First photograph of light as both a particle and wave

[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

 

[Gort]

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?

If certain minds didn't wander from current knowledge, there would be little progress in science. Michael Faraday and Maxwell come to mind. Learning about current knowledge is good. But so is wandering. And asking questions. And, hopefully, putting those questions in the form of real experiments.

 

[TrickyDicky]

Michael Faraday and Maxwell come to mind.

Actually much more Faraday than Maxwell. Faraday even came up with probably the first "theory of everything" in the modern sense, too bad he lacked the math to support it. Maxwell used Faraday's insights but departed from Faraday's theory to construct Maxwell's equations as close to the Newtonian ideas as he could.

 

[mfb]

Learning about current knowledge is good. But so is wandering. And asking questions. And, hopefully, putting those questions in the form of real experiments.

Yes, but without the first step it does not work.

 

[Gort]

Yes, but without the first step it does not work.

I might question the "does not work". Maybe has a low probability amplitude. But I think there could be a case made for not being shackled with the beliefs of the past. I know progress is usually made "on the shoulders of giants". But perhaps, if someone is blissfully unaware of some current line of research, that person could go off on a fruitful tangent.

 

[mfb]

I might question the "does not work". Maybe has a low probability amplitude.

The number of successful theories from persons who did not know the previous theories is zero. At least I never saw an example (and I did search).
Even the weaker question "who found something new without being in contact with experts" just lead to one example.
But that is too far away from the topic of this thread I think.

 

[bhobba]

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

The highlighted bit is the issue.

Thanks
Bill

 

[Shri13]

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

Sir bhobba,
Thank you very much for your help in trying to make me understand about space.
But I think none of you has understood the TRUE point of my question.

According to Sir Bhobba, yes I of course agree that Euclidean geometry, minkowski,etc... have really defined the space to their best, but in mathematical way!

What I am saying is that space is not defined structurally ( like how an atom is structally defined well i.e it has nucleons, electrons, orbitals, etc...).
My query is that we don't know what actually the SPACE is made of!
I would have been satisfied if space was somewhat defined as following ( just an e.g.):-
"Space is made up of fundamental numerous space cells known as 'pixons' ( you can compare them with pixels or the tiniest led of a computer screen) arranged in 3-dimensional grid, which can vary their energy content and other attributes to resemble the existence, motion, actions, etc... of an entity ( entities like electron, quarks or macro scaled planets, galaxies,etc.)" {This is comparable to our computer screen, we know how a cs represents various graphical objects in virtual reality. I wish we also had knowledge of how our space does that structurally.}[Here you can presume a pixon to be of Planck length and a group of them considered together resemble an entity. The group doesn't moves when the entity moves in space. The info and attribute gets transferred to further pixons which resembles its motion.]
( this is not a theory and I just gave an e.g, of how our space should have actually be defined in a rather structural way...I hope some unnecessary Q's don't arise on the above quoted content.)

Wouldn't such structural definition of space help us to find out more and improve our present day physics? ( I think we do need to think OOB and approach newer ideas. Of course without neglecting the CORRECT results of earlier theories.)
[ for e.g such a structural definition, may even help us to define what gravity is... like considering above quoted theory, one can say gravity is actually attraction of less energy pixon to higher energy pixon so as to stabilise the later, as pixons itself are fundamental of space, we see that space is curved.(here energy can be taken as the mass of the entity represented by group of pixons. The higher energy pixon may be at the centre of mass of that entity, which pulls other low energy pixon and hence curves the surrounding space.)] (I am just giving an e.g. I don't want to make any fuss.)

Thanks guys.

 

[bhobba]

My query is that we don't know what actually the SPACE is made of!

First you need to show, not with philosophical waffle, but an actual physical argument, it needs to be made of anything. Then you need to experimentally verify it - otherwise all you have is conjecture and opinion - which basically means diddley squat.

BTW we already have tons of conjectures along those lines eg LQG, probably even string theory - but that's all they are.

If you want to join the ranks of those that conjecture on that sort of thing - be my quest - but - as MFB said - to actually do that you need to understand current physics a lot better than your posts indicate you do.

Thanks
Bill

 

[bhobba]

have really defined the space to their best, but in mathematical way!

Whenever I see such statements my hands go over my face and a sigh escapes - its involuntary.

Mathematics, like English, is a language - much more precise and perfect for logical thought - but still a language. Experience has shown its the best language for expressing physical concepts. Over in another thread , before it was closed (correctly IMHO), we spent a lot of time basically trying to explain simple ideas in Linear Algebra that are really the basis of QM. You can't do it without the math.

Now I have to ask what exactly is to be gained by ignoring that language and describing issues in a non mathematical way - presumably by English? And your idea of space having a structure - that needs mathematical development as well - so nothing is gained.

I get the VERY strong feeling those that harp on about such for some reason don't like math or don't want to learn it. Sorry - you will not make progress in physics, either learning it or trying to form new theories (which should not be done until you have learned a lot of it) without the language of math.

Statements like its just math, defined in a mathematical way etc etc are silly, yes silly. You must use some language and English has proven woefully inadequate to the task.

Thanks
Bill

 

[Shri13]

I get the VERY strong feeling those that harp on about such for some reason don't like math or don't want to learn it. Sorry - you will not make progress in physics, either learning it or trying to form new theories (which should not be done until you have learned a lot of it) without the language of math.

Hey, I think even after "showing each nerve of my brain", none of you quite understood my point.
First of all Sir Bhobba, maths is my most favourite subject and I can sacrifice everything of my life to learn it whole. Even if I don't understand high level maths ( like tensors, spinors, etc...) right now, but I am interested in learning it. I just love its concept of symbolising complex ideas into compact form like equations.
For me, maths is the language of universe, and it must be the language in which our universe is actually written!
No doubt I accept sir that no other language will be perfect for representing physics laws, but that was not my point.
What I asked was that (for e.g.) didn't structural knowledge of atom helped us to reach this level of quantum physics? What would have happened if we just have stopped after knowing mathematically that atom is sphere of so and so radius, situated on so and so axis, with so and so volume, etc...
Would such mathematical definition have helped us to develop QED, QCD,etc.?

What I am saying is together with mathematical knowledge shouldn't we work to retrieve structural knowledge of space too.?

I know there are some persons who just want to stick what is already known, and neglect everything else. They just make theoretical predictions based on known facts, that this should happen, that supposed to exist, etc... without even seeing what new directions are showing us. This would just make us to rotate our brain around the sun again and again , showing the same things in different views.

I know there are experts who are working on this, may even have found something new, but I am not here to argue on anything or anyone. I just want to share my views on science especially physics. I am still learning and want to learn more...
I hope everyone has understood my point.

I would suggest to stop discussing about questions arising from my posts, and resume back to the original theme of these featured forum.

Thanks guys for giving me place in this forum.

Goodbye.