How Does the Particle Horizon Expand Beyond the Age of the Universe?

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Discussion Overview

The discussion revolves around the concept of the particle horizon in cosmology, particularly how it expands beyond the age of the universe. Participants explore implications of detecting distant objects and the philosophical considerations surrounding the Big Bang model and the nature of the universe.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants note that the age of the universe is 13.7 billion years, while the particle horizon is about 47 billion light-years, suggesting that early light traveled differently due to the universe's expansion.
  • One participant questions whether the age of the universe would need to be revised if a source were detected 100 billion light-years away, proposing that it could either indicate a misunderstanding of cosmology or a misinterpretation of distance measurements.
  • Another participant argues that if something were detected at such a distance, it would not imply the existence of another universe, as anything observable must exist within our universe.
  • Conversely, a different viewpoint suggests that while detectable objects exist in our universe, they may not necessarily originate from our Big Bang event, opening the door to the possibility of multiple events in nature.
  • A participant challenges the understanding of the particle horizon, suggesting that if one could see beyond the current boundary, the observable universe could extend infinitely, raising questions about the implications for inflationary models.

Areas of Agreement / Disagreement

Participants express differing views on the implications of detecting distant objects and the nature of the universe, with no consensus reached on whether the Big Bang model could accommodate such findings or the philosophical implications of multiple events.

Contextual Notes

The discussion includes assumptions about cosmological models and the interpretation of distance measurements, which remain unresolved. The implications of detecting objects beyond the current particle horizon are speculative and depend on the definitions and frameworks used in cosmology.

Chronos
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I was thinking about posting this in the cosmology forum, but, concluded the more philosophically inclined souls would have more fun with it:

http://www.arxiv.org/abs/astro-ph/0602280
Issues in the Philosophy of Cosmology

A thought provoking paper, IMHO.
 
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Chronos said:
I was thinking about posting this in the cosmology forum, but, concluded the more philosophically inclined souls would have more fun with it:

http://www.arxiv.org/abs/astro-ph/0602280
Issues in the Philosophy of Cosmology

A thought provoking paper, IMHO.

Indeed thought provoking. The statement that the Universe must be older than the oldest star was interesting. I was wondering if this implies that if, in the future, using more powerful space telescopes, we should locate something more distant than, say 20 billion light-years out, would we then say the Big Bang model was wrong or just change the variable and say the Universe is not 13.7 billion years old, it is now 20+ billion years old.
 
Last edited:
The age of the universe is 13.7 billion years. However, the particle horizon, the greatest distance we can theoretically see, is not 13.7 billion light-years, but instead about 47 billion light-years. The universe was not always as big as it is today, so early light did not take as long to cross it as it would today.

- Warren
 
chroot said:
The age of the universe is 13.7 billion years. However, the particle horizon, the greatest distance we can theoretically see, is not 13.7 billion light-years, but instead about 47 billion light-years. The universe was not always as big as it is today, so early light did not take as long to cross it as it would today.

- Warren

Thank you for the response. To ask the question another way: If an energy source should be detected 100 billion light years away, would the Big Bang theory require that the age of the Universe be increased to 100+ billion years or would the energy source be thought of as originating in another universe (a different big bang universe)? Or is the question so unreasonable to even consider in an abstract mode? (I realize that the probability of detecting this speculative energy source would be extremely small, but 'what if'?)
 
If we detected something 100 billion light-years away, two things are possible:

1) Our understanding of cosmology is entirely wrong, and the universe is much older than previously thought.

2) Our understanding of cosmological distance indicators is wrong, and the objects are not really 100 billion light-years away.

Keep in mind that our measurements of distances are themselves based on a model of cosmological expansion, which could be wrong.

Either way, there's no "other universe" involved because, by definition, anything we can see exists in this universe.

- Warren
 
chroot said:
Either way, there's no "other universe" involved because, by definition, anything we can see exists in this universe.

- Warren

I agree that anything we can detect exists in this universe, but it does not necessarily mean that it originated in our Big Bang event. I have no problem with 'science' being limited to one Big Bang event, but philosophically I can see no reason that if nature produced one event we should not expect to find more than one. In the cosmology section of the science department I would not suggest such a thing, but I would hope that in the philosophy department it is OK.
 
chroot said:
The age of the universe is 13.7 billion years. However, the particle horizon, the greatest distance we can theoretically see, is not 13.7 billion light-years, but instead about 47 billion light-years. The universe was not always as big as it is today, so early light did not take as long to cross it as it would today. Warren
Hi Warren,
You failed to bring attention to a very simple fact. Your boundary is set via the phrase, "the greatest distance we can theoretically see". By the common theory, that boundary occurs when light begins to propagate as an independent entity (I'll let others clarify that statement). The issue you should have raised to sd01g is the fact that the "Big Bang" starts with a point universe and that, if we could see through that impenetrable boundary which light cannot penetrate (which of course we can, in our minds eye), the boundary to which we could see would recede to infinity. :biggrin:

Personally, I think there is a lot of confusion about that issue and it bears directly on the inflation issues often talked about. That is to say, a layout of the universe presuming special relativity is sufficient is logically inconsistent at such distances.

Have fun -- Dick
 

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