First photograph of light as both a particle and wave

[Greg Bernhardt]

I think this is really neat! Anyone with thoughts about it?

(Phys.org)—Light behaves both as a particle and as a wave. Since the days of Einstein, scientists have been trying to directly observe both of these aspects of light at the same time. Now, scientists at EPFL have succeeded in capturing the first-ever snapshot of this dual behavior.

http://phys.org/news/2015-03-particle.html

 

[kq6up]

In reference to this article:

http://phys.org/news/2015-03-particle.html

I don't understand how this is any different than using a photographic emulsion to capture a diffraction pattern. Since my understanding of the photochemical process that reduces Silver Halides requires two photons over a certain decay time to reduce a silver atom in a Silver Halide crystal lattice. Therefore the principle seems to work the same. Any thoughts guys/gals?

Chris

 

[jedishrfu]

Pretty cool!

 

[Jazzdude]

As far as I understand, they're looking at a many photon state and they're measuring the semiclassical classical field interaction together with discrete momentum transfer. I don't see how that would allow for their bold claims or in fact be any different from observing the Compton effect while measuring the classical EM field.

So no surprises for me as a theorist. But maybe someone can enlighten me or point me to the experimental aspects that I'm missing.

 

[mfb]

an experiment with a clever twist: using electrons to image light

How revolutionary! Okay, all eyes and all photographic devices ever evolved/built use electrons...
Fine, they used free electrons, that is not so common.

I do not see anything fundamentally new here. Every diffraction pattern hitting a sufficiently sensitive detector does the same, just with bound electrons instead of free electrons.

 

[ellipsis]

The power of marketing: replace

"capturing a photographic emulsion, and deriving a computer-generated image from those results based on mathematical models"

to

"First photograph of light as both a particle and a wave!"

and you become successful. Nobody calls you out on it because few people are confident enough on the subject matter to do so.

 

[tijana]

Absolutely beautiful.
Now this pic in primary schools.

 

[atyy]

http://www.nature.com/ncomms/2015/150302/ncomms7407/full/ncomms7407.html
Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field
L Piazza, T.T.A. Lummen, E Quiñonez, Y Murooka, B.W. Reed,B Barwick & F Carbone
Nature Communications 6, 6407
Surface plasmon polaritons can confine electromagnetic fields in subwavelength spaces and are of interest for photonics, optical data storage devices and biosensing applications. In analogy to photons, they exhibit wave–particle duality, whose different aspects have recently been observed in separate tailored experiments. Here we demonstrate the ability of ultrafast transmission electron microscopy to simultaneously image both the spatial interference and the quantization of such confined plasmonic fields. Our experiments are accomplished by spatiotemporally overlapping electron and light pulses on a single nanowire suspended on a graphene film. The resulting energy exchange between single electrons and the quanta of the photoinduced near-field is imaged synchronously with its spatial interference pattern. This methodology enables the control and visualization of plasmonic fields at the nanoscale, providing a promising tool for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits.

 

[TrickyDicky]

So much for the Complementarity principle.

 

[Ranvir]

It might be a good time to point out that light, or for that matter any quantum mechanical entity, is neither a particle nor a wave they just follow equations which, in a classical sense, are attributed to waves and particles. It's time we stop publicizing interesting experiments like this in a pseudo-scientific fashion and throw some 'light' on the the real quantum physics for the masses.

 

[elierd jay]

I think this is really neat! Anyone with thoughts about it?
http://phys.org/news/2015-03-particle.html

View attachment 79827

does it follows pattern?

 

[Shri13]

Hi this pic looks cool, but I am still learning high school physics and very curious to learn. Can anyone elaborate the pic please?
How is that pic taken?
What are those bulges which looks like waves?
How is this pic showing both particle as well as wave nature simultaneously? (Means how I can see both natures in these pic)

Sorry if I am poking my nose in the experts thread

Thank you in advance.

 

[elierd jay]

Hi this pic looks cool, but I am still learning high school physics and very curious to learn. Can anyone elaborate the pic please?
How is that pic taken?
What are those bulges which looks like waves?
How is this pic showing both particle as well as wave nature simultaneously? (Means how I can see both natures in these pic)

Sorry if I am poking my nose in the experts thread

Thank you in advance.

me nether, still first year college. ... the evidences of light as a wave-particle are explained by refraction or reflection of light into a medium. also light has the property almost of the electron, that's why scientist use electron to identify if light has particle property, if light is not a particle there would be no effect. by proving the wave property of light, scientist provide a thin slit where light can pass, so that light will be as a thin sheet of ray and it form diffraction phenomenon and is describe as the interference of wave according to Huygens Fresnel principle. as you can see on the image, the blue part rises, this is because there is an encounter between light and electron, if two balls hit each other there will be a change of direction, depending on the forces of each ball. hope my explanation helps... well the color tells the us the energy...

 

[tijana]

Hi this pic looks cool, but I am still learning high school physics and very curious to learn. Can anyone elaborate the pic please?
How is that pic taken?
What are those bulges which looks like waves?
How is this pic showing both particle as well as wave nature simultaneously? (Means how I can see both natures in these pic)

Sorry if I am poking my nose in the experts thread

Thank you in advance.

As I see it I am not an expert also. It is just like you through rock in the pond. So you see the waves it produce it.

 

[Mabel]

It might be a good time to point out that light, or for that matter any quantum mechanical entity, is neither a particle nor a wave they just follow equations which, in a classical sense, are attributed to waves and particles. It's time we stop publicizing interesting experiments like this in a pseudo-scientific fashion and throw some 'light' on the the real quantum physics for the masses.

I question your basic concept that light is neither a particle or a wave. Since we DO see photons behaving as particles in bubble changers in pair production. This is NOT an equation. It is experimental OBSERVATION. As for wave, I leave that to someone else.

 

[phinds]

I question your basic concept that light is neither a particle or a wave.

Then you should continue your studies until you get to the part where this is explained. Light ACTS like a particle and ACTS like a wave but it is neither one. It is a quantum object.

 

[Gort]

The argument on the nature of light is part of the argument - can we ever determine the true "nature" of nature? Physics develops models which explain observation. If the model closely matches observation (under particular circumstances or initial conditions), then it's a good model. Wave theory is a good model of light (under certain circumstances). Particle physics (of which photons form a part) is a good model, too. So what is "light"? Physics cannot answer that question! To get into models a bit deeper, consider Quantum Field Theory. The wave nature of light is part of that theory. QFT considers all of nature as excitations of "fields". What, exactly, are "fields"? No one knows! But the mathematics works well enough that QFT can accurately describe much of nature. What about Quantum Electrodynamics (QED)? For a long time, Feynman was convinced that photons and electrons (and their interactions) are explained only in terms of particles taking different paths in space and time (and summing those paths). That works well, too - so well that the electromagnetic fine structure constant is predicted by QED to within 10^-8 of the observed value. So are photons particles? Do some photons travel at less than c, others at greater than c, and not in a straight line in space-time? At least that's what QED says, and it makes accurate predictions! So is light just a particle of "energy"? No one knows! Physics can't even define "particle" or define "energy" (even though QFT starts with describing a system by the Lagrangian - the difference between kinetic and potential energy). So all of this simply says - physics doesn't provide answers into the true nature of reality. Physics provides mathematical models to describe observation. That's all. IMHO.

 

[Derek Potter]

In reference to this article:

http://phys.org/news/2015-03-particle.html

I don't understand how this is any different than using a photographic emulsion to capture a diffraction pattern. Since my understanding of the photochemical process that reduces Silver Halides requires two photons over a certain decay time to reduce a silver atom in a Silver Halide crystal lattice. Therefore the principle seems to work the same. Any thoughts guys/gals?

Chris

I don't think silver halide photography needs two photons but even if it did you could pre-expose the film so that a good number of grains only needed one more photon. So I agree except that it's even simpler than you say

 

[Derek Potter]

Then you should continue your studies until you get to the part where this is explained. Light ACTS like a particle and ACTS like a wave but it is neither one. It is a quantum object.

If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.

 

[Gort]

I would add "and has the DNA of a duck..." But ducks are not "fundamental" - they are (presumably) composed of many fundamental "things" or "entities". While it is easy to define macro objects (they 'are' because we say they 'are'), it is not so easy to define the true nature of fundamental entities. I can't even call those entities particles, waves, fields, energy, or anything else, because we simply don't know.

 

[Derek Potter]

I would add "and has the DNA of a duck..." But ducks are not "fundamental" - they are (presumably) composed of many fundamental "things" or "entities". While it is easy to define macro objects (they 'are' because we say they 'are'), it is not so easy to define the true nature of fundamental entities. I can't even call those entities particles, waves, fields, energy, or anything else, because we simply don't know.

In that case it can't be a quantum object either as we have no macro concept of such things. "Quantum object" becomes a catch-all for "ducking" the question

 

[Gort]

I agree. I wouldn't call light a wave, a particle, a quantum object, or even a duck. Because that would imply we somehow understand it. We don't. Continue to call it "light". Or a wave if we're doing optics. Or a photon if we're doing spectroscopy. But be clear - we don't understand its 'true' nature (if it even has one).

 

[tijana]

The main problem is we are talking about QM but at the end we have to do classical physics experiments in order to explain it to another person. That is a trouble.

 

[Derek Potter]

The main problem is we are talking about QM but at the end we have to do classical physics experiments in order to explain it to another person. That is a trouble.

I don't see why it's a trouble. It means there is continuity between QM and classical. That should be encouraging.

 

[Gort]

Point well taken. That, perhaps, is our limitation and why we may not get answers to the fundamental nature of reality. We can, of course, devise experiments which try to get at the QM nature of things. We can measure QM tunneling across a superconducting Josephson junction, but we're really measuring the current through an ammeter. And we infer (through a model) that a complex order parameter field (field theory) and Cooper pairs (particle physics) are responsible. We can even use these results to build SQUIDs - to measure magnetic fields. All the while not knowing what the basic building blocks of the SQUID really are - or even what a "magnetic field" really is.

So we, as macro beings, can use a lot of physics without understanding the real nature of things. And we don't have to, either. But I was taught that's the goal of physics - to understand nature. Her true reality. I've now changed my view. We model nature. Perhaps (with a big Maybe) if we were quantum beings (instead of classical ones) and lived in 10, 11, or 20 dimensions (instead of 4) we might be able to devise experiments which would get answers to the fundamental questions.

I guess that's my pet peeve. When physics papers say that "particles are composed of strings" or "the Big Bang happened 13.7 billion years ago", or...etc. Every paper should start out with "Our model predicts..." and it should be made clear that it's a model.

 

[tijana]

Encouraging enough yes. Even conservative like Plank had to introduce quanta in order to explain experiments,although he was concentrated to "small" problem.

Changing your way of thinking is hard, even a small step.Lots of stumble in this area ( A.Einstein and many others).
Even today after 100 years we see that changing or "enlightenment " of mind maybe is waiting for evolution of mankind. Although I would not go that far now.

 

[mfb]

That works well, too - so well that the electromagnetic fine structure constant is predicted by QED to within 10^-8 of the observed value.

The value of the fine structure constant is not predicted at all. It is a purely experimental value. Different measurement methods agree with incredible precision, however.

 

[Derek Potter]

So we, as macro beings, can use a lot of physics without understanding the real nature of things.

We happen to be born with a tendency to make sense of the world in a certain way. When this inherited "common sense" breaks down, we create abstract models. No-one is claiming any metaphysical insight into Ultimate Reality, it is sufficient to say that a concept which works satisfactorily must refer, directly or indirectly, to something that exists. An entity *is* that which is described by its attributes. A child may describe an elephant as a big animal with a trunk and so it is; and I'll stick with photons being real particles which display wave-like characteristics due to QM.

Not that I wish to be polemical about it of course

 

[Gort]

The value of the fine structure constant is not predicted at all. It is a purely experimental value. Different measurement methods agree with incredible precision, however.

I hope this isn't getting too far off-topic (from the wave-particle duality question). There's a course offered by the Institute for Theoretical Physics in Zurich - entitled "Particle Physics Phenomenology 1". Chapter 6 deals with tests of QED. See http://www.itp.phys.ethz.ch/education/hs10/ppp1/PPP1_6.pdf . It says the "precision tests of the theory [QED] which usually consist in the measurement of the electromagnetic fine structure constant α in different systems. Experimental results are compared with theoretical predictions. The validation process requires very high precision in both measurements and theoretical calculations. QED is then confirmed to the extent that these measurements of α from different physical sources agree with each other. The most stringent test of QED is given by the measurement of the electron magnetic moment."

So I believe QED does make predictions. It's based on multiple QED loops. But I only bring this up to show there are multiple ways to get "nearly correct" answers. None is necessarily right or wrong. But I hate it when someone says "Light is BOTH waves and particles - it's been photographed!" Hogwash.

 

[mfb]

The theory predictions are just the relation between the fine-structure constant and the measured quantity. Theory alone cannot make any prediction for the value.

QED is then confirmed to the extent that these measurements of α from different physical sources agree with each other.

This is the important part.

 

[Gort]

Agreed. Good point.

 

[Science2020]

neat...

 

[bhobba]

I guess that's my pet peeve. When physics papers say that "particles are composed of strings" or "the Big Bang happened 13.7 billion years ago", or...etc. Every paper should start out with "Our model predicts..." and it should be made clear that it's a model.

I think that's more or less assumed.

Things like 'understand', 'reality' etc etc are all basically big question marks in philosophy that no consensus has ever been reached.

Physics bypasses all that with a bit of common sense. Reality is what our models describe. Understanding is we have a model that's supported by experiment. Good old Euclidean geometry is the template. Points and lines are its primitives - their definitions don't really mean much in a rigorous sense - points are supposed to have position and no size - lines length but no breath - such don't really exist - but as the theory is developed and applied you get a feel for what they mean. But the theory can't define it exactly - its a primitive of the theory. The same with QM. A primitive is an observation - you can't rigorously define it in the theory in a practical way - you can abstractly and advanced texts do - but applying it requires a bit of intuition - like point and lines in Euclidean geometry do.

There are extremists like Penrose that think the math is literally the reality - but most don't go that far - it simply describes it leaving what reality is up in the air because more simply isn't required.

Thanks
Bill

 

[Gort]

Reality is what our models describe.
Bill

I would submit that "Observation is what our models describe". Reality is the Holy Grail. This thread started from an article which described an "experiment able to capture both natures of light". That implies that light HAS two natures. That's simply not true, or at least misleading. I don't know the "nature of light" and I don't think the researchers reporting this experiment do, either.
Perhaps we, as physicists, understand the subtleties. But perhaps not. And the lay public is even more susceptible to blindly believe grandiose statements of "fact" by the scientific community.

 

[Derek Potter]

The experiment doesn't demonstrate anything about the nature of light anyway. That's the province of particle phycics. It just demonstrates that light is subject to QM like everything else.

 

[Shri13]

Okay...as most of you are saying that physics is just approximating the mathematical models towards reality and not actually describing the true nature of reality. As we are talking about '' true nature '' of reality now, my question is, have we(humans) defined what actually ''space'' is? ( here I mean the space in which all matter, everything exist and not explicitly that which begins after crossing Earth's upper atmosphere.)
We have many theories, models on particles and matter, but I have heard very little on space( for e.g. definitions like 3d, 4d space, empty region where there is no matter, etc.) But are those definitions enough to define the ''true nature''!
Don't we have to first define the true nature of the ''thing''(space) in which all other ''things''(matter) not only exist, but also move, collide, accelerates, etc.
So how space is allowing all those collisions, reactions, etc? How is matter able to move in space, what exactly happens to space when matter moves, or how matter exactly interacts with space, what are the '' laws of space'' ?
Is nature of space also quantised? Will its quantisation help us to define the true nature of reality? Are our space analogous to the computer screen which is formed of pixels? (Of course in the 3D sense, and also the pixels of space if they even exist then wouldn't they help us to firmly establish the quantum nature of reality?)
I think physicist should start making models, and defining the mechanics of space, and then argue on the nature of a photon. Only after knowing what exactly space is then only I think we will know from where does this particles come from and what their true nature is.
( Sorry guys, I may be going off the topic... but I think it was necessary to ask this question.)

 

[bhobba]

Okay...as most of you are saying that physics is just approximating the mathematical models towards reality and not actually describing the true nature of reality.

I don't think that's what's being said at all - at least I am not saying it.

Since there is no agreement what reality is physics adopts a much more common-sense approach. It describes reality - whatever that is. How good a description it is experiment determines.

This has led to some very deep truths such as the pivotal role of symmetry rather than getting bogged down in questions that lead no where.

We have many theories, models on particles and matter, but I have heard very little on space( for e.g. definitions like 3d, 4d space, empty region where there is no matter, etc.)

Didn't you study Euclidean Geometry at school?

But are those definitions enough to define the ''true nature''!

True nature? Like reality, good luck in getting agreement on what that is. Personally I think its what our theories describe.

Don't we have to first define the true nature of the ''thing''(space) in which all other ''things''(matter) not only exist, but also move, collide, accelerates, etc.

Its called Minkowski space. It is believed space-time is locally Minkowskian. And there is a very elegant argument from some rather common-sense symmetry assumptions why that's the case:
http://www2.physics.umd.edu/~yakovenk/teaching/Lorentz.pdf

Some theories challenge that but they have yet to meet experimental verification - Minkowski space is very well tested.

So how space is allowing all those collisions, reactions, etc?

There was this guy called Kant who tried to answer questions like that and reached the conclusion that a-priori Euclidean geometry must be true. He exerted a strong influence on thinkers of his time and guys like Gauss didn't publish their discoveries that challenged it. Gauss was correct - he was wrong. Maybe physicists and mathematicians have found a better way?

Is nature of space also quantised?

That is being investigated. You are welcome to join them if you wish.

I think physicist should start making models, and defining the mechanics of space, and then argue on the nature of a photon.

Maybe you might like to give that a go. BTW what exactly about QED do you think is inadequate to describe the nature of a photon?

Only after knowing what exactly space is then only I think we will know from where does this particles come from and what their true nature is.

Or maybe we already know that. Maybe space doesn't exist independently, maybe its, as Minkowski said - Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality. Maybe everything is quantum fields that inhabit space-time and what we call particles are knots in those fields. That's the view of Quantum Field theory.

Thanks
Bill

 

[Gort]

Maybe everything is quantum fields that inhabit space-time and what we call particles are knots in those fields. That's the view of Quantum Field theory.

But that's the point - we don't know what a "field" is in QFT. We don't know what a "particle" is in QED or QCD. We don't know what a "string" is in string theory. We don't know what "energy" is (to write down a Lagrangian or a Hamiltonian). We don't really know what space or time is, either. I think physicists know all this and the models work well within the constraints of the models. Our mathematics can do operations on abstract entities like "wave functions" and we can use them to build transistors or superconductors.

But the article that started all this seemed to imply (to me, anyway) that we understand more than we do. And many articles for the lay public are equally guilty. And some scientific refereed articles do the same, too. Even physics courses are guilty. This is NOT a criticism of physics. It's a criticism of the way physics "discoveries" are reported. Nothing more.

 

[mfb]

we don't know what a "field" is in QFT

How would such a knowledge look like? Would you replace one model by another model?

 

[Gort]

This has led to some very deep truths such as the pivotal role of symmetry...

While symmetry is a powerful tool in developing some models, it remains to be seen if it is a "deep truth". This is the point I'm making - even knowledgeable people can assume that there is "truth" when there are only "ideas".

...rather than getting bogged down in questions that lead no where.

I don't think that asking fundamental questions necessarily lead no where. Take "action at a distance" or "Force". Something we use all the time but don't understand. Can be "explained" by bending space-time; objects "tend" to enter a lower energy state. Whatever those terms mean. That's explaining something by using other undefined terms. I can also argue (Devil's advocate) that force is caused by 21 angels pushing on matter, simply because that's what angels do. Prove me wrong.

Or you can explain force between particles as an exchange of virtual particles (the QED approach). Mathematically, works well, but again, "explains" force in terms of unexplained entities. Personally, I think that an understanding of the "true nature" of "force" would lead to a unification of the four (or more?) basic forces.

It is believed space-time is locally Minkowskian.

Yes - "it is believed". Works well with classical mechanics and relativity. Not so well in the subatomic world (if you require 10 or more dimensions for string theory). So even space is not well defined, in my opinion (except for certain circumstances).

I'm really not trying to be philosophical (although, I think, modern quantum theory and cosmology beat me to it there!). But I feel people should realize the limitations of our current understanding of the physical world. Maybe, in 2420, we'll reach the Holy Grail. But I don't think we've even got the scent of it yet.

How would such a knowledge look like? Would you replace one model by another model?

I think I said earlier that I'm not sure if we'll even know when we reach the Holy Grail - and find some fundamental truth. That's why I don't know what it would look like. But as an example, suppose we could measure some quantitity permeating space. [I hate to use undefined terms like "space", but I'll do it anyway!]. Let's call it the Higgs Field. Or the Ether. Or something else. Let's suppose we not only can measure it, but we find out what "it" is - the stuff making it up. Not one of the 118+ known elements or conjectured elementary particle matter (e.g., quarks and gluons), but a new type of exotic matter or non-matter. If that matter/non-matter supported undulations in space-time (4 dimensions) or multiple other dimensions, then perhaps we could describe those "waves" as QFT fields. Or at least changes in fields. Then, we might start to understand what fields really are. It still might be model, but the model may begin to reflect "reality". Again, I'm not sure if we'll know! I think the Higgs field is an excellent start, but it's just a start.

 

[Gort]

Let me change that. My last argument is bad. (I wish all physicists could admit errors! )

The only correct part of it was:

"I think I said earlier that I'm not sure if we'll even know when we reach the Holy Grail - and find some fundamental truth. That's why I don't know what it would look like."

Pure and simple. It could be another model. But we'll keep striving for the Holy Grail.

 

[mfb]

Let's suppose we not only can measure it, but we find out what "it" is - the stuff making it up. Not one of the 118+ known elements or conjectured elementary particle matter (e.g., quarks and gluons), but a new type of exotic matter or non-matter. If that matter/non-matter supported undulations in space-time (4 dimensions) or multiple other dimensions, then perhaps we could describe those "waves" as QFT fields. Or at least changes in fields.

You would replace one field by another field. I don't see a qualitative difference.

The only special thing about the Higgs field is its non-zero vacuum expectation value, by the way. All fields exist everywhere in QFT.

 

[bhobba]

But that's the point - we don't know what a "field" is in QFT. We don't know what a "particle" is in QED or QCD.

Hold on. I may have been misinterpreting what you were writing. But if that's your position then I must disagree. QFT tells us exactly that. And I have been reliably informed that Weinberg's advanced textbooks on it gives an unambiguous precise definition - although its somewhat more advanced than I am at the moment (even though I have a copy of the three texts - maybe one day).

We don't know what a "string" is in string theory.

Its not a string - its a quantised string and we know exactly what that is the same way we know what quantised spin angular momentum is in usual QM. You are possibly asking what are the strings of string theory made of - who knows - but again that answer will also require other primitives the theory will not answer.

We don't know what "energy" is (to write down a Lagrangian or a Hamiltonian).

You put the cart before the horse - from a Lagrangian we know exactly what energy is - its the conserved Noether charge from time translation invariance - as relativists know only too well because you don't have time translational invariance in curved space-time - which poses a big problem in uniquely defining energy in GR. The issue is we don't know why nature chose some of the Lagrangian's it did in QFT eg the QED Lagrangian. Its is constrained strongly by symmetry - QED is constrained by U(1) gauge symmetry and other forces similarly. But why nature is like that we don't know. It very elegant mathematically - but why is nature like that - maybe string theory will explain - but right now we don't know. But gee every explanation requires some assumptions by the very nature of explanation. As far as we can tell its not turtles all the way down.

We don't really know what space or time is, either.

Space in an inertial frame (and they to a high degree of accuracy exist in interstellar space) is described by Euclidean geometry. The difference between what something 'really' is and what models like Euclidean geometry describe is philosophy and what the cautionary tale of Kant and Gauss showed is its basically an impediment to progress - at least that's the past experience anyway - who knows what future progress may bring. Time is what a clock measures - again beyond that has not led to any progress.

But the article that started all this seemed to imply (to me, anyway) that we understand more than we do. And many articles for the lay public are equally guilty. And some scientific refereed articles do the same, too. Even physics courses are guilty. This is NOT a criticism of physics. It's a criticism of the way physics "discoveries" are reported. Nothing more.

That I agree with.

Once you have gone a bit deeper than beginner or even intermediate texts in QM and progress to textbooks like my favourite - Ballentine - you know the wave-particle duality is a crock of the proverbial:
http://arxiv.org/abs/quant-ph/0609163

The article is basically a bit of sensationalism written for the lay audience along the lines QM is magic type of stuff you see on TV. It's not mystical rubbish like - What The Bleep Do We Know Anyway which IMHO is very harmful - but its definitely not written for the professional or the more advanced amateur like me.

I am in too minds if such are positive or negative. The positive is, here in Australia, kids are not taking advanced math and science in HS and this definitely may inspire them. The negative - well - its wrong. But physics can be a bit like that - what you learn at the beginner level can be overthrown as you learn more.

Thanks
Bill

 

[bhobba]

How would such a knowledge look like? Would you replace one model by another model?

Very good point.

People often forget by the very nature of explanation you always assume something.

Once you realize that, questions like what's really going on, what, really, is a quantum field, what exactly is time beyond what a clock measures, etc, takes on a whole new light.

Thanks
Bill

 

[Gort]

Everyone's really made great points. But just a few more comments.

You would replace one field by another field. I don't see a qualitative difference.

Very true. That's way I retracted my (stupid) comment.

QFT tells us exactly that. And I have been reliably informed that Weinberg's advanced textbooks on it gives an unambiguous precise definition - although its somewhat more advanced than I am at the moment (even though I have a copy of the three texts - maybe one day).

The definition of "field" is quite mathematical. I was told many moons ago (but that could be in error, too) that unless you can teach some concept to someone in simple terms, then you don't really understand the concept. I fully know that fields have been very well "defined" in QFT. But I could also "define" the mathematics of how my 21 angels push matter together (causing gravity). I'm calling "angels" my "field". Having it mathematically work doesn't make it so. Do we believe in QED - that photons have a probability amplitude to travel at ANY speed and follow ANY course, yet sum up to velocity c and straight line (in Minkowski space)? Experiment shows exactly that. Is it so? Do we know what "so" is?

Its not a string - its a quantised string and we know exactly what that is the same way we know what quantised spin angular momentum is in usual QM.

Both the terms "quantised string" and "quantised spin angular momentum" are not well defined (although, again, they can be mathematically described). Spin, as you know, is not classical spin. It's a quantum number. Used to differentiate states. But what actually IS QM spin??
And strings deserve another whole thread. My position on that is nicely summed up by Peter Woit's excellent book "Not Even Wrong", in which he argues that string theory cannot be shown (experimentally or otherwise) to be either right or wrong. It's conjecture.

To bring this full circle, articles (especially for the lay public) should describe what we know we know (which is limited) and describe models of what we know we don't know.

 

[bhobba]

I was told many moons ago (but that could be in error, too) that unless you can teach some concept to someone in simple terms, then you don't really understand the concept.

That's an old one.

Feynman commented on it. In his view, and I agree with him, even if you are really really good at explaining complex physical ideas in lay terms you eventually run into the fact physics, while not mathematics, is written in the language of math and you can't go any further.

But what actually IS QM spin??

Again we get back to this idea you believe, along with a lot of lay people, there is something more than the math. All I can do is reiterate the tale of Gauss and Kant. Kant believed there was more to it and thought philosophy was the answer. It lead to a wrong view that was disproved by Gauss who thought the math was the key. I think subsequent developments sided with Gauss - but who knows what the future will bring.

Thanks
Bill

 

[Gort]

Thanks, guys. In spite of my sometimes arguing the points, I appreciate the views. It gives me a new perspective and points to ponder. My world-view has always been that Nature has an underlying simplicity - that we need mathematical tools to get at that simplicity. And maybe it is still simple - but cannot be described in verbal language, but only in mathematical language. Perhaps God is a mathematician, after all. And He plays dice!

 

[audire]

I really don't see how this pic is any better than the one i saw in my physics textbook 5 years ago.. that's just me though maybe the concept is getting through to more people now.

 

[Shri13]

That's why I don't know what it would look like. But as an example, suppose we could measure some quantitity permeating space. [I hate to use undefined terms like "space", but I'll do it anyway!]. Let's call it the Higgs Field. Or the Ether. Or something else.

That's what i was trying to say, we hadn't defined exactly what space is ( relatively what I meant is matter, particles,etc. are more heavily defined than space in our physics. Defining space in rather elegant way [as sir gort tried in the above post] will help us to fine tune our present day physics, as space is actually the 'thing' where every other 'physics' phenomenon take place).

One more thing, I just remembered Huygen's wave theory of light in which he had failed to prove the existence of mysterious 'ether'( the medium in which light waves were supposed to travel).
Is it possible that space itself is ether?
Also our instruments are in the space( or are made up of space itself..) they won't be able to measure or detect the space itself. And that's why I think Huygen wasn't able to detect ether( or our space ).

( I might not be able to exactly explain or put forth my views from my tiny mind, as I am not good in English.)

 

[bhobba]

That's what i was trying to say, we hadn't defined exactly what space is

Can you explain to me in what way Euclidean geometry hasn't defined what space is? Even curved space is locally Euclidean. Minkowski space assumes space is Euclidean in inertial frames. It really is the foundation on which our conception of space and space-time is built.

One more thing, I just remembered Huygen's wave theory of light in which he had failed to prove the existence of mysterious 'ether'( the medium in which light waves were supposed to travel). Is it possible that space itself is ether?

Ideas like the ether is space itself have been put forward. Trouble is we know gravity is space-time curvature.

Can I make a suggestion? Instead of letting your mind wander in all sorts of directions at odds with current knowledge why not learn about that current knowledge?

Thanks
Bill