturbation theory (which relies on corrections to a known ground state solution). For a given energy scale, all possible particle interactions needs to be expressible. Symmetries (and their breaking) identify which particles should be taken into account.

The above very simplistic summary is not meant to describe how to do quantum field theory (even a simplistic overview takes a whole book), instead I tried to highlight the most general factors which must be considered when applying the theory, which are relevant to the referenced papers.

So in the papers, the authors consider quantum fluctuations of elementary fermions (the quarks and leptons). This is because a vacuum would represent the "ground state" of quantum field theory. The vacuum speed of photons (speed of light) is linked to the vacuum constants, which in turn are intimately connected to charge symmetry and to the ground state (the vacuum). Thus, the authors employ an elementary model to determine a predicted range of flight time fluctuations if photon propagation is described in terms of interactions via fermion-antifermion virtual pairs. It is important to note that the paradigm for all of this is quantum field theory. In this light, it should be understood that the interactions are effective and not at all to be interpreted as physical. This is explicitly stated in the Leuchs et al. paper, from which I quote: "Indeed, from this picture, the vacuum can be understood as an effective medium". This does not mean that we throw away our physics textbooks and rewrite them with references to the "luminiferous aether" and delete any reference to the vacuum of space. Instead, this would represent another phenomena which can be explained in terms of quantum field theory.

Quantum field theory, at its heart, is a mathematical description. We use terms like virtual particle interactions, but note, the theory implies an infinite number of degrees of freedom (something which is quite obviously not physical nor intended to be viewed as such). The focus on quantum field theory arose historically with the astonishing success of quantum electrodynamics. The theory has also been applied successfully (though not nearly with the same degree of accuracy) to nuclear forces. In a sense, quantum field theory is ab initio (it relies on the most fundamental symmetries and interactions). Yet, the names we apply to the mathematical entities which compose quantum field theory should not be viewed as physical. After all, the theory relies on a solution which arises as an approximative correction. In other words, we do not think of all square waves as actually being composed of an infinite summation of sine and cosine waves in light of Fourier series.

To help with the analogy vs. the physical, consider other mathematical artifacts which are employed in quantum mechanics, the wavefunction for instance. The wavefunction yields the probability of various observables for a given quantum state, and is a fundamental component of quantum theory. However, we do not think of the world as existing as an endless superposition of all possibilities. Another phenomena is quantum tunneling, yet we don't think that particles physically "drill through" non-physical potentials. These are just phenomena which have relatable analogies.

The FTL Drive

A theory or model should only be applied where applicable and application of quantum field theory must come with justification based upon the energy scale and symmetries involved. Lets go through your FTL drive point by point:

  • Emitters around the bow and sides of the vessel produce colliding ion streams with sufficient collision energy to create Higgs bosons.

A Higgs boson has a mass-energy of 125 GeV! For comparison, the chiral symmetry breaking scale is on the order of 1 GeV; that is to say the hadrons in the emitter would have been disintegrated long before a Higgs boson is produced.

  • The Higgs fluctuations reduce the coupling between charge and mass, "de-massing" (reference) even virtual particles

The virtual particles at play here are going to arise from whatever interactions are taking place during the creation or decay of the Higgs particle; they are not going to be the same as the ones described in the paper because the energy scale is very different. Recall the paper describes a vacuum and this situation is most certainly not approximated by a vacuum due to the degrees of freedom present.

Also, what is meant by "Higgs fluctuations reduce the coupling between charge and mass"? Higgs bosons are very massive and have no charge.

  • The "de-massed" virtual particles keep their kinetic energy, meaning their velocity would increase. Reducing the virtual particles in the Higgs-illuminated volume.

Particle Kinetic energy is not typically described with the classical relationship of velocity, instead it is described through momenta. This situation is complicated by the fact that virtual particles do not obey the dispersion relationship.

Also, I'm not sure what is meant by this in connection with either the paper, the Higgs Boson or the Higgs field. As concerns the paper, photons are already massless, so I'm not sure how having a massless ship would remedy the situation. Virtual particles do not have mass in the same way as particles (see the comment in the paragraph above). As concerns the Higgs boson, they would not create a massless field that I'm aware of from the theory (I could not find any scientific paper which references "unmassing" or "demassing", or any reference thereto outside of pop or fringe publications). The Higgs boson appears due to symmetry breaking, for analogy see the pion triplet. The pion is the mediator of the nuclear force on the nuclear energy scale, their existence does not make the nuclear force disappear but rather they become the mediators of the force. My understanding is that the Higgs bosons would do the same for the Higgs field by analogy (both are Goldstone bosons) at the appropriate energy scale. The existence of the Higgs boson is significant in that it confirmed portions of the Higgs field theory, not because it can be used to zap particles into a massless state.

  • Per original article, the reduction of virtual particles in the volume outside of the ship creates a region of "superpermittivity" (better permittivity than ϵ0) outside the vessel.

The article in question describes a vacuum calculation. The presence of super massive particles like the Higgs boson already renders the basic assumptions invalid.

  • This field remains ahead of and around the ship much like a sonic shockwave.

What field and how does it remain "ahead and around the ship"? From the previous reference to a "Higgs-illuminated volume" it would appear that the Higgs field is being misunderstood. The "Higgs field" refers to an algebraic symmetry which mathematically describes the Higgs mechanism and not to a visible R3 space field.

  • The vessel and all the local space with it, travel behind the shockwave using ordinary rocket propulsion at ordinary sub-light speeds, but enjoying both an effective mass decrease and access to absolute velocities higher than c without violating any causality, because the ship never exceeds the speed of light locally.

There seems to be a lot of conflating of concepts here. Trish does an excellent job of summarizing the causality issue which would arise. It seems to me like frame-dragging is also being referenced. Unfortunately, the physics doesn't make sense at all. Consider the frame-dragging of "local-space", why would a massless form of particles cause dragging of space-time, which is specifically an effect of mass propagation? Also, as regards causality, since the ship is traveling slower than the speed of light in its own reference frame and faster than the speed of light in all other references frames, there could exist a scenario in which a cause is observed to precede its effect (the very definition of causality violation) [for a quick example consider if you flew your ship in a circle, you'd catch-up to and pass yourself which is absurd paradox, easily resolved with the causality restriction].

  • $\begingroup$ Thank you. That's a great answer. I'm going to have to look at it some more to understand it all, but what I did understand made sense. $\endgroup$ Nov 30, 2020 at 12:55
  • $\begingroup$ I'm curious, if you might know - the papers suggested a method using very high energy photons. While the change I made using Higgs might be ridiculous, does the set-up suggested for changing permitivitty in the original papers sound right? $\endgroup$ Nov 30, 2020 at 12:59
  • $\begingroup$ @JamesMcLellan The Urban et al. paper is suggesting that spontaneous pulse widening of high energy photons in a vacuum may be evidence that permittivity can be explained by effective virtual fermion-antifermion interactions. The experiment does not attempt to change the permittivity of a vacuum. As AlexP pointed out, changing permittivity through in-media interactions is well known and understood. Elements of the quantum vacuum (such as permittivity) are not currently well-understood through QFT, hence the interest of these sort of papers which are very preliminary in their nature. $\endgroup$
    – user110866
    Nov 30, 2020 at 23:26
  • $\begingroup$ @JamesMcLellan to elaborate, if the permittivity can be explained through QFT then this means that the phenomena arises from fundamental interactions. This does not imply we would be able to change it (for instance, we known the fundamental unit of charge "e" but we cant change it). We could only change the phenomena if the fundamental interactions could somehow be modified. Since the presence of particles is not a vacuum by definition, the only way to modify the fundamental interactions in a vacuum would be by some unknown physics, well outside the scope of current theory. $\endgroup$
    – user110866
    Dec 1, 2020 at 0:01
  • $\begingroup$ Gotcha. Thank you. $\endgroup$ Dec 15, 2020 at 10:06

= NO

Currently, we describe particles by their speed compared to the speed of light using the light-cone:

  • Light that moves with the speed of light is light-like. The totality of events that create such particles lies on the surface of a cone of past and future, both crossing in the point of "now" (the spectator). Anything on the cone can be seen at the moment.
  • Events inside the cone can have a causality to one another: Any event has its own light cones, and if another event is in the fututre cone of a past event, then the past event can be the cause of the other one. Likewise, any event that has another event in its past cone, can be caused by it. As an extension: Any movement of an object can only happen upwards inside the light cone.
  • Anything outside of the cone is defined as "Space-like". That is, particles or events outside of the observable cone (the light cones) exist, but you can not interact with them (yet) and they can not be the cause for events that happen there.

Ergo, the butterfly can only cause the storm if enough time has elapsed so the particles could interact and cause the storm pattern. Or in other words: Cause and Effect are not instantaneous.

A drive that would force an item to interact with space-like objects - and nothing else is FTL - is prohibited by causality.

  • $\begingroup$ There are two published articles in the original post (first line) that suggest both that the speed of light can be manipulated, and how to do it using extremely high-energy photons. Do you have any link that refutes them? $\endgroup$ Nov 26, 2020 at 17:19
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    $\begingroup$ no, and I don't need to: causality is the harder mistress. Your drive violates causality. $\endgroup$
    – Trish
    Nov 26, 2020 at 17:36
  • $\begingroup$ @JamesMcLellan you also misinterpret the article: there is no sonic shockwave to be had. $\endgroup$
    – Trish
    Nov 26, 2020 at 17:48
  • $\begingroup$ I was using sonic shockwaves as a model for propagating a wavefront of this changed space. $\endgroup$ Nov 26, 2020 at 17:53
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    $\begingroup$ @JamesMcLellan: The speed of light can be very easily manipulated at low energies, no need for fancy physics: just make it propagate through a suitable medium, such as glass or water, and you will immediately notice a change of speed. (And for more mind beding, there are materials with refractive indexes below 1: and no, they don't allow the propagation of information faster than c.) $\endgroup$
    – AlexP
    Nov 26, 2020 at 22:47

Since it is hard-science then answer is no, it is unreal

  1. By current concept "speed of light" is not determined by any constants. It is a fundamental constant c of space-time by itself. Even light does not define this constant. It just happens so that light is traveling with this speed (because it is "massless"). It means that changing $\epsilon_0$ and/or $\mu_0$ could not make light traveling faster than c (localy) due to consequences of Theory of Relativity.

  2. You are not breaking local casuality, but, since your are not bending space-time, your are breaking "global" casuality. It means that possibility of such ship is still a disproof for Theory of Relativity.

  3. Im not expert in quantum field, so this part is not that hard. It is really very little known about actual properties of Higgs field (actually only aproximate mass is known for sure). But there are lots of ion streams in space with ordres higher energy than we achived in accelerators. And no one ever observerd efects of local light speed increase or other consequences of "mass effect". It means that there shuold be some mechanism preventing it.

  • $\begingroup$ The idea that c is more fundamental constant is a new one to me. Where can I learn more about that? Thanks for the rest of the answer! $\endgroup$ Nov 19, 2020 at 11:00
  • $\begingroup$ Some variation has been measured - theboar.org/2020/06/… $\endgroup$ Nov 19, 2020 at 11:08
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    $\begingroup$ Changing $\varepsilon_0$ or $\mu_0$ would very obviously change the speed of light in a vacuum. Of course, that would also very obviously induce entirely new physics. $\endgroup$
    – AlexP
    Nov 26, 2020 at 11:56
  • $\begingroup$ I’d like to accept this answer, but it ignores the premise of the two published articles in the original post, without some support. Namely, that the speed of light may be manipulated. If you could add refute links, it’d be perfect! $\endgroup$ Nov 26, 2020 at 17:16

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