Why galaxies are rushing apart

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in weinberg's first three minutes he wrote:
The galaxies are not rushing apart because of some mysterious force that is pushing them apart, just as the rising stone in our analogy is not being repelled by the earth. Rather, the galaxies are moving apart because they were thrown apart by some sort of explosion in the past.
I'm starting to regret reading this book. he came out with an updated edition in 1993 but it looks like he didn't correct his mistakes. it looks like he just put a small forward at the end of the book because clearly there are some things that were known in 93 but not in 79 that should have forced him to correct some passages. in any case dark energy was not known until 1998, so i just want to make sure that galaxies are rushing apart due to dark energy and that the above passage is wrong.
 

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  • #2
phinds
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in weinberg's first three minutes he wrote:

I'm starting to regret reading this book. he came out with an updated edition in 1993 but it looks like he didn't correct his mistakes. it looks like he just put a small forward at the end of the book because clearly there are some things that were known in 93 but not in 79 that should have forced him to correct some passages. in any case dark energy was not known until 1998, so i just want to make sure that galaxies are rushing apart due to dark energy and that the above passage is wrong.
Quite a bit of the book is outdated, as is the issue you are concerned about, and you are correct that his "updates" were inadequate, but it is still a book worth reading.

EDIT: and yes, in direct answer to your specific question, he didn't know about dark energy, which IS the name we give to WHATEVER it is that is causing the ACCELERATION of the expansion of the universe (but not the expansion itself). See:

www.phinds.com/balloonanalogy for a small amount of further discussion.
 
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No, dark energy is not causing the expansion if the universe. It's causing the acceleration of the universe. The concept of an expanding universe is an effect of general relativity, and has been well understood since Friedman proposed an expanding universe. In general relativity, distance is defined in terms of the metric. When we say the universe is expanding, we mean the metric is changing - the distance between galaxies is changing. If you held rulers in between every galaxy, you would find that, after time, these rulers no longer measured the full distance.

This effect of expansion is caused by the presence of any matter or energy in a particular space-time. This was Einstein's dilemma - he tried to introduce the cosmological constant to avoid this fact. But, you know how the story goes from there.

However, Weinberg's statement that galaxies were driven apart by an explosion is also incorrect.
 
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What I think the shape of the universe before the big bang was a few millions giant stars each star equals to a billion times of the size of earth .......
 
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phinds
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What I think the shape of the universe before the big bang was a few millions giant stars each star equals to a billion times of the size of earth .......
You really should not post nonsense on a serious physics forum. It doesn't go over well here.
 
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Drakkith
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