Commentary on Alcubierre's "Warp Drive."

Journal of Student Research

Warp drives, though first envisioned in science fiction, have become a topic of scientific interest within theoretical physics. Miguel Alcubierre was the first one to propose a warp drive spacetime in 1994. His geometry is, however, considered unphysical: it violates all energy conditions and requires large amounts of exotic matter. Several modifications to his metric have been proposed which reduce these energy requirements, but it is still unlikely that warp drives will ever be technologically useful. Even so, they make for very interesting thought experiments, forcing physicists to face the limits of their current theories. Here we will discuss the Alcubierre drive, its energy condition violations, and its energy requirements as obtained from the quantum inequalities. The general definition of superluminal travel is briefly discussed. We also study the horizon problem and the possibility of closed timelike curves within this spacetime. Some recent progress in warp drive research ...

2012

Warp Drives are solutions of the Einstein Field Equations that allows superluminal travel within the framework of General Relativity. The first of these solutions was discovered by the Mexican mathematician Miguel Alcubierre in 1994.The Alcubierre warp drive seems to be very attractive because allows interstellar space travel at arbitrarily large speeds avoiding the time dilatation and mass increase paradoxes of Special Relativity. However it suffers from a very serious drawback:Interstellar space is not empty:It is fulfilled with photons and particle dusts and a ship at superluminal speeds would impact these obstacles in highly energetic collisions disrupting the warp field and placing the astronauts in danger.This was pointed out by a great number of authors like Clark,Hiscock,Larson,McMonigal,Lewis,O'Byrne, Barcelo,Finazzi and Liberati. In order to travel significant interstellar distances in reasonable amounts of time a ship would need to attain 200 times the speed of light but according to Clark,Hiscock and Larson the impact between the ship and a single photon of Cosmic Background Radiation(COBE)would release an amount of energy equal to the photosphere of a star like the Sun.And how many photons of COBE we have per cubic centimeter of space?This serious problem seems to have no solution at first sight. However some years ago Harold White from NASA appeared with an idea that may well solve this problem:According to him the ship never surpass the speed of light but the warp field generates a Lorentz Boost resulting in an apparent superluminal speed as seen by the astronauts on-board the ship and on the Earth while the warp bubble is always below the light speed with the ability to manoeuvre against these obstacles avoiding the lethal collisions. In this work we examine the feasibility of the White idea using clear mathematical arguments and we arrived at the conclusion that Harold White is correct.

A solution of general relativity is presented that describes an Alcubierre [1] propulsion system in which it is possible to travel at superluminal speed while reducing the energy density and energy by an arbitrary value, and eliminating the event horizon, for superluminal motions,which would have otherwise led to to explosion of the spaceship (instability of the warp bubble [7]).

Physics Essays, 1996

In SETI (Search for Extraterrestrial Intelligence) conventional wisdom has it that the probability of direct contact by interstellar travel is vanishingly small due to the enormous distances involved, coupled with the velocity-of-light limitation. Alcubierre's recent "warp drive" analysis [Class. Quantum Grav. 11, L 73 (1994)] within the context of general relativistic dynamics, however, indicates the naivete of this assumption. We show here that Alcubierre's result is a particular case of a broad, general approach that might loosely be called "metric engineering," the details of which provide yet further support for the concept that reduced-time interstellar travel, either by advanced extraterrestrial civilizations at present or ourselves in the future, is not, as naive consideration might hold, fundamentally constrained by physical principles.

A solution of general relativity is presented that describes an Alcubierre [1] propulsion system in which it is possible to travel at superluminal speed while reducing the energy density and energy by an arbitrary value, and eliminating the event horizon, for superluminal motions,which would have otherwise led to to explosion of the spaceship (instability of the warp bubble [7]).

Classical and Quantum Gravity, 1994

It is shown how, within the framework of general relativity and without the introduction of wormholes, it is possible to modify a spacetime in a way that allows a spaceship to travel with an arbitrarily large speed. By a purely local expansion of spacetime behind the spaceship and an opposite contraction in front of it, motion faster than the speed of light as seen by observers outside the disturbed region is possible. The resulting distortion is reminiscent of the "warp drive" of science fiction. However, just as it happens with wormholes, exotic matter will be needed in order to generate a distortion of spacetime like the one discussed here.

Alcubierre-Cacci A New Frontier for Spacetime Propulsion and Interstellar Travel, 2024

The Alcubierre-Cacci Drive represents an innovative theoretical advancement in faster-than-light propulsion, combining Alcubierre’s concept of spacetime curvature with novel enhancements for improved efficiency and stability. This model leverages the manipulation of spacetime through negative energy densities and exotic materials, hypothesizing a practical pathway for superluminal travel while minimizing the energy requirements traditionally associated with warp drives. Key innovations include a refined energy distribution system and adaptive field stabilization mechanisms, designed to address quantum fluctuations and mitigate potential causality violations. The Alcubierre-Cacci Drive integrates elements of quantum field theory, general relativity, and advanced material sciences, aiming to overcome significant barriers in spacetime engineering. This proposal not only extends the theoretical foundations of warp technology but also introduces a framework for experimental validation in the future, paving the way for a transformative era of interstellar exploration.

2016

The main purpose of this paper lies in the attempt to identify a different meaning concerning equations usually classified as relativistic, such as the well known Lorentz Transformations. On the one hand, we can no longer deny that several phenomena can be effectively described by the above-mentioned equations; on the other hand, generally speaking, we should acknowledge that, although some mathematical relations have proved to be evidently suitable for describing the phenomenological reality, their meaning could be deeply different from the one we are used to ascribing to them. The current cosmological theories contemplate the possibility that our Universe could be characterized by a positive curvature. In this case, with the usual hypothesis of homogeneity and isotropy, our Universe is commonly imagined as evenly spread on the surface of a four dimensional ball. In this paper, the existence of at least a further spatial dimension is at least contemplated: in other terms, from a topological point of view, the Universe is no longer assimilated to a three dimensional spherical shell, but rather to a closed 4 - ball. As a consequence, the concept of material point should be replaced by the one of material segment. The angular distance between two points is equal to the angle formed by their radial extensions; the geodesic distance depends on the value of the speed. Naturally, the speed of light is still to be considered constant and independent of the motion of the source. Time is considered absolute. Among the various results, the possibility of travelling apparently faster than light stands out.

Fernando Loup, 2013

Warp Drives are solutions of the Einstein Field Equations that allows superluminal travel within the framework of General Relativity. There are at the present moment two known solutions: The Alcubierre warp drive discovered in 1994 and the Natario warp drive discovered in 2001. However as stated by both Alcubierre and Natario themselves the warp drive violates all the known energy conditions because the stress energy momentum tensor is negative implying in a negative energy density. While from a classical point of view the negative energy is forbidden the Quantum Field Theory allows the existence of very small amounts of it being the Casimir effect a good example as stated by Alcubierre himself.The major drawback concerning negative energies for the warp drive is the huge amount of negative energy able to sustain the warp bubble.In order to perform an interstellar space travel to a ”nearby” star at 20 light-years away with 3 potential habitable exo-planets(Gliese 667c) at superluminal speeds in a reasonable amount of time a ship must attain a speed of about 200 times faster than light.However the negative energy density at such a speed is directly proportional to the factor 1048 which is 1.000.000.000.000.000.000.000.000 times bigger in magnitude than the mass of the planet Earth!!! Some years ago Barcelo,Finazzi and Liberati published a work in which the composed mixed tensor hTµ ν i obtained from the negative energy density tensor Tµν µ = 0, ν = 0 of the 1 + 1 dimensional Alcubierre warp drive metric diverges when the velocity of the ship vs exceeds the speed of light.(see pg 2 in [19]).We demonstrate in this work that in fact this do not happens and their results must be re-examined.We introduce here a shape function that defines the Natario warp drive spacetime as an excellent candidate to low the negative energy density requirements from 1048 to affordable levels.We also discuss Horizons and Doppler Blueshifts that affects the Alcubierre spacetime but not the Natario counterpart.