Alcubierre Warp Drive Slashes Energy Demand as Quantum Limits Loom

PBS Space Time

Mathematical refinements reduce the Alcubierre drive's negative energy requirements to milligram scales, but quantum chronology limits and the lack of macroscopic negative mass keep practical deployment centuries away.

AI-assisted summary of Is The Alcubierre Warp Drive Possible? | Space Time | PBS Digital Studios — original source. Check the original for full context.

Source published: 2015-10-28

Key ideas

Physicist Miguel Alcubierre formulated a general relativity metric allowing effective faster-than-light travel by contracting spacetime in front of a flat bubble and expanding it behind, avoiding acceleration forces on the ship. (2:03)
The primary physical barrier to the Alcubierre warp drive is the requirement for negative mass-energy, which lacks confirmed macroscopic existence despite small negative pressure effects seen in the Casimir effect. (2:03)
Theoretical modifications—such as field wall thickening, oscillation, and expanding internal volume—have reduced hypothetical energy requirements from more mass-energy than the observable universe down to milligrams. (3:57)
NASA's Eagleworks Laboratory has utilized miniature Michelson interferometers to test whether positive energy fields could yield detectable warp effects, though practical warp travel remains centuries away. (6:10)

Detailed notes

## Background Published by PBS Space Time on YouTube on October 28, 2015, this video explores whether humanity can realistically achieve faster-than-light travel using Miguel Alcubierre's warp drive metric. The episode investigates whether the fabric of spacetime can be warped to break the cosmic speed limit and examines why NASA's Eagleworks Laboratories has looked into the concept.

## TL;DR Host Matt explains how the Alcubierre warp drive bypasses the cosmic speed limit by expanding and contracting spacetime around a flat-space bubble rather than moving an object through space. Although mathematically valid within general relativity, the concept demands exotic negative mass-energy, encounters causality paradoxes under Hawking's chronology protection conjecture, and likely requires pre-built 'warp highways.' While theoretical refinements have dramatically lowered the required energy from cosmic scales down to milligrams, practical warp capability remains centuries away from realization. The episode concludes with a community Q&A covering the eLISA mission, the BICEP2 cosmic dust false alarm, and the debunking of alien megastructure theories around KIC 8462852.

## Atmosphere & style The presentation blends rigorous theoretical physics with an approachable, dry wit that leans into classic science fiction fandom, playfully referencing everything from Hitchhiker's Guide to the Galaxy to Doctor Who. Matt's delivery is measured and intellectually engaging, steadily walking viewers down from wide-eyed speculative sci-fi fantasies into the stark realities of negative energy and general relativity. The concluding community Q&A gives the video a warm, communicative atmosphere, ending on self-aware deadpan humor about spectroscopic methane detection and his production team.

## Bulletin - [02:03](https://www.youtube.com/watch?v=94ed4v_T6YM&t=123s) Physicist Miguel Alcubierre formulated a general relativity metric allowing effective faster-than-light travel by contracting spacetime in front of a flat bubble and expanding it behind, avoiding acceleration forces on the ship. - [02:03](https://www.youtube.com/watch?v=94ed4v_T6YM&t=123s) The primary physical barrier to the Alcubierre warp drive is the requirement for negative mass-energy, which lacks confirmed macroscopic existence despite small negative pressure effects seen in the Casimir effect. - [03:57](https://www.youtube.com/watch?v=94ed4v_T6YM&t=237s) Theoretical modifications—such as field wall thickening, oscillation, and expanding internal volume—have reduced hypothetical energy requirements from more mass-energy than the observable universe down to milligrams. - [06:10](https://www.youtube.com/watch?v=94ed4v_T6YM&t=370s) NASA's Eagleworks Laboratory has utilized miniature Michelson interferometers to test whether positive energy fields could yield detectable warp effects, though practical warp travel remains centuries away.

## Key takeaways - [00:03](https://www.youtube.com/watch?v=94ed4v_T6YM&t=3s) While special relativity bars matter and information from moving through space faster than light, general relativity imposes no such speed limits on the expansion or contraction of spacetime itself. - [02:03](https://www.youtube.com/watch?v=94ed4v_T6YM&t=123s) Miguel Alcubierre reverse-engineered Einstein's field equations by first proposing a metric with a flat interior bubble and curved outer walls before calculating the required mass-energy distribution. - [02:03](https://www.youtube.com/watch?v=94ed4v_T6YM&t=123s) A vessel inside an Alcubierre warp bubble remains in an uncurved, inertial local frame, experiencing zero g-forces despite superluminal apparent velocity. - [02:03](https://www.youtube.com/watch?v=94ed4v_T6YM&t=123s) Generating the Alcubierre geometry demands negative energy density, which would require exotic matter with negative mass that may not physically exist. - [03:57](https://www.youtube.com/watch?v=94ed4v_T6YM&t=237s) Faster-than-light trajectories can create closed timelike curves, leading Stephen Hawking to propose the Chronology Protection Conjecture, which suggests quantum gravity would prevent warp drive operation. - [03:57](https://www.youtube.com/watch?v=94ed4v_T6YM&t=237s) Warp drive generation requires field components positioned ahead of the ship, suggesting paths would need to be pre-constructed at sub-light speeds as 'warp highways'. - [03:57](https://www.youtube.com/watch?v=94ed4v_T6YM&t=237s) Iterative refinements reduced the theoretical negative mass-energy budget from the scale of the observable universe down to the mass of Jupiter, an asteroid, and ultimately milligrams using TARDIS-style internal geometric expansion. - [06:10](https://www.youtube.com/watch?v=94ed4v_T6YM&t=370s) Eagleworks Laboratories attempted to detect micro-scale warp field signatures using a mini-Michelson interferometer, but results remain inconclusive and debated. - [06:10](https://www.youtube.com/watch?v=94ed4v_T6YM&t=370s) Sub-light propulsion technologies like the artificial black hole Kugelblitz engine present fewer fundamental physics obstacles and will likely precede any potential warp travel. - [07:12](https://www.youtube.com/watch?v=94ed4v_T6YM&t=432s) eLISA is a planned European Space Agency gravitational wave mission targeting higher-frequency sources like galactic binary systems, slated for 2034 after NASA withdrew due to budget cuts. - [07:12](https://www.youtube.com/watch?v=94ed4v_T6YM&t=432s) The claimed BICEP2 primordial gravitational wave detection was shown to be galactic dust interference, highlighting why gravitational wave detectors enforce rigorous data verification. - [07:12](https://www.youtube.com/watch?v=94ed4v_T6YM&t=432s) As with quantum mechanics leading unpredictably to the transistor and modern computing, basic research into general relativity and gravitational waves can yield unforeseen technological revolutions. - [07:12](https://www.youtube.com/watch?v=94ed4v_T6YM&t=432s) Irregular light curve dips in star KIC 8462852 are overwhelmingly likely to be natural phenomena like cometary debris rather than alien megastructures. - [09:33](https://www.youtube.com/watch?v=94ed4v_T6YM&t=573s) The initial discovery of extraterrestrial life is more likely to arise from spectroscopic detection of biogenic atmospheric methane on exoplanets than from artificial radio transmissions.

## Detailed walkthrough ### [00:03](https://www.youtube.com/watch?v=94ed4v_T6YM&t=3s) Turning Science Fiction into General Relativity

Faster-than-light (FTL) travel has long been a staple of science fiction, enabling starships in franchises like *Star Trek* to cross galaxies at hundreds of times the speed of light. Without such narrative shortcuts, realistic travel capped at the cosmic speed limit of $c$ would make for painfully boring storytelling—Han Solo, for instance, would have required 40 years to complete the Kessel Run in 12 parsecs if limited to light speed. Inspired directly by Gene Roddenberry's choice of the word "warp," Mexican physicist Miguel Alcubierre set out to turn this iconic concept into an actual mathematical solution within Albert Einstein's theory of general relativity. In doing so, he produced what Matt characterizes as “pretty much the ultimate in fan fiction.”

Yet the research is treated seriously enough that NASA's Eagleworks Laboratories has conducted experiments attempting to produce and detect warp fields. The theoretical loophole that makes this concept conceivable rests on the definition of the cosmic speed limit itself. Einstein's speed limit governs matter, energy, and information moving *through* space, but general relativity places no such restriction on the motion or expansion of spacetime itself. In the natural universe, distant galaxies recede from one another faster than light due to the expansion of space, and inside the event horizon of a black hole, spacetime cascades toward the central singularity faster than light, sweeping matter, light, and everything else along with it.

[02:03](https://www.youtube.com/watch?v=94ed4v_T6YM&t=123s) Reverse-Engineering Einstein's Equations: The Alcubierre Metric

Standard solutions in general relativity begin with a known mass-energy distribution—such as the extreme positive energy density at a point that defines a black hole—to deduce how spacetime curves. Alcubierre instead worked backward: he wrote down a metric tensor describing the desired geometry first, effectively giving the answer before knowing the question. As Matt puts it: “It's sort of like giving the answer before you have the question. So, 42.”

Alcubierre’s metric describes a bubble of flat spacetime enclosed within a shell of severe curvature. Spacetime contracts directly in front of the bubble and expands behind it, causing the bubble itself to be pushed and pulled along like a conveyor belt. A starship riding inside this bubble remains in an uncurved local frame, experiencing zero acceleration or g-forces, while moving at speeds constrained only by the warp field's intensity.

```mermaid flowchart LR accTitle: Alcubierre Warp Bubble Geometry accDescr: Diagram illustrating spacetime contracting in front and expanding behind a flat central bubble. subgraph WarpDrive["Alcubierre Warp Mechanism"] direction LR A["Contracting Spacetime (In Front of Bubble)"] --> B["Flat Spacetime Bubble (Starship at Rest / Zero Gs)"] B --> C["Expanding Spacetime (Behind the Bubble)"] end ```

The mathematical validity of working backward does not guarantee physical feasibility. When solving Einstein's field equations for the Alcubierre metric, the required energy density turns out to be negative. To establish the necessary geometry, a toroidal ring of negative energy density must encircle the ship. While negative pressure effects exist on quantum scales via the Casimir effect, producing macroscopic negative energy densities would require exotic matter with negative mass—a hypothetical substance reminiscent of sci-fi's "element zero" that may simply not exist.

[03:57](https://www.youtube.com/watch?v=94ed4v_T6YM&t=237s) Physical Paradoxes and Energy Optimization

Beyond the elusive requirement of negative mass, the Alcubierre warp drive faces formidable theoretical hurdles: - **Causality and Time Travel:** Any mechanism allowing faster-than-light travel can theoretically be configured as a closed timelike curve (a time machine). - **Hawking's Chronology Protection Conjecture:** Matt highlights that “Stephen Hawking chronology protection conjecture states that quantum mechanics will always stop causality-breaking actions.” This implies that a unified theory of quantum gravity would inherently forbid warp drives, possibly by bombarding the interior of the bubble with lethal Hawking radiation generated by the extreme curvature of the bubble walls. Matt jokes: “Does anyone else get the idea that Stephen Hawking really doesn't want us to build time machines? Suspicious.” - **Field Placement (Warp Highways):** Because parts of the negative energy distribution must sit outside the warp bubble itself, an unassisted ship would leave its own warp-generating field behind upon accelerating. A proposed workaround involves laying down external negative-energy conditions along a pre-constructed route ahead of time—a "warp highway." This requires the initial construction run to be completed at conventional, sub-light speeds.

```mermaid flowchart TD accTitle: Reduction of Warp Drive Energy Requirements accDescr: Flowchart tracking how theoretical revisions dramatically dropped the negative energy requirements. subgraph EnergyOptimizations["Theoretical Mass-Energy Reductions"] A["Original Alcubierre Metric (Exceeds Positive Energy of Observable Universe)"] --> B["Early Refinements (Equivalent to Mass of Jupiter)"] B --> C["Thickened Field Walls (Mass of the Moon or an Asteroid)"] C --> D["Rapid Field Oscillation / Hyperspace (Reduced to Kilograms)"] D --> E["TARDIS-Style Internal Expansion (Reduced to Milligrams / Quantum Scale)"] end ```

Early calculations of the Alcubierre drive called for more negative mass-energy than the entire positive mass-energy present in the observable universe. Subsequent mathematical refinements systematically reduced these catastrophic energy demands: - Adjusting bubble geometries dropped the requirement to the mass equivalent of Jupiter. - Thickening the walls of the warp field lowered the negative mass-energy target to the mass of the Moon or an asteroid. - Rapidly oscillating the warp field to tap hypothetical higher-dimensional modifications reduced the necessary exotic mass to kilograms. - Shrinking the external boundary while expanding the interior volume—reminiscent of the *Doctor Who* TARDIS—reduced the mass requirements to milligrams, opening the possibility that microscopic Casimir-effect vacuum fluctuations might suffice without macroscopic exotic matter.

[06:10](https://www.youtube.com/watch?v=94ed4v_T6YM&t=370s) Laboratory Tests and Long-Term Feasibility

Inspired by these optimized calculations, NASA's Eagleworks Laboratory constructed an experiment using a mini-Michelson interferometer—analogous to the interferometers used for gravitational wave detection—to look for minuscule optical path-length shifts produced by artificial warp fields. While Eagleworks tests utilize positive energy density and have yielded occasional intriguing readings, interpreting the signals remains extraordinarily difficult and contentious.

Matt argues that practical warp travel remains centuries away, if it is possible at all: - Human expansion into deep space will rely on sub-light interstellar starships centuries before warp physics is mastered. - Theoretical alternatives like the Kugelblitz engine (a starship powered by a microscopic artificial black hole) present fewer fundamental physics hurdles than the warp drive. - Realizing warp capability will demand the industrial and scientific scale of an advanced interplanetary or interstellar civilization: “Honestly, I think it's going to take an actively interstellar, or at least interplanetary, human race to motivate the monumental advancements needed to build the first warp drive.”

[07:12](https://www.youtube.com/watch?v=94ed4v_T6YM&t=432s) Community Q&A: Gravitational Waves and Megastructures

Matt transitions to answering viewer questions stemming from the previous episode on gravitational waves:

- **eLISA / LISA Mission:** In response to Renato Grigoli and others, Matt discusses the Evolved Laser Interferometer Space Antenna (eLISA), an upcoming space-borne European Space Agency mission scheduled for launch in 2034. Originally a joint project with NASA before US funding cuts forced NASA's withdrawal and a downscaled mission profile, eLISA will target higher-frequency gravitational waves than Advanced LIGO, allowing it to detect galactic binary star systems. - **BICEP2 and Quadrupoles:** Responding to psantochi regarding BICEP2's claimed detection of primordial B-mode polarization in the cosmic microwave background, Matt notes that the detection is now widely attributed to galactic dust interference rather than gravitational waves, prompting the rule of thumb: “The lesson-- quadruple check your quadrupole.” This false alarm explains why the LIGO collaboration has maintained strict silence pending exhaustive end-of-year data checks. - **Practical Applications of Foundational Physics:** To MrSh1pman's question about whether finding gravitational waves will ever produce tangible technology, Matt draws an analogy to the early pioneers of quantum mechanics: “Quantum mechanics began as an abstract musing on the nature of reality. And I doubt that Max Planck and Schrodinger and Bohr imagined that this crazy theory would lead to the invention of the transistor, a quantum mechanical device, let alone the computer, the smartphone, the Apple Watch.” - **Kepler's "Alien Megastructure" (KIC 8462852):** Addressing viewer Tenebrae regarding media sensationalism around Kepler Space Telescope observations of a star undergoing irregular, 20% drops in luminosity, Matt remains deeply skeptical of alien megastructures. The asymmetrical, fragmented light curve points strongly toward natural debris, such as a large swarm of disintegrating comets, reiterating the channel's standard maxim: “It's never aliens.”

[09:33](https://www.youtube.com/watch?v=94ed4v_T6YM&t=573s) Responding to Viewer Comments: Radio Telescopes, Methane, and Gentle Captors

Wrapping up the discussion and addressing community feedback from previous episodes, Matt notes that radio telescopes are currently aimed at an astronomical target of great interest, meaning answers could arrive in short order. Shifting humorously to a comment left by viewer Un Disclosed, Matt defends what might have seemed like a laughable prospect regarding the search for extraterrestrial intelligence. As Matt explains to the commenter, “To Un Disclosed, I say, you laugh, but the first evidence of alien life may be the spectroscopic signature of biogenetic atmospheric methane on another world.” Rather than flashy radio broadcasts or alien spacecraft, humanity's initial confirmation of life beyond Earth may simply come down to detecting the chemical byproduct of biological processes lingering in an exoplanet's atmosphere.

Finally, Matt offers a lighthearted response to viewer Simon Martin's apparent concern over his well-being or studio conditions, playfully assuring the audience with deadpan humor, “To Simon Martin, don't worry. They're holding me very gently.”

## Notable quotes > [06:10](https://www.youtube.com/watch?v=94ed4v_T6YM&t=370s) Honestly, I think it's going to take an actively interstellar, or at least interplanetary, human race to motivate the monumental advancements needed to build the first warp drive. — Matt

## Mentioned Miguel Alcubierre, Albert Einstein, Gene Roddenberry, Star Trek, NASA, Eagleworks Laboratories, Han Solo, Stephen Hawking, Doctor Who, eLISA, European Space Agency, Advanced LIGO, BICEP2, Max Planck, Erwin Schrödinger, Niels Bohr, Kepler Space Telescope, KIC 8462852, Renato Grigoli, psantochi, MrSh1pman, Tenebrae, Un Disclosed, Simon Martin

## Video description Is mankind capable of achieving warp speed?

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Help translate our videos! http://www.youtube.com/timedtext_cs_panel?tab=2&c=UC7_gcs09iThXybpVgjHZ_7g

Inspired by Gene Roddenberry’s Star Trek, physicist Miguel Alcubierre set out to transform one of the cornerstones of science fiction iconography, the Warp Drive, into reality. But is it even possible? Can we "warp" the fabric of reality so that we can break the speed of light? And why is NASA actually exploring this potentiality? Join Matt on this week’s episode to learn the physics of what's physically possible!

“What Happens At The Edge of the Universe”: https://www.youtube.com/watch?v=AwwIFcdUFrE

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COMMENTS:

Renato Grigoli (Chopin) https://www.youtube.com/watch?v=1Tstyqz2g7o&lc=z12rc15qaqynfjuyo04cefsiomezc32hm0g

psantochi https://www.youtube.com/watch?v=1Tstyqz2g7o&lc=z130zhkbkkbfgbrdd23qz1twqyqlfzflq

MrSh1pman https://www.youtube.com/watch?v=1Tstyqz2g7o&lc=z12utvsankqryxov022pcpaxuqifg1hwn04

Tenebrae https://www.youtube.com/watch?v=1Tstyqz2g7o&lc=z12etzi4azrbiri4k04ccdxhuufvuvkomd0

Un Disclosed https://www.youtube.com/watch?v=1Tstyqz2g7o&lc=z13jdpchdnzudxmwn04ch3fb0kqgtb1xr2w

Simon Martin https://www.youtube.com/watch?v=1Tstyqz2g7o&lc=z121dldrsnaxunuh404cdhlwdsytfjiaabk

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REFERENCES:

Alcubierre 1994 http://arxiv.org/abs/gr-qc/0009013

Krasnikov 1995 http://arxiv.org/abs/gr-qc/9511068

Van Den Broeck 1999 http://arxiv.org/abs/gr-qc/9906050

Krasnikov 2002 http://arxiv.org/abs/gr-qc/0207057

Harold White, Warp Field Mechanics 101 http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110015936.pdf

Harold White, Warp Field Mechanics 102 http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130011213.pdf

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[Source](https://www.youtube.com/watch?v=94ed4v_T6YM)

中文简报

阿库别瑞曲速引擎大幅降低能量需求，但仍面临量子限制挑战数学模型的改进已将阿库别瑞引擎所需的负能量降至毫克级别，但量子时序限制以及宏观负质量的缺失，使其实际应用仍需数个世纪。主持人马特解释了阿库别瑞曲速引擎如何通过在平坦空间泡周围膨胀和收缩时空，而非推动物体穿越空间，从而突破宇宙速度限制。尽管在广义相对论中具备数学上的可行性，但该构想需要奇异的负质能，在霍金的时序保护猜想下面临因果律悖论，并且可能需要预先构建“曲速公路”。虽然理论上的优化已将所需的能量从宇宙量级骤降至毫克级别，但实用的曲速能力在几个世纪内仍难以实现。本期节目最后以社区问答作结，探讨了 eLISA 任务、BICEP2 宇宙尘埃虚警事件，以及对 KIC 8462852 外星巨构理论的辟谣。物理学家米格尔·阿库别瑞提出了一种广义相对论度规，该度规通过收缩平坦空间泡前方的时空并膨胀后方的时空来实现超光速旅行，同时避免了飞船承受加速力。 (2:03) 阿库别瑞曲速引擎的主要物理障碍是对负质能的需求，尽管卡西米尔效应中观察到了微弱的负压效应，但宏观负质量的存在尚未得到证实。 (2:03) 诸如加厚场壁、振荡以及扩展内部体积等理论改进，已将假设所需的能量从超过可观测宇宙的质能大幅降低至毫克级别。 (3:57) 美国国家航空航天局（NASA）的鹰工厂实验室已利用微型迈克尔逊干涉仪测试正能量场是否能产生可探测的曲速效应，不过实用的曲速旅行距离实现仍有数百年之遥。 (6:10)

Reading summary

Physicist Miguel Alcubierre's warp drive metric provides a mathematically valid solution within general relativity by manipulating spacetime rather than moving matter through it, yet immense energy demands, causality paradoxes, and the requirement of negative mass make physical realization highly speculative. The Spacetime Metric Loophole (2:03) Einstein's cosmic speed limit establishes that no matter, energy, or information can travel through space faster than light. However, general relativity places no such restriction on the expansion or contraction of spacetime itself, as demonstrated by the accelerating expansion of the distant universe and the faster-than-light cascade of space within a black hole's event horizon. Physicist Miguel Alcubierre exploited this theoretical opening by reverse-engineering Einstein's field equations, determining the required spacetime geometry first rather than beginning with a known mass-energy distribution. Alcubierre's resulting metric defines a bubble of flat spacetime surrounded by a shell of extreme curvature. By contracting spacetime directly ahead of the bubble and expanding it behind, the bubble travels forward like a conveyor belt. A starship positioned within the flat interior would remain in an unaccelerated local frame, experiencing zero g-forces while effectively traveling at speeds limited only by the intensity of the warp field. Exotic Matter and Energy Optimization (3:57) Solving Einstein's equations for the Alcubierre geometry reveals that producing the required curvature demands a toroidal ring of negative energy density surrounding the vessel. Generating this macroscopic negative energy requires exotic matter possessing negative mass—a hypothetical substance that has never been observed and may not physically exist, even though localized negative pressure phenomena appear at quantum scales via the Casimir effect. Early evaluations showed the original Alcubierre design required more negative mass-energy than the total positive mass-energy of the observable universe. Subsequent mathematical models drastically reduced these requirements: adjusting bubble geometries lowered the threshold to the mass of Jupiter, thickening the field walls brought it to the mass of an asteroid, oscillating the field reduced it to kilograms, and contracting the exterior while enlarging the interior volume—analogous to a TARDIS—reduced the need to milligrams, suggesting quantum-scale Casimir fluctuations might theoretically suffice. Causality Paradoxes and Practical Roadblocks (6:10) Even if the mass-energy hurdles are cleared, warp drives introduce profound theoretical paradoxes. Because faster-than-light travel can be arranged to produce closed timelike curves, an operational drive could function as a time machine. Matt notes that Stephen Hawking's chronology protection conjecture suggests quantum gravity will forbid such causality violations, likely by destroying the warp bubble with lethal Hawking radiation generated by the intense wall curvature. Furthermore, because key components of the negative energy field reside outside the bubble, an unassisted ship cannot project its own field forward; external conditions would have to be pre-laid along a "warp highway" at conventional sub-light speeds. Experimental attempts by NASA's Eagleworks Laboratories to detect minute optical path-length shifts with a mini-Michelson interferometer remain contentious. Matt argues that warp drives remain centuries away, projecting that humanity will rely on sub-light interstellar travel or simpler concepts like black-hole-powered Kugelblitz engines long before achieving the scientific and industrial maturity of an interstellar civilization necessary to build a warp drive. Gravitational Wave Observatories and Biosignatures (7:12) Addressing audience questions on related observational physics, Matt emphasizes that foundational research routinely produces unpredictable technological revolutions, comparing gravitational wave studies to early quantum mechanics leading to transistors and modern microprocessors. He details the upcoming European Space Agency eLISA mission, scheduled for 2034 to detect higher-frequency gravitational waves from galactic binary stars following NASA's withdrawal, and cites the BICEP2 collaboration's dust-contaminated false alarm to illustrate why current observatories exercise extreme caution before announcing detections. Regarding the search for extraterrestrial intelligence, Matt dismisses media speculation surrounding Kepler's observations of KIC 8462852, attributing its irregular 20 percent luminosity drops to natural phenomena such as disintegrating comet swarms rather than alien megastructures. He argues that initial confirmation of alien life will almost certainly arrive through spectroscopic detections of biogenetic atmospheric gases like methane on exoplanets, rather than artificial artifacts. While Alcubierre's metric demonstrates that faster-than-light warp geometries are mathematically compatible with general relativity, overcoming negative-mass requirements, quantum causality barriers, and immense engineering hurdles will require scientific advances far beyond humanity's current capabilities.

精炼阅读摘要

主持人 Matt 指出，物理学家 Miguel Alcubierre 提出的曲率驱动度规在数学上证实了广义相对论允许时空产生超光速位移，其核心在于利用时空本身膨胀不受光速限制的几何漏洞；然而，该理论要求尚无法证实的负能量奇异物质，并在因果律、量子引力辐射及工程实现上面临严峻的物理限制。时空膨胀漏洞与阿库别瑞度规的逆向求解 (0:03) 爱因斯坦相对论中的宇宙速度上限 c 仅限制物质、能量和信息在时空内部的相对运动，而广义相对论对时空本身的膨胀、收缩与流动速度并未设立限制。例如在自然宇宙中，遥远星系因空间膨胀以超光速相互远离，而在黑洞事件视界内部，时空以超光速向奇点坍缩并拖拽内部的一切物质。受科幻概念启发，物理学家 Miguel Alcubierre 逆向运用了爱因斯坦场方程：传统的引力计算通常根据已知的质量-能量分布推导时空曲率，而 Alcubierre 则先写下所需几何形态的度规张量，再反推对应的能量条件。该度规构建出一个被强烈弯曲壳层包裹的平直时空泡。泡体前方时空急剧收缩，后方时空急剧膨胀，如同传送带般推动时空泡前进。身处平直气泡内部的飞船处于无弯曲的局部惯性系中，不会承受任何加速度或过载过载，其理论移动速度仅取决于曲率场的强度。负能量密度要求与理论质量尺度的优化 (3:57) 阿库别瑞度规在数学上的自洽性并未解决其物理实现困境。代入爱因斯坦场方程计算后，维持该几何形态必须在飞船外围布置一个环形的负能量密度分布。尽管量子力学中的卡西米尔效应（Casimir effect）展示了微观尺度的负压现象，但宏观负能量需要具备负质量的奇异物质，而这种物质在物理现实中可能根本不存在。在最初的数学推导中，维持该气泡运转所需的负质量能量甚至超过了整个可观测宇宙的正质能总和。随后的理论修正逐步降低了极端能量要求。研究者通过调整气泡形状将负质能需求降至木星质量，再通过增加场壁厚度将其降低至月球或小行星质量；随后，引入快速场振荡及假想的高维空间修正，将需求缩减至数千克；而采用类似外部极小、内部膨胀的结构，更将质量需求压缩至毫克级别，使利用微观量子真空涨落维持曲率场在理论计算中成为一种极微小的可能性。因果律悖论、量子霍金辐射与现实工程壁垒 (6:10) 在物理自洽性层面，超光速曲率驱动面临根本性的因果律难题。任何超光速移动机制在相对论框架下均可被构造成闭合类时曲线，从而形成时间旅行悖论。史蒂芬·霍金提出的“时序保护猜想”主张量子效应将阻止破坏因果律的行为，这意味着强弯曲泡壁所诱发的极端高能霍金辐射可能会直接摧毁曲率泡内部的飞船。此外，由于部分负能量场必须延伸至曲率泡之外，未受辅助的飞船在加速时会脱离自身产生的场，因此该方案需要预先在航线上以亚光速铺设场发生装置，构建一条“曲率公路”。在实验与工程层面，NASA Eagleworks 实验室虽曾利用微型迈克尔逊干涉仪尝试探测正能量诱发的人造曲率场微弱位移，但其测量信号极其难以解读且充满争议。Matt 认为，实际的曲率推进技术如果可行，也至少需要数百年时间发展；在此之前，人类将完全依赖亚光速深空探测飞船。相比曲率驱动，基于人造微型黑洞的 Kugelblitz 引擎等替代方案在基础物理层面的阻碍较少，而真正的曲率推进将必须依赖成熟的星际或行星际文明工业体系。基础物理转化、引力波探测与深空搜寻警示 (7:12) 关于基础物理发现的现实价值，Matt 以量子力学发展史进行类比：普朗克、薛定谔和玻尔最初进行理论构建时，并未预料到这一框架最终催生了晶体管、计算机与移动通信设备；对引力波等极端物理特性的研究同样蕴含不可预测的长远应用潜力。欧洲空间局计划于 2034 年发射的 eLISA 空间干涉仪，将针对比 Advanced LIGO 更高频段的引力波展开探测，目标锁定银河系内的双星系统。针对前沿观测的可靠性，BICEP2 团队此前误将银河系星际尘埃判定为原初引力波偏振信号的事件，警示科学界必须严格复核四极矩等数据。这种审慎态度也体现在对异常天文现象的解释上：对于开普勒望远镜观测到恒星 KIC 8462852 高达 20% 的不规则光变，Matt 驳斥了外星巨构建筑的媒体炒作，指出不对称的碎裂光变曲线更符合彗星群瓦解等自然演化特征。地外生命的首次确证更可能来自于系外行星大气层中生物来源甲烷的光谱证据，而非人造巨型工程。阿库别瑞曲率驱动从数学上拓宽了广义相对论的应用边界，但受制于负能量物质的缺失、量子引力对因果律的潜在惩罚以及铺设外场的技术限制，目前仍停留在高度假想阶段。在人类文明建立起成熟的行星际工程能力并厘清量子引力统一理论之前，这一概念依然属于理论物理与科学幻想交界的推演模型。

Detailed notes — zh

## Background 本内容由科普频道 PBS Space Time 于 2015 年 10 月 28 日在 YouTube 平台发布。视频由主持人 Matt 讲解，简介指出本期节目探讨了人类是否可能实现超光速曲速飞行、阿库别瑞曲率驱动的物理学原理，以及为何 NASA 鹰工厂实验室（Eagleworks Laboratories）会对此类前沿理论展开实际探索。 ## TL;DR 本期节目深入解析了物理学家米格尔·阿库别瑞提出的“曲率驱动”理论，说明其如何通过压缩前方空间、膨胀后方空间的机制绕过狭义相对论的光速限制。随后，Matt 探讨了该方案面临的严峻物理阻碍，包括需要难以企及的宏观负能量密度、可能引发霍金辐射破坏飞船，以及违背因果律而形成时间机器的悖论。尽管后续理论模型与 NASA 鹰工厂实验室尝试优化并微缩能量需求，但人类距离制造实体曲速飞船仍需数个世纪的突破；最后，节目针对引力波探测、LISA 项目延迟以及塔比星“外星巨型结构”猜想等网友提问进行了严谨澄清。 ## Atmosphere & style 整期视频洋溢着极客硬核科普的思辨魅力与幽默风趣的自嘲气息。Matt 在讲授广义相对论度规张量与量子真空效应等枯燥物理学时收放自如，既能把复杂的时空几何比作“时空传送带”，又频频抛出《星际迷航》和银河系漫游指南“42”等科幻梗。面对外星异构狂热与时间旅行悖论，他始终坚持科学怀疑主义的冷静与克制，在充满智性探索趣味的同时，为观众营造出一种既仰望星空又脚踏实地的沉浸式科普体验。 ## Bulletin - [00:03](https://www.youtube.com/watch?v=94ed4v_T6YM&t=3s) 阿库别瑞曲率驱动利用广义相对论引力场方程的精确解，通过压缩前方时空并膨胀后方时空来规避狭义相对论的光速限制，但必须依赖宏观负能量密度物质维持曲率泡。 - [05:02](https://www.youtube.com/watch?v=94ed4v_T6YM&t=302s) 理论构型优化已将曲率驱动所需的负质量从超越全宇宙质能总和大幅削减至毫克级，NASA 鹰工厂实验室正利用干涉仪尝试探测微型曲率场效应。 - [02:24](https://www.youtube.com/watch?v=94ed4v_T6YM&t=144s) 曲率驱动面临将超光速转化为时间机器的理论悖论，霍金的时序保护猜想及剧烈的霍金辐射可能从根本上阻止其实际运行。 - [07:12](https://www.youtube.com/watch?v=94ed4v_T6YM&t=432s) 针对塔比星（KIC 8462852）异常亮度骤降的外星巨型结构假说，光变特征更符合自然成因的彗星碎片群遮挡，人类首个地外生命迹象更可能来自系外行星的大气甲烷光谱。 ## Key takeaways - [00:03](https://www.youtube.com/watch?v=94ed4v_T6YM&t=3s) 阿库别瑞曲率驱动受《星际迷航》启发，是物理学家通过爱因斯坦广义相对论引力场方程推导出的精确数学解。 - [01:23](https://www.youtube.com/watch?v=94ed4v_T6YM&t=83s) 宇宙光速极限只约束信息和物质在空间内部的局域运动，并不限制两个独立时空区域之间的相对膨胀或收缩速度。 - [01:23](https://www.youtube.com/watch?v=94ed4v_T6YM&t=83s) 曲率泡的运动机制类似时空传送带：前方时空被压缩、后方时空被膨胀，飞船在内部平直时空中保持静止且不承受加速度。 - [01:23](https://www.youtube.com/watch?v=94ed4v_T6YM&t=83s) 阿库别瑞采取逆向求解引力场方程的方法，先设定所需的时空几何度规，再反推出实现该结构所需要的质能分布。 - [02:24](https://www.youtube.com/watch?v=94ed4v_T6YM&t=144s) 维持曲率泡需要包覆一圈具有负能量密度的奇异物质环，但物理学界尚无法证实宏观负质量物质在现实中是否存在。 - [02:24](https://www.youtube.com/watch?v=94ed4v_T6YM&t=144s) 超光速机制可能诱发时间旅行悖论，霍金的时序保护猜想指出底层量子力学定律可能会阻止因果律被破坏。 - [02:24](https://www.youtube.com/watch?v=94ed4v_T6YM&t=144s) 曲率泡边缘极端的时空弯曲可能会激发剧烈的霍金辐射，在曲速航行时对内部飞船造成致命破坏。 - [02:24](https://www.youtube.com/watch?v=94ed4v_T6YM&t=144s) 部分维持曲率场的负能量物质必须布置在曲率泡外部，可能需要人类提前以亚光速沿途铺设“曲速高速公路”。 - [05:02](https://www.youtube.com/watch?v=94ed4v_T6YM&t=302s) 通过加厚曲率场外壁、高频振荡时空场以及引入类似 TARDIS 的高维几何构型，理论所需负质量已被压缩至微观量级。 - [05:02](https://www.youtube.com/watch?v=94ed4v_T6YM&t=302s) NASA 鹰工厂实验室利用迈克尔逊干涉仪探索微型曲率场的光程变化，但信号微弱且解释难度极高。 - [05:02](https://www.youtube.com/watch?v=94ed4v_T6YM&t=302s) 曲率驱动的实际工程实现面临巨大阻碍，相比之下利用微型黑洞作为动力的 Kugelblitz 引擎在物理上更具可行性。 - [07:12](https://www.youtube.com/watch?v=94ed4v_T6YM&t=432s) 由于欧洲空间局 LISA 项目预算受挫及发射推迟，引力波空间探测的发展进程显著慢于地面 LIGO 观测台。 - [07:12](https://www.youtube.com/watch?v=94ed4v_T6YM&t=432s) BICEP 2 误将银河系尘埃偏振信号当成原初引力波的教训，警示引力物理学界在发布前必须严格复核四极矩数据。 - [07:12](https://www.youtube.com/watch?v=94ed4v_T6YM&t=432s) 塔比星的不对称非规整光变曲线表明其遮挡物更可能是彗星碎片群，而非外星文明建造的戴森球或人造巨型结构。 - [09:33](https://www.youtube.com/watch?v=94ed4v_T6YM&t=573s) 人类发现地外生命的第一项确凿证据很可能是系外行星大气层中的生物成因甲烷光谱，而非智慧文明的人造信号。 ## Detailed walkthrough ### [00:03](https://www.youtube.com/watch?v=94ed4v_T6YM&t=3s) 超光速旅行与阿库别瑞曲率驱动的起源超光速旅行（FTL）始终是科幻作品的核心基石。在《星际迷航》（*Star Trek*）中，曲速引擎能让飞船以数百倍光速穿梭银河；若是严格遵守宇宙光速上限，很多经典桥段就会索然无味——比如汉·索罗以光速完成“12秒差距的凯塞尔航线”，足足需要耗费40年时间。然而，这种浪漫幻想不仅吸引了科幻迷，也激发了理论物理学家的探索欲。墨西哥物理学家米格尔·阿库别瑞（Miguel Alcubierre）正是受到吉恩·罗登伯里选用“曲速”（Warp）一词的启发，决心用严肃物理学将这一构想变为现实。阿库别瑞运用爱因斯坦广义相对论的数学语言构建了一种“曲率场”（Warp field），给出了广义相对论引力场方程的一个精确解，从而在理论上实现了超光速旅行。主持人 Matt 调侃这简直是“终极同人小说”，但这一设想远不止停留在幻想层面。NASA 的鹰工厂实验室（Eagleworks Laboratories）甚至已经着手尝试制造并探测微型曲率场。正如主持人所发问的：“如果 NASA 都在研究它，那它一定是靠谱的，对吧？那么我们究竟什么时候才能在银河系中曲速穿梭呢？” ```mermaid flowchart LR accTitle: 从科幻构想到阿库别瑞物理方案 accDescr: 展现从星际迷航概念到阿库别瑞提出广义相对论解并引发 NASA 实验研究的脉络。 A["科幻概念：星际迷航曲速引擎"] --> B["阿库别瑞构建引力场方程精确解"] B --> C["时空几何：曲率泡驱动"] C --> D["前沿验证：NASA 鹰工厂实验室"] ``` --- ### [01:23](https://www.youtube.com/watch?v=94ed4v_T6YM&t=83s) 时空传送带：曲率泡的物理机制与逆向求解曲率驱动之所以没有打破狭义相对论的光速限制，关键在于宇宙速度极限只约束了物质、能量和信息在“空间之中”的运动，广义相对论对两个独立时空区域之间的“相对运动速度”没有任何上限限制。宇宙的加速膨胀就是一个典型例子：即便遥远星系在各自的局域参考系中相对静止，它们彼此远离的速度依然可以大幅超越光速；在黑洞事件视界内部，时空本身向中心奇点瀑布般坍缩的速度同样超越光速，将光线、物质甚至猴子一并卷入其中。通常情况下，物理学家是求解给定正能量密度（质量与能量分布）下的引力场方程，借此推导时空的弯曲方式。但阿库别瑞采取了“反向操作”的巧妙手法：他先假定一个时空度规张量（Metric tensor），描述一个包裹在剧烈弯曲时空外壳中的平直时空泡（曲率泡）。在这个外壳的作用下，泡体后方的空间被急剧膨胀，前方空间被急剧压缩。由于时空本身的推拉，曲率泡能够以理论上不受限制的速度移动，而内部的星舰在平直时空中漂浮，完全感受不到任何加速度。主持人形象地比喻道：“这有点像用时空本身建造了一条传送带。你相对于传送带保持静止，但传送带本身却以超光速运行。” - 宇宙局域光速极限仅限制物体在空间内部的运动，不限制时空织体本身的延展与收缩。 - 曲率驱动机制：前方空间压缩、后方空间膨胀，借助时空本身的动力推动泡体。 - 逆向求解爱因斯坦方程如同“在提出问题之前先给出答案：42”。 --- ### [02:24](https://www.youtube.com/watch?v=94ed4v_T6YM&t=144s) 负能量、时间机器与曲率驱动的物理阻碍虽然数学上可以随心所欲假定时空度规并反推所需的质能分布，但由此推导出的物质形态并不一定符合物理现实。要维持阿库别瑞曲率泡，必须在星舰周围布置一圈具有“负能量密度”（Negative energy density）的物质环。在微观量子尺度上，物理学家可以通过卡西米尔效应（Casimir effect）诱发负压强，但要将其放大到宏观尺度，可能需要诸如《质量效应》中“零号元素”那样的奇异负质量物质，而现代物理学甚至无法确定这种物质是否存在。除了负能量难题，曲率驱动还面临着深刻的理论悖论。原则上，任何超光速装置都可以被改装为时间机器，而斯蒂芬·霍金提出的“时序保护猜想”认为，量子力学定律将始终阻止因果律被破坏。在更深层次的大统一理论（万物理论）中，曲率驱动可能会被底层法则直接扼杀。例如，曲率泡边缘极其剧烈的时空弯曲可能会激发出极其强烈的霍金辐射，瞬间将内部的飞船彻底“烤焦”。面对霍金的种种论断，主持人半开玩笑地质疑道：“还有其他人觉得斯蒂芬·霍金是真的不想让我们造出时间机器吗？这太可疑了。”此外，生成曲率场所需的负能量物质有一部分必须置于曲率泡外部，进入曲速时这部分物质会被抛在身后；一种理论补救方案是像铺设“曲速高速公路”那样，先以亚光速飞完全程并沿途布置负能量场，但这无疑增加了实现的复杂度。 --- ### [05:02](https://www.youtube.com/watch?v=94ed4v_T6YM&t=302s) 能量需求的缩减与 NASA Eagleworks 的实验探索在阿库别瑞最初的计算中，维持曲率泡所需的负能量总量极其惊人，甚至远超整个可观测宇宙中所有正质量与能量的总和。随后的理论修正逐步优化了几何构型： 1. 范登布鲁克（Van Den Broeck）等人的优化将能量需求降至相当于木星质量的量级； 2. 增加曲率场外壁的厚度，可将负质量/能量需求削减至月球乃至小行星级别； 3. 使曲率场高速振荡，借由高维效应“软化”时空织体（字面意义上的“超空间曲速驱动”），所需质量骤降至千克级； 4. 借鉴“TARDIS（神秘博士神秘飞船）”结构，在缩小外部曲率泡的同时扩大内部容积，最终能将所需负质量压缩至毫克级别。当所需尺度缩小到极微观时，或许仅凭卡西米尔效应操控量子真空能量就能满足条件。基于这种乐观前景，NASA 鹰工厂实验室搭建了一台基于迈克尔逊干涉仪的小型装置，试图利用正能量密度制造并测量曲率场引起的微小光程变化。虽然实验室探测到了一些耐人寻味的数据，但信号的解读极具挑战性。Matt 坦言，即便曲率驱动在物理上可行，人类要真正制造出曲速飞船至少还需要几个世纪的时间；相比之下，利用黑洞作为动力源的微型黑洞引擎（Kugelblitz engine）面临的物理障碍都比曲率驱动要少。正如他所预言的那样：“老实说，我认为人类必须先成为一个活跃的星际甚至行星际种族，才能具备推动建造第一台曲速引擎所需的宏大突破。” --- ### [07:12](https://www.youtube.com/watch?v=94ed4v_T6YM&t=432s) 读者问答：引力波、LISA、BICEP 2 与“外星巨型结构” 节目后半段针对上期关于引力波与高级 LIGO（Advanced LIGO）的内容回答了网友提问。关于欧洲空间局主导的太空引力波探测项目 LISA（现为 eLISA，演化型激光干涉空间引力波天文台），Matt 解释其目标频段远高于地面 LIGO，主要用于捕捉银河系内的双星系统。由于预算削减，NASA 退出了该计划，导致整体规模缩水，预定发射时间推迟至 2034 年，令人扼腕。针对此前 BICEP 2 实验宣称探测到宇宙微波背景辐射偏振各向异性（原初引力波）的轰动新闻，后续交叉验证证实该信号其实来自银河系内部尘埃的干扰，Matt 为此总结了物理学界的血泪教训：“这一教训就是——一定要反复四次核查你的四极矩（quadruple check your quadrupole）。”这也是为何 LIGO 在公布任何重大发现前都极度审慎。对于引力波探测是否有实际用途，Matt 认为基础研究往往孕育意想不到的技术跃升：量子力学起初不过是对现实本质的抽象思索，普朗克、薛定谔和玻尔当时绝不可能预见到它会催生晶体管、计算机、智能手机乃至智能手表。最后，针对开普勒太空望远镜观测到塔比星（Tabby's Star，KIC 8462852）亮度骤降 20% 并在媒体上引发的“戴森球/外星巨型结构”狂欢，Matt 给出了冷静的科学判断：光变曲线显示出高度不对称和碎片化的碎屑特征，更吻合彗星群的遮挡。对此他重申了节目的黄金法则： > “现在，这绝对不是一个规整的几何结构。它看起来必须是某种碎片化的团块物质，比如假定中的彗星群。这表明它更可能起源于自然。尽管我可以想象它可能是一个极其庞大、杂乱无章地环绕母星的空间结构殖民地——除了一点：它永远都不可能是外星人。” ### [09:33](https://www.youtube.com/watch?v=94ed4v_T6YM&t=573s) 观众互动与外星生命迹象探讨在节目的结尾互动环节中，主持人马特（Matt）回应了上一期视频留下的悬念以及来自社区观众的评论。针对此前讨论的天体目标（当时备受瞩目的潜在外星异构天体），他提到射电望远镜目前已经对准了该目标展开观测，因此或许很快就会迎来确切的调查结果。随后，马特针对名为“Un Disclosed”的网友留言给出了兼具幽默与科学严谨性的回应。对于观众对某些外星生命推测的调侃，马特指出：尽管大家可能会觉得好笑，但在现实的科学探索中，人类发现地外生命存在的第一项确凿证据，很可能并非直接接收到来自高等智慧文明的信号，而是在另一个世界的系外行星大气层中检测到生物成因的大气甲烷光谱特征。马特原话强调道：“To Un Disclosed, I say, you laugh, but the first evidence of alien life may be the spectroscopic signature of biogenetic atmospheric methane on another world.” 最后，马特以一贯的幽默风格回应了观众 Simon Martin 表达的关心或调侃。他安抚对方无需为他担心，并开玩笑说：“To Simon Martin, don't worry. They're holding me very gently.” 这句调侃仿佛暗示自己是在某种“被胁迫”但被温柔以待的状态下录制节目，为整期节目画上了一个轻松诙谐的句号。 ## Notable quotes > [05:02](https://www.youtube.com/watch?v=94ed4v_T6YM&t=302s) 我认为人类必须先成为一个活跃的星际甚至行星际种族，才能具备推动建造第一台曲速引擎所需的宏大突破。 — Matt ## Mentioned PBS Space Time, Matt, 米格尔·阿库别瑞, 爱因斯坦, 吉恩·罗登伯里, 斯蒂芬·霍金, 马克斯·普朗克, 埃尔温·薛定谔, 尼尔斯·玻尔, 范登布鲁克, 哈罗德·怀特, 星际迷航, 质量效应, 神秘博士, NASA, 鹰工厂实验室, 欧洲空间局, LIGO, LISA, eLISA, BICEP 2, 开普勒太空望远镜, 塔比星, 卡西米尔效应 ## Video description Is mankind capable of achieving warp speed? Tweet at us! @pbsspacetime Facebook: facebook.com/pbsspacetime Email us! pbsspacetime [at] gmail [dot] com Comment on Reddit: http://www.reddit.com/r/pbsspacetime Support us on Patreon! http://www.patreon.com/pbsspacetime Help translate our videos! http://www.youtube.com/timedtext_cs_panel?tab=2&c=UC7_gcs09iThXybpVgjHZ_7g Inspired by Gene Roddenberry’s Star Trek, physicist Miguel Alcubierre set out to transform one of the cornerstones of science fiction iconography, the Warp Drive, into reality. But is it even possible? Can we "warp" the fabric of reality so that we can break the speed of light? And why is NASA actually exploring this potentiality? Join Matt on this week’s episode to learn the physics of what's physically possible! “What Happens At The Edge of the Universe”: https://www.youtube.com/watch?v=AwwIFcdUFrE ------------------------------------------------- COMMENTS: Renato Grigoli (Chopin) https://www.youtube.com/watch?v=1Tstyqz2g7o&lc=z12rc15qaqynfjuyo04cefsiomezc32hm0g psantochi https://www.youtube.com/watch?v=1Tstyqz2g7o&lc=z130zhkbkkbfgbrdd23qz1twqyqlfzflq MrSh1pman https://www.youtube.com/watch?v=1Tstyqz2g7o&lc=z12utvsankqryxov022pcpaxuqifg1hwn04 Tenebrae https://www.youtube.com/watch?v=1Tstyqz2g7o&lc=z12etzi4azrbiri4k04ccdxhuufvuvkomd0 Un Disclosed https://www.youtube.com/watch?v=1Tstyqz2g7o&lc=z13jdpchdnzudxmwn04ch3fb0kqgtb1xr2w Simon Martin https://www.youtube.com/watch?v=1Tstyqz2g7o&lc=z121dldrsnaxunuh404cdhlwdsytfjiaabk ------------------------------------------------- REFERENCES: Alcubierre 1994 http://arxiv.org/abs/gr-qc/0009013 Krasnikov 1995 http://arxiv.org/abs/gr-qc/9511068 Van Den Broeck 1999 http://arxiv.org/abs/gr-qc/9906050 Krasnikov 2002 http://arxiv.org/abs/gr-qc/0207057 Harold White, Warp Field Mechanics 101 http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110015936.pdf Harold White, Warp Field Mechanics 102 http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130011213.pdf ------------------------------------------------- Let us know what topics you want to learn more about:http://bit.ly/spacetimepoll [Source](https://www.youtube.com/watch?v=94ed4v_T6YM)

Source quotes

[5:02] Matt: 我认为人类必须先成为一个活跃的星际甚至行星际种族，才能具备推动建造第一台曲速引擎所需的宏大突破。

Source quotes

[6:10] Matt: Honestly, I think it's going to take an actively interstellar, or at least interplanetary, human race to motivate the monumental advancements needed to build the first warp drive.

Original transcript

[0:03] Rumor has it NASA is actually working [0:04] on a real faster than light warp drive. [0:07] So when do we get our first starship? [0:14] Faster than light travel is a staple of science fiction. [0:17] Star Trek warp drives zip around the galaxy [0:19] at hundreds of times the speed of light. [0:21] But traveling at the real cosmic speed [0:23] limit of 1 times the speed of light [0:25] would make for some pretty dull sci-fi. [0:27] It would have taken Han Solo 40 years [0:29] to make the Kessel Run in 12 parsecs, [0:32] traveling at only light speed. [0:33] It's understandable that both physicists and sci-fi fans [0:40] was so inspired by the idea that he [0:42] decided that the Star Trek warp drive should become a reality. [0:45] In fact, he was inspired by Gene Roddenberry's choice [0:48] of the word "warp." [0:50] Alcubierre constructed a warp field [0:52] in the mathematical language of Einstein's theory [0:55] of general relativity, a real solution [0:57] to the equations of GR that would actually [0:59] allow faster than light travel. [1:01] Yep, pretty much the ultimate in fan fiction. [1:04] But is it actually fiction? [1:06] NASA doesn't seem to think so. [1:08] It's Eagleworks Laboratories is actually [1:10] trying to produce and detect warp fields. [1:13] More on that later. [1:15] But if NASA's researching it, it must be legit, right? [1:19] So when are we going to be warping around the galaxy? [1:21] Let's break this idea apart. [1:23] First, it's important to note that this idea does not [1:25] contradict the principle of a cosmic speed limit. [1:27] That limit, the speed of light, refers [1:29] to things-- mass, energy, information-- [1:32] traveling through space. [1:34] However, according to general relativity, [1:36] there's no limit on the relative speeds of two separate patches [1:39] of spacetime. [1:40] For example, as we talk about in this episode, [1:42] the expansion of the universe means [1:43] that very distant galaxies are moving apart [1:45] from each other faster than light, [1:47] even if the galaxies are relatively still [1:49] in their local frames of reference. [1:51] Also, below the event horizon of a black hole, [1:55] spacetime cascades towards the central singularity [1:58] faster than light, carrying light, matter, monkeys, [2:02] and everything else with it. [2:03] Now, the spacetime around and within a black hole [2:06] is predicted by solving Einstein's field equations [2:09] around a point of extreme positive energy density. [2:12] Basically, mass and energy tell us how space should warp. [2:16] But if you're cheeky, you can actually just make up [2:18] a solution to the equations of GR [2:20] without starting with a real mass/energy distribution. [2:23] That's what Alcubierre did. [2:24] He developed a spacetime description, a metric tensor, [2:27] that describes a volume of nice, flat spacetime enclosed [2:31] in a bubble of extreme curvature, [2:33] a pinching or warping of spacetime in the surrounding [2:36] shell that causes space to expand behind [2:39] and contract in front of the bubble. [2:42] As a result, the bubble is pushed and pulled by spacetime [2:45] itself, moving at speeds only limited [2:47] by the intensity of the warp. [2:49] A starship inside the bubble is carried along for the ride [2:53] while feeling no acceleration at all. [2:55] It's sort of like building a conveyor belt out of spacetime. [2:58] You stand still with respect to the conveyor belt, [3:00] but the belt itself moves faster than light. [3:03] But is this even valid? [3:05] Can you just make up a spacetime description [3:07] and then essentially solve the Einstein equations [3:09] backwards to figure out what arrangement [3:11] of matter and energy would be needed to create it? [3:13] It's sort of like giving the answer [3:15] before you have the question. [3:16] So, 42. [3:17] Yeah, sure you can do this. [3:19] There's just no guarantee that the resulting mass/energy [3:21] distribution would be physically meaningful. [3:24] In fact, when you try to do this for the warp field, [3:26] you find that you need to produce [3:28] a ring of negative energy density in a band [3:31] around the ship to produce the right warp bubble. [3:34] That means our ship looks something like this in order [3:36] to produce a spacetime curvature like this. [3:38] Unfortunately, it may not even be [3:40] possible to make negative energy densities [3:42] on large enough scales. [3:44] We can create something like it, a negative pressure, [3:46] on quantum scales via Casimir effect. [3:49] But on macroscopic scales, you'd probably [3:51] need some sort of exotic negative mass matter, [3:54] like element zero, which is tricky, because there [3:56] may be no such thing. [3:57] There are other minor issues. [3:59] Any FTL device can, in principle, [4:01] be used to make a time machine. [4:03] Excellent! [4:04] Except Stephen Hawking chronology protection [4:08] conjecture states that quantum mechanics will always stop [4:11] causality-breaking actions. [4:13] It suggests that there's something [4:15] in the deeper union of GR and quantum [4:17] mechanics, the theory of everything, [4:19] that prohibits the warp drive. [4:21] One possible quantum disaster is that the extreme spacetime [4:24] curvature of the warp bubble walls [4:26] would roast the interior with crazy Hawking radiation. [4:30] Does anyone else get the idea that Stephen Hawking really [4:32] doesn't want us to build time machines? [4:34] Suspicious. [4:35] Here's another challenge. [4:37] Assuming that you can even make negative mass matter, [4:39] to make a warp field, some of it would [4:41] need to go outside the warp bubble, which [4:43] means it gets left behind when you go to warp speed. [4:46] There are some proposed solutions, one of which [4:49] is to lay down the external negative energy [4:51] conditions along the path before you leave, sort of like a warp [4:54] highway. [4:55] The first trip has to be made at sub light speed. [4:58] But I'm personally cool with the awesomeness of warp highways. [5:02] Last tricky thing-- as Alcubierre [5:04] devised the warp bubble, he figured [5:06] it would take a lot of negative energy. [5:08] In fact, it would take significantly more negative [5:11] energy than there is positive mass/energy [5:13] in the entire observable universe. [5:16] Later refinements brought this down [5:17] to the mass equivalent of Jupiter. [5:20] Either way, not practical. [5:21] Happily, recent reworkings of the bubble geometry [5:24] have cut this down further. [5:25] Thicken the walls of the warp field, [5:27] and you get the negative mass/energy requirement down [5:29] to the equivalent of maybe the moon or even an asteroid. [5:33] Rapidly oscillate the warp field, [5:35] and you hypothetically soften the fabric [5:38] of space via higher dimensional effects-- [5:40] literally, a hyper space warp drive. [5:43] And this brings mass needed down to kilograms. [5:46] Given that we're just making up solutions [5:47] to the Einstein equations, we could even [5:49] shrink down the warp bubble while expanding [5:52] the internal volume, Tardis style, which [5:54] could get us down to needing only milligrams [5:56] of negative mass. [5:58] If the bubble is small enough, then we may not even [6:00] need actual exotic matter. [6:02] Quantum scale manipulation of the vacuum energy [6:05] a la the Casimir effect may be enough. [6:07] Check the description for the sources of all of these ideas. [6:10] Now, this sort of wild optimism has inspired NASA's Eagleworks [6:14] Laboratory to try an experiment to create and detect [6:16] a warp field. [6:18] Now, this would be a field created by positive, not [6:20] negative, energy density. [6:21] But baby steps, right? [6:23] It uses a Michelson interferometer, [6:25] like a mini version of the one being [6:26] used to detect gravitational waves, [6:29] To measure the tiny changes in path length created by a warp [6:32] field. [6:33] Now, some intriguing results have been detected. [6:36] But interpretation is very, very challenging. [6:38] So when are we going to be warping around the galaxy? [6:40] If it's even possible, it'll take several centuries [6:42] at a minimum. [6:44] As I've argued before, we'll reach the stars [6:46] by sub light speed starships long before that. [6:49] Even the Kugelblitz engine, the black hole drive, [6:52] has fewer physics hurdles than the warp drive. [6:54] Honestly, I think it's going to take an actively interstellar, [6:57] or at least interplanetary, human race to motivate [7:00] the monumental advancements needed to build the first warp [7:03] drive. [7:04] The good news is we're going to need a ton of physicists [7:08] to get to that point. [7:09] Let's make it so on the next episode of "Space Time." [7:12] Last week, we talked about gravitational waves, [7:15] and whether the advanced LIGO Observatory has maybe [7:18] seen them. [7:18] You guys had lots of amazing questions, [7:21] so let's get to them. [7:22] Renato Grigoli and others asked, what about the LISA Mission? [7:25] LISA is amazing, although now it's ELISA, the Evolved Laser [7:29] Interferometer Space Antenna. [7:31] It'll be an orbiting gravitational wave observatory [7:33] designed to detect much higher frequency gravitational waves [7:37] than advanced LIGO. [7:38] And this should actually allow it to detect binary star [7:40] systems in our galaxy. [7:42] The program is being developed by the European Space Agency. [7:45] NASA was originally a part of it, [7:47] but had to drop out due to funding cuts. [7:49] And so now, the original plan is scaled back significantly. [7:53] Now, that seems a shame, doesn't it? [7:55] The scheduled launch date is 2034. [7:58] psantochi asks if we have any comments on the BICEP 2 [8:00] experiment. [8:01] OK. [8:01] So this was the much hyped gravitational wave detection [8:06] based on polarization anisotropies [8:08] in the cosmic microwave background radiation that [8:10] came out earlier this year. [8:12] Yeah. [8:12] So now, the money is on the signal actually [8:14] being due to dust, not G waves. [8:17] The lesson-- quadruple check your quadrupole. [8:20] This is why LIGO won't say anything [8:23] until at least the end of the year. [8:24] Now, MrSh1pman wants to know, if we find these G waves, [8:27] will it change anything? [8:29] Can we build something cool with them? [8:31] Well, maybe. [8:32] Quantum mechanics began as an abstract musing [8:35] on the nature of reality. [8:36] And I doubt that Max Planck and Schrodinger and Bohr [8:40] imagined that this crazy theory would [8:42] lead to the invention of the transistor, [8:44] a quantum mechanical device, let alone [8:46] the computer, the smartphone, the Apple Watch. [8:49] Tenebrae wants our thoughts on that amazing new Kepler Space [8:52] Telescope result that the media is [8:53] hyping that there's an alien megastructure eclipsing [8:56] a distance star. [8:57] Now, this is a stunning result. But as we say on "Space Time," [9:01] it's never aliens. [9:03] Check out the actual signal that reveals [9:05] this eclipsing material. [9:06] Those dips are the drops in the star's brightness [9:08] from some stuff moving in front of the star. [9:11] It's dimmed by a crazy 20% at some points. [9:14] Now, this is definitely not a clean geometric structure. [9:17] It looks like it has to be some fragmented clumpy material, [9:20] like the proposed swarm of comets. [9:22] That suggests a natural origin. [9:24] Although I imagine it could possibly be insanely vast [9:27] ragtag colony of space structures surrounding a parent [9:30] planet== except it's never aliens. [9:33] Radio telescopes are now pointed at it. [9:35] So perhaps we'll know pretty soon. [9:37] To Un Disclosed, I say, you laugh, [9:39] but the first evidence of alien life [9:41] may be the spectroscopic signature [9:43] of biogenetic atmospheric methane on another world. [9:46] To Simon Martin, don't worry. [9:48] They're holding me very gently.