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Universe expansion rate mystery deepens

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Sir Smoke aLot

That which we do not see it doesn't exist. Not so long ago belief was that Universe is only our galaxy and that every object on the sky was a star. But then we learned that some of those lights on the sky were actually other galaxies. I hope that some new advance will come relatively soon and maybe get us ahead as much as prior advances did.

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bison

The numbers obtained: 73, 67, and 69.8  km/sec/Mpc  aren't so very different. It could be that the average velocities of the sets of objects used by Hubble, Planck, and the Red Giants in distant galaxies survey honestly differ from one another, to this extent. If so,  these three could be averaged to give a figure of 69.8 km/sec/Mpc as the generalized rate of expansion of the universe.   

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AllPossible

I'm curious if that includes our galaxy or just the dark matter pushing apart galaxies from each other

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bison

Most galaxies separated by large distances  are detectably retreating from each other. This is due to the expansion of space started by the 'big bang'. Dark matter interacts gravitationally with the rest of the matter in the universe. It helps hold individual  galaxies together and contributes in a major way to the gravitational force that causes nearby galaxies to be attracted to each other.     

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pallidin

Perhaps it should be formally noted that both "dark energy" and "dark matter" are, currently, mathematical constructs ONLY.

There is no actual empirical evidence for the existence of either one, and it is my understanding that there are no currently possible experiments to validate these issues.

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bison

There is a good deal of evidence, of varied sorts, for dark matter. One of these is the way galaxies hold together and rotate, while their conventional matter is seen to be insufficient to explain this degree of gravitational attraction.  The excerpt from an article, linked below, explains this and other lines of evidence for dark matter:

https://en.wikipedia.org/wiki/Dark_matter#Observational_evidence

 

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Berwen

What if the star that they are measuring from is not travelling at the same rate as its neighbors? Would they not get different readings from each star?

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bison

They undoubtedly do get different figures of recession for each star or other celestial object they measure, even in cases where these would be about equal on the basis of the expanding universe alone. Since a single figure for the Hubble Constant is given by each survey, they can be assumed to have averaged the figures for many target objects in space. 

My suggestion was that even with such averaging, there may still be biases introduced by the selection of objects for the  groups of objects treated by each survey.  

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sci-nerd
On 7/18/2019 at 10:50 PM, bison said:

The numbers obtained: 73, 67, and 69.8  km/sec/Mpc  aren't so very different. It could be that the average velocities of the sets of objects used by Hubble, Planck, and the Red Giants in distant galaxies survey honestly differ from one another, to this extent. If so,  these three could be averaged to give a figure of 69.8 km/sec/Mpc as the generalized rate of expansion of the universe.   

It is actually much more serious than that. The experts are talking about a crisis, and a fundamental change of the ΛCDM theory

https://www.quantamagazine.org/cosmologists-debate-how-fast-the-universe-is-expanding-20190808/

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bison

Thanks for linking that informative article, sci-nerd. Judging by what is written there, there still seems to be considerable uncertainty about the reality of the discrepancy between early and current expansion values. The effects of confounding factors are not altogether clear. I note with interest that the range of current values of expansion is slightly greater than the difference between the mean of that range and the calculated values for early expansion of the universe.  As the article says-- tension or crisis -- its not yet clear. Further measurements in the near future may help settle this question.  

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sci-nerd
10 minutes ago, bison said:

Thanks for linking that informative article, sci-nerd. Judging by what is written there, there still seems to be considerable uncertainty about the reality of the discrepancy between early and current expansion values. The effects of confounding factors are not altogether clear. I note with interest that the range of current values of expansion is slightly greater than the difference between the mean of that range and the calculated values for early expansion of the universe.  As the article says-- tension or crisis -- its not yet clear. Further measurements in the near future may help settle this question.  

Yeah, we'll only need to wait a decade. It's like Ents talking :D

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spartan max2
Posted (edited)

I never understood how nonething is "expanding" into nonething 

Or does the expanding just mean that planets are moving in a direction outwords?

Edited by spartan max2
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sci-nerd
Posted (edited)
17 minutes ago, spartan max2 said:

I never understood how nonething is "expanding" into nonething 

Or does the expanding just mean that planets are moving in a direction outwords?

Some people imagine the universe as a thing they look at from the outside. But there is no outside, because the universe is everything.
So if we look at it the right way, from the inside, things are getting further and further apart, at a higher and higher speed.
And it is that "higher and higher speed" that this thread is about. Where does that speed come from??

Edited by sci-nerd
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spartan max2
6 minutes ago, sci-nerd said:

Some people imagine the universe as a thing they look at from the outside. But there is no outside, because the universe is everything.
So if we look at it the right way, from the inside, things are getting further and further apart, at a higher and higher speed.
And it is that "higher and higher speed" that this thread is about. Where does that speed come from??

If the universe is everything, and it's expanding, then what happens if someone was to get to the edge and step forward? Like would they hit a wall lol

It's incomprehensible . 

I hope my question makes sense. 

It seems like it would have to be expanding in to nonething and that their would have to be an endless amount of nonething to move into. 

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sci-nerd
1 minute ago, spartan max2 said:

If the universe is everything, and it's expanding, then what happens if someone was to get to the edge and step forward? Like would they hit a wall lol

It's incomprehensible . 

I hope my question makes sense. 

It seems like it would have to be expanding in to nonething and that their would have to be an endless amount of nonething to move into. 

That someone would be a part of the universe, and by stepping forward, be part of the expansion of 'everything'.

Our minds are not built to comprehend this stuff, so we invent concepts like 'nothing' or 'emptiness', but there isn't even emptiness beyond our universe.

I call the place "does not exist".

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bison

Space-time itself is expanding. There is no pre-existing space that we can see or reach, and into which the material universe can expand. It's as if we were living in a universe on the surface of an expanding sphere. Anywhere we can go is on the surface of that sphere. Away from or outside the surface of the sphere does not exist for us, as a part of our universe. 

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sci-nerd

Fun facts:

- The universe actually has a relative center, where the big bang started. But no matter where you are, in the universe, if you reversed time back to it, you would stay in the same place, and everything else would move closer to you.

- The observable universe is not the entire universe. Most distant galaxies are so far away, their light will not reach Earth while it exists.
The center of the observable universe is our sun.

- The fact, that the universe is expanding, proves the Big Bang Theory.

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lightly
Posted (edited)
32 minutes ago, sci-nerd said:

Fun facts:

- The universe actually has a relative center, where the big bang started. But no matter where you are, in the universe, if you reversed time back to it, you would stay in the same place, and everything else would move closer to you.

- The observable universe is not the entire universe. Most distant galaxies are so far away, their light will not reach Earth while it exists.
The center of the observable universe is our sun.

- The fact, that the universe is expanding, proves the Big Bang Theory.

The sun is the center of our solar system.  The center of my observable universe is Me .  I am at the center of my observable universe?  I guess we could say..the earth is at the center of our observable universe?

Q 1....Space is expanding...does that mean it is becoming less dense?  (If the amount of space is finite)  OR.....

does the expansion/inflation create new and identical space ??   ( which would indicate an infinite "amount" of space)

Q 2....is all space identical in nature?   ( whether it is interstellar space..Or..the space within the area of our very atoms )????

... ..  ..  ..  ..  ..

              .....the space within our solar system is expanding at the same rate as the space outside our solar system...but local forces keep our system together.  the space in your living room is expanding at that same rate as well.

Edited by lightly

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lightly

It's been said that everywhere is the Center of the universe.   If that is somehow actually true...then space is the greatest illusion Ever!  I know how crazy it sounds to question "space".   .   It's obvious.....isn't it?   ;

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sci-nerd
11 minutes ago, lightly said:

I guess we could say..the earth is at the center of our observable universe?

No, because Earth is changing position all the time.
In our observable universe, the sun is the only relatively stationary object. From our POV, it stays the same place always, unlike everything else.

13 minutes ago, lightly said:

Q 1....Space is expanding...does that mean it is becoming less dense?

Yes! The density of spacetime/everything-that-exists is decreasing.

17 minutes ago, lightly said:

Q 2....is all space identical in nature?   ( whether it is interstellar space..Or..the space within the area of our very atoms )????

That is very much a question of which theory you lean against. In QFT, spacetime consistent of Planck units. Those units can hold a number of values, like matter or gravity. Even in the void inside atoms.

12 minutes ago, lightly said:

It's been said that everywhere is the Center of the universe.

Only relatively. There is a true place of the start of expansion, but we can never know where, as long as most of the universe is invisible to us.

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Essan
ust remember that you're standing on a planet that's evolving
And revolving at 900 miles an hour.
It's orbiting at 19 miles a second, so it's reckoned,
The sun that is the source of all our power.

Now the sun, and you and me, and all the stars that we can see,
Are moving at a million miles a day,
In the outer spiral arm, at 40, 000 miles an hour,
Of a galaxy we call the Milky Way.
 
Our galaxy itself contains a hundred billion stars;
It's a hundred thousand light-years side to side;
It bulges in the middle sixteen thousand light-years thick,
But out by us it's just three thousand light-years wide.
 
We're thirty thousand light-years from Galactic Central Point,
We go 'round every two hundred million years;
And our galaxy itself is one of millions of billions
In this amazing and expanding universe.
 
Our universe itself keeps on expanding and expanding,
In all of the directions it can whiz;
As fast as it can go, at the speed of light, you know,
Twelve million miles a minute and that's the fastest speed there is.
 
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth;
And pray that there's intelligent life somewhere out in space,
'Cause there's b***** all down here on Earth!

(may not be entirely correct ;) But who cares?)

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SmartAZ

Let's think this through: 
"Big Bang" is implied by 
"Receding Galaxies", which are implied by 
"Doppler Effect", which is caused by 
"Motion Away From Us", which is assumed from 
"Red Shifted Light" 

So we have this remarkable train of logic all based on a single phenomenon and an assumption. If that assumption is wrong then most of what we think we know about the universe ain't so. Well, Doppler effect is not the only cause of red shift. So there you are: guesses offered in lieu of actual science.

"Redshift is A Shaky Measuring Rod"
http://www.science-frontiers.com/sf138/sf138p03.htm

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sci-nerd
8 minutes ago, SmartAZ said:

Let's think this through: 
"Big Bang" is implied by 
"Receding Galaxies", which are implied by 
"Doppler Effect", which is caused by 
"Motion Away From Us", which is assumed from 
"Red Shifted Light" 

So we have this remarkable train of logic all based on a single phenomenon and an assumption. If that assumption is wrong then most of what we think we know about the universe ain't so. Well, Doppler effect is not the only cause of red shift. So there you are: guesses offered in lieu of actual science.

"Redshift is A Shaky Measuring Rod"
http://www.science-frontiers.com/sf138/sf138p03.htm

The expansion has actually been measured by eight methods, all agreeing about expansion, but not on the speed:

HubbleConstant_560B.jpg

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SmartAZ
13 hours ago, sci-nerd said:

The expansion has actually been measured by eight methods, all agreeing about expansion, but not on the speed:

If you look at something from two positions it appears to shift by some angle depending an how far away it is and the length of your baseline. If you look from opposite sides of the Earth's orbit, that is the longest baseline we have, and accurate measurements can be made out to about 3200 light years. Beyond that we are guessing. Highly scientific guessing, but guessing all the same. 

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