sign in sign up
<<
Home , Boris Podolsky, Cosmic time, Exotic matter, Nathan Rosen, Pair production, Planck length

AIAA 95-2599

Report on the NASAIJPL Workshop on Advanced /Relativity Theory Propulsion

Gary L. Bennett, Metaspace Enterprises, Boise ID Robert L. Forward, Forward Unlimited, Malibu CA Robert H. Frisbee, Jet Propulsion Laboratory, Pasadena CA

31st AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit July 10-12, 1995 I San Diego, CA

For permission to copy or republish, contact the American Institute of Aeronautics and Astronautics 370 L'Enfant Promenade, S.W., Washington, D.C. 20024 Report on the NASA/JPL Workshop on Advanced Quantum/Relativity Theory Propulsion

1 Gary L. Bennett , Robert L. Forward 2 , and Robert H. Frisbee 3

1 Metaspace Enterprises; 7517 West Devonwood Drive; Boise ID 83703 2 Forward Unlimited; P.O. Box 2783; Malibu CA 90265 3 Jet Propulsion Laboratory; 4800 Oak Grove Drive; Pasadena CA 91109

ABSTRACT In an effort to address the FTL question the Office In May 1994, NASA and JPL sponsored a of Advanced Concepts and Technology (OACT) of workshop on advanced quantum/relativity theory NASA Headquarters and the Jet Propulsion propulsion concepts to establish and use new Laboratory (JPL) sponsored a workshop on frames of reference tor thinking about the advanced quantum/relativity theory propulsion at taster-than-light (FTL) question. Using the horizon JPL on 16-17 May 1994. Appendix 1 lists the mission methodology, the participants reviewed attendees at the workshop. : a hypothetical where the (c) is a lower bound; and the physics The first premise of the workshop was that of additional space dimensions. While the theoretical perspectives exist in advanced participants did not identity any obvious method to quantum and relativity theory that could achieve FTL travel they did identity enough open conceivably perm~ FTL travel or information issues in physics that FTL travel could not be ruled transfer. A second premise was that investigation out. Moreover, several experiments were of these perspectives from other frames of identified that could elucidate some possible reference could possibly provide fresh insights. FTL-related phenomena. The purpose of the workshop was to establish and 1. INTRODUCTION use new frames of reference for thinking about the FTL problem. The objectives of the workshop Contained within the paradigm of the human race were to as a species genetically predisposed toward exploration is the view that eventually our species • identify theoretically permitted "scientific will expand beyond the Solar System. In order to windows" that could permit FTL travel or realize interstellar civilizations in which the vast information transfer; distances between star systems must be spanned in times much less than the lifetimes of the crew • identify manifestations of the underlying physics; and the people remaining on the planets, there must be a revolution in transportation technology. • identity avenues of scientific and technological However, the general opinion within the physics research to explore and validate the possibilities; community has been that the special theory of relativity precludes such short transit times • define (where possible) enabling technology because they would involve taster-than-light (FTL) concepts tor FTL travel; and travel. 1 • introduce the horizon mission methodology as Copyright © 1995 by the American Institute of a tool tor thinking in other frames of reference. Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The critical reader should be aware that even The U.S. Government has a royalty-free license to though the special theory of relativity seems to exercise all rights under the copyright claimed herein for insurmountable obstacles to FTL travel or Governmental Purpcses. All other rights are reserved communication (infinite , by the copyright owner. paradoxes, etc.) there are at least thirteen '1hings" 1 American Institute of Aeronautics and Astronautics that move faster than light 2.3.4 highly productive" 8

• Scissor-blade intersection As shown in Figure 1, the HMM is based on • Searchlight beam image creating a future frame of reference for evaluating • Eclipse shadow a topic. In the case of the advanced • Perfectly rigid rod quantum/relativity theory propulsion workshop the • Galloping waves invited participants were asked to imagine that • expansion they were in the future where FTL travel or • velocity information transfer had been achieved and then • Marquee light to "look backward" to see how it was • Comet tail accomplished. In essence, are there theoretically • Riptide permitted reinterpretations of physics or "scientific • Oscilloscope trace windows" that could permit FTL travel? • Expansion of • "Practical speed" of a nearly-as-fast-as-light These scientific windows could be expressed in spaceship terms of new axioms or principles such as

More recently there have been a series of • Cosmic (spacetime) tunnels exist and can be experiments showing either that light quanta can used. tunnel through barriers or that microwaves can travel through the '1orbidden regions" of a wave • There exists an "entire physics" in which the guide at speeds greater than the speed of light, speed of light (c) is a /ower bound. aHhough it is not certain that this technique allows signals (in Einstein's sense of transmitting useful • Other, perhaps "higher" dimensions exist that information) to be sent.5·6 Even Einstein wrote can interact with the spacetime that we know. that " ... our result shows that, according to the general theory of relativity, the law of the For each of these scientific windows background constancy of the velocity of light in vacuo, which information was provided by specialists in the field constitutes one of the two fundamental and then the participants discussed the particular assumptions in the special theory of relativity and scientific window using the horizon mission to which we have already frequently referred, methodology to "look backward" to see how that cannot claim any unlimited validity. A curvature of particular scientific window could have led to FTL rays of light can only take place when the velocity travel or communication. of propagation of light varies with posftion". 7 The following sections discuss these three scientific windows as they were covered in the 1.1 Horizon Mission Methodology workshop. For each scientHic window, the participants were asked to consider the following Recognizing that solving a problem in advanced questions: missions or technology by extrapolating from the conventional technology can create obstacles to • What properties does it have? breakthrough solutions, John L. Anderson of • What is the evidence for/manifestation of? NASA Headquarters developed the horizon • What are the alternative physics interpretations? mission methodology (HMM). As Anderson has • What are the implications and manifestations of written, "The Horizon Mission Methodology is a these aHernative interpretations? highly structured process for both creating and • What avenues and approaches can be taken for thinking within a new frame of reference. It is not validation? a process of forecasting, scenario-generation or • What are the potential technological concepts? brainstorming. It first poses a truly challenging, relevant space future that is beyond our reach. 1.2 ETL Horizon Missions The process then places people mentally in that 'fixed' future, which is treated as an accomplished Robert H. Frisbee, who was the JPL host and fact. Next it stimulates the imagination to generate organizer of the workshop, followed the HMM breakthrough-based aHernatives for accomplishing discussion with an overview of the three principal that future and to reconstruct pathways that could scientific windows. He noted that any interstellar have led to it. This process requires signHicant mission, whether conventional or FTL, will require mental discipline to 'stay in character,' but it is 2 American Institute of Aeronautics and Astronautics major investments by human society. For not even survive the trip to the horizon. Even example, an interstellar fusion rocket will require variations on the classic static present on the order of 37 TW of power while a laser problems. A Schwarzschild (spherically lightsail will require 1500 TW. In contrast, an symmetric) would pinch off into infinite Apollo Saturn V at liftoff produced 0.04 TW. tidal before anything could get through. (Current power production by human technology The horizon of a black hole is a one-way on Earth is about 1 TW or an annual membrane, i.e., once inside nothing can get back production of about 1o 4 TWh.) out. For Kerr (rotating) black holes and Reissner-Nordstrom (charged) tunnels, Morris For wormholes and warp drives, Frisbee noted observed that while they are mathematically exact that the traditional fiction assumption is for they are unrealistic with ring-shaped singularities on-board ''Warp" engines but that the newer and that the interim tunnels are unstable. approach is to use wormholes (either artnicial or natural). Two recent novels have Morris listed the following desired properties for been based on the wormhole theory developed by traversable wormholes (see also Ret. 16 and 17): Michael Morris and Kip s. Thorne.9,10 R. L. • Wormholes are spherically symmetric, static Forward had earlier reviewed various concepts of (time independent) ; space warps. 11 • Wormholes are tunnels that connect For physics where "c" is a lower bound, Frisbee asymptotically flat regions; included , imaginary , advanced solutions to the Maxwell and/or • They everywhere satisfy the Einstein field Schrodinger equations, and quantum equations; connectedness. One of us (GLB) has used this approach with tunnels to higher dimensions in a • They must have no horizons; science fictional view of FTL.12 • Tidal forces must be everywhere bearably small; For additional space dimensions, Frisbee noted the possible relevance of , extra • Travel time must be convenient; dimensions (e.g., theory) and quantized spacetime. • The tunnels must be perturbatively stable;

Additional written material on possible FTL • The assembly must be feasible; and physical phenomena was provided to the participants in advance of the workshop. This • Any construction material must be possible to material has since been published for a more get. general readership. 13 Summaries of the workshop have been separately published to a Morris noted that the first tour properties contain the key features ("basic wormhole criteria") while wider audience by Cramer and Forward.13-15 the fifth and sixth properties are conveniences tor human comfort ("usability criteria"). (The first 2. WORMHOLE PHYSICS property permits finding simple solutions to Einstein's equations.) The seventh and eighth The participants began by reviewing wormhole properties are dynamical questions which are not theory, wormhole engineering and then easily addressed. Figure 2 is a sketch of a considering wormholes within the context of FTL traversable wormhole tunnel without horizons HMM. connecting Earth with the Sirius star system. 2.1 Traversable Wormholes and Tlmeholes Morris outlined the wormhole solutions to the that might allow humans to Michael S. Morris provided an overview of traverse the wormhole. To overcome the horizon wormhole theory. He began by showing that black problem with black holes the wormhole must not holes are not traversable. He showed there can have a horizon in its throat. Coupling this be enormous tidal forces even at the horizon of a constraint with the Einstein field equations leads to black hole so that unless the black hole is very a form of "exotic " to generate the 5 large (> 10 solar ) a human being could wormhole's curvature. This material must have a 3 American Institute of Aeronautics and Astronautics radial tension approaching the at the Riemann tensor to have the appearance of a delta center of a massive star: function.

42 2 2 Tension- 10 dynes/cm [10 meters/b ] To minimize the use of exotic matter Visser 0 considered a case in which the wormhole throat where b is the throat radius. 0 has one face that is flat. On such a flat face the radius of curvature would be infinite. A traveler Morris observed that for humans to be able to intercepting the flat face would feel no forces (tidal survive a trip through the wormhole, even in a or otherwise) and would encounter no exotic suitable spaceship, this exotic material must not matter. The traveler would simply be shunted into couple strongly to ordinary matter. the other universe. In effect, while exotic stress energy may be necessary for wormhole Another serious problem is that the tension of this construction, it may be hidden from the traveler. exotic material must exceed the material's density of mass-energy which violates the weak energy Visser reviewed the concept of exotic matter, condition (the condition in which it is forbidden to noting as Morris had that there is have observers seeing a densny ("exotic matter'') at the throat of the density).16- 18 While Morris commented that the wormhole. He pointed out that exotic matter is not violation of the weak energy condition was deeply the same as . For example, where a troublesome it is not possible to rule out such positive energy focuses light, negative energy exotic material by any present-day knowledge of defocuses light and violates the weak energy physics. He listed other examples of violations of condnion. the weak energy condftion in (1) in curved spacetime; (2) the Unruh As another example of mtmm1z1ng the use of near the horizon of a black hole; (3) the squeezed exotic matter Visser considered the possibility of state of the vacuum; and (4) the . the throat of a wormhole being a cube with rounded edges and rounded comers as illustrated An additional potentially serious problem with in Figure 4. This gives six flat faces with infinite wormholes is that while one static wormhole curvature, twelve edges that are quarter cylinders tunnel in the universe seems to cause no dHficulty and eight corners which are octants. In a cubical with causality violations, two wormholes can cause wormhole all the stress energy would be violations of causality. concentrated in the twelve struts which from Einstein's equations would have a mass per unn 2.2 Wormhole Engineering (J.L) of -1.52 x 1043 J/rn

Matt Visser summarized our knowledge of Visser estimated that a 1-m cube would require a wormholes and then discussed how wormholes field with a total negative mass equal in magnitude might be constructed. References 19-27 describe to that of Jupiter. some of Visser's work on wormholes. Visser noted that one approach to constructing a The struts would have to be buill out of negative wormhole is to surgically modify Minkowski space, tension classical strings which certainly poses a i.e., "cutting similar holes in two regions of challenge to current technology! However, as space-time and then sewing the edges together''. Cramer has observed, "The Visser Cube of wormhole mouths is reminiscent of the familiar SF Referring to Figure 3, Visser suggested taking two notion of a ".14 copies of Minkowski space (with time suppressed) and excising two identical compact regions n1 and 2.3 HMM Discussion of the Physics of ~· Next one identifies the two boundaries an1 = Wormholes an . Visser observed that the surface ()Q x (time) 2 The workshop participants discussed the physics is now a timelike hypersurtace, that is, it is the of wormholes in the context of looking backward throat of a wormhole. He pointed out that this from the future. It was generally agreed that the spacetime is geodesically complete and that it has desirable properties of wormholes should include two asymptotically flat regions. By inspection he those elucidated above by Morris and Thorne. said the Riemann tensor is identically zero except The participants noted that creating wormholes out at the throat (iJQ) where we would expect the of the of the vacuum would require 4 American Institute of Aeronautics and Astronautics mass-energies on the order of Jupiter applied to such backward-causal events actually occur in length scales on the order of the Planck-Wheeler , COP requires that they appear length backward-causal in all reference frames ... COP is not part of relativity but is an extra assumption Lp.w = (Ghf2~tc3 ) 112 = 1.6 x 1o· 33 em concerning the presumed nature of causal relations in space-time·.2 where G = 6.673 x 10·8 dyne-cm2ig2 is Newton's It is also worth noting that this is not the first time 27 gravitation constant; h/27t = 1.055 x 1o· erg-sec that the issue of causality has arisen. Henry is Planck's quantum mechanical constant divided Margenau, in discussing the philosophical legacy by 27t, and c = 2.998 x 1010 em/sec is the speed of of the quantum theory has stated that "causality is light. a methodological, nonempirical regulative maxim which belongs to the metaphysical domain" Even the Visser cubes would require negative [emphasis in origina1].28 Margenau went on to mass strings with linear mass densities of the point out that ". . . if we insist on the older order of 28 Earth-masses per meter. While these definition of states even with respect to subatomic physical requirements may be possible for a systems, it turns out that there is no law known to sufficiently advanced civilization they appear to be science by which such states are propagated in well beyond current extrapolations of human time. Hence, those who feel that an , for capabilities. example, is still a and as such must be described by the good old Newtonian concept of The group considered the issue of moving one state (position and velocity) are forced to admit wormhole mouth relative to its companion which that causality has failed".28 As a consequence, has the effect of creating a time machine similar to Margenau specifically called attention to the the "twin paradox" that occurs in special relativny philosophical consequence that our classical (where one twin travels at a high speed relative to concept of causality had to be abandoned in the other twin and so ages less). While there quantum theory in favor of a new relation termed appears to be no physical reason to prohibit time 28 travel or even the causality violations associated stochastic or statistical causality. In this way with FTL wormhole travel and signals, they are physicists were allowed to get on with the certainly not observed in nature. application of quantum theory which has been shown to be one of the most successful theories in As an aside, it is worth noting that Hawking physics. By analogy, one is entitled to wonder if a believes that nature abhors time machines and he new definition of causamy is in order for has gone so far as to propose a chronology FTL -related phenomena. protection conjecture "which says that the laws of physics do not allow time machines" [emphasis in Kip S. Thorne and his colleagues have investigated closed tirnelike curves (CTCs) (e.g., original].17 As Thorne has explained it: time machines) finding "that CTC's rnay not be as "Whenever one tries to make a time machine, and nasty as people have assumed" bee au se "they do no matter what kind of device one uses in one's not affect Gauss's theorem and thus do not affect attempt (a wormhole, a spinning cylinder, a the derivation of global conservation laws from '', or whatever), just before one's differential ones. The standard conservation laws device becomes a time machine, a beam of remain valid globally, and in asymptotically flat, vacuum fluctuations wHI circulate through the wormhole spacetimes they retain a natural, device and destroy if' [emphasis in original]. 17 quasilocal interpretation".29 Thorne has observed that "It may turn out that on macroscopic Earlier, Herbert had written that ''To plug these lengthscales chronology is not always protected, leaks and clearly establish all notions of and even if chronology is protected superluminal transport as heretical, physicists macroscopically. quantum may well give added an extra assumption to Einsteinian finite probability amplitudes tor microscopic relativity, an assumption we call the causal 30 ordering postulate, or COP ... A curious aspect of spacetime histories with CTCs". Whether or not COP is that it does not require that a cause always CTCs exist, such theoretical explorations into the precede its effect. COP actually permits backward frontiers of quantum and relativity theory will causality, in which an event in the future clearly add to our understanding of the universe. influences what happens in the past. However if 5 American Institute of Aeronaulics and Astronautics Two of the workshop participants had earlier objects (MACHO's) of positive mass. While the considered causality as one of several boundary analysis is discussed in terms of wormholes, the conditions on assumed FTL travel.31 observational test proposed is more generally a search tor compact negative mass objects of any Having considered the construction of wormholes, origin. We recommend that MACHO search data the group then considered the possible occurrence be analyzed tor GNACHO's." of natural wormholes, perhaps even wormholes left over from the creation of the As a result of this work, the astronomers searching universe. If one of a pair of wormhole mouths tor evidence of MACHOs will also examine their accretes "normal" pos~ive mass then the other data for the specific double-peaked light intensity mouth will in effect have a negative mass. If profile that is predicted to be caused by the wormholes exist they could signal their presence gravitational lensing of a negative mass. One through the appearance and disappearance of double peak has been found by the Optical mass or through the repulsive grav~ field of the Gravitational Lensing Experiment (OGLE) group negative energy density exotic matter. Related to and confirmed by the MACHO team but the shape, such primordial wormholes there has been which was different from that predicted tor theoretical speculation that cosmic strings may GNACHOs, suggested gravitational lensing that have been created iri the big bang; could then was caused by a binary system. 37 cosmic strings of negative mass have been created that might hold open the mouth of a Morris, in his presentation, and Cramer noted that wormhole? the vacuum is squeezed near a black hole and therefore has negative energy density (and mass). Several workshop participants suggested an This effect does not integrate out to a significant astronomical search tor such negative mass negative mass near a stellar-mass black hole wormholes. It is known that dark body objects because only wavelengths greater than about 5 termed massive compact halo objects (MACHOs) km are affected. Near Planck-mass quantum will cause a lensing effect if they pass between black holes (-10 llg), all wavelengths greater than Earth and a distant star. In effect the starlight is the Planck-Wheeler length (-10·35 m) would be bent causing an increase of the perceived squeezed. Cramer talked about the possibility of brightness of the star. 32-35 using this negative energy to stabilize a Morris-Thorne wormhole. The participants A negative mass object would cause a different wondered if there is any way to experimentally brightness versus time profile. The gravitational verity the existence of negative energy in a region field of the negative mass would the starlight of squeezed vacuum. One question raised was into a paraboloid shape such that an observer on whether the integral of the negative energy in the Earth would first see an increase in brightness volume of squeezed vacuum around a quantum followed by a sharp cutoff followed by another black hole might equal the Planck mass which peak that gradually tapers off. The cutoff results might explain why the high mass-energy density of from the shadow zone or demagnification zone the vacuum fluctuation "quantum foam" is not within the paraboloid. These workshop observed. participants subsequently published a paper in with this abstract:36 Following the workshop, a letter by of the University of Wales in Cardiff "Once quantum mechanical effects are included, proposed a mechanism tor expanding and the hypotheses underlying the positive mass contracting spacetime near a spaceship to achieve theorem of classical tail. As an FTL travel. 38·39 His abstract states:38 example of the peculiarnies attendant upon this observation, a wormhole mouth embedded in a "It is shown how, within the framework of general region of high mass dens~ might accrete mass, relativ~. and without the introduction of giving the other mouth a net negative mass of womholes, it is possible to modify a spacetime in a unusual gravitational properties. "The lensing of way that allows a spaceship to travel with an such a gravitationally negative anomalous arbitrarily large speed. By a purely local compact halo object (GNACHO) will enhance expansion of spacetime behind the spaceship and background stars with a time profile that is an opposite contraction in front of it, motion faster and qualitatively different from that than light as seen by observers outside the recently observed for massive compact halo disturbed region is possible. The resutting 6 American Institute of Aeronautics and Astronautics distortion is reminiscent of the '· of E = m c2 = f11.oC2_ science fiction. However. just as happens with wormholes, exotic matter will be needed in order (1 . 82 )112 to generate a distortion of spacetime like the one described here." or in terms of the square of the energy which is often what is measured This, in effect, reaffirms the view of the workshop participants that a search should be made for the effects of negative matter ("exotic matter") in astronomical lensing data where p is the of the particle. For a 3. PHYSICS WHERE THE VELOCITY OF LIGHT which, by definttion, has a velocity v > c. IS A LOWER BOUNP the following properties apply in order to have measurable (real) numbers for the energy and R. H. Frisbee set the stage for this portion of the momentum workshop which was concerned with a is imaginary (m = i lm where i = -J-1) hypothetical physics in which the veloctty of light • m0 0 0 1, (c) would be the lower bound. As noted earlier • E2 = p2 c2. mo2 c4 this area includes tachyons (hypothetical FTL ). imaginary mass neutrinos, advanced • B > 1 (v> c always); note that B = pc/E solutions to the Maxwell and/or Schrodinger • p = E Blc as usual and it cannot go to zero • When lp I = lm c I (the minimum value) equations, and quantum connectedness. 0 B ···> oo 3.1 General Overview of Physics Where the E···> 0 Velocity of Light is a Lower Bound • The lowest values of the mass-energy is zero (not i lm I c2 ), and there B ="" J. G. Cramer summarized the theory of tachyons 0 which are hypothetical FTL particles first postulated by 0. M. Bilaniuk. V. K. Deshpande, From the foregoing, Cramer listed the following 40 42 properties for "bradyons" ("normal", sublight and E. C. G. Sudarshan · From the special matter) and tachyons: theory of relativHy we know that the following relationship holds between the mass m of a Property Bradyons Tachyons particle and tts rest mass m0 Minimum m = ITlo--- speed 0 c Maximum (1 • 82 )112 speed c 00 Minimum where B = vic and m is the mass measured in the 0 mass-energy m c2 0 proper ("rest") frame of the particle. This 0 well-known relationship clearly illustrates the Minimum problem in pushing any object to and beyond the momentum 0 lm0 c I speed of light. Similarly. a time interval IJ.t Mass-energy between two events measured in a frame moving momentum wtth velocity ±v relative to a frame in which the relation E 2 = p2c2 + m 2c4; p2 = (Bc)2 + lmic4 corresponding time interval M' is proper (i.e., the 0 two events occur at one place) is given by Cramer called attention to the fact that (at the time of the workshop) some of the published values of M = --""--- the electron mass-squared (mv 2) were negative such that the mass of the electron The total energy (E) for a fintte mass particle is neutrino might be about 12ieV (1.8 ix 10·36 kg= given by the sum of the kinetic energy of the 2 ix 10"6 electron mass) meaning that the electron particle and tts rest-frame energy (EoJ: neutrino could be a tachyon. Forward summarized the measurements on the 7 American Institute of Aeronautics and Astronautics neutrino mass reporting that the latest (at the time provide a finite recoil momentum at no energy cost of the workshop) implied a mass of about 0.4 i which would make them ideal "rocket fuel". MeVtc2 (7 ix 10-31 kg= 0.8 i electron mass). Cramer listed several problems that need to be It was noted that a small number of neutrinos had addressed: been detected in various detectors just before the visual observation of (SN) 1987A. The • Are neutrinos tachyons? participants wondered nthere was any correlation • Are there any nuclear reactions that would between the arrival time and the energy of the produce such a tachyon drive? neutrinos. (A faster, lower-energy tachyon would • How would one go about solving the engineering arrive sooner than a nearer "c", higher-energy problems? tachyon.) 3.2 The Casimir Effect Crarner and Forward suggested (and the attendees heartily agreed) that there was a need Cramer called the workshop's attention to the to rneasure accurately the mass of the electron Casimir effect in which closely spaced, grounded neutrino. (Since the workshop, there have been capacitor plates allow only the electromagnetic reports, but no peer-reviewed published scientffic modes that '1it into the gap" (only with evidence, that the masses of both the muon and wavelengths less than twice the separation electron neutrinos lie somewhere between 0.5 eV distance of the plates are allowed). Consequently the free energy of the vacuum between the plates and 5 ev.43 However, the last published scientific is lowered and the plates experience a paper known to the authors showed imaginary compressive force pushing them together. mass. Since the neutrino was originally thought to be massless and to travel at the speed of light According to quantum electrodynamic (OED) such measurements, if confirmed, would require a theory, photons can change into a variety of fundamental rethinking of neutrinos. Neutrinos short-lived or "virtual" particles (such as virtual with mass might also account for some of the electron and virtual pairs) as they travel. missing mass of the universe.) Based on sorne theoretical work done by K. Scharnhorst some of the modes Cramer noted the following rnay be eliminated for a traveling between the plates which should have the effect of • Unlike normal matter and light (photons), in increasing the speed of light. For photons theory, tachyons can escape from a black hole traveling perpendicularly between plates because they travel faster than the speed of light. separated by 1 J.Lrn, the speed of light is increased Theoretically a tachyon moves in the opposite 36 manner to normal matter--as energy is removed by about one part in 1o over its value in the the tachyon speeds up until at zero energy a vacuum. 4547 tachyon would move at infinite speed. Thus, as the gravity field of a black hole removes energy 3.3 The Formalism of Qyantum Mechanics from a tachyon the tachyon would speed up to infinite speeds. According to theory, information In view of the relevance of to (negative entropy) is trapped in a black hole. questions of causality (which arise in studying FTL "" would remove mass-energy phenomena) and fts possible allowance of FTL, from a black hole but not information. However, a Cramer provided an overview of the formalism of "stripped" tachyon could remove information at quantum mechanics. As infinite speed. (For the interested reader, Jayant has observed: ''The quantum is the 'crack' in the V. Narlikar, among others, has studied the armor that covers the secret of existence. And I interaction of tachyons with gravity .44) think we have to find out what lies under that armor to get to the bottom of things. That's the • If neutrinos have a mass of 12 i eV then it biggest mystery". 48 should in principle be possible to construct a nuclear reaction (for example, one in which the One of the puzzling aspects to quantum products are an and an electron mechanics was elucidated by , anti-neutrino) in which tachyons are emitted with , and in 1935, the zero energy (hence infinite speed) but with so-called "EPR" thought experiment in which the momentum of 12 eV/c. The tachyons would three physicists considered the interaction of two 8 American Institute of Aeronautics and Astronautics correlated particles. Applying quantum travel paradoxes inherent in FTL travel. According mechanical rules to the EPR thought experiment to this interpretation the universe is constantly one sees that any measurement of particle 1 branching (in other words, all of the possible immediately influences the state of particle 2 no outcomes of a quantum mechanical calculation matter how far apart they may be. If the distance are real) so that the past a traveler could separating the particles is space-like (non-local) theoretically return to would be in one of these then the influence that tells particle 2 what state to parallel universes and not in the universe he/she be in when a measurement is made on particle 1 left. Hence, there would be no way lor the travel must be traveling at FTL velocities. Attempts to to cause or create paradoxes. 53 explain this by sub-quantum effects (such as "hidden variables") were excluded by the work of 3.4 HMM Discussion of Phvsics Where "c" Is a John S. Bell. Cramer cited two works which Lower Bound experimentally showed that quantum mechanics (and not some hidden variable theory) correctly The workshop participants discussed tachyon predicts the correlation of two particles.49,50 theory, the Casimir effect and quantum theory. It Thus, quantum mechanics has buried wfthin it the was noted that while there had been some idea of instantaneous, i.e., FTL, communication possible evidence for tachyons in measurements between particles no matter how far apart they of cosmic ray showers in the 1970s there are. appeared to be no confirmatory support for the existence of tachyons. (The interested reader is Cramer showed that from a quantum mechanical referred to references 54 to 57 for reports on some perspective the EPR non-locality could not be of the early searches for tachyons. Michael N. used for FTL communication. However, he called Kreisler concluded in 1973 that "... the limns on attention to some work by Steven Weinberg the existence of tachyons have been pushed qutle showing the possibility of small, non-linear effects low. This author, at least, would be very surprised in quantum mechanics which, H present, would Hthey were found".ss) allow an FTL signal to leak through based on theoretical work by . Related to the Casimir effect, one idea suggested during the workshop was surrounding a moving The workshop participants noted that both spaceship wfth a "bubble" of highly quantum mechanics (via the Schrodinger energy-depleted vacuum where the speed of light equation) and classical electrodynamics (via would be greater so the spaceship could travel at Maxwell's equations) allow two solutions: waves FTL velocities. Cramer has written that "This traveling forward in time ("retarded wave" solution) speculation produced the following thought and waves traveling backward in time ("advanced experiment. Suppose that one produces an wave" solution). As Cramer has wrnten, "The energy-depleted region of space using the Casimir advanced-wave solutions of the electromagnetic Effect and then somehow makes the parallel wave equation are usually ignored as unphysical conducting plates disappear. What happens to because they seem to have no counterpart in the 'bare' volume of energy-depleted space left nature".51 If, however, advanced waves could be behind? Does it return to normal space? If so, found they could conceivably provide a way to where does the energy come from to make up for send messages to the past. To overcome the the energy that is missing? Does the volume of apparent paradoxes in the standard Copenhagen energy-depleted space persist as a 'bubble'? If so interpretation of quantum mechanics, Cramer has what shapes does it assume? Does it expand or developed a '1ransactional interpretation" of contract?"15 quantum mechanics in which a quantum event is described by the exchange of advanced and The workshop participants discussed the retarded waves.51 · 52 It is possible that some possibility of determining if an FTL signal could be combination of retarded and advanced (if they transmftting through modulating a beam of exist) waves could be used for FTL neutrinos. To take advantage of the possible low communication. mass (-12 i eV) of the neutrino, it was suggested that the target nuclei (such as doubly charged At this point it is worth observing that if the many helium-3) be accelerated into the neutrinos. worlds interpretation of quantum mechanics first Detection of such neutrinos is not currently proposed by Hugh Everett Ill is valid, then feasible. quantum mechanics offers a way out of the time 9 American Institute of Aeronautics and Astronautics Other obseNations and comments from the • Good, confirmatory, unambiguous participants included the following: measurements of the mass of the three flavors of neutrinos (electron, muon, and neutrinos) • If neutrinos have a non-zero rest mass (of any should be undertaken to clarffy whether or not the kind), then a will affect them neutrino is a tachyon. Are there any other differently from how the lens affects phOtons. (It neutrino rest mass experiments possible other was noted that photons have zero rest mass to than using molecular tritium and decay? 10·20 ev from a reported measurement of the (One idea to overcome questions about the magnetic dipole field structure of Jupiter.) experimental effects of molecular tritium which is usually used in measuring the mass of the • Neutrino oscillations (which is a postulated electron neutrino would be to put tritium or phenomenon that has been proposed as an K-capture in a Penning or other trap, cool explanation of why we don't obse!Ve all the them to millidegrees Kelvin, and then measure the neutrinos predicted to be released from the energy of all particles and photons emitted.) nuclear reactions in the ) require a non-zero rest mass. What do neutrino oscillations mean ff • Good measurements of the velocity of light the square of the neutrino mass is negative? If the perpendicular to the Casimir plates should be has a positive or zero rest mass, made to determine if the speed of light is could a neutrino oscillate from a tachyonic electron increased as predicted. (This may be measurable neutrino to a bradyonic or luxonic tau neutrino (in ff the effect can be turned into a frequency effect "tunneling" through or to the speed-of-light measurement.) Because the mass of a particle is barrier)? related to the energy and speed of light through Einstein's equation m = EJc2, changes in "c" • Are monoenergetic neutrinos produced in should lead to changes in "m"; therefore, K-capture processes? Would this make them Casimir-type experiments could also focus on easier to detect? Could such neutrinos be measuring the mass of particles between the directed by orienting the ? plates. Would the rest mass of a particle between Casimir plates be less than the rest mass in a • Is a +itachyon different from a -itachyon or are vacuum? Since the velocity of light between they just of each other? Casimir plates is anisotropic (greater than "c" normal to the plates but equal to "c" parallel to the • What properties would a non-neutrino tachyon plates) does this mean that the rest mass is also have that would be experimentally obseNable? anisotropic? Can this be measured?

• Will a charged tachyon (if it exists) emit • Experiments run at very high energies (to reach Cerenkov radiation in a vacuum? (Here there is a the smallest scales and times) could possibly difference of opinion depending on the model one determine if there are any Weinberg-type uses. The model that explains Cerenkov radiation nonlinearities in quantum mechanics that could be as coming from the re-radiation reaction of the exploited for FTL communication. atoms in the transparent material surrounding the particle path would not predict such radiation from • Using a laser to focus enough energy in "empty" a charged tachyon. The model that explains space might cause negative-energy virtual pairs to Cerenkov radiation as being caused by "kinks" in become positive-energy pairs thereby proving the the electrostatic field emitted by the charge on the existence of virtual particles. tachyon would predict such radiation.) • Good, time-phased studies of cosmic ray • Is the Higgs a tachyon? showers should be undertaken to determine if tachyons are present. R. L. Forward suggested a • Could a neutrino-antineutrino "Cooper pair" be a space-based experiment in which the cosmic rays bosonic tachyon? and their secondary particles would impact incident and secondary targets respectively of The workshop participants agreed that the known compositions on board a specially following experiments would provide extremely designed as illustrated in Figure 5. useful information regarding physics where "c" is a Detectors located a known distance from the lower bound: targets (such as on a long tether that would provide gravity gradient stabilization to maintain 10 American Institute of Aeronautics and Astronautics pointing toward the zenith) would sense any effect the unseen addrrional dimensions are "rolled particles arriving ahead of the main shower, up" into this Planck-length radius. This approach thereby providing a more unambiguous avoids the infinities that occur with point particles. measurement uncomplicated by the Earth's While the group noted that some string theories atmosphere for the presence of FTL particles. predict the existence of tachyon-like particles there Careful design work would be needed to provide was no obvious way identified to use strings for an optimal ratio of the target thickness to target FTL travel and communication. Forward has area that could both (1) be placed in space observed that "One could 'unroll' a rolled-up economically and (2) provide enough events per dimension, use tt to travel in a tachyonic mode, day to make the experiment worth doing. then roll it up. If dimensions in general can be rolled up then it might be possible to roll up one of • The detection of a nearby black hole that was a our three space dimensions, rapidly move to a source of neutrinos would show that neutrinos new point in the rolled up dimension, then unroll must be tachyons since only FTL particles can it".13 escape from a black hole. (Could tachyon emission be the reason why we have not observed Forward noted that some cosmic string theories the postulated explosions of primordial black predict the temporary production of a time holes?) machine when two of these hypothetical galaxy-sized cosmic strings left over from the Big • Some equations of state for neutron stars Bang pass each other fast enough. predict that the speed of sound in matter will be greater than the speed of light. 4.1.2 Penrose TwjS)or Space Measurements of the frequency of the acoustical modes of a neutron star (similar to measurements Forward described twistor space which is a that have been made of the Sun's acoustical concept that has been mathematically developed modes) could possibly detect such an effect.' by Roger Penrose. Twistor space is an eight-dimensional complex space developed by 4. PHYSICS OF APDITIONAL SPACE Penrose as a non-local theory of spacetime. PIMENSIONS Twistor space represents an effort by Penrose 'to probe a region deeper than the fields and particles The workshop participants next considered the of quantum mechanics" by using "abstract possibility of additional space dimensions. geometrical objects which operate in a TradHionally, science fiction has explained FTL by higher-dimensional complex space that underlies invoking higher dimensions as a way to get around space-time. . :58 (Penrose has categorized the speed limrr of light in normal four-dimensional twistor theory as 'tentative" which is the second spacetime. lowest in his scheme for the fourfold classification 58 4.1 General Overview of Physics of Additional of theories. ) Forward explained that in twistor Space Dimensions space both space and time are naturally quantized and combinations of twistors form the known R. L. Forward provided a general overview of particles. In twistor theory, twistor space space-time structures, including superstring generates the observable lour-dimensional theories, Penrose twistor space, vacuum spacetime and 8-D distortions cause 4-D forces. If fluctuations, charge-parity-time (CPT) "space" the 8-D twistor space is warped enough then the asymmetries, point particles, and spin space. The 4-D known space would "disappear'', in effect following paragraphs summarize the discussion of providing a means for FTL travel. However, these topics. Forward has commented that ''This is not really FTL travel, since the disappearance of space will 4.1.1 Superstring Theories probably happen at light speed, but it achieves the same resutt". 13 Regarding superstring theories, Forward observed that there are ten-dimensional (1 0-D) and 4.1.3 Vacuum Fluctuations twenty-six dimensional (26-D) versions in which particles are mathematically treated to be like the Forward categorized vacuum fluctuations into vibrations of strings. The strings have dimensions electromagnetic fluctuations, virtual particle on the order of the (-1o-35 m). In fluctuations and quantum fluctuations (see discussion in Section 2). 11 American Institute of Aeronautics and Astronautics 4.1.5 Point Particles Forward explained that electromagnetic fluctuations have been experimentally confirmed Forward reviewed a number of experimental and through studies of surface energy and tension; theoretical results showing that Van der Waals force; and the Casimir force between conducting plates (see Section 3). • , , and are points Forward noted that electromagnetic fluctuations (e.g., the radius of the electron must be less could be a possible alternative ''source field" than 10-20 em) theory and that there is a remote possibil~y that • black holes are point-like (fin~e circumference they could be a source of energy but he saw no and area with zero radius and volume) obvious FTL application. and reminded everyone that point charges Regarding virtual particles, Forward commented produce infinities. The question, then, is: are that they have been experimentally "confirmed" by point charges warping spacetime? Could point the measured shift in the energy of the electron in particles be quantum black holes? Forward noted the hydrogen atom (sometimes referred to as the that the hyperfine structure of a hydrogen atom "" or "Lamb-Rutherford" shift). Another agrees to within an almost exact factor of two with outcome of the presence of virtual particles is the hyperfine structure one would get if the contained in Stephen Hawking's calculations was replaced by a theoretical subatomic version of about the evaporation of black holes. Forward the Kerr-Newman black hole. Forward has asked: observed that virtual particles also represented an "Do we need to understand alternative "source field" theory which appears to elementary particles? Is nature trying to tell us work Hcharged particles are nearby but the theory something?"13 fails for virtual by laser. While virtual particles may be a possible source of 4.1,6 Spin Space energy Forward saw no obvious FTL application. Forward briefly reviewed the concept of spin as Quantum fluctuations, which have been discussed applied to elementary particles, noting that spin is in Section 2, occur at the of the Planck length not the same as the classical 3 (~1o-35 m) and Planck dens~y (~10 93 g/cm ). of a rotating object. In particular, particles with a Theoretical models include Wheeler's spacetime spin of 112 (h/2x) (e.g., electrons, , '1oam" and Hawking's "baby universes". At and neutrinos) have some very peculiar present there is no good theory of quantum properties. As an example, they must be rotated fluctuations and it is unknown if they could be a 720° in order to be turned completely over. source of energy. For FTL purposes, the question Forward wondered if this implied the existence of would be, as Morris and Thorne have wondered, a "half" dimension for these particles. What is spin could quantum wormholes be "grown" large space? enough to provide a mechanism for FTL travel? 4.2 HMM Plscusslon of Phvslcs of Additional 4.1.4 CPT "Space" Asymmetrjes Space Pimenslons

Forward reviewed CPT (charge-parity-time) Matt Visser suggested that instead of having the symmetry theory which says there should extra dimensions rolled up into Planck-length symmetry in particle behavior when charge, parity dimensions, these dimensions could form a bowl and time are interchanged. He observed that in which our universe lies at the bottom. experiments have not borne out the symmetry Somehow energy or momentum would have to be predicted by the theory. Forward called the added to a spaceship to move it out of this well but group's attention to the charge asymmetry if such a well existed it may be that the velocity of between protons and anti-protons; the neutrino light would be different from "c". Using parity asymmetry; and the K0 (neutral ) five-dimensional Kaluza-Kiein models it might be particle lime asymmetry, asking if these possible to develop a 5-D drive that operates by asymmetries might provide a handle on lime that jumping out of this 4-D "" into a could lead to lime travel or if some particles (e.g. "higher state", allowing access to the fifth neutrinos) occupy a different "space" from other dimension, traveling in that dimension, then particles (e.g. photons). dropping back into our 4-D spacetime.

12 American Institute of Aeronautics and Astronautics 5. SOME OPEN ISSUES IN PHYSICS the participants identified a number of experiments, which have been summarized in Over the course of the two-day workshop the Appendix 2, that could help elucidate possible participants identified a number of "open issues" in FTL -related phenomena. physics. As one participant commented these "embarrassing unsolved physics problems . . . The odd aspect of postulated FTL travel is that it is may prove to be chinks in the FTL armor''. The the reverse of the normal interplay between theory issues or problems (many of which have been and experiment. In the past our theories have summarized in the preceding sections) are been the limtting statements which were summarized below: eventually overthrown or expanded by subsequent experiments that pressed beyond the boundaries • "Point-like" (zero dimensional) properties of of known physics. In the case of FTL phenomena electrons, muons, and quarks. the reverse seems to be true: our theories permit • Lack of a quantum theory of gravity. such phenomena but our experiments don't find • FTL "quantum connectedness" of distant them. Even H we find that the speed of light is the entangled particles. ultimate speed limit, theoretical and experimental • Extreme predicted (but unobserved) denstties studies of FTL-related phenomena, which for vacuum fluctuations. represent a frontier in quantum and relativity • Existence of spin. theories, should help us better understand the • Internal structure of elementary particles. universe. • CPT asymmetries. • Lack of a theory of inertia. In conclusion we offer the words of Henry • Missing mass in the Milky Way Galaxy, galactic Margenau: "If the history of science teaches clusters, and the universe. anything at all it is that there are no eternal verities • Excess of matter over antimatter in the universe. which man can grasp and hold forever. Science is • Non-zero . a flux of understanding, deepening and yielding • Garnma-ray bursters. ever greater satisfaction, tt appears, but the river • CENTAUROs. of discoveries is never dammed and made into a • FTL -appearing blobs emitted from . stagnant pool ... [the philosopher or the scientist) (One participant commented that the involved must swim wtth the flow and try, if possible, to be geometry being used to explain why the FTL effect abreast of n. He may be able to judge tor some is not real FTL movement was beginning to look distance ahead where he is moving, but his final like the "cycles wHhin cycles" of Ptolemaic destination is also unknown".29 .) Lack of cosmic censorship of naked singularRies 7. REFERENCES in existing theories of gravity. • Existing theories allow time machines. 1. G. L. Bennett, "Interstellar Transportation: An • Heavy-ion collisions produce e+e- pairs 100 Enabling Technology for Interstellar Civilizations", angstroms away, implying an intermediate Proceedings of the Thirtieth Space Congress, pp. neutral particle. What is H? 3-1 to 3-9, held in Cocoa Beach, Florida, 27-30 decay into two and three gamma April1993. rays does not agree with theory. • Failure to detect the bursts from the 2. N. Herbert, Faster Than Light, Superluminal final stages of evaporation of the predicted Loopholes in Physics, New American Library, New miniature primordial black holes. York, , 1988.

6. CONCLUQING REMARKS 3. M. A. Rothman, ''Things That Go Faster Than Light", Scientific American, Vol. 203, No. 1, pp. After considering three principal FTL scientific 142-152, July 1960. windows (wormholes, FTL particles, and higher dimensional spaces) the participants were not able 4. R. L. Smtth, ''The Velocities of Light", American to identrry a specific or obvious method to achieve Journal of Physics, Vol. 38, No. 8, pp. 978-983, FTL travel or communication. However, the August 1970. participants noted that there are enough cracks in the armor of physics that FTL travel or 5. R. Y. Chiao, P. G. Kwiat and A. M. Steinberg, communication could not be ruled out. Moreover, "Faster than Light?", Scientific American, August 13 American Institute of Aeronautics and Astronautics 1993, pp. 52-60. 'Wormholes, Time Machines, and the Weak Energy Condition", Physical Review Letters, Vol. 6. J. Brown, "Faster Than the Speed of Light", 61, No. 13, 26 September 1968, pp. 1446-1449. New Scientist, Vol. 146, No. 1971, pp. 26-30, 1 April1995. 19. M. Visser, "An Exotic Class of Kaluza-Kiein Models", Physics Letters, Vol. 158B, No. 1, 12 7. A. Einstein, Relativity, The Special and the September 1985, pp. 22-25. General Theory, Crown Publishers, Inc., New York, New York, 1961. 20. M. Visser, ''Traversable wormholes: Some simple examples", Physical Review D, Vol. 39, No. 8. J. L. Anderson, "Leaps of the Imagination 10, 15 May 1989, pp. 3182-3184. Using the Horizon Mission Methodology", Ad Astra, Vol. 7, No. 1, January/February 1995, pp. 21. M. Visser, "Wormholes, baby universes, and 37-40. causalfiy", Physical Review D, Vol. 41, No. 4, 15 February 1990, pp. 1116-1124. 9. C. Sagan, Contact, Simon & Schuster, New York, New York, 1985. 22. M. Visser, "Quantum mechanical stabilization of Minkowski signature wormholes", Physics 10. R. L. Forward, Timemaster, Tom Doherty Letters B, Vol. 242, No. 1, 31 May 1990, pp. Associates, New York, New York, 1992. 24-28.

11. R. L. Forward, "Space Warps: A Review of 23. M. Visser, "Quantum wormholes", Physical One Form of Propulsionless Transport", Journal of Review D, Vol. 43, No. 2, 15 January 1991, pp. The British Interplanetary Society, Vol. 42, pp. 402-409. 533-542, 1989. This paper was first presented as paper AIAA-89-2332 at the 24. M. Visser, 'Wheeler wormholes and topology AIAAIASMEISAEIASEE 25th Joint Propulsion change: A minisuperspace analysis", Modern Conference held in Monterey, Calijornia, 10-14 Physics Letters A, Vol. 6, No. 29, (1991) pp. July 1989. 2663-2667.

12. G. L. Bennett, The Star Sailors, St. Martin's 25. M. Visser, "From wormhole to time machine: Press, New York, New York, 1980. Remarks on Hawking's chronology protection conjecture", Physical Review D, Vol. 47, No. 2, 15 13. R. L. Forward, "Faster-than-Light", Analog January 1993, pp. 554-565. Science Fiction and Fact, Vol. CXV, No. 4, March 1995, pp. 30-33, 36-40, 42-44, 46-48, 50. 26. M. Visser, ''van Vleck determinants: Geodesic focusing in Lorentzian spacetimes", Physical 14. J. G. Cramer, "NASA Goes FTL Part 1: Review D, Vol. 47, No. 6, 15 March 1993, pp. Wormhole Physics", Analog Science Fiction and 2395-2402. Fact, Vol. CXIV, No. 15, Mid-December 1994, pp. 118-122. 27. M. Visser, Lorentzian Wormholes From Einstein to Hawking, American Institute of Physics 15. J. G. Cramer, "NASA Goes FTL Part 2: Press, New York, 1995. Cracks in Nature's FTL Armor'', Analog Science Fiction and Fact, Vol. CXV, No. 3, February 1995, 28. H. Margenau, ''The Philosophical Legacy of pp. 99-103. Contemporary Quantum Theory", in Mind and Cosmos, Essays in Contemporary Science and 16. M.S. Morris and K. S. Thorne, "Wormholes in Philosophy, R. G. Colodny, Editor, University of spacetime and their use for : A Pittsburgh Press, Pittsburgh, Pennsylvania, 1966. tool for teaching general relativity", American Journal of Physics, 56 (5), May 1988, pp. 395-412. 29. J. Friedman, M. S. Morris, I. D. Novikov, F. Echeverria, G. Klinkhammer, K. S. Thorne, and U. 17. K. S. Thorne, Black Holes and Time Warps, Yurtsever, "Cauchy problem in spacetimes with Einstein's Outrageous Legacy, W. W. Norton & closed timelike curves", Physical Review D, Vol. Company, New York, New York, 1994. 42, No.6, pp. 1915-1930, 15 September 1990.

18. M. S. Morris, K. S. Thorne, and u. Yurtsever, 30. K. S. Thorne, "Closed Timelike Curves", 14 American Institute of Aeronautics and Astronautics GRP-340, California lnstnute of Technology, 43. G. Taubes, "Found: Candidate for Missing Pasadena, California, February 1993 (submitted to Mass?", Science, Vol. 267, pp. 789-790, 10 Proceedings of the 13th International Conference February 1995. on General Relativity and Gravitation, ed. C. Kozameh, Institute of Physics, Bristol, England). 44. J. V. Narlikar, "Cosmic Tachyons: An Astrophysical Approach", American Scientist, Vol. 31. G. L. Bennett and H. B. Knowles, "Boundary 66, pp. 587-593, September-October 1978. (See Conditions on Faster-Than-Light Transportation also "Letters to the Editors", American Scientist, Systems", AIAA-93-1995, paper presented at the Vol. 67, No.1, p. 4, January-February 1979.) AIAA/SAEIASMEIASEE 29th Joint Propulsion Conference and Exhibit, held in Monterey, 45. K. Scharnhorst, "On Propagation of Light in California, 28-30 June 1993. the Vacuum Between Plates", Physics Letters B, No. 236, No.3, pp. 354-359, 22 February 1990. 32. B. Paczynski, "Gravitational Microlensing by the Galactic Halo", The Astrophysical Journal, 46. S. M. Barnett, "Photons faster than light?" 304: 1-5, 1 May 1986. Nature, Vol. 344, p. 289, 22 March 1990.

33. C. J. Hogan, "In search of the halo grail", 47. M. Chown, "Can photons travel 'faster than Nature, Vol. 365, pp. 602-603, 14 October 1993. light'?" New Scientist, p. 32, 7 April 1990.

34. C. Alcock et al., "Possible gravitational 48. B. Parker, Cosmic Time Travel, A Scientific microlensing of a star in the Large Magellanic Odyssey, Plenum Press, New York, New York, Cloud", Nature, Vol. 365, pp. 621·623, 14 October 1991. 1993. 49. S. J. Freedman and J. F. Clauser, 35. E. Aubourg et al., "Evidence tor gravitational "Experimental Test of Local Hidden-Variable microlensing by dark objects in the Galactic halo", Theories", Physical Review Letters, 28, 938-941, Nature, Vol. 365, pp. 623- 625, 14 October 1993. 1972.

36. J. G. Cramer, R. L. Forward, M. S. Morris, M. 50. A Aspect, P. Grangier, and G. Roger, "Experi­ Visser, G. Benford, and G. A Landis, "Natural mental Realization of Einstein-Podolsky-Rosen­ wormholes as gravitational lenses", Physical Bohm Gedankenexperiment A New Violation of Review D, Vol. 51, No. 6, pp. 3117-3120, 15 Bell's Inequalities", Physical Review Letters, Vol. March 1995. 49, pp. 91 ff, 1982.

37. J. Glanz, "EROS, MACHO, And OGLE Net A 51. J. G. Cramer, "The transactional interpretation Haul of Data", Science, Vol. 268, No. 5211, pp. of quantum mechanics", Reviews of Modern 642-643, 5 May 1995. Physics, Vol. 58, No.3, 647-687, July 1986.

38. M. Alcubierre, "The warp drive: hyper-fast 52. J. G. Cramer, "An Overview of the travel within general relativity", Classical and Transactional Interpretation of Quantum Quantum Gravity, 11 (1994) L73-L77. Mechanics", International Journal of , Vol. 27, No.2, pp. 227-236, 1988. 39. A. Goddard, "Surfing to the stars on warped space", New Scientist, p. 18, 11 June 1994. 53. D. Deutsch and M. Lockwood, "The Quantum Physics of Time Travel", Scientific American, Vol. 40. 0. M. P. Bilaniuk, V. K. Deshpande, and E. C. 270, No.3, pp. 68-74, March 1994. G. Sudarshan, "'Meta' Relativity", American Journal of Physics, Vol. 30, No. 10, pp. 718-723, 54. A M. Gleeson, M. G. Gundzik, E. C. G. October 1962. Sudarshan, and A. Pagnamenta, "Phenomenology of Complex Spin Tachyons", Particles and Nuclei, 41. 0. M. Bilaniuk and E. C. G. Sudarshan, Vol. 1. No.1, pp. 1-9, 1970. "Particles Beyond the Light Barrier'', Physics Today, pp. 43-51, May 1969. 55. P. V. Ramana Murthy, "Search tor Tachyons in the Cosmic Radiation", Lettere a/ Nuovo 42. 0. M. Bilaniuk et al., "More About Tachyons··, Cimento, Vol. 1, No. 22, pp. 908-912, 29 May Physics Today, pp. 47-52, December 1969. 1971. i 5 American Institute of Aeronautics and Astronautics 56. M. N. Kreisler, "Are There Faster-than-Light Particles?", American Scientist, Vol. 61, pp. APPENDIX 1: 201-208, March-April1973. LIST OF ATTENDEES/PARTICIPANTS AT THE WORKSHOP ON ADVANCED 57. R. W. Clay and P. C. Crouch, "Possible QUANTUM/RELATIVITY THEORY observation of tachyons associated with extensive PROPULSION air showers", Nature, Vol. 248, pp. 28-30, 1 March (Organizational affiliations listed for identification 1974. purposes only)

58. M. Gardner, "Foreword" to The Emperor's Dr. John L. Anderson New Mind, Concerning Computers, Minds, and NASA Headquarters The Laws of Physics by Roger Penrose, Oxford University Press, New York, New York, 1990. Dr. University of California, Irvine

Dr. Gary L. Bennett NASA Headquarters (now retired)

Dr. John G. Cramer

Dr. Pauline B. Cramer Boeing Commercial Airplane Group

Dr. Robert L. Forward Forward Unlimited

Dr. Robert H. Frisbee Jet Propulsion Laboratory

Dr. H. B. Knowles H. B. Knowles Physics Consulting

Dr. Geoffrey A. Landis NYMA, Inc. (Lewis Research Center)

Dr. Franklin B. Mead, Jr. Phillips Laboratory

Dr. Marc G. Millis Lewis Research Center

Dr. Michael S. Morris Butler University

Mr. Roy Patrick Rawlings Science Applications International Corporation

Dr. Matt Visser Washington University

16 American Institute of Aeronautics and Astronautics APPENPIX 2: SUMMARY OF EXPERIMENTS PROPOSED BY THE WORKSHOP PARTICIPANTS TO ELUCIDATE POSSIBLE EASTEB·THAN-L!GHT IFILl PHENOMENA

Wormhole Physics

Astronomical search for possible gravitationally negative anomalous compact halo objects (GNACHOs) by examining any gravitational lensing effects on light emitted by distant stars. (This would be an adjunct experiment to the search tor massive compact halo objects [MACHOs].)

Physics Where the Velocity of Light Is a Lower Bound

• Good, confirmatory, unambiguous measurements of the mass of the three flavors of neutrinos (electron, muon, and tau neutrinos) to clarify whether or not the neutrino is a tachyon.

• Good measurements of the velocity of light perpendicular to the Casimir plates to determine if the speed of light is increased as predicted.

High-energy experiments to determine if there are any Weinberg-type nonlinearities in quantum mechanics that could be exploited for ETL communication.

• Use of a laser to locus enough energy in "empty" space to determine if negative-energy virtual pairs can become positive-energy pairs thereby proving the existence of virtual particles.

Good, time-phased studies of cosmic ray showers to determine if tachyons are present (see Figure 5).

Search tor neutrinos from a nearby black hole since if neutrinos are being emitted they must be tachyons because only FTL particles can escape from a black hole.

Measuring the frequency of the acoustical modes of a neutron star to determine if the speed of sound in neutron star matter is greater than the speed of light (as predicted by some equations of state for neutron stars).

17 American Institute of Aeronautics and Astronautics "BACK FROM THE FUTURE" I

CAP LITIES HORIZON MISSIONS FRAME OF REFERENCE (enabled by Breakthroughs")

CURRENT FRAME REFERENCE

Break· through"

PRESENT FUTURE • Breakthrough Perspective or Technology Option

Figure 1. Diagram of the Horizon Mission Methodology (Ref. 8).

z Throat of Wormhole • Sirius

Figure 2. Diagram of a Wormhole Tunnel Without Horizons Connecting the Region Near Earth With the Region Near the Star Sirius (after M. S. Morris).

18 American Institute of Aeronautics and Astronautics Universe #1 Universe #2

Wj~ !_a, /Ill II

Figure 3. Diagram of Two Compact Regions of Minkowski Space {With Time Suppressed) Used to Create the Throat of a Wormhole (after M. Visser).

Figure 4. Sketch of a Wormhole Throat in the Form of a Cube With Rounded Edges and Rounded Corners {after M. Visser). The Struts are Built Out of Negative Tension Classical Strings.

19 American Institute of Aeronautics and Astronautics fXp--t:::-LJf.l>;1---7fCCNflAfY41tt:rl~RY AIT AL!L!NW ALONC, A (ffAVII'( f(IN~ F/..A/f-;7 . CIICAV\ENT AHI7 :CoNNCO:i:fE17 t7 Y A TCll-JE.j:: .

VETiliDR7Tf:'COtJI 1:' MC:rTE l2.1B.S

Figure 5. Sketch of a Satellite-Based Experiment Designed to Search for Tachyons in Cosmic Ray Showers (Visualization by Pat Rawlings from a Concept Proposed by Robert L. Forward).

20 American Institute of Aeronautics and Astronautics