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There was a time where relativists realized that instead of solving the Einstein equations subject to initial conditions coupled to some matter stress energy te

There was a time where relativists realized that instead of solving the Einstein equations subject to initial conditions coupled to some matter stress energy terms, they could instead fully specify what spacetime looks like, ram it through the Einstein equations and get a stress energy tensor on the right hand side. The Einstein equations became a recipe generator: if you want this spacetime, then you need this matter/energy. Unfortunately, all the interesting spacetimes (such as the Alcubierre drive) require exotic matter, matter unlike anything we have ever seen. Other spacetimes people were interested in generating were stable wormholes. If we could ever produce such matter then we could start some spacetime engineerinng. Meanwhile, we are left with these oddities. I heard that Alcubierre somewhat regrets having his name on this spacetime as he gets contacted by all kinds of Star Trek fans and other people who believe they can produce the drive. He has done all kinds of other quality research in General Relativity, but this is what he will be famous for.

King-Aaron 8y ago
> he gets contacted by all kinds of Star Trek fans and other people who believe they can produce the drive. I would genuinely love to read some of the exchanges between Alcubierre and these people.
- ailideex 8y ago
  What makes you think he engages with them?
  - SiempreViernes 8y ago
    Some might be polite and somewhat knowledgeable (though most won't be either).
  - memberZero 8y ago
    make it so
  - thanatropism 8y ago
    In the late 90s to early 2000s I was a teenager and communicated with various scientists and academics via email, some of which had something of a mentor role. By those experiences I'd say someone like Alcubierre is more likely to engage young ducklings than, say, Michio Kaku.
- light_hue_1 8y ago
  No problem: https://www.youtube.com/watch?v=5q_z8BjiYng https://www.youtube.com/watch?v=5q_z8BjiYng This is one example of many. The original poster was just spreading FUD and saying nasty things about Alcubierre as a researcher. He gives talks like this all the time, he refers to his own work as a warp drive, he quotes and shows off Star Trek, etc. This isn't an issue of crazies trying to steal someone's research.
magicalhippo 8y ago
That Michio Kaku episode[1] on Discovery where he said[2] that we might be able to harness the Casimir effect as a source of the negative energy needed for the Alcubierre drive probably didn't help. There are more realistic explanations[3] for the Casimir effect however, so no Alcubierre drive for us anytime soon. [1]: Think it was this show https://en.wikipedia.org/wiki/Sci_Fi_Science:_Physics_of_the_Impossible https://en.wikipedia.org/wiki/Sci_Fi_Science:_Physics_of_the... [2]: To be fair, Alcubierre suggested it himself first [3]: https://en.wikipedia.org/wiki/Casimir_effect#Relativistic_van_der_Waals_force https://en.wikipedia.org/wiki/Casimir_effect#Relativistic_va...
- ben_w 8y ago
  Even if your [3] doesn’t apply, I believe the Casimir effect doesn’t scale fast enough — even a cavity made from proton-sized parts will never exclude more vacuum energy than the mass energy of those protons: https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casimir-cavity-be-used-to-construct-true-negative-mass-metamaterials/ https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casim...
EastLondonCoder 8y ago
This is very true, it’s also worth mentioning that all ways of faster than light travel means travel back in time in some reference frame which in breaks causality.
- magicalhippo 8y ago
  Here's a good (IMHO) video showing how this works out, by looking Minkowski diagrams for different observers. https://www.youtube.com/watch?v=HUMGc8hEkpc https://www.youtube.com/watch?v=HUMGc8hEkpc
- computerfriend 8y ago
  Breaking causality is allowed, though.
- garmaine 8y ago
  Breaking causality is allowed by the laws of physics.
- zamalek 8y ago
  You don't travel faster than light with the Alcubierre Drive, you circumvent travel entirely. Spacetime does the traveling, not the ship.
Razengan 8y ago
> If we could ever produce such matter then we could start some spacetime engineering. Imagine the exotic "pollution" caused by civilizations which are advanced enough to tinker with the fabric of spacetime, but not advanced enough to understand (or care about) the long-term consequences of that tinkering. Destabilizing solar systems or even entire galaxies, maybe even violating causality.. Imagine the home (and only) planets of younger, insignificant civilizations being caught up in those cataclysms, all traces of their existence wiped from cosmic history in what might amount to the equivalent of a traffic accident or "oil spill" of a greater civilization. ..maybe that has already happened and some of the leviathanic voids we've observed were a result of that? :) [0] https://en.wikipedia.org/wiki/Void_(astronomy) https://en.wikipedia.org/wiki/Void_(astronomy)
- SiempreViernes 8y ago
  Well, there was that time Earth was demolished to make room for a bypass. I'm not sure I recall all the details but I think the universe ended as a convoluted consequence?
  - Razengan 8y ago
    Yep, that is exactly what I was thinking about. :)
- golergka 8y ago
  That sounds like some great sci fi, actually.
  - Razengan 8y ago
    Ever since I played the awesome old RPG called Planet's Edge [0] and the better-known Star Control II, I've been taken to muse about cosmic coincidences. Popular sci-fi like Star Wars or Star Trek etc. don't really touch on those possibilities in a convincing way. As in, very few fiction truly conveys the ..indifference.. of the universe, and all the actors in it going about their own businesses and interacting only incidentally, even if to monumental consequences to each other, but without a lot of conscious intent or an overarching plan. Kind of like how most of Earth's history has played out, even if it may all seem interconnected and purposeful due to the much more relatable scales involved. [0] https://en.wikipedia.org/wiki/Planet%27s_Edge https://en.wikipedia.org/wiki/Planet%27s_Edge
Hydraulix989 8y ago
Is there nothing interesting within the constraint of a reasonable stress energy tensor?
- Eochei5h 8y ago
  Black holes and possibly topological defects.
exoesquitur 8y ago
.... But you make one warp drive....
JumpCrisscross 8y ago
> all the interesting spacetimes (such as the Alcubierre drive) require exotic matter Does it have to be matter? Or could we coax the vacuum into behaving as if it were occupied by exotic matter?
- ailideex 8y ago
  Matter is just excitation in the vacuum. But excitation with positive energy. What is needed is excitation with negative energy.
light_hue_1 8y ago
> I heard that Alcubierre somewhat regrets having his name on this spacetime as he gets contacted by all kinds of Star Trek fans and other people who believe they can produce the drive. He has done all kinds of other quality research in General Relativity, but this is what he will be famous for. This is untrue, it's really offensive to a person that's dedicated years of his life to this research, and it set a terrible tone for the rest of the comments. He gives talks all the time to groups that are interested in developing a "warp drive". He puts up photos of Star Trek in his talks! He even refers to his own work as potentially developing a "warp drive". Look at one of his recent talks https://www.youtube.com/watch?v=5q_z8BjiYng https://www.youtube.com/watch?v=5q_z8BjiYng and please stop spreading negative rumors about scientists.
- warent 8y ago
  As an aside, I'm loving this talk (the YouTube video). Thank you for sharing

King-Aaron 8y ago

> he gets contacted by all kinds of Star Trek fans and other people who believe they can produce the drive. I would genuinely love to read some of the exchanges between Alcubierre and these people.

ailideex 8y ago
What makes you think he engages with them?
- SiempreViernes 8y ago
  Some might be polite and somewhat knowledgeable (though most won't be either).
- memberZero 8y ago
  make it so
- thanatropism 8y ago
  In the late 90s to early 2000s I was a teenager and communicated with various scientists and academics via email, some of which had something of a mentor role. By those experiences I'd say someone like Alcubierre is more likely to engage young ducklings than, say, Michio Kaku.
light_hue_1 8y ago
No problem: https://www.youtube.com/watch?v=5q_z8BjiYng https://www.youtube.com/watch?v=5q_z8BjiYng This is one example of many. The original poster was just spreading FUD and saying nasty things about Alcubierre as a researcher. He gives talks like this all the time, he refers to his own work as a warp drive, he quotes and shows off Star Trek, etc. This isn't an issue of crazies trying to steal someone's research.

magicalhippo 8y ago

That Michio Kaku episode[1] on Discovery where he said[2] that we might be able to harness the Casimir effect as a source of the negative energy needed for the Alcubierre drive probably didn't help. There are more realistic explanations[3] for the Casimir effect however, so no Alcubierre drive for us anytime soon. [1]: Think it was this show https://en.wikipedia.org/wiki/Sci_Fi_Science:_Physics_of_the_Impossible https://en.wikipedia.org/wiki/Sci_Fi_Science:_Physics_of_the... [2]: To be fair, Alcubierre suggested it himself first [3]: https://en.wikipedia.org/wiki/Casimir_effect#Relativistic_van_der_Waals_force https://en.wikipedia.org/wiki/Casimir_effect#Relativistic_va...

ben_w 8y ago
Even if your [3] doesn’t apply, I believe the Casimir effect doesn’t scale fast enough — even a cavity made from proton-sized parts will never exclude more vacuum energy than the mass energy of those protons: https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casimir-cavity-be-used-to-construct-true-negative-mass-metamaterials/ https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casim...

EastLondonCoder 8y ago

This is very true, it’s also worth mentioning that all ways of faster than light travel means travel back in time in some reference frame which in breaks causality.

magicalhippo 8y ago
Here's a good (IMHO) video showing how this works out, by looking Minkowski diagrams for different observers. https://www.youtube.com/watch?v=HUMGc8hEkpc https://www.youtube.com/watch?v=HUMGc8hEkpc
computerfriend 8y ago
Breaking causality is allowed, though.
garmaine 8y ago
Breaking causality is allowed by the laws of physics.
zamalek 8y ago
You don't travel faster than light with the Alcubierre Drive, you circumvent travel entirely. Spacetime does the traveling, not the ship.

Razengan 8y ago

> If we could ever produce such matter then we could start some spacetime engineering. Imagine the exotic "pollution" caused by civilizations which are advanced enough to tinker with the fabric of spacetime, but not advanced enough to understand (or care about) the long-term consequences of that tinkering. Destabilizing solar systems or even entire galaxies, maybe even violating causality.. Imagine the home (and only) planets of younger, insignificant civilizations being caught up in those cataclysms, all traces of their existence wiped from cosmic history in what might amount to the equivalent of a traffic accident or "oil spill" of a greater civilization. ..maybe that has already happened and some of the leviathanic voids we've observed were a result of that? :) [0] https://en.wikipedia.org/wiki/Void_(astronomy) https://en.wikipedia.org/wiki/Void_(astronomy)

SiempreViernes 8y ago
Well, there was that time Earth was demolished to make room for a bypass. I'm not sure I recall all the details but I think the universe ended as a convoluted consequence?
- Razengan 8y ago
  Yep, that is exactly what I was thinking about. :)
golergka 8y ago
That sounds like some great sci fi, actually.
- Razengan 8y ago
  Ever since I played the awesome old RPG called Planet's Edge [0] and the better-known Star Control II, I've been taken to muse about cosmic coincidences. Popular sci-fi like Star Wars or Star Trek etc. don't really touch on those possibilities in a convincing way. As in, very few fiction truly conveys the ..indifference.. of the universe, and all the actors in it going about their own businesses and interacting only incidentally, even if to monumental consequences to each other, but without a lot of conscious intent or an overarching plan. Kind of like how most of Earth's history has played out, even if it may all seem interconnected and purposeful due to the much more relatable scales involved. [0] https://en.wikipedia.org/wiki/Planet%27s_Edge https://en.wikipedia.org/wiki/Planet%27s_Edge

Hydraulix989 8y ago

Is there nothing interesting within the constraint of a reasonable stress energy tensor?

Eochei5h 8y ago
Black holes and possibly topological defects.

exoesquitur 8y ago

.... But you make one warp drive....

JumpCrisscross 8y ago

> all the interesting spacetimes (such as the Alcubierre drive) require exotic matter Does it have to be matter? Or could we coax the vacuum into behaving as if it were occupied by exotic matter?

ailideex 8y ago
Matter is just excitation in the vacuum. But excitation with positive energy. What is needed is excitation with negative energy.

light_hue_1 8y ago

> I heard that Alcubierre somewhat regrets having his name on this spacetime as he gets contacted by all kinds of Star Trek fans and other people who believe they can produce the drive. He has done all kinds of other quality research in General Relativity, but this is what he will be famous for. This is untrue, it's really offensive to a person that's dedicated years of his life to this research, and it set a terrible tone for the rest of the comments. He gives talks all the time to groups that are interested in developing a "warp drive". He puts up photos of Star Trek in his talks! He even refers to his own work as potentially developing a "warp drive". Look at one of his recent talks https://www.youtube.com/watch?v=5q_z8BjiYng https://www.youtube.com/watch?v=5q_z8BjiYng and please stop spreading negative rumors about scientists.

warent 8y ago
As an aside, I'm loving this talk (the YouTube video). Thank you for sharing