Expanding Universe: What We See & How We Know

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Discussion Overview

The discussion centers around the concept of the expanding universe, exploring how observations of distant stars and galaxies relate to our understanding of cosmic expansion. Participants delve into the implications of light travel time, the nature of the universe's edge, and the driving forces behind expansion, including the Big Bang and dark energy.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that observing distant stars means we are seeing them as they were in the past, raising questions about their current existence.
  • Others clarify that light years measure distance, not time, and that the light we see from stars reflects events that occurred long ago.
  • There is a discussion about whether the universe has an edge, with some arguing that current models suggest a flat and infinite universe.
  • Participants mention the expansion of the universe, noting that it is not only expanding but accelerating, potentially due to dark energy.
  • Some express confusion about what the universe is expanding into, with analogies drawn to the surface of a balloon or the Earth’s surface expanding without an external boundary.
  • Questions arise regarding the nature of the singularity at the Big Bang and the concept of "nothing" beyond the universe.
  • There are differing views on the implications of the Big Bang and whether the universe's expansion is a result of it or influenced by other factors.

Areas of Agreement / Disagreement

Participants generally agree that the universe is expanding and that light from distant objects represents past events. However, there are multiple competing views regarding the nature of the universe's edge, the implications of dark energy, and the interpretation of the Big Bang, leaving the discussion unresolved on these points.

Contextual Notes

Participants acknowledge limitations in understanding the universe's expansion, particularly regarding the nature of time before the Big Bang and the concept of "nothing." There is also a recognition that current models may evolve with new data.

  • #31
Thank you for taking all the time helping me too understand about the expansion. I was watching some videos on YouTube about the expansion of the universe. It was very interesting. It was saying that the outer most stars that are in the red shift that space around them could reach faster than the speed of light, and that they could soon get past the point of us being able to see them anymore. Are they too reach those speeds because of less gravity? Swimfit
 
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  • #32
Swimfit said:
Thank you for taking all the time helping me too understand about the expansion. I was watching some videos on YouTube about the expansion of the universe. It was very interesting. It was saying that the outer most stars that are in the red shift that space around them could reach faster than the speed of light, and that they could soon get past the point of us being able to see them anymore. Are they too reach those speeds because of less gravity? Swimfit

The "outermost stars" in the OBSERVABLE UNIVERSE are moving away from us at 3 times the speed of light because of the not-understood phenomonon we call "dark energy", which seems to be the same thing as the "cosmological constant" which causes the DIMENTIONS between not-gravitationally-bound systems to increase, and to increase more the farther apart they are.
 
  • #33
After I sent that last message the thought came to me dark energy. It's funny I always thought that nothing could travel faster than the speed of light. But that rule pertains to massive objects and space has no mass, so can go as fast it wants. Now does dark matter have mass? Or is that an unknown, or unmeasurable? God all this stuff fascinates me. Swimfit
 
  • #34
Swimfit said:
After I sent that last message the thought came to me dark energy. It's funny I always thought that nothing could travel faster than the speed of light. But that rule pertains to massive objects and space has no mass, so can go as fast it wants. Now does dark matter have mass? Or is that an unknown, or unmeasurable? God all this stuff fascinates me. Swimfit

Since dark matter is known exclusively through it's gravitational effects, and since gravitation implies the existence of mass, I'd guess that it does indeed have mass. But if it's a kind of mass which does not interact electromagnetically with ordinary mass, we'd have no way of detecting it other than gravitational effects.
 

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