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-   -   Big Bang Radiation (http://www.physicsforums.com/showthread.php?t=108064)

trichop Jan25-06 05:48 PM

Big Bang Radiation
 
According to the Big Bang scenario, after the "explosion" , matter and radiation spreads, while the newborn space grows.
My question is:
This firstly emmited radiation (which I think was spread radially, right?)
shouldn't somewhere in time be attracted back, due to the gravity effect?
Does this make any sense?

DaveC426913 Jan25-06 06:01 PM

Yes, in the far distant future, everything will come back in a "Big Crunch".

varsha Jan26-06 05:59 AM

Quote:

Quote by DaveC426913
Yes, in the far distant future, everything will come back in a "Big Crunch".

when there's this "big crunch", don't you think there will be a big bang again?
but this time with some reason? hmm.....this get's me to another question...right now we (scientists) think that nothing happened before the big bang. but what if there was a universe and there was a big crunch thus resulting in a big bang...?

DaveC426913 Jan26-06 08:34 AM

That is one hypothesis, yes.

BTW, it's not that scientists think there was nothing before the Big Bang, it's that scientists don't study what came before the Big Bang - there's nothing to study. That's the realm of philosophers and theologians.

George Jones Jan26-06 08:43 AM

Quote:

Quote by DaveC426913
Yes, in the far distant future, everything will come back in a "Big Crunch".

Current interpretation of observational evidence indicates that this is very unlikey - cosmologists think that the expansion is accelerating, not slowing down.

Some physicists even speculate (wildly?) that if the acceleration accelerates, then there might be a "Big Rip".

Regards,
George

varsha Jan27-06 04:00 AM

Quote:

Quote by George Jones
Current interpretation of observational evidence indicates that this is very unlikey - cosmologists think that the expansion is accelerating, not slowing down.

Some physicists even speculate (wildly?) that if the acceleration accelerates, then there might be a "Big Rip".

Regards,
George

well, because big bang was an explosion things heated up and are expanding. but don't you think they will cool down and contract thus resulting in a 'big crunch' rather than a 'big rip'?

George Jones Jan27-06 06:27 AM

Quote:

Quote by varsha
well, because big bang was an explosion things heated up and are expanding. but don't you think they will cool down and contract thus resulting in a 'big crunch' rather than a 'big rip'?

Current interpretation of observational evidence (mainly) from Type Ia supernovae indicates that the expansion is accelerating. Physcists think that the cause of the acceleration is dark energy/cosmological constant. I am not completely convinced by this evidence that dark energy/cosmological constant exists, but I do find the evidence to be suggestive.

I do not find the evidence for a Big Rip to be nearly so suggestive, but ths is something that I would like to look into in more detail. Results from the study of gamma-ray bursters recently presented give somewhat weak evidence that not only is the universe accelerating, but that the acceleration itself is increasing.

Sean Carroll has a nice discussion of the future of the universe over on the blog Cosmic Variance. The gamma-ray stuff is discussed in the first link in this article.

Regards,
George

SpaceTiger Jan27-06 12:46 PM

I recently added a post to my Review of Mainstream Cosmology that directly addresses some of these issues.

Quote:

Quote by George Jones
I do not find the evidence for a Big Rip to be nearly so suggestive, but ths is something that I would like to look into in more detail. Results from the study of gamma-ray bursters recently presented give somewhat weak evidence that not only is the universe accelerating, but that the acceleration itself is increasing.

They announced this at the recent AAS and further review suggests that there are some serious problems with their methods of data analysis. I would approach this result with extreme skepticism for the time being.

Frizz Jan27-06 01:53 PM

As I understand it, there's a satalite being sent up called plank...One of the experiments on board is to determine the value of 'h' the hubble constant. Once 'h' is determined then we'll know which way the universe will go.

Please correct me if I'm wrong...It's been years.

Frizz

SpaceTiger Jan27-06 02:18 PM

Quote:

Quote by Frizz
As I understand it, there's a satalite being sent up called plank...One of the experiments on board is to determine the value of 'h' the hubble constant. Once 'h' is determined then we'll know which way the universe will go.

Among many other things, yes, the Planck satellite is expected to give an accurate measurement of Hubble's constant. It's a CMB mission like WMAP, but it's looking at anisotropies on smaller angular scales. Here's a description of the science goals from the Planck website:

The Planck Mission

varsha Jan28-06 03:00 AM

Quote:

Some observations, including the new gamma-ray-burst results, show a tiny preference for an increasing dark energy density

how do they know that there is an increase in the density of the dark energy with the help of gamma-ray-burst results?


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