I have a quick question that can probably answered with a link. I'm wondering why the LT engine and it would seem most physics engines require some amount of drag? Is it to do with a mathematical equation having a zero at the bottom of a fraction or something similar (square root of a negative number)?

vector67 wrote:I have a quick question that can probably answered with a link. I'm wondering why the LT engine and it would seem most physics engines require some amount of drag? Is it to do with a mathematical equation having a zero at the bottom of a fraction or something similar (square root of a negative number)?

I haven't looked it up but the PCG might not be able to keep up with a vessel moving at almost 186,000 mi/s. Then again maybe it could. Also mechanics (before ftl travel) get rather interesting near the speed of light. Just being able to perceive the universe becomes a challenge. There was a game that NASA released called the "speed of light" that demonstrated the effects one undergoes when approaching such velocities.

Math in computers isn't as precise or as beautiful as math on paper or in someone's head, without drag numbers get too high or imprecise and shit starts exploding.
Most often this is caused by floating point accuracy restrictions. http://en.wikipedia.org/wiki/Floating_p ... y_problems
It's kind of like how entropy is a good thing.

Sometimes though, drag is just a good gameplay mechanic. It's more intuitive to the human being to think that things stop on their own since we're used to friction.

I think it's not precisely drag that is 'necessary', it's a maximum velocity. There's no reason zero drag would cause a divide-by-zero error or similar; a drag coefficient of zero just results in a drag force of zero, no problem. As Katawa mentioned, it's infinitely increasing velocities that cause engines problems. Drag provides an implicit maximum velocity, but you could just impose an artificial top velocity instead (and I think there are plenty of games that don't have drag, and take that approach).

I don't think PCG has anything to do with it. In LT you move between systems with wormholes, so travel speed isn't an issue.

General Drag also acts as Damping in physics systems.

And in general gameplay-wise, high (not necessarily relativistic though) velocities aren't conducive to the kind of gameplay that people expect from, well, a space sim. I'm not sure how a game where it takes days (real life time) to stop your ship plays out. Hence, the few attempts at implementing something like that are typically experimental indie games, or examples like Evochron (which is well under relativistic).

Revoke wrote:I think it's not precisely drag that is 'necessary', it's a maximum velocity. There's no reason zero drag would cause a divide-by-zero error or similar; a drag coefficient of zero just results in a drag force of zero, no problem. As Katawa mentioned, it's infinitely increasing velocities that cause engines problems. Drag provides an implicit maximum velocity, but you could just impose an artificial top velocity instead (and I think there are plenty of games that don't have drag, and take that approach).

I don't think PCG has anything to do with it. In LT you move between systems with wormholes, so travel speed isn't an issue.

So how fast can your computer render things from distance in a very short amount of time, possibly with a great deal of objects at a speed that you would find it difficult to ascertain what was going on in the universe.

An example. At 186,000mi/s, if the engine renders objects 25 miles away from you you will have approx 0.0001 seconds to react to something in appearing in front of you. Or one ten-thousanth of a second! You would be colliding with this object before you registered there was one there and left wondering what the hell you hit. So there becomes a point where such speed makes the game unplayable. Let acceleration ratings combined with a "manageable" top speed be a more usable system of Newtonian physics. I don't think it will apply in LT however, I believe Josh has already made reference to this.

A few things

1) The question of drag is, first and foremost, a gameplay question. As others have pointed out, a game in which speeding up and then coming to a stop takes "realistic" times is....probably not one that I want to play. On the other hand, if you can speed up and slow down in a "reasonable" time, without a drag force, it also implies that you can reach insanely fast speeds in a reasonable time. Frankly, I think it makes for bad gameplay. That's a personal opinion, nothing more and nothing less

2) Limited top speed without drag is, I would argue, even less Newtonian than having a drag force. There's nothing non-Newtonian about a drag force. True, there's no medium to exert drag in space. But I think it would be better to call it "unrealistic" instead of "non-Newtonian," which somehow suggests that the real "Newtonian" physics uses some kind of advanced internal machinery, when in reality, both methods will always use discrete Newtonian integration. Just that one applies a drag force and the other doesn't. Interestingly, a hard cap on the velocity without drag does not fit into the framework of Newtonian mechanics (please correct me if I am mistaken), because it cannot be implemented with a force! Velocity cap without drag suggests either a hack or relativistic mechanics, both of which are highly-non-Newtonian

3) Although it's not the major issue, there are some technical problems with unlimited-top-speed systems. Precision, as others have mentioned, will be problematic. But mitigated substantially by double precision. A bigger issue, though, is collision detection. You simply won't be able to perform accurate collision detection in a timely manner with unbounded velocities. It will become either too inaccurate or too expensive. If you're willing to sacrifice CD accuracy, then my guess is that you wouldn't have too much trouble implementing a game with unlimited top speeds. Of course, at some point, you need to cap the velocity. But I suppose if you use real relativistic equations then you get a speed cap automatically.

4) BONUS ROUND! You mentioned a zero at the bottom of an equation. Which is an interesting thought. Incidentally, if you set the drag coefficient in the LT engine to be zero, you will indeed get several zero denominators in various places and cause things to blow up. The reason is that any piece of code or equation that expects a finite top speed will blow up in the absence of any drag. So the AI, for example, is using it's knowledge of the drag force to make more accurate predictions of where objects will be when they come to a stop. If drag is set to zero, an object in motion will never come to a stop unless acted upon externally, so the AI would totally fail. It would actually require a different steering algorithm than the one LT uses to manage AI pilots in a zero-drag, no-speed-limit setting!

Right about the relativistic physics in "relation" to Newtonian physics! Then again all that mankind knows is a matter of relativity.

The only way to realistically implement a lower top speed would be to alter the physics of said universe, say the speed of light itself.

All in all we know that the game-play is more important than scientific accuracy here... well to a point. I don't see a purpose myself for lethal confetti cannons and homing pinatas. I believe what is intended for LT is the correct answer in any case.

Relativistically speaking the "force" that limits objects to almost the speed of light is inertia which increases to infinity as one approaches light speed. For an interesting "real world" theory on how to reach FTL travel look up the alcubierre warp ship. It's a neat concept.

C.J. Cherryh has made a pretty good living writing SF novels that try to show what relativistic combat might be like.

To severely oversimplify, a ship moving at near-lightspeed is nigh impossible to deter -- by the time you can sense it, it's already dropped its payload on you and you're extremely dead.

If you posit a few things, though, you might get a chance:

1. Ships can't just "warp" directly to the location of a target -- they have to come in from the outskirts of the system.
2. Ships aren't moving at exactly the speed of light; they're just at near-lightspeed.
3. And they probably have to slow down a little bit to drop their payload, anyway, since they're ships carrying living people and presumably care about preserving the lives of those people.

Add up those assumptions, and about the one thing you can do is dump a really large number of listening posts throughout the system. If a high-speed object appears in-system, these posts can signal their home system... and those signals can travel at lightspeed.

This gives you a few minutes -- or maybe an hour or two at best depending on how far in-system the object appears -- before death arrives. That's when you get to start playing probabilistic games -- what was that object's last heading? was it seen jinking? how fast was it going? Based on those calculations, you try to throw rocks where you think the intruder might be going. If you're still around in a couple of hours, your calculations were probably right. If not....

(If the incoming object is not a ship -- such as a missile or a big rock -- the problems are worse, since that object won't have to slow down for anything. You get less time to guess where it might be. On the plus side, it might be moving in a straight line... maybe.)

Being the attacker means seeing that problem from the other side. Anything entering a defended system will be tracked immediately. If you are not seen to be slowing waaaaaaaay down right away, you will be assumed to be a relativistic threat and treated accordingly. One nasty option is to be a ship (or ships) unloading a large number of smaller objects, each traveling at very high speed. Most won't do much damage to a planet shielded by a thick atmosphere, but objects in space can be severely damaged or destroyed by even very small objects traveling at pretty low speeds, to say nothing of relativistic speeds.

Space is just plain dangerous even before sentient beings invent ever-more-creative ways to obliterate each other....

There's also some clever tactics to be employed there. Like a MIRV where most of the warheads are decoys. Which do you shoot down given the time? Also a clever bugger might send say a hundred ships in at relativistic speeds. Have them stop and start all over the system essentially making prediction all but impossible! How about having a "civie" drop some warheads in system that then ratchet it up to relativistic speeds in system at a later time or even date. This would then play into the geopolitical situation as you would never know just how many weapons the enemy or potential enemy would have in your systems.

In the end given time this would result in something similar to MAD. Only on a system wide scale.

Kinetic Energy = Mass x Velocity sq. so> 1kg x 299338000m/s squared = 8.96 x 10 to the 16th! Or 896 000 000 000 000J! Or just 896 terajoules! Ouch that can hull 40k ships! Imagine megatonne objects!

Grumblesaur wrote:

is that an archievement from kerbal space program?

One more thing to consider: although we're talking science fiction here, so that supposedly you could stick some kind of magical "inertial dampener" on a ship, without that, even at very fast speeds, you're still putting (as Jim Lovell of Apollo 8 and Apollo 13 famously said) "Sir Isaac Newton in the driver's seat."

In other words, it takes a long time to accelerate an object of appreciable size to relativistic speed, and it takes an equally long time to decelerate (assuming you prefer to do so in one piece). Anything speeding up to near-lightspeed would be detected during that process.

Similarly, inertia means it's hard to change course by much when you're going extremely fast. So calculated trajectories could still work, although you're still trying to hit a bullet with a bullet (only several orders of magnitude worse than that).

Again, though, as science fiction you can handwave away inertia... but then stories (and game mechanics) get stacked so far in favor of the attacker that it's no fair and no fun.

Cornflakes_91 wrote: is that an archievement from kerbal space program?

Note the watermark.

Flatfingers wrote:One more thing to consider: although we're talking science fiction here, so that supposedly you could stick some kind of magical "inertial dampener" on a ship, without that, even at very fast speeds, you're still putting (as Jim Lovell of Apollo 8 and Apollo 13 famously said) "Sir Isaac Newton in the driver's seat."

In other words, it takes a long time to accelerate an object of appreciable size to relativistic speed, and it takes an equally long time to decelerate (assuming you prefer to do so in one piece). Anything speeding up to near-lightspeed would be detected during that process.

Similarly, inertia means it's hard to change course by much when you're going extremely fast. So calculated trajectories could still work, although you're still trying to hit a bullet with a bullet (only several orders of magnitude worse than that).

Again, though, as science fiction you can handwave away inertia... but then stories (and game mechanics) get stacked so far in favor of the attacker that it's no fair and no fun.

Lightspeed is too slow anyway.