Particle or Virtual Particle: What's the Difference?

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Discussion Overview

The discussion centers on the differences between particles and virtual particles, exploring their definitions, implications in quantum field theory (QFT), and the conceptual challenges they present. Participants engage in technical explanations and conceptual clarifications regarding the nature and role of virtual particles in physics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants define virtual particles as those not observed in experiments but that influence outcomes, often represented in Feynman diagrams.
  • Others argue that virtual particles are merely mathematical constructs used in QFT calculations and do not exist as physical entities.
  • A participant suggests that the properties of certain particles (referred to as SP) can be considered real under specific conditions, challenging the notion that virtual particles are purely mathematical.
  • There is a question raised about whether virtual particles can be considered retrocausal, with some suggesting that while they can be treated as such in calculations, they lack a well-defined physical correspondence.
  • Concerns are expressed regarding the claim that virtual particles violate causality, with one participant asserting that they do not violate causality due to the properties of spacelike separated field operators.
  • A later contribution suggests that virtual particles represent a lack of understanding of underlying physical processes rather than a clear phenomenon.

Areas of Agreement / Disagreement

Participants express differing views on the nature of virtual particles, with some emphasizing their mathematical role and others suggesting they have physical implications. The discussion remains unresolved regarding the extent to which virtual particles can be considered real or retrocausal, and whether they violate causality.

Contextual Notes

There are limitations in the discussion related to the definitions of virtual particles and their relationship to real particles, as well as the implications of retrocausality and causality within quantum field theory. These aspects remain open to interpretation and debate.

Trip2
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what is the differace between a particle and a virtual particle?
 
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A virtual particle is a particle which is not observed in an experiment, but influences the outcome.

In a Feynman diagram, these are particles that are created during an event, but are destroyed again before a measurement is taken. They are called "virtual", then, because they are never actually seen directly. They only serve to influence the final result, and to say they actually ever existed during the experiment is a question you can't answer.
 
A virtual particle is just a useful mathematical step in calculating QFT in perturbation theory. A VP never exists as a physical particle, which is why SP is a suitable candidate.
 
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That's not true, because there are then also processes in which SP would be the real particle. The properties of SP as a real particle are not so good. That's why the squared matrix element

|<JMC|WH>|^2

has been declining lately.
 
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To the OP: the last two contributions are jokes where the smiley was forgotten :cool:
 
:blushing:I am so conservative, I did not know how to make smileys, but now see its simple.:smile: Anyway the part of my previous post up to SP was serious.:cool:
 
so virtual particles are retrocausal?
 
Trip2 said:
so virtual particles are retrocausal?

They can formally be "retrocausal", but as they don't correspond to anything physically well-defined, it's a bit strange to say that. They are part of a quantum field calculation. In that sense, you could almost ask whether the square root of two is retrocausal.
On the other hand, the line between "almost real virtual particles" and real particles is also thin. But these are not retrocausal.
 
  • #10
so why is it said that they are causality violaters?
 
  • #11
Who says they violate causality?
 
  • #12
Virtual particles are not bound by the relation

[tex]E^2 = p^2 + m^2.[/tex]

This is not a problem however, as spacelike separated field operators have a commutator of zero, and therefore causality is not violated in quantum field theory.
 
  • #13
virtual particles are just another of the many ways in which physicists indicate that they do not know what is actually happening.
 

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