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[wierd]

1) Polished surface vs lasers.

No.  Space is not empty. There are tiny particles of dust, particles of ice, and small rocks out there. Those will cause abrasion on such surfaces, leaving them less than perfectly smooth. That will leave areas where the laser's light will not be perfectly reflected, causing ablation, then penetration. These tiny scratches would be all over every centimeter of the ship after just a few months in space.

1a) Heavily mass-sheilded ship vs everything else

This means the ship will be very heavy. There are structural limits to what building materials can handle. Simply because there is substantially less gravity in space, does not magically remove inertia from the equasion. This means that the heavier the ship is, even with some super new-fangled drive tech, turning it quickly will rip the ship apart. This means that big heavy ships will move like big heavy ships.

2) biological resources as reason for war.

Possible causes:

Technologically superior species wants a 2 for 1 deal. Takes technologically inferor species, and forcibly implants cybernetics into their brains, and turns them into slaves. This destroys the rival culture, provides wetware for advanced servitors that are easier to control that pure software intelligences, and gives the old "our race is the bestest!" spot a good stroking all at once.

While potentially habitable planets seem to be plentiful in our galaxy (according to Kepler survey), planets with compatible or desirable flora/fauna may be a significantly smaller fraction of those. Given the number of useful organic compounds our own planet produces (basically ALL of our medicines we now use with the exception of the wholly synthetic ones-- and even those, if you consider that humans make them.) a technologically superior speces may wish to capitalize on such resources if they are biologically compatible with that biosphere. The native inhabitants would naturally be at odds with this, as the exploitation of their biosphere could be highly detrimental to them and their culture. See colonialism.

A large and powerful civilization might have very decadent tastes in entertainment or companionship. Exotic pets may be a thing.  Humans as dangerous exotic pets could be a thing, right along with lions, tigers, and bears.

[Starver]

Discussion of civilisations wiped out through stellar engineering reminds me of "The Star", the Arthur C. Clarke short story.

(Explanation, with full spoilers of course, here.)

[Cryxis, Prince of Doom]

(Just clerifying the current civs in game are Dyson sphere tech level. Yes I am going very soft scifi with this. The civs are at war for a few reasons and one of them is profeteiring from the war through producing weapons, contracting for finding cheaper resources (finding areas where whatever you are looking for is more abundant), mercenaries, being the guys who transport everything, and basicaly everything a civ would pay for to help in a war. Once again the war is religion/racism on both sides so even though they should be at that point where they are past war they still want all the competition gone. So the warning civs would be like Cold War Soviet Union and America. Two power houses trying to show off their strength but since in this setting if they fight eachother not everyone dies there isn't much keeping them from using their weapons on each other.)

Edit: also on the wearing down of the polished finish. Much like ships now, the surfaces would be regularly kept up by the crew (today ships or at least military ones are constantly being repainted and taken care of as best as possible to decrease erosion and deterioration of the ship. Much would be the same with these ships being regularly polished and repainted)

[Radio Controlled]

One could perhaps put a layer of protective material over the reflecting layer, if needed with empty space between them. The outer layer takes the corrosion of the space dust, and when it's laser time it can burn through the external layer, then hit your smooth anti-laser layer.

[wierd]

The problem is the ablation itself.

When the laser strikes the target, it causes it to vaporize into a cloud of hot vapor.  That vapor can either directly scar the surface below, or condense on the surface below. In both cases, it damages the reflectivity of the surface, allowing "point blank" ablation when the laser hits.

Also, it would be very costly to maintain such a setup. A micrometerorite cloud would mean you then have to spend months in the shipyard getting new wallpaper put on.

A magnetic envelope filled with a dense plasma would work better. The laser would diffuse in the already energetic plasma, and the extent of the bubble would be large enough that most micrometeorites would get caught in it/deflected before they struck the hull, unless moving at absurd speeds.

[Sheb]

Yeah, if you know where the laser is coming from, it's easy enough to send something in its way. Of course, the issue is that laser travels at lightspeed, so you don't get much warning.

[Cryxis, Prince of Doom]

While it is costly it's the same (or well similar to) what we do now with military ships. Which is more expensive? Maintaining the ship or replacing it?
How would you keep the plasma around the ship while it's traveling through space? Wouldn't it just get whipped back like the tail of a commet?

[Starver]

While it is costly it's the same (or well similar to) what we do now with military ships. Which is more expensive? Maintaining the ship or replacing it?
How would you keep the plasma around the ship while it's traveling through space? Wouldn't it just get whipped back like the tail of a commet?

Travelling?  Not necessarily.  If coasting, the plasma would be doing whatever it would do for a 'stationary' ship in orbit.  Which might depend on the nature of the plasma.

And if you're holding it around you a magnetic bubble/whatever, you just make sure the bubble is sufficient to keep ahold of the plasma even under the forces of acceleration (so it doesn't trail) or deceleration (so it doesn't 'lead') or indeed get whipped in whatever direction a comet's tail does (whichever way the solar wind/etc pushes; backwards, forwards, sideways...).

(But it'd probably ruin the chances of stealth in such a ship, all that active plasma round it.)

[Cryxis, Prince of Doom]

Also clerifying why there are fighters being used.

Since most battles are happening outside of planets they would be used as transport to the surface, dogfights in atmosphere, taking out other fighters entering atmosphere, strategic attacks on enemy ships (while yes you can just shoot a missile and guid it to where you could get a fighter you could just equip a more powerful weapon on a fighter and more accurately hit where you want to), possibly used to shoot enemy munitions (just cause they are replacing missles for ship to ship fighting doesn't mean they are replacing missiles for firing onto the planet).

[GiglameshDespair]

Wouldn't lasers lose focus at a distance? There are bits of space dust everywhere stealing your laser's power, too. You might end up heating your ship more than your opponent's.

Absolutely, they'll lose focus over distance subject to defraction. Lasers are also quite ineffecient, so you'll have a lot of problems with losing the heat once you've fired the laser. You could get around that with using some kind of heatsink, but then you're limited by the heat capacity of it. Radiators would be large but impossible to armour.

Indeed, I mentioned to diffraction previously. Blooming is generally used for thermal blooming, which doesn't occur in space so much due to the lack of atmosphere. The beam does spread out via diffraction, but smaller wavelength lasers can reduce that. As a result lasers are much more effective in space than they are on Earth.

Your lead shield idea... wouldn't that require both ships to be keeping the lead mist in between them? At their sort of velocities, that seems like you'd need one hell of a lot of lead to keep a shield up.

If you can detect the railgun projectile coming, you should be able to send it off course. Unevenly heating one side until it evaporates and produces thrust to knock it off course should work - I remember such a thing being discussed for asteroid diversion.

A railgun projectile isn't very large, which means a ship would only have to move a tiny amount to dodge. If the enemy ship is a mere light second away, and your railgun is sci-fi powered to shoot at 1%c, that's still 100 seconds for the enemy to detect and dodge. Even if they aren't already undertaking evasive manoeuvres they can probably detect the stabilising propellant you use to counteract the recoil.

Travelling?  Not necessarily.  If coasting, the plasma would be doing whatever it would do for a 'stationary' ship in orbit.  Which might depend on the nature of the plasma.

And if you're holding it around you a magnetic bubble/whatever, you just make sure the bubble is sufficient to keep ahold of the plasma even under the forces of acceleration (so it doesn't trail) or deceleration (so it doesn't 'lead') or indeed get whipped in whatever direction a comet's tail does (whichever way the solar wind/etc pushes; backwards, forwards, sideways...).

(But it'd probably ruin the chances of stealth in such a ship, all that active plasma round it.)

As mentioned, there isn't really much stealth in space.

[Starver]

(But it'd probably ruin the chances of stealth in such a ship, all that active plasma round it.)

As mentioned, there isn't really much stealth in space.

Indeed, but of the stealth you might have had (the ultimate being to either drift in a ship utterly blackened or 'shiny to perfectly reflect the blackness of space', using thrusters only sparingly as required, and on the side of your ship facing away from your ultimate prey until and unless you absolutely need to, to slow down again), purposefully lighting yourself up in some band(s) or other of the electromagnetic spectrum like a weirdly inverted florescent tube (that would probably be purposefully looked for, if it was known 'shield' technology) would probably highlight your location and possible intentions at a far greater distance...

[mainiac]

What if you purposefully radiate energy in a specific direction?  Or rather, dont radiate in the specific direction you know the detection to be?  A few layers of one sided emmissive surfaces separated by micro-vacuum would cut the emissions down by several orders of magnitude if the radiators are allowed to freely radiate in the opposite direction.

[mainiac]

Maybe... but who knows what the future comparative economic competitiveness of something like magnetic sails vs. solar sails vs. rockets will look like?  I think we stand about as much chance of understanding space combat as Richard Gatling stood of understanding combined arms.

[Starver]

What if you purposefully radiate energy in a specific direction?  Or rather, dont radiate in the specific direction you know the detection to be?  A few layers of one sided emmissive surfaces separated by micro-vacuum would cut the emissions down by several orders of magnitude if the radiators are allowed to freely radiate in the opposite direction.

Well, that was what was pretty much behind my "sparingly use the thrusters that are only on the opposite side of the ship" idea, although I suspect that some of the concepts behind space-stealth is something clever (with thermocouples?) that makes the 'facing' side emit only radiation similar to the 4°K 'background' of space (radiating the difference above all the 'normal' system excesses out at the far side?), as well as dealing with the visible/radar aspects of the ship a la terrestrial/aircraft 'stealthing' materials.

But the original "you're going to have problems with stealth" reference was regarding the 'plasma shield' idea (for both dispersing ship-on-ship weaponry and protecting against micrometeorites).  You couldn't have it on and be trying to stay as inconspicuous as possible.  Wait until you're potentially in danger (from enemy weapons of a now alert enemy, or natural hazards more dangerous to you than that of newly alerting the enemy) and then boot it up (especially on the leading edge, as you're approaching those hostiles) and effectively become a 'beacon of light', within the human visible-spectrum or otherwise.

[mainiac]

A bit like submarines.  If you can be stealthy, be very stealthy.  If you can't then push everything to the limit and get very noisy indeed.