Star size comparaisons

Interesting video on APOD here

Is Gravity Control Propulsion viable? Part 4

From the previous post, we'll follow on from  the general idea of an accelerating quantum vacuum composed of virtual particles interacting with mass which we perceive as gravity (spacetime curvature) and responsible for weight emphasising that this is only a hypothesis that appears to fit General Relativity and may provide an avenue to make new testable quantum predictions on gravity. We haven't ruled out the other possibilites though which are graviton exchange between mass, a combination of quantum vacuum electromagnetic interactions and gravitons, or other interactions via unknown particles. As noted in the previous post, the graviton hypothesis is not a testable model for the foreseeable future and cannot be proved or disproved by experiment so can't be ruled out although is not helpful for our aim for Gravity Control Propulsion (GCP) since we have no control of graviton interactions. We will also look at Gravitoelectromagnetism (vacuum dragging effects). Although there are similarities between Maxwell's field equations and the GR field equations, we'll show later that it appears this cannot be used for GCP. Both classical electromagnetism and gravity operate under Gauss's inverse square law in a three dimensional space, this is where the similarities end, however gravitoelectromagnetism is a useful tool to model the effects of gravity under certain circumstances (such as gravitational waves). Our main aim is to investigate if there is any direct relation between electromagnetism and gravity and understand Nature's mechanism for spacetime curvature due to mass and energy density. Since we are good at manipulating experiments that are electromagnetic based, if there is a relation there would be avenue for GCP related experiments down the track. If there is no relation between electromagnetism and gravity, GCP is in trouble.

The accelerating quantum vacuum is composed of the full spectrum of virtual particles which have their counterpart real particles. Among them there are virtual electrons and positrons (part of the lepton family of particles) both of which have electric charge which means there is avenue for interaction via electromagnetism. We will also need to look at the mix of virtual particles that have zero charge. The diagram below shows the situation quite well for a particle with charge q, velocity v, and the effect of the Lorentz force on this test charge (negative, positive or neutral) due to a magnetic field B coming out of the screen perpendicular to you.



Deflection of a test charge q due to a magnetic field coming out of the screen. Image: Wikipedia.



 Let's have a look at another paper that proposes a similar hypothesis to the previous paper: Does the Quantum Vacuum Fall Near the Earth? The Downward Acceleration of the Quantum Vacuum is Responsible for the Equivalence Principle.

This paper makes several modifications to the previous accelerating quantum vacuum model and although it makes several interesting points it also introduces some highly speculative propositions. In summary the paper proposes:

The downward acceleration of the virtual electrically charged fermion particles of the quantum vacuum is responsible for the Einstein Weak Equivalence Principle and for our perception of 4D space-time curvature near the earth. Since the virtual fermion particles of the quantum vacuum (virtual electrons for example) possess mass, we assume that during their short lifetimes the virtual fermions are in a state of downward acceleration (or free-fall) near the earth. Many of the virtual fermions also possess electrical charge, and are thus capable of interacting electrically with a real test mass, since a test mass is composed of real, electrically charged, fermion particles. The electrical interaction between the downward accelerated virtual fermions with nearby light or matter is responsible for the equivalence of inertial and gravitational mass, and also responsible for our perception of 4D space-time curvature near the earth.

The opposition to acceleration of a test mass by the reverse process is explained to be the cause of inertia. Key point here that is of interest to us is where it is mentioned that the virtual fermions are interacting electrically with mass. It remains to be seen if this hypothesis (ElectroMagnetic Quantum Gravity or EMQG) is correct and if this is the only cause of gravity. The paper does not give a mechanism for the root cause of the downward acceleration of the quantum vacuum however the concept as outlined is enough to explain GR and vacuum dragging effects which is why the model is interesting. We are also moving on from the classical explanation of GR to a quantum model of gravity:

 4D curved Minkowski space-time is now a consequence of the behavior of matter (particles) and energy (photons) under the influence of this (statistical average) downward accelerated ‘flow’ of charged virtual particles of the quantum vacuum. This coordinated ‘accelerated flow’ of the virtual particles can be thought of as a special ‘Fizeau-like vacuum fluid’ that ‘flows’ through all matter near a gravitational field (and also in matter undergoing accelerated motion). Like in the Fizeau experiment (which was performed with a constant velocity water flow) the behavior of photons, clocks, and rulers are now affected by the downward accelerated flow of the virtual particles of the quantum vacuum caused by gravity.

We'll note that the vacuum's net electric charge is neutral and there must be equal numbers of virtual electrons and virtual positrons (anti-electrons) at a given time due to pair creation and annihilation processes. Since these two particles have equal and opposite electrical charge they both react to magnetic fields. Also since this "Fizeau-like vacuum fluid" of virtual particles interacts with normal matter, we can deduce that motion of matter can also influence this "vacuum fluid" which we observe as vacuum dragging effects (gravitomagnetism), normal matter being made of protons and neutrons which are made of charged quarks with our usual cloud of charged electrons surrounding the nucleaus for a standard atom. Also note that this is not a Superfluid Vacuum Theory or Aether model although there are some similarities. 

Real electron and positron curl in opposite directions in a bubble chamber magnetic field. Image:  Britannica

On p8 the paper talks about Hawking radiation for black holes which is of interest to us because here is a special case where the virtual particle and anti-particle pairs do not undergo annihilation at the event horizon and offers further insight on the physics of the quantum vacuum virtual particle field. Vacuum polarisation also shows that our observations of real electron charge is affected by the cloud of virtual positrons of the quantum vacuum that congregate around the electron (also known as charge screening). On p11 the paper goes on to explaim the EMQG model of gravity involving two particle exchange mechanisms:

What is unique about EMQG theory is that gravitation involves both the photon and graviton exchange particles operating at the same time, where now the photon plays a very important role in gravity! In fact, the photon exchange process dominates over the pure gravitational interaction, and is in the most part, responsible for the principle of equivalence of inertial and gravitational mass. The photon particle is also responsible for another property that all matter possesses, the inertial force that acts to give a mass the property of Newtonian inertia.

We cannot verify part of the claim that gravitation involves graviton exchange particles as explained previously (although this is the current accepted norm in Physics) however we can verify photon exchange mechanism in principle. It is mentioned on p13 that there appears to be a deep connection between electromagnetism and gravity because Coulomb's electrical force law: \(F=\frac{KQ_{1}Q_{2}}{r^{2}}\) and Newtonian gravitational force law: \(F=\frac{GM_{1}M_{2}}{r^{2}}\) are similar. Both classical electromagnetism and gravity operate in a three dimensional space where Gauss's inverse square law is applicable. Gravitomagnetism was devised well before GR as a tool to model gravity using the similarities between the two forces. Gravitational waves for eg can be modeled by splitting the gravitomagnetic and gravitoelectric components just like electromagnetic waves can be split into their electric and magnetic field vector components. It appears that no further insight will be gained with this approach since this is a classical tool devised for a classical model of gravity although useful to explain vacuum dragging effects and gravitational waves. We'll keep it as a set for our classical toolbox though. Attempts to discover direct mechanisms to convert electromagnetism to gravity based on the gravitoelectromagnetic field equations are expected to be unsuccessful (see for eg Coupling of Gravitation and Electromagnetism in the Weak Field Approximation).    

Examples of vacuum dragging: Thirring and Thirring-Lense effects. Image: Motion Mountain, Vol 2, p150

On p14 interesting questions are put forward:

Does the graviton particle move in a 4D flat space-time like the photon of QED? Does the graviton exchange process somehow ‘produce’ curvature on an otherwise flat background 4D space-time, when propagating from one mass to another? If the graviton is not responsible, then what is it about mass that is directly capable of producing 4D space-time curvature surrounding the mass? In other words, if the 4D space-time curvature is not caused by the graviton exchanges, then what is the connection between matter and 4D space-time? If you double the mass, you change the amount of space-time curvature. Why?

To our knowledge, these questions remain unanswered. In EMQG, we propose a quantum action based on the quantum vacuum and the existence of graviton particles (that have characteristics very similar to the photon) that resolves these questions. It turns out that the state of acceleration of the quantum vacuum with respect to another test mass represents the quantity of 4D space-time curvature!

 The concept of an accelerating quantum vacuum responsible for 4D spacetime curvature is plausible and also can explain vacuum dragging effects. We will look at some of the problems with the model though and possible modifications required without resorting to new particles (such as the paper's "masseon" particle). Although EMQG also resorts to gravitons for part of their explanation for 4D curvature, it is not clear at this stage if this is a requirement for a successful model since we are unable to question Nature if she is actually using gravitons to mediate gravity. It should be noted that from p16 regarding a derivation for GR, there is a relatively straightforward derivation offered in Motion Mountain Vol 2 Ch 4 "Simple General Relativity: Gravitation, maximum speed and maximum force". Just like Special Relativity is based on maximum speed c in Nature, GR can be derived from the following: There is in Nature a maximum force: \(F\leq\frac{c^{4}}{4G}=3.0\cdot10^{43}N.\) Both maximum speed c and maximum force are properties of the vacuum. It is interesting to note here from Motion Mountain Vol 2 p33:

However, there is at least one system in nature where the speed of sound is indeed a limit speed for energy: the speed of sound is the limit speed for the motion of dislocations in crystalline solids. (We discuss this in detail later on). As a result, the theory of special relativity is also valid for dislocations, provided that the speed of light is replaced everywhere by the speed of sound! Indeed, dislocations obey the Lorentz transformations, show length contraction, and obey the famous energy formula \(E=\gamma mc^{2}\). In all these effects the speed of sound c plays the same role for dislocations as the speed of light plays for general physical systems.

The observation above is interesting for the model of the accelerating quantum vacuum which we are looking at. On p 35, the paper asks the important questions:

Does the general downward acceleration of the virtual particles of the quantum vacuum near a large mass affect the motion of photons propagating within the gravitational field? Or is the deflection of photons truly the result of an actual spacetime geometric curvature (which holds down to the tiniest of distance scales)? 

The answer to this very important question hinges on whether our universe is truly a curved, geometric Minkowski 4D space-time on the smallest of distance scales, or whether curved 4D space-time results merely from the activities of quantum vacuum virtual particles interacting with other real quantum particles. EMQG takes the second view. 

According to postulate 4 (appendix A-11) of EMQG theory, light takes on the same general acceleration as the net statistical average value of quantum vacuum virtual particles, through a ‘Fizeau-like’ scattering process involving many virtual particles. By this we mean that the photons are frequently absorbed and re-emitted by the electrically charged virtual particles, which are (on the average) accelerating towards the center of the large mass. When a virtual particle absorbs the real photon, a new photon is re-emitted after a small time delay in the same general direction as the original photon. This process is called photon scattering (figure 5). We will see that photon scattering is central to the understanding of space-time curvature.

The second view looks plausible however the EMQG model as proposed in the paper with its introduction of several new hypothetical particles other than gravitons to explain how gravity is mediated is highly speculative and doesn't appear to be correct. We'll keep this aside for the time and make a mental note that this part of the model still needs work. The explanation from p39 on photon scattering in a static and accelerated quantum vacuum is interesting. It is feasible that the photon undergoes a time delay between absorption and re-emission between each charged virtual particle it encounters in the quantum vacuum and undergoes a "photon vacuum delay" which gives an average light velocity of 300000 Km/s. It is not clear however if there is a higher "raw light velocity" of the photon between each charged virtual particle, at this stage this cannot be verified (however see the following paper: Does the speed of light depend upon the vacuum?). One can speculate if the density of the charged virtual particles could be reduced somehow in a given volume of the quantum vacuum, this average light velocity could be increased as the number of encounters with charged virtual particles is decreased. The charged virtual particles can be seen as offering resistance to the propagation of the photons. This fits in well with photon scattering processes in materials, Fizeau's moving water experiment mentioned earlier in the paper and the equations of motion of dislocations in crystalline solids mentioned above.  We'll follow on from p44:

We are now in a position to understand the concept of the geodesic proposed by Einstein. The downward acceleration of the virtual electrically charged masseons of the quantum vacuum serves as an effective ‘electromagnetic guide’ for the motion of light (and for test masses) through space and time. This ‘electromagnetic guide’ concept replaces the 4D space-time geodesics that guide matter in motion in relativity. For light, this guiding action is through the electromagnetic scattering process of section 9.5. For matter, the electrically charged virtual particles guide the particles of a mass by the electromagnetic force interaction that results from the relative acceleration. Because the quantum vacuum virtual particle density is quite high, but not infinite (at least about \(10^{90}\) particles \(/m^{3}\), the quantum vacuum acts as a very effective reservoir of energy to guide the motion of light or matter.

If the overall model turns out to be correct and we can devise a method to interfere with the electrical interaction of the vast numbers of falling virtual charged particles with the real, electrically charged matter particles for a test mass then there is an avenue to carry out GCP related experiments. What is interesting here is that although the details in the gravity mediation process is still unclear at this stage, the effect isn't and if the  secondary cause is via electrical interactions we can in principle interact or interfere with the process even if the root cause turns out to be via neutral gravitons which we cannot interact or modify.

At this stage however using the above model (if correct) we can for example rule out the Podkletnov and Tajmar experiments which both rely on rotating superconducting rings. Podkletnov's experiment claimed a 2% weight reduction on a test mass in the center of the ring. The magnetic field generated by the rotating superconducting ring is not preventing the accelerating quantum vacuum charged virtual particles from interacting with the test mass at its center as the field configuration in incorrect. Another experiment by Tajmar was devised to look at gravitomagnetic and gravitoelectric fields is also incorrect. As mentioned previously above, one should not confuse vacuum dragging effects that can be modeled with classical gravitomagnetism with actual real fields in Nature.

Podkletnov's experiment: no weight reduction can be obtained with this configuration.  

Tajmar's experiment: no gravitoelectric and gravitomagnetic fields can be found,
only vacuum dragging effects can be measured.

In Part 5 of these series, we'll look at some of the problems with the EMQG model and modifications required that doesn't rely on hypothetical particles. We also need to deal with the neutral virtual particles that make up the accelerating quantum vacuum and look at some testable predictions that can be verified by experiment.

CI.

Update: Interesting post on Backreaction: Quantum gravity phenomenology detecting gravitons

Is Gravity Control Propulsion viable? Part 3

If one does a survey of the online preprints on arXiv and viXra and does a search for terms gravity and quantum vacuum, one will find a large number of papers dealing with the subject. Most of the papers that I went through appear to be highly speculative or introduce many assumptions to their models or have contradictions to known Physics. The papers that were more useful described their model rigorously and propose an experiment to verify their hypothesis with testable predictions together with good references.

Getting back to assessing the viability of gravity control propulsion, our inability to understand the physical mechanism of the bending of spacetime by mass and energy density is the main stumbling block to answering this question. All current proposed alternative models to GR are either unconfirmed, speculative or have their own problems.
 

Let's have a look at the following paper by Alfonso Rueda and Bernard Haisch on Gravity and the Quantum Vacuum Inertia Hypothesis. We'll first note "Neither our approach nor the conventional presentations of GR for that matter, can offer a physical explanation of the mechanism of the bending of spacetime as related to energy density", however from their hypothesis the authors explain:

 

"Inertial mass arises upon acceleration through the electromagnetic quantum vacuum, whereas gravitational mass — as manifest in weight — results from what may in a limited sense be viewed as acceleration of the electromagnetic quantum vacuum past a fixed object. The latter case occurs when an object is held fixed in a gravitational field and the quantum vacuum radiation associated with the freely-falling frame instantaneously comoving with the object follows curved geodesics as prescribed by general relativity."

In others words one only feels weight while for eg sitting on a chair but not while in free fall when jumping out of an airplane. We know the quantum vacuum consists of a sea of particles created and annihilated in very short time frames (these are called virtual particles). Among these virtual pairs of particles are positive and negative electrons popping in and out of existence. Note that this process is also responsible for determining the universal speed limit of light, mass and energy in vacuum  \(c_{0}=\frac{1}{\sqrt{\mu_{0}\epsilon_{0}}}\)  (see The quantum vacuum as the origin of the speed of light). Is an accelerating quantum vacuum with its sea of virtual particles interacting with every atom in an object and responsible for weight? Is gravity electromagnetic in origin? If this were the case one still has to explain the physics of what causes the acceleration of the quantum vacuum by mass and energy density. According to the paper the Quantum Vacuum Inertia Hypothesis is consistent with GR and the authors derive the same result using both SED and QED. They also propose that "at least part of the inertial force of opposition to acceleration, or inertia reaction force, springs from the electromagnetic quantum vacuum." This Rindler frame force as it is called stems from the local interaction of mass with the electromagnetic quantum vacuum when accelerated however there is no force on objects with constant velocity (inertial frames) and is proportional to acceleration imparted on the object. 

 "We have called the notion that at least part of the inertia of an object should be due to the individual and collective interaction of its quarks and electrons with the quantum vacuum as the quantum vacuum inertia hypothesis with the proviso that analogous contributions are expected from the other bosonic vacuum fields."

 The Rindler frame force (or the vacuum electromagnetic counteracting reaction force) is derived as

$$-f^{zp}=\left[\frac{V_{0}}{c^{2}}\int\eta\left(\omega\right)\rho\left(\omega\right)d\omega\right]a.$$ This is a description of the electromagnetic component of the proposed reaction force and it remains to be seen what the other components of the force are. An experiment is proposed with a cavity resonator to verify the following: "First, some confirmation would be given to the electromagnetic vacuum contribution to inertial mass concept, or quantum vacuum inertia hypothesis. An important confirmation would be the reality — or virtuality — of the zero-point field."

Note that if the above hypothesis is confirmed, this would rule out Mach's principle and inertia would be shown to be purely a local effect between mass and the quantum vacuum (I tend towards the local effect hypothesis and think Mach's principle is incorrect). The paper also suggests that gravity even in part is electromagnetic in origin so before continuing on let us look at what options we have for electromagnetic shielding.

In Part 1 we looked at the hypothetical gravitational shielding concept. Although unrelated, it is useful to explore the following two effects in physics which are confirmed by experiment. Electromagnetic shielding or the Faraday cage is widely used in electronics and the lab to exclude both static and non-static electric fields inside a metal cage which is due to the electrons in the metal shield rearranging themselves to effectively cancel the outside electric field inside the cage as shown below. It will also shield the inside from the fluctuating magnetic field component of electromagnetic waves (such as radio waves) but cannot block static or slowly varying magnetic fields (such as the Earth's magnetic field).

 



The Faraday cage excludes electric fields inside the cage. Image: Magnet Lab

For magnetic fields we have the Meissner effect, a property of superconductors which exclude magnetic fields inside the object when a critical cold temperature is reached as shown below and this also applies to hollow superconductor objects.

 

The Meissner effect for superconductors, magnetic field lines are excluded from the object
when a critical cold temperature is reached. Image: Wiki

 

Questions:

 

• If the dynamic quantum vacuum is partly responsible for gravitational effects as suggested in the paper, is there a means to shield an object from the accelerating quantum vacuum?
• Can we stop the interaction of electrons and quarks of the object inside the shield from the outside accelerating dynamic quantum vacuum? 
• If a shielded object was disconnected from the outside quantum vacuum, how would this affect the object's mass and the quantum vacuum inside?
• Is it plausible to have a static quantum vacuum within an accelerating quantum vacuum?

Getting back to the paper the Equivalence Principle is explained:

"The physical basis for the principle of equivalence is the fact that accelerating through the electromagnetic quantum vacuum is identical to remaining fixed in a gravitational field and having the electromagnetic quantum vacuum fall past on curved geodesics."

According to the paper the hypothesis appears to agree with GR and also explains the bending of light near mass etc "However this does not mean that we have explained the mechanism for the actual bending of space-time in the vicinity of a material object. This is the origin of so-called active gravitational mass that still requires an explanation within the viewpoint of the quantum vacuum inertia hypothesis." There's a useful reference to the (highly recommended) textbook Gravitation by  Misner, Thorne and Wheeler and points to Chapter 17 "How mass-energy generates curvature" which describes the alternative models and provides a good insight on the various approaches to this problem. The sixth model by Sakharov begins with general vacuum considerations as did the authors of this paper.

 

The paper also gives an explanation of mass "it was made clear that within the quantum vacuum inertia hypothesis proposed therein, the mass of the object, m, could be viewed as the energy in the equivalent electromagnetic quantum vacuum field captured within the structure of the object and that readily interacts with the object."

So it appears from the above hypothesis that the key is to understand how electrons and quarks in  atoms interact with the dynamic quantum vacuum. Note that as the authors point out though we also haven't established the mechanism responsible for the acceleration of the quantum vacuum due to mass and energy density. Getting back to the original question regarding Gravity Control Propulsion it appears that this answer cannot also be answered by GR, the current alternate models to GR or the above hypothesis, however they do provide some good pointers to follow. The problem is pointing us to quantum physics and particle physics, we lack the understanding of the quantum processes that occur between matter - dynamic quantum vacuum interactions. The particles mentioned in the paper ie electrons and quarks both have electric charge. We cannot interact with quarks as they are locked in the nucleus of protons and neutrons due to colour confinement so we will look at the lepton family of particles. We'll continue with this next time. Till then ponder on the Koide formula below:

$$Q=\frac{m_{e}+m_{\mu}+m_{\tau}}{\left(\sqrt{m_{e}}+\sqrt{m_{\mu}}+\sqrt{m_{\tau}}\right)^{2}}\thickapprox\frac{2}{3}$$

CI.

Is Gravity Control Propulsion viable? Part 2

So far Gravity Control Propulsion doesn't look promising, we know spacetime tells mass how to move and mass tells spacetime how to curve (gravity) however with our current understanding of GR and QFT we don't understand the underlying quantum processes that causes this, GR however models the above very well. In QFT, a hypothetical particle called the graviton is thought to mediate gravity. Problem is there is no means to detect a single graviton by any experiment today or the foreseeable future, they are predicted to have no mass and no electric charge hence do not interact with photons and the absorption of a single graviton by a particle would only change its spin or position however the change would be indistinguishable from a quantum fluctuation. So this will remain a hypothetical particle, although detecting gravitational waves would be possible, this wouldn't  confirm the graviton hypothesis since other models can explain gravitational waves.


The Gravity Probe B experiment confirmed spacetime effects predicted by GR. Image: NASA

Is it possible for mass  not to tell spacetime how to curve? From the previous post, mass doesn't appear to influence \(h\), the gravitational shielding constant, in any way which makes sense since mass and energy \((E=mc^{2})\) are the cause of the spacetime curvature in the first place. What if we modify the vacuum energy density? In 2013 this can be done in the lab (with great difficulty) by Casimir plates.

 

Let's have a look at a third interesting paper that touches on these topics called Gedanken experiments with Casimir forces, vacuum energy, and gravity by Gordon Maclay. In the abstract it is mentioned "we demonstrate that a change \(\Delta E\) in vacuum energy, whether positive or negative with respect to the free field, corresponds to an equivalent inertial mass and equivalent gravitational mass \(\Delta M=\Delta E/c^{2}\)." He also looks at the energy considerations of a hypothetical gravitational shield. Further on "We are interested in considering several aspects of vacuum energy and Casimir forces, including the inertial mass associated with vacuum energy, the interaction of vacuum energy and gravity, and the possibilities of utilizing vacuum energy for propulsion or other purposes.". Three concepts of mass are outlined:

• gravi-inertial mass: inertial mass that resists acceleration.
• active gravitational mass: mass that generates a gravity field around it.
• passive gravitational mass: mass that reacts to a gravitational field.

In GR, all three are equal and equivalent, for the purposes of this discussion however it is useful to look at the three concepts separately. It is mentioned that the vacuum field seems to contribute to inertial mass and "the general consensus is that only changes in vacuum energy act as a source of a gravitational field".  Several interesting gedanken experiments are outlined to answer the following questions:

 

1. Is a change in inertia of a system associated with a change in the vacuum energy of the system?
2. Is a gravitational field generated by the change in vacuum energy (equivalent active gravitational mass)?
3. If an external gravitational field is present, is there a change in the gravitational energy of the system that is associated with the change of vacuum energy (equivalent passive gravitational mass)?

The interesting (yet unconfirmed by experiment) Scharnhorst effect is also mentioned. Why resort to gendanken experiments (thought experiments)? Because the quantum vacuum effects looked at are so small, it makes it a real challenge with 2013 lab technology to measure these with enough precision. High precision experiments in Physics unfortunetly means high costs. There's an interesting quote from the late Arthur C. Clarke:

 

"If vacuum fluctuations can be harnessed for propulsion by anyone besides science-fiction writers, the purely engineering problems of interstellar flight would be solved."

In Gedanken Experiment two, the author refers to another paper: A Gedanken spacecraft that operates using the quantum vacuum (Dynamic Casimir effect). Unfortunetly the thrust generated if confirmed is tiny although interesting as the Dynamic Casimir Effect was only verified recently in the lab in 2011, where mirrors (SQUIDs) are vibrated very fast at \(\frac{1}{4}c\) which created real photons out of the quantum vacuum. It's very unlikely that down the track this Gedanken spacecraft will replace rockets anytime soon.

Casimir plates partly suppressing vacuum fluctuations. Image: Wiki

In Gedanken Experiment Three: Vacuum Energy Contributes to Inertial Mass, the paper considers an isolated sphere with a battery operated motor which can move Casimir plates inside the sphere. As the plates are moved closer, what happens to the total energy of the system? Total energy of the sphere is conserved however the distribution of the energy within the system has changed from the vacuum energy between the plates and the battery. The paper "suggests that it might be possible to make components that have negative inertial mass. Such objects would tend to rise in a uniform gravitational field. Indeed negative vacuum energy in the stack of parallel plate capacitors considered theoretically by Calloni et al resulted in a force in a gravitational field that was in the opposite direction from that experienced by normal positive matter, but the positive force due to the mass of the silicon wafers, was much larger. Could one make an object that floated in a gravitational field?" 

 

One needs to be careful here with the terms "negative vacuum energy" and "negative inertial mass."  Lower vacuum energy between the Casimir plates, by restricting the wavelengths of photons and reducing the vacuum energy does not necessarily imply a negative vacuum energy compared to the vacuum energy outside the plates. It is a lower energy density state compared to the outside environment but does not imply negative energy and mass, the distinction is important and here the answer to the author's last question would be no. Negative mass also has not been observed in Nature so this is a hypothetical concept. Nevertheless the paper proposes an experiment to measure the ratio of the gravitational force to the Casimir force. Note that we are not talking about anti-matter here (which is also predicted to fall with gravity just like normal matter). Here's what Schiller also has to say on negative mass in Motion Mountain Vol 1, p98:

 

"Indeed, a negative (inertial) mass would mean that such a body would move in the opposite direction of any applied force or acceleration. Such a body could not be kept in a box; it would break through any wall trying to stop it. Strangely enough, negative mass bodies would still fall downwards in the field of a large positive mass (though more slowly than an equivalent positive mass). Are you able to confirm this? However, a small positive mass object would float away from a large negative-mass body, as you can easily deduce by comparing the various accelerations involved. A positive and a negative mass of the same value would stay at constant distance and spontaneously accelerate away along the line connecting the two masses. Note that both energy and momentum are conserved in all these situations. Negative-mass bodies have never been observed. Antimatter, which will be discussed later, also has positive mass."

Gedanken Experiment three doesn't look promising. GE 4 shows that "Vacuum energy couples to gravity the same way any other form of energy is expected to couple to gravity.", all forms of energy (mass) couple to gravity as shown further in GE 5. GE 7 concludes that "our assumption that vacuum energy does not contribute to active gravitational mass is not true."

In the last GE 8, the paper looks at energy considerations of a hypothetical gravity shield and asks "Would a box that shields against vacuum fluctuations be fundamentally impossible?"

The paper has been useful in outlining various concepts related to the quantum vacuum, gravity and mass. It is clear that more experiments are needed to answer some of the questions. It would be useful for eg to be able to modify the vacuum energy without having to resort to Casimir plates to carry out experiments in this difficult field and to be able to carry out measurements with other geometries other then parallel plates and spheres to verify the various models of Casimir forces in these conditions. Is Quantum Vacuum Engineering a viable field in the future for eg? In the next part we'll have a deeper look at how the quantum vacuum might contribute to gravity.

CI.

Update: Read this post from Sean Caroll, it has an interesting discussion in the comments section on the Higgs particle, inertia and mass.

Is Gravity Control Propulsion viable? Part 1

In 2013 the answer is no. It seems that our reliance on chemical rocketry to get hardware into orbit will be with us for a long time to come. Private space companies are making Low Earth Orbit more accessible and cheaper however the fundamental high cost of launching hardware into orbit (between $20000/Kg to $50000/Kg depending on the launch platform) with its limitations for deep space exploration and restrictions to small payloads will still be there. Getting hardware out of Earth's gravity well only 150 Km above the surface requires vehicles with high thrust (rockets) which can expel large amounts of energy in a short period of time to overcome Earth's relentless gravitational pull. Rockets provide enough escape speed (11.2 Km/s) to reach a stable orbit. The alternatives outlined in a previous post ie the space elevator, external nuclear pulse propulsion and the Skylon Project all have some shortcomings. As usual funding is a big problem for research and whether they one day come to realisation seems to depend on economics,  politicians or the profit potential for private investors.

Can we one day replace rockets with an alternative (less expensive) propulsion method? (Photo: NASA)

 

Been looking at other alternatives such as Gravity Control Propulsion. If the weight problem can be reduced or eliminated altogether then this would change things. This would be a game changer for space exploration but is the concept viable or simply fantasy? Physics at the moment tells us that there is no means to shield an object from gravity or even control gravity for propulsion purposes. In a scene in the latest StarTrek movie, the Enterprise is built on the ground in a shipyard. This solves many problems with cost and practicalities of building the starship instead of assembling it together in space, however one begs the question: when the starship is finished, how do they get this big chunk of hardware into orbit? In the StarTrek universe, have they found a means to circumvent the effects of gravity? In the movie one doesn't see the crew floating around on the bridge of the Enterprise when galloping the galaxy as well, have they developed a means to create artificial gravity deck plating? Recreating Earth's gravity environment in the Starship is important, it solves many health issues for the astronauts who would otherwise be exposed to a zero-gee environment for long periods, not to mention doing basic tasks easier (space radiation exposure is another problem I won't discuss here). 

 

Can a Starship be built and launched from the ground? (Photo: StarTrek)

Mastery of Gravity Control Propulsion implies a deep understanding of the physics of gravity and the origin of weight on mass. So where are we up to? We have General Relativity, all experiments agree with it so far. Problem is GR explains very well how mass moves in spacetime but not the why. It is not a quantum theory of gravity and currently there are no such proven models. More specifically it does not explain for eg the dynamics of the quantum vacuum near mass and how mass interacts with the dynamic quantum vacuum. Why does mass affect spacetime? These are some of the questions that need to be answered. Closely related, what is the origin of inertia? Is Mach's principle a local or universal effect?

 

Let's have a look at several papers that touch on these topics starting first with Marc Millis on  Assessing Hypothetical Gravity Control Propulsion. The paper refers to hypothetical gravity propulsion as a propellantless vehicle which can manipulate gravity, inertia or spacetime. The primary goal is to eliminate the need for propellant to get the vehicle into orbit. A space drive is defined as "an idealised form of propulsion where the fundamental properties of matter and spacetime are used to create propulsion forces anywhere in space without having to carry and expel a reaction mass". The space drive would convert potential energy into kinetic energy for this purpose. The paper also compares the energy efficiencies of the hypothetical space drive compared to the conventional rocket equation, these are very preliminary calculations. It is noted that rockets can only levitate (hovering with no change in altitude) an object for a short period of time until their propellant runs out. The ability of a vehicle to hover indefinitely would be a big advantage. So Marc has outlined what is meant by hypothetical gravity propulsion. The elimination of the need for propellant is the big advantage here.

So in 2013 are there any loose ends in General Relativity? According to Schiller's Strand Model of Physics which looks promising, one of his many predictions include "No deviations from special or general relativity appear for any measurable energy scale. No doubly or deformed special relativity arises in nature." Let's have a look at the paper from Orfeu Bertolami et al. on General Theory of Relativity: Will it survive the next decade? Yes. However several interesting comments are made. It is mentioned on p2 "Even at the classical level, and assuming the Equivalence Principle, Einstein’s theory does not provide the most general way to establish the spacetime metric." This is an important point which we'll come back to later. Note the Equivalence Principle ie freely falling bodies have the same acceleration in the same gravitational field independent on their compositions (second important point we'll come back to later) which means a feather and a cannon ball for eg dropped in a vacuum will touch the ground at the same time, watch this video. It is also mentioned that GR does not provide an understanding how gravity should be described at the quantum level. Many researchers are concentrating their efforts on a unified theory of Physics that would include the electromagnetic, weak and strong interactions with gravity. Currently Quantum Field Theory fails in strongly curved spacetime metrics (ie where GR is applicable) while GR only works when Planck's constant (Quantum Field Theory) is ignored. The two models when considered separately work very well though at describing Nature on the large and small scales however concepts such as warp drives and wormholes for eg which are allowed in GR are denied by QFT (more specifically the physics of the quantum vacuum see Vol 5 p116 of Motion Mountain). The paper goes on to describe the many solar system wide experiments that have been carried out that confirm GR to great detail.

Section 3.4 deals with the interesting concept of gravity shielding. An earlier paper by Majorana in 1920 suggested the introduction of a screening or extinction coefficient, \(h\) to measure the shielding of a material of density \(\rho\text{(r)}\) of the gravitational force between two masses which can be modelled as follows
 

$$F'=\frac{G\, m_{1}\, m_{2}}{r^{2}}exp\left[-h\int\rho\text{(r) dr}\right].$$

There is currently no avenue in physics to derive \(h\), the gravitational shielding constant, without violating the equivalence principle and there are no materials known that would affect this coefficient. According to the paper the modern laboratory constraint is currently set at  \(h\leq4.3\times10^{-15}m^{2}kg^{-1}\). So is gravitational shielding a dead concept? It appears that no materials regardless of their density or composition will do the job, we'll get back to this topic in Part 2. The rest of the paper looks at other cosmological studies to confirm GR, alternate models of gravity and talks about dark matter (made of conventional matter and black holes surrounding galaxies) and dark energy (vacuum energy).

 

In the next post I'll look at a few more interesting papers and further thoughts on Gravity Control Propulsion.

CI.

Nuts and Bolts

Hi everyone,

There's a very interesting ABC radio interview available online titled The future of Interstellar Travel worth a listen. Various issues are talked about including getting Helium-3 for future fusion reactors and the challenges involved for interstellar travel.

Interesting post on Centauri Dreams regarding Icarus Interstellar. Impressive list of projects they got going. Myself I think it is 100 years too early to start designing starships in 2013 especially since we currently don't have a working industry grade fusion power plant let alone a flight ready version to put on a starship. However the two projects they have listed ie Project Bifrost and X-Physics Propulsion & Power Project  are worth pursuing now. I stopped looking at warp drives and wormholes last year. Although the field equations in General Relativity do have solutions that allow these spacetime curvatures, GR doesn't take into account the properties of the quantum vacuum and isn't a unified model of Physics. The solutions are not realistic in nature and are purely interesting exercises in GR. As for extracting energy out of the quantum vacuum, there are currently no mechanisms to do this.

Another interesting SBS article: Space: the mining frontier. Seems like space mining is making more headlines these days. Interesting issues raised include who owns the Moon, Mars, Asteroids etc and their minerals? Free for all who can afford to develop the space mining infrastructure? No doubt the UN needs to start developing some kind of legal framework as the private space sector is catching on. I wouldn't hold your breath though, one should remember that the International Space Station cost $150bn to build and this is in low earth orbit.

CI. 

Titan descent movie

Saw this on APOD, what a great movie!

Book Review: Deep Space Propulsion

Recently finished reading Deep Space Propulsion - A Roadmap to Interstellar Flight by Kelvin F. Long, 2012. A book review has already been written here so won't duplicate however will comment on a few points made in this excellent introductory text.  A rundown of current known propulsion schemes is given outlining their pros and cons for interstellar flight ranging from electric and nuclear based propulsion, solar sails, beamed power, nuclear fusion and external nuclear pulse propulsion, antimatter etc. Projects Daedalus and Icarus are also mentioned.

 

 

Some interesting points I picked up while reading the book:

Seven key motivations for interstellar travel are given:

 

Continued survival ie the ability of humans to survive on another planet would greatly increase our prospects for long term survival and also makes the point that while some suggest we should be focusing inwards on our problems on Earth and remain home  the author's reply to this is "These attitudes will only lead to one result: stagnation and regression of the human race" which I agree with. If one looks back in history some of those nations that went to the trouble of building ships to explore new worlds are fairly well off financially and increased our knowledge base (scientifically and culturally).

Balance of resources given the rate of population growth there will be a breaking point as far as the need for resources to sustain the future population unless more resources outside earth are found. When a nation runs out of critical resources they either buy more, take it by force or perish.

Economic opportunities ie plenty of money to be made by mining asteroids etc. Very rare minerals/metals required for certain key technologies on Earth may be in abundance in other places in our solar system.

Quest for knowledge ie Are we alone for eg? How many Earth like planets are there within 50 ly from Earth for eg? Astronomy / AstroPhysics / Universe etc

Spreading of life

Freedom factor

Starstuff driver ie the atoms in our bodies were made in stars and the author hints that we have a longing to return to what created us.

 

Another interesting point made by the author: "Any material that is launched into Earth orbit will cost typically around $50000 / Kg." This needs to be reduced substantially for any large scale space exploration. The current alternatives to chemical rockets are:

 

 The space elevator: feasible however the technology to mass fabricate the Earth to Orbit cable using high strength carbon nano-tubes is not in place (steel wire cable won't do the job).

 

 Project Orion: (external nuclear pulse propulsion): the energy release from nuclear reactions is of the order a million times greater than that from a typical chemical reaction making this vehicle a feasible alternative to chemical rockets. However detonating nuclear bombs in earth's atmosphere to get the vehicle off the ground leaving a radioactive trail behind isn't a good idea.

 

 Skylon Project: although this proposed spaceplane still would use a liquid oxygen/hydrogen rocket to reach orbit it is worth a mention because this is a step in the right direction as far as reducing the cost of getting hardware into orbit is concerned however not the breakthrough solution I am after (ie an elegant non-chemical propulsion solution).

All in all a good introductory text worth a read, has nice colour pages of the various designs talked about in the book.

CI.

Dampier, WA with Red Dog.