You've just contradicted yourself. Several times actually.

Lasers are light. Light is a [very common*] form of electro-magnetic energy. The light from a laser is not a by-product, it is the end-all-be-all of what a laser is.

The reason it shouldn't work is because glass [or similar substances] are transparent and don't reflect light in the same way that opaque matter will. In essence, transparent matter does not absorb the vast majority of light energy and lets it pass straight through.

Now, combine what I've listed there with what we know about lasguns, that they emit energy on the same level as an assault rifle of the same size. 99% [or more] of which will pass straight through glass, thus not affecting it and definitely not destroying it.

So no, a laser will not burn through glass at the level of a lasgun, in-universe explanation or not. And there is more to this. It's called suspension of disbelief, which is completely a totally #$^%ing shattered by a laser [of all things], burning through glass. This laser thing was only the last straw though. I could have lived with it if there weren't so many other things that are blatantly ridiculous. For instance, apparently a single strike cruiser can carry two thousand Astartes and numerous war vehicles. Alone. And don't try to tell me it was a daemon ship or some crap like that. The author gave no indication, not even a hint or an allusion, to the fact that it could be different than a normal ship.

If it says it fires a laser, which it does if your quotes are to be believed, then it fires and damn laser and behaves like a damn laser. I will not concede this point, no matter what you say. Ever **. A laser that fires with the power of a bullet will not and should not destroy glass.

Besides, any self respecting science fiction author should at the very least know the basics of science. If he doesn't then he needs to be responsible for his own ignorance and stupidity. Honestly, who doesn't know how a laser works?

Power weapons are something that has no real world equivalent, so suspension of disbelief can be held because it doesn't directly contradict something that is extremely well known.

*: Light is infact 100% of all electro-magnetic energy, but for the purposes of this discussion I am talking about visible light only, which is what a lasgun emits and is in fact an extremely small part of the electro-magnetic spectrum.

**: Unless you happen to have some irrefutable evidence to the contrary. Like solid math and theory that has been tested in the real world.

This is the end of any off-topic discussion I will have on the matter. Good day sir.

So no, a laser will not burn through glass at the level of a lasgun, in-universe explanation or not. And there is more to this. It's called suspension of disbelief, which is completely a totally #$^%ing shattered by a laser [of all things], burning through glass. This laser thing was only the last straw though. I could have lived with it if there weren't so many other things that are blatantly ridiculous. For instance, apparently a single strike cruiser can carry two thousand Astartes and numerous war vehicles. Alone. And don't try to tell me it was a daemon ship or some crap like that. The author gave no indication, not even a hint or an allusion, to the fact that it could be different than a normal ship.

Assuming the Astartes were content to live in conditions which make canned tuna seem spacious, I think that would actually work - what's the normal crew of a cruiser? Somewhere near 20000?

Other than that, yes, I prefer my lasguns to be actual lasers. Didn't stop stuff like Gaunt's sniper having to adjust his LongLas's scope for distance and lasguns having recoil in the novels.

I would like to say that a lasgun should have recoil, since any large burst of energy is likely to cause a backlash. But I'm not sure.

As for the crew of a cruiser… Over 100k I believe. But the Astartes passenger limit isn't decided by how tightly packed they are, but by the gear and facilities it requires to maintain the warriors. Not to mention, how arrogant do you have to be to cram all of your elite soldiers in one ship. It would be awefully unfortunate if they all got blown up.

 I realize you said you don't want to discuss it, but I just wanted to say a couple things (not in argument):

First, I do realize lasers are light. I do realize the quotes I mentioned seem to imply it's both a laser and not-a-laser. I think, as you rightly point out, that I seem to have a much higher tolerance for suspension-of-disbelief in the way that lasguns work in the 40k universe; there is so many other things that are utterly fantastical in the 40k universe that I have no problem with a lasgun not operating according to real-world physics. With that said that, I can totally see how you differ in that regard, which is totally understandable.

So again, no argument, just wanted to clarify my position: it just seems like a fundamental difference in how we view the 40k universe, which I have no problem with. :-)

 I'm no physicist, but a laser burning a hole through a window in not entirely impossible. Lasers work as weapons because they transmit high amouts of energy to the target, and the sudden increase of heat causes shockwaves. No material is 100% transparent (open air is not 100% transparent, that's why lasers have a maximum effective range) and actually a window in a battlezone will be dirty as hell, so a laser shot at it may concievably transmit enough energy to heat it up to a melting point. Notice that GW has never specifically stated the actual power range of a lasgun (at least not in real-world units, anyway), but it is enough to cause the head of a full-grown man to explode on a solid hit. That quite a powerful laser.

And about the space marines in a Strike Cruiser, Strike Cruisers are comparable to Imperial Light Cruisers, and a Dauntless-class is a 4'5km long, 0'5km wide vessel with a standard crew of 65.000 souls. Being an Astartes cruiser, it is designed and optimized for troop transportation because, even though the vast majority of the crew are Chapter serfs, they always carry a minimum detatchment of around a company strong of Space Marines for boarding actions and ground operations. FFG revealed lately that a barracks in a ship can hold a single Imperial Guard regiment, which is around 2.000-5.000 men. Space Marines are a lot bigger, but they also live in extremely spartan conditions, so they don't really take up that much space, so yeah, it IS putting all your eggs in one basket, but carrying that number on a single cruiser is feasible.

Also, wouldn't the ionisation of the air create heat, which would damage the glass?

Either way, I think it's fairly obvious from the fluff that lasguns aren't meant to be able to be reflected by just a piece of glass or a standard mirror. Most fluff has them as acting, mostly, in the same way as a ballistic weapon.

HTMC said:

I was being satyrical. I'm up for discussing it, but this thread is probably not the best place.

@JuankiMan: That is true for both subjects. But I don't think a laser with power output equivalent to your standard solid projectile rifle or pistol has enough power to damage a window in that way. I know a lasgun is that powerful because it has been said in official fluff that a lasgun is roughly equivalent to one of their autoguns.

As for Strike Cruisers, I'm fairly certain that one can only support about 200 Astartes and their support. In the book there were not only 2000 Astartes, but at least 50 dreads as well and a whole lot of other war machines as well.

@MILLANDSON: It's not that the glass should have reflected the las beam, it's that the glass should have been totally unaffected by it. In the book the beam burned a hole through the glass which a daemon stuck his finger through and used it to rip the window out.

DJSunhammer said:

Regardless of power, if the glass is not perfectly squeaky clean the energy passing through it would interact with it in some way, either burning it and blackening it or melting a hole through it. Lasguns are comparable to autoguns in lethality, but they're incomparable in power because they inflict damage in wholly different ways. Regardless, even a rifle round at half power would still punch through a glass window. 

 You halved your armour value against non-primitive weapons iirc, which meant the best-plate suit was still as good as flak armour against non-primitive weaponry, but even more so against primitive weaponry.

Mirrors can get warped or even destroyed by enough input. A perfectly reflective mirror is pretty much theoretical, and would in fact be immune to las weapons.

However, just about everything has imperfections. Some measure of the energy is absorbed when striking these imperfections and will begin the process of heating the target point. Slow at first, as heat accumulates enough to begin various reactions in the material, its going to most likely darken or ablate in a widening zone around the point, accelerating the process and eventually vaporise. In EITHER of those cases, once it finally happens, the incoming energy is now being absorbed at a far greater rate; if striking a small gas-plume from vaporization or sublimation, its basically shocked into a plasma state.

Once that happens, you can forget about 'protection'; you have a superheated surface you might very well be WEARING, which depending on its composition may just have ignited, cracked, suffered an explosion, or at the very least been burnt through.

Chances are 'reflec' anti-las coatings would be ablative in nature, protecting against a certain amount of total las damage  per protected section. Say it grants 10AP vs las weapons: hit it with six, its absorbed. Next time six again? two goes through [4 was left] into the normal armor's value, and that's it for the mirroring.

Of course you'd be extremely hard to miss in any sort of lighting conditions beyond total darkness…

Better to just field thick refractive aerosol grenades or something.