Timeline for What could possibly power an Alcubierre drive?
Current License: CC BY-SA 4.0
17 events
| when toggle format | what | by | license | comment | |
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| Oct 18, 2019 at 15:24 | vote | accept | HolocronCollector | ||
| Oct 9, 2019 at 14:07 | comment | added | Eric Towers | @MichaelS : If I follow the link I gave, I find the story for a readily observed effect: the predicted current in semiconductors is too low if you only account for electrons. Call them quasiparticles, as the widely available literature does, or call them nonexistent as you do, they are a necessary component of the current, so by any reasonable definition, they exist. And, to your second comment: You are describing the Dirac Sea; the Dirac sea story is already present in the Answer. | |
| Oct 9, 2019 at 4:11 | comment | added | MichaelS | @stix: The fact that holes require the existence of protons is critical to the analogy. Protons are already the positively-charged matter we want, so it's trivial to conclude positively-charged matter can exist. The Casmir effect analogy would be a world with zero protons (positrons, etc.) anywhere, then creating a positively-charged particle by removing an electron that isn't there. | |
| Oct 9, 2019 at 4:07 | comment | added | MichaelS | @EricTowers: If you follow the link you gave, you'll find that electron holes don't exist. They're a convenient shorthand to describe complex systems in a simple way. A hole really is just a proton (or the collective effect of billions of protons acting on billions plus a couple of electrons). It's not the sudden emergence of a positively-charged, electron-like thing out of a vacuum. | |
| Oct 8, 2019 at 15:19 | comment | added | J... | @stix Yes, it is bad phrasing - science only works because we are very precise in what we say. It is not just misleading, it is fundamentally wrong to say that a doped semiconductor is charged. Needs revision. It's otherwise quite a good answer. | |
| Oct 8, 2019 at 15:14 | comment | added | stix | @MichealS This is not true. Holes are very much treated as mobile in semiconductor design. The fact that they come from the existence of protons is irrelevant since it is the absence of the electron's charge cancelling the proton's charge that makes them exist. It's just as correct to say the hole annihilates with an electron and a new hole takes its place one atom over as it is to simply say the hole moved. It is this property that makes them directly analogous to the Dirac Sea. | |
| Oct 8, 2019 at 15:01 | comment | added | Eric Towers | @MichaelS : Electron holes are mobile quasiparticles and protons are not. In a semiconductor valence band, electron states with energies near the top of the band have negative effective masses -- meaning they move as if they were positively charged -- and these states contribute to current in the material. In semiconductors, p-doped regions have negatively charged particles and excess positively charged quasiparticles moving in opposite directions. Both contribute to conductivity. | |
| Oct 8, 2019 at 14:53 | comment | added | stix | @J... Bad phrasing on my part. The doping makes it easier for specific charges to flow. | |
| Oct 8, 2019 at 13:38 | comment | added | J... | Doped silicon is not charged - it is charge neutral. | |
| Oct 8, 2019 at 12:18 | comment | added | M i ech | As Hypnosifl and benrg noted, this answer mixes true basic statements with errors and misconceptions in way which crafts convincing sounding lie (I always say that best lies have foundation of truth, especially when based on widely known or easily verifiable facts, and introduce fabrications in parts which due to complexity mark is likely to just trust the con artist after accepting and verifying the foundation). Now, since question is not marked with "hard science" or even "science based" tag, this answer fits general needs of soft sci-fi author's worldbuilding. | |
| Oct 8, 2019 at 11:41 | comment | added | Jens | The absence of something is not equivalent to negative something. While the Einstein Field Equations allow for negative curvature of space time, the hard physics is that the prerequisites for an Alcubierre drive are best described as Use unobtainium here plus let some magic happen. There exist as much unicorns as working ADs and there's every reason it will be like that for eternity. | |
| Oct 8, 2019 at 7:14 | comment | added | benrg | The Casimir force is a quantum correction to the electromagnetic force that has been widely misunderstood as a vacuum effect because it doesn't go to infinity in the α→∞ limit. See Jaffe (2005). Gravity is different from the other forces because it is spin-2 and the others are spin-1. Spin-1 forces have a charge conjugation symmetry while spin-2 forces don't. Monopole doesn't mean what you seem to think. This answer is a mess of misconceptions and fringe science; please don't upvote it just because it suggests that we'll have a Star Trek future. | |
| Oct 8, 2019 at 2:59 | comment | added | MichaelS | Of note: "Holes" in electrical components are, in fact, positively charged particles, also known as protons. The distinction is that protons are usually tightly bound in the nucleus and don't actually move, instead forcing the electron to come to the hole. (Ions, such as minerals dissolved in water, often have moving charges that are both positive and negative, moving in opposite directions.) | |
| Oct 8, 2019 at 0:51 | comment | added | Hypnosifl | "the accelerating expansion means that empty space has negative curvature" I don't think this is correct either, according to general relativity's Friedmann equations used in cosmology, the question of whether space has positive, zero, or negative (hyperbolic) curvature depends on whether the average energy density of matter/energy throughout space is above, equal to, or below a certain (positive) "critical density", see here for example. | |
| Oct 8, 2019 at 0:42 | comment | added | Hypnosifl | "This may not sound weird, but what it's basically saying is that the negatively-curving space has a negative mass-energy density!" As I said in my comment on Starfish Prime's answer, this is a misconception--dark energy is sometimes said to have negative pressure, but in the main cosmological models that use it, especially the lambda-CDM model which is the current favorite, dark energy has positive energy density. | |
| Oct 7, 2019 at 23:29 | history | edited | stix | CC BY-SA 4.0 |
grammar fixes
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| Oct 7, 2019 at 22:09 | history | answered | stix | CC BY-SA 4.0 |