Share Your Thoughts: An Idea to Consider

In summary, the conversation discusses the different solutions of Einstein's equation for describing an expanding universe, including FLRW solutions and Schwarzschild solutions. It is noted that at smaller scales, spacetime is better described by other solutions, and the expansion of the universe is only relevant at larger scales. There is also a mention of the expansion of massless particles and its effects on the electromagnetic spectrum.
  • #1
filegraphy
93
0
This really is just an idea, but I want to hear what you think.
 
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  • #2


The solutions of Einstein's equation that describe an expanding universe are the same ones that describe a universe in which matter is distributed homogeneously and isotropically. (FLRW solutions). The universe is only approximately homogeneous and isotropic at scales much larger than galaxies. At smaller scales, spacetime is much better described by other solutions. For example, near the sun, spacetime is approximately a Schwarzschild solution, in which there is no expansion.

Since Einstein's equation isn't linear, we can't just add these solutions to get the correct one, but I think we can expect the most accurate solution that describes spacetime near the sun to be a lot like Schwarzschild and a little bit like FLRW, with a local expansion that's non-zero, but many, many orders of magnitude smaller than the cosmological expansion (what the FLRW solution predicts).

So never mind elementary particles. Even galaxies (which contain hundreds of billions of stars) are too small for expansion to be relevant.
 
  • #3


In that is non-zero that can mean that the objects are expanding. Thanks it is more clear now.
 
  • #4


But if they are bound then I think the forces just pull the object back together.
 
  • #5


Hi, filegraphy.
Yes, for massless particles e.g. photon. The expansion of universe cause expansion of wave length of photon as Hubble discovered. I am not sure of it for particles with mass.
Regards.
 
  • #6


Is that what red shift is? When the photon wave is stretched out, causing it to have a lower frequency. This causing the waves in the electromagnetic spectrum to be moving towards the red side. Or am I mistaken? Thank you for your help also.
 

1. What is the purpose of "Share Your Thoughts: An Idea to Consider"?

The purpose of "Share Your Thoughts: An Idea to Consider" is to encourage individuals to share their unique ideas and perspectives on a specific topic or issue.

2. How can I participate in "Share Your Thoughts: An Idea to Consider"?

To participate, you can either submit your thoughts and ideas through a designated platform or share them through social media using a specific hashtag.

3. Is there a specific format or length requirement for submissions?

No, there is no specific format or length requirement for submissions. You can choose to write a short paragraph, a longer essay, or even create a visual representation of your idea.

4. Will my submission be published or shared publicly?

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5. Can I submit multiple ideas or only one?

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