How powerful could a hard sci-fi civilization be?

[Luke Skywalker]

What is the strongest science fiction faction a socially, politically, intellectual and morally enlightened civilization, that has passed all significant threats of extinction, defeat?

The only time limit on its development is the natural age of the universe. The only limits on its technological advancement are our current understanding of laws of physics and inherent engineering limitations; this means no FTL. Could this civilization conceivably match down the UFP in a total war? Or even the Galactic Empire?

[inspired by this thread:

http://bbs.stardestroyer.net/viewtopic.php?f=4&t=114575 ]

[Jub]

How much area do they cover? What tech are we deeming as feasible enough to allow or are we stuck with only mature technologies that we have today?

[Luke Skywalker]

How much area do they cover?

As much as they can within practicality.

What tech are we deeming as feasible enough to allow or are we stuck with only mature technologies that we have today?

Whatever does not violate our current understanding of physics and a civilization could conceivably produce within the universe's timespan and inherent engineering parameters. So it's debatable, of course.

[Jub]

How much area do they cover?

As much as they can within practicality.

What tech are we deeming as feasible enough to allow or are we stuck with only mature technologies that we have today?

Whatever does not violate our current understanding of physics and a civilization could conceivably produce within the universe's timespan and inherent engineering parameters. So it's debatable, of course.

Okay given a galaxy of ever expanding Von Neuman machines and enough spare energy/time to create the crazy materials needed for space elevators and Dyson rings/spheres/shells we could be very nasty. If we assume that we eventually crack fusion and later how to store and use antimatter we'll likely be able to stand up Trek at the least. Their FTL will be nasty, but if we can get to them we can hurt their ships and they have less resources than we do. Other sci universes will be very case by case and I'm not really sure where we start being unable to win except to say that I still like we'd lose to something like Star Wars.

[GrandMasterTerwynn]

This is a bit ... open-ended. If a civilization were hell-bent on capturing every bit of solar output and putting it into useful work, they could absolutely carpet a system with orbital solar collectors. There are 750,000 asteroids with a mean radius of 1 km or greater in our solar system. If you assumed that every last one of them was a 1 km asteroid, and that you hammered each one into a cylinder with meter thick walls, you'd have over 392 million square kilometers of living space. If you assumed that each orbital habitat you built had the same population density as New York City . . . well, you'd get a population of just over four trillion people. This is before you add in any potential living are gained by pulling in KBOs, or disassembling terrestrial planets. A civilization restricted to STL physics could conceivably disassemble Mercury with enough Von Neumann machines and mass-drivers, turning the mass into solar collectors that might be used to build a massive network of lasers to propel laser-sail ships across the solar system, or to power huge banks of particle accelerators to create antimatter for use outside the solar system.

The inhabitants of this solar system would be no laughing matter either. Given the stunning pace of development of computational and bioengineering technologies that are taking place right now ... a future with biologically immortal human beings with lifespans of 1000 years (if you live long enough, the probability of accidental death approaches one,) isn't inconceivable. These humans might also have a definition of "personhood" that would be utterly alien to you or I. In that future, you may live a couple centuries as a flesh-and-blood human on an orbital habitat, and then have your mind digitized and downloaded into an engineered body that can operate on the methane lakes of Titan; or you could have multiple copies of you at once.

These beings might attempt to use nanotechnology to turn the highly-conductive interiors of gas giants into enormous computational structures. Certainly, they could make a layer of those meter-thick orbital habitat walls into a pure computing substrate, and add these substrates to the backs of all those solar collectors they sacrificed the planets of Mercury and Mars to build. All of it could be networked through those giant lasers I mentioned earlier, and a network of smaller lasers. Given the latency induced by all those hours of lightspeed lag, it wouldn't be an especially fast computing network, but it would be one of stupendous computing power (although a supercomputer the size of New York City would be bad enough to try to defeat.) Given that this network would be host to, possibly, trillions of mind-uploads, it would be similarly stupendous in its deviousness.

To make a long story short, a mature STL physics solar system would be undefeatable by anything less than the most stupendously-overpowered sci-fi franchises. Just one mature STL physics solar system would have more population than the entire Federation of Star Trek. It would be far too diffuse a target for a Death Star, or a flotilla of Imperial Star Destroyers to kill; and the solar system could use all those solar collectors, mass drivers, lasers, and antimatter factories to obliterate the invaders anyway. Sure, the invaders might have FTL technology, but they have baseline human command staff aboard their ships . . . pitted against a civilization which finds the digitization and simulation of a baseline human mind to be a relatively trivial computational task (i.e. we know where you're going to move your ships, we can predict when they're going to get there, and you're going to get a face-full of hard x-rays when you emerge from your quantum hyperwarpspace drive.)

A whole galaxy of such civilizations . . . well, you could have surprisingly cohesive interstellar empires within this framework. Physical ships might jet between the stars at somewhere between three to fifty percent of the speed of light, powered by antimatter engines; but with a big enough laser, you could send huge quantities of data at light speed . . . up to, and including digitized minds. And if you're someone who can expect to live for at least a thousand years, hopping into the digital teleporter and making the ten year trip to Tau Ceti suddenly doesn't seem like such a long time at all.

[Patrick Degan]

I have to say, Terwynn, that is a stunning vision you put forth. You should turn that into a novel.

[sirocco]

From his point of view, the greatest enemy a STL civilization would have would be a second STL civilization. That's a good basis for a solar system equivalent of the World War or the Cold War depending on the level of technological advancement reached by each party.

However, just a note: shouldn't you reduce the estimate for your total population?

I think that New York is not really a good example, since it's not self-sufficient. You could look at Ecological footprint concept and Biosphere 2.

As a reminder 100 hectares is 1 square kilometer
So if we consider that the hard sci-fi civilizaton perfected the Biosphere concept, the 392 million square kilometers of living space wold be able to sustain:

- living like EAU (10 hectares needed per capita): 3.92 billion people
- living like US (8): 4.9 billion people
- living like France (5): 7.84 billion people
- living like Haiti (0.68): 57.6 billion people

It's just an estimate however, but I think it's safe to assume that if people are going to live hundreds or thousands of years, they'd rather live like the Emiratis than the Haitians. And from my understanding of the concept of Ecological footprint, it does not take into account the industry and various services needed in a orbital habitat.

To me that doesn't seem a lot.

[Jub]

From his point of view, the greatest enemy a STL civilization would have would be a second STL civilization. That's a good basis for a solar system equivalent of the World War or the Cold War depending on the level of technological advancement reached by each party.

However, just a note: shouldn't you reduce the estimate for your total population?

I think that New York is not really a good example, since it's not self-sufficient. You could look at Ecological footprint concept and Biosphere 2.

As a reminder 100 hectares is 1 square kilometer
So if we consider that the hard sci-fi civilizaton perfected the Biosphere concept, the 392 million square kilometers of living space wold be able to sustain:

- living like EAU (10 hectares needed per capita): 3.92 billion people
- living like US (8): 4.9 billion people
- living like France (5): 7.84 billion people
- living like Haiti (0.68): 57.6 billion people

It's just an estimate however, but I think it's safe to assume that if people are going to live hundreds or thousands of years, they'd rather live like the Emiratis than the Haitians. And from my understanding of the concept of Ecological footprint, it does not take into account the industry and various services needed in a orbital habitat.

To me that doesn't seem a lot.

You're ignoring the fact that we can grow food in greater amounts per hectare with hydroponic methods and that these methods could be built into spaces that aren't currently usable if we planned a city around this. For example, growing food in the space between high rises or in massive vertical planters over intersections. Building green walls into buildings.

[sirocco]

You're ignoring the fact that we can grow food in greater amounts per hectare with hydroponic methods and that these methods could be built into spaces that aren't currently usable if we planned a city around this. For example, growing food in the space between high rises or in massive vertical planters over intersections. Building green walls into buildings.

Hum right, I assumed that any advanced form of space agriculture would just be as good as Earth. But even with higher yield, don't they require more energy, water or nutrients?

After it's not really a problem, since you could have asteroids dedicated to food production, with the right combination of factors to boost the production.

[Jub]

You're ignoring the fact that we can grow food in greater amounts per hectare with hydroponic methods and that these methods could be built into spaces that aren't currently usable if we planned a city around this. For example, growing food in the space between high rises or in massive vertical planters over intersections. Building green walls into buildings.

Hum right, I assumed that any advanced form of space agriculture would just be as good as Earth. But even with higher yield, don't they require more energy, water or nutrients?

After it's not really a problem, since you could have asteroids dedicated to food production, with the right combination of factors to boost the production.

You could even grow food in domes on the outside of the habitat with access tunnels for harvesting it. That way it takes up very little inside space to grow your food.

[Luke Skywalker]

or to power huge banks of particle accelerators to create antimatter for use outside the solar system.

Is this practical? From what I know, creating antimatter is always a net loss, energy-wise.

Just one mature STL physics solar system would have more population than the entire Federation of Star Trek.

There's still the issue of being STL though. I can understand your civilization beating the Federation if they act like idiots (hardly a stretch) and show up in Napoleonic battlelines, but it's difficult to think of a defense against warp strafing or even rapid hit and run attacks, given that it would take many minutes for information of any kind to cross just the single star system.

It would be far too diffuse a target for a Death Star, or a flotilla of Imperial Star Destroyers to kill; and the solar system could use all those solar collectors, mass drivers, lasers, and antimatter factories to obliterate the invaders anyway.

I'm not sure about this, either. Even barring realistic competence, a single star destroyer has a power output comparable to a small sun. And I don't see how you could even scratch a Death Star through its shielding. It has all the time in the world to blow shit up, dispersed or not.

[Jub]

or to power huge banks of particle accelerators to create antimatter for use outside the solar system.

Is this practical? From what I know, creating antimatter is always a net loss, energy-wise.

When harvesting the stellar output of all the galaxies stars the loss is something that can be swallowed.

Just one mature STL physics solar system would have more population than the entire Federation of Star Trek.

There's still the issue of being STL though. I can understand your civilization beating the Federation if they act like idiots (hardly a stretch) and show up in Napoleonic battlelines, but it's difficult to think of a defense against warp strafing or even rapid hit and run attacks, given that it would take many minutes for information of any kind to cross just the single star system.

If you load your systems with guns and/or mines then linked systems don't much matter. We also see warp strafing happen in the show just about as often as we see the UFP attacking with massed fleets.

It would be far too diffuse a target for a Death Star, or a flotilla of Imperial Star Destroyers to kill; and the solar system could use all those solar collectors, mass drivers, lasers, and antimatter factories to obliterate the invaders anyway.

I'm not sure about this, either. Even barring realistic competence, a single star destroyer has a power output comparable to a small sun. And I don't see how you could even scratch a Death Star through its shielding. It has all the time in the world to blow shit up, dispersed or not.

A Star Destroyer, as has been demonstrated, doesn't need the full output of a star to be defeated. It would be a struggle, but you can put one down with just what weapons can be amassed in a single solar system. The Death Star is harder, but you could eventually figure out where it will head next and choke off it's fuel supply ships.

[Sea Skimmer]

And how exactly do you propose to choke off fuel supplies when you'll need tens of thousands of years to cross a single galaxy even if nothing actually delayed your advance? The Empire built one Death Star in at max, 20 years if we accept the episode III one was the original, much less time by other estimates. Your going to have an awful lot of Death Stars to deal with after 10,000 years either way.

[Luke Skywalker]

When harvesting the stellar output of all the galaxies stars the loss is something that can be swallowed.

Why would you swallow it if its energy potential is lower than the energy consumed to make it?

If you load your systems with guns and/or mines then linked systems don't much matter. We also see warp strafing happen in the show just about as often as we see the UFP attacking with massed fleets.

Then the HSF's survival banks on just how long the UFP stays stupid. Surely they would learn to abuse warp strafing quickly as soon as they realize that their opponent has no FTL. Typically, they fight against warp capable enemies, so warp strafing is of limited usefulness.

A Star Destroyer, as has been demonstrated, doesn't need the full output of a star to be defeated. It would be a struggle, but you can put one down with just what weapons can be amassed in a single solar system.

You'd need around e24 watts to overload its heat dissipation rate. Theoretically it's possible, I guess. But against a fleet, you're screwed.

The Death Star is harder, but you could eventually figure out where it will head next and choke off it's fuel supply ships.

[/quote]

But that's the problem; the Death Star can move faster than the HSF civ can communicate. It'll be at the next system within hours, while warning of the attack won't arrive for years.

[Jub]

And how exactly do you propose to choke off fuel supplies when you'll need tens of thousands of years to cross a single galaxy even if nothing actually delayed your advance? The Empire built one Death Star in at max, 20 years if we accept the episode III one was the original, much less time by other estimates. Your going to have an awful lot of Death Stars to deal with after 10,000 years either way.

If you find out where they are coming from, IE through a wormhole, you can blockade them with ships from local systems and prevent them from getting the ships in to build a new Death Star. If they're attacking from another galaxy their going to take a long time to reinforce anything and I doubt they send the DS through as part of the first wave. So you crush the scouts and construction vessels and then you have time to ready yourself for the next attack while preparing to send your own scouts to attack them back. The STL galaxy will likely be on the back foot, but eventually they should be able to force a draw or at least convince the Empire that they aren't worth it.

When harvesting the stellar output of all the galaxies stars the loss is something that can be swallowed.

Why would you swallow it if its energy potential is lower than the energy consumed to make it?

Why do we spend energy to make batteries?

If you load your systems with guns and/or mines then linked systems don't much matter. We also see warp strafing happen in the show just about as often as we see the UFP attacking with massed fleets.

Then the HSF's survival banks on just how long the UFP stays stupid. Surely they would learn to abuse warp strafing quickly as soon as they realize that their opponent has no FTL. Typically, they fight against warp capable enemies, so warp strafing is of limited usefulness.

They haven't shown that much ability to get better at fighting so far, why should we assume they'll get any smarter now?

A Star Destroyer, as has been demonstrated, doesn't need the full output of a star to be defeated. It would be a struggle, but you can put one down with just what weapons can be amassed in a single solar system.

You'd need around e24 watts to overload its heat dissipation rate. Theoretically it's possible, I guess. But against a fleet, you're screwed.

Except that this clearly isn't the case. Look at the X-Wing books and look at how far less energy is used to overwhelm a single shield section so the fighter squadron can attack the ship directly.

The Death Star is harder, but you could eventually figure out where it will head next and choke off it's fuel supply ships.

But that's the problem; the Death Star can move faster than the HSF civ can communicate. It'll be at the next system within hours, while warning of the attack won't arrive for years.

Yes, but it does have a recharge time and finite amounts of fuel. It'll be tough to pin it down, but if the supplies have to filter in through a worm hole or be manufactured in a star system you can still starve it.

This is also assuming that any AI or scientists working for the HSF universe don't discover FTL the moment they know it's possible. It also assumes that in a scenario where the universes are connected by wormholes that the HSF universe hasn't managed to stabilize wormholes and use those to create an effectively FTL means of travel.

[Luke Skywalker]

Why do we spend energy to make batteries?

For this, you could use fusion, or the sun. Correct me if my understanding of physics is wrong, but the only practical use I'd see for antimatter power (if this is even feasible) would be for long-term journeys where you need a ship that can produce large amounts of energy on the fly, and are therefore willing to expend more energy to create said antimatter...more of which could be stored on ships. Or you discovered large natural reservoirs.

They haven't shown that much ability to get better at fighting so far, why should we assume they'll get any smarter now?

They'd used warp strafing before. Its noted rarity may be because the Federation typically faces off against warp capable civilizations that can counter it. It's very difficult to base an entire argument on the assumption that the enemy would be too stupid to perform even the most basic and self evident tactics, such as spamming Picard maneuvers with impunity.

Except that this clearly isn't the case. Look at the X-Wing books and look at how far less energy is used to overwhelm a single shield section so the fighter squadron can attack the ship directly.

You can't be referring to EU-wank novels where a single squadron takes out an entire star destroyer, even though Ackbar makes it clear in the RotJ novel that the starfighters would only stand a chance if the main fleet could bring the star destroyers' shields down. Not to derail the topic, but those starfighers were likely using multi-gigaton shaped charges, and even in Traviss novels, it's rare to down a functional ISD using such tactics.

And it's going to be especially difficult to target an ISD accelerating at a few thousand G's.

Yes, but it does have a recharge time and finite amounts of fuel. It'll be tough to pin it down, but if the supplies have to filter in through a worm hole or be manufactured in a star system you can still starve it.

How long would it take to reach the Death Star's supply base? Years? Decades? Centuries? Millenia? How long would it take to even find out about it? How the hell would they locate it? And what's to stop the Death Star from refueling by stopping off in a random point in space while ships rendezvous at said location and supply it?

This is also assuming that any AI or scientists working for the HSF universe don't discover FTL the moment they know it's possible.

"the moment"? So after failing to discover FTL in however many years, they'll instantly reverse engineer hyperdrive without even having a working model?

It also assumes that in a scenario where the universes are connected by wormholes that the HSF universe hasn't managed to stabilize wormholes and use those to create an effectively FTL means of travel.

I was vague on what the context of the conflict was. I guess we can discuss a variety of scenarios. But I don't think a strict HSF universe permits "stabilizing wormholes" to go FTL.

[Jub]

Why do we spend energy to make batteries?

For this, you could use fusion, or the sun. Correct me if my understanding of physics is wrong, but the only practical use I'd see for antimatter power (if this is even feasible) would be for long-term journeys where you need a ship that can produce large amounts of energy on the fly, and are therefore willing to expend more energy to create said antimatter...more of which could be stored on ships. Or you discovered large natural reservoirs.

Use fusion for the engines and anti-matter for the missile warheads. You use AM for greater energy density.

They haven't shown that much ability to get better at fighting so far, why should we assume they'll get any smarter now?

They'd used warp strafing before. Its noted rarity may be because the Federation typically faces off against warp capable civilizations that can counter it. It's very difficult to base an entire argument on the assumption that the enemy would be too stupid to perform even the most basic and self evident tactics, such as spamming Picard maneuvers with impunity.

Not often and not in cases where it would have been useful. They're also shown to be pretty bland and boring in their tactics, such as updating their computer security or making a phaser that is easy to hold and aim.

Except that this clearly isn't the case. Look at the X-Wing books and look at how far less energy is used to overwhelm a single shield section so the fighter squadron can attack the ship directly.

You can't be referring to EU-wank novels where a single squadron takes out an entire star destroyer, even though Ackbar makes it clear in the RotJ novel that the starfighters would only stand a chance if the main fleet could bring the star destroyers' shields down. Not to derail the topic, but those starfighers were likely using multi-gigaton shaped charges, and even in Traviss novels, it's rare to down a functional ISD using such tactics.

And it's going to be especially difficult to target an ISD accelerating at a few thousand G's.

Those novels are cannon, if you don't like them then that's too bad.

Just because you can't get a missile to go FTL doesn't mean you can get it accelerating at retarded speeds.

Yes, but it does have a recharge time and finite amounts of fuel. It'll be tough to pin it down, but if the supplies have to filter in through a worm hole or be manufactured in a star system you can still starve it.

How long would it take to reach the Death Star's supply base? Years? Decades? Centuries? Millenia? How long would it take to even find out about it? How the hell would they locate it? And what's to stop the Death Star from refueling by stopping off in a random point in space while ships rendezvous at said location and supply it?

That depends, are we talking about a war between galaxies where the Empire is going to have a looong supply tail, or a wormhole where the HSF side can just defend the choke?

This is also assuming that any AI or scientists working for the HSF universe don't discover FTL the moment they know it's possible.

"the moment"? So after failing to discover FTL in however many years, they'll instantly reverse engineer hyperdrive without even having a working model?

If the physics of the universe allow for FTL then shouldn't the HSF universe eventually discover it? If it doesn't how is the Empire moving faster than light?

It also assumes that in a scenario where the universes are connected by wormholes that the HSF universe hasn't managed to stabilize wormholes and use those to create an effectively FTL means of travel.

I was vague on what the context of the conflict was. I guess we can discuss a variety of scenarios. But I don't think a strict HSF universe permits "stabilizing wormholes" to go FTL.

Why not? It's thought to be theoretically possible.

[Sea Skimmer]

Those novels are cannon, if you don't like them then that's too bad.

So is the ICS saying that star destroyers have 200 gigaton turbolasers. This does not bode well for your concept of large numbers of asteroid bases.

Just because you can't get a missile to go FTL doesn't mean you can get it accelerating at retarded speeds.

Speed doesn't solve the problem of the enemy being able to change course to evade, and fire 200 gigaton shots, and that turbolasers have the range according to certain novels, well one anyway, to shoot across a star system. We have canon evidence that Star destroyer is just going to be able to appear by hyperspace near one of these super systems, fire a few dozen shots blowing up a few dozen asteroid bases, and then zip away before any sublight weapon could possibly reach it. Since FTL sensors are not possible for a hard sci fi force, an attack could appear anywhere around the system without warning and predicting it would be pure random chance no matter how smart your computers are.

[Jub]

Those novels are cannon, if you don't like them then that's too bad.

So is the ICS saying that star destroyers have 200 gigaton turbolasers. This does not bode well for your concept of large numbers of asteroid bases.

Just because you can't get a missile to go FTL doesn't mean you can get it accelerating at retarded speeds.

Speed doesn't solve the problem of the enemy being able to change course to evade, and fire 200 gigaton shots, and that turbolasers have the range according to certain novels, well one anyway, to shoot across a star system. We have canon evidence that Star destroyer is just going to be able to appear by hyperspace near one of these super systems, fire a few dozen shots blowing up a few dozen asteroid bases, and then zip away before any sublight weapon could possibly reach it. Since FTL sensors are not possible for a hard sci fi force, an attack could appear anywhere around the system without warning and predicting it would be pure random chance no matter how smart your computers are.

Depends on how far out your defenses go and how densely packed they are. That and how many shots can an SD fire before they're reactor runs dry? We have some evidence that says hours to minutes for a high powered bombardment.

Also, if Star Wars teach has always worked and is physically possible in both galaxies/universes, why are we assuming that this hard sci-fi race can't discover it? If it doesn't work why do the Star Wars ship still function on the HSF teams turf?

[Sea Skimmer]

Depends on how far out your defenses go and how densely packed they are.

Highly unlikely to be effective at such great ranges, and the bigger the perimeter the less densely packed it will be.

That and how many shots can an SD fire before they're reactor runs dry? We have some evidence that says hours to minutes for a high powered bombardment.

I doubt more then low hours, but the hell if it matters when the Empire could build tens of millions of heavy warships in the time it would take a hard sci fi power to travel even a fraction of the way across one galaxy, even by the low end figure of 25,000 star destroyers. This also tends to make it meaningless that the hard sci fi power might spread to thousands or galaxies, since none but the closest would have any relevance in less then millions of years of sublight travel,, by which time the Empire could expand to an absurd degree behind hundreds of thousands of Death Stars. Of course, by the same card, how long are any of the high power 'hard' weapons you postulate actually going to be able to sustain fire for, and how well are they going to work at ranges of millions of kilometers? You basically can't answer that.

Also, if Star Wars teach has always worked and is physically possible in both galaxies/universes, why are we assuming that this hard sci-fi race can't discover it? If it doesn't work why do the Star Wars ship still function on the HSF teams turf?

Because that would you know, invalidate the entire premise of the thread.

[Blayne]

I believe if I recall from that Atomic Rockets site that a Hard Scifi civilization could deploy crazy powerful relativistic rail/coil guns capable of burning off the crust of a planet it struck which would be impossible to detect if our understanding of physics is limited to STL stuff.

So we could wipe the life from every world in the Galactic Empire, every space colony, and every immobile station there and in the UFP; just not the starships which can dodge.

I'm presuming we're a Type IV on the Kardashev Scale and harnassing the power of more than our galaxy.

I'm a little confused though, stuff like Wormholes and Alcubierre drives should be attainable under our current understanding of physics, especially if we're harnessing the energy output of a galaxy.

My roommate is arguing we could defeat Q and the Vorlons, though I don't have a reasoning from him to back that up c'est le vie.

[Sky Captain]

A hard STL civilization if attacked by other soft sci fi FTL civilization would be vulnerable to hit and run attacks. Even if it controls nearly the entire output of a star it would take relatively long to respond to an attack. FTL warship could just jump in blast everything valuable within range then jump to different location and repeat. When information about attack reaches nearest military asset that could respond with enough force to kill the attacker it is likely that FTL warship already has departed and blasts stuff elswere.
A one warship blasting few hundred habitats per day may be nothing to a civilization that have dozens of millions of such habitats, but if there are thousands of such ships blowing up solar colectors, military bases, space habitats, supercomputer centers it would soon become major problem.

[Alerik the Fortunate]

Has anyone read Ian McDonald's short story "Verthandi's Ring?" It's a brief poetic tour across several important actions in a millennia long war between multiple-galaxy-spanning STL superpowers. It touches on a number of items Terwyn mentioned. It isn't inconceivable that given enough time and resources, an advancing civilization without hyperdrive could still pull off something resembling Xeelee scale engineering.

Also, Greg Egan's novels feature a variety of galaxy-spanning STL civilizations with immortal posthumans, occasional relativistic ships, and most people traveling by uploading their minds and being transmitted across the galactic data networks and downloaded into custom built bodies at the other end.

[bilateralrope]

I believe if I recall from that Atomic Rockets site that a Hard Scifi civilization could deploy crazy powerful relativistic rail/coil guns capable of burning off the crust of a planet it struck which would be impossible to detect if our understanding of physics is limited to STL stuff.

Plenty of the soft scifi settings have FTL sensors.

So we could wipe the life from every world in the Galactic Empire, every space colony, and every immobile station there and in the UFP; just not the starships which can dodge.

I wouldn't call UFP stations immobile. Not after how much DS9 moved in the first episode, and that was a kludge. With FTL sensors, they would have much more time to get a working solution.

Also, you're overlooking just how long such a weapon would take to hit. Years for the closest targets to the hard setting, which is plenty of time to drop an asteroid in the way, watch the asteroid get hit, calculate how the asteroid has changed the path or the attack, then go pick up a new asteroid. Repeat daily until the weapon is not going to hit anything important with enough energy to overwhelm its shields.

As for the further targets, you're talking hundreds or thousands of years from firing the weapon till it hitting for the UFP. Tens of thousands for the Empire.

[sirocco]

A hard STL civilization if attacked by other soft sci fi FTL civilization would be vulnerable to hit and run attacks. Even if it controls nearly the entire output of a star it would take relatively long to respond to an attack. FTL warship could just jump in blast everything valuable within range then jump to different location and repeat. When information about attack reaches nearest military asset that could respond with enough force to kill the attacker it is likely that FTL warship already has departed and blasts stuff elswere.
A one warship blasting few hundred habitats per day may be nothing to a civilization that have dozens of millions of such habitats, but if there are thousands of such ships blowing up solar colectors, military bases, space habitats, supercomputer centers it would soon become major problem.

For me it's the same setting as traditional guerilla war. As in real life, it would work as long as they can hide their base or are always on the run. And Voyager's Year of Hell episode shows that the latter solution is hardly sustainable.