Is the Universe Collapsing or Expanding?

[pnjabiloafer]

Reversing of the universe??

Okay.. this is just an idea out of the blue sky, but.. what if we (the universe) is going through reversal right now? IS there any way for us to know or to detect that? I mean, if the Density of the universe was able to overcome the expansion rate.. and then the universe started collapsing back onto itself.. I know that all matter in the universe is moving away from each other but.. what if its just an effect of it collapsing back into a single point? Please explain this concept, thank you.

 

[pnjabiloafer]

the red-shift and the blue shift wouldn't apply to this question.. becuase.. i am assuming that.. all the objects which are red-shifted.. are moving away from us (and are in front of us).. therefore are.. going closer to the "center" faster then we are, and the objects which are blue shifted.. are still behind us.. and seem to be coming towards us, and we are going faster towards the center then they are..

 

[FZ+]

The universe doesn't have a centre. (As far as we know) The theories of expansion involve space itself expanding more or less uniformly at all levels - each point is getting further away from each point, not running away from a certain, specific point. First rule of Fight Clu... I mean... special relativity: there is no absolute coordinate system.

The conjecture that space is contracting, and we happen to be in special place in the universe where it appears to be expanding is, unfortunately, unacceptable, because it is ultimately unfalsifiable. It can't be proved or disproved. We can only make meaningful inferences if we assume our observations mean something.

 

[pnjabiloafer]

oooh thank you.. but it would have helped if it was in lil bit simpler terms... thank you anyways.. i got tha point of it

 

[Chronos]

We are hosed. We have no definitive way to detect whether the universe is expanding or contracting at the 'present time'. Observational evidence suggests it may be in both states. We perceive the ancient universe as flying apart at incredible speeds. We percieve the more recent universe as being stationary. This implies the universe has a time dependent feature. Is the universe flat [infinite] or curved [finite, yet boundless]? Perhaps both. Even topological models fall 'flat' on their face when singularities appear in the solution. I think the real problem is our limited grasp of mathematics, not observation. We will not find a way to resolve observations until we find a way to 'renormalize' mathematical singularities

 

[FZ+]

Er no, Chronos. By the data we currently have, the only models that we have positive evidence for is one where the universe is currently expanding. And what's more, expanding at an accelerating rate. The only question is whether the present expansion will continue, and all signs seem to say yes.

 

[shrumeo]

I think what Chronos was trying to say is that our understanding of what we observe, at least in the case of cosmology, is always limited to our grasp of math. All these models that say the universe is doing whatever it's doing, as you know better than I, are mathematical. I would also say that our understanding will also always be limited by our observational capabilities.

The better the observation, the better the model, the better our understanding.

2200 or so years ago, Aristotle and others had worked out their model of the universe pretty well. Their mathematical model of 55 concentric crystal spheres accurately described what they saw to the limits of their observational abilities. The only question was whether the crystal spheres existed, and all signs pointed to yes.

edit: spelling

 

[pnjabiloafer]

since everything that we see when we look up at the sky is "ancient", light is taking time to get to us, so the farther we look, the back in time we go right? so, what if expansion has already stopped and the light we are getting still is not up that poiint, it is before that point, then we are still going into expansion, meaning nothing is spontanious right? time has different effect on different parts of the universe? so in astronomy... nothing is certain, right? so my point is that, all the things we predict will hapen have maybe already occured, and we have no way of finding out right?

 

[Phobos]

Welcome to Physics Forums, pnjabiloafer!

since everything that we see when we look up at the sky is "ancient", light is taking time to get to us, so the farther we look, the back in time we go right? so, what if expansion has already stopped and the light we are getting still is not up that poiint, it is before that point, then we are still going into expansion, meaning nothing is spontanious right? time has different effect on different parts of the universe? so in astronomy... nothing is certain, right? so my point is that, all the things we predict will hapen have maybe already occured, and we have no way of finding out right?

It is certain that nothing is certain.

However, we can make predictions about the fate of the whole universe based on observations from what is around us. In order for the universe to collapse back on itself, it would have to have enough stuff in it to result in enough gravity to pull it all back. From what we can see, there is not enough matter (gravity) to collapse the universe.

Also, recent measurements of the cosmic microwave background (CMB) (for example, from COBE, BOOMERANG, WMAP) also show that the universe will not collapse back upon itself (i.e., they show that the topology of the universe is not "closed", which is what would be required for a collapse.)

But the universe is a weird place full of surprizes...stay tuned.

 

[shrumeo]

The interpretations of these data say that.

 

[pnjabiloafer]

we are constantly discovering new things, and in order to explain them, we either make new theories to explain these phenomenon or we alter the ones we had before.. in fact, i think that, there will never be a universal theory of everything. Things we discover in our own solar system surprise us somtimes, so i think creating a theory of everything will be a quite difficult task. If uu look at it, our place in the universe is nothing. We are like a speck of dust, in this huge universe. (http://www.planetary.org/voyager25/images/voyager1-earth-pale_blue_dot.jpg ).. this picture was taken by the voyager spacecraft , the littel point of light is the Earth from 4 billion miles away.