Why is the universe expanding?

[gttjohn]

can anyone tell me why is the universe expanding faster and faster and not slower and slower or moving at a constant speed ,if a bomb explodes everything close to it accelerates away then slows down as time moves on ,in the void of space i would think things would just carry on expanding not acceleration

 

[phinds]

The universe did not "explode like a bomb". This is a common misconception and is addressed here with great regularity.

The actions of the universe were anything but ballistic. Early on (VERY early on) there was a period called "inflation" when the size of the universe grew by MANY orders of magnitude in a tiny fraction of a second. Then things slowed down and expanded somewhat ballistically for billions of years. Then at some point, the density become low enough that some mysterious, not at all understood, mechanism (which we call "dark energy") overcame gravity and started accelerating the universe's expansion.

This is all cosmology 101 and you can find zillions of explanations on the internet (some of them wrong, by the way)

Come to think of it, I think the FAQ section of the Cosmology section of this forum is a good place to start.

 

[gttjohn]

good thanks for the reply it is always nice to get a really good answer i look up all of questions on this forum because of the scientific sense people make

 

[phinds]

good thanks for the reply it is always nice to get a meaningless answer i look up all of questions on this forum because of the scientific sense people make

Hm ... I hope that you meant "meaningful" and not "meaningless".

 

[D H]

gttjohn, phinds answer was not at all meaningless. Your original post expressed a common misconception of the big bang, that it was an explosion in space.

As far as why the expansion of the universe is accelerating, he answered that too: We don't know. Answering that question is but one part of the biggest prize in theoretical physics, a theory of everything. Nobody has one that prize yet. The best answer to your question remains "We don't know."

 

[D H]

Hm ... I hope that you meant "meaningful" and not "meaningless".

Look at the "Last edited by" in the bar above gttjohn's post. I replaced a phrase that isn't allowed at this site with "meaningless". He apparently did not like your answer. In that edit I tried to stay faithful to the intent of gttjohn's post but at the same time stay within the bounds of our rules.

 

[phinds]

Look at the "Last edited by" in the bar above gttjohn's post. I replaced a phrase that isn't allowed at this site with "meaningless". He apparently did not like your answer. In that edit I tried to stay faithful to the intent of gttjohn's post but at the same time stay within the bounds of our rules.

Ah ... I saw a response in an email that had a bunch of asterisks, where I assume he had put BS, but I thought that he had meant to say NOT BS. If he doesn't like my answer, he's not going to do well in astronomy or cosmology.

 

[D H]

You might be right with regard to that string of asterisks. If you are right your "meaningful" would be a better interpretation than was my "meaningless".

 

[gttjohn]

guys i liked the answer i got i did not read the rules regarding what is considered offensive language sorry, but i really did appreciate the first reply ,come on lads don't put meaningless where i did not type it that's just childish , i thought you guys where among the most intelligent people in the world ,honestly let down so i am. i will repost the second post to what i meant.

 

[gttjohn]

good thanks for the reply it is always nice to get a really good answer i look up all of questions on this forum because of the scientific sense people make

 

[phinds]

guys i liked the answer i got i did not read the rules regarding what is considered offensive language sorry, but i really did appreciate the first reply ,come on lads don't put meaningless where i did not type it that's just childish , i thought you guys where among the most intelligent people in the world ,honestly let down so i am. i will repost the second post to what i meant.

Offensive language is not allowed on the board, so DH had to change your language or delete your entire post and I think he did the right thing. I see from the original post (which I have in my email, prior to the change) that he just saw the BS (or whatever word you used) and did NOT see the "no" in front of it, so he put an inappropriate "meaningless" where "meaningful" would have been appropriate. That's at least as honest a mistake as your having used offensive language in the first place.

I do agree w/ you that it does seem that on an adult board, language rules could be a bit more lax, but there are two problems. First, where do you draw the line? Second, there ARE kids on this board.

 

[D H]

I see from the original post (which I have in my email, prior to the change) that he just saw the BS (or whatever word you used) and did NOT see the "no" in front of it.

I saw something other than "no BS". All I saw was a string of asterisks which I interpreted to be the progressive tense of a certain four letter word. (Go to New York City and you'll hear this word used quite often.) Perhaps I'm a bit jaded from mentoring and seeing too many posts along the lines of

i don't want to learn this stupid *** subject i'll never use it after I pass this stupid ******* class ... one of you ******** should just tell me the the stupid ******* anser

Anyhow, sorry for the confusion that resulted from my erroneous cleanup.

 

[gttjohn]

True gentleman thank you

 

[Naty1]

gtt: ok back to science...why the Universe is expanding and accelerating, as noted, is not fully understood. In fact we are not
even positive about why this universe is here...that is, not positive about why it even exists let alone why it has the characteristics it does. And we are unsure if there are other universes...maybe even an infinite number of "parallel" universes.

One reason is this:

...Negative pressure is a property of vacuum energy, but the exact nature of dark energy remains one of the great mysteries of the Big Bang...Results from the WMAP team in 2008, which combined data from the CMB and other sources, indicate that the contributions to mass/energy density in the Universe today are approximately 73% dark energy, 23% dark matter, 4.6% regular matter and less than 1% neutrinos.[35] The energy density in matter decreases with the expansion of the Universe, but the dark energy density remains constant (or nearly so) as the Universe expands. Therefore matter made up a larger fraction of the total energy of the Universe in the past than it does today, but its fractional contribution will fall in the far future as dark energy becomes even more dominant.

http://en.wikipedia.org/wiki/Big_Bang#Dark_energy



there is great debate about just what dark energy and dark matter means...What the above implies is that convention matter (and energy) remains more or less steady but as space expands with new space containing dark matter and dark energy, it's relative effect may increase... 'Empty' space is NOT empty...
it appears the expansion is powered by a cosmological constant, which many believe
is dark energy...so based on the description above, gravity decreases and expansion rate
increases as the universe evolves. [The cosmological constant was a factor that also fooled Einstein as he developed general relativity.]

Just what "expansion" means can also be confusing...assuming you are interested enough to read an article, here is one good one:
http://dept.dawsoncollege.qc.ca/finearts/Faculty/AManniste/Big Bang.pdf
[There are other versions of this article with graphs and charts.]

You can also search in these forums for "cosmological expansion" .

 

[gttjohn]

thanks Naty1 that was a very good read ,now i have many more questions but i think i will let them stew in my mind for a while until i can ask them in the best logic i can muster up without sounding a bit thick , so actual matter as a posed to dark matter /dark energy amount is very little indeed it seams as though the more the universe expands the more dark matter /dark energy there is ,now i would love to know exactly what dark matter /dark energy is but then so would anyone else as interested as i ,thanks again

 

[phinds]

thanks Naty1 that was a very good read ,now i have many more questions but i think i will let them stew in my mind for a while until i can ask them in the best logic i can muster up without sounding a bit thick , so actual matter as a posed to dark matter /dark energy amount is very little indeed it seams as though the more the universe expands the more dark matter /dark energy there is ,now i would love to know exactly what dark matter /dark energy is but then so would anyone else as interested as i ,thanks again

Yes and no. Yes, the more the universe expands, apparently the more dark energy there is, but no, I'm not aware of anything suggesting that the amount of dark matter has changed over time (beyond, let's say, the surface of last scattering). I'm NOT, however, any kind of expert on this and could be wrong.

 

[gttjohn]

ok thanks a mill ill do a bit of searching and digging , curiosity is a pain isn't it but it is all worth while when you get the answer

 

[DWEdmondson]

Has anyone ever considered that as the universe expands that the individual bodies are in fact not traveling in a straight line but in fact curving around other bodies in a degrading orbit and accelerating as they are drawn in towards the centre of the orbit only to eventually end up in another "big bang" to start all over again?
Is the "known Universe" actually just the tip of something much larger that is constantly revolving etc. etc.?

 

[SHISHKABOB]

Has anyone ever considered that as the universe expands that the individual bodies are in fact not traveling in a straight line but in fact curving around other bodies in a degrading orbit and accelerating as they are drawn in towards the centre of the orbit only to eventually end up in another "big bang" to start all over again?
Is the "known Universe" actually just the tip of something much larger that is constantly revolving etc. etc.?

I think the problem with your suggestion is that there is no way to know if the known Universe is just the tip of something because it is by definition all we can see at this point. Therefore it would be difficult to verify your idea.

 

[Drakkith]

Has anyone ever considered that as the universe expands that the individual bodies are in fact not traveling in a straight line but in fact curving around other bodies in a degrading orbit and accelerating as they are drawn in towards the centre of the orbit only to eventually end up in another "big bang" to start all over again?
Is the "known Universe" actually just the tip of something much larger that is constantly revolving etc. etc.?

This is not possible. We can see billions of light years out from Earth and we observe the universe to be expanding. IE we see that everything is getting further away from us, and further away from everything else. This is very confusing and doesn't seem to make sense at first and there are many many threads dedicated to this concept here in the astronomy or cosmology forums.

 

[DWEdmondson]

Thanks for the replies. I agree with SHISHKABOB in that it would be difficult to verify my idea. However if the universe is of infinite size then all we could ever possibly see would be a point that is infinitely small even though we can see billions of light years from Earth. Perhaps the bit we are in is indeed expanding and indeed accelerating. Why could it not be possible that other parts of the unknown universe also be expanding or contracting from other points an infinite times over? I think the answer will always be theoretical and could never be proved beyond doubt. Astronomers need to not just believe in only what can be seen but believe that if it could be possible it IS probable. Please feel free to blow me out of the water on this!