# Expansion and Contraction of Universe

1. Jan 2, 2012

### 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.

2. Jan 3, 2012

### 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

3. Jan 3, 2012

### 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."

Last edited: Jan 3, 2012
4. Jan 3, 2012

### 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

5. Jan 4, 2012

### Cosmo Novice

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.)

6. Jan 4, 2012

7. Jan 4, 2012

### phinds

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.

Last edited: Jan 5, 2012
8. Jan 4, 2012

9. Jan 4, 2012

### 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

10. Jan 5, 2012

### Cosmo Novice

11. Jan 5, 2012

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.

12. Jan 5, 2012

### phinds

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

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.

13. Jan 5, 2012

### vinayjain

14. Jan 5, 2012

### Staff: Mentor

15. Jan 6, 2012

### Cosmo Novice

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

16. Jan 6, 2012

### Cosmo Novice

17. Jan 6, 2012

### Staff: Mentor

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.

18. Jan 8, 2012

### vinayjain

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

19. Jan 9, 2012

### Cosmo Novice

No problem - glad we could help

20. Jan 18, 2012

### 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.