The True (but modest) Heroes of Microworld
    By Vladimir Kalitvia... | December 4th 2013 08:18 AM | 2 comments | Print | E-mail | Track Comments
    About Vladimir

    Born in 1958 in Kharkov, USSR. Graduated from Kharkov State University in 1981 with major in Theoretical Nuclear Physics. Discovered positive charge...

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    I'm speaking of bare particles. "Heroes" is maybe too pathetic, but blocks or "bricks" would be OK since everything is made of them despite their being non-observable. Why are they non-observable? Because they are non-interacting particles or particles "before interaction". Inaccessible, for short.

    Let us take QED - the first QFT Nobel prises were given for. Its Lagrangian is the following:

    It is relativistic and gauge-invariant because the bare electrons, positrons, and photons are such. Parameters  and are bare electron mass and charge and the term  is how bare particles interact. Of course, bare particles have spin and other quantum numbers.

    You may wonder how do we physicists know all that if the bare particles are non-observable (and why do they interact if they are non-interacting particles)?

    Good questions. Very intelligent! The answer is - due to our physical insights. You know, insight is the ability to see the invisible, to penetrate mentally into the unknown, to figure out everything correctly from small, rare, and distorted pieces of a whole picture. Factually we, from long distances (from low-energy experiments with physical particles), penetrated to the end - to the point  where bare particles live. Thus we insightful nailed the bare particle properties and their interaction laws correctly despite their hiding from us.

    And yes, the bare non-interacting particles do interact and even self-interact. It is they who permanently do this hard work. At a first, naive, glance these statements are inconsistent, but no. It is a kind of duality in physics. This duality is not much advertised because the bare particles are really modest bricks.


    You write: "and why do they interact if they are non-interacting particles"

    First, it is quantum FIELD theory. And the fields are very clearly interacting, since there is a coupling right there in the Lagrangian. I don't understand why you keep saying they are non-interacting.

    The particles are then excitations of these fields, and yes due to interactions the particles as seen in experiments are "dressed" by the interacting terms and not "bare".


    You write: "the bare non-interacting particles do interact ... At a first, naive, glance these statements are inconsistent, but no. It is a kind of duality in physics."

    No, those statements are inconsistent. Non-interacting particles, by definition, do not interact. There is no mystical duality here, you are just making confusing statements. It is not clear what you are trying to convey with this article.

    Vladimir Kalitvianski
    "I don't understand why you keep saying they are non-interacting."

    Isn't it a definition of a bare particle? I just give it here, I invent nothing in this respect. And you yourself distinguish "dressed" particles from "bare" ones by taking into account interaction terms.

    So there are particles without interaction (bare particles with certain properties) whose interaction makes real particles. This is a mainstream doctrine, isn't it? I am not guilty if it is confusing, I myself do not like this inconsistency and I am conveying here my disappointment with it.