Universal Expansion

[Trajk Logik]

I agree that it is undeniable that the universe is expanding. What I don't understand is why one would conclude that the universe has always been expanding. Could it not be possible that the universe is eternal and that the expansion is something that started happening recently? Could it be possible that some outside force may be pulling on the universe from the outside?

 

Another idea is that maybe the big bang did happen but the universe hasn't been expanding at a constant rate. Think about a rip in your shirt, or a crack in your windshield and how they can go through spurts of expansion due to outside forces causing the crack or rip to become wider or longer. Maybe the universe is a rip or crack in some exotic medium?

 

And how is it that the cosmic background radiation has been tied to the big bang as evidence supporting the big bang and not evidence of something else?

 

I hope that these questions aren't to newbish.

 

Thanks for any education that the more educated would be willing to impart.

[Airbrush]

I agree that it is undeniable that the universe is expanding. What I don't understand is why one would conclude that the universe has always been expanding. Could it not be possible that the universe is eternal and that the expansion is something that started happening recently? Could it be possible that some outside force may be pulling on the universe from the outside?

 

Another idea is that maybe the big bang did happen but the universe hasn't been expanding at a constant rate. Think about a rip in your shirt, or a crack in your windshield and how they can go through spurts of expansion due to outside forces causing the crack or rip to become wider or longer. Maybe the universe is a rip or crack in some exotic medium?

 

And how is it that the cosmic background radiation has been tied to the big bang as evidence supporting the big bang and not evidence of something else?

 

I hope that these questions aren't to newbish.

 

Thanks for any education that the more educated would be willing to impart.

 

Before someone with more expertise replies, here are my best guesses to these good questions;

 

Dark flow is what they call an anomaly to big bang expansion. Instead of expanding exactly the same everywhere, there is a region of unexplained directional expansion. Other than that, what you propose is beyond what can be observed. The simplest explanation is big bang. Also, some experts will say there is no "outside" the universe, since the universe is everything and everywhere. What can pull from the outside? Dark flow may indicate something outside. What you propose is the universe expanding at a constant rate, and then change rate. What can change the rate of expansion? What outside forces?

 

According to string theory, the big bang was the result of a collision of higher dimensions, like two great sheets that came into contact and at the regions of contact big bangs started.

 

The uniformity of the cosmic background radiation is evidence for the big bang and cosmic inflation as we know it.

[Trajk Logik]

Before someone with more expertise replies, here are my best guesses to these good questions;

 

Dark flow is what they call an anomaly to big bang expansion. Instead of expanding exactly the same everywhere, there is a region of unexplained directional expansion. Other than that, what you propose is beyond what can be observed. The simplest explanation is big bang. Also, some experts will say there is no "outside" the universe, since the universe is everything and everywhere. What can pull from the outside? Dark flow may indicate something outside. What you propose is the universe expanding at a constant rate, and then change rate. What can change the rate of expansion? What outside forces?

 

According to string theory, the big bang was the result of a collision of higher dimensions, like two great sheets that came into contact and at the regions of contact big bangs started.

 

The uniformity of the cosmic background radiation is evidence for the big bang and cosmic inflation as we know it.

 

Thanks for the reply. I'll do some more research into dark flow and string theory. As for what can change the rate of expansion - I'm not sure. But then, what could cause the expansion of the Universe from a singularity? Our physical universe may be governed by a single basic energy structure - a basic substrate for all matter and all more complex forms of matter may have evolved from this basic energy structure. But it also seems possible that this structures may have also itself evolved from a more fundamental phenomena that is nested within its structure and that this phenomenon may have the potential to produce many different energy structures - each of which would produce different forms of matter that would have different physical laws. There may even be still more fundamental phenomena nested within this structure giving rise to the possibility of a nested set of fundamental energy structures.

 

[IM Egdall]

I agree that it is undeniable that the universe is expanding. What I don't understand is why one would conclude that the universe has always been expanding. Could it not be possible that the universe is eternal and that the expansion is something that started happening recently? Could it be possible that some outside force may be pulling on the universe from the outside?

 

Another idea is that maybe the big bang did happen but the universe hasn't been expanding at a constant rate. Think about a rip in your shirt, or a crack in your windshield and how they can go through spurts of expansion due to outside forces causing the crack or rip to become wider or longer. Maybe the universe is a rip or crack in some exotic medium?

 

And how is it that the cosmic background radiation has been tied to the big bang as evidence supporting the big bang and not evidence of something else?

 

I hope that these questions aren't to newbish.

 

Thanks for any education that the more educated would be willing to impart.

 

The universe has not been expanding at a constant rate throughout its lifetime. In fact, at this very moment the expansion is speeding up: The big bang/ inflation theory holds that the universe first expanded enormously in an extremely brief moment of time, then continued to expand at a much much slower uniform rate for billions of years, and then this expansion began to speed up (I think some 5 to 7 billion years ago) due to an unknown entity called dark energy. The reason this scenerio is considered our best model on the origin and evolution of the universe is because of all the evidence found which supports it, like the comsic microwave background.

 

Suggest you look at link below on how big bang theory predicts the cosmic microwave background:

 

http://www.astro.ubc.ca/people/scott/cmb_intro.html

[pantheory]

Trajk Logik,

 

......... What I don't understand is why one would conclude that the universe has always been expanding. Could it not be possible that the universe is eternal and that the expansion is something that started happening recently? Could it be possible that some outside force may be pulling on the universe from the outside? .

Of course there are possibilities but the BB model does not allow such possibilities. Only in a Steady State Universe could these possibilities be real. Few presently believe in the possibility of a Steady State universe, even one that is expanding.

.

Another idea is that maybe the big bang did happen but the universe hasn't been expanding at a constant rate.....

That the universe is not expanding at a constant rate is the basis for the dark energy hypothesis, which has now been included in the BB model.

Edited June 23, 2011 by pantheory

[Widdekind]

Type Ia SN are the evidence for the acceleration, of the expansion, of our space-time fabric. Essentially, SNIa are standard candles, of inferrable absolute brightness. And, when observed 'out there' in space, they become dramatically dim, as if they were very far away, even when the emitting SNIa occurred relatively recently (low-to-moderate z).

 

Thus, even 'recent' SNIa are far too faint, and hence far too far away, for any kind of Cosmology, but one in which our spacetime fabric has been stretching 'way-too-fast' -- to wit, an accelerating expansion, for the past 5-7 Gyr.

 

 

Question re: CMBR

 

I understand, that analysis of CMBR data 'shows', that our space-time is 'flat', and 'un-curved'. Does that mean, that our space-time was flat, back at z=1000 when the CMBR was generated? Or, more stringently, does that mean, that our space-time both was flat, and has remained flat, ever since?? Could our Cosmos have begun quasi-flat, and then 'developed' a curvature, later on ?? Do the CMBR data deny, actively, that our space-time fabric's curvature could have changed, after the CMBR was generated ??

[pantheory]

Widdekind,

 

..... even 'recent' SNIa are far too faint, and hence far too far away for any kind of Cosmology ...... (...to explain without using dark energy)

(bold and parenthesis added)

 

Even though most have never heard of it, there is a cosmology that requires / and predicts type 1a supernova to have the observed brightnesses without dark energy being needed or implied. It is a cosmology that requires a somewhat different Hubble formula to calculate distances and brightnesses. Based upon these different distance and brightness calculations, a straight line concerning supernova vs. distance is drawn implying no need, use, or existence of dark energy. Upon your request I can provide you links to this cosmology/ model but a discussion, if desired, must take place in the speculation forum since it is not a mainstream cosmology.

Edited June 25, 2011 by pantheory

[Widdekind]

Would it be possible, to post a link to the SF, from this thread ?

[IM Egdall]

And we must remember that the data supporting a flat universe is only data from the visible part of the universe, that is the part of the universe we can see.

 

"In Big Bang cosmology, the observable universe consists of the galaxies and other matter that we can in principle observe from Earth in the present day, because light (or other signals) from those objects has had time to reach us since the beginning of the cosmological expansion." Wikipedia

 

So what about the rest of the universe we cannot see? How can we know whether the entire universe, whether finite or infinite, is indeed flat (net zero spacetime curvature)?

[pantheory]

I ME,

 

So what about the rest of the universe we cannot see? How can we know whether the entire universe, whether finite or infinite, is indeed flat (net zero spacetime curvature)?

We can never observe the entire universe according to almost every possible cosmology mainstream or otherwise, therefore as you suggest, we could never know for sure whether the universe as a whole is flat or not. Observation presently suggests that the universe is flat, but Einstein's cosmological equations without a cosmological constant imply that the universe is not flat. With this constant added along with the Inflation hypothesis, the universe seemingly could be flat and open.

.

Edited July 1, 2011 by pantheory