Expanding universe and Conservation of energy.

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Discussion Overview

The discussion centers around the implications of the expanding universe on the conservation of energy, particularly regarding the fate of light energy at the "edge" of the universe. Participants explore theoretical concepts, potential boundaries of the universe, and the relationship between expansion rates and energy conservation.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants assert that if the universe is expanding, it must have an edge where energy from light would go when it reaches this boundary.
  • Others challenge the notion of a physical boundary to the observable universe, suggesting it implies a preferred reference frame and a center.
  • There are conflicting views on the expansion rate of the universe, with some arguing that galaxies can recede faster than the speed of light, while others seek clarification on the frames of reference involved.
  • Some participants propose that galaxies outside the observable universe belong to a different system and thus do not affect the conservation of energy law.
  • A later reply questions whether energy is conserved in the universe, referencing ongoing debates in other threads.

Areas of Agreement / Disagreement

Participants express disagreement on the existence of a boundary to the universe and the implications of expansion rates on energy conservation. There is no consensus on these points, and the discussion remains unresolved.

Contextual Notes

Participants note the complexity of discussing recession speeds and frames of reference, as well as the potential semantic issues surrounding the definitions of systems in relation to the observable universe.

Alistair
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It is accepted that the universe is expanding yes? and it is also expanding at a slower rate than the speed of light. therefore what happens when light hits "the edge of the universe"? where does this energy go? and i know that the universe is "everything" but if the universe is 'expanding' then it must have an edge to it. a point at which the universe 'ends' and a point where 'nothing' starts. and the conservation of energy LAW states that 'energy in a closed system cannot be created or destroyed,it can only be transformed.' so back to my question. where does the energy from the light that hits this 'barrier' go?
 
Space news on Phys.org
John Baez wrote a brief article on this subject:

http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html"
 
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I think it is illogical to apply the concept of a physical 'boundary' to the observable universe. This implies a preferred reference frame that would also insist the universe also has a 'center'.
 
Alistair said:
It is accepted that the universe is expanding yes? and it is also expanding at a slower rate than the speed of light. therefore what happens when light hits "the edge of the universe"? where does this energy go?...
What did you mean by "and it is also expanding at a slower rate than the speed of light"? I think it is accepted that the apparent recession speed of galaxies outside of our observable universe is larger than c.
 
Oh gosh, here we go again.. When you say 'moving faster than the speed of light', identify the frames you are talking about.
 
Jorrie said:
What did you mean by "and it is also expanding at a slower rate than the speed of light"? I think it is accepted that the apparent recession speed of galaxies is larger than c.

I would like to point out that "galaxies outside of our observable universe" would be part of another system wouldn't they? and thus do not factor into the conservation of energy law.
 
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Haelfix said:
Oh gosh, here we go again.. When you say 'moving faster than the speed of light', identify the frames you are talking about.
Not clear which statement from which post you refer to, but if it goes about my: "... apparent recession speed of galaxies ...", then the frame is obvious, is it not?

Granted, redshift and recession speed outside of our observable universe may be meaningless, but the context is Alistair's statement: "It is accepted that the universe is expanding yes? And it is also expanding at a slower rate than the speed of light…" I wanted the poster to state what this means.
 
Alistair said:
I would like to point out that "galaxies outside of our observable universe" would be part of another system wouldn't they? and thus do not factor into the conservation of energy law.
I would not quite call regions outside of our observable universe "part of another system"! The flat LambdaCDM model assumes that the universe is infinite in size. In practice it must be at least many times larger than what we can observe.

In any case, we may be wasting time on semantics. The real issue is whether energy is conserved in the universe. This has been debated in other threads and ST has given you a link about it above.
 

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