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"Magic technology"


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14 hours ago, Terwin said:

I was under the impression that the objective of the Alcubierre drive was to shrink space in front of the vessel and expand space behind it, so that you are not 'moving' the vessel at all, except perhaps using some chemical thrusters to cross the much shortened distance, or am I thinking of the wrong drive tech?

That's sort of the general idea. It'd be more precise to say that the objective is to move a region of space without accelerating it, and all the compression/expanding stuff is just the fallout of the math involved. But the idea is that, yes, you create a bubble around the ship, you move that bubble somewhere else, and you drop the bubble. Since ship never accelerated, you didn't expend any propellant.

But the math only works out if space-time outside the bubble is flat. So the mass of the ship + bubble still has to be exactly zero. And then you don't need to understand fancy GR math to understand why Alcubierre Drive can move without expending propellant. If net mass is zero, net momentum is zero no matter how fast the ship is moving, and so you can change your velocity without needing a reaction mass.

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17 hours ago, K^2 said:

If net mass is zero, net momentum is zero no matter how fast the ship is moving, and so you can change your velocity without needing a reaction mass.

But don't photons have momentum? Is there a distinction between rest mass and relativistic mass here, or am I just comparing apples and oranges?

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38 minutes ago, SOXBLOX said:

But don't photons have momentum? Is there a distinction between rest mass and relativistic mass here, or am I just comparing apples and oranges?

Zero gravitational mass is what we care about here, but yeah, that's equivalent to zero relativistic mass. For which zero rest mass is a necessary condition, but not a sufficient one, as photons clearly demonstrate.

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On 2/18/2021 at 8:51 PM, K^2 said:

Alcubierre Drive is a good example to illustrate why all of these "magical" drives really are a bit too magical. Standard way of deriving the warp metric is to say that space-time is flat inside and outside the bubble, with all curvature contained in bubble walls. Problem is, the moment you place something inside the bubble, the space-time is no longer flat due to gravity of that object. This doesn't really cause any problems inside the bubble, but outside, it results in gravitational waves produced whenever the bubble accelerates. Emitted gravitational waves actually compensate for the momentum of the ship, and in effect, you have a graviton drive, which is positively not what you want for warp. Graviton drive is subject to the same efficiency limits as photon drive in linearized case and gets worse at higher energies due to self-interaction. What does it mean for the warp drive? It means that you might as well have a photon drive rocket, and you'll need infinite energy to reach light speed. So forget about FTL.

How do you fix this problem? Well, you need to flatten exterior space-time. That's easy. Well, easy if you have negative energy you need to make a warp bubble in the first place. You just uniformly increase negative energy contribution throughout the bubble, meaning you now have more negative energy than positive energy. In fact, the total mass of ship and the bubble combined needs to be exactly zero to keep exterior space-time flat. A ship in that configuration requires no energy to accelerate, and if you were to match the masses perfectly, would be capable of going superluminal. Of course, there is no known way to match these perfectly, so you'll still be traveling at the light speed at the most, but given that interior time can run arbitrarily slowly, this is still great for interstellar travel. Despite all the problems, warp might still be the answer to how we go to the stars even if we can't beat the light barrier.

That said, lets look at this situation from an alternative perspective. Solving all of the above is a lot of math. Original Alcubierre paper did not include any of these nuances, because this is computationally heavy, and yet, these limitations could have been called out immediately with a bit of thought. Here's why.

You can look at movement of anything through space - flat or warped - as flow of energy. This way, we don't have to distinguish between light, gravity waves, energies in the warp bubble, or the ship itself. If we are talking about general relativity, we do have to consider the entire stress energy tensor, of which energy is just a projection, but the advantage it gives us is that it contains information about momentum as well. More crucially, it's not just a conserved quantity but a conserved current due to symmetries of Minkowski metric.

νTμν = 0

That equation is just a very fancy way of saying that energy and momentum are neither created nor destroyed, and can only flow from one location to another. Moreover, momentum is the flow of energy. Without getting into mathy details, we can apply a generalized version of Divergence Theorem to this.

S nνTμν dS = ⨌VνTμνdV = 0

That's a lot to unpack, but vaguely speaking, if you imagine a boundary around a region of space-time, same amount of stress energy flows into it as out of it in total. So now, let us construct a specific case for a ship preparing to depart.

image.png

So time flows upwards, and one of the spatial directions is across. Picture a hypercylinder in space-time region surrounding the departure event. We can consider ship prior to the departure sitting still in space. As it does so, it moves forward in time, so it "flows" into the cylinder of interest through the bottom face. At this point, the only energy the ship has is its mass energy, so that's the exact amount of stress-energy that enters the cylinder through the bottom face as indicated by the bottom arrow. The exact same ammount must now flow out of the cylinder. If the ship was to remain at rest, all that mass energy would flow out of the top face and the net change would be zero, which is exactly what we expect. However, we are picturing a ship that by some means of propulsion departs this area of space. So the top arrow indicates the flow of stress-energy out through a side wall.

This is where things get exciting. We must still have the total mass-energy of the ship depart, so there is energy flow. But the side-walls of this cylinder are purely spatial boundaries. Flow of energy through a spatial boundary is momentum. So the stress-energy that leaves this cylinder is mass-energy plus some quantity of momentum. But no momentum entered the cylinder. The only way to rectify that and have the total be zero is for something else to depart this cylinder with opposite amount of momentum.

This is why you cannot have propulsion without exhaust. That exhaust can be matter, light, or even gravity waves. But there has to be something emitted that carries away momentum.

The warp drive gets around this by having on board the ship a source of negative energy enough to create the bubble. Because the total energy cannot change, the total mass of a warp-capable ship is precisely zero even before it goes into warp. Because of that, the mass-energy of the bottom arrow is zero, and so the energy and momentum of the top arrow can be zero as well, allowing a warp ship to depart with no exhaust. That, however, leads to other problems. If the net mass of warp-capable ship is zero before the jump, what if something applies a force to it? A slightly more realistic version is a ship whose total mass is just a few grams, allowing it to reach ludicrous speeds on a graviton emission alone once it forms a warp bubble, but such a ship will be strictly sub-light capable.

As for FTL or exhaust-free ships, this principle, unfortunately, puts an very heavy damper on the very idea.

There are other means of going from point A to point B faster than light, like wormholes, but that comes with its own set of caveats and is another long story. I hope that the above is at least somewhat helpful in filtering out impossible magic ideas in propulsion from ones that are simply incredible. Like antimatter beamed core rocket or a wormhole drive. Both of which are still total science fiction for now, but with at least the physics of how it would work being completely clear.

 

*Rubs eyes*

Is that....a Quadruple Integral? And i thought Triple Integration was a pain.

Back to the topic at hand though, would it be possible to null out the majority of an object's mass (Say 98-99% of it). And then accelerate it, gaining momentum the entire way. At which point it would have so much energy just from the velocity component, that it could form a singularity/black hole if you used the warp field to increase it's mass instead at that point. 

Basically, my thought goes like this. We know Wormholes can do what we want, and that the quantities of Negative Energy needed for a full Warp Drive might be downright unobtainable. So instead of making the entire ship warp capable, why not use the same techniques on a much smaller scale to induce local tears in Space-Time with something akin to a relativistic missile. With the only issue being that you can't really control the endpoint (That's a rather large one mind you). And if i remember correctly, you would still need some energy input to stabilize the singularity. But because you only want it around just long enough to traverse it, i figured an intense pulse of radiation (A laser or similar) might be able to do it.

 

 

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23 minutes ago, Incarnation of Chaos said:

Back to the topic at hand though, would it be possible to null out the majority of an object's mass (Say 98-99% of it). And then accelerate it, gaining momentum the entire way. At which point it would have so much energy just from the velocity component, that it could form a singularity/black hole if you used the warp field to increase it's mass instead at that point. 

The only thing that partially compensating mass with negative energy lets you do is get to higher fraction of c without expending more propellant. It's like a boost to your ISP. So, you know, still great if we ever figure out how to do it and might make a difference between being able to travel between stars and not, but it's not going to do anything nearly as dramatic as you describe.

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On 2/18/2021 at 7:31 PM, Arec Johnson said:

Wow, Great quote by Arthur C. Clarke, Thanks for sharing.

I have commented on this before, I hate that quote. It presupposes that there is, and will alsways be, a sufficiently large gap in knowledge for "magic tech" to remain a possibility.

That basically presupposes that the laws of physics are essentially unknowable.

Sure that quote holds true for primitives with almost no knoweldge of how things work. It holds true to a lesser extent for people of the 17th century.

As knowledge expands, the tech that would appear to be magic retracts. 500 years from now, there may be no possibly tech that would appear to be magic... or maybe 50,000 years from now, or maybe 50, or maybe now.

This is essentially just a god of the gaps fallacy.

 

In my view, magic tech is anything that conradicts known facts about the universe, or tech that just does whatever without even a hint of the mechanism at work.

A fusion drive would not be magic tech, because it doesn't contradict known physics, and while the details aren't worked out, the mechanism is specified, and thus we can already make assumptions about how it works, its limitations, etc.

When you don't specify a mechanism, implicit or explicit, then it can simply do whatever you want, without limitation, and can be overcome however you want, without limitation. Its function becomes arbitrary and random, depending only on the needs of the plot

IMO, fictional magic stories that don't clearly define the rules for magic end up with just arbitrary outcomes, and I find its often just a cover for lazy writing. Superhero stories often have the same problems.

I would say the star trek teleporter is magic tech, and probably the warp drive, because what stops them from working is basically just random and completely unpredictable. They will simply stop working for *insert technobabble reason" when the plot demands that the protaganist be trapped.

Such things don't happen with non-magic sci-fi tech like a fusion drive... at least not to any extent greater than such things happen with real tech - like the horror movie cliche of a car failing to start after a couple attemps, as the killer closes in... etc

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4 hours ago, KerikBalm said:

I have commented on this before, I hate that quote. It presupposes that there is, and will alsways be, a sufficiently large gap in knowledge for "magic tech" to remain a possibility.

That basically presupposes that the laws of physics are essentially unknowable.

Sure that quote holds true for primitives with almost no knoweldge of how things work. It holds true to a lesser extent for people of the 17th century.

As knowledge expands, the tech that would appear to be magic retracts. 500 years from now, there may be no possibly tech that would appear to be magic... or maybe 50,000 years from now, or maybe 50, or maybe now.

This is essentially just a god of the gaps fallacy.

There will always be specialists that understand a given technology.

Even today, no one can be a specialist in all technologies.  If you are a rocket scientist, then the ability to produce a child with three genetic mothers is probably not something you hae a through understanding of, and if you are a genetic engineer, then a continuous transmission probably seems pretty out-there, and if you are a mechanical engineer, then the design and operations of VLS IC design(the methods use to make modern computer CPUs and GPUs) probably seems pretty obscure and arcane, and if you are an IC electronic engineer(who does not play KSP) then orbital mechanics and the rocket equation are unlikely to be intuitive.

This says nothing about the guy who plays in a garage band and checks out groceries to afford an amp that 'goes to 11'.

 

Personally, I find quantum mechanics to be weird, but not half so strange as politicians and other 'social people'.

 

Even that approach may be looking at the quote the wrong way, as I have a good understanding of how Alexa and other digital assistants function, but when they work as intended, it 'looks' magical.

I could easily see 'does what I want without needing to worry about the details' as 'magical' tech, even when I fully understand how it works.

After all, how functionally different is this personal transport drone from a magical flying carpet:

If I can summon it with a few words and it can take me where I want to go, it seems pretty similar to me... (sure the current version has lots of limitations, but as the technology develops those limitations will become less and less relevant for most users)

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I'm pressing squares with letters on the board lying in front of me, and then can see text appearing on the flat vertical glass, like various people are talking to me, and even see pictures...

So strange. How could they live in this flat glass? And why do I see nobody?

Maybe the glass and the letters are magic?

I have never seen any of them, and probably they even don't exist.

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11 hours ago, Terwin said:

After all, how functionally different is this personal transport drone from a magical flying carpet

I only have two complaints. They tend not to do well when rolled up and, "Why don't you come with me, little girl, on a personal transport drone ride," doesn't have the same ring. (Context)

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21 hours ago, Terwin said:

After all, how functionally different is this personal transport drone from a magical flying carpet:

idk, in that one Asterix comic they used it to fly them all the way from Gaul to India so unless it can fly all that long on a whim it's not quite functionally the same.

Edited by YNM
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21 hours ago, Terwin said:

There will always be specialists that understand a given technology.

Even today, no one can be a specialist in all technologies.  If you are a rocket scientist, then the ability to produce a child with three genetic mothers is probably not something you hae a through understanding of, and if you are a genetic engineer, then a continuous transmission probably seems pretty out-there, and if you are a mechanical engineer, then the design and operations of VLS IC design(the methods use to make modern computer CPUs and GPUs) probably seems pretty obscure and arcane, and if you are an IC electronic engineer(who does not play KSP) then orbital mechanics and the rocket equation are unlikely to be intuitive.

This says nothing about the guy who plays in a garage band and checks out groceries to afford an amp that 'goes to 11'.

 

Personally, I find quantum mechanics to be weird, but not half so strange as politicians and other 'social people'.

 

Even that approach may be looking at the quote the wrong way, as I have a good understanding of how Alexa and other digital assistants function, but when they work as intended, it 'looks' magical.

I could easily see 'does what I want without needing to worry about the details' as 'magical' tech, even when I fully understand how it works.

After all, how functionally different is this personal transport drone from a magical flying carpet:

If I can summon it with a few words and it can take me where I want to go, it seems pretty similar to me... (sure the current version has lots of limitations, but as the technology develops those limitations will become less and less relevant for most users)

I say the technology has to bee uncommon or new for some seeing it as magic. Current day excample: how can 5G cause an virus infection, only way to explain this is that you have no clue that an radio transmitter do. 
On the other hand gunpowder was probably seen as magic by most for quite some time until it became common. People did still not know how chemistry worked so in practice it was alchemy.

http://freefall.purrsia.com/ff300/fv00255.gif

http://freefall.purrsia.com/ff300/fv00255.htm

 

 

 

 

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On 2/23/2021 at 5:44 AM, KerikBalm said:

It presupposes that there is, and will alsways be, a sufficiently large gap in knowledge for "magic tech" to remain a possibility.

I think you may have missed the point. Clarke said "sufficiently advanced". He was saying that, given a flashlight or car, people who lived before these things were widely understood would cry " Black Magic!" or "the work of the gods!" He's not making the global statement "There will always be a sufficiently large gap possible, regardless of our current knowledge...", but only " Given a sufficient gap...". 

Although it doesn't really apply to Clarke's Third, I agree with you. The laws of physics have got to be knowable.

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21 hours ago, SOXBLOX said:

He's not making the global statement ...

He said "any"

There were no qualifiers or limiters for that. That implies that, for a given society (with no tech level specified), a sufficiently advanced technology would be indistinguishable from magic. 

The key term here is sufficiently advanced. I would argue for a sufficiently advanced society, no technology is indistinguishable from magic. Thus in that case, we'd have to conclude that sufficiently advanced technology is impossible, and hence something indistinguishable from magic is impossible. 

If we just assume that a sufficiently advanced technology is possible, then the statement is a global statement of the sort I made.

If we don't, then the statement is functionally identical to saying magic may or may not exist*, which is an asinine statement.

* Well, really the conclusion is that something "indistinguishable from magic" may or may not exist, which I conclude to be functionally identical to saying magic may or may not exist.

Edited by KerikBalm
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IMO Magitech is when some advanced technology clearly breaks existing physics. That is, it relies heavily on science going in a spectacularly unlikely direction for it's operating principles to be sound.

 

Clarketech is equally advanced technology that relies heavily on science going in a relatively plausible, if arbitrary and convenient, direction. It does not go out of its way to retcon out existing physical laws but develops on existing science in a way that is at least sort of realistic.

 

Hard sci fi tech relies on neither. It doesn't make many easy to challenge assumptions about the direction of new basic physical principles. No FTL, no teleportation, no disappearing an object by converting it to neutrinos, no stable wormholes, no portals to other dimensions, etc.

 

Note that these are a bit blurry categories. Is a ceramic made of known elements that doesn't melt at 12000 K in a vacuum hard sci fi or Clarketech? Would a nuclear reactor be considered Clarketech or Magitech with an 1880s understanding of physics? When does it change? The discovery of radioactivity? The discovery of mass energy equivalence? The discovery of the Neutron? What about cold fusion? It's not provably impossible but it seems highly improbable. Is Clarketech required to consider cold fusion a reasonable technology or would it make sense as "hard sci fi?"

Edited by Pds314
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On 2/22/2021 at 2:58 AM, K^2 said:

The only thing that partially compensating mass with negative energy lets you do is get to higher fraction of c without expending more propellant. It's like a boost to your ISP. So, you know, still great if we ever figure out how to do it and might make a difference between being able to travel between stars and not, but it's not going to do anything nearly as dramatic as you describe.

Also the best way we currently know to make negative energy is having huge amounts of positive energy and IIRC you can't really end up with gravitational fields (negative energy) that outweighs the positive. You can reduce mass from the POV of an external observer arbitrarily much as the thing gets very close to its own event horizon, so for example a neutron star could theoretically have really large mass up close compared to what would be felt far away, but IIRC there's no known way to make self-contained structures with a negative overall mass.

 

And furthermore, I don't think GR would expect there to be, at least not using gravity as your negative energy source.

Edited by Pds314
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