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The Dresden Files => DF Spoilers => DF Reference Collection => Topic started by: knnn on May 31, 2013, 09:58:33 PM
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In "It's My Birthday, Too" Harry uses gravity magic to kill two Blampires. The description in the text is as follows:
In technical terms, I didn’t actually increase the gravity of the earth beneath it. I only concentrated it a little. In a circle fifty yards across, for just a fraction of a second, gravity vanished. The cars all surged up against their shock absorbers and settled again. The thin coat of snow leapt several inches off the parking lot and fell back. In that same fraction of a second, all of that gravity from all of that area concentrated itself into a circle, maybe eighteen inches across, directly at the vampire’s feet. There was no explosion, no flash of light—and no scream. The vampire just went down, slammed to the earth as suddenly and violently as if I’d dropped an anvil on him.
There are a number of points I'd like to make:
1) Note that the fact that the text is talking about circles in two dimensions seems to imply that Harry didn't "turn off" gravity in general, but "merely" concentrated the gravity coming from the center of the Earth. Otherwise, the effect should have more spherical -- all the concentrated gravity would have turned the center of the blampire into a nice, dense ball of matter. Similarly in the second example, there would have been no reason for the second floor to fall down (rather than up/in/ whatever).
----> We have established that Harry's spell is pretty likely earth-centric.
2) The description of what would happen if Earth's gravity vanished for a split-second is pretty much spot on. Consider that we're on a rotating planet, and the thing that keeps us "anchored" is gravity. If gravity stopped for a given object, it would continue in a straight line (modulo secondary gravitational effects like the sun) rather than curve around the earth. Since the Earth is rotating at about 1/3 of a mile an hour (at the equator), if you let something go in a straight line instead of curving around the earth, it would appear to float upward (probably wobbly -- a whole bunch of secondary effects come into play) for nearly a minute (as the earth dropped away), and then move "west" in increasing speed. Since Harry describes the process of the spell to take a "fraction of a second", the description appears to be spot on.
3) Power -- So how much gravity did the poor blampire experience? Well, it's kinda hard to say since you can't really concentrate gravity in that way -- certainly not in a 2D form. Still, let's assume that it works in the same way a magnifying glass works when you use it to light a fire.
In a magnifying glass, all the energy of the light rays passing through the glass get concentrated at one point. The effective temperature at that point is essentially determined by how much energy is being concentrated. The better the lens (i.e. better parabola), the smaller the area in which the energy is concentrated and hence the hotter it gets. Ditto for size -- make the lens ten times bigger and you get ten times the energy (think Tavi at the bridge).
Fortunately, Harry tells us the measurements: he concentrates the gravity from a circle 50 yards across to a circle 18 inches across -- a ratio of 100:1. Thing is, the number that counts is the area of those circles, something that goes as the ratio squared. Thus, we get an energy ratio of 10000:1.
Now the "energy" of gravity is pretty much linear in scale (GM/R is the Newtonian function that comes to mind), so this gives us the whopping number of 10000G, or localized gravity 10,000 times what we normally feel on planet earth.
4) Effect:
So what does this feel like? A LOT. Just for comparison, did you know that gravity on the surface of the sun is only 28G (which makes the whole ending of the Green Lantern movie really stupid)? 10,000G is what you get on the surface of a neutron star.
From wikipedia:
The neutron star's compactness gives it a surface gravity of up to 7×1012 m/s² with typical values of a few ×1012 m/s² (that is more than 1011 or makes the gravity roughly 10,240 times that of Earth). One measure of such immense gravity is the fact that neutron stars have an escape velocity of around 100,000 km/s, about a third of the speed of light.
No wonder the vampire got flattened. With that kind of gravitational force, it's interesting that we didn't see all kinds of weird-science side effects. Light that happened to pass through those 18 inches during the spell would have been distorted up the wazoo with Doppler effects that would have done cool things to it. Air particles would have been smashed down causing a temporary vacuum that would have sucked outside air in, causing an implosion effect. Under that kind of pressure, the air inside would actually solidify on the bottom of the cylinder of concentrated gravity. Heck, the speed in which those air molecules would collide would resemble the inside of a Super-collider. I'm surprised Harry didn't discover the Higgs Boson on the spot.
5) Scaling up:
Finally, consider what would happen if Harry had made the "zero gravity" circle just 10 times larger. Going by the radius squared law, we'd get a 100-fold increase in gravity at the center which would easily take us into the black-hole range.
(Note that the surface gravity of a black hole is very hard to measure because of a lack of a "surface". You can use the Schwarzschild radius, but then you get the weird effect where the larger the black-hole is, the weaker amount of surface gravity it has. Nevertheless 1,000,000G is very comfortably a black hole).
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Not much more to say here, except that wizards are dang powerful.
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You seem to be assuming that magic is 100% efficient. I would like to call to the witness stand the Second Law of Thermodynamics. :)
Granted, it's kind of difficult to measure the thermodynamics of magic, given that wizards not only draw energy from the environment in ways that are hard to tell–like dropping the temperature of an area of a square mile to fuel a fire spell, for instance.
In addition, of course Harry didn't discover the Higgs Boson. He has no way to observe it, except big time maybe through the Sight.
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3) Power -- So how much gravity did the poor blampire experience? Well, it's kinda hard to say since you can't really concentrate gravity in that way -- certainly not in a 2D form. Still, let's assume that it works in the same way a magnifying glass works when you use it to light a fire.
In a magnifying glass, all the energy of the light rays passing through the glass get concentrated at one point.
That part never made any sense to me.
The situations are very different:
light is divided among its targets, not gravity (which is normal since light is a form of energy and gravity is a force). Gravity is not a limited ressource, I can put how many objects I want near the Earth, they'll get attracted just as strongly as the first one.
So what is the point of transferring gravity? Why not simply choose a bigger G constant in the area of effect?
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The text explicitly states that Harry concentrated the gravity, both in the story and later in Chichén Itzá.
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The text explicitly states that Harry concentrated the gravity, both in the story and later in Chichén Itzá.
It does. That doesn't mean I understand how it works.
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Well. That's actually pretty simple. Magically, Harry thinks it should work that way, so it does.
Physically is a bit more complicated. But, not impossible under wave-particle duality. If you assume that Harry used his magic to, on a subatomic level, move the gravitons (the particle expression of the gravitational force) from those areas (probably not all of them, but most of them at least) and concentrated them, boom. Flat vamps.
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If you want to see some more crazy numbers figure the amount of Ice it would take to Float that building section in CD, then see how much power it would take to make that much ice. The numbers become crazy if you assume free floating ice.
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Physically is a bit more complicated. But, not impossible under wave-particle duality. If you assume that Harry used his magic to, on a subatomic level, move the gravitons (the particle expression of the gravitational force) from those areas (probably not all of them, but most of them at least) and concentrated them, boom. Flat vamps.
Gravitons (if they exist...) are fermions bosons, they have energy. They carry the energy when gravity does work, that is when gravity accelerates something. The objets in the big circle weren't accelerated, so there was no transfer of energy, so there was no graviton to move in the first place.
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Incorrect. Gravitons (if they exist...) are fermions, they have energy. They carry the energy when gravity does works, that is when gravity accelerates something. The objets in the big circle weren't accelerated, so there was no transfer of energy, so there was no graviton to move in the first place.
There was absolutely acceleration. Things don't just fall into nearly two dimensions from three. There had to be a force to make it happen. Ergo, there was an acceleration.
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There was absolutely acceleration. Things don't just fall into nearly two dimensions from three. There had to be a force to make it happen. Ergo, there was an acceleration.
There was no acceleration at the moment Harry used the spell, the cars and so on where immobile, so there was no stream of gravitons.
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There was no acceleration at the moment Harry used the spell, the cars and so on where immobile, so there was no stream of gravitons.
In Changes, Harry specifically mentions everyone floating up outside the target circle. Not as much as the things moving down in the inner circle, but then, Harry is drawing on fewer gravitons per unit area then he is concentrating them in the same.
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sorry Knnn but it can't be affecting gravity, realy. what I think his spell does is borrow weight (the force of gravity) on objects in an area and concentrate it.
why can't it be what you suggest?
well, he's still there. :D
Gravity is a field.. you 'cancel' it somehow and it 'cancels' for everything.. including the several kilometers of air above the point. Which would have exploded outwards, then gotten drawn back in by your 'mini black hole'.. Im too tired to do the math, but as a WAGstimate I'd put the resulting force well into the atomic bomb category. (the initial explosion would have been more than 1 metric ton per square cm of area changed)(the secondary implosion would have been much, much worse)
Frankly, the whole city should have been redecorated..
I'd estimate it more like conservation of energy, he 'borrows' force from the objects around then concentrates it; what the vampire got hit with was the weight of several cars; not several cars, and several trillion tons of air.
;D
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Where are you getting the 1Mg/cm^2 figure from? Air pressure on earth is about 1Kg/cm^2.
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M and K are close on the keyboard, I think.
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Someone should write a book on the Physics of the Dresden Files
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I'm wagging like a dog tail on crack here.. but on the conservative side.
imagine a cone from the center of whatever 'cancel' harry is doing. the radius will be the same as the 'area' that harry hits, then propagate upwards .. what the mass of all that air? (not the barometric pressure, the actual mass)
how much force is it going to create when it displaces?
http://www.pilotfriend.com/training/flight_training/met/atmos_wt.htm (http://www.pilotfriend.com/training/flight_training/met/atmos_wt.htm)
ok, who has got a spreadsheet, some time, and feels ambitious?
;D
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Someone should write a book on the Physics of the Dresden Files
we've come close.. the original calculations on Mab ran about 40 pages.. and that's just that run.
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we've come close.. the original calculations on Mab ran about 40 pages.. and that's just that run.
Ooh! Where are they?!
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Ooh! Where are they?!
board auto wipes everything not saved im afraid
we concluded Mab's 'waste heat' output was between 10^17th - 10^20th Joules, based on how much power it takes it to snow across the entire Chicago area in may.. 4 feet deep
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board auto wipes everything not saved im afraid
we concluded Mab's 'waste heat' output was between 10^17th - 10^20th Joules, based on how much power it takes it to snow across the entire Chicago area in may.. 4 feet deep
That's the waste? Holy... Wow. I guess she isn't the Queen of Air and Darkness because she had her card punched 12 times.
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That's the waste? Holy... Wow. I guess she isn't the Queen of Air and Darkness because she had her card punched 12 times.
the idea is that any immortal, on earth, warps reality around them to match. Odin gets thunderstorms. Shaaggy cause corruption.
Mab.. makes things colder.
the six months she spent sitting on that island made it snow .. 4 feet deep.. the other side of the county.
that's a LOT of cold to be putting out.
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Well, I guess she's just that...wait for it... cool. 8)
Although, that's over a period of months. Certainly, the energy is impressive. But the power... Wait. 6.4 MILLION kW?!
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Well, I guess she's just that...wait for it... cool. 8)
Although, that's over a period of months. Certainly, the energy is impressive. But the power... Wait. 6.4 MILLION kW?!
we estimated the energy of the total time period to be quite a bit higher :)
it's not just enough to chill the air, you have to keep it chilled against incoming sunlight, and against loss due to convection and conduction.. the variance is caused by:
how much the average temp per month can vary (say was it a cold summer to begin with?)
how big the are was.. we can estimate the cylinder (with the isle at the center) covering Chicago, but where is murphys house in the suburbs?
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we estimated the energy of the total time period to be quite a bit higher :)
it's not just enough to chill the air, you have to keep it chilled against incoming sunlight, and against loss due to convection and conduction.. the variance is caused by:
how much the average temp per month can vary (say was it a cold summer to begin with?)
how big the are was.. we can estimate the cylinder (with the isle at the center) covering Chicago, but where is murphys house in the suburbs?
I used your estimate for the calculation. Granted, I used the low end...and rounded down...point still stands.
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This topic makes me wonder how much time Jim spends thinking about the physics of things and how much energy various spells would take or how much strength would be needed to lift something.
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This topic makes me wonder how much time Jim spends thinking about the physics of things and how much energy various spells would take or how much strength would be needed to lift something.
I'd say probably not much :)
Man's got enough to worry about.. lol
it's like when I crunched the numbers for the black court master in the short story.. if she can do what she did, how the frak did they ever lose??
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I'd say probably not much :)
Man's got enough to worry about.. lol
it's like when I crunched the numbers for the black court master in the short story.. if she can do what she did, how the frak did they ever lose??
Because Harry can call upon neutron star level gravity?
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Because Harry can call upon neutron star level gravity?
so why is the building still there?
;)
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so why is the building still there?
;)
In case you noticed, it isn't.
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In case you noticed, it isn't.
em getting set on fire and burning down later doesn't quite count ya know
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em getting set on fire and burning down later doesn't quite count ya know
I know... But still. It technically isn't.
And he did collapse a fair amount of the building. Not all of it, but a fair amount.
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Gravity is a field.. you 'cancel' it somehow and it 'cancels' for everything.. including the several kilometers of air above the point. Which would have exploded outwards, then gotten drawn back in by your 'mini black hole'.. Im too tired to do the math, but as a WAGstimate I'd put the resulting force well into the atomic bomb category. (the initial explosion would have been more than 1 metric ton per square cm of area changed)(the secondary implosion would have been much, much worse)
If anything, if what Harry did is impossible, I think that is more an argument for debunking all of the attempts to apply actual physics to magic. I realize JB/Harry are the source of claiming magic obeys said laws, but in the end, the specific demonstrations in the text trump anything Harry or even JB says. Harry stole the gravity from a large area and transferred it to a small area. It obviously applied to the cars and snow in the area and probably didn't apply to the air (which would likely happen if Harry doesn't think of air as being affected by gravity, because the spell would only do what he thinks it should).
If you want to do an energy calculation, Harry gives us the answer. The amount of force applied to the vamp was equal to the force it would take an anvil to squash the vamp flat cartoon-style. Any excess energy was probably transformed somehow into preventing all of the other negative effects that should have happened, but didn't. Who knows, maybe there are certain things that are possible in physics that we just don't understand. Otherwise, well, I guess it's magic.
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I know JB tries to mostly follow basic rules like hot air rises and such, but the DV isn’t real and JB does not hold PhDs in physics, so I tend to cut him some slack some times.
In the DV magic is real and gods can alter reality around them. The SL can make flowers sprout out of Mac’s wooden beams breaking all sorts of natural laws for heaven’s sake. Also it looks like at least some gods were once wizards – so why can’t a wizard alter the reality around a Bvamp and squish it?
Don’t take me wrong; I don’t want to keep folks from having fun and debating what gravity may or may not be, but in fantasy settings like the DV we are already altering reality a lot by having magic and the NN etc… So for me I like to just go with it - particularly if it deals with a subject that is far from set in stone in the real world’s science text books.
The upcoming MM and TT books are other examples of Harry treading where we real world folks don’t have a good grip on things yet – so I’ll just smile and enjoy whatever rules JB comes up with for alternate universes and time travel.
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I'm wagging like a dog tail on crack here.. but on the conservative side.
imagine a cone from the center of whatever 'cancel' harry is doing. the radius will be the same as the 'area' that harry hits, then propagate upwards .. what the mass of all that air? (not the barometric pressure, the actual mass)
how much force is it going to create when it displaces?
http://www.pilotfriend.com/training/flight_training/met/atmos_wt.htm (http://www.pilotfriend.com/training/flight_training/met/atmos_wt.htm)
ok, who has got a spreadsheet, some time, and feels ambitious?
;D
Yeah, but when it comes to things like that, barometric pressure IS mass. It's the amount of mass whatever column of air of X area would be. And neutralizing gravity doesn't somehow cause it to instantly expand. As we saw when he used it in Changes, it mostly just made them rise up a little bit as their force pushing off of the ground was no longer canceled by gravity. Eliminating gravity doesn't mean that the other air there will suddenly stop holding it in or anything like that. Even if it's in a cone and not a cylinder, the air isn't going to instantly bounce off the air under the effect of gravity, it's still got inertia to deal with. So no superimplodey vacuum, much less an explosion.
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Yeah, but when it comes to things like that, barometric pressure IS mass. It's the amount of mass whatever column of air of X area would be. And neutralizing gravity doesn't somehow cause it to instantly expand. As we saw when he used it in Changes, it mostly just made them rise up a little bit as their force pushing off of the ground was no longer canceled by gravity. Eliminating gravity doesn't mean that the other air there will suddenly stop holding it in or anything like that. Even if it's in a cone and not a cylinder, the air isn't going to instantly bounce off the air under the effect of gravity, it's still got inertia to deal with. So no superimplodey vacuum, much less an explosion.
Im sorry, but I don't believe that is correct. In a hyperstatic fluid, the force in one direction (aka the pressure) is only a very small part of it; there other factors than just gravity at play (compression, vectors, expansion due to temperature..)
(http://upload.wikimedia.org/math/8/d/7/8d7d6f94a14ff782b294356960b3c3b9.png)
.. and that's the simplified version
as to the inertia question you may be correct but as Knnn pointed out, the forces involved are far larger than most bombs. Your theory would then say bombs can't explode, because of the inertia of the air around them.
:D
this is far enough out of my field I'd rather not tackle the proof, while I had three years of physics in college I'm not an expert, and this is a lot more complex than the Mab or Harry calculations ( for one thing the equation above is only for static, laminar flows. oops.)
even ignoring the air issue, that much of gravity should have drawn in all the mass around it, instead of just squishing down.
(http://officespam.chattablogs.com/archives/world-largest-mine-thumb.JPG)
oops...
it looked to me like harry just concentrated all the weight of the cars on the vampire, for a fraction of a second. that's several tons of force, more than enough to make vampire pancakes.. and not so much it would wreck half the city.
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I'd say probably not much :)
Man's got enough to worry about.. lol
it's like when I crunched the numbers for the black court master in the short story.. if she can do what she did, how the frak did they ever lose??
Does this mean that we can never use arguments based on calculations again?
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Does this mean that we can never use arguments based on calculations again?
No, just be aware they have a large fudge factor :)
It's enough to know Mab outclasses every wizard on earth, we don't need to know by exactly how much
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as to the inertia question you may be correct but as Knnn pointed out, the forces involved are far larger than most bombs. Your theory would then say bombs can't explode, because of the inertia of the air around them.
No, because my argument is that what is happening is not like a bomb exploding. There's a lot of energy, but it's affecting a wide area of volume* or large amount of mass at once, not just a small part and then expanding. Even if I agree that there's nuclear bomb levels of energy being released (which I don't) it's the difference between spreading it out or releasing it at one point and then having the effect diminish. Because of the inertia of all that other mass in the way. Not instantly, but eventually.
Nuclear bombs in Nevada don't wipe out cities in California. Or even cities just a few miles away from ground zero. What Harry was doing was effectively spreading out that blast from a hypothetical bomb over the whole area at once. So the center is greatly reduced, but the outskirts get a bit of a rise in damage.
*Yeah, I know, area of volume.
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No, because my argument is that what is happening is not like a bomb exploding. There's a lot of energy, but it's affecting a wide area of volume* or large amount of mass at once, not just a small part and then expanding. Even if I agree that there's nuclear bomb levels of energy being released (which I don't) it's the difference between spreading it out or releasing it at one point and then having the effect diminish. Because of the inertia of all that other mass in the way. Not instantly, but eventually.
Nuclear bombs in Nevada don't wipe out cities in California. Or even cities just a few miles away from ground zero. What Harry was doing was effectively spreading out that blast from a hypothetical bomb over the whole area at once. So the center is greatly reduced, but the outskirts get a bit of a rise in damage.
*Yeah, I know, area of volume.
im not talking about Nevada. im talking he was three feet away.
and the mall was a few hundred... ooops
its simple; amount of force could not have been in the range Knnn calculated. even ignoring my first two points, the impact from that force hitting the pavement would have made an immense hole, and the shockwave would have redecorated nicely
not mention conservation of energy.. harry can't manipulate power on that scale... hes never done anything even close.
the effects of the spell match what the weight of a few cars would do, if they were dropped on someone. not megatons.. tons.
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Harry didn't create the super heavy gravity field that crushed his enemies. He diverted and focused it. That takes a lot less power. For example a large river has tremendous power. You can use a little bit of force to dig some and divert the large river. Harry just diverted gravity for a fraction of a second.
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board auto wipes everything not saved im afraid
we concluded Mab's 'waste heat' output was between 10^17th - 10^20th Joules, based on how much power it takes it to snow across the entire Chicago area in may.. 4 feet deep
Here is a thread (http://www.jimbutcheronline.com/bb/index.php/topic,35811.0.html) on the subject.
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Here is a thread (http://www.jimbutcheronline.com/bb/index.php/topic,35811.0.html) on the subject.
thanks!
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Um, this isn't even close to neutron star gravity. Neutron stars are hundreds of billions of times Earth gravity.
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Um, this isn't even close to neutron star gravity. Neutron stars are hundreds of billions of times Earth gravity.
Knnn omitted the ^.. surface gravity of a neutron star is 10^11 g, not 1011 g :D
even so, 1011 g (assuming knnn's math is correct, I haven't done it myself) is more than enough to have wrecked the city, even for a tenth of a second.
since Harry is still walking and talking, I assume the force was purely kinetic, not gravitational, and was much less.
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things are a bit err Squishy on this but maybe what happened is that Harry opened a Picogram sized Black Hole for a Picosecond so that the effect was SPLAT! (and what we "saw" was the result of Harry bending Space/Time how he wanted).
Of course Now since Harry is The Winter Knight and can tap The Winter WellSpring he might decide that an entire BLOCK needs to be flatter.
I could also see Harry making a Staff and Cane combo for when Father Forthill needs to Rebuke Mountains.
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things are a bit err Squishy on this but maybe what happened is that Harry opened a Picogram sized Black Hole for a Picosecond so that the effect was SPLAT! (and what we "saw" was the result of Harry bending Space/Time how he wanted).
Of course Now since Harry is The Winter Knight and can tap The Winter WellSpring he might decide that an entire BLOCK needs to be flatter.
I could also see Harry making a Staff and Cane combo for when Father Forthill needs to Rebuke Mountains.
nothing happens in either of those scenes that can't be explained by Harry simply 'moving' the weight onto a smaller target.. for a second, the cars weighed much less and the vampire much more.
all he did was transform potential energy into kinetic energy.. much like a water wheel does. It wasn't a gravitational effect, since nothing else was changed.
the thing about gravity is it propagates at either light speed or a bit above it ( it's been measured at 1.5 c, but that's controversial) and since it only decreases with the square of distance (and a very long wave form, maybe) everything should have been squished, not just the vampire.
frankly Harry's a wizard, not a physicist ;D
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Maybe. On the other hand, unless Harry has decided to start lying to us about what it is he's actually doing, what he did, because it's what he chose to do, and thought he did, was condense gravity onto a small area. He's never made any mention of black holes or such.
Also, a tiny black hole wouldn't necessarily have any more gravity than anything else. A black hole as massive as the sun wouldn't change the gravity of the solar system at all. A picogram black hole would be no different than a picogram anything else.
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Yeah, peregrine is right, a picogram black hole would be totally irrelevant.
nothing happens in either of those scenes that can't be explained by Harry simply 'moving' the weight onto a smaller target.. for a second, the cars weighed much less and the vampire much more.
How is that different from Harry's description? Weight is just force due to gravity.
all he did was transform potential energy into kinetic energy.. much like a water wheel does. It wasn't a gravitational effect, since nothing else was changed.
No, he concentrated force from a large area to a small area.
the effects of the spell match what the weight of a few cars would do, if they were dropped on someone. not megatons.. tons.
Where do the megatons come from? The initial post talks about 10,000 G. A blampire is pretty desiccated, so we're probably talking 100 pounds or less. 10,000 G would then make it weigh 500 tons or less... not millions of tons.
And the spell reduced the vampire to mostly pulp in a fraction of a second. Momentary accelerations of 100 G in crashes are apparently survivable... sometimes, sometimes not (http://en.wikipedia.org/wiki/Orders_of_magnitude_%28acceleration%29#cite_note-nhtsa.dot.gov-7) and Blampires are tougher than humans.