Hey folks. I thought given some of the wonderful intellects we have here it would be fun to have an “ask an expert” thread. Don’t get hung up on if you’re an expert or not, if you want to ask a question or supply an answer, have at it!
I was flying into LAX two nights ago and I could see the moon (nearly full) being reflected in a body of water. I began thinking about how the light of the sun had bounced off of the moon and the water create the image in my eyes, like a game of photonic billiards. Which brings me to my question:
If photons are being reflected (“bouncing”) off of the face of the moon, shouldn’t the edges of the moon appear dimmer because the angle should be less favourable to bouncing photons my way?
I’m not sure why you think the angle would be less favorable. Because of the curvature, there a lot more lunar surface at that steep angle. The extra surface, as a source of possible reflection, should at least partially compensate for the steepness of the angle.
No, not an expert. Worse, it’s a cloudy night so I can’t look as a cross check.
You could test this by photographing a sphere lit by a point source.
http://fp.optics.arizona.edu/Palmer/moon/lunacy.htm
It would be (much, anyhow) less favorable to bouncing photons your way only if it were a specular surface, like polished metal, or a largely waveless liquid. When the surface is dust, sand, or even just rock with random mineral orientations (by far the most rock ever seen), the chance of light being reflected at any angle and toward yourself would be just about the same.
With a specular surface, it wouldn’t be just the edges (limbs) that would be dark, everything would be nearly dark (well, nothing’s perfect, so it’s not going to zero) except for a small area in the center. Cassini controllers noticed lakes of hydrocarbons on Titan because there were “dark spots” in their radar imaging. Black spots, basically. Oceans on earth wouldn’t be so dark, though, because there are always waves, while little wind on Titan produces little wave action.
The moon reflects, but with solid particles that are randomly oriented, hence the reflected light is randomly scattered (for the most part–there may be some slight directionality).
Glen Davidson
just a little point.
The image is not made in the eyes but rather the eyes translate the image to the memory and one reads the memory or recording of the image.
Its so fast its as if one is seeing it in real time but actually its a repeat. A past event.
To me this means sight is entirely about us reading our memories. Sight is just a function of the memory. Therefore the hand is not quicker then the eye but only quicjer then memory of what was seen. The eye is perfect.
This is my hypothesis because we have a soul only. So the soul connection to the material world could only be through a simple mechanism.
So its just the memory. Everything of sense comes from our reading our memory therefore.
I would more or less agree with this 🙂 Hence Edelman’s phrase: The Remembered Present
But this phenomenon photographs. See my link, where comparisons are made between photos of the moon and of a ball.
Indeed. I just thought I’d endorse Robert’s general comment.
If this is true, doesn’t it prove there really is no distinction between “historical science” and “observational science”? 😉
Along the same vein, I have a question about starlight. It’s always puzzled me.
I don’t know how many photons a star might produce per square inch per second, but the trajectory vector a photon must travel from that star to hit the target Earth must be extremely narrow for all stars (if we’re thinking of a photon in terms of a particle) – to say nothing of hitting a human retina that happens to be looking to the sky.
It seems more probable If photons are to be considered as expanding fields of probable quantum collapse as they move away from a star in the general direction of Earth, it seems more likely that an upturned eye would “collapse” the wave, which might be larger than the solar system at that point, into a point of visible light.
Even so, would there be enough photons in the vicinity, sent from distant stars and reaching this tiny vector (even as expanding fields of potential collapse), to serve potentially billions of upturned eyes, and keep the whole image ongoing for as long as they look? It seems to me that at some point you wouldn’t have enough photons in the area to accommodate and someone would look up and see nothing but black where stars should be.
It also seems to me that if there are enough photons (as particles or waves) to serve billions of upturned eyes for as long as they look in what would be from any star an extremely tiny vector given the distance, space must be chock full of photons – packed with photons – from all directions.
If the eye is collapsing a wave (which seems more likely, given the tiny vector), does the eye/brain get information off of the probability wave in order to place it at the correct spatial coordinate in terms of where we see the star, given that a wave larger than our solar system might have been collapsed as a point of light on our retina?
Or am I somehow just thinking about all of this the wrong way?
The luminosity of the Sun is
joules per second. The energy of a typical photon emitted from the Sun is about 2 eV, or 
joules. That gives roughly 
photons per second.
Suppose you are 1 light year away from the Sun. That’s about
meters. A sphere with that radius will have an area of about 
square meters. In the dark, a human eye pupil has the diameter of 5 millimeters and an area of 
square meters. So it receives a tiny fraction, 
, of the photon flux. That still makes it 20 million photons per second.
4 light years away (distance to the nearest star), the flux will be down by a factor of 16, still around 1 million photons per second getting into an eye pupil.
The bottom line is that you can model photons as point particles shot in all directions by a star.
See;
http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html
on the sensitivity of the human eye.
OK, while we’re on photons and waves, I have a query wrt the duality. Indeed, no lesser a personage than Lamb casts doubt on their reality as particles.
It would be possible to construct a ‘macro’ version of the Young’s Slit experiment using only waves, if one’s detector consisted of discrete ‘hidden-variable’ buckets. If one set up a wave tank such that the energy brought to the detector by a wave was accumulated, resulting in detection only when a threshold had been reached (eg a real bucket with a tipping-and-emptying point), one could set the apparatus up with a double slit and see an increase of ‘firing’ at the intersections of wave fronts. No particles pass, and if the detectors start with a random level, the next one to fire would be random, but influenced by its position on the wave front.
If you place a double slit in the path, and record firing over an extended period, a pattern would build up identical to the clustering of single-photon shots in the classic experiment. If one was wedded to the idea of the wave-as-particle, one might think of ‘quanta’ of energy hitting the detector in chunks, and threfore have the puzzle as to which slit it goes through, and how independent quanta can possibly interfere with each other. You might even invoke separate realities in which the quanta go through a different slit in each, or model the wave as a wave of detection probability.
I know this is naive, and that Young’s Slit behaviour is observed on electrons and even atoms, which have a better claim to particle status. But I wonder why the model of a ‘firing threshold’, which would have detector atoms at varying, undetectable intermediate states, and travel (at the quantum level) being entirely ‘wavy’, is invalid. Detection is clearly quantised, but must the underlying energy transfer be also?
It’s good to see that being questioned. I tend to think of photons as an idealized construct that is part of a mathematical model, rather than as anything resembles our intuitive idea of what should be a particle. Note, however, that I am not a physicist.
Allan Miller,
Allan, I think you are barking up the wrong tree. In your model, the discreteness of energy transfer between the electromagnetic field and the detectors (and on) is a bug of the detectors, rather than a feature of the electromagnetic field. No matter what the radiation frequency, energy is transferred through the detectors in the same quantized amounts.
That model is inconsistent with the photoelectric effect, which demonstrates that light can only cause a metal to emit electrons when its frequency exceeds a certain threshold. The photoelectric effect indicates that energy of an electromagnetic wave can be changed in finite portions proportional to its frequency, E = hf.
olegt,
If there is more energy transferred by the waves, the buckets fill up more quickly, and hence fire more often, retaining proportionality between incoming energy and firing. I guess I am saying that all detectors have this ‘bug’. You only detect a ‘photon’ when you get a flash. There is no information available about possible internal continuity of energy state in any detector.
An emitted electron is a bucket going off. You only detect the discrete nature of an effect. Light of below-threshold wavelength passes invisibly through and does not progress the ‘hidden variables’ towards cumulative detectability – the firing threshold.
OK, I freely admit I am probably exposing my ignorance, but Lamb must have been aware of the counter-arguments?
[eta: non-paywall source]
Yes, it does 🙂
I think the trouble is in supposing that the wave is large, when it’s just the probability that expands greatly. And I don’t believe that there is any interference between probabilities, so that even though the probabilities for each photon from a distant quasar may have spread over a huge swath of space, that doesn’t cause any problem for them actually collapsing nanometers apart from each other at virtually the same time.
Oh, and the fact that the wave packet is wide, the probability is perhaps spread over the entire solar system, doesn’t change the probabilities of your eye collapsing photons from the distant quasar. The chance of collapsing any one solar-system wide photon probability is tiny, but the other part of spreading wave probabilities is that you’ve got a whole lot of solar-system wide probabilities zipping past your eyes, a few of which will be stopped by your eyes. I mean, it balances out, the probability wave of a single photon is spread out over a distance of the solar system and has a small chance of collapse, but you have a small chance of collapsing a huge number of photons because many photons are within that huge probability space. The chances of collapse are the same whether they’re points or extremely spread-out probabilities, then, because as the distances increase the point of light becomes much less likely to “hit the target,” your eye, while the chance of your eye collapsing a solar-system wide photon probability is also much less.
But I’m no expert on this. Here’s a link, and I hope that it helps
If buckets are getting filled continuously, why is there a frequency threshold? Furthermore, you can change the threshold by applying a voltage. Light that previously was unable to produce photoemission becomes efficient. Why? Because it’s light that comes in buckets. If the bucket is less than what an electron needs to jump out, there is no emission.
As to Lamb, he did not deny that the energy of electromagnetic waves is quantized. He doubted that one can make a well localized photon packet. That’s a well-known feature of photons, massless spin-1 particles. In Landau and Lifshitz’s Quantum electrodynamics, they write about it at the very beginning. See Ch. 3 (Google books) and Ch. 4 (Amazon). There is just no analog of the wavefunction whose square could be interpreted as a positive-definite probability density.
Allan Miller,
I wouldn’t get too hung up on the shortcomings of the bucket model – it’s a representation of a macro system, using waves only, that would look like particles if all you could see was the discrete event – a bucket tipping. The point is to illustrate something where we know there are no lumpy particles, but it could (if you knew nothing more) appear as if there were.
If you had a detector screen covered in a mole of fluorescent particles, with a random distribution of closeness to actually going off, and bathed it in a gentle wave, you would next trigger the particle closest to threshold, but it would also depend on local energy input, which is greater at reinforced wave crests.
It would appear that all the energy had gone into that detector atom, and you could describe it as ‘collapsing a probability wave’. But all that’s happened is that an element in the detector has been nudged over its threshold.
I realise the quantum world is supposed to be weird! 😉 But there does seem at least a naive possibility of a more relatable reality. Einstein thought there was, though most people think he was wrong, and I understand the Aspect experiment did not go well for hidden-variablists.
I’m showing where the bucket model fails. It’s incompatible with the photoelectric effect. Electrons have buckets, but so does light. Without making the energy of light quantized, you can’t explain the photoelectric effect.
olegt,
OK, fair enough!
Also, quantization of light energy,
, resolves the paradox known as the ultraviolet catastrophe. As far as I know, there is no other way to explain the observed spectrum of black-body radiation.
olegt,
BTW, I wasn’t suggesting that the wave itself was continous. Given that energy only ‘gets out’ when an event occurs – a threshold is reached in an atom of the source, and quantised energy release is triggered as it falls all the way back to the lower energy state – the wave would consist of discrete ripples. Energy builds up in a continuous manner in an atom of source or target, but only comes out in quanta (in the model).
Allan Miller,
To try and be clearer, what I’m arguing against is not the discreteness of the phenomena, but against the idea that this in itself forces us to visualise actual particles, containing all the energy, passing through one slit or the other, and interfering by some observational ‘probability-wave-collapse’ or ‘many-world’ rationalisation.
Although there may be other things that force that conclusion.
I have long doubted that there are entities that satisfy our intuitive sense of what a particle is. I rather think “particle-like behavior would be more accurate.
It’s another case of more is different. Wave-like phenomena congregate to produce particle-like phenomena. As atoms congregate to form molecules.
It’s useful to have words to denote higher order phenomena.
Great link. The internet is such an effective source of information (if you know where to look!).
Google-fu. The art of asking.
I wonder if anyone is working on how innate behaviours are passed on in the gametes.
I’ll wander into this trap.
What’s inherited is not the behavior, but the tendency to be reinforced by certain chemicals or certain sensory inputs. The behavior evolves. That’s what brains do. Evolve behavior to maximize reinforcement.
Rather more quickly than genetic evolution.
No trap, I assure you. It’s bothered me since 1968, my first seminar discussing the genetic code and protein synthesis. If all DNA triplets were read as amino acids (this was in ’68 and only a few years after the UUU experiment) where was the blueprint stored? Of course there have been huge advances since with the whole HOX gene saga and evo-devo;
But across the gamut of organisms, there are complex behaviours that are programmed in. Spiders, termites, birds; the list is vast. It must be in the zygote. It must be chemical. It must be fascinating. But there’s a knowledge gap. Perhaps a bit like neuroscience between psychology and brain chemistry.
ETA If it wasn’t obvious, it must be heritable, variable and selectable.
I’ll take birds, for example. I’m no expert, but as a kid we had free range bantam chickens in the yard. the population varied from half a dozen tho nearly a hundred. they were “pets.” We fed them a bit, but mostly they foraged.
I’ve watched maybe 50 hens learn to be effective mothers. I’ve heard the concept of instinct, but what I observed is that chickens are not born knowing how to raise chicks.
First time mothers invariably lost the entire brood. Mostly by stepping on them. there are a number of other things that effective mother hens do that seemed to be learned. Calling, protecting, teaching. Some time about the third brood, these things are mastered.
I suspect they are mastered the same way other skills are mastered. By trial and error, positive and negative reinforcement. the skill is not instinctive, but the reinforcer set seems to be, and I suspect it is fairly simple.
I’d say petrushka is about right.
Take birds. It is quite impossible that a bird could innately know how to build a nest. The bird has to find suitable materials that are available locally. And the details of construction depend on kind of materials used. I’ve see robins use material that included human synthetics (scraps of plastic).
My presumption is that there is an internal drive to build some kind of nest, but that they have to learn how to do it as they go along.
I’m not sure about spiders. I think a common assumption is that they innately move in certain patterns. Geometric patterns can often be make out of simple moves. There’s usually quite a bit of irregularity in a spider web, probably because they are not all that accurate in carrying out their motions.
I do think people have a tendency to overestimate how much need be innate.
That there’d be some learning would be, I think, inevitable. But they know how to make their nests. Just look at this nest. There are more elaborate ones, this was just the best I could find quickly.
You don’t just want a nest and end up learning how to make nests like that. Humans make pretty poor simple nests at first, although they can outdo the best animal constructors by truly learning. As noted in one program I watched, birds and other animals can make exquisite structures without learning (much, at least), and humans can make nothing at all well without first learning a good deal. Which seems okay for us, but wouldn’t do for non-lingual short-lived animals.
I don’t think that anyone knows how they know what to do. Otherwise they seem clueless, as it turns out that if you make a hole in a nest so that any egg laid will fall out, the female will just lay eggs in the nest again and again (she probably gives up before the nesting season is over, but it seems without ever catching on. All birds? I don’t know, certainly some). Hole? What difference should that make?
So sure, some learning, but they can make splendid nests in a few days, or weeks at most, the first year, while an untutored human would have little more than a mound of thatch with a sort of depression in it by the time their first nests are done (slightly exaggerated, probably, but not by a lot).
Glen Davidson
I take “know how to make their nests” as implying knowledge of the sequence of steps required. That seems unlikely.
What I see as more important, is being able to evaluate the suitability of what is already built. And if the bird can see that what it has started building isn’t very good, then it can make changes. Or, to say it differently, I see it as a trial and error situation. It’s the feedback — the ability to recognize failure — that may need to be innate.
Memory. What’s it made of?
I do a bit of quizzing, and it amazes me how facts untouched for 30-40 years can be dredged up at a small prompt. I also do a bit of public performance, and in learning a song it amazes me how it takes shape in muscle memory, but slowly – words or chord changes that you know but can’t quite get from line to line quickly enough in ‘real time’. Leave it for a day or two, and there it is, flowing. I now incorporate that into the process: sometimes you learn most when you’re not even doing anything, provided you’ve done the spade-work.
But it is a weird thing – weirder than direct sensory input.
Allan Miller:
Memorrhoids.
I don’t think it is weird. What your experiencing is the power of the memory.
We are almost, I say, just bug memory machines. no brain influence at all.
A soul, the thinking thing, working with a great complex called memory.
its so fantastic that nothing we do is unrelated to memory.
this is why, i say, all mental problems are only from triggering problems with the memory.
Its impossible for our souls to rise or fall in intelligence.
Even as baby’s we are already as intelligent as adults. babies are simply very retarded people. or rathe people whose triggering mechanism for the memory is not very good yet..also no original info is stored.
therefore prodigy kids are not smart kids but only kids whose memories have been provoked more in some direction. tHats why they only do things defined by memory like music recall.
We are just souls tied to a memory machine. no brain wiring is going on at all. jUst memory wiring.
I think healing in areas could be accomplished with this christian creationist presumption better and faster then otherwise. lIke curing mental problems and blindness. one can dream.
olegt,
That’s a physicist’s answer!
Also, even in the wave representation, single photon wave fronts do not expand spherically in all directions, they still have a directionality. Nor does an eye necessarily interact with a photon, even if its wave front passes through it. Wave fronts aren’t fragile, like soap bubbles.
Robert Byers,
Yebbut … what’s it made of?
In what form does the ‘bug memory machine’ (heh heh – I guess you meant ‘big’) store memory? I realise you don’t know, but that was my question.
If only there was a cream.
petrushka,
Yes, I tend to visualise things as getting more ‘wavy’ the lower we go. Matter, in the point-particle sense, is not ‘really like that’ when you get down inside the atom. The conceptual difficulty arises when these localised energy traps move and interact. Movement itself involves energy, and there is a ‘waviness’ to motion as well as that of the object itself.
But when you get interference between slits, for example, when your detector is indicating single events, it still makes me wonder if it is correct to talk of ‘a’ photon passing through one slit or the other, with strange rationalisations such as ‘observational wave function collapse’ or ‘many-worlds’ called upon to explain ‘slit choice’ because you get a discrete event at the detector. That’s all you can get, if intermediate states give no outward sign.
In other words, whether quantum reality is just ‘all wave’. Quantisation of state changes is not the same thing as localisation of an object, or its path when moving.
I have a question.
I recall seeing a video many years ago of land plants flowering under water (fresh water). As I recall, it was happening in streams draining out of a limestone formation. The proposed expanation was that the high concentration of dissolved carbonates in the water allowed the land plants to bypass the normal first stage of having to dissolve atmospheric CO2 inside their leaf cells, and were able to grow and flower while submerged as a result.
Does anyone know if this happens, and whether it has been studied?
timothya,
I’m not an expert, but it strikes me that the ‘normal’ way of getting CO2 in is actually in solution. Plants evolved from unicellular algae. They would have been bathed in a CO2 solution that contains a lower ppm than the atmosphere, but that atmosphere was very rich in CO2, before we large organisms started scrubbing the air of the stuff.
Land plants would have evolved, initially, in a high CO2 environment. Gradually this carbon got locked away, in biomass and sediment – particularly carbonate rock. Land plants had to evolve to deal with lower and lower CO2 concentrations – but always, once through the stomata, it has to dissolve. So the fundamental CO2 source is no different when an air plant reverts to an aqueous environment, except that the CO2 is already in solution.
Use of bicarbonate seems to be an ’emergency’ mechanism, an adaptation for some plants, when CO2 in solution falls below a threshold, rather than an immediate alternative source on immersion. One would expect plants possessing this capacity to have evolved in an aqueous environment where limiting CO2 concentrations are regularly experienced. Fresh flowing water should have plenty.
http://www.tropica.com/en/tropica-abc/basic-knowledge/co2-and-light.aspx
I’ll have a go 🙂
I think it’s helpful to think of memory not a store of files, as in a computer, but as a repertoire of thoughts, as it were, which are made more likely in future by the fact that you’ve had them before (because “what fires together wires together”) – and, specifically, will be made even more likely if one of the elements associated with a particular item in in the repertoire is activated by some related stimulus (a voice, a photo, a word), or by some related thought.
And each time you remember – re-enact an item from the repertoire – it is more likely to be re-re-enacted in future. Although the problem is, that the item itself can change! So you start “remembering” interpolations that got in there since the original neural cascade, and didn’t necessarily actually happen.
This is a good description. Another way I have come to understand memory is as many vague neurological sensations or stimuli. As you note, “what fires together, wires together”, thus when given neuron clusters create a stimulation, the brain re-images or recalls pieces of past experience. But these are just fragments and it takes other systems in the brain (defense mechanisms, filters, schema, etc) to whittle through the fragments a create a gestalt. Through repetition and focus, we can refine the gestalt into more accurate representations of experience, but I submit that for the most part, most memories are inherently muddled.
Does this apply to procedural (“muscle”) memory as well? If so, how can one be consistently accurate at (eg) playing a musical piece. If not, what is the neurological difference in different types of memory?
By the way, I highly recommend Rusbridgers “Play it again” which touches on these topics in interviews with neuroscientists and famous pianists. It also has fascinating asides on his interactions with Assange, the British phone hacking scandal, Gaddafi’s sons, and other aspects of Rusbridgers work life as editor of the Guardian.
Play it again
Yes I think it does. Certainly many instrumental teachers will tell you (as mine told me!): never make a mistake when you practice, because you will learn the mistake, and it will happen again. That’s why slow practice is so often advocated – learn pieces at a speed at which you can play them perfectly.
Another piece of advice is: don’t practice until you get it perfect – up to that point you aren’t “practising” at all – you are if anything repeating getting it wrong! Only when you can play it perfectly do you then start to practice Another piece of advice is – play it right many more times than you’ve ever played it wrong. Used to have two bowls of beads, A and B. Each day I started with A full. Every time I played a scale right, I’d put move a bead from A to B. Every time I made a mistake I’d move two beads from B to A. The idea is to keep going until bowl A is empty.
Lizzie:
Yes, and even the things you might think could be stored sequentially, computer-style — like grocery lists, memorized poems, or the procedure to follow when your engine fails on takeoff — are in fact stored associatively.
I almost always have a piece of music playing in my head, and this affords many opportunities to see the associative nature of memory in action.
Two examples:
1. Reading a magazine, I came across an article entitled “It’s just a phase you’re going through”, and immediately the Art Garfunkel song “Break Away” started playing in my head, right at the point where those words appear:
A remembered song is just a cascade of associations, and the cascade can be started at any point, including in the middle.
2. Sometimes one song will consistently morph into a particular second song when I “play” it in my head. If I pay attention I can see when and why this happens, and it’s usually because a) a musically similar phrase appears in each song, and b) I know the second song much better than the first.
In this case the first song’s associative cascade is interrupted when the phrase from the first song stimulates the second song’s cascade, right at the point where the musically similar phrase appears.
Thanks for realizing I didn’t mean BUG. The memory is real and there and simply we can say its even bigger and indeed most of what is called the brain.