Could it be possible that gravity is the reason why the universe is expanding?

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Discussion Overview

The discussion explores the relationship between gravity and the expansion of the universe, questioning whether gravity could be a driving force behind this phenomenon. Participants examine historical perspectives, theoretical frameworks, and implications of General Relativity (GR) in relation to cosmic expansion.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant proposes that gravity waves from dying stars could contribute to the universe's expansion, suggesting a mechanism where these waves drag celestial objects as they pass.
  • Another participant counters that such a mechanism would disrupt galaxies, noting that expansion does not occur on galactic scales and attributing the universe's expansion to momentum and dark energy.
  • Several participants discuss the historical context of General Relativity (GR) and the cosmological constant, indicating that GR was initially seen as complete but later modified with the introduction of Hubble's observations of redshift and expansion.
  • Some participants argue that GR with or without a cosmological constant can be compatible with Hubble expansion, but they also highlight that the specifics of the observed expansion in our universe may require a cosmological constant or an alternative explanation.
  • One participant emphasizes that cosmic acceleration necessitates a cosmological constant or a similar form of dark energy, while also reiterating the compatibility of GR without a cosmological constant with Hubble expansion.

Areas of Agreement / Disagreement

Participants express differing views on the role of gravity in cosmic expansion, with some supporting the idea of gravity waves influencing expansion and others rejecting this notion in favor of momentum and dark energy explanations. There is no consensus on the mechanisms behind the universe's expansion or the implications of GR.

Contextual Notes

The discussion touches on complex theoretical concepts, including the implications of GR, the cosmological constant, and the nature of cosmic acceleration, which may not be fully resolved or agreed upon among participants.

brianthewhitie7
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Could it be possible that gravity is the reason why the universe is expanding?

When stars die and some create gravity waves, those waves are expanding at/around the speed of light. The waves then are traveling faster than a planets'/suns' gravity. Therefore the wave would pull in until it passed a planet/sun then it would end up dragging the objects as it passed. Though the gravity is weak; enough dying stars could possibly create the expanding the universe.

Does this idea sound even plausible? If it does not, then why?
 
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This would tear galaxies apart when the stars within them died. We observe that expansion does not occur on the scales of galaxies. In any case, there is no mystery as to why the Universe expands, it is akin to momentum, once the Universe begins to expand then just like a ball thrown it the air it continues to do so until the forces slowing in down (gravity) succeed in reversing the expansion, or if there is not enough material in the Universe then the expansion never slows to a stop, or dark energy (that accelerates the expansion) takes over and then continues to drive an increase in the rate of expansion forever.

The mystery is why the expansion began in the first place, with inflation. However if we accept that for whatever reason that initial kick occurred, then the subsequent expansion after that impulse just follows from the conservation of momentum.
 
Could it be possible that gravity is the reason why the universe is expanding?

Historically GRT (General Relativity Theory) was essentially complete, but had a cosmological constant. Then came Hubble and his redshifting of galaxies, intrepreted as expansion of universe. So the cosmological constant was dropped. Thus Hubble expansion is not part of GRT. In GRT one can have affine parameterization along a null geodesic, with a finite velocity of a photon. Yet the Hubble expansion (also a local description) can have superluminal stretching of the manifold (continuum i.e. inbetweeness). So pseudo-Riemannian spacetime manifold has a finite velocity for photon; while Hubble expansion of overall manifold, as well as for a local patch, can have a superluminal stretching. This always sounds somewhat strange (a koan), that the same manifold can have two such apparently disparate conceptual descriptions.
 
zankaon said:
Historically GRT (General Relativity Theory) was essentially complete, but had a cosmological constant. Then came Hubble and his redshifting of galaxies, intrepreted as expansion of universe. So the cosmological constant was dropped. Thus Hubble expansion is not part of GRT.
GR with a cosmological constant is fully compatible with the Hubble expansion.
 
MeJennifer said:
GR with a cosmological constant is fully compatible with the Hubble expansion.

GR without a cosmological constant is also fully consistent/compatible with the Hubble expansion.

Garth
 
Garth said:
GR without a cosmological constant is also fully consistent/compatible with the Hubble expansion.

Garth

Just not the particulars of the expansion observed in the Universe we happen to live in. In our Universe there is either a cosmological constant (or something like it) or GR is wrong.
 
Wallace said:
Just not the particulars of the expansion observed in the Universe we happen to live in. In our Universe there is either a cosmological constant (or something like it) or GR is wrong.
The point I was making was that "GR without a cosmological constant is also fully consistent/compatible with the Hubble expansion."

It is cosmic acceleration that requires a cosmological constant or some similar form of DE.

I tend to answer assuming others have read the preceding posts.

Garth
 
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