Yeah, but they are also immobile and at least somewhat rare (looks at Eden Prime incident where a 'prosperous colony' didn't have any installed) without a clear and present threat (ME2, where Ashley is doing the thing with turrets. incidentally, weren't those something like "punch a hole through a slightly underbuilt frigate" grade of firepower?).
Oh canon... Eden Prime had something that was being used to fire at the attackers there were streams of AA fire IIRC. And well the ME2 things can't be laser based GARDIANs, the shots are visible and STL. Laser based GARDIAN clearly use RL speed of light lasers from the fluff. (Stupid cut scenes

)
That said in the quest things that have happened and been said have encouraged the SA to speed more money on putting GARDIAN systems up in SA colonies.
And spacecraft do have countermeasures to Guardian fire, even if it's ablative armor.
I didn't say it was instant win I'm just saying they can trade fire, you can put ablative armor around the ground based GARDIAN. I'm basically pointing out a classic case of what good for one is good for the other.
Sorry if this was answered, like, a month ago, but how effective would compressing 'cold' plasma and ablative/reflective particles with a pair of mass effect barriers be to reduce laser strike power?
Well technically you can't have multiple barriers active as those interfere with each other (or so claims ME2 lore). But you can suspend particles in a field or just use magnetics, same effect.
Anyway it works great against non vacuum frequencies and less good against vacuum frequencies.
If I'm remembering right, the Quarian shielding hero was going to be doing stuff like this. We picked the Krogan instead.
The Asari could have done similar things she was the plasma person.
Okay, yeah, 0.001c makes more sense. I was specifically going after 0.1c because anything over around 0.03c puts your entire ship dangerously near the velocity needed to overcome the Coulomb barrier, that is, the velocity at which atoms collide with enough energy to undergo nuclear fusion. You don't ever want to travel at near that speed without a protective NME barrier around (or some other space magic/large EM shield) because random particles will bathe your ship in neutrons and gamma rays, and running into something even as small as 0.1 grams will be the equivalent of standing at ground zero of a nuke.
Huh cool hadn't considered that. Hmm... well lets see Hydrogen-Titanium fusion is an issue at... 0.0939c I think? Not including ME stuff...
And 0.1g is a bit less then a MOAB at 0.1c. Ironically reverse cubic scaling a dreadnought (assuming a dreadnought's shields can take at least one dreadnought spinal) tells me fighters can take that... I'm not sure that's sane. Especially as the effects aren't exactly cubic... still weird.
Actually the energy from the particle impacts looks shield able to, ~600.866-72,103.932 watts of continuous bombardment at 0.1c at guess. Letting it hit the hull and fuse generates ~1,999.680-239,961.568 watts? I think? (Obviously its different for other elements. Carbon and Tungsten both produce less) No sure what conclusions to draw from that just started having fun with math.
That's probably also why dreadnoughts don't fire as more than ~0.015c, too. Fire faster than that and it becomes trivial to block a MAC shot: just sandblast the area between you and the dreadnought (an easy thing to do since we're already venting vaporized lithium everywhere as a heat sink), and the shot will nuke itself, disintegrating on approach.
Problem is that the shot then has pretty poor range as the lag time extend into seconds (supposedly dreadnought dual at ten of thousand of kilometers). Which starts meaning you can use the GARDIANS to intercept the shots or maneuver out of the way. It's why I theorize ME rounds carry a NME dark energy "charge" with them, since that's a thing you can do and faster shot would be a good thing.
As for it disintegrating, it's not going to spread out enough if what I've read is true... of course the only source I've ever seen actually thinking about this is XKCD so YMMV.