[Space] Ditching Relativity, with minimal collateral damage

[teviet]

Originally Posted by malloyd

I don't think this even makes sense. What exactly do you think a reference frame is?

But suppose it did. If there is only one reference frame in which FTL is possible, then it's pretty much useless, since the *point* is to travel between places in our universe faster than light. An observer on each of those places defines a reference frame. If you can't make an FTL trip in those frames, then when you leave Earth for Alpha C with your "FTL" drive you must arrive at least 4 years later by the clocks of both Earth and Alpha C. Make the round trip and you cannot come home to a family less than 8 years older than when you left. What exactly have you gained?

Again, it's not that FTL only works in one frame, it's that FTL works differently in different frames. In one particular frame (maybe) your drive gives you a specified FTL speed in every direction. But in any other frame your FTL speed will vary, often by a large factor (infinity is a large factor!), depending on what direction you try to move.

TeV

[David Johnston2]

Originally Posted by teviet

Again, it's not that FTL only works in one frame, it's that FTL works differently in different frames. In one particular frame (maybe) your drive gives you a specified FTL speed in every direction. But in any other frame your FTL speed will vary, often by a large factor (infinity is a large factor!), depending on what direction you try to move.

TeV

You know, that's funnily like Star Trek FTL seems to work.

[cmdicely]

Originally Posted by teviet

Again, it's not that FTL only works in one frame, it's that FTL works differently in different frames.

Which is exactly what it does under relativity, which is the source of the problems with causality.

[Anthony]

Originally Posted by cmdicely

Which is exactly what it does under relativity, which is the source of the problems with causality.

Actually, no. The problem with FTL for relativity is that it doesn't behave differently. If I have a very simple FTL model: when I turn on FTL I travel at 10c relative to the frame in which I initiated the FTL, I get time travel. If instead I have the model of: when I turn on FTL I travel at 10c relative to the privileged reference frame, I don't.

[malloyd]

Originally Posted by teviet

Again, it's not that FTL only works in one frame, it's that FTL works differently in different frames. In one particular frame (maybe) your drive gives you a specified FTL speed in every direction. But in any other frame your FTL speed will vary, often by a large factor (infinity is a large factor!), depending on what direction you try to move.

TeV

Oh, OK. Yes that should work, it's equivalent to the formulation where the laws of physics include a term for velocity of the measuring frame relative to the preferred frame, with the velocity independent forms applying only in the preferred frame. You can show this by clocking an FTL trip and a light beam travelling between the same points. Since the trips are the *same* trip in all frames, if the FTL trip varies in speed relative to c in different frames, it should be obvious c varies by the same factor between those frames.

[vicky_molokh]

Originally Posted by teviet

Not much if you're careful. The only main consideration is what is the preferred frame? It can't just be the "fixed" frame of the stars, because of course the stars aren't fixed. And if you allow the frame/medium to be dragged along with, say, the Galactic rotation, then you have the possibility of traveling back in time if you circle the Galaxy backwards with your FTL. The obvious choice for a preferred frame is the CMB rest frame, which is moving a few hundred km/s relative to the Sun and other local stars.

So . . . what do we get if we do pick the CMBR frame as the privileged frame?

[Anthony]

Originally Posted by vicky_molokh

So . . . what do we get if we do pick the CMBR frame as the privileged frame?

Depends what you have that can make use of the privileged frame. The existence of a privileged frame implies the existence of at least one experiment (equivalent to Michelson-Morley) that can determine velocity relative to the privileged frame, but does not by itself imply much else.

[oldgringo2001]

Choosing the right FTL drive for your universe depends on what kind of universe you want and how "realistic" it is given that this type of cheating Einstein is allowed.

I've been playing Traveller since the year it came out, but I saw a giant flaw in its Jump drives immediately. By allowing ships to jump as soon as they got 100 diameters away from the planet and escape all detection (even Star Wars had tracking of ships in hyperspace) it made borders meaningless. As Larry Niven and Jerry Pournelle pointed out in Building the Mote in God's Eye, you'd get interstellar government by the latest space-pirates to show up. Larry and Jerry fixed this by making their jump drive work only along tramlines, hyperspace connections between hard-to-find pairs of points between star systems. This is the kind of FTL all the Traveller universes should have, but don't, and all because of the Millennium Falcon making that cool escape from Mos Eisley.

If your adventures involve pirates or swagmen outwitting The Patrol in space or paratime, this kind of jumping around is just what you need, but it also means any power with the means and the nastiness can Pearl Harbor entire worlds. That's exactly what Infinity is considering to solve the Reich-5 problem. That's also why the Snatcher needs to be brought on line Really Soon.

[Anaraxes]

it also means any power with the means and the nastiness can Pearl Harbor entire worlds.

Did you ever play Fifth Frontier War from GDW? It's a board of that conflict (of course). Impie fleets versus Zhos, along with ground troops. Defense in depth becomes important. The "border" isn't a single line, but it's a fuzzy zone more than six parsecs deep. Also, I found that people tended to concentrate defense on the most important worlds (e.g, Rhylanor). Spreading your forces out just invites defeat in detail. Presence of an enemy fleet nearby does, however, tend to prevent the enemy fleet from moving deeper, particularly once it takes a valuable world. (Why abandon that one for a less valuable world?)

I noticed similar effects in the old computer game Reach For The Stars. It usually paid to have most or all of your mobile fleet together to slam individual star systems, for much the same reasons.

So yes, you can Pearl Harbor entire worlds -- but if you're the Traveller Imperium, you have 11,000 more where that came from. Individual worlds aren't a particularly big concern on this scale. It's like saying France and Germany can't have a border because a surprise attack can grab any border city easily, and therefore all Europe must be anarchic.

This is the kind of FTL all the Traveller universes should have

Gets pretty close to saying people are having WrongBadFun.

[oldgringo2001]

Originally Posted by Anaraxes

Did you ever play Fifth Frontier War from GDW?

I certainly did. I remember the Imperials had to plot four turns ahead, but those evil Zhos with their filthy Psionics only had to plot three turns ahead.