Death Star shields vs Alderaanian debris: to scale

[Batman]

I disagree. Both shields and turbolasers are powered by a ships main reactor. If shields could withstand energy orders of magnitude greater than the power which they consume then the output of turbolasers would be comparatively trivial.

Which is why the power draw of as wall that can withstand a MJ laser for a considerable amount of time is...oh wait, there isn't any. There's no reason to assume that blocking/reflecting/deflecting/refracting/technobabbling it out of your area of concern takes the same amount of energy.
I repeat-the power consumption of a wall is zero.

[Sea Skimmer]

Well, the wall is drawing some fraction of its strength from the compressive effect of gravity and however the hell that energy flow works, but yeah, no reason exists why a deflection mechanism has to consume energy in real terms, nor does its manufacturing method need to be linked to its ability to absorb energy. Its more about thresholds above which yield-fracture-crumbling kinds of damage occur then anything else. Some materials will change properties from impacts, like steel can be heated and loose its temper from sustained gunfire, while others loose mass like boron carbide for body armor, but none of it is about consuming energy directly.

We also have no reason to assume that shielding resistance is actually uniform across a ship or other object. With say armor plate, the edges of the plate are weaker for multiple reason (including the front and back, relative to the axis of impact) and shields may well be similar making precise comparisons impossible without highly detailed information. Star Wars shields really do seem to behave more like armor that crumbles from heavy impacts, but doesn't really give a damn about minor ones, then an energy draining forcefields that treaty all energy equally.

[Simon_Jester]

Wait... so people argue that a "chainreaction of events" is what destroyed Alderaan? And that that PLANET WIDE reaction, took, what, a millisecond? Isn't that completely implausible based on physics alone?

An effect propagating outwards from the beam path at lightspeed could cover an entire Earthlike planet in, oh... let's see, radius roughly six thousand kilometers, so... yeah. Twenty milliseconds.

Which is short enough to take about one frame in a movie, if that.

And I think that's what Simon is getting at. At least as he sees it, the destruction of Alderaan as seen in the movies isn't compatible with real world physics*. I happen to disagree, but I also seriously suck at anything involving math.

*It's incompatible with real world physics anyway because even if it is a DET event there's no 'real world' way in hell to generate that much energy in something the size of the Death Star, but from what I can tell Simon is saying 'even if we dump Mike's calculations (and more) into the planet, the results wouldn't look like that'.

It's like... Put this way. If you fire a bullet into an apple, you can shred that apple into pieces. But if you watch, the apple doesn't just go "bang" like an exploding firecracker. Not even if it ends up in about as many pieces as if you had lit a firecracker inside it.

If you pour massive energy into an object along a single, linear beam path, you do not get a spherically symmetrical blast front propagating outward in all directions.

Since there is no possible way that the energy needed can be generated from the planet itself (or any chain reaction involving the planet) it must have come from an external source. It is actually easier to hypothesize ways in which the energy could be generated inside the Death Star than it is to explain any impossibly energetic chain reactions involving the planet itself, which is composed of known materials (mostly silicon and iron).

We can accept that the Death Star itself has impossible energy sources, but we can't accept that the Death Star makes other things draw energy from impossible sources?

There's such a thing as having too little imagination to be qualified to comment on SF.

The energy required to accelerate mass into motion is impossible to circumvent, so there is no way of getting rid of those 1e38 Joules regardless of where they come from.

Yeah, yeah, I heard that the first time five years ago. I don't argue the point. I don't care about the numbers, I have no interest in arguing them up or down.

But seriously, Alderaan blowing up looks more like a spherical blast front, as though the planet itself exploded. It looks very little like what you'd expect if some energetic beam carved through the planet and blew it apart like a bullet smashing through a glass vase.*

*Yes, I know, it wouldn't look exactly like a bullet hitting a glass vase, let's not be willfully obtuse here. Everyone gets the point, I imagine.

[Channel72]

And let's not forget the dreaded Special Edition praxis ring!

Anyway, if the movie was made now instead of in the 70s, the scene would look more like this: http://www.youtube.com/watch?v=qBAZGtBfcY4

Then we wouldn't be having these silly debates.

[Eternal_Freedom]

External Freedom, the density of those superheated blobs is probably orders of magnitude lower than the planet. I believe the best method would be to divide the total mass of the planet by the total volume of the explosion by this point of expansion, and then work out what fraction of that explosion is represented by the big fiery ball in the bottom left. Then multiply the calculated density minus the huge fiery sphere by the volume of the superheated debris...

If you'd like to do this calculation before I do then you could derive the info you need from this page http://www.galacticempirewars.com/death-star-firepower.

First, I'm not doing the work for you. Second, those calculations of mine are back-of-the-envelope, order-of-magnitude ones.

Third, your method would only work if the planet had been totally vaporised into an explanding gas cloud, which as we clearly see, didn't happen. There are clearly lumps of rock flying out in various directions, and that was what the OP considered, if those lumps of rock would hit the Death Star and if so what energy would they have. Since those lumps of rock came from the planet I can only use the average density of an Earth-type planet as an estimate; I could go the "assume a spherical mass of iron" route, but since I know better and more plausible figures I used those.

My calculations are full of assumptions, as I said at the time. First, assume the planet is exactly Earth-like (not unreasonable). Second, assume the "six planetary diameters" distance figure is accurate (to one s.f. anyway). Third assume the debris takes 3-4 seconds to reach the Death Star's apparent position (I used 4 seconds to be conservative). Fourth, assume the debris is evenly spread in all directions (which isn't what we see but it's the best I could come up with at the time). Fifth, assuem those fragments are 100 km^3 fragments (as per the OP). Sixth, assume only 1/100th of the fragments hitting the Death Star transfer all their kinetic energy (since I don't know how to calculate what fraction they'd transfer when hitting at an angle, how many would hit at an angle and so on).

With all those assumptions the best you can get is an order of magnitude estimate.

EDIT: Incidentally, why do you assume the fragments are a lot less dense than the planet's average density?

[ZOmegaZ]

I suggested this, oh, fifteen years ago or so. Never expected it to come back up.

The Death Star and the planet aren't the only variables in play. There's also the planetary shield. Since shields in Star Wars are largely unknown, it's at least imaginable that if you dump enough energy into the shield to overwhelm it, the shield itself becomes the immediate mechanism of the planet's destruction. Again, not to reduce the destructive power of the Death Star. (It could probably fry a planetary surface with just its surface turbolasers!)

In other words, the destruction of a shielded planet might look very different from the destruction of an unshielded one.

[Havok]

http://lightsinthedark.wordpress.com/20 ... rom-above/

I'm going to throw this image out every time there is an "Alderaan Shields" discussion thread now.

[Vance]

EDIT: Incidentally, why do you assume the fragments are a lot less dense than the planet's average density?

Because the mass of the planet is spread dispersed over a larger area (the diameter of the "fireball") I think it is fairer to adjust density accordingly.

[Eternal_Freedom]

EDIT: Incidentally, why do you assume the fragments are a lot less dense than the planet's average density?

Because the mass of the planet is spread dispersed over a larger area (the diameter of the "fireball") I think it is fairer to adjust density accordingly.

That would make the average density lower, but since we still see actual fragments they would still have approximately the same density.

[Borgholio]

http://lightsinthedark.wordpress.com/20 ... rom-above/

I'm going to throw this image out every time there is an "Alderaan Shields" discussion thread now.

Right but would that halo around the planet actually absorb energy from the superlaser blast?

[Patroklos]

The problem with the chain reaction idea is a practical one as well. If we accept it as a valid theory then we must believe the empire to be so stupid that it build a weapon of mass destruction that is not usable against all planets but only against all planets which have a similar geographical markup.

I don't think we can make that conclusion based on our sample size of one as far as visual effects of planet destruction via super laser goes.

It could simply be the super laser affects planets of various geography differently. In the end we don't actually know the makeup of Alderaan. Alderaan might blow up, other planets might not.

[Borgholio]

Alderaan might blow up, other planets might not.

Seems a bit of a waste to build a Death Star at great expense if it might not work all the time. Plus as pointed out earlier, a planet that is a bomb waiting to happen is unlikely because a planet must be stable to even form in the first place.

[Patroklos]

I didn't say it would not work as far as destroying a planet, I said it might look different depending on the specific characteristics of a planet. I can definetly see the propogation of destructive energy within a molten core or solid core having greatly differnet physical outcomes concerning immediate surface effects. Some our our system's moons have planet wide liquid oceans under their crust. Titan for instance has a good portion of its under surface volume consisting of liquid and then ice water, what would flash boiling/vaporizing it look like from orbit?

We can input large amounts of energy into many different types of materials with a more than reasonable expectation that that energy will be enough to destroy them, that doesn't mean the visual results will look the same.

[Vance]

I disagree. Both shields and turbolasers are powered by a ships main reactor. If shields could withstand energy orders of magnitude greater than the power which they consume then the output of turbolasers would be comparatively trivial.

Which is why the power draw of as wall that can withstand a MJ laser for a considerable amount of time is...oh wait, there isn't any. There's no reason to assume that blocking/reflecting/deflecting/refracting/technobabbling it out of your area of concern takes the same amount of energy.
I repeat-the power consumption of a wall is zero.

Very well. Still impressive nonetheless.

That would make the average density lower, but since we still see actual fragments they would still have approximately the same density.

The debris on the OP look at least molten to me. Those blobs certainly aren't just "lumps of rock".

[Eternal_Freedom]

In the end we don't actually know the makeup of Alderaan. Alderaan might blow up, other planets might not.

We can make some reasonable assumptions. One, it's a blue-green marble, with plenty of liquid water, which means it's in the habitable zone of it's star. Two, it is able to support average human beings (Leia, Bail Organa, all the dudes we see on his ship in ROTS, General Rieekan (although him being ALderaanian is from the EU), this means it has a similar temperature range to Earth, with similar gravity (+/- 10% or so). Supporting humans means it's pretty likely it has a magnetic field similar to Earth's, which means it's got a rotating liquid outer core.

In other words, everything we see about Alderaan tells us it's a typical blue-green planet, similar enough to Earth to support humans. Ergo, it almost certainly has a similar composition.

Plus, as others have pointed out, why would the Empire build a weapon, expressly for the purpose of intimidating ALL the other planets in the galaxy that relies on certain planetary compositions? It would be pretty damn stupid of them.

[Patroklos]

Who said it relies on certain planetary compositions? That exactly the opposite of what I said in my post, which was only to point out that planets of different compositions might not all be destroyed in exactly the same fashion and would probably have varying visuals.

Did you even read my post? And no, we don't have nearly as much information about Alderran as you suggest. We don't know the characteristics of Alderaan's star so we don't know how much of a magnetic field it needs to be habitable. We don't know the density of Alderaan so there is to reason to assume its human comfortable gravity means it is a similar size to Earth. Not only that, humans can supposedly readily adapt to gravity upwards of more than thirty percent over or under of 1g. Not only that Alderaan is a settled world, no matter how long ago that was, which means its natural habitability might not be the paradise thousands of years of galactic level technology makes it today. Do you really know what the climate of Alderran is? Do you know whether or not its desert tundra for 50% of its surface around the poles? I don't.

We just don't know, and your assumptions are irresponsible. At best you can come up with a range it's characteristics might fall into but even then it's a crapshoot. Even within those ranges your calculations would vary wildly.

[Eternal_Freedom]

Irresponsible? That's interesting. Anyway, to answer some objections you raised, no we don't know the details of Alderaan's primary, but like I said we assume that it's similar to Sol, or at the very least that Alderaan is in the habitable zone. Whilst it's possible the star is less massive it is unlikely to be much more massive than the Sun since it wouldn't last long enough on the main sequence for a Earth-like planet to emerge. Consider, a sun twice as massive as ours only lives for approximately 1/8th of the Sun's lifespan (a star's main-sequence lifetime is, very roughly, 10,000,000 years (the Sun's estimated lifespan) divided my mass cubed (in solar masses)). A 2 solar mass star would only be on the MS for 1.25 billion years, and that is (as far as we know) not enough time for an Earth-type planet to reach a stage where it's inhabitable to humans.

As for the magnetic field, true, without knowing about the star we can't say how strong it needs to be, but the magnetic field also protects us from galactic cosmic rays and other such nasty stuff, so Alderaan must have a magnetic field, which means it has a rotating outer core.

As for the gravity, yes, AFAIK humans can live and adapt to ranges of 0.7-1.3 g, but that will have effects on the humans that live there, making them non-average (they'd be taller and lankier, or shorter and stockier for instance) and all the Alderaanians we see are average humans.

As for the nonsense about it being "desert tundra for 50% of its surface around the poles?" we see a typical blue-green marble. We see it close enough to see that there appears to be large, green landmasses. I certainly didn't see any vast stretches of desert.

As for the average density part, yes, you could be right, the planet could be made of an abnormally dense metal. But Earth is already mostly nickel and iron, so Alderaan would need to be mostly made of a denser metal. But those are comparatively rare and AFAIK only iron, nickel or cobalt are able to create a magnetic field if they're a rotating liquid outer core.

Yes, the best I can come up with is a range of parameters, but that's fine.

Now, every observation and description we have shows Alderaan to be essentially Earth-2. Plenty of liquid water, varied terrain including mountains and plains, an Earth-type atmosphere and similar gravity. Yes, it might have a radically different composition, but what evidence do we have that it isn't Earth-2/M-Class.

Naturally different planetary compositions are going to react differently to be whacked by a superlaser. But as far as we have observed, planets are either small and rocky, balls of ice or gas giants (very roughly). The rockey planets will explode like Alderaan, the ice planets will, I dunno, probably explode/shatter/boil/vaporise in a similar way, and gas giants I have no idea. But the Empire is only likely to be targeting rocky or icy planets since that's where people seem to live in SW (I know, don't mention Bespin, that's a special case).

[Patroklos]

I would mention Naboo, which does not have a solid core at all apparently and not only that it is full of water. I don't have any real world science to explain that but the SW universe apparently has such things. Naboo is portrayed as a paradise world dispute this odd geology.

The star might be smaller, not larger. Alderaan might be much larger than earth but less dense to provide the same gravity as earth. It's star might be exactly the same as the sun, only 500 million years older and thus different in character. Alderaan does not have any large oceans and does have at least one icecap according to wookipedia. Tundra doesn't look much different than any other green terrain from orbit. Again, lots of differences are possible.

As far as gravity goes its more probable that most humans are growing up on worlds with some rather different gravities given the number of settled worlds in the Empire. I doubt there just happens to be millions of perfect earth clones out there. Then there are all those aliens operating just fine on every human populated world we see. Usually dozens to hundreds of species per world actually. Did all of them evolve on Earth vanilla 1g worlds too? Are there whole societies of alien civilizations living on higher or lower gravity worlds that we don't even see? How many quadtrillions are they?

And yes "irresponsible" is the wrong word, sorry.

[Eternal_Freedom]

Those are all good points, but they are also entirely speculation. So, do we have any evidence from the films that Alderaan is anything other than an Earth-type world?

As for Naboo, the water-filled core was explained in the (no longer canon) EU. That line about "going through the planet's core" was bullshit, I just interpreted it to mean Naboo has really deep oceans and a lot of cave systems that link up (probably as a result of ancient volcanic activity). The planet having a mostly hollow rock core filled with water means its real hard to get a magnetic field and the rate of heating from radioactive decay would be a lot less, making the planet cool down and die much faster.

Your points about all the aliens being fine in 1-g environments is a good one. As for humans living on planets with widely different gravity, it's possible, but there is only so much they can adapt to it before they become a different species (of course, this might help explain how certain alien species can interbreed while others can't).

[Borgholio]

I have always doubted that Boss Nass was literally meaning the center of the planet. Given the observed speed of the sub the Jedi were in, it would take weeks to go straight through the center of the planet (if they could at all). I'm thinking Nass was just being dramatic, and he was referring to really deep submarine cave networks. The Gungans and the Naboo really aren't all that far apart in actuality.

[Sea Skimmer]

It also just wouldn't have made sense for the Trade Federation invasion force to land some vast distance away from the capital when it intended to advance upon it with fairly slow moving hovertanks and was trying to capture the princess. Why land on the other side of the planet? Naboo barely had a military even had it chosen to fight.

It doesn't take that great of a surface distance across a circular world to make a straight line shortcut underground shorter by miles, and it really seemed like Nass was screwing with them, and maybe hoping Jar Jar got eaten. While it might not be cannon the ICS book for Episode 1 IIRC claimed the distance was 40 miles. Or maybe it was 40km. Something like that, they had an actual map.

[Eternal_Freedom]

Not to mention that the pressure in the planet's "core" would have been immense, I can't imagine large fish being able to survive at those depths. Not in those shapes anyway.

[Borgholio]

Physics question...what would happen to water if it was compressed that much? Would it turn solid like iron in Earth's core or hydrogen in Jupiter's core? Or would it remain fluid...just incredibly viscous?

[Batman]

Last I checked one of the more annoying qualities of water was that you can't compress it.

[Eternal_Freedom]

Well generally as pressure increases so does the melting/boiling points. That's why water in some nuclear reactor designs can still be liquid at several hundred degrees. As for the effect at that pressure...I honestly have no idea. It may well turn solid. Unless....there was a great heat source around, like a planet's worth of uranium, thorium etc keeping the water liquid by decay heat. But that would work since the water would a) be many hundreds of degrees C and b) the water thus heated would rise by convection to the surface, spreading the heat out again. Which would probably do very strange things indeed.