Expansion and Contraction of Universe

[vinayjain]

Hi everyone,

I have seen this reference

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

and I have seen in this reference that the ultimate fate of the universe could be a big crunch which means that after the expansion of the universe comes to the limit of the expansion it will start contracting and the ultimately it will compress and result in extinguishing all the dimensions and thus leads to the place where big bang has not yet occured.

Is it possible as what I understand by this is that universe is streching like a elastic and when it reaches the limit it will be released and hence comes to the rest position.

 

[DarioC]

Well I made a reply, but my security system locked everything up--maybe later. Probably just as well as someone here would likely climb all over my backside about my simplified version. Standard.
DC

 

[Bobbywhy]

vinayjain, According to the Wiki reference you used the recollapse (big crunch) of the Universe is not expected because of observational evidence. I copied a few paragraphs from the Wiki page about this. See the very last sentence:

"The current scientific consensus of most cosmologists is that the ultimate fate of the universe depends on its overall shape, how much dark energy it contains, and on the equation of state which determines how the dark energy density responds to the expansion of the universe.[citation needed] Recent observations have shown that, from 7.5 billion years after the Big Bang onwards, the expansion rate of the universe has actually been increasing, commensurate with the Open Universe theory.

Open universe
If Ω < 1, the geometry of space is open, i.e., negatively curved like the surface of a saddle. The angles of a triangle sum to less than 180 degrees, and lines that do not meet are never equidistant; they have a point of least distance and otherwise grow apart. The geometry of such a universe is hyperbolic.

Even without dark energy, a negatively curved universe expands forever, with gravity barely slowing the rate of expansion. With dark energy, the expansion not only continues but accelerates. The ultimate fate of an open universe is either universal heat death, the "Big Freeze", or the "Big Rip", where the acceleration caused by dark energy eventually becomes so strong that it completely overwhelms the effects of the gravitational, electromagnetic and strong binding forces.

Conversely, a negative cosmological constant, which would correspond to a negative energy density and positive pressure, would cause even an open universe to recollapse to a big crunch. This option has been ruled out by observations."

 

[vinayjain]

need to ask one thing more...

I have read a thing about the rotating objects is that there are two types of forces that implies on a rotating object i.e. centripital force and centrifugal force which keeps them in an alignment

so all the objects in a galaxy is revolving aroung a common centre so how it be expanding

 

[Cosmo Novice]

need to ask one thing more...

I have read a thing about the rotating objects is that there are two types of forces that implies on a rotating object i.e. centripital force and centrifugal force which keeps them in an alignment

so all the objects in a galaxy is revolving aroung a common centre so how it be expanding

The expansion is between gravitationally bound structures, so superclusters, clusters, galaxies and star systems are spared expansion due to their own gravitational well. The space between galaxies is what is expanding, or rather than saying space is expanding (as this endows space with measurable properties) it is better to say that geometrically all non strongly gravitationally bound mass in the Universe is expansion.

Its basically Gravity vs Expansion (Expansion wins out on very large scales but Gravity wins on smaller scales.)

 

[vinayjain]

The space between galaxies is what is expanding, or rather than saying space is expanding

Space between galaxies is increasing it is pretty known to me but the thing is the diameter of our galaxy is also increasing with a rate as the diameter of the galaxy which is known to me is 150 billion light years as of now but it is the resultant of contineous expansion from big bang so it means our galaxy is also expanding every second....so if there is a supermassive black hole present at the centre of our galaxy which is binding everything in our galaxy than how could it be expanding...

Just curious as I don't know the fact

 

[phinds]

The space between galaxies is what is expanding, or rather than saying space is expanding

Space between galaxies is increasing it is pretty known to me but the thing is the diameter of our galaxy is also increasing with a rate as the diameter of the galaxy which is known to me is 150 billion light years as of now but it is the resultant of contineous expansion from big bang so it means our galaxy is also expanding every second....so if there is a supermassive black hole present at the centre of our galaxy which is binding everything in our galaxy than how could it be expanding...

Just curious as I don't know the fact

No, our galaxy is not expanding. In fact, the entire Local Group is not expanding. "Dark Energy" does not have any effect on gravitationally bound objects such as Galactic Clusters, Galaxies, Solar Systems, Planets, and you.

 

[vinayjain]

No, our galaxy is not expanding. In fact, the entire Local Group is not expanding. "Dark Energy" does not have any effect on gravitationally bound objects such as Galactic Clusters, Galaxies, Solar Systems, Planets, and you.

So you mean to say that our galaxy is not expanding but is adding extra space in it as all other galaxies except andomeda galaxy is moving away from us

 

[DarioC]

I have a feeling I'm going to regret this but:

When you say "adding extra space in," it conflicts with what you were just told by responders and with what you say in the remainder of the sentence.

Galaxies are not expanding. Local groups of galaxies, wherever they are, are not expanding. They are moving away from EACH OTHER as witness by redshift of their light.

The latest finding is that they are moving away at an ever increasing speed.

One can call that by whatever name one chooses. Most people refer to it as the expansion of the universe.

DC

 

[Cosmo Novice]

So you mean to say that our galaxy is not expanding but is adding extra space in it as all other galaxies except andomeda galaxy is moving away from us

No there is no "adding of space". This implies space as a measurable property, space is geometry.

So from the point of view of our galaxy everything is moving away from us (disregard Andromeda as this is just Kinematic motion) However from the point of view of every other galaxy, everything is moving away from them. Distances between non gravitationally bound objects increase, geometric expansion doesn't require "new space".

Hope this helps

 

[read]

The expansion is between gravitationally bound structures, so superclusters, clusters, galaxies and star systems are spared expansion due to their own gravitational well. The space between galaxies is what is expanding, or rather than saying space is expanding (as this endows space with measurable properties) it is better to say that geometrically all non strongly gravitationally bound mass in the Universe is expansion.

Its basically Gravity vs Expansion (Expansion wins out on very large scales but Gravity wins on smaller scales.)

Is it possible to calculate the critical scale between "large scales" and "smaller scales"? Possibly "large scales" mean just absence of an average force?

Another question: If we assume that the galaxy is slightly stationary larger because of expansion, but gravitational forces overcome the expansion, how to calculate this small increase in size? From Hubble low we have a velocity but not the acceleration.

 

[phinds]

Is it possible to calculate the critical scale between "large scales" and "smaller scales"? Possibly "large scales" mean just absence of an average force?

There's no fixed amount. It is, as you say, dependant on local force. Things that are gravitationally bound are "small scale"

Another question: If we assume that the galaxy is slightly stationary larger because of expansion, but gravitational forces overcome the expansion, how to calculate this small increase in size? From Hubble low we have a velocity but not the acceleration.

But it ISN'T slightly larger. The expansion has no effect on gravitationally bound objects. It's like an ant pushing on a tank. It doesn't have infinitesimal effect, it has ZERO effect, because it cannot overcome the other forces to ANY extent.

 

[vinayjain]

No there is no "adding of space". This implies space as a measurable property, space is geometry.

So from the point of view of our galaxy everything is moving away from us (disregard Andromeda as this is just Kinematic motion) However from the point of view of every other galaxy, everything is moving away from them. Distances between non gravitationally bound objects increase, geometric expansion doesn't require "new space".

Hope this helps

then you mean to say that at the time of big bang out milky way galaxy was formed at this radius only as our galaxy is not expanding.

 

[Drakkith]

then you mean to say that at the time of big bang out milky way galaxy was formed at this radius only as our galaxy is not expanding.

Our galaxy has not been expanding since it's creation. It has remained about the same size. Any change is not due to expansion but due to gravitational interactions within our galaxy and with other galaxies nearby.

 

[Cosmo Novice]

Our galaxy has not been expanding since it's creation. It has remained about the same size. Any change is not due to expansion but due to gravitational interactions within our galaxy and with other galaxies nearby.

I didnt say that, for some reason you have quoted vinayjain and it has quoted me! Please amend!

 

[Cosmo Novice]

then you mean to say that at the time of big bang out milky way galaxy was formed at this radius only as our galaxy is not expanding.

When galaxies form their growth can be attributed to more than expansion. Gravitationally bound structures are spared expansion. Local gravity> Expansion. Expansion is geometric - as in distance expansion not an overall "growth".

Gravitationally bound objects do not expand because gravity binds the objects together. You do not need a massive object for this, an asteroid for example traveling through an interstallar void would not be broken up by expansion.

 

[Drakkith]

I didnt say that, for some reason you have quoted vinayjain and it has quoted me! Please amend!

Sorry! It's too late for me to edit the post! I think vinayjain's post are a bit messed up and the successive quotes didn't go through correctly.

 

[vinayjain]

Well Thanx Everyone for clearing my doubt and Cosmo really sorry if my post are messed up...

 

[Cosmo Novice]

Well Thanx Everyone for clearing my doubt and Cosmo really sorry if my post are messed up...

No problem - glad we could help

 

[fishspawned]

this discussion has left me a little confused. if anyone can clarify the following it would be a great help.

there has been suggestions that the expansion of the Earth is accellerating due to an increase in the a force that is related to space itself - that the void between things has an unknown force that increases as the space itself increases. it comes from attempts to explain dark energy i believe - i believe it is a property of space suggested through einstein's work.

with this in mind - is not this inferring that space is indeed being 'increased' and that at a certain point the cummulative force attributed to space becomes so great it overwhelms the force of gravity - thus explaining the sudden shift of the expansion of the universe to one of increase acceleration?

please help me out on this one as the mention that space was not being added to was wrong has left me a little confused.

 

[DarioC]

FS,
No one actually knows if space is expanding OR adding extra space. Those two ideas are pretty much semantics in the first place.

What they DO know is that gravitationally linked groups of bodies APPEAR to be moving away from each other at at an increasing rate. This is inferred from the redshift in light from far away celestial objects.

That is making the assumption that some other characteristic of space is not causing the observed effect.

That is more or less the sloppy bottom line.

DC

 

[phinds]

fs,
no one actually knows if space is expanding or adding extra space. Those two ideas are pretty much semantics in the first place.

What they do know is that gravitationally linked groups of bodies appear to be moving away from each other at at an increasing rate. this is inferred from the redshift in light from far away celestial objects.

That is making the assumption that some other characteristic of space is not causing the observed effect.

That is more or less the sloppy bottom line.

Dc

huh ? Is that REALLY what you intended to say?

 

[DarioC]

Please note the word GROUPS. The groups are moving away from each other, not the objects in the groups moving away from each other. My sentence could have been better I admit. I avoided saying that objects appear to be moving away from each other, because you know what question or comments would follow that.
DC

 

[phinds]

Please note the word GROUPS. The groups are moving away from each other, not the objects in the groups moving away from each other. My sentence could have been better I admit. I avoided saying that objects appear to be moving away from each other, because you know what question or comments would follow that.
DC

You're right, of course. Your sentence is correct when read correctly, but it is subject to misinterpretation (mine, for example )

 

[fishspawned]

Those two ideas are pretty much semantics in the first place.

this is why i was confused.

i think what i am referring to is the idea of the cosmological constant. the idea that empty space has its own energy that increases as space increases. it is from this that i generally think of space as 'building up'. but like you said, this is a matter of description.

 

[Drakkith]

there has been suggestions that the expansion of the Earth is accellerating due to an increase in the a force that is related to space itself -

No, the expansion of the Universe is not an acceleration. It does not result in movement through space. The nature of expansion wouldn't even make sense if it were a simple acceleration. Which way are we being accelerated? It would be in completely different directions depending on your point of reference.

with this in mind - is not this inferring that space is indeed being 'increased' and that at a certain point the cummulative force attributed to space becomes so great it overwhelms the force of gravity - thus explaining the sudden shift of the expansion of the universe to one of increase acceleration?

Maybe. Whether space is being added, created, or it's just that matter is being pushed away from all other matter is mostly an interpretation I believe. I believe the math simply says that the distance between all points in space is increasing.

please help me out on this one as the mention that space was not being added to was wrong has left me a little confused.

Understandable. It is not an easy thing to grasp. Consider the following. If I put a line of particles stationary to each equally spaced apart stretching across the void between our galaxy cluster and the next one, and then I measure the distance between each particle later in time, I will measure an increased distance between each particle. None of the particles have moved out of the line, and each particle has the same increase in distance from their adjacent particles. From the point of view of each particle, every other particle has "moved" away from them without actually moving through space. Not only that, but each particle sees the more distant particles from itself as having moved further away than closer particles.

Notice that this says nothing about space itself and whether it is being added, created, stretched, or whatever. To my knowledge, which could be wrong, it doesn't really matter.

 

[fishspawned]

drakkith, i will for now on, indicate that the rate of expansion is increasing and nevermore use the word acceleration. i respect that you want everyone to be precise in what they say, but you will find that the term accleration is used very commonly when describing the expansion of the universe. i would not be the first soul to make such a blunder.

as far as the math that you refer to - no, in fact einstein's modified field equation uses a cosmological constant.

Notice that this says nothing about space itself and whether it is being added, created, stretched, or whatever. To my knowledge, which could be wrong, it doesn't really matter.

well, no - it does if the energy associated with space [as in nothing] is a property proportional to how much of 'it' there is, which is exactly what is suggested by the cosmological constant.

 

[DarioC]

FS, you can use acceleration as long as you include the word RATE as you did the second time above. The only thing it modifies (as in refers to) is rate, not the universe or space or the objects in space.

Y'all probably want to check the dictionary before you jump on this like a mountain lion on a sick calf.

The only excuse I can offer is that I am bored this evening.
DC

 

[vinayjain]

FS, you can use acceleration as long as you include the word RATE as you did the second time above. The only thing it modifies (as in refers to) is rate, not the universe or space or the objects in space.

Y'all probably want to check the dictionary before you jump on this like a mountain lion on a sick calf.
DC

DC please do not quote anything in the discussion which would be ethically wrong or hurt someone.

and in this discussion I also thinks that after the big bang it is not like that all the galaxies including our milky way was created upto this magnitude...it has been a matter of fact that it might be increasing its area but we don't know about that

and can anyone please tell me that the light spectrum of any other far away cellestial object which we see has been red shifted reaches in how much time to us.....what i think in this is that when a light emitted from a cellestial object it takes several years from that object to reach us and during the journey it has to pass several other object's gravitational force as well and might get distorted so in that case what we see on Earth might not be the true picture.

I might be wrong in this thinking...please reply

 

[DarioC]

Vin'
I think you misunderstood my Y'all comment, and I understand why. I should have used the word ME instead of THIS. As in " ...before YOU OTHER GUYS jump on ME like a mountain lion..."

I just thought ME was too personal, but I guess this made it sound like I was somehow criticizing/insulting FS.

Just the opposite, I was DEFENDING his use of the word acceleration when it is used in combination with rate.

Too bad you misunderstood, it seems to be a recurring situation on the Internet where something is taken out of context.

Perhaps since the Internet is viewed world wide, outside of English speaking countries, I should be extremely careful with casual use of clever language twists.

DC

 

[vinayjain]

Vin'
I think you misunderstood my Y'all comment, and I understand why. I should have used the word ME instead of THIS. As in " ...before YOU OTHER GUYS jump on ME like a mountain lion..."

I just thought ME was too personal, but I guess this made it sound like I was somehow criticizing/insulting FS.

Just the opposite, I was DEFENDING his use of the word acceleration when it is used in combination with rate.

Too bad you misunderstood, it seems to be a recurring situation on the Internet where something is taken out of context.

Perhaps since the Internet is viewed world wide, outside of English speaking countries, I should be extremely careful with casual use of clever language twists.

DC

It is absolutely ok...but the thing is what I misunderstood in your reply there might be others who will misunderstood this reply, so I was just saying that please be careful...