For Astronomy lovers who would love to discuss about celestial objects.

## (unreasonable poll) What do you think about universe(shape and scale)?

1 Infinity
3
60%
2 Spherical
1
20%
3 flat
0
4 between Spherical and flat
0
5 others
1
20%

kamrul2010
Posts: 120
Joined: Wed Dec 08, 2010 2:35 am
Contact:

ইয়ে মানে, যেইটা scientifically true, সেইটা নিয়া কি কোনো পোল করা উচিত? ব্যাপারটা একটু কেমন না!
যুক্তি চাইলে ঠিক আছে,কিন্তু সমর্থন চাওয়াটা একটু দৃষ্টিকটু,এইটা তো আর নির্বাচন না, দেখলে মনে হয় বিজ্ঞানীরা ভুল বলসে,আমরা এইটা মানি না! আসো,ভোটাভুটি করি! সংখ্যাগরিষ্ঠরা যা বলবে,তাই ঠিক!

এই লিংকটা দেখতে পারো! যে কোনো কিছুইতেই,উইকির উপরে কিছু নাই!
http://en.wikipedia.org/wiki/Shape_of_the_Universe

ওমেগার তিন রকম মানের জন্য মহাবিশ্বের চেহারা এই তিন রকম হইতে পারে!
http://en.wikipedia.org/wiki/File:End_of_universe.jpg (ছবিটা দিতে পারতেসি না কেনো জানি,এই কারণে লিংক দিয়া গেলাম!)
If computers have no doors or fences, who needs Windows and Gates?

mubtasim123
Posts: 37
Joined: Tue Dec 14, 2010 3:03 am
Location: NY,USA

lol I know I shouldn't have done it
but with the evidences we still have to make a educated "guess" about this type of thing..
In that poll I used some choice that are major "educated" guess to astronomers...
In this thread I should have post it like "choose which method you support best"..

yep there is no value on voting on on this part of science but I wanted to know the major choice people choose between em'
ইয়ে মানে, যেইটা scientifically true, সেইটা নিয়া কি কোনো পোল করা উচিত? ব্যাপারটা একটু কেমন না!
যুক্তি চাইলে ঠিক আছে,কিন্তু সমর্থন চাওয়াটা একটু দৃষ্টিকটু,এইটা তো আর নির্বাচন না, দেখলে মনে হয় বিজ্ঞানীরা ভুল বলসে,আমরা এইটা মানি না! আসো,ভোটাভুটি করি! সংখ্যাগরিষ্ঠরা যা বলবে,তাই ঠিক!

P.S.
This was not a good idea to post that poll
Blah blah blah blah -----blah blah blah

arnob54
Posts: 13
Joined: Wed Dec 08, 2010 4:53 pm
Location: Dhaka

i think who ever posted this, has a bit of misconception about the shape of universe, the shape of universe depends on a constant called "Rho Critical" that is the density of the universe, based on current research, there are only 3 possible options:
1. Flat Universe
2. Spherical Universe

so there isnt anything "in between" or any "other" option, and the concept of finite and infinite is defined by some other parameters.
Tanveer

mubtasim123
Posts: 37
Joined: Tue Dec 14, 2010 3:03 am
Location: NY,USA

@ arnob54
I am really kid at those stuff. Making this poll was really a bad idea.
I don't wanna argue with what I don't know (don't read below if it's not a theory) but..
the "Rho Critical" you mentioned sounds like a theory (sry if I am wrong cause I have no idea about it)
If you said based on the theory there is no "in between" or others then ok but the term "theory" itself has in between or others....so..
I think I made my mind.

**Once again every-one I was really "foolish" to make this poll
I made this because I saw no people posted anything here so to get their attention on this topic of forum...lol
Blah blah blah blah -----blah blah blah

arnob54
Posts: 13
Joined: Wed Dec 08, 2010 4:53 pm
Location: Dhaka

its okay bro no worries, we all start by asking meaningless questions, and that's how we start learning science

well about the idea of Rho Critical, its actually not a theory but its a constant term, for example $G=6.675X10^{-11} Nm^2kg^{-2}$

now you might ask how we derive this value? if you know our class 9-10 physics you can derive it yourself!
here's how:

we consider a galaxy at a distance "r" from the Earth and it's receding from us with a velocity "v" which is equal to the escape vel. now if we consider a sphere with the radius "r" then by Newton's Gravitation Law we can say that , that galaxy is pulled backwards by the mass "M" which is the mass of all the matter in the sphere. ( Consider the whole sphere as a single mass).

Now, we know the equation mass density and volume,

$M= \frac{4}{3} \pi r^3 X \rho_0$ ---------------------(i)

now, escape vel, "v" is given by,

$v=\sqrt{\frac{2GM}{r}}$

or,

$v^2=\frac{2GM}{r}$ ----------------------------------(ii)

But, galaxy's velocity is also given by Hubble's Law: ( this comes from Doppler effect, if you don't know about this you might want to get the basic idea of it from any physics book)

$v=H_0r$
or, $v^2={H_0}^2r^2$ where $H_0$ is known as "Hubble's Constant". ------------------------(iii)

Equating (i)and (ii) and putting the values from (iii) we get,

$\rho_0=\frac{3{H_0}^2}{8\pi G}$

So this is your "Rho Critical", we see that $\rho_0 \propto {H_0}^2$

Therefore, by finding out the real value of the Hubble's Constant, we can actually find out the fate of the universe.

* Interesting fact, $\frac{1}{H_0} =$ age of universe
Hope this helped!
Tanveer

mubtasim123
Posts: 37
Joined: Tue Dec 14, 2010 3:03 am
Location: NY,USA