Alternate way to get the 100 diameter limit?

[whulorigan]

What I am trying to say is that if you sum up the gravitational forces in a system, you don't get equilibrium at the lagrange points. The Earth-Sun L2 point isn't where Earth and Sun's gravity balance out, it's where Earth and Sun's gravity with centrifugal force as viewed from a frame co-rotating with Earth balance out, and it is exactly the same viewpoint that places an object in orbit - gravity is balanced out by centrifugal force in a frame co-rotating with the satellite. If jumps from a lagrange point are allowed, jumps from orbit (any orbit) should also be allowed. (attached: force plot of the sum of real and fictitious forces for and Earth size and mass object in a frame rotating at 0.001144 radians/sec - orbital velocity for an object at 350 km orbit altitude. The gravitational and centrifugal (and coriolis and euler) forces balance out.
View attachment 4555

If you do a similar two body plot, for example Assiniboia and Regina, summing up forces as viewed from the frame co-rotating with Regina, the L1 and L2 points pop out as expected:
View attachment 4556

Of course, those points don't pop out if you simply sum the gravitational forces of the Assiniboia-Regina (et al) system:

View attachment 4557

Where I'm going with that is if you allow jumps from "sum-of-real-and-fictitious-forces-is-zero", a jump from a very low orbit is just as valid as a jump from a lagrange point.

Yes, I understand. What I am saying is that Einstein would say (via General Relativity) that they are formally the same thing in the Physics, and thus equivalent (i.e. in the examples you mention above).

Thus your point:

... if you allow jumps from "sum-of-real-and-fictitious-forces-is-zero", a jump from a very low orbit is just as valid as a jump from a lagrange point.

is vaild. Since this is not the case in Travelller (and would break the game's Jump paradigm), there must be more going on than just having zero-net forces/pseudo-forces from the (accelerated) reference frame of the jumping ship. This is one of the reasons I favor the gravitation-gradient / tidal-force model; it is not the absolute G-field at a given locale, but rather the differential-gravity across the physical dimension of the ship end-to-end, yielding a slightly different Jump-solution at different points along the surface of the vessel. You want this to be as close to zero as possible (within a given tolerance) in order to avoid a misjump due to the ship potentially entering jumpspace "differentially" along its longitudinal dimensions.

The concept of the "gravitational-mass projection" or "shadow" into jumpspace in some mathematically transformed way must also play a role.

I simply take it as a bit of Pseudo-Quantum Mechanics & Relativity:

• We know that Time flows normally in both Jump-space & Normal-space without mutual cross-space dilation or discrepancy, so we can infer that time is Real-valued in both spaces.
• We know that Distance/Spatial relationship is Real-valued in N-Space, but can infer that distance/spatial relationship is Imaginary-valued in J-Space relative to N-Space (and visa versa) because a ship in Jump space has no Real-valued N-Space coordinates (i.e. its relative position cannot be determined in N-Space) and objects in N-Space have no Real-valued J-Space coordinates (i.e. their relative positions cannot be determined in J-Space) as regards the ship.
• We know that Velocity is Real-valued in N-Space, but can infer that velocity is Imaginary-valued in J-Space relative to N-Space (and visa versa) because Jump-space transition speed does not scale linearly or smoothly with N-Space (in fact, jump-line blockage causing precipitation from J-space at the end of the same one-week time period is a good illustration of this - i.e. you do not drop out of jump early, just at the end of the same one-week period at the 100-D limit of the blockage object).

Over on the Traveller Wiki I made a brief contribution to the Jumpspace page under the Jumpspace Theory heading:

While originally conceived as an alternate universe, Jumpspace is correctly defined as an extension of our universe, where there are more dimensions than are usually perceived. According to this theory, Jumpspaces are alternate spaces, each only dimly understood from the standpoint of our own universe. Jumpspace is related to normal Einsteinian Space (or "N-Space") in a non-linear fashion. As such, both velocity and positional information take on imaginary values for objects in Jumpspace relative to Normal Space, resulting in a transition from point-to-point in N-space with a typical expectation value of approximately 168 (± 10%) hours (though the temporal probability curve extends along a steep normal distribution in both directions), the N-Space distance of the Jump only limited by the "weave" of the particular level of J-Space with respect to the 4 dimensions of Einsteinian space. While in a particular "level" of J-Space, the positional and velocity values for objects in the N-Space universe have corresponding imaginary values relative to the object in J-Space. Since T=D/V (where T= time, D= distance, and V= velocity), the imaginary components of position and velocity cancel each other in the fraction, yielding a common Real-valued time coordinate "T" in both the N-Space and J-Space environments. Since mathematically gravity is uniquely a curvature of both Spatial and Temporal coordinates in Einsteinian spacetime, the only interaction and object in a J-Space manifold has with the N-Space universe is the Complex-valued J-Space "shadow" of gravitational sources in N-Space that project into J-Space via a complex non-linear (and not well understood) interaction. ​

 

[sudnadja]

Yes, I understand. What I am saying is that Einstein would say (via General Relativity) that they are formally the same thing in the Physics, and thus equivalent (i.e. in the examples you mention above).


I simply take it as a bit of Pseudo-Quantum Mechanics & Relativity:

• We know that Time flows normally in both Jump-space & Normal-space without mutual cross-space dilation or discrepancy, so we can infer that time is Real-valued in both spaces.
• We know that Distance/Spatial relationship is Real-valued in N-Space, but can infer that distance/spatial relationship is Imaginary-valued in J-Space relative to N-Space (and visa versa) because a ship in Jump space has no Real-valued N-Space coordinates (i.e. its relative position cannot be determined in N-Space) and objects in N-Space have no Real-valued J-Space coordinates (i.e. their relative positions cannot be determined in J-Space) as regards the ship.
• We know that Velocity is Real-valued in N-Space, but can infer that velocity is Imaginary-valued in J-Space relative to N-Space (and visa versa) because Jump-space transition speed does not scale linearly or smoothly with N-Space (in fact, jump-line blockage causing precipitation from J-space at the end of the same one-week time period is a good illustration of this - i.e. you do not drop out of jump early, just at the end of the same one-week period at the 100-D limit of the blockage object).

I think Traveller 5 seems to disagree that Jump space, or an object in jump space, has no real world coordinates in that one of the rules states (T5.10 book 2 p.111-112):
Gravity sources in Real Space affect Jumplines: a straight line course cannot pass through a bubble surrounding a mass of any appreciable size (within Safe Jump Distance of a gravity source larger than the ship; gravity sources smaller than the ship have no effect).

Savvy astrogators take advantage of the effect of Gravity Sources in plotting their courses. A Jump Drive without a Jump Governor cannot do shorter Jumps: an astrogator can plot a course that intersects a gravity source (a planet, a star) and the course automatically terminates at the 100D limit from the gravity source. This strategy works equally well for Hop, Skip, and higher level drives.

"Plot a course that intersects", to me, indicates that the real-space line between two points and the jump-space line between two points have to deal with obstacles that are in the real-space coordinate system.

 

[Spinward Flow]

The concept of the "gravitational-mass projection" or "shadow" into jumpspace in some mathematically transformed way must also play a role.

My personal preference is to hearken back to something that happened in the very first episode, which is subtly incredible in its implications ... and has bearing on our discussions here ... but in a "higher dimensions than usual are relevant" kind of way.

I give you (audio) from 8:09 to 8:42 of Barbra Wright and Ian Chesterton not understanding Susan Foreman in ... An Unearthly Child ...

In a very simplified geometry, the parameters of A, B and C are "enough" to solve a lot of problems on a flat plane ... but things get a LOT more complicated when you include D (time) and E (space). What I want people to key in on is that notion of E being its own coordinate parameter ... defining "SPACE" ... in a way that A, B, C and D cannot independently of E.

For example:

• We know, as a matter of basic geometry, that a triangle on a single plane has internal angles that always add up to 180º EXACTLY ... in Euclidian Space.
• In Hyperbolic Space the internal angles of a triangle always add up to LESS THAN 180º.
• In Spherical Space the internal angles of a triangle always add up to MORE THAN 180º.

In other words, having a "dimension parameter" that can control for "the kind of space you're working with" can make a lot of difference to the answers your geometry will give you.

And what do we *KNOW* as a matter of basic understanding about gravity wells?
THEY BEND SPACETIME.

Space AND Time.



So gravity wells "change the answer" you'll get out of a geometry problem involving A, B and C ... if you don't ALSO include D and E.

For "most" geometry problems, the "extra precision" you need in order to account for "D and E" isn't necessary (especially if both dimensional parameters are arbitrarily set to zero for simplification and/or ignorance) ... but when you start getting into Astrogation challenges and interstellar travel in the (so called) "real world" with your starship, well ... ... you don't exactly get to have that luxury anymore. The "quality of the space" that you're going to be jumping (or hopping or skipping, etc.) through starts becoming a variable that needs to be TIGHTLY controlled (if you don't want to misjump). There are ... thresholds ... of variance that must be honored, or something is going to happen that you didn't want to occur ... and it will happen in an uncontrolled way (resulting in a misjump).

Which is a long winded way of saying that the "foundational math" for jump technologies rely on some pretty tight tolerances on how much "curvature" the spacetime around a starship can have and NOT misjump. The accepted "rule of thumb" for this limit is expressed most simply as being 100 diameters from planetary and stellar objects (although I'm thinking that this 100D relationship breaks down for extremely DENSE objects such as white dwarfs, neutron stars and black holes, for what ought to be obvious reasons).

If you're "too close" to a gravity well, then the type of space you're dealing with can "shift too far" out of the desired (and designed for) parameters of Spherical Space ... meaning that when you jump your "drives are ... OFF ... from what they need to be doing" in order to jump "correctly" through the kind and quality of gravity influenced space "shaping" around your starship, meaning that your jump calculations controlling what is supposed to happen DO NOT MATCH with "real" conditions ... and you misjump in an uncontrolled way.

The way to ensure that you don't experience those kinds of errors in calculation (or at least, keep the error bounds within acceptable tolerances) ... is to move away from gravity wells until you're "outside the jump shadow" of all known gravity wells. The insanely fiddly mathematical modeling and computations are then able to "work reliably" and you're unlikely to misjump (barring other factors such as unrefined fuel and skipped maintenance, etc.).



Or it could just be the Flying Spaghetti Monster toying with you.
Hard to tell for sure.
Can I get a research grant to investigate this possibility?

 

[whulorigan]

I think Traveller 5 seems to disagree that Jump space, or an object in jump space, has no real world coordinates in that one of the rules states (T5.10 book 2 p.111-112):
Gravity sources in Real Space affect Jumplines: a straight line course cannot pass through a bubble surrounding a mass of any appreciable size (within Safe Jump Distance of a gravity source larger than the ship; gravity sources smaller than the ship have no effect).

Savvy astrogators take advantage of the effect of Gravity Sources in plotting their courses. A Jump Drive without a Jump Governor cannot do shorter Jumps: an astrogator can plot a course that intersects a gravity source (a planet, a star) and the course automatically terminates at the 100D limit from the gravity source. This strategy works equally well for Hop, Skip, and higher level drives.

"Plot a course that intersects", to me, indicates that the real-space line between two points and the jump-space line between two points have to deal with obstacles that are in the real-space coordinate system.

But it is "fuzzy" in a sense, from the Jumpspace-side (i.e. it is a non-linear relationship and perhaps probabilistic based on a wave-equation of state). But in a sense that is the point I am trying to bring out: N-Space Spacetime is a unified Space/Time 4-dimensional construct, which J-Space will perceive as having both a Real-valued component and an Imaginary-valued component (i.e. the projection will be a Complex-valued number related to mass/gravity and its J-space "shadow" location). In other words it will perceive the mass/gravity field in J-Space at a "location" in J-space in some form (i.e. its "projection"), but perhaps not in a way that is immediately recognizable to N-space sensibilities. So intervening mass along the N-Space courseline will interfere with a Jump-line plot, but the actual interference is caused by the J-space projection, or "shadow", in J-space.

 

[Condottiere]

Actually, jumpsapce is two dimensional.

 

[whulorigan]

Actually, jumpsapce is two dimensional.

So I have heard. I am not sure if I am going to adopt that one yet or not.

 

[kilemall]

Actually, jumpsapce is two dimensional.

So the jump ends when the ship triangle hits the Flatland gravity circle, literally?

 

[Condottiere]

Yes.

Of course, where that circle actually protrudes in relation to a foreign object, depends on when the cat observes it.

 

[kilemall]

Yes.

Of course, where that circle actually protrudes in relation to a foreign object, depends on when the cat observes it.

So 90 diameter jump tech improvements depend in part on trained observer cats?

True high technology indeed.

 

[Condottiere]

Female Aslan might actually have an affinity for astrogation.

 

[Jame]

Female Aslan might actually have an affinity for astrogation.

Try taking one for a ride to orbit.

 

[Silverhawk]

(although I'm thinking that this 100D relationship breaks down for extremely DENSE objects such as white dwarfs, neutron stars and black holes, for what ought to be obvious reasons).

Which is one of the things that I liked about Weber in his Honorverse Series. The limit to enter hyperspace was mass based so a bigger mass object projected a further shadow than a smaller mass. In at least one book there was a gas giant that was outside the limit of the star but projected its own hyper limit due to its mass. I took the given distances from the early books and figured out that there is a relationship that I might try using in the future if I can the time and players.

 

[mike wightman]

In no particular order.

Jump space or hyperspace is an alternate universe, but the canon says this:

JUMP THEORY
There are several differing theories of jump space, and although jump
technology has been used for star drives for thousands of years, a precise
understanding of it is not necessarily a prerequisite; high quality data on
jump space is difficult to obtain.
The basic concept of jump space is that of an alternate space. Theoretically,
jump spaces are alternate universes, each only dimly understood from the
standpoint of our own universe. Within jump space, different physical
laws apply, making energy costs for reactions and activity different and
imposing a different scale on size and distance.

The concept of a jump line has a major flaw, it requires FTL information, the jump drive must know the location of everything now, and in a weeks time, and how it moves while the ship is in jump.

A thought occurred to me when the comment about tidal forces was made upthread, could a smaller ship jump closer to the 100D limit than a big ship?


We do not know how fast time ticks, or even if time exists within jump space. The ship is in a protective bubble of normal space where our universe's laws work no broblem.

Spacetime is not space and time.

 

[Condottiere]

You'd assume you have to overcome the starship's inherent narcissism.

 

[Spinward Flow]

The concept of a jump line has a major flaw, it requires FTL information

Which, with jump drives ... is obtainable ... because jump drives are FTL.
The point that you're eliding past is that the "FTL information" is both obtainable and predictable ... IF ... you have sufficient observational/survey data available for the path to be jumped.

(Substantially/sufficiently) complete information is fine.
INcomplete information is where things start to get risky and potentially dangerous (that whole "stella incognita" stuff).
Jumping blindly ... well ... that kind of voids the warranty, doesn't it?

the jump drive must know the location of everything now, and in a weeks time, and how it moves while the ship is in jump.

In Traveller we call that the Navigation skill for crew and is a requirement to be qualified for that crew position.
In LBB2.81 computer programming, we call that the Navigation program AND the Generate program. (LBB2.81, p41)
The Generate program plots the (safe) course.
The Navigation program actually controls the jump when executed.
The crew position of Navigator oversees those processes and verifies the information/answers the computer produces.
Questions?

A thought occurred to me when the comment about tidal forces was made upthread, could a smaller ship jump closer to the 100D limit than a big ship?

The jump shadow "size" does not change between the two alternatives, so ... NO.

The smaller ship has a "smaller hit box" than the bigger ship does, so ... it kinda sorta depends on your point of view (and how desperate you are to make "rounding errors" relevant, I guess).

Key thing being that both ships breakout from jump at 100D, regardless of ship size.
It's not like the small ship is forced to break out from jump at 99D while the big ship is forced to break out from jump at 101D (which would be silly).

We do not know how fast time ticks, or even if time exists within jump space.

Where do you get that idea from?
Time is contiguous in both normal space and jump space.

A jump transit that takes 168 hours in normal space (as detected by independent observers) ALSO takes 168 hours in jump space.

However, if you're trying to assert that time OUTSIDE of jump bubbles containing starships flows differently in jump space than it does in normal space, you're going to quickly run into an "observer problem" due to the fact that no observations of jump space OUTSIDE of jump bubbles is possible with KNOWN Traveller technologies (sit down Grandfather, we're not talking about what YOU know ).

Or we could just appeal to Kiri-Kin-Tha's First Law of Metaphysics.

 

[coliver988]

re: Time is contiguous in both normal space and jump space.

Book 2:
A misjump is an unpredictable random jump. Throw one die to determine the number of dice thrown (1 to 6); throw that number of dice to determine the
number of hexes in length the misjump is. Then throw one die to determine the direction of the misjump (one of the six directions possible on the hex grid). Finally, throw one die to determine the number of weeks spent in jump space before the
ship re-emerges at its new location.

does seem to support the idea that time is 1:1 with jump space/normal space. Though I seem to recall something I read where there was a time differential in some misjumps and that you can out a week later from jump space but much more/less time passed in the normal universe. But I may be conflating other RPGs/books.

 

[mike wightman]

I will try t explain what I mean.

We have no idea how much time passes in jump space, we don't even know if the time dimension exists in jump space.

We know that 1 week of time passes within the ship that is in a protective normal spacetime bubble in jump space, and we know that the ship is absent from our universe for one week.

Back to the jump line.

The ship's computer must be able to model everything that exists along the jump line from the instant the big jump button is pressed to the instant the ship emerges. It has to solve hyperspatial n-body general relativity equations for every object that could affect the jump and model it.


How fast does the ship travel along that jump line? Does it accelerate at first then decelerate, travel at constant pseudospeed? After one day in jump space what happens if something big moves onto its jump line. Does artificial gravity count for creating a 100D zone? How does the jump drive "know" if something happens during that week long transit?

 

[Enoki]

In no particular order.

Jump space or hyperspace is an alternate universe, but the canon says this:


The concept of a jump line has a major flaw, it requires FTL information, the jump drive must know the location of everything now, and in a weeks time, and how it moves while the ship is in jump.

A thought occurred to me when the comment about tidal forces was made upthread, could a smaller ship jump closer to the 100D limit than a big ship?


We do not know how fast time ticks, or even if time exists within jump space. The ship is in a protective bubble of normal space where our universe's laws work no broblem.

Spacetime is not space and time.

The question with using gravity is...

Is gravity instantaneous and continuous? That is does a mass immediately exert gravity on everything else at any distance from it, or does it take time to travel there?

 

[mike wightman]

We already know the answer to this, gravitational waves travel at c.

Gravitational wave - Wikipedia

en.wikipedia.org

 

[Spinward Flow]

How fast does the ship travel along that jump line?

Regardless of distance/parsecs traveled ... it takes 168 hours (+/- 10%) of duration ... both objectively (independent observers outside the starship) and subjectively (inside the starship in the jump bubble).

After one day in jump space what happens if something big moves onto its jump line.

At the end of your 1 week in jump you breakout at a location where the jump shadow intercepted your jump line on day 1.
You "hit the wall" and stop there ... and at the end of the week in jump, that's where you end up (instead of where you wanted to be).

Does artificial gravity count for creating a 100D zone?

Higher tech levels can "weaponize" jump shadows.
Depending on the climb through the tech tree, that can be an advantageous use of the tech to ASSIST with navigation in a controlled way, rather than being purely a hazard.

How does the jump drive "know" if something happens during that week long transit?

By "hitting it" ... so to speak.
Kind of like playing tennis, really.

Q: How does the tennis ball "know" that a tennis racquet is going to hit it before flying over the net to the other side of the tennis court?
A: The ball doesn't "know" anything ... it's up to the TENNIS PLAYER(s) to control how the ball is being hit (when, where, how hard, etc.).