Difference between particle horizon and cosmological event horizon?

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Discussion Overview

The discussion focuses on the differences between the particle horizon and the cosmological event horizon, exploring their definitions, implications, and the confusion surrounding these concepts within cosmology.

Discussion Character

  • Debate/contested

Main Points Raised

  • Some participants propose that the particle horizon represents the limit of what can be observed today, as it takes longer than the present age of the universe for light from beyond this horizon to reach us.
  • Others argue that the cosmological event horizon indicates the limit of what may ever be observed, regardless of how long one waits, and is determined by the universe's geometry and expansion history.
  • A participant requests further elaboration on the cosmological event horizon, indicating a desire for deeper understanding.
  • One participant expresses the opinion that discussions about horizons create more confusion than clarity, suggesting that the observable universe's surface of last scattering is the true observational limit.
  • This participant also mentions the potential for super-hubble fluctuations to leave imprints on the cosmic microwave background (CMB), though they note that this is debatable.
  • There is a suggestion that it is impossible to observe entities that may or may not have existed prior to recombination in a temporally bounded Big Bang universe.

Areas of Agreement / Disagreement

Participants express differing views on the clarity and implications of the particle and event horizons, indicating that multiple competing perspectives remain without consensus.

Contextual Notes

Some limitations include the dependence on definitions of horizons and the unresolved nature of certain claims regarding observational limits and the implications of super-hubble fluctuations.

touqra
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What is the difference between particle horizon and cosmological event horizon?
 
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touqra said:
What is the difference between particle horizon and cosmological event horizon?
The Particle Horizon is the limit of what we can see today, (it takes longer than the present age of the universe for light to reach us from beyond the PH), the Event Horizon is the limit of what we may ever see, even if we wait for ever. (the EH is determined by the geometry and expansion history of the universe)

Garth
 
Garth said:
the Event Horizon is the limit of what we may ever see, even if we wait for ever. (the EH is determined by the geometry and expansion history of the universe)

Garth

Could you elaborate further on the Cosmological EH?
 
The horizons thing creates more confusion than clarity, IMO. In our [observable] universe, the surface of last scattering is the observational limit - again IMO. Super-hubble fluctuations may have left trace imprints on the CMB - albeit that is debatable - but in a temporally bounded BB universe, it is impossible to observe entities that [may or may not have] existed prior to recombination.
 

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