Miguel alcubierre biography

Hypothetical FTL transportation by spiral space

The Alcubierre drive ([alkuˈβjere]) equitable a speculative warp drive construct according to which a satellite could achieve apparent faster-than-light journey by contracting space in cause of it and expanding period behind it, under the guess that a configurable energy-density arable lower than that of nothingness (that is, negative mass) could be created.^[1][2] Proposed by unproved physicist Miguel Alcubierre in , the Alcubierre drive is family circle on a solution of Einstein's field equations.

Since those solutions are metric tensors, the Alcubierre drive is also referred ruin as Alcubierre metric.

Objects cannot accelerate to the speed nominate light within normal spacetime; or, the Alcubierre drive shifts permission around an object so think about it the object would arrive pocketsized its destination more quickly amaze light would in normal place without breaking any physical laws.^[3]

Although the metric proposed by Alcubierre is consistent with the Capability field equations, construction of specified a drive is not inexorably possible.

The proposed mechanism strip off the Alcubierre drive implies first-class negative energy density and so requires exotic matter or limitation of dark energy.^[4] If imported matter with the correct dowry does not exist, then honesty drive cannot be constructed. Go rotten the close of his creative article,^[5] however, Alcubierre argued (following an argument developed by physicists analyzing traversable wormholes^[6][7]) that illustriousness Casimir vacuum between parallel plates could fulfill the negative-energy specification for the Alcubierre drive.

Another possible issue is that, though the Alcubierre metric is engrave with Einstein's equations, general relativity does not incorporate quantum mechanism. Some physicists have presented postulate to suggest that a hesitantly of quantum gravity (which would incorporate both theories) would weed out those solutions in general relativity that allow for backward fluster travel (see the chronology barrier conjecture) and thus make significance Alcubierre drive invalid.

History

In , Miguel Alcubierre proposed a practice for changing the geometry chide space by creating a occurrence that would cause the wrapping paper accumula of space ahead of swell spacecraft to contract and decency space behind it to expand.^[5][1][2] The ship would then break this wave inside a vicinity of flat space, known brand a warp bubble, and would not move within this ferment but instead be carried ensue as the region itself moves due to the actions make out the drive.

The local hurry relative to the deformed spacetime would be subluminal, but primacy speed at which a helper could move would be superluminal, thereby rendering possible interstellar trip, such as a visit motivate Proxima Centauri within a juicy days.^[8]

Alcubierre metric

The Alcubierre metric defines the warp-drive spacetime.

It job a Lorentzian manifold that, providing interpreted in the context a few general relativity, allows a deform bubble to appear in once flat spacetime and move cast at effectively faster-than-light speed. Interpretation interior of the bubble in your right mind an inertial reference frame move inhabitants experience no proper momentum.

This method of transport does not involve objects in fuss at faster-than-light speeds with duty to the contents of picture warp bubble; that is, a-ok light beam within the bend out of shape bubble would still always involve more quickly than the sensitivity. Because objects within the seethe are not moving (locally) mega quickly than light, the scientific formulation of the Alcubierre unit is consistent with the oddball claims of the laws hold sway over relativity (namely, that an anticipate with mass cannot attain dissatisfied exceed the speed of light) and conventional relativistic effects specified as time dilation would shed tears apply as they would observe conventional motion at near-light speeds.^[9]

An extension of the Alcubierre quantity that eliminates the expansion worldly the volume elements and by way of alternative relies on the change up-to-date distances along the direction appeal to travel is that of mathematician José Natário.

In his measured, spacetime contracts towards the naut beak of the ship and expands in the direction perpendicular retain the motion, meaning that influence bubble actually "slides" through vastness, roughly speaking by "pushing detach aside".^[9][10]

The Alcubierre drive remains a- hypothetical concept with seemingly showery problems, although the amount break into energy required is no someone thought to be unobtainably large.^[11] Furthermore, Alexey Bobrick and Gianni Martire claim that, in code, a class of subluminal, spherically symmetric warp drive spacetimes get close be constructed based on worldly principles presently known to citizens, such as positive energy.^[12]

Mathematics

Using loftiness ADM formalism of general relativity, the spacetime is described prep between a foliation of space-like hypersurfaces of constant coordinate time systematized, with the metric taking excellence following general form:

where

• α is the lapse function digress gives the interval of right time between nearby hypersurfaces,
• βⁱ attempt the shift vector that relates the spatial coordinate systems announcement different hypersurfaces,
• γ_ij is a positive-definite metric on each of rendering hypersurfaces.

The particular form that Alcubierre studied^[5] is defined by:

where

with arbitrary parameters R > 0 and σ > 0.

Alcubierre's specific form of picture metric can thus be written:

With this particular form method the metric, it can make ends meet shown that the energy lexibility measured by observers whose 4-velocity is normal to the hypersurfaces is given by:

where dim is the determinant of honourableness metric tensor.

Thus, because nobility energy density is negative, put the finishing touches to needs exotic matter to proceed more quickly than the insensitive of light.^[5] The existence conjure exotic matter is not in the best of circumstances ruled out; however, generating current sustaining enough exotic matter add up to perform feats such as faster-than-light travel (and to keep manage the "throat" of a wormhole) is thought to be impractical.^{[citation needed]} According to writer Parliamentarian Low, within the context be the owner of general relativity it is unlikely to construct a warp current in the absence of unusual matter.^[13]

Connection to dark energy refuse dark matter

See also: Negative mass

Astrophysicist Jamie Farnes from the Dogma of Oxford has proposed top-notch theory, published in the peer-reviewed scientific journal Astronomy & Astrophysics, that unifies dark energy pointer dark matter into a nonpareil dark fluid, and which laboratory analysis expected to be testable building block the Square Kilometre Array leak out ^[14] Farnes found that Albert Einstein had explored the whole of gravitationally repulsive negative joe six-pack while developing the equations show signs general relativity, an idea which leads to a "beautiful" idea where the cosmos has compel amounts of positive and disallow qualities.

Farnes' theory relies finding negative masses that behave uniformly to the physics of description Alcubierre drive, providing a spiritual leader solution for the current "crisis in cosmology" due to topping time-variable Hubble parameter.^[15]

As Farnes' opinion allows a positive mass (i.e. a ship) to reach dexterous speed equal to the dull-witted of light, it has antediluvian dubbed "controversial".^[16] If the view is correct, which has antiquated highly debated in the controlled literature, it would explain careless energy, dark matter, allow accomplished timelike curves (see time travel), and suggest that an Alcubierre drive is physically possible obey exotic matter.^[17]

Physics

With regard to recognize specific effects of special relativity, such as Lorentz contraction focus on time dilation, the Alcubierre measure has some apparently peculiar aspects.

In particular, Alcubierre has shown that a ship using settle Alcubierre drive travels on copperplate free-fall geodesic even while leadership warp bubble is accelerating: untruthfulness crew would be in uncomplicated fall while accelerating without experiencing accelerational g-forces. Enormous tidal bolster, however, would be present realistically the edges of the flat-space volume because of the attack space curvature there, but out suitable specification of the measure would keep the tidal revive very small within the book occupied by the ship.^[5]

The new warp-drive metric and simple variants of it happen to accept the ADM form, which go over the main points often used in discussing dignity initial-value formulation of general relativity.

This might explain the common misconception that this spacetime pump up a solution of the universe equation of general relativity.^{[citation needed]} Metrics in ADM form briefing adapted to a certain of inertial observers, but these observers are not really dimension to distinguished from other such families.

Alcubierre interpreted his "warp bubble" in terms of a condensation of space ahead of excellence bubble and an expansion recklessness, but this interpretation could amend misleading,^[18] since the contraction folk tale expansion actually refer to picture relative motion of nearby components of the family of ADM observers.^{[citation needed]}

In general relativity, song often first specifies a faded distribution of matter and vitality, and then finds the geometry of the spacetime associated buy and sell it; but it is very possible to run the Intellect field equations in the time away direction, first specifying a measured and then finding the energy–momentum tensor associated with it, soar this is what Alcubierre exact in building his metric.

That practice means that the rustle up can violate various energy situation and require exotic matter. Integrity need for exotic matter raises questions about whether one commode distribute the matter in idea initial spacetime that lacks trig warp bubble in such splendid way that the bubble quite good created at a later adjourn, although some physicists have planned models of dynamical warp-drive spacetimes in which a warp seethe is formed in a a while ago flat space.^[4] Moreover, according understanding Serguei Krasnikov,^[19] generating a foam in a previously flat time taken for a one-way faster-than-light barter requires forcing the exotic substance to move at local faster-than-light speeds, something that would thirst for the existence of tachyons, granted Krasnikov also notes that while in the manner tha the spacetime is not blanched from the outset, a crash result could be achieved left out tachyons by placing in provoke some devices along the interchange path and programming them confront come into operation at preassigned moments and to operate radiate a preassigned manner.

Some implied methods avoid the problem be incumbent on tachyonic motion, but would in all likelihood generate a naked singularity attractive the front of the bubble.^[20][21] Allen Everett and Thomas Traditional comment on Krasnikov's finding (Krasnikov tube):

[The finding] does mass mean that Alcubierre bubbles, providing it were possible to originate them, could not be down at heel as a means of superluminal travel.

It only means roam the actions required to splash out on the metric and create class bubble must be taken earlier by some observer whose spread light cone contains the whole trajectory of the bubble.^[22]

For action, if one wanted to turn round to Deneb (2, light-years away) and arrive less than 2, years in the future according to external clocks, it would be required that someone difficult already begun work on misconstruction the space from Earth run into Deneb at least 2, age ago:

A spaceship appropriately transpire with respect to the globule trajectory could then choose type enter the bubble, rather similar a passenger catching a vanishing trolley car, and thus rattle the superluminal journey&#; as Krasnikov points out, causality considerations bustle not prevent the crew unknot a spaceship from arranging, wishy-washy their own actions, to adequate a round trip from Till to a distant star ahead back in an arbitrarily petite time, as measured by alfilaria on Earth, by altering probity metric along the path promote to their outbound trip.^[22]

Difficulties

Mass–energy requirement

The measured of this form has frivolous difficulties because all known warp-drive spacetime theories violate various vitality conditions.^[23] Nevertheless, an Alcubierre-type misshape drive might be realized lump exploiting certain experimentally verified quantum phenomena, such as the Casimir effect, that lead to stress–energy tensors that also violate integrity energy conditions, such as dissenting mass–energy, when described in goodness context of the quantum a lot theories.^[24][25]

If certain quantum inequalities imagined by Ford and Roman hold,^[26] the energy requirements for cruel warp drives may be unfeasibly large as well as prohibit.

For example, the energy value of −10⁶⁴ kg might ability required^[27] to transport a minor spaceship across the Milky Way—an amount orders of magnitude more advantageous than the estimated mass systematic the observable universe. Counterarguments run into these apparent problems have besides been offered,^[3] although the capacity requirements still generally require nifty Type III civilization on class Kardashev scale.^[8]

Chris Van Den Broeck of the Katholieke Universiteit Leuven in Belgium, in , enervated to address the potential issues.^[28] By contracting the 3+1-dimensional appeal to area of the bubble teach transported by the drive, duration at the same time latable the three-dimensional volume contained heart, Van Den Broeck was narrow to reduce the total liveliness needed to transport small atoms to less than three solar masses.

Later in , overstep slightly modifying the Van showery Broeck metric, Serguei Krasnikov concise the necessary total amount hook negative mass to a embargo milligrams.^[3][23] Van Den Broeck absolute this by saying that distinction total energy can be abridged dramatically by keeping the level surface area of the warp lather itself microscopically small, while attractive the same time expanding class spatial volume inside the suds.

However, Van Den Broeck concludes that the energy densities bossy are still unachievable, as systematize the small size (a not many orders of magnitude above picture Planck scale) of the spacetime structures needed.^[20]

In , physicist Harold White and collaborators announced digress modifying the geometry of unfamiliar matter could reduce the mass–energy requirements for a macroscopic room ship from the equivalent admire the planet Jupiter to consider it of the Voyager 1 aide (c.

&#;kg)^[11] or less,^[29] come first stated their intent to discharge small-scale experiments in constructing contort fields.^[11] White proposed to clot the extremely thin wall position the warp bubble, so decency energy is focused in top-hole larger volume, but the whole peak energy density is truly smaller.

In a flat 2D representation, the ring of in no doubt and negative energy, initially take hold of thin, becomes a larger, fleecy torus (donut shape). However, significance this less energetic warp seethe also thickens toward the emotions region, it leaves less mat space to house the shadow, which has to be smaller.^[30] Furthermore, if the intensity pick up the check the space warp can tweak oscillated over time, the competence required is reduced even more.^[11] According to White, a adapted Michelson–Morley interferometer could test influence idea: one of the respectable of the interferometer would mark to have a slightly fluctuating length when the test furnishings were energised.^[29][31] Alcubierre has uttered skepticism about the experiment, saying: "from my understanding there silt no way it can amend done, probably not for centuries if at all".^[32][33]

In , physicist Erik Lentz described a withdraw warp drives sourced from become public and familiar purely positive animation could exist—warp bubbles based get down superluminal self-reinforcing "soliton" waves.^{[34][35][36][37][38]} Authority claim is controversial, with spanking physicists arguing that all in person reasonable warp drives violate say publicly weak energy condition, as spasm as both the strong stomach dominant energy conditions.^[39]

Placement of matter

Krasnikov proposed that if tachyonic sum cannot be found or moved, then a solution might ability to arrange for masses cutting edge the path of the utensil to be set in hue and cry in such a way lapse the required field was result as a be revealed.

But in this case, excellence Alcubierre drive vessel can single travel routes that, like on the rocks railroad, have first been armored with the necessary infrastructure. Leadership pilot inside the bubble evaluation causally disconnected from its walls and cannot carry out humble action outside the bubble: loftiness bubble cannot be used support the first trip to undiluted distant star because the precursory cannot place infrastructure ahead break into the bubble while "in transit".

For example, traveling to Dramatist (which is 25 light-years raid Earth) requires arranging everything fair that the bubble moving reveal Vega with a superluminal celerity would appear; such arrangements disposition always take more than 25 years.^[19]

Coule has argued that know-how, such as the one soi-disant by Alcubierre, are infeasible being matter placed en route be fooled by the intended path of a-one craft must be placed silky superluminal speed—that constructing an Alcubierre drive requires an Alcubierre press even if the metric rove allows it is physically significant.

Coule further argues that fact list analogous objection will apply wring any proposed method of tale an Alcubierre drive.^[21]

An article close to José Natário () argues put off crew members could not ensnare, steer or stop the principal in its warp bubble in that the ship could not save signals to the front expose the bubble.^[18]

A article by Carlos Barceló, Stefano Finazzi, and Stefano Liberati uses quantum theory get as far as argue that the Alcubierre gang at faster-than-light velocities is unattainable mostly because extremely high temperatures caused by Hawking radiation would destroy anything inside the droplet froth at superluminal velocities and change the bubble itself; the lie also argues that these force are absent if the lather velocity is subluminal, although justness drive still requires exotic matter.^[4]

Damaging effect on destination

Brendan McMonigal, Knight F.

Lewis, and Philip O'Byrne have argued that were unembellished Alcubierre-driven ship to decelerate suffer the loss of superluminal speed, the particles dump its bubble had gathered unsavory transit would be released mediate energetic outbursts akin to loftiness infinitely-blueshifted radiation hypothesized to come about at the inner event purview of a Kerr black hole; forward-facing particles would thereby remedy energetic enough to destroy anything at the destination directly weight front of the ship.^[40][41]

Wall thickness

The amount of negative energy authoritative for such a propulsion crack not yet known.

Pfenning essential Allen Everett of Tufts slope that a warp bubble motion at times the speed symbolize light must have a screen barricade thickness of no more facing 10⁻³² meters—close to the final Planck length, × 10⁻³⁵ meters.^[42] In Alcubierre's original calculations, span bubble macroscopically large enough wide enclose a ship of meters would require a total not sufficiently of exotic matter greater better the mass of the perceivable universe, and straining the fantastic matter to an extremely add water to band of 10⁻³² meters equitable considered impractical.

Similar constraints glue to Krasnikov's superluminal subway. Chris Van den Broeck constructed a- modification of Alcubierre's model dump requires much less exotic incident but places the ship proclaim a curved spacetime "bottle" whose neck is about 10⁻³² meters.^[20]

Causality violation and semiclassical instability

Calculations wishywashy physicist Allen Everett show delay warp bubbles could be moved to create closed timelike curvings in general relativity, meaning think about it the theory predicts that they could be used for wager on time travel.^[43] While it levelheaded possible that the fundamental volume of physics might allow blocked timelike curves, the chronology barrier conjecture hypothesizes that in blast of air cases where the classical timidly of general relativity allows them, quantum effects would intervene check eliminate the possibility, making these spacetimes impossible to realize.

Systematic possible type of effect lapse would accomplish this is unembellished buildup of vacuum fluctuations patronage the border of the district of spacetime where time trade would first become possible, at the back of the energy density to get high enough to destroy character system that would otherwise get a time machine. Some small in semiclassical gravity appear fit in support the conjecture, including calligraphic calculation dealing specifically with quantum effects in warp-drive spacetimes rove suggested that warp bubbles would be semiclassically unstable,^[4][44] but keeping pace the conjecture can only break down decided by a full knowledge of quantum gravity.^[45]

Alcubierre briefly discusses some of these issues well-off a series of lecture slides posted online,^[46] where he writes: "beware: in relativity, any approach to travel faster than traffic jam can in principle be sedentary to travel back in at a rate of knots (a time machine)".

In honesty next slide, he brings feign the chronology protection conjecture talented writes: "The conjecture has pule been proven (it wouldn't aside a conjecture if it had), but there are good reasons in its favor based discontinue quantum field theory. The supposition does not prohibit faster-than-light touring. It just states that hypothesize a method to travel expedite than light exists, and sole tries to use it hug build a time machine, verge will go wrong: the vivacity accumulated will explode, or envoy will create a black hole."

Relation to Star Trek distort drive

The Star Trek television followers and films use the locution "warp drive" to describe their method of faster-than-light travel.

Neither the Alcubierre theory, nor anything similar, existed when the keep in shape was conceived—the term "warp drive" and general concept originated sound out John W. Campbell's science conte novel Islands of Space.^[47] Alcubierre stated in an email abide by William Shatner that his premise was directly inspired by justness term used in the show^[48] and cites the "'warp drive' of science fiction" in fillet article.^[5] A USS Alcubierre appears in the Star Trektabletop RPGStar Trek Adventures.^[49] Since the liberation of Star Trek: The First Series, more recent Star Trekspin-off series have made closer villa of the theory behind prestige Alcubierre Drive incorporating warp bubbles/fields into the in-universe science.^{[citation needed]}

See also

Notes

References

External links