# byrnema comments on The Graviton as Aether - Less Wrong

13 04 March 2010 10:13PM

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Comment author: 04 March 2010 11:01:19PM 1 point [-]

Interesting. I think there are fundamental things we don't know about gravity yet.

A basic physics question about light waves: I understand how water waves are a property of the medium. My analogy for how it works mechanically is potential energy and kinetic energy swapping in a (mostly) self-sustaining rhythm. I don't understand light waves though. What causes them to oscillate?

Comment author: 04 March 2010 11:09:09PM *  6 points [-]

Changes in electric fields induce magnetic fields. Changes in magnetic fields induce electric fields. If you combine the equations describing these effects, you get a wave equation. The wave described is light.

ETA: The section in the linked wikipedia article with the heading "In vacuum" has the equations in convenient form, and some links that look promising for describing this in more detail.

Comment author: 06 March 2010 08:29:12PM *  3 points [-]

I really am grateful for JGWeissman for helping me click on the fact that light isn't something that obeys the wave described by the Maxwell equation, but is that wave. The difference is imagining light as a type of substance compelled to oscillate with the wave pattern, and there being a wave pattern, resulting naturally from causal interactions, that is interpreted by our vision as "light".

Thus this is the explanation I would give my past self for strikethrough(why light oscillates) what light is:

A charge creates an electromagnetic field. If the charge moves, the electromagnetic field will have to change. However, while the field is defined over infinite space, the field cannot update instantaneously over all of space. Instead, the field updates at the speed of light from the new position of the charge. At a small, fixed moment in time after the point charge has moved, the field has updated within a sphere of a certain radius, but has not yet updated outside this radius. What we call 'light' is the defect radiating outward though space like a ripple. When our eyes intercept this defect, we gain information about the point charge's displacement and -- in some way I don't understand, and don't need to for the immediate explanation -- the field no longer needs to keep updating and the ripple stops propagating (the waves collapses to an intercepted particle / photon).

So I no longer see light as a thing traveling though space, but as information about an updated field traveling in finite time.

Does this make sense? I suppose it could be completely wrong, but it is what I mean by a 'mechanical' explanation.

Oh, and I'll add that light oscillates because the electric and magnetic fields update each other in finite time, and there is a slight lag, so that the wave has an amplitude. I see this as analogous to predator-prey oscillations in a Lotka-Volterra model; if the fields responded instantaneously there would be no oscillation.

Comment author: 06 March 2010 11:38:33PM 1 point [-]

This is a nit-pick, but the oscillation is not because there is any direct delay in the interaction between the electric and magnetic portions, it's because the electric and magnetic portions effect each other through derivatives. This is similar to how the the acceleration (second time derivative of position) is directly related to position in any number of mechanical oscillators, such as springs, pendulums, and even circular orbits, when viewed right. For light, while there are still two time derivatives, they are coupled so that one time-derivative arises between magnetic and electric, and the other arises between electric and magnetic.

Comment author: 06 March 2010 11:50:48PM 0 points [-]

the oscillation is not because there is any direct delay in the interaction between the electric and magnetic portions

I don't see where Byrnema claimed there was such a direct delay.

Comment author: 07 March 2010 05:09:50AM 0 points [-]

update each other in finite time

Comment author: 07 March 2010 05:16:38AM 0 points [-]

Ok, now I am wondering how I completely missed that last paragraph. I agree with your nit-pick.

Comment author: 07 March 2010 05:24:02AM *  0 points [-]

It's OK -- it's a matter of language, and not being very precise. Very loosely, in the case of a pendulum, you could say that in the upswing of the pendulum, it takes finite time (a delay) for the pendulum to respond to the downward force of gravity and start moving to 0. By the time it gets to 0, it already has momentum in the other direction and overshoots the equilibrium again. I see how this is the result of the dynamics being described by changes in the derivative of the motion, rather than -- say -- in the direction of motion itself.

Comment author: 07 March 2010 02:26:46PM 1 point [-]

Right. I'd describe that as a delay for gravity to finish overcoming the motion, rather than a delay in response.

Comment author: 07 March 2010 06:07:46AM 0 points [-]

There is no delay for the pendulum to respond to gravity, it starts accelerating immediately. There could be a delay before it achieves a velocity large enough to be perceived.

Comment author: 07 March 2010 12:13:46AM 0 points [-]

Most excellent. Now, glasshoppah, you are ready to lift the bowl of very hot red coals. Try this

Comment author: 06 March 2010 08:51:04PM 0 points [-]

That is broadly correct. The details of the propagation (and even of the electric field before the charge moves) can be derived from the local laws of how how charges and fields interact.

I know you said you don't need to understand why the field doesn't need to keep updating, but the way that you detect the light is that it moves a charged electron within a molecule in your eye, and that movement of the charged electron causes a light wave that (along the blocked path) approximately cancels the original wave.

Comment author: 07 March 2010 04:10:15AM 0 points [-]

Interesting. That has a nice symmetry, that to intercept light you need to move a charge in your eye that counters the original wave.

What I was referring to particularly was the quantum mechanical aspect: the wave propagates from the source in three dimensions -- an expanding sphere of information. Yet as soon as your eye detects the light, the entire wave collapses into a particle. And this is instantaneous, with no delay.

But that's QM, outside my pay grade.

Comment author: 07 March 2010 04:21:50AM 1 point [-]

Yet as soon as your eye detects the light, the entire wave collapses into a particle. And this is instantaneous, with no delay.

Well, that is one of the many reasons that points to Many Worlds being superior to Collapse theories.

But if we are talking about light you see with your eye, that actually registers in your brain, there is way more than one photon emitted, and classical electromagnetic theory is a good enough approximation. Photons are roughly a discrete unit of amplitude of the light wave. For a high enough amplitude wave, you can ignore that it is discrete.

Comment author: 07 March 2010 04:38:41AM 0 points [-]

Many Worlds made sense to me as a solution when I considered the case of an apparently random choice. Instead of the world collapsing on an arbitrary choice, each world gets one choice. In the case of interaction with a propagating wave of light, though, I don't see how it would work. Perhaps something is incorrect with my fledgling model of light.

Let's consider a single photon. That would still propagate as a spherical wave from the source. The wave expands uniformly from the source and I suppose that according to a classical theory (?), that wave could be perceived simultaneously by different people in different places around the source. Even if I interact with the wave by moving an electron that approximately cancels that wave, then my cancellation would propagate only at the speed of light, not instantaneously.

So how would Many Worlds work in this case?

Comment author: 07 March 2010 05:06:23AM 2 points [-]

I suppose that according to a classical theory (?), that wave could be perceived simultaneously by different people in different places around the source.

That is indeed what the classical theory says. It is wrong. This is where the assumption that domain of the amplitude is continuous is a bad approximation.

So how would Many Worlds work in this case?

Quantum amplitude flows into separate configurations. For each detector, there is a configuration such that that detector was the only one to detect the photons. There are also configurations where no detector detected it. So, if in some configuration, a detector detects the photon, and goes to check on another detector, it will find that the other detector has not detected the photon, not because some instantaneous space spanning signal collapsed the wave function, but because in that configuration the photon did not go that way.

Comment author: 07 March 2010 05:40:03AM 0 points [-]

I see, so the photon left the source as a particle and the wave picture represents the idea that the particle could have been anywhere, until you know which world you're in.

But the mechanical-model-that-made-me-so-happy was that the photon was actually just the electromagnetic field trying to update. The electromagnetic field would have to update isotropically ... it couldn't just update along the route to a given detector.

Comment author: 07 March 2010 06:03:51AM 0 points [-]

Well, there is a similar mechanical model to the evolution of the Schrodinger wave function, which is to particles (including photons) as the electric and magnetic fields are to light in the classical model. This wave function is fundamental, the particles, and the configurations, or "worlds" are derived consequences.

Comment author: 07 March 2010 04:15:02AM 0 points [-]

What I was referring to particularly was the quantum mechanical aspect: the wave propagates from the source in three dimensions -- an expanding sphere of information. Yet as soon as your eye detects the light, the entire wave collapses into a particle. And this is instantaneous, with no delay.

Well, it you believe in a collapse postulate. Which I don't think many people around here do.

Comment author: 07 March 2010 04:27:47AM 0 points [-]

You know, I didn't even know that was the same thing as the collapse postulate. So when people talk about the 'collapse of the wave function', they're talking about -- for example -- the perception of light. OK, sure, that makes sense.

So our solution to that was Many Worlds...

Comment author: 04 March 2010 11:31:07PM 1 point [-]

Nothing basic about that question. It may not even be a meaningful thing to ask.

Comment author: 04 March 2010 11:48:38PM *  0 points [-]

I agree it may not be so basic -- I added that it in because I wasn't sure.

But I feel I understand things when I understand them mechanically and locally. If the universe doesn't actually work that way, I'm at a loss.

(And if it's not understood that way -- though I would bet someone does -- I would think that to some extent, we don't really fully understand it yet.)

Comment author: 05 March 2010 12:51:58AM 2 points [-]

I think understanding the universe in terms of concepts and intuitions that humans developed innately is unlikely to be possible. No reason the ways of thinking about the world helpful in the ancestral environment have to be helpful for describing the fundamental nature of reality.

Comment author: 05 March 2010 01:03:18AM *  1 point [-]

Wow. You and I have had this type of discussion at least once before here on Less Wrong, about whether we 'really' understand something (for example, gravity) or if we understand it 'well enough'. I suspected an underlying difference in the way we were thinking about things.

I don't believe this: that there are physically realized things that we can't understand.

I think that our concepts and intuitions are flexible enough to accommodate any possible reality. Quantum mechanics, and even light, are really weird. But there's still hope for an aether -- or whatever is required for this mechanical/local understanding I'm talking about -- to bring it back down to human comprehension. The fact that these things are mathematically coherent (explicitly and fully described by equations) is especially compelling, since you can interrogate the equations to build structures in your mind that would model it.

For me, so far, the Maxwell equations are just floating in the air with no physical structural basis. However, if you spent time with them, wouldn't you start building a physical intuition about them?

Comment author: 05 March 2010 03:29:45AM *  1 point [-]

Let me see if I understand your claim:

Let physics be described by whatever math is necessary. You predict that human general intelligence will be flexible enough to understand it. If someone is consciously "doing math" rather than "applying intuition", then they don't understand it yet. But the solution to that may involve growing an intuition, rather than changing the math.

That... sounds reasonable enough. But I question whether the intuition always comes in the form of a mechanism, or even any additional concepts at all.

Comment author: 06 March 2010 04:52:17PM *  1 point [-]

Let me see if I understand your claim:

I would only qualify my earlier statement: while human intelligence is flexible enough to understand anything that is possible, it might not be large enough. If there's too much going on, the brain may simply not be able to compute it. In which case, the non-understanding doesn't feel non-intuitive, it just feels too complicated.

I question whether the intuition always comes in the form of a mechanism, or even any additional concepts at all.

Even correct intuition? I guess I don't mind putting forth a more definitive assertion that intuition must be based on a mechanical understanding. (While it's likely I'm wildly guilty of the typical mind fallacy, that's nevertheless my view.)

I've been considering the hypothesis that mathematical intuition (especially intuition about highly abstract, non-physical things) comes from an ability to model that math physically in the brain. When we interrogate our 'intuition', we're actually interrogating these (mechanical) models. Modeling is a high-intelligence activity, and a model 'correct enough' to yield intuition may be hardly recognizable as such, if we were forced to explain in detail how we knew.

(If we have a correct intuition about mathematics outside our experience, how else could we have it?)

Comment author: 07 March 2010 02:00:33AM 1 point [-]

I've been considering the hypothesis that mathematical intuition (especially intuition about highly abstract, non-physical things) comes from an ability to model that math physically in the brain.

New post?

Comment author: 06 March 2010 05:24:24PM 1 point [-]

I've been considering the hypothesis that mathematical intuition (especially intuition about highly abstract, non-physical things) comes from an ability to model that math physically in the brain. When we interrogate our 'intuition', we're actually interrogating these (mechanical) models.

This is correct, but there is a useful layer of abstraction to consider. There are a set of operations the brain does that we can be conscious of doing, and inspect the structure of how they interact within our own brains. These operations are, of course, implemented by physics, they come from the structure of neurons and other supporting biological components. And therefore, the structures that are built out of these operations are also, ultimately, implemented by physics, though a lot can be learned by looking at the introspectively observable structure. These operations can be used to build a model of arithmetic. This does give us some power to "explain in detail how we knew".

Comment author: 04 March 2010 11:32:55PM 0 points [-]

Perhaps you can elaborate? My first instinct was to reply as JGWeissman did, but I felt a slight sense of disquiet about doing so - it would be interesting to find my sense of disquiet justified.

Comment author: 05 March 2010 12:45:38AM 1 point [-]

So JGWeissman explained why we describe light as a wave. The behavior of light can be accurately modeled with a certain kind of equation, this is the same kind of equation we use to describe traditional waves. But that doesn't seem to answer byrnema's question "What causes them to oscillate?". Some interpretations won't even leave us with waves and I don't know if there can be causal histories of wave oscillation when the wave doesn't have a medium. I guess you could generate an EM wave and go "Look!" but it seemed like byrnema was asking something like "why does light move like a wave" which is more or less unanswerable right now and probably will be for some time.

Comment author: 04 March 2010 11:45:53PM 0 points [-]

You're right. I was looking for a mechanical/local answer. (I have been since high school physics when I completely rejected the way magnetism was explained, only to find that was the way it is always explained).

If I found such an answer here - and I wouldn't be totally surprised if I did -- I would use that answer about light to try and maybe finally understand electromagnetism better.

Comment author: 04 March 2010 11:59:42PM 7 points [-]

What do you mean "mechanical/local"? Maxwell's equation's (in what I consider their most fundamental form) describe how the electric and magnetic fields change at any point based on derivatives of those fields, the charge, and the movement of charges at that point. That is certainly local. And, together with the laws describing the forces experienced by charges in the fields (also local), they mechanically describe how a system will evolve.

Comment author: 05 March 2010 12:39:30AM *  0 points [-]

OK, I'll update again that it is just me that doesn't understand the light wave mechanically. (I didn't mean this facetiously -- I know light is really strange for everyone, I just meant that I can't seem to possibly understand it.)

Comment author: 05 March 2010 01:41:41AM 2 points [-]

Do you mean that you do not understand Maxwell's equations? That you don't understand how the wave mechanics are derived from Maxwell's equations? Or that some part of this is not "mechanical"?

Comment author: 05 March 2010 02:47:47AM 3 points [-]

I'm beginning to suspect that my insistence on understanding things a certain way is peculiar and possibly overly narrow.

But suppose that I look outside my window and see a light wobbling across the horizon. I think that I don't understand the trajectory of the light. Then someone finds the equation that describes the motion of the light: it turns out to be perfectly regular and periodic. I still feel I don't understand it. For me, the path of the light isn't understood until you discover that the light is a reflector attached to the wheel of a car, and the trajectory you see is a combination of the car's linear movement and wheel's rotation. This is what I mean by a mechanical understanding.

I could study Maxwell's equations, but I know they wouldn't help. Do we have a 'mechanical' understanding of the motion of light, or just the equation description?

Comment author: 05 March 2010 02:58:40AM 3 points [-]

Are you saying you want to understand light as being made out of components that behave like the macroscopic objects you are used to interacting with? That isn't going to happen, because light does not work that way.

Comment author: 05 March 2010 03:13:40AM *  1 point [-]

I don't mind if light behaves in different ways than I'm used to, but I still expect that these ways are causally dependent upon other things. Especially with a spatial pattern, I expect that any pattern produced by certain geometric rules can be reproduced by a model of those rules.

Even at the macroscopic scale -- if a model is possible (physically realizable) at that scale. If it is not possible, I would have to spend a lot of mental energy modeling those rules mentally, but that would still lead to mechanical understanding. My problem is that I haven't heard (or don't believe I've heard) exactly what rules should be modeled.

Comment author: 05 March 2010 05:46:53PM 1 point [-]

I remember you and I also discussed what it means to understand something, and I definitely sympathize and largely agree with your standard for what counts as "understanding". (I'll find the link to that discussion when I get a chance.)

My standard is that you understand something if and to the extent that:

1) You have a mathematical model that generates the observations with good success. (Not necessary here what labels you use -- this part can be "Chinese room"-ish.)

2) That model is deeply connected (via the entities it shares, quantities it uses, mutual interaction, etc.) to your model for everything else, and thus connected, ultimately, to your intuitive (raw, qualia-laden) model of the world.

Correct me if I'm wrong, but I think this is where you are: for light, you understand it in the sense of meeting 1), but don't meet it with respect to 2). Would you say that is accurate?

Comment author: 05 March 2010 07:42:32PM 4 points [-]

I am not certain if this is going to be helpful, but I'm going to try re-expressing what the equations describe, in non-mathy words. It seems to me that the local understanding you are looking for actually is contained in Maxwell's equations, and that you are blocking on something in that description. Of course I could be quite mistaken in this; it's hard to understand a multi-year confusion based on a few forum posts. So if I'm not helpful here, sorry!

Let me start with an antenna; that is, a straight, electricity-conducting piece of metal. I run an electric current through it, or more accurately, I start running a current. As I'm doing this, the electric field within the antenna is changing; electrons are moving around, spitting out photons, and generally changing their state, heading towards the steady movement they'll have when the current is fully established. Before they can get there, however, I perversely and maliciously reverse the current's direction, and the electrons scramble to attain a completely different steady state! In fact, at no time in the following is the antenna going to be in an equilibrium state; I, the experimenter, am constantly changing its condition and keeping the electrons hopping.

Now, when I change the electric field in this manner, that change causes a magnetic field to arise. It seems possible to me that this step is the cause of your confusion, so I'll digress a bit: Why does a changing electric field cause a magnetic field? Maxwell's equations do not say anything about the causation; they merely quantify the observed fact. Studying Maxwell does not give you any greater understanding of the causation than you would have from the good old 1830s experiment of running a current through a wire and seeing a nearby compass needle deflected; all it does is to allow you to calculate how much deflection to expect. I often see this sort of confusion in the way basic physics is taught; because the equations are the full description of what's going on, people expect them also to contain the full understanding at the causal level. So there is confusion about Maxwell, and also about special relativity; people ask "What does it mean that the time-direction's sign is reversed in the inner product?", and the answer is that it describes the way matter behaves, but the causality is much deeper. It may be a mistake to teach Newton before anything else in physics, just because F=ma is so intuitively clear; we all see that this is just a formalisation of the way rocks behave. Throw the rock harder and it hits the other monkey faster, causing more damage: Our brains are well adapted to this piece of physics! But it does us a disservice in studying other equations, because we expect them to be similarly clear and contain a similar causal-level explanation, and they just don't.

At any rate, then, the crucial point is that when I move the electrons, they cause a magnetic field to exist. If you look deeply enough into QED, you can find an explanation of this in the way the force-carrier photons are moving, but personally I am quite unable to visualise this; all I can do is go through the math that shows Maxwell's equations coming out as the classical limit of QED. (Well, anyway, I could do it for an exam some years ago.) However, it may be helpful to visualise it like so: When I accelerate the electrons, the virtual photons that they spat out a few nanoseconds ago (messengers for their electric field) are 'unable to return home' (home having moved) and must find something else to do; the something else is to interact with other particles, which we measure as a magnetic field.

Now, because I'm varying the acceleration of the electrons, the size of the magnetic field caused by their acceleration is also changing. And a varying magnetic field... causes an electric field. It is inaccurate, but possibly helpful, to view this as being caused by the aforementioned no-longer-so-virtual photons interacting with electrons in the quantum foam and moving them around, creating a momentary polarisation of space.

So now there is a changing electric field not just at the antenna where I'm doing my thing with the electric current, but also some distance away where the resulting magnetic field is causing a reflection of that process. Rinse and repeat: This electric field's changing causes a magnetic field over here, which causes... You will get a chain of electric/magnetic fields running across the entire universe. This is what is meant by a 'light wave'.

Maxwell allows us to describe in numbers what I just described in words, but the causal understanding is all in the observed fact that a changing (not a steady) electric current causes a compass needle to deflect. You can take this as unadorned, experimental observation, "We don't know why that happens", or you can try to visualise it in terms of messenger photons as I outlined above. I hope that helps.

Comment author: 06 March 2010 05:24:39PM 1 point [-]

Thank you for this explanation, it includes exactly the sort of mechanical explanations I was looking for. Not necessarily simple or easy to understand, but about entities with certain properties interacting in certain ways.

When I accelerate the electrons, the virtual photons that they spat out a few nanoseconds ago (messengers for their electric field) are 'unable to return home' (home having moved) and must find something else to do; the something else is to interact with other particles, which we measure as a magnetic field.

For example, this is a mechanical explanation. It's probably somewhat inaccurate due to being expressed verbally, but a person can then turn to the equations to get the detailed, accurate picture.

I often see this sort of confusion in the way basic physics is taught; because the equations are the full description of what's going on, people expect them also to contain the full understanding at the causal level.

I think I would have done so much better in physics if they had explained the causality with the equations. For me, now, understanding that light is the interaction of the electric and magnetic fields has been a wonderful paradigm shift in way I view things. I had already assimilated that most things I experience are electrostatic -- that a table is non-compressible and the chair supports me because of electrons and their interactions. And now my idea of light has changed -- I no longer see it as an independent substance reaching me, but as information about the change in an electric field propagating towards me at a fixed speed from whatever sources are emitting or reflecting the light.

My ideas are topsy-turvy at the moment, it will take some time and reading for them to settle in any accurate way. But I'll share some of my first-day thoughts . For example: A room full of light is 'bright' because the light contains so much information. And: it seems amazing that visible light is so faithful (non-noisy) when you think of it as a wave propagating in all directions; only a particle at the moment of observation.

Comment author: 15 March 2010 08:41:27PM 1 point [-]

A room full of light is 'bright' because the light contains so much information. And: it seems amazing that visible light is so faithful (non-noisy) when you think of it as a wave propagating in all directions; only a particle at the moment of observation.

I find that your bright room-observation and an analogy with low-light photography almost helps me grasp how come the world seems classical despite its quantum “underwear”:

Think of a (digital) photograph taken in very low light. Something like this.

Think of being in a pitch black room, and imagine your eyes are perfectly sensitive. You have a flashlight pointed away from you.

Now imagine the flashlight is very dim: it only sends one photon every few seconds, by moving one of its electrons; the electric field propagates at c as a spherical wavefront to “notify the universe” of the change. Whenever this front passes through another electron (say, of the wall before you), it may be absorbed. If it’s not absorbed, the electron does nothing (in a way, it doesn’t care that the first electron changed position). However, if it is absorbed (the two electrons exchanged a photon), then the absorbing electron now changes position to conform to the new information; doing so starts another wave-front communicating this information. Note that this second wave-front is not just going back, it’s still a spherical front starting from the wall electron. Again it starts propagating through space until it hits another electron. Suppose this last electron is used by your eye as a detector. Then you just noticed a tiny “flash” of light somewhere in your vision field.

Note that the two absorptions happen (until now) randomly. If you use just that flashlight you’ll only see random flashes in the room. More precisely, in the many-worlds interpretations, from a single train of emission-absorption-reemission-detection “events”, each you in every world will see the tiny flash in random parts of their vision field. This is both because different wall electrons would have done the absorption-reemission, and because of different electrons in your eyes would do the detection. You can extend this metaphor a bit more: in worlds where the re-emitted photon didn’t hit your eye, but (say) another electron deeper in the wall, that world’s version of you won’t notice anything. (The absorption-reemission chain will just bounce electrons and nuclei randomly throughout the wall, which just means heat.)

OK, here’s the “brightness” part: even though the absorption-reemission electron is randomly chosen by each world, not all of them are equally likely to be chosen. The wave-functions of the particles, and the interactions of those wave-functions as given by QM equations, cause the distribution of “picks” to have a certain “shape”.

Imagine that you take your flash-light and you increase its brightness; say it sends 10, then 100, then a million photons at the same time. You’ll start seeing several flashes, from random positions in your field of vision. (Each of you in the many-worlds will see the flashes coming from different places.) But the wave-function says how likely it is that you’ll see flashes from different places: even if each version of you sees different flashes, each of them will see more flashes coming from bright (white) objects than from dark (black) objects. As a result, you’ll see a grainy image of room in all worlds, even though a different one (that is, with the grain positioned differently) in each. The more photons your flashlight sends, the more “smooth” your image will be, converging on the “shape” of the wave-function. The image above shows a noisy image obtained in low light (although for normal cameras the source of noise is different).

Imagine you take several consecutive photos in those conditions; each image will be very grainy and dim, and the position of grain will vary among your many-world alternates. However, if you combine your successive photos in one, you’ll accumulate a brighter, clearer image (the more so as you add more photos). Each many-world version of you will get a different one, but they’ll converge to the same: the shape of the world’s wave-function. (Of course, the different worlds will eventually diverge in shape, too.)

You can stretch this analogy to visualize all sorts of interactions. For bright objects the re-emission is more likely to occur “towards” the outside of the object (or, inversely, electrons within bright objects tend to not communicate between themselves the news about outside). For dark objects it’s the other way around: photons are more likely to be passed among the object’s electrons rather than towards you.

Or take diffraction: A photon is emitted, passes through a screen with two holes (thus, it’s not absorbed by its electrons), and hits a wall. Even if you send photons one-by-one, they’ll still form a diffraction pattern on the wall. You can imagine it this way: the initial emission (the wave-front carrying the message) is spherical; when it hits the screen, either it’s absorbed (the message was passed to the screen), and you see nothing), or not: the message passed through both holes. But from each hole the message continues to propagate in a sphere centered on that hole. When the “message” hits the detector area, it is both these spheres that hit; depending on the difference in distance of the two paths, in some areas the two “copies” of the message can contradict each other or agree; you’ll have successful detection (a movement of an electron in the detector wall) only where the two copies agree, thus forming the interference pattern—but, for a single photon, exactly what point of the interference pattern will be hit is random.

Comment author: 05 March 2010 10:48:47PM 0 points [-]

Nitpick: s/similar causal-level explanation/similar intuitive appearance of a causal-level explanation/