What is the Nature of Photons?

[haloshade]

I've been wondering this for a while now, and I've looked into it but I'm still confused.

I understand that photons are emitted when an electron jumps energy levels, or (correct me if I'm wrong) when an electron and positron collide (annihilate) with each other.

But these don't answer my question, is a photon just a a pure form of energy from the electromagnetic force put into a particle-wave form, or do scientist just simply not know yet?

 

[Vanadium 50]

I don't think you will be satisfied with the answer. "Pure form of energy" is more of a science fiction concept than a scientific one. Science can say "a photon is the thing that behaves in this way (and then list its properties)", but it sounds like you will find that answer unsatisfactory.

Note that no matter what you are talking about, you can eventually get to this point. What is water? What is air? "Yes, but what is it really" is a question that ultimately has only the answer, "the thing with these properties".

 

[DaTario]

Hi, besides the two contexts you pointed out in the OP where photon concept arises, I would add the photon as an elemetary mode of the EM field inside a cavity.

Observe that when an atom decays inside a ressonant cavity in a way that its photon propagates along the cavity axis, at the moment of decay you may have a photon in atomic sense but still not in cavity sense. I hope I have helped to make things more complete.

Best wishes

DaTario

 

[RedX]

Quantum mechanics says that the world is pervaded by an electromagnetic field, and it is excitations of this field that are photons. so if you imagine a trampoline, then the field is a trampoline, and when a charge jumps on the trampoline, then this causes the whole trampoline to displace as the disturbance is transmitted through the stitching of the trampoline - this disturbance is a photon.

 

[raknath]

Hi, besides the two contexts you pointed out in the OP where photon concept arises, I would add the photon as an elemetary mode of the EM field inside a cavity.

Observe that when an atom decays inside a ressonant cavity in a way that its photon propagates along the cavity axis, at the moment of decay you may have a photon in atomic sense but still not in cavity sense. I hope I have helped to make things more complete.

Best wishes

DaTario

So would you say that resonance is possible for the photon?

I am not sure such a simplistic explanation is possible.

Could we go in for a move qm type of an explantation, something on the lines of

The photon is that piece of the universe which when non accurate observations are done wrt a particle hypothesis behaves as a particle and when more accuracy is sought tends to behave as a wave

 

[HallsofIvy]

A photon is the particle that mediates the electro-magnetic force!

 

[haloshade]

Thank you everybody for your answers, you sort of helped me understand what a photon is a bit, but I'm assuming science can never truly answer my question, since my question was focused more on the "why/ how does it really form" of what a photon is.

It's a shame that science (at least modern day science) will never be able to tell us the "whys" of live but can tell everything else. I myself am a devoted wanna-be-physicist, and I hope to put my research into the theories of "why" and "what".

But thank you everybody for your input, there's still so much more I need to learn about physics before I can even start thinking of a plausible theory.

 

[TriTertButoxy]

Thank you everybody for your answers, you sort of helped me understand what a photon is a bit, but I'm assuming science can never truly answer my question, since my question was focused more on the "why/ how does it really form" of what a photon is.

It's a shame that science (at least modern day science) will never be able to tell us the "whys" of live but can tell everything else. I myself am a devoted wanna-be-physicist, and I hope to put my research into the theories of "why" and "what".

But thank you everybody for your input, there's still so much more I need to learn about physics before I can even start thinking of a plausible theory.

I beg to differ: science can answer quite a lot of 'why's. For example, it can answer why the sky is blue, why water is transparent, etc. In your case, the question of why the photon forms, and how it actually forms is well known (has been known for decades). The answer, unfortunately, must be given in terms of more advanced concepts which you may/may not have an intuitive understanding of, and the answers provided in the previous posts may have appeared mystifiying, as a result. But, I assure you, the 'why' the 'what' and 'how' of a photon is well known.

 

[kexue]

What is a photon?

First understand the harmonic oscillator and what happens when it is quantized.

Next understand what happens when a chain of many coupled harmonic oscillators is quantized. Understand what normal modes are, what a Fock space is and what people mean
when they say quasi particle phonon.

Next note that a field can be understood as infinite many coupled harmonic oscillators.

 

[haloshade]

I beg to differ: science can answer quite a lot of 'why's. For example, it can answer why the sky is blue, why water is transparent, etc. In your case, the question of why the photon forms, and how it actually forms is well known (has been known for decades). The answer, unfortunately, must be given in terms of more advanced concepts which you may/may not have an intuitive understanding of, and the answers provided in the previous posts may have appeared mystifiying, as a result. But, I assure you, the 'why' the 'what' and 'how' of a photon is well known.

Thanks, I might try looking into some books over light and quantum particles then, any good suggestions?

 

[Sir Pwn4lot]

A photon is the carrier of the electromagnetic force. Anything involving electrodynamics from radio waves to visible light to gamma rays is carried by the photon.

A photon is both a wave and a particle. In Thomas Young's Experiment he discovered that light behaves differently when being observed. Well that was the electron but it's the same principle...

His experiment consisted of two horizontal slits that allowed light to pass through them, and based on the resulting pattern of light distribution you can tell whether it's a wave or a particle.

The photons go through the two slits and you'd expect to see two bands if it were a particle. But Physicists found that it behaves like a wave and creates a pattern expected of waves. This is interesting because it doesn't act like a wave when there's only one slit, it acts like a particle.

When the photon shoots out, it breaks itself in two before reaching the slits so it can go through both of them. In reality, all of these possibilities occurs, the photon goes through BOTH slits, the left one, the right one and none at all. All of these possibilities are superposition with each other.

Even weirder, when they tried to observe which slit the photon went through, it behaved like a particle! The very act of observing eliminated the other possibilities.

Sigh... got to love the uncertainty principle...

 

[mikelepore]

the photon goes through BOTH slits

I don't know why people continue to speak of photons traveling through space, either through the slits or on any other occasion. Does anyone here know of evidence for that? As far as I know, the photon is the quantized behavior that is observed only at exactly two times: the instant when the electromagnetic wave is emitted, and the instant when the electromagnetic wave is absorbed. If there is any evidence that photons exist during the trip, after emission and before absorption, please point it out to me.

 

[Greenie]

Ok, so a photon is like Gertrude Stein’s rose - it’s a photon.

It is easy to accept the Bohr model of an atom, or a more advanced similar, though more sophisticated model which comes to much the same concept. So there is no problem with seeing that “excited” atoms emit photons of a particular energy/wavelength.

Planck’s “black body” theory derives a distribution of energy levels, and hence the spectrum, of em radiation from a hot object, though everyone keeps quiet about where the photons actually come from. But it is clearly not a single wavelenth phenomenon.

But what price the energy/wavelength of a photon emitted by an accelerated elctron? (if it does! Feynman has quite a bit to say about this).

Or by an electron moving harmonically in an antenna. Why should there be any connection with the excitation frequency in the antenna and the wavelength of the emitted photons, which is what always seems to be tacitly assumed in the literature?

Or am I completely missing the point please?

 

[Evolver]

I've been wondering this for a while now, and I've looked into it but I'm still confused.

I understand that photons are emitted when an electron jumps energy levels, or (correct me if I'm wrong) when an electron and positron collide (annihilate) with each other.

But these don't answer my question, is a photon just a a pure form of energy from the electromagnetic force put into a particle-wave form, or do scientist just simply not know yet?

A photon is a form of electromagnetic radiation. It is theoretically massless and is the force carrier particle for electromagnetism... meaning that it is the reason that electromagnetism can be observed as a force at all.

Also a photon is the "particle" responsible for visible light. I have particle in quotations because light exhibits a strange phenomenon of duality in that it has characteristics of both particles and waves.

Don't feel bad if you don't understand stuff of this nature... even Feynman said he didn't understand QED... a theory which he himself pioneered!

 

[Tipi]

Hi,

I was not here for that, but it was the first post and I found that question so cute...

I'm not sure anyone will like my answer but, since it seems different from yours, I thought I should give it.

This is a pragmatic or instrumentalist answer : ask an experimentalist working with photons.

He will answer not with a description of the objective properties of an element of reality, but probably (if not, let's imagine he will) in terms of what the photon can do.

I think that if you can make a list of all the things a photon can do, you will be close to my definition of a photon (even if I don't know this list). This point of view is remakably well cristalize in a famous quote by Jammer. In my memory, it is something like that : "A physical entity does not do what it does because it is what it is, but is what it is because it does what it does". Read it 2 or 3 times, there really is a lot of juce in that sentence.

I think this way of understand the nature of things, like photons, electron, etc., is the way that fit the most with the formalism of quantum mechanics. The most eloquent text on this point of view is, in my opinion, the magistral book of Reichenbach on the philosophy of quantum mechanics. It's free from right, somewhere on the internet.

Good luck in your quest for a definition of what things are!



Tipi

PS : English is not my primary language, so forgive my mistakes.

 

[haloshade]

Hi,

I was not here for that, but it was the first post and I found that question so cute...

I'm not sure anyone will like my answer but, since it seems different from yours, I thought I should give it.

This is a pragmatic or instrumentalist answer : ask an experimentalist working with photons.

He will answer not with a description of the objective properties of an element of reality, but probably (if not, let's imagine he will) in terms of what the photon can do.

I think that if you can make a list of all the things a photon can do, you will be close to my definition of a photon (even if I don't know this list). This point of view is remakably well cristalize in a famous quote by Jammer. In my memory, it is something like that : "A physical entity does not do what it does because it is what it is, but is what it is because it does what it does". Read it 2 or 3 times, there really is a lot of juce in that sentence.

I think this way of understand the nature of things, like photons, electron, etc., is the way that fit the most with the formalism of quantum mechanics. The most eloquent text on this point of view is, in my opinion, the magistral book of Reichenbach on the philosophy of quantum mechanics. It's free from right, somewhere on the internet.

Good luck in your quest for a definition of what things are!



Tipi

PS : English is not my primary language, so forgive my mistakes.

Haha, it's ok your English is really good. Thanks for letting me know of that quote, it seems like more quantum physicist know what the quantum particles do, not what they are. My question is what is a photon, which appears to be something that modern day physicist can't seem to figure out.

I hope one day to figure this out on my own, my goal in life is to know what everything in this universe and why did it get there. Maybe that's every bodies, if it is then let's all try to figure this out!

 

[Phrak]

I don't know why people continue to speak of photons traveling through space, either through the slits or on any other occasion. Does anyone here know of evidence for that? As far as I know, the photon is the quantized behavior that is observed only at exactly two times: the instant when the electromagnetic wave is emitted, and the instant when the electromagnetic wave is absorbed. If there is any evidence that photons exist during the trip, after emission and before absorption, please point it out to me.

You seem to be asking for direct evidence where is it precluded, and unwilling to accept indirect evidence. If you're demanding an answer to this duality question, you're chances of getting one are as vanishingly small here, as on any of the 1000's of previous threads discussing the issue.

 

[Tipi]

Haha, it's ok your English is really good. Thanks for letting me know of that quote, it seems like more quantum physicist know what the quantum particles do, not what they are. My question is what is a photon, which appears to be something that modern day physicist can't seem to figure out.

I hope one day to figure this out on my own, my goal in life is to know what everything in this universe and why did it get there. Maybe that's every bodies, if it is then let's all try to figure this out!

With all respect, I think you did'nt understand my answer. For me (at this moment in my psychological evolution), the photon is what he do. Nothing more, nothing less. I understand your question. And I will take a little more time to help you understand my answer.

Feynman, in his thesis supervised by J. H. Wheeler, reformulate the Maxwell theory in terms of action-at-a-distance. It is equivalent in its prediction to Maxwell theory in which waves of light travels, but in the former there is nothing traveling. Acting here on a source make shining there the screen, nothing traveling between them.

Now, the question is not which of the wave picture or action at a distance picture is the right description of reality (it is an unfalsifiable question, i.e. a non-scientific one). It is only for you to realize that a physical theory describing (classical waves, for my purpose) perfectly the effect of lights on apparatus do not need the existence of a thing called photon.

With this in mind, you must know that the same situation appear everywhere in physics. Quantum mechanics, for example, can not in its actual formulation, state aboute the nature of things, about what they really are. This is why some people say it is incomplete.

Asking your cute and profound question about photon is equivalent to asking for a completion of quantum mechanics, in such a way it can finally be able to state about the nature of reality or of the things it describe. Today, QM can only give you information about what things do. It is really important that you understand that. It means that, today, any question (like yours) about what things are is metaphysics and not falsifiable. This question cannot be answered by today's science, since our scientific theories are, at the moment and by definition, unable to answer this type of question.*

It is now a philosophical concerns to state about the role of science : should it describe the nature of things stating what they are (even if its not falsifiable at the moment) or should it describe how nature work, how things interact and how to link different observations and manipulations? I don't know...

TP

*I advise you that there is some personal opinion in these last statement and I'm not sure everyone will agree with that for all physical theories. I'm as extremist as Reichenbach, who explain very well (in his philosophy of QM) why even classical physics (considered as a science) can only state about what things do, not what they actually are.

 

[Evolver]

It is now a philosophical concerns to state about the role of science : should it describe the nature of things stating what they are (even if its not falsifiable at the moment) or should it describe how nature work, how things interact and how to link different observations and manipulations? I don't know...

I feel what you're describing is the same thing (similar to what you said in a previous post of yours). It would seem that things ARE what they do. If describing an apple; it is red to our eyes because of the wavelengths of light it absorbs and reflects. It is smooth because of it's molecular structure (which obviously can be broken down to atomic structure, etc.) An apple is an apple because of how it interacts with the forces around it, right down to it's most elementary make-up.

I don't think science intends to differentiate between the two, as I think the two statements you're saying are actually just one. Because your description of "what they are" is vague and undefined... you would realize that if you tried to define what it is "to be", that it would fall in accordance with the last statement of "how they work".

It therefore is an unnecessary argument and will only convolute scientific thought.

 

[Tipi]

I don't think science intends to differentiate between the two, as I think the two statements you're saying are actually just one. Because your description of "what they are" is vague and undefined... you would realize that if you tried to define what it is "to be", that it would fall in accordance with the last statement of "how they work".

It therefore is an unnecessary argument and will only convolute scientific thought.

There is a difference. If you describe the properties of things with quantum mechanics, you violate relativity. I mean, if the equations describe the properties of something that really exist in space and time, a photon propagating between to events, then Bell showed you violate fundamental laws of relativity since then there is an action at a distance so that cause and effect can not be uniquely defined.

However, there is no problem considering equations giving information about what things do.

TP

 

[Evolver]

There is a difference. If you describe the properties of things with quantum mechanics, you violate relativity. I mean, if the equations describe the properties of something that really exist in space and time, a photon propagating between to events, then Bell showed you violate fundamental laws of relativity since then there is an action at a distance so that cause and effect can not be uniquely defined.

However, there is no problem considering equations giving information about what things do.

TP

Relativity and descriptions of quantum interactions (such as QED) are still incomplete theories. They are not laws. Meaning that there are still pieces of the puzzle missing... perhaps very large pieces. The violation of one from the other proves nothing.

Other than that, I was observing your poor choice of words: Saying "What something is" vs. "How something behaves". These are the same statement if you look deeper, and you are dissecting them into two, unnecessary groupings.

There is no other way to describe "What something is" without using "How it behaves" as a descriptor. They are the same and thus the logic is flawed.

Try to describe to me an apple without using any of it's properties of matter or interaction of forces... it's impossible and therefore this is a superfluous argument.

 

[lightarrow]

I don't know why people continue to speak of photons traveling through space, either through the slits or on any other occasion. Does anyone here know of evidence for that? As far as I know, the photon is the quantized behavior that is observed only at exactly two times: the instant when the electromagnetic wave is emitted, and the instant when the electromagnetic wave is absorbed. If there is any evidence that photons exist during the trip, after emission and before absorption, please point it out to me.

I don't know about direct evidence, but I know that photons cannot pass through one slits or the other or both, otherwise there wouldn't be an interference pattern. About the both slits: it can't because it's an indivisible particle (if not, then the wave description would be enough and we wouldn't need to talk about photons at all). Actually it's not possible to talk about photons in between source and detector, at least in the sense of corpuscoles well localized in space which have an individual existence (I mean, of which you can track the path between source and detector).

 

[DeShark]

I don't know why people continue to speak of photons traveling through space, either through the slits or on any other occasion. Does anyone here know of evidence for that? As far as I know, the photon is the quantized behavior that is observed only at exactly two times: the instant when the electromagnetic wave is emitted, and the instant when the electromagnetic wave is absorbed. If there is any evidence that photons exist during the trip, after emission and before absorption, please point it out to me.

What about passing photons through polarizers? Unless you want to say that the photon is absorbed by the polarizer and then has a probability to be re-emitted in either direction depending upon the spin of the photon. Does this count as detection/observation? Also, the time delay (distance divided by the speed of light) indicates some sort of travel or existence in between, unless we suppose it disappears and then reappears later at our detection apparatus with given probabilities and who's to say that this doesn't count as travel? It depends on your definition of the word travel. Additionally, if we're talking about wave functions, then a wave packet can travel. If this traveling wave packet is no good because of some sort of "Oh well that's just a mathematically theoretical description", then we're well into the realm of philosophy.

Either way, if we're going to discuss anything to do with anything, then some sort of language is needed. I'll accept that the only unambiguous language is mathematics, but this isn't always that lucid and has some nuances which aren't clear upon first glimpse. Additionally, at some point in time, we have to move from the world of mathematicss to the world as people view it (the macroscopic world if you like). Without this transition, we're just dabbling with mathematics, not explaining things like "Why the sky is blue and why is water transparent". The mathematical description of transparent is one thing, but until we equate it with the word transparent in common usage we know nothing.

Forgive the rant, but I don't know why people continue to speak of the world only in terms of what we can taste, touch, see and smell and hear without believing that there might be something going on outside of this sensory perception. While I accept that it's the only *verifiable* truth, to think that it is the *only* truth is to say that nothing else matters. Love has no mathematical description and you can't measure it, but intuitively, I hope you believe it exists. I'm not advocating some sort of leap and bound from what we can measure to the belief of a flying spaghetti monstor, but to go from "The photon is at point A at time t_0 and then at point B at time t_1" to "The photon traveled from point A to point B" is not on this scale.

 

[Naty1]

We know about as much about what a photon is as we do what energy is or an electron or how many universe there are. Why should there even BE a photon, why not some other entity? But we are rather skilled at some descriptions, some which have evolved from theory and some from experiments.

String theorists might describe a photon one way, quantum people another and relativists yet another. (Maybe analogous to three blind men touching different parts of an elephant.) As noted here by others, most of physics describes behaviors and characteristics which enable us to predict future events and often measure those behaviors while fundamental understanding of the type you seek largely eludes us.

How recent was it that the "atom" was thought to be "fundamental"?...we have a lot to learn and a lot to discover.

It seems (via theory) that everything around us emerged from a primordial "big bang" (or small bang) and during a phase transition extremely unstable high energy conditions morph into the everyday things we now observe...and probably some we don't yet even know much about...like dark matter or dark energy. Why our universe is composed of the specific constituents it is is unknown.

Maybe we'll be able to answer you question when mankind develops some additional senses or intellect. After all, it appears an ant is ill equipped to discover general relativity but is quite good at what it does.

 

[RUTA]

I don't know why people continue to speak of photons traveling through space, either through the slits or on any other occasion. Does anyone here know of evidence for that? As far as I know, the photon is the quantized behavior that is observed only at exactly two times: the instant when the electromagnetic wave is emitted, and the instant when the electromagnetic wave is absorbed. If there is any evidence that photons exist during the trip, after emission and before absorption, please point it out to me.

There are interpretations of quantum physics whereby the photon is no 'thing' precisely as you imply.

Genuine Fortuitousness:
A. Bohr & O. Ulfbeck, Rev. Mod. Phys. 67, 1-35 (1995)
A. Bohr, B. Mottelson & O. Ulfbeck, Found. Phys. 34, #3, 405-417 (2004)

Relational Blockworld:
Michael Silberstein, Michael Cifone & W.M. Stuckey, Stud. Hist. Phil. Mod. Phys. 39, #4, 736–751 (2008)
W.M. Stuckey, Michael Silberstein & Michael Cifone, Found. Phys. 38, #4, 348–383 (2008)

 

[Tipi]

Relativity and descriptions of quantum interactions (such as QED) are still incomplete theories. They are not laws. Meaning that there are still pieces of the puzzle missing... perhaps very large pieces. The violation of one from the other proves nothing.

It think this is a point of view. I prefer to say that theories are exact in a certain domain, or class of phenomenon, but I know not everybody will agree with that.

Other than that, I was observing your poor choice of words: Saying "What something is" vs. "How something behaves". These are the same statement if you look deeper, and you are dissecting them into two, unnecessary groupings.

I think it is a complex task to discuss that in few words. I am convinced that these two statements are the same, but it is false that everybody think this way. Some people ask more, a model in addition, which explain all these behaviors in terms of fundamental objective entities, independent of the subject. For the poor choice of word, forgive the history of philosophy. These have their root in the (very) old subject-object problem. John S. Bell call beable a property of an object, and observable something linked to its behavior. Bohr, and Heisenberg, and Einstein, and... discussed this old problem with these "poor" words. See, for instance, the book of Jammer or d'Espagnat on the philosophy of QM.

There is no other way to describe "What something is" without using "How it behaves" as a descriptor. They are the same and thus the logic is flawed.

Try to describe to me an apple without using any of it's properties of matter or interaction of forces... it's impossible and therefore this is a superfluous argument.

I could say it is made of strings...

TP

 

[bjacoby]

Thanks, I might try looking into some books over light and quantum particles then, any good suggestions?

I'll beg to differ with science answering the question "why?". Yes, it's a small semantic point but a very important one. Science asks "how" not why. Why implies some unknown motivations. The sky is blue rather than red because blue was God's favorite color. How the sky appears blue is a different question, having to do with the scattering of light and HOW that occurs.

By now it should be pretty clear that nobody here has a clue what light is, let alone "photons".

A lot of properties are known, but physics isn't a list of properties. Physics is an UNDERSTANDING of natural phenomena. And what that means is not to know "why" but rather to have recourse to a "model" that gives insight into what we are studying. Maxwell's model for electricity and magnetism is based upon a fluid flow idea. That gives lots of insight if you are already familiar with how fluids behave. However it is not correct at all for light. Many people still pretend it is, but it's not. A close study of light shows that the whole structure falls apart. Light has some wave properties but it's clearly not simply electromagnetic waves as originally thought. It something far more concentrated and powerful and able to send energy through nothing at all like a particle. Yet even at the particle level wave effects do still appear under certain conditions.

So what is the model that "works"? Nobody knows (yet). You can make mathematical models that ape certain properties but they are not reality. I'm sorry but "simple harmonic oscillators" or even an infinite number of them (whatever that is supposed to mean) is not reality. "infinity" is not reality. It's pure imagination...which is to say mathematics. Mathematics is not more real than reality. So what is the model that predicts the nature of light without getting lost in mathematical complexities or violations of common sense such as the laws of causality? There have been some decent tries at creating such a model, but as far as I know nobody has done it yet.

So for now there is light and how it behaves. Beyond that it's open season. Think of it like the old problem of the motion of the planets when the Earth is regarded as the center of the universe. You can develop complex mathematical systems that actually predict what is going on to a degree, but they are not the model you are looking for because the complexity keeps you from understanding. But a simple shift of point of view can suddenly produce the model that provides great insight into HOW it all works (not why!)

So are you the next Galileo? Well that depends if you can figure out a new model of light that covers all the properties and yet through a new point of view provides insight as to how all the properties of light arise. Good luck.

 

[Evolver]

I think it is a complex task to discuss that in few words. I am convinced that these two statements are the same, but it is false that everybody think this way. Some people ask more, a model in addition, which explain all these behaviors in terms of fundamental objective entities, independent of the subject. For the poor choice of word, forgive the history of philosophy. These have their root in the (very) old subject-object problem. John S. Bell call beable a property of an object, and observable something linked to its behavior. Bohr, and Heisenberg, and Einstein, and... discussed this old problem with these "poor" words. See, for instance, the book of Jammer or d'Espagnat on the philosophy of QM.

Yes, John S. Bell also thought that quantum mechanics, by nature, was non-deterministic. I do not believe in this line of thinking so readily. Humans have a habit of stating something is mystical or undefined when they have not clearly understood some aspect of it. QM is non-deterministic with our current understanding of it, but it's our understanding of it that makes it that way. We can presently only measure the position or the velocity of an electron with our limited technological level and understanding of QM. But this does not mean that an electron does not have both a position and a velocity. It merely means that our relatively primitive means of observing it interferes with the electron itself, and thus gives us a result based on probabilities, which are non-deterministic.

We have to come up with a new mathematical way of expressing this thought more accurately than probablilities, and subsequently better technologies utilizing these new mathematics. Just as geometry, algebra and calculus were invented to deal with different types of problems... we again need to invent a new mathematical language of QM. A new mathematical language would accurately describe the universe of QM by "how it behaves"... thus explaining "why things exist". So I still feel the word choice is poor... though that's just my opinion.

I could say it is made of strings...

You would then still be describing the properties of matter, since matter would be made of the oscillations of 1-dimensional strings. And you have thus, still failed to describe the apple as "being" without describing "how it behaves."

Besides, string theory is even more ill-defined than the previous two theories.. and some even think they are no longer strings, but branes as in m-theory. Goes to show you how long lasting these theories really are. On top of which, there are many alternatively viable theories (supergravity for example) that don't use strings or alternative dimensions at all, so you might actually find it hard to say matter is made up of strings after all.

 

[kote]

Yes, John S. Bell also thought that quantum mechanics, by nature, was non-deterministic.

From http://plato.stanford.edu/entries/qm-bohm/

Wigner to the contrary notwithstanding, Bell did not establish the impossibility of a deterministic reformulation of quantum theory, nor did he ever claim to have done so. On the contrary, over the course of the past several decades, until his untimely death in 1990, Bell was the prime proponent, for a good part of this period almost the sole proponent, of the very theory, Bohmian mechanics, that he is supposed to have demolished.​

The article also quotes Bell's 1987 book:

But in 1952 I saw the impossible done. It was in papers by David Bohm. Bohm showed explicitly how parameters could indeed be introduced, into nonrelativistic wave mechanics, with the help of which the indeterministic description could be transformed into a deterministic one. More importantly, in my opinion, the subjectivity of the orthodox version, the necessary reference to the ‘observer,’ could be eliminated. ...

But why then had Born not told me of this ‘pilot wave’? If only to point out what was wrong with it? Why did von Neumann not consider it? More extraordinarily, why did people go on producing ‘‘impossibility’’ proofs, after 1952, and as recently as 1978? ... Why is the pilot wave picture ignored in textbooks? Should it not be taught, not as the only way, but as an antidote to the prevailing complacency? To show us that vagueness, subjectivity, and indeterminism, are not forced on us by experimental facts, but by deliberate theoretical choice?​

 

[Evolver]

From http://plato.stanford.edu/entries/qm-bohm/

Wigner to the contrary notwithstanding, Bell did not establish the impossibility of a deterministic reformulation of quantum theory, nor did he ever claim to have done so. On the contrary, over the course of the past several decades, until his untimely death in 1990, Bell was the prime proponent, for a good part of this period almost the sole proponent, of the very theory, Bohmian mechanics, that he is supposed to have demolished.​

We are of course talking about Bell's Theorem here of which John S. Bell was the main proponent. The theorem implies that reality is based on non-locality interactions. Meaning that particles could affect one another instantaneously... aka faster than light.

I'm sure you can see the implications this has for theories of relativity and theories of QM based on locality. I'm saying Bell did not have an alternative theory to replace relativity or locality QM, he simply showed that they were in defiance of non-locality. So according to his theorem, the current models of the universe based on locality would always be non-deterministic.

The Bohm interpretations you speak of are non-local as well as non-relativistic... but since locality and relativity ever pervade modern models of our current theories... I am then able to conclude that Bell's belief was that the universe is non-deterministic.

 

[kote]

The Bohm interpretations you speak of are non-local as well as non-relativistic... but since locality and relativity ever pervade modern models of our current theories... I am then able to conclude that Bell's belief was that the universe is non-deterministic.

Except that Bell didn't accept locality as necessary. From http://plato.stanford.edu/entries/bell-theorem/:

Although the main result of Bell [1964] is his theorem demonstrating the the impossibility of recovering the statistical predictions of quantum mechanics with a local realistic theory, Section 3 of this paper concludes with the construction of a nonlocal model — violating Remote Context Independence but not Remote Outcome Independence-- which does recover the statistical predictions of a particular entangled quantum state.​

There's also still the fact that Bell published the statement that "indeterminism [is] not forced on us by experimental facts."

Locality is certainly an important concept. But Bell did not deny determinism - he supported it.

 

[Tipi]

You would then still be describing the properties of matter, since matter would be made of the oscillations of 1-dimensional strings. And you have thus, still failed to describe the apple as "being" without describing "how it behaves."

I don't agree. Saying an apple is made of strings (beables) is a statement stronger than saying it behave like it is made of strings (observables). The difference manifest itself when you consider entangled states of QM. Beables (hidden variables) are then non-local concepts, while observable are completely local. If you want to avoid non-locality, you have to avoid statement about what things are, that is, beables. This is why I don't agree with you, since it seems you say that beables are ultimately the same things as observables.

I thought I was clear on that subtlety in a previous post... maybe it is just hard for us to communicate.

My point here was that the "cute" question seems to ask for a beable as an answer because it ask what the thing is. I then tried to argue that it is a question impossible to answer with my actual understanding of QM since then it will lead to non-local properties of things. I then suggest to answer the question in terms of the observables attached with the thing, discussing what it do instead of what it is.

If you don't agree with all that, it doesn't matter. It is just that we see things differently. Some people, as Bohm and maybe you, think only the observable have to be relativistically invariant. So, it doesn't matter to him his theory has non-local beables, since these beables lead to completely relativistic observation. That means that in bohmian mechanics, the violation of relativity is, by definition, unobservable!


TP

 

[Evolver]

Except that Bell didn't accept locality as necessary. From http://plato.stanford.edu/entries/bell-theorem/:

Although the main result of Bell [1964] is his theorem demonstrating the the impossibility of recovering the statistical predictions of quantum mechanics with a local realistic theory, Section 3 of this paper concludes with the construction of a nonlocal model — violating Remote Context Independence but not Remote Outcome Independence-- which does recover the statistical predictions of a particular entangled quantum state.​

There's also still the fact that Bell published the statement that "indeterminism [is] not forced on us by experimental facts."

Locality is certainly an important concept. But Bell did not deny determinism - he supported it.

I know, that's precisely what I'm saying. Bell argued for non-locality, but he did not offer an alternative theory as complete and thorough as say relativity or QED, which are the modern paradigms of our description of the universe. This being said, that implies that Bell's determinism only comes about via non-locality, and our models are based on relativity and locality. So since Bell disagrees with the locality of these models, his theorem then states that our understanding of the universe currently is non-deterministic. The current models result in only probabilities, and these are obviously not an accurate representation of information.

And that's precisely why I said I don't agree with this before, because I don't think you can mix Bell's theorem with our current models... a new model is required. That's all I was saying when I said Bell thought of the universe as non-deterministic.

I don't agree. Saying an apple is made of strings (beables) is a statement stronger than saying it behave like it is made of strings (observables). The difference manifest itself when you consider entangled states of QM. Beables (hidden variables) are then non-local concepts, while observable are completely local. If you want to avoid non-locality, you have to avoid statement about what things are, that is, beables. This is why I don't agree with you, since it seems you say that beables are ultimately the same things as observables.

I thought I was clear on that subtlety in a previous post... maybe it is just hard for us to communicate.

My point here was that the "cute" question seems to ask for a beable as an answer because it ask what the thing is. I then tried to argue that it is a question impossible to answer with my actual understanding of QM since then it will lead to non-local properties of things. I then suggest to answer the question in terms of the observables attached with the thing, discussing what it do instead of what it is.

If you don't agree with all that, it doesn't matter. It is just that we see things differently. Some people, as Bohm and maybe you, think only the observable have to be relativistically invariant. So, it doesn't matter to him his theory has non-local beables, since these beables lead to completely relativistic observation. That means that in bohmian mechanics, the violation of relativity is, by definition, unobservable!TP

You're right, I don't agree because you are attempting to avoid non-locality. I'm not saying non-locality is right, but I'm not saying it's wrong either. There are many great physicists that support non-locality, Bell and Bohm among them... but the real problem comes with science's limited grasp of QM. Richard Feynman said he didn't understand Quantum Electrodynamics and he invented the theory. Einstein, Bohr, Bohm, Bell, Von Neumann and many others all sought to discuss locality and non-locality and among them they came up with incredibly different opinions. The problem is we are arguing two sides of an undefined coin. Neither of us can prove anything and therefore this thread is nothing more than individual philosophy.

 

[Tipi]

You're right, I don't agree because you are attempting to avoid non-locality. I'm not saying non-locality is right, but I'm not saying it's wrong either. There are many great physicists that support non-locality, Bell and Bohm among them... but the real problem comes with science's limited grasp of QM. Richard Feynman said he didn't understand Quantum Electrodynamics and he invented the theory. Einstein, Bohr, Bohm, Bell, Von Neumann and many others all sought to discuss locality and non-locality and among them they came up with incredibly different opinions. The problem is we are arguing two sides of an undefined coin. Neither of us can prove anything and therefore this thread is nothing more than individual philosophy.

I deeply respect your point of view. I studied it two years and put my conclusions in a master thesis : I saw no "real" contradiction between realistic quantum mechanics and relativity. However, at the end, I was strongly convinced that the actual formalism of quantum theory has to be interpreted in a non-realistic way, i.e. that it is constructed in such a way that it can make statement only about results of measurements. I think the "realist" point of view is not suitable for the actual formalism, but it could be for something else to come.

So, I think teachers should adopt a strong instrumentalist point of view (no statement about what things are) to avoid contradicting what is said in other courses (e.g. all nature is invariant under the Poincaré group...), and that the realist point of view should be kept for researchers, or very initiated peoples.

Cheers,

TP

 

[Evolver]

I deeply respect your point of view. I studied it two years and put my conclusions in a master thesis : I saw no "real" contradiction between realistic quantum mechanics and relativity. However, at the end, I was strongly convinced that the actual formalism of quantum theory has to be interpreted in a non-realistic way, i.e. that it is constructed in such a way that it can make statement only about results of measurements. I think the "realist" point of view is not suitable for the actual formalism, but it could be for something else to come.

So, I think teachers should adopt a strong instrumentalist point of view (no statement about what things are) to avoid contradicting what is said in other courses (e.g. all nature is invariant under the Poincaré group...), and that the realist point of view should be kept for researchers, or very initiated peoples.

Cheers,

TP

This I do agree with. ;)