Positive Energy Warp Drive from Hidden Geometric Structures • Hacker News Board

Re: Positive Energy Warp Drive from Hidden Geometric Structures

#161

Post by ISV_Damocles » Tue, Jul 13, 2021, 4:09 PM UTC

effingwewt wrote: post #104

godelski wrote: post #92

Earlier quoted context omitted.

I wouldn't say primary plot of Ender's Game. I'd say it was a higher focus in Speaker for the Dead. Still, the device is used in a lot of Sci-Fis. Card wasn't even the first to use the term Ansible, though he did use that exact word.

It was most definitely one of if not the most central plot point of the series. Not sure how far you got, but the entire series including the prequels is worth a read imho.

Here's why I believe you are being downvoted:

1. The original topic was about Ender's Game only, not the entire series, so you basically shifted the goalposts. 2. More importantly, I think you are using the wrong literary terminology and you and the others are talking over each other. Where you say "plot point" I believe you meant "plot device."

The Ansible is definitely the primary plot device that makes so much of the story and how it flows possible, but the ansible is not the point of the plot itself.

Throughout Ender's Game the plot point is reinforced that the rules of civilization will be broken when a credible threat shows itself. That is shown with the various physical conflicts Ender has with the other children at the individual level, it is shown with the tolerance the military has in order to shape Ender at the organizational level, and it is shown with the vilification of Ender so society at large does not have to grapple with just how badly it broke its own rules - so it can be done again if necessary for survival.

Re: Positive Energy Warp Drive from Hidden Geometric Structures

#162

Post by pontifier » Tue, Jul 13, 2021, 4:10 PM UTC

fho wrote: post #118

foota wrote: post #82

Earlier quoted context omitted.

You don't even need FTL for that, just move quicker than your cpu!

I assume that in theory this would also work the other way around ... find a way to make your CPU move (spatially) a lot slower than you and perform millenias worth of computation in your coffeebreak.

"I will slow myself down relativistically and declare that the universe has sped up." seems like the equivalent of the mathematical joke of "I build the fence around myself and declare that I am outside it."

I highly approve.

Re: Positive Energy Warp Drive from Hidden Geometric Structures

#163

Post by prox » Tue, Jul 13, 2021, 4:24 PM UTC

cowboysauce wrote: post #157

prox wrote: post #139

Earlier quoted context omitted.

Does this reverse time though? 0.9c is 90% of lightspeed, and for the sake of your example, 500c is just instantaneous. If light is just information, wouldn’t it just be a matter of seemingly getting something very fast?

If you're traveling at 0.9c then there will be significant time dilation. Since velocity is relative, both parties will see each other as severely time dilated which can lead to somebody receiving a reply to a message before they send it.

But how do you know that you need to send a message or what if you don’t send a message? How can you get a reply?

Everytime I think I get it, I don’t!

Re: Positive Energy Warp Drive from Hidden Geometric Structures

#164

Post by harpersealtako » Tue, Jul 13, 2021, 4:28 PM UTC

circlefavshape wrote: post #146

sigmoid10 wrote: post #15

Earlier quoted context omitted.

General relativity actually tells us nothing about whether causality is absolute. You can easily make up spacetime configurations that violate causality and still conform to general relativity. It's just that most people believe that causality should be protected, because... well it would be really weird if it wasn't. But it's just a conjecture and not like a theorem or anything.

I've never managed to see how causality is a problem for FTL travel If we perceived the world through sonar then causality would be violated by anything supersonic. If you were shot then you'd feel the bullet first and then "see" it moving back into the gun. AFAICS if information can travel at >c, then physical objects traveling at >c doesn't violate causality

Here's a good explanation of why FTL causes causality issues.

http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-ti...

The sonar example works only if everything is traveling in roughly the same frame of reference. You're not accounting for relativity and its effects on space and time in your analogy.

Re: Positive Energy Warp Drive from Hidden Geometric Structures

#165

Post by sxp » Tue, Jul 13, 2021, 4:28 PM UTC

circlefavshape wrote: post #146

sigmoid10 wrote: post #15

Earlier quoted context omitted.

General relativity actually tells us nothing about whether causality is absolute. You can easily make up spacetime configurations that violate causality and still conform to general relativity. It's just that most people believe that causality should be protected, because... well it would be really weird if it wasn't. But it's just a conjecture and not like a theorem or anything.

I've never managed to see how causality is a problem for FTL travel If we perceived the world through sonar then causality would be violated by anything supersonic. If you were shot then you'd feel the bullet first and then "see" it moving back into the gun. AFAICS if information can travel at >c, then physical objects traveling at >c doesn't violate causality

Comparing to sonar isn't valid since objects at subsonic and supersonic speeds still obey the rule that 1 + 1 = 2. For high velocities, this rule is no longer true and you need to resort to using a spacetime diagram to compute velocities.

If you draw a tachyon on a spacetime diagram going faster than the speed of light, you can create situations where the tachyon travels back in time for certain observers.

> AFAICS if information can travel at >c, then physical objects traveling at >c doesn't violate causality

If information can travel faster than c, then you can create situations where it's also violating causality.

Re: Positive Energy Warp Drive from Hidden Geometric Structures

#166

Post by grishka » Tue, Jul 13, 2021, 4:52 PM UTC

phendrenad2 wrote: post #122

sigmoid10 wrote: post #15

Earlier quoted context omitted.

General relativity actually tells us nothing about whether causality is absolute. You can easily make up spacetime configurations that violate causality and still conform to general relativity. It's just that most people believe that causality should be protected, because... well it would be really weird if it wasn't. But it's just a conjecture and not like a theorem or anything.

So we're traveling away from one another at 0.9c. I send a paper airplane in your direction at 500x the speed of light. You receive it and send it back (at 500c). Does it not arrive before I sent it, from my perspective?

See, the formula for velocity is v=s/t. We know the distance the object has traveled, so it's the time it took to get there that gets adjusted so as the resulting velocity never exceeds the speed of light. At least that's my understanding of it. I might be entirely wrong.

Re: Positive Energy Warp Drive from Hidden Geometric Structures

#167

Post by jjk166 » Tue, Jul 13, 2021, 5:27 PM UTC

gary_0 wrote: post #9

What do the authors of these warp drive papers think will happen causality-wise when the proposed vehicle effectively moves faster than c? You can't do that without doing nasty things to your light cone[0] and effectively traveling into your own past. Is a prerequisite of entertaining the idea of a warp drive that we disregard causality? As far as I know, there aren't any plausible loopholes in General Relativity tha…

Why would causality need to be one way?

It's not unusual for (anticipation of) future events to affect the present. For example if I think it will rain, I grab an umbrella. While typically my belief that it will rain is based on something in the past (previously weather patterns for example), does it really change anything if a time traveler claiming to be me from the day after tomorrow told me it's going to rain tomorrow?

We only think of causality as going from past to future because that is the way we live. We also find the idea that particles can have an indeterminate location or pop randomly into or out of existence is weird, because our minds which have evolved to experience and understand the macroscopic world have no method of really processing that, but our intuition is not reality. If we can accept that our concept of position of objects in space is merely an approximation of a more complicated reality, the same for position of events in time should not be much harder.

People get bent up about paradoxes, but we have things like the Novikov self consistency principle [0] which allow us to avoid paradoxes even without one way causality.

[0] https://en.wikipedia.org/wiki/Novikov_self-consistency_princ...

Re: Positive Energy Warp Drive from Hidden Geometric Structures

#168

Post by saalweachter » Tue, Jul 13, 2021, 5:27 PM UTC

godelski wrote: post #50

Everyone always talks about FTL travel for spacecraft, but there's also an interesting perspective from weapons side (and this a reason to be a bit careful and think about some ethics as we move along). A FTL kinetic weapon would be devastating. If it comes with a collapsing warp bubble then there's basically a gamma ray "gun" that travels right in front of your mass that is traveling at tremendous speeds. You look a…

There's more than one way for the Fourth World War to be fought with stones.

Re: Positive Energy Warp Drive from Hidden Geometric Structures

#169

Post by jjk166 » Tue, Jul 13, 2021, 5:49 PM UTC

gradschool wrote: post #151

nine_k wrote: post #38

Earlier quoted context omitted.

AFAICT, GR is symmetric in relation of the direction of time, as are most other important physical theories. What may add the arrow of time is the second law of thermodynamics: a statistical evolution of a system is not symmetric. I wonder now how a violation of causality could either circumvent of contradict the second law.

I would envision two chambers A and B connected by two vents X and Y, like Maxwell's demon but with two vents instead of one and both vents permanently open. Whereas X is an ordinary vent, Y has the property that any particle passing from A to B through it reaches B shortly before it leaves A. Any particle passing from B to A through Y disappears for a short time before reappearing in A. It seems to me that this setu…

Let's look at the two possible timelines here:

At some point a particle pops up into existence in B, increasing B's pressure.

Some time later, a particle from A disappears, decreasing A's pressure.

This pressure differential would cause flow from B to A through X.

Alternatively, a particle randomly disappears from B, decreasing B's pressure.

Some time later, a particle appears in A, increasing A's pressure.

This would cause flow from A to B through X.

The more particles that cross from A to B via Y, increasing B's pressure, the more likely it is for particles to pass from B to A via Y, keeping these two effects equal.

These two pressure differentials would cancel out for large numbers of particles.

You've essentially just hooked up the system to itself, but at a future point in time. Unless the overall pressure of the system is changing, there is nothing to induce the flow. If you are increasing the pressure, valve Y is essentially just a standard one-way valve.

Re: Positive Energy Warp Drive from Hidden Geometric Structures

#170

Post by [deleted] » Tue, Jul 13, 2021, 5:49 PM UTC

AnimalMuppet wrote: post #40

sigmoid10 wrote: post #15

Earlier quoted context omitted.

General relativity actually tells us nothing about whether causality is absolute. You can easily make up spacetime configurations that violate causality and still conform to general relativity. It's just that most people believe that causality should be protected, because... well it would be really weird if it wasn't. But it's just a conjecture and not like a theorem or anything.

That conjecture is one of the two foundational principles of relativity - that the laws of physics are the same in all valid frames of reference. "Violating causality" means that in some valid frame of reference A, event X caused event Y, and in some other valid frame of reference B, event Y caused event X. The laws of physics cannot be the same in A and B for both of those to be true.

[deleted]