What Defines the Identity of Elementary Particles in Physics?

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Discussion Overview

The discussion revolves around the concept of identity in elementary particles within the framework of physics, particularly focusing on how particles are classified, their indistinguishable nature, and the implications of quantum states. It touches on theoretical aspects, including the graviton and approaches like string theory and loop quantum gravity.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that while elementary particles like electrons are identical in their fundamental properties, they can be distinguished by their quantum states, which are probabilistic in nature.
  • One participant questions how particles can be identified without knowledge of their quantum states and expresses concern about distinguishing true identities from false identities, particularly in the context of the graviton.
  • Another participant asserts that the same particles share the same probability function, suggesting a link between identity and quantum states.
  • Concerns are raised about the graviton, which is theorized to have zero mass, zero charge, and spin 2, leading to questions about how such a particle can be detected given its properties.
  • One participant references string theory, suggesting it may provide insights into the graviton's existence despite its seemingly negligible properties, emphasizing that these zeros carry information relevant to experimental detection.
  • Another participant contrasts string theory's approach of moving from quantum mechanics to general relativity with loop quantum gravity's reverse approach, discussing the implications of reaching a state of perfect symmetry and infinite entropy.

Areas of Agreement / Disagreement

Participants express a range of views on the nature of particle identity and the challenges in identifying particles like the graviton. There is no consensus on how to resolve the questions raised about true versus false identities of particles or the implications of their properties.

Contextual Notes

Limitations include the dependence on theoretical frameworks like string theory and loop quantum gravity, as well as unresolved questions regarding the experimental detection of particles with minimal properties.

Antonio Lao
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What is Identity in Physics ?

The universe is made of varieties of elementary particles. Physicists classify these into fermions and bosons. Modern cosmology can even give the ratios of number of particles such as the ratio of number of protons and photons in the universe.

Quantum mechanics tells us that an electron in the universe is identical to every other electron. They have exactly the same electric chage, same rest-mass, exactly the same responses to the interaction of the weak and strong force, and the same total spin. All other particles are also identical to these distinctive properties.

But what can distinguish two electrons is their quamtum states. The quantum state is a probability. And there are many kinds of probability. The probability of being in a particular location of spacetime. The probability of the spin pointing in a particular direction. And the probability of having a particular velocity and energy.
 
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Was that a statement or a question?
 
Gza said:
Was that a statement or a question?

Sorry. I leftout the key question for this thread. Thanks for noticing the problem. The question is without knowing the quantum states (probability) how can same species of particles be identified?

And given some states, how can one be very sure that it's the true identity and not some false identities of other particles?
 
the same particles have the same probability function.
 
Should have known there is simple answer to unfounded complicated question. Thanks. But still my question about true identity and false identity would not go away. This has to do with the search for the elusive graviton.

Theory says that graviton has zero mass, zero charge, spin 2 , it only interact with itself and other gravitons, it always travel at the speed of light in vacuum but yet their quantum state is also zero. How can a particle with almost all its properties zero be found?
 
Theory says that graviton has zero mass, zero charge, spin 2 , it only interact with itself and other gravitons, it always travel at the speed of light in vacuum but yet their quantum state is also zero. How can a particle with almost all its properties zero be found?


I think string theory has some answers from the topical study I've done on the subject. It's supposed to predict a particle of zero mass, zero charge, and spin 2, better known to its friends as the graviton. So the fact that many of the properties are zero doesn't really matter when it comes to finding the particle. The fact that these properties are zero is information in itself. The only problem where all these zeros will manifest themselves is in actual experiment, to experimentally determine its existence.
 
The approach of string theory is from the small (qunatum mechanics) to the large (general relativity). The approach of loop quantum gravity is from the large to the small. The arrival of both approaches is at a state of perfect symmetry which is a state of zero information content and a state of infinite entropy.
 

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