There is  a beautiful note in Wikipedia: Please check

http://en.wikipedia.org/wiki/Vacuum

Actually, this elegant  mathematical theory relies on the harmonic forces, that  have no counterpart in real nature, which operates completely nonlinear fashion at the absence of reversibility!! 

But this approach doesn't bother me since it has the capacity to give me some mental picture  to visualize some  physical phenomena in terms of classical mechanics concept such as particles. We shouldn't forget we can only understand or generate mental picture of those ideas, which can find their  counterparts in what our brains have  been receiving  through the our  five sense plus the our collective memory.

Zoltan, 'virtual particles do not exist' looks like an extremely bold statement.....

Beyond the mathematical formalism, virtual particles have been ascertained through their indirect material effects on the real world, such as the tunnel effect, radioactive decay, even the onset of certain cancers, and under some scenarios (such as Tryon), they are viewed as being the ultimate cause of certain types of Big Bangs.

Mind you, you state 'the virtual particles' rather than 'virtual particles', thereby indicating that you are referring to a given, specific class of VPs rather than broadly all of them, could you further specify which VPs you have in mind and what grounds, mathematical or experimental, lead you to belie their virtual-foam existence?

Thanks

Dear Dr. Ransford; first of all I agree with your  comments.  The operational definitions  of virtual particles and their mathematical manipulations they  relying on premises that  one should establish  a common verbal platform, which gives experimentallist    some mental pictures that they can visualize or to get feeling what was really going deep under the surface of a reality  That  is in fact forever hidden from us!  As a mathematical physicist, for me all of those abstract things are created by human brains in order to interrelate or correlate information systematically,  as we have perceived from the nature or human manipulated world. I believe in Plato, and respect Dirac' approach!. Since I have been working in Solitons theory last 35 years, and Natural Science last  54 years,  I have seeing it in many different occasions during the computer simulation studies, I have more sound operational definition of particles (Perring and Skyrme, Nucl. Phys.31:550,1962) then may be most people. Unfortunately, virtual particle, which rely on the linear Schrödinger equation doesn’t have Soliton like particle properties; such as localized confinement in space, keeping its integrity and identity after collisions etc. But it is an elegant discovery and very useful indeed. Best Regards

Dear Chris, my point is to present the physical (“real”) vacuum content without using virtual particles (generally). The virtual particles are not “real” and do not have physical meaning. As I understand, the virtual particle concept is a mathematical term, which is used in the quantum field theory to describe particle interactions.

This is a very difficult question because it can leads to Gedankenexperiment trap, so we have to be careful. The problem is to agree on the indirect observation (or not) of virtual particles. If such an observation is unambiguous, then we can further proceed. Otherwise, stop!

Dear Dr. Christopoulos, This is the positivist way to approach any theory,which relies on the few hypothesis that needs experimental  verifications without end.!  But that doesn't stop us in thinking why that seemingly stupid looking thing works so well. Best Regards. 

Dear Zoltan!

If you check commutation relation, e.g. for a harmonic oscillator, you see that [hat x, hat N] NEQ 0 where hat N is an operator for a number of particles. Consequently, according to the Heisenberg uncertainty principle one cannot observe a coordinate and a number of particles simultaneously. Similar reasoning is true for any physical field obeying "reasonable" dynamic equations, i.e. for electromagnetic field [hat E, hat N] is also non-zero. Thus, if you observe an absence of a field, for instance by a trial charge, you cannot say that there are no particles in this quantum state. Conversely, in the state with no particles, there is (indefinite) field. That's pretty much it. 

Extensive explanation of underlying physical principles can be found in a book Quantum Vacuum of my (evil) mentor Peter Milonni, if you take into account that in year 1994 when it came out, most interesting results were not yet observed. 

Dear Zoltan,

The notion of 'virtual particles' refers to certain mathematical elements within the perturbation algorithm of e.g. quantum electrodynamics. There is no experimental evidence that they describe real physical (off-shell) particles. However, that does not mean that virtual particles 'do not exist'. They do exist in a mathematical sense as part of Feynman diagrams and usually contribute to transition amplitudes. There are some Feynman diagrams that are not connected to incoming or outgoing lines and therefore do not contribute to transition amplitudes. These diagrams are interpreted as 'vacuum fluctuations' (not to be mixed up with 'vacuum polarization'). In the presence of vacuum fluctuations we speak of a 'physical vacuum'. But again, there is no experimental evidence that vacuum fluctuation is a real physical phenomenon.

The Casimir effect, which is often claimed to prove the physical existence of vacuum fluctuations, can be fully described by quantum electrodynamics in the sense of van der Waals forces - therefore it is wrong to say that it proves the existence of vacuum fluctuations.

Dear Cameron,

I do not think that the treatment of the Casimir effect by quantum electrodynamics means an 'exception'. On the contrary: quantum electrodynamics is the standard and experimentally well-founded theory for all electromagnetic phenomena. The Casimir effect does not make an exception, although, for historical reasons, it is usually treated by a heuristic model of the pre-QED age. 

I have nothing against heuristic models. My point was that we do not need the concept of zero-point energy to explain the Casimir effect. For this reason the Casimir effect cannot be considered as an experimental proof for the existence of vacuum fluctuations.

Best,

Walter

I have no idea whether virtual particles exist or not, but in my opinion vacuum cannot be just emptiness.

When two electric charges are at a distance from one another, in vacuum, how do they feel the presence of one another? If two massive objects are at some distance from one another, in vacuum, how do they feel the presence of one another? We usually say that there exists a field between them. But there is vacuum there. Field cannot mean emptiness, field is some type of matter, or is carried in some way by some type of matter. Just, it is not a travelling field, i.e. no electromagnetic respectively gravitational waves, it's static field. But, what type of matter is there between the two charges (electrical or gravitational) that carries, or makes possible (whatever expression one would pick), the respective static field?

I have in mind an eventual analogy with a capacitor between whose plates there is a dielectric. The dielectric transmits the field by getting polarized. The vacuum might behave in a similar way if there would be something in it that could become polarized. But, it there something in the vacuum? Is the vacuum not empty?

Dear Sofia, I think this is at least few hundred  years of debate. Some said the space is full of ETHER type substance without  mass but has the property of transmit  light waves.  This was highly regarded claim before the popularity of corpuscular theory of light set forward by Einstein 1913.  Best Regards

But I don't  believe the existence of ETHER or the need of  any type of media for the communication of two objects far-apart from each other. This recent quantum entanglement experiments puzzle me allot,  which was claimed that  to show that the communication speed is faster than the speed of light?   BEST REGARDS

I also don't believe  that there exit any perfect vacuum but a space full of cosmic particle but having no role for the transmission of information of any type.

What  are the quantum people talking about as  the 'Vacuum State ' is completely a mathematical abstraction, and its existence doesn't rely on  any  operational definition, which  makes it a reality.

Thank you so much Prof. Oğurtani,

So, shall I summarize your saying as vacuum is not virtual particles, but real cosmic radiation? If so, why should it behave as some sort of dielectric in presence of charges? Charged elementary particles (protons, electrons, pions, etc.) in this radiation, are free charges, they rather may form a weak current between two opposite charges and cause a steady discharge during the time. In a dielectric appear fixed electric dipoles that don't move - no current.

The same thing with virtual particles: virtual electrons and protons would only contribute to a discharge between two opposite charges. Then, do you see any possibility that neutral elementary particles in the cosmic radiation become polarized in presence of charges? Could it be such a thing?

Now, what about the dark matter? What's your opinion, could it be a candidate for explaining how two massive bodies feel gravitationally one another?

Have my best regards too!  

Dear Sofia; Firstly: I hate to spell the word ''vacuum',which implies an empty space in regards to any conceivable objects as such  that their very existences should  be operationally definable in the sense of Bridgman!!!  Secondly: I spelled  the words of cosmic particles.  What do you means by saying cosmic radiation?  The people are claiming that interstellar space filled  by all those charge particles, molecular hydrogen etc.  But the earth is affected from solar wind generated by the electrons and protons escaping from the gravitation field of sun because of their very high kinetics energy and forming a bow shock at the edge of the heliosphere. 

''Charged elementary particles (protons, electrons, pions, etc.) in this radiation, are free charges, they rather may form a weak current between two opposite charges and cause a steady discharge during the time''   What do you mean by '' a  weak current'' ?  In the High School I had been thought    that  -the electrical current is flow or flux of charged particles-  Dear Sofia, I am sorry to say now you are contradicting your self by postulating a flow of magical charge particles driven by electrostatic forces between oppositely  charges fundamental particles constitute the cosmic radiation ?

I am not expert on Aurora radiation taking  place on  the North and South poles due to magnetic field of earth. WIKIPEDIA:  '' Auroras are caused by charged particles in the solar wind , mainly electrons and protons, entering the atmosphere from above causing ionisation and excitation of atmospheric constituents, and consequent optical emissions. Incident protons can also produce emissions as hydrogen atoms after gaining an electron from the atmosphere.''

The deformation of neutral particles  can't create electric dipole moment but the change particle may.  If one thinks the mathematical nature of the multi-pole expansion of the  charged objects having finite extent  in space such as nucleus exposed to deformation one can get electrical dipole unless the center of mass and the center of charge coincide. That is call parity, which is experimentally proven exist for nucleus. Nucleus in equilibrium also experiences   zero average electric field.  But the quadruple moment exist for those nucleus non-spherical  shape  and it interacts with the electric field gradient.

I have no idea about the mathematics behind that theory!  The model, which is given from the fluid mechanics makes it very plausible.  But I can't answer the question WHY does nature need Black Holes?   That means the universe ends up with self destruction. This can't be the stationary non-equilibrium state for the universe. Definitely,  another BİG BANG  follows it!!!

Dear Prof. Oğurtani,

there has to be some misunderstanding: I am not "contracting myself" to something, neither do I "postulate" anything, because I really don't know the answer to the problem. I am just pondering what type of matter can be the candidate for mediating, or carrying (whatever expression would one prefer), the field between two electric charges in what we call vacuum. I understand that what we call vacuum is not emptiness because there is still some radiation present, of different origins. So, I pondered which part of such radiation would be an answer to the question.

Elementary charged particles, electrons, positrons, pions, etc., real or virtual, can get deformed in presence of charges? I never heard of such things and I would be glad to know. As to nuclei or atoms, they can be deformed but how abundant such particles can be in the vacuum that we produce in our labs? Can they justify the presence of the field between charged bodies?

Well, I can tell you that these question that I ask, are very frequent.

There exist new issues on this old debate: Higgs field is present anywhere and 'gives' 'mass' to all other particles, so, could we argue that this field fulfills all the 'empty space'?

Dear Demetris, I thank you that you have brought a new dimension to this puzzle, which keeps us busy for a while.  If I would use the teaching of Kant I shouldargue  that if the function of Higgs field is to give  the mass to any particle any where then it should be there but otherwise no where!!!   unless the whole universe is occupied by particles without leaving any space among themselves. Then  I would rather say massive fuzzy particles  fill the whole space like  jelly having some premature nodes, which we called them particles that  spread all around. 

Here also I may use the operation definition of the existence of any object, which is its property to be detectablity. Existence = Detectability.

What puzzled me when I was going through the mathematical of  structure of general theory of relativity while I was reading the Sokolnikoff's  Book on the Tensor analysis that Einstein assumes that the field of a large gravitational mass is such that the potential function gij   one gets after the contraction of Einstein tensor  Rij   =  0,  where  Rij  is the Ricci tensor. Actually there were -if I remember properly- more then 200 possibilities each of which  has the same  right to be selected but the one he selected later proven to be a simple relation involving the curvature tensor, and hence desirable one. (See: ibid footnote in p.276). 

Note: The first time I met the generalized relativity which was  in 1957 while I was reading tensor analysis just for curiosity  from  the book entitled as Absolute Calculus by Levi Civita,.  At that time I was not aware of the arbitrary mathematical structure of this theory. 

Dear Tarik, we have talked about Gen. Rel. with a lot of passion here:

https://www.researchgate.net/post/Can_somebody_solve_the_next_problem_by_using_only_general_relativity

while with less tension here is a discussion for the absense of grav. waves:

https://www.researchgate.net/post/What_if_gravitational_waves_will_never_be_found?_tpcectx=profile_questions

What I have understood about GR?

• General Relativity is one of the most certain ways to suffer without any result at the end of the day

But, here we talk for something that reminds Aether, although we must not mention that forbidden object (again due to another relativity theory, but for special relativity our friend Johan Prins has done an excellent job, look here:

https://www.researchgate.net/publication/265163606 )

So, the actual question is:

• Does Aether exist or not? (Its properties may not be what in 19th century was supposed to be...)

Book Updated: Einstein=Genius: But a genius sometimes blunders

Dear Demetris,  I thank you for pointing out above mentioned discussion sections took place RG platform. I went through quickly the first two RG discussions. Especially the negative comments made  by Dr.Crothers     on GR  were not surprised me since without consulting any body  solely with my own instinct and plus the deep expedience on  the mathematical structure of  nonlinear systems I have had great disappointment on GR theory as Einstein postulated without giving  any justification why he made that choice. If he would be faithful person I could understand if he would claimed that  'the Creator preferred to design the Universe and every thing in it with the simplicity   of mathematical physics''

I also congratulate you for showing great courage not following the main stream of scientific though without deliberation of their very basic foundations, which mostly rely on few hypothetical ad hoc arguments.  

 BEST REGARDS