How can galaxies exist with the expansion of space?

[Lazarus]

I have seen comments that galaxies should not exist with the expansion of space. I cornered some Cosmology instructors at Arizona State University and asked the this question: "Since photons expand because of the expansion of space, galaxies separate because of it, two stars in different galaxies separate BUT two stars in the same galaxies do NOT separate. How can that be?"

 

The only answer I could get was that galaxies just hang together. I even mentioned the analogy of pennies on a balloon that is very weak logic. I said if the pennies were painted on the balloon the result would be very different. After a few iterations of the discussion I just said thank you and left disappointed.

 

I would like to hear a believable explanation.

[zapatos]

The expansion of space is weaker than gravity on the scale of galaxy clusters and smaller. That is why galaxy clusters will expand away from each other, but galaxies within a cluster, or stars within a galaxy, will remain bound.

[Lazarus]

Zapatos,

 

Thank you for the reply.

 

If gravity is holding the stars to the center of the galaxy at the present distance from the star to the center of the galaxy the increase in the distance weakens the force of the gravity. I don't feel that made a strong case for the galaxy taking exception to the expansion of space. Photons seem to 'hold together" pretty well but still are stretched by the expansion of space.

[beefpatty]

Zapatos,

 

Thank you for the reply.

 

If gravity is holding the stars to the center of the galaxy at the present distance from the star to the center of the galaxy the increase in the distance weakens the force of the gravity. I don't feel that made a strong case for the galaxy taking exception to the expansion of space. Photons seem to 'hold together" pretty well but still are stretched by the expansion of space.

 

There is no increase in distance since gravity is overpowering the expansion. If the expansion could overcome the force of gravity, then you would see an increase in distance and therefore the effects of gravity would become weaker as it expanded.

 

Photons are quite different, in that they are both massless and fundamental, meaning there is no internal structure binding them together, such as quarks bound via the strong force to create protons, neutrons, etc.

[Bill Angel]

Some cosmologists have speculated that ultimately the accelerating expansion of the universe will rip apart all matter.

See the section in this article about "The Big Rip"

http://hubblesite.org/hubble_discoveries/dark_energy/de-fate_of_the_universe.php

Edited February 3, 2013 by Bill Angel

[ACG52]

The force of expansion is less than the attractive force of gravity below 200 million light years. Galaxies which are 200 million lys and closer are gravitationally bound

[Lazarus]

ACG52,

 

If the force of gravity is equal to the space expansion at about 200 million light years and stars orbit the center of the galaxy then anything closer will fail to orbit and be sucked into tthe center. The contention that space is expanding but galaxies are exempt is an extraordinary claim and needs a least ordinary proof. The ball is still in your court.

[zapatos]

If the force of gravity is equal to the space expansion at about 200 million light years and stars orbit the center of the galaxy then anything closer will fail to orbit and be sucked into tthe center.

It will? Hmm. That seems to be at odds with observation and known physics. Can I have a citation please?

The contention that space is expanding but galaxies are exempt is an extraordinary claim and needs a least ordinary proof. The ball is still in your court.

It is not an extraordinary claim. It is based simply on observation. I'd say the ball is in your court to find some kind of evidence that that gravity and expansion do not happen as observed.

[ACG52]

ACG52,

 

If the force of gravity is equal to the space expansion at about 200 million light years and stars orbit the center of the galaxy then anything closer will fail to orbit and be sucked into tthe center. The contention that space is expanding but galaxies are exempt is an extraordinary claim and needs a least ordinary proof. The ball is still in your court.

Why would anything 'fail to orbit'? Does the earth 'fail to orbit' the sun? Cosmological expansion has nothing to do with galactic orbits.

 

Galaxies are not 'exempt', they are gravitationally bound. As far as evidence goes, we have observations. Within our local galactic supergroup, there is no recession between galaxies. Outside the supergoup, at about 200 million lys, we see recession.

[Lazarus]

AG52 & ZAPATOS

 

Of course "failing to orbit" doesn't match observations. That is why there is a question.

 

Do you agree that although the force of gravity decreases with distance, the effect of

space expansion increases with distance?

[zapatos]

No. The effect of gravity decreases as the distance between objects increase. The effect of space expansion remains constant as the distance between two objects increases. The rate of space expansion has changed over time though.

 

Note that gravity emanates from mass, but expansion emanates from space itself.

Edited February 3, 2013 by zapatos

[ACG52]

 

Do you agree that although the force of gravity decreases with distance, the effect of

space expansion increases with distance?

 

The rate of expansion increases with distance because it is a scaling factor. The effect does not increase. Gravity is stronger than expansion at distances of less than 200 million lys. That's what observation shows us.

[Lazarus]

It is very nice to have some feedback from knowledgeable individuals. I appreciate it immensely.

 

Let me try to explain what I meant by the effect of space expansion increases with distance.

 

I would like to push Mars to 186 million miles from the Sun and fatten it to match the mass of earth to make the arithmetic simpler for me. Then use the Sun, Earth and Mars for examples. Even though I majored in mathematics a million years ago, now I have to use a calculator to add two and two so anything that helps is good.

 

The picture:

 

!

!

!

! S 1 E 1 M 2
Time 1 ! x.................................y..............................z Space
!
!
!
!
! S 1 E 1 M
Time 0 ! x...............y................z Space
------------!------------------------------------------------------------------
! Distance
!

 

At time zero the earth is orbiting with gravity and space expansion in balance.

 

The time scale is such that from T0 to T1 space has doubled.

 

In Newtonian space the gravitational force is proportional to g divided by r squared.

 

In the expanding space model gravity is Newtonian gravity plus the additional
amount needed to compensate for the expansion.

Say g' = g + a. a is the acceleration needed to move Earth enough to match the expansion.

 

So the force g' on Earth is proportional to (g +a) / r*r.

 

However, the force required to hold Mars in place is (g + 2a) / r*r.

 

Which implies that g' is insufficient to hold Mars in place.

 

Is this wrong?

[ACG52]

 

In the expanding space model gravity is Newtonian gravity plus the additional

amount needed to compensate for the expansion.

 

 

There is no need for any additional gravity. The force of expansion is far too weak and gravity, without any additional force, completely overwhelms expansion..

 

 

Say g' = g + a. a is the acceleration needed to move Earth enough to match the expansion

 

The force of expansion does not balance gravity. Expansion is so small that it doesn't even play any part on distances smaller tham 200 million lys.

[Lazarus]

Even an infintesimal force will change an orbit.

 

The same rules should apply across the universe so the expansion would be there whether one mile or 250 million light years. The effect should be the similar with stars 150 or 250 million light years apart.

 

If this examplle doesn't work for you, please post a link or something that gives a logical explanation of the reason that galaxies do not expand while the space in which they reside is expanding. I have not been able to find anythig but generalizations of the problem.

 

Thanks again for taking the time to reply.

[Airbrush]

Lazarus, your questions don't make sense. I don't know what you are talking about. Your question has been answered redundantly. Are you just trying to be difficult? I have no problem with the explanations given above by ACG & Zapatos, but your questions and speculations seem baseless. You want someone to draw you a map to a book about cosmology?

Edited February 6, 2013 by Airbrush

[ACG52]

Even an infintesimal force will change an orbit.

 

The same rules should apply across the universe so the expansion would be there whether one mile or 250 million light years. The effect should be the similar with stars 150 or 250 million light years apart.

 

If this examplle doesn't work for you, please post a link or something that gives a logical explanation of the reason that galaxies do not expand while the space in which they reside is expanding. I have not been able to find anythig but generalizations of the problem.

 

Thanks again for taking the time to reply.

Start off with this.

 

http://en.wikipedia.org/wiki/Metric_expansion_of_space

 

After you've read it, you can come back and tell us you don't understand it and so it therefore can't be correct.

[Lazarus]

There is nothing in Wikpedia article that gives any logical answer to why

galaxies are exempt from the expansion of space. The ants on a rubber

analogy is as worthless as the pennies on a balloon excuse.

 

I originally asked for a logical explaination of why galaxies don't expand

like everything else. No answer was forthcomming. The debating ploy

of asking for proof of the question was used. I responded with a

straighforward example. The response did not point out an error

in my example but used the Athority says so technique.

 

I realize that you all would like to put me in the crackpot column but

I am just asking for a believable reason.

 

All of the respondents must know that is not intuitive or kind to

common sense that space is expanding along with everything in it

except galaxies.

 

My question has not been answered.

 

Thanks to everyone that has posted or read this thread.

 

If you wish to yell at me privately email

[ACG52]

 

I originally asked for a logical explaination of why galaxies don't expand

like everything else. No answer was forthcomming

 

You were given the answer. Gravity is overwhelmingly stronger than expansion. Galaxies don't expand. Stellar systems don't expand, The space between atoms doesn't expand. There's a whole bunch of things which don't expand.

 

Now, you don't like the answer, or simply can't understand it. That's your problem, not the universe's.

[Lazarus]

Dear ACG52,

 

There is no way we are going to agree on this but I thank you

and appreciate what you are doing.

[Spyman]

I originally asked for a logical explaination of why galaxies don't expand

like everything else.

All of the respondents must know that is not intuitive or kind to

common sense that space is expanding along with everything in it

except galaxies.

 

My question has not been answered.

Ok, I have read through this thread a couple of times now and it seems as you do accept what observations tells us, that very distant galaxies recede from us but close galaxies don't and you want to understand how they can resist the expansion.

 

Is that correct, or do you want to deny current interpretation of observations or contest the metric expansion of space?

[StringJunky]

Lazarus

 

Maybe looking at a model of the formation of the large scale structure of the universe might help. There's a movie, of which these stills are a part of, you can download at the link below if you wish;

 

 

 

 

http://cosmicweb.uchicago.edu/filaments.html

Edited February 6, 2013 by StringJunky

[zapatos]

There is nothing in Wikpedia article that gives any logical answer to why

galaxies are exempt from the expansion of space. The ants on a rubber

analogy is as worthless as the pennies on a balloon excuse.

Galaxies are not 'exempt' per se. The same force that is being exerted on galaxies that are 200 million LY apart is being exerted between the earth and the sun (or even between atoms in your body). Presumably the sun and the earth are some immeasurably small distance further apart than they would be if there was no expansion. However, with or without expansion you would still see the earth orbiting the sun.

I originally asked for a logical explaination of why galaxies don't expand

like everything else. No answer was forthcomming.

You may not have liked it but the answer was given in (among other places) post #2. "The expansion of space is weaker than gravity on the scale of galaxy clusters and smaller."

 

If you have a ball bearing touching a magnet, and a slight breeze blowing over the ball bearing, the ball bearing will not roll away. Magnetism at that close range is stronger than the slight breeze.

If the ball bearing is moved to one foot away from the magnet, now the slight breeze blowing on the ball bearing is stronger than the magnetic field and the ball bearing will move away from the magnet.

Edited February 6, 2013 by zapatos

[Airbrush]

"Even an infintesimal force will change an orbit."

 

An orbit is not the same as the GRAVITY in a galaxy, vs dark energy.

 

"There is nothing in Wikpedia article that gives any logical answer to why galaxies are exempt from the expansion of space." - Yes it does, GRAVITY.

 

"I originally asked for a logical explaination of why galaxies don't expand like everything else. No answer was forthcomming." - Yes it was, GRAVITY.

 

I responded with a straighforward example." - No you didn't, your example is convoluted.

 

"I am just asking for a believable reason." - Here it is again, GRAVITY.

 

"All of the respondents must know that is not intuitive or kind to common sense that space is expanding along with everything in it except galaxies." - No we don't. It is perfect common sense that GRAVITY is stronger than dark energy on local scales. Not only don't galaxies expand but galaxy clusters don't expand, and galaxy superclusters don't expand.

 

"My question has not been answered." - A number of people here believe your question has been answered redundantly. Everyone is crazy except for you?

 

"Thanks to everyone that has posted or read this thread." - You are welcome, and I don't know why I bother to post this, I guess I like you in spite of your difficulty, and I don't understand the unlimited patience of those who made the effort to explain GRAVITY to you, but in vain, they must like you also.

Edited February 6, 2013 by Airbrush

[Lazarus]

I will try one more time to get someone to take an objective look at why galaxies
don't expand with the expansion of space.

 

It is only logical that if space is expanding the distance between objects should
increase.

 

The reasons that I received are:

1. Gravity "overwhelms the expansion of space".

"Overwhelms is hardly a measure of anything"

 

2. At a distance of 199 million light years
expansion has no effect. At 201 million
light year it has the effect of driving galaxies apart.

Weird!

3. Referred to Wikipedia's "ants on arubber band"

analogy. As useless as the pennies on a balloon analogy.

I didn't think analogies proved much.

 

4. The distance between objects doesn't change the

effect of space expansion.
Doesn't set well with the contention effects only occur when objects
are 200 million light years apart.

 

5. You are a dummy, go away. May be so.

 

Can you really accept any of these responses as answering the question?