Fundamental limitations on ‘warp drive’ spacetimes

2005

Warp drive" spacetimes are useful as "gedanken-experiments" and as a theoretician's probe of the foundations of general relativity. Applying linearized gravity to the weak-field warp drive, i.e., for non-relativistic warp-bubble velocities, we find that the occurrence of energy condition violations in this class of spacetimes is generic to the form of the geometry under consideration and is not simply a side-effect of the "superluminal" properties. Using the linearized construction it is now possible to compare the warp field energy with the massenergy of the spaceship, and applying the "volume integral quantifier", extremely stringent conditions on the warp drive spacetime are found.

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.

Fernando Loup, 2012

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. Recently McMonigal,Lewis and OByrne presented an important analysis for the Alcubierre warp drive:A warp drive ship at superluminal speeds in interstellar space would trap in the warp bubble all the particles and radiations the ship encounters in its pathway and these trapped bodies would achieve immense energies due to the bubble superluminal speed.As far the ship goes by in interstellar space, more and more particles and radiations are trapped in the bubble generating in front of it a blanket with extremely large amounts of positive energy. The physical consequences of having this blanket of positive energies with enormous magnitudes in front of the negative energy of the warp bubble are still unknown. When the ship finishes the trip it stops suddenly releasing in a highly energetic burst all the trapped particles and radiations contained in the blanket damaging severely the destination point. In this work,we reproduce the same analysis for the Natario warp drive however using different mathematical arguments more accessible to beginners or intermediate students and we arrived exactly to the same conclusions. While in a long-term future some of the physical problems associated to the warp drive science(negative energy,Horizons) seems to have solutions(better shape functions for the negative energy problem and a theory that encompasses both General Relativity and non local quantum entanglements of Quantum Mechanics for the Horizons problem) and we discuss these solutions in our work,the analysis of McMonigal,Lewis and OByrne although entirely correct do not have a foreseeable solution and remains the most serious obstacle against the warp drive as a physical reality

We carefully criticize Alcubierre's analysis of a solution to the Einstein Field Equations which he claims represents hyper-fast (fasterthan-light) travel in general relativity. We show that his solution is really just a solution of special relativity, reducible to the usual Twin Paradox, and that his conclusions are completely fatitiutous.

A solution of general relativity is presented that describes an Alcubierre 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).

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]).

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.

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]).

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 ...

A solution of general relativity is presented that describes an Alcubierre propulsion system in which it is possible to travel at superluminal speed while reducing the components of the energy-impulse tensor (thus reducing energy density) by an arbitrary value. Here we investigate the negative energy in the Pfenning zone, and the quantum inequalities involved.