Showing posts with label physics. Show all posts
Showing posts with label physics. Show all posts

Sunday, January 26, 2014

What is Spin? A Concrete Explanation.

To say that a particle has "spin 1/2" is to say that it must be rotated through 720 degrees before it can return to its original configuration.  This is not something normally witnessed in the world of classical mechanics, and so this aspect of quantum mechanics is often piled up with unhelpful metaphors and mysticism.

I wrote a post previously trying to point out that quantum mechanical spin is just a degree of freedom.  Spin tells you the components of a particle in a combination of two wave states with the same energy.  You can make pseudospins and isospins with any two such states, no matter what they are.  When you rotate the system, the components get mixed up -- just like angular momentum states.  You have to rotate the system by 720 degrees before the components get mixed up enough to be un-mixed up (i.e. back to there they were).  That's all it is.

What gives spin states this weird property is that the space of rotation is three dimensional, but the spin "vector" is only two-dimensional.  Rotations of typical vectors with three components (even if one of those components is zero) work just the way you'd think they should.  But, it's not completely surprising that 2D objects in 3D space don't rotate like 3D objects in 3D space.

To illustrate where spin comes from, and how it contrasts to orbital angular momentum, consider the case of rotation in 2 dimensions.  The best way to talk about rotations is to start at the unit circle.

Thursday, January 23, 2014

Everything Cool is Impossible


Physics has known for a long time how to build a time machine.  The possibility in a real spacetime geometry was first noted by Van Stockum, but this possibility was only really first analyzed by Frank Tipler in the 70's.  All you need is a massive rotating cylinder.  And also it has to be infinitely long.

This illustrates how frame dragging
can lead to time travel 
Since then, at least a dozen other possibilities have been proposed for time travel to the past, and physicists have proven that these spacetime geometries result in what are called "Closed Timelike Curves" (CTCs), which are trajectories a massive object could follow to go back in to its own past.  We know that they would work within the theory of General Relativity.  But, they're all impossible.  They either require the universe to be rotating (it isn't), they require infinitely large systems (we can't make them), they require negative-mass matter (no such matter exists), or they require you perform your time travel within the interior event horizon of a Kerr black hole (which is fine, but then you can't leave).

This situation is worse than merely having a concept of physics that excludes time travel, or that merely says that time travel is impossible.  For if time travel was excluded by theory, then we could always say the theory was incomplete.  What we have instead is a system that fully allows time travel possibilities without prejudice, as long as we're able to break some other law of physics to get there.  It's not just the stubborn "no" of a parental figure; it's like having your parents describe step-by-step exactly what you can do to eat chocolate cake for breakfast, and one of those steps is "eat infinite broccoli".

Physics also knows how to effect FTL travel.  The speed of light puts a prohibitive barrier on
our ability to explore the stars, but a number of work-arounds have been proposed.  Technically, relativity only prohibits local FTL movement, but says nothing of global FTL travel.  So if you can distort space and time in just the right way, you can move however fast you want.  One of the more frequently explored proposals is wormhole travel.    Wormholes produce a kind of "short cut" in spacetime, and it is actually a Federal Law that when you want to discuss how wormholes work you must draw two dots on a sheet of paper, "A" and "B", draw the straight line connecting them, then fold your paper so "A" and "B" touch and jab a pencil through it.  While going along the line you draw may take billions of years, going through the wormhole may take minutes.
My lawyers also recommend I show you this diagram

Sadly, you can't make a wormhole.  And even if you made a wormhole, the throat collapses when you try to travel inside of it, so you can't even use the wormhole for travel anyway.

Another proposal is the Alcubierre warpdrive.  This contracts spacetime in the front and expands it in the back, producing what some call a "wave" of spacetime contraction that "tips over" the light cones inside the warp bubble.  Locally, you're moving slower than light, but globally you may be moving, in theory anyway, as fast as you want.

But you can't make the Alcubierre warp drive either.  If you took the mass of the universe and made it negative, the Alcubierre warp drive requires ten times that number in negative-mass matter to move a standard-sized spaceship.   To clarify, we haven't even found one single particle of negative-mass matter.

Science knows how to make a Bag of Holding, and can even make a Bag of Holding that slows down time (see chapter 3 here).  You can store a lifetime supply of hot pies and ice cream in the same box, and whenever you take them out the pie is still oven-fresh and the ice cream still ice cold, and so even twenty years later you can serve yourself delicious pie a la mode.  But, like so many awesome things, it requires either negative mass or impossible mater distributions and can't be made.

I just made a post about how the Bag of Holding (aka, Van den Broeck Bubble) can be exploited to, potentially, travel to parallel worlds (if any even exist).  This one is a lot more speculative, requiring ideas way beyond established science, but is at least partially based in what we already know about general relativity and curved-space geometry.  It isn't really scientific, but if we wanted to know if there were other universes, this has potential to actually find them.  But it also requires not only negative mass, but infinitely much of it.  So we won't ever be able to try.

Pictured: A guy wearing a green screen.
Not Pictured: An invisibility cloak 
Science has pretty recently discovered (less than ten years ago) how to make a literal cloak of invisibility.  It involves bending light in just the right way.  We know what that just-the-right-way way is, and we even know how to make materials that bend light in just that way.  Sadly, it only works for a single frequency (i.e. color) of light at a time.  There's no way to be completely invisible, because there don't exist materials with  the right optical properties naturally.  So you can be green-invisible, but you'll still be perfectly visible in red and blue.  I guess you'll just look slightly more purple?

I recently calculated (as part of my research) how to make a slightly different kind of cloak, namely a shadow cloak.  Also something you'd read about in fantasy books, the shadow cloak works on the same spacetime distortion principle as for a black hole, but now modified to work with optical materials (so not requiring it be made of actual black holes).  A perfect realization  would allow light to enter, but trap it there.  If you were wearing it, you would appear to be not just covered in a black garment, but actually swathed in shadows.  (Look at a black object, then look at an unlit hole; there's a big visual difference)  You'd also probably heat up a lot (since all the energy is trapped), which would make this kind of material perfect for solar panels, increasing their efficiency probably to near 100%.  But you can't make the shadow cloak, because it requires material parameters that are both infinite and negatively infinite.  Like with the invisibility cloak, you can only realize this (if at all) for a single color of light at a time.  Which vastly diminishes its coolness.

You can probably see where my knowledge tends to specialize, but physics knows a lot more cool things in the quantum domain, such as teleportation devices and solutions to the P=NP problem.  All of which, we know how it would work, and only minor technicalities render it impossible.  Things like wavefunction collapse, quantum decoherence, and the no-cloning theorem.

Any time there's something cool in physics, there's something else that renders it impossible.

Again, this isn't the situation of wanting to do something incredible and merely lacking a theoretical model to describe it.  Our formulations of physics account for it exactly.

It's just that all the cool stuff is impossible.

More and more, it just seems like the Universe comes equipped with fail-safes against our ever doing the cool things of science fiction.

Tuesday, January 14, 2014

Sailing Away to Narnia


I stumbled upon an article a few months ago that I've been meaning to blog for a while and never got around to.

The original article is by Chris van den Broeck, and deals with the subject of warp drives.

Yes, warp drives.  The Alcubierre warp drive engine is a device that stretches the spacetime around a spaceship, forming what is known in scientific literature as the "warp bubble" (really, that's what we call it).  Within the warp bubble, the ship is moving at "normal speeds", but outside of the bubble, the ship is moving faster than the speed of light.  The geometry for this is known and well understood, and the means of producing it are also fully understood.

You're probably wondering, if we know how to make a warp drive, why we haven't actually... you know... made a warp drive.  And that's a wonderful question.  We haven't made a warp drive because it requires a lot of stuff that probably doesn't exist, namely negative energy mass.  It requires a whole lot of it.  Like, ten times the positive mass of the entire universe in negative mass.

Van den Broeck proposed an idea to get around this, one elegant in both its simplicity and apparent absurdity.

Here's what you do: Take a bag.  Distort space, so that the inside of the bag is bigger than the outside of the bag.  The inside is big enough to hold a spaceship, and the outside if around the Planck length.  Now stick your spaceship inside of the bag, and then put a warp bubble around the bag.   It requires a lot less negative energy.  Voila!  Crisis averted.
Schematic from original article.
Region II is the bag.
Region I is where the ship is.
Region IV is the warp bubble
Now, warp drives are cool of themselves, but what I really want to talk about is the device that distorts space so the inside of the bag is bigger than the outside of the bag.  This is sometimes called a "van den Brocek bubble", or, somewhat more appropriately, a Bag of Holding.

We've gone from warp drives to the bag of holding, and we're not even done yet.  We're going all the way to Narnia.

Saturday, December 21, 2013

The Cross-Section of Angels

Solidity is an illusion.

You may or may not already know this.  Matter is mostly empty space: when you smack your hand against a table, what prohibits the further movement of your hand is the interaction of electrons, protons, and neutrons.  At base, everything is likely a point particle, and all appearance of volume is caused by energetic excitations.

When you fire one point particle at another point particle, from a strictly geometric standpoint, the probability of collision is 0%.  Nothing should ever hit anything else.  And yet, two electrons launched at one another will "bounce"; the reason there being the electromagnetic repulsion.  To account for this discrepancy between the expected geometric probability of scattering and the empirical measured scattering caused by the interaction, physicists who study such collisions use a quantity called a scattering cross-section.  A scattering cross section is, more formally, a fictitious area describing the strength of interaction between two particles.  This is given as a ratio: number of scattered particles divided by total incoming particles.

This ratio can be measured empirically in the lab by mere bean counting, but it can also be derived theoretically from considerations of the interaction potential.  This is how we know the majority of what we know about anything on scales smaller than molecular.  The existence of the nucleus within the atom, for instance (as opposed to Thompson' plum-pudding model) was discovered through a scattering experiment.  We only know about quarks and the strong interaction through scattering.  The recently discovered Higgs particle is also a result of scattering experiments.  In all of these cases, just bouncing particles off of something and measuring the exact way that the particles bounce is enough to tell us what a thing is made of, how it is shaped, and -- more importantly -- the kinds of interactions that it undergoes.

Visible light is not normally useful to this purpose at subatomic lengths, but actually normal vision is an example of a kind of scattering experiment.  Light from a bulb bounces off of an object and to your eye: you in a sense "measure" the angular deflection and intensity of this incoming light, and can thus determine the size, shape, and color of the object in question.

All of the things that you can see scatter light because all of the things that you can see are made of charged particles.  Charged particles participate in the electromagnetic interaction, as does light, which means that normal matter is able to scatter light (as opposed to, say, dark matter).  Were it not for the interaction (or coupling) between light and matter, then the electromagnetic cross-section of matter would be zero; light would see every surface as having zero area and therefore not bounce off of it.

To make this point more clearly, consider the neutrino.  Neutrinos are not known to participate in any interaction besides the weak interaction.  Therefore, neutrinos can fly right through the planet without slowing down.  They're not flying through it like bullets, boring tiny holes; they're just flying through it.  The solid matter of the earth is, to them, intangible and ethereal.  They don not undergo the electromagnetic interaction, and so do not "see" the earth there.

I say all of this as introduction.  What I really want to discuss are angels.  In particular, how do we see them?

Sunday, May 26, 2013

Whether Something Can Come From Nothing, and Quantum Mechanics

It is very popular  in certain circles that place a high value on the classical scholastic arguments for the existence of God to ask "why is there something rather than nothing?"  Ex nihil, nihil fit, is the Latin phrase, that from nothing, nothing comes.  If there is something, then why?  How did it get here?

It is then popular in certain circles that place a high value on scientific understanding --- people who perhaps don't understand math well enough to study it for real, but who nonetheless appreciate human efforts to understand the natural world in terms of rational processes and read as much of it as they can understand --- to make the rebuttal claim that, according to the physical understanding of quantum mechanics, something can come from nothing.


You can see an example of this conversation in the below video:


The idea is that in quantum field theory, study has shown that even in the state representing a vacuum, i.e. a system with zero particles, there is still the constant process of random particle-antiparticle pair creation and annihilation going on all the time.  You start with zero particles, and for brief instances you have two particles.  Or, in higher order interactions, four, or one hundred and twenty four.  Therefore, something -- particle-antiparticle pairs -- can come from nothing -- the quantum vacuum.

This idea is right, and it's wrong.  I think both people are talking past each other, and in this post, I would like to try to clarify.

I'm not a field theorist.  I've had some grad classes in it, but it's not anything in which I'm an expert (in fact, there probably isn't anything in which I'm an expert, but it's a helpful caveat).  Still, what I'm about to say is very basic to field theory (if anything in field theory can be called "basic"), and I'm more or less directly citing the text Field Quantization by Greiner and Reinhardt (available on Amazon for only $\$20$!).  What follows is a very, very brief outline of how quantum field theory leads to the understanding of the quantum vacuum, but also how the results therein do not mean what many people think it means.  I have some wikipedia links throughout, so that hopefully people who do not understand math can at least follow along with what I'm trying to say -- the math isn't important, but the physics is.

The Uncertainty Principle and Energy Non-Conservation, part 2

Quantum mechanics is typically interpreted to mean that the conservation of energy can be violated as long as the time scales involved are short.  An old professor of mine used to summarize it as "there is such a thing as a free lunch, if you can eat it fast enough."

Here's how the argument goes.  From quantum mechanics, we get the uncertainty relation
$$\Delta E \Delta t \geq \hbar,$$
where $\Delta E$ is the uncertainty -- or statistical spread -- of the energy, and $\Delta t$ is the uncertainty of the time.

Following this, physicists reinterpret the uncertainty $\Delta E$.  Rather than representing a quantification of our lack of knowledge about the energy of a system, this is interpreted as being, somehow, the amount of "free" energy that a system can borrow in violation of the First Law of Thermodynamics.  So if we have mean energy $E$ and uncertainty $\Delta E$, it means we "actually have" energy $E$, and then Nature gracefully lends us $\Delta E$ to overcome some energy barrier, which we quickly repay in time $\Delta t$.

However, that puts us at 
$$\Delta E \geq \hbar/\Delta t$$
which puts no limitation how much energy we can borrow.  Or, rather, it puts a lower bound; we must borrow at least $\hbar/\Delta t$ worth of energy.  Or, we could borrow even more!   If this is true, then we have infinite energy forever!

The oil companies will go bankrupt!

Wednesday, May 15, 2013

What is Spin? A More Simpler Explanation

The Copenhagen interpretation of quantum mechanics wasn't supposed to be mystical.  In fact, it was made precisely to avoid mysticism: "Shut up and calculate!" is probably the best summary of it possible.  Who cares what wavefunctions are or how they collapse, gimme the expectation value.  It's supposed to be practical, simple.  It's logical positivism at it's more rarified.

courtesy SMBC
Somehow, the refusal to address the complications of quantum and to just skate on by, has led to all sorts of weird mysticism stuff like quantum healing.  Today most non-physicists have misunderstandings of entanglement and many-worlds and why Schrodinger hated cats so much.  And very sadly, most physicists have no ability to correct them, as all they can do is draw squiggly tridents and funny S's and say "here is the answer".  That's all we're taught!  "It's a mystery, no one knows so shut up and calculate!"

The result is that no one really knows anything.  Physicists have a blackbox of expectation values and non-physicists have neat anecdotes for cocktail parties.

Sunday, May 5, 2013

Computer Simulation of a Rift in the Space-Time Continuum Devouring the Universe

Part of my research involves computer simulation of bizarre materials with exotic optical properties; materials that can bend light in almost any manner desired.

I work on the theoretical side of things; I can say that I have in fact touched a beaker and used a pipet to move water from said beaker to another nearly identical beaker (I did this just to feel science-y and say I've done it) but I have no lab experience and would probably destroy everything in your lab if you let me use it.  All this to say, though I can sort of describe these materials (whilst gesticulating with a pipe, and with a dreamy glaze over my eyes and lulling drawl to my voice) I -- me -- am incapable of producing them.  So if I want to convince someone with a lab and knowledge (and a budget) to actually make them, I have to give more than my impressive pipe-gesticulations.

Hence, I use computer algorithms to make simulational models of the bizarre materials, send some simulated light in to them, and can thus prove to these experimental people with labs that the totally awesome sailing ship I just blew through a smoke ring can in fact be built and sailed through physical rings.

Tuesday, March 19, 2013

The Width of Narnia

As is revealed in Voyage of the Dawn Treader, the world of Narnia is a flat earth.  Characters can literally fall of the edge of the world.

I started wondering, at one point, how thick is that edge?

Characters from our world report no differences in the gravity (or whatever) on Narnia; they don't feel any greater or lesser weight walking around.  Arguably, if Narnia had a lower gravity, then the Pevensies might have had, at least, an easier time crossing through the snow.  And contrariwise, if Narnia had a much higher gravity, then the adventure would have mostly been about aching knee joints.

Further, when the Pevensies stay in Narnia as kings and queens, they eat the food there, and this does not make them sick.  The food they eat they report as tasting equivalent to earth food.  When they grow up, they marry dryads and naiads and other mythological things and have children.  Weird as this is, it all proves pretty much conclusively that Narnia is made of the same kind of "stuff" as Earth; this is important.

So we know three things.  We know Narnia has the same overall downward-pulling force as Earth's gravity, we know that Narnia is made of the same kind of stuff as Earth, and we know that Narnia is a flat earth with a literal edge that you could fall off.

This is enough to calculate, to a very good approximation, how thick Narnia is.

Friday, February 22, 2013

Vectors are Not 1-Forms

So, I recently moved in to a new research area.  It's new to my advisor, too.  Actually, generally speaking, it's pretty new period, first appearing some ten years ago or less.  Anyway, this new field deals fairly heavily with Maxwell's Equations in curved spacetime, so to understand it we are needing to review differential geometry and general relativity, two fields which are not in the normal purview of my advisor's expertise.  I was asked to prepare a chalk-talk that would introduce the key concepts of differential geometry to them, and another talk to segue in to Maxwells Equations in curved spacetime.

Not like I'm an expert on differential geometry, but I've studied it some privately and as an undergraduate.

While studying for this, it dawned on me suddenly, like the storm clouds that pile higher and higher until the first bolt of lightning strikes the ground, that vectors and 1-forms are different.

Every thing I have ever read in physics equates them.  Or not really.  Everything I have ever read in physics doesn't even demonstrate that it understands why those two should occupy different semantic domains.

What the heck am I even talking about?

Saturday, January 5, 2013

The Uncertainty Principle and Energy Non-Conservation and Why Your Textbook is Wrong

I read this all the time, in physics books and articles and on the internet: Apparent violation of conservation of energy is possible at the quantum scale for very short periods of time due to the Heisenberg uncertainty relation:
∆E∆t ≥h/2π
In that equation, ∆E is the "uncertainty" in the energy and ∆t the "uncertainty" in the time, meaning the accuracy to which we are able to measure these values.  The h in the equation is Planck's constant (which I didn't write as h-bar because I didn't want to encode LaTeX for one equation).  The two are inversely proportional, so as one goes up, the other must go down, so for short times, you can get enough "free" energy to send a particle through an energy barrier.

This is wrong.  Wrong, wrong, wrong.

Tuesday, January 1, 2013

Why Travel to Hyperspace Would Instantly Kill You

So, I've wondered a lot about a way to construct a "system of magic" (as often appear in modern fantasy works) from a collection of physical laws.  And until I got carried up in classes last semester, that was one of my main focuses of attention.

I was thinking that, in an alternative universe, there's no reason why they should have the same number of spatial dimensions as us.  So why not four, or five, or ten?

Because if you traveled to four-dimensional space, then you would find your skin insufficient to contain all of the air, blood, half-digested food, and maybe even internal organs that now find an extra degree of freedom within which to diffuse.

Five and higher dimensions makes it worse; the many things inside of you that keep you alive would disperse and splatter even faster.

So far I have discovered that to have any sort of meaningful adventure in a parallel universe, it must have the same number of spatial dimensions as we do (namely 3), it must have at least one time-like dimension, the electromagnetic interaction must exist and must recognize and interact with your electrons and protons.  Gravity would be nice, and I don't know enough about weak and strong interactions to know if they would be necessary.
http://abstrusegoose.com/457

There are most likely other limitations and dangers in such fantastic travel that have not yet come to mind.

In short, the inter-universe questing of children from our universe can never be to any world truly alien from our own.  Which is very sad.

Friday, November 9, 2012

The Dirac Sea: Turtles All the Way Down


This semester, I am taking a course on relativistic quantum mechanics.  Currently we are covering the "hole interpretation" of negative energy solutions to the Dirac equation.

I've done this stuff before, as an undergraduate, in private study, and in various grad-level courses.  So I'm used to the interpretation being given.  But I decided recently that it is perfectly absurd.

Sunday, September 2, 2012

Thought Experiment on Entropic Restrictions in Time Travel


In a discussion of time travel, questions will come up about freewill and causation.  I have always found this conversation frustrating because the common view is just so plainly wrong.

The common view is the one espoused in Back to the Future, which arguably is where most Americans get their understanding of time travel. (I guess as opposed to empirical time travel science?)  Everyone knows this so I don't even have to summarize it, but here goes:  You go back in time but you have to watch out that you don't accidentally change anything, because if you change something because then you will change the future.  In particular, you need to make sure that your introduction to your parents when they were in high school doesn't keep them from falling in love, or else you would undo your own existence, the fact of which alone should point out that there is something screwy here.
source

In this idea, because you can change the future you came from, there are different "timelines".  When you go back in to the past you go to a different timeline or split the universe or whatever and the effects of your meddling will be in the new timeline and not the one you came from.

So why do we think there are multiple timelines?

Thursday, August 23, 2012

The Berenstein Bears: We Are Living in Our Own Parallel Universe

if only facebook would make this the preview photoWhen I was growing up, all through elementary school we would watch movies and read books about the Berenstein Bears.  I still even remember the theme song for the TV show, mostly, which wasn't a song so much as a guy in a gruff bear voice speaking in rhyming couplets.  If you don't know who the Berenstein Bears are, they were nuclear family of anthropomorphic bears who lived in a tree out in Bear Country and had family-based situational comedy and taught life lessons.  And Ma Bear always wore a blue shower cap.

These bears appeared in a series of children books by the married Stan and Jan Berenstein, that later became a TV series, that got beamed to 3rd grade classrooms all over the country.  Anyone between the ages of 23-30, and maybe more, will know who the Berenstein Bears are.  And they will remember the flashy cursive bubble-letters on the front of every single book and in the opening credits of the show.  The bubble letters that spelled out "Berenstein Bears".

About a year ago, Jan Berenstein passed on, as had Stan some time before.  And appearing in headlines across the internet, I saw "Jan Berenstain Dies at 88".

BerenstAin.

They misspelled her name.  In her obituary.  Gosh, that's really just morbidly embarrassing.  "Berenstain" doesn't even make sense.

Sunday, July 1, 2012

The Physics of a Chess Board


In Through the Looking Glass by the Reverend Lewis Carol, Alice walks through a mirror in her living room and finds the chessboard that normally resides there to be teeming with little chess pieces running around.  Leaving her mirror-house, the entire country around it has been transformed in to a chessboard.  Alice starts as a pawn and has to walk forward one step at a time to the end, when she will become a queen and be able to run as fast as she wants across the country.

While Carol's story is whimsical and fun, what would be the implications of living in a chess board?  What are the "physical laws" experienced by a given chess piece?

So imagine all the universe to be a discrete 8X8 grid, alternately tiled with black and white, and conceive of a chess piece as being a kind of elementary particle in this bizarre chess world.  We will look mostly at the free dynamics of such a chess particle - that is, how it behaves dynamically in the absence of other pieces.

Monday, June 25, 2012

Zeno's Paradox and Why It Annoys Me


I have always been greatly annoyed by Zeno's paradoxes.

The reason why is due mostly to my stubborn pride at being ignored when I'm right.  When I was in 10th grade trig, we learned Zeno's paradox of Achilles and the Tortoise.  The problem so presented is an extremely simple algebraic equation, immediately solvable to anyone who has finished high school.

So in grade school, when I was taught this "paradox", I did solve it algebraically, almost before my teacher had finished reading it from the book, and I told her the answer, and she sort of gave me this exasperated smile and said "Yes, I know, but don't think about it that way."  And ever since, mention of this paradox as anything other than an ancient Greek misunderstanding of mathematics has infuriated me.

Basically, Zeno's paradox amounts to asserting that the geometric series cannot be summed.  Which is absurd; Archimedes was quite proficient at it, even in terms that Greeks would accept.  Some examples are below.  In terms of modern algebra, let $S$ be the sum of a geometric series; then
$$S = \sum_{n=0}^\infty a^n = 1+a+a^2+\cdots = 1+a\left(1+a+a^2+\cdots\right)=1+aS,$$
and rearranging, $S = \frac{1}{1-a},$ the formula you hopefully learned in high school.

Monday, June 18, 2012

To Stand on Charn

Since C.S. Lewis showed us a world on the other side of a wardrobe (and perhaps before), fantasy and science-fiction stories have abounded with this idea of traveling to parallel universes and experiencing strange new worlds.  It's almost iconic: awkward teenager struggling in school and with bullies, gets sucked in to an alternate magical world, meets fascinating elves and confronts evil, and finds confidence to face real-world issues on his or her return.

Typical example

So here's my question: how do they interact with matter in the alternate universe?

Friday, June 15, 2012

Virtual Aristotelian Physics


I spent several hours the other day looking up some sort of reference to a computer simulation of Aristotelian physics.

The thought came to me in connection to fantasy worlds.  Good fantasy authors will create their own fictional worlds with different histories, cultures, languages, and religions, similar to Tolkien's Lord of the Rings.  Lately authors have started going kind of crazy, and have been experimenting with alternative physics, like flat earths and sentient quanta.

I was thinking, why not Aristotelian physics?  Is it that impossible?  A professor of an old friend of mine, remarking to a room of Thomistic philosophy students, asked why they were so enamored with Aristotle when you couldn't make your car run on Aristotelian physics.  Maybe not their cars, but any car?  Can a car run in a world of Aristotelian physics?
Aristotle with impetus