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jpvoid
2008-Sep-25, 02:17 PM
Hi,
I wanted to know how big the universe is and why do we treat it that way and why do we not follow newton's theory that the universe is infinite? Please do reply even though this question may seem kiddish.
Yours truly,
Jayendra

Lepton
2008-Sep-25, 02:32 PM
Hi,
I wanted to know how big the universe is and why do we treat it that way and why do we not follow newton's theory that the universe is infinite? Please do reply even though this question may seem kiddish.
Yours truly,
Jayendra

There is a "horizon" that is the age of the universe in light years. As long as the universe is increasing in size, that "horizon" will always be and anything past that point can't have anything said by science. What is the point of conjecturing about something unknown and unknowable?

jlhredshift
2008-Sep-25, 02:52 PM
There is a "horizon" that is the age of the universe in light years. As long as the universe is increasing in size, that "horizon" will always be and anything past that point can't have anything said by science. What is the point of conjecturing about something unknown and unknowable?

I don't know if it has been proven to be unknowable in the future. We just don't know. Cojecturing about the unknown is what Humans do.

As to the OP's question: because of General Relativity, and 13.7 bly comes to mind; plus or minus.

Lepton
2008-Sep-25, 02:57 PM
I don't know if it has been proven to be unknowable in the future.
Can you show mathematically how it is possible to see beyond the travel time of light?

Cojecturing about the unknown is what Humans do. No, it is what some people do but regardless of how many people do or don't, it is still pointless to conjecture about the unknown or unknowable.

jlhredshift
2008-Sep-25, 03:04 PM
Can you show mathematically how it is possible to see beyond the travel time of light?
No, it is what some people do but regardless of how many people do or don't, it is still pointless to conjecture about the unknown or unknowable.

Either we have entirely different definitions of words used here or you missed my statement "I do not know" and "future".

When research is being conducted is it something "known" or is it an attempt to find things out that our unknown? To me, I define "conjecture" equal to hypothesis.

Lepton
2008-Sep-25, 03:09 PM
Either we have entirely different definitions of words used here or you missed my statement "I do not know" and "future".

When research is being conducted is it something "known" or is it an attempt to find things out that our unknown? To me, I define "conjecture" equal to hypothesis.

No. You claimed that my saying anything outside the "horizon" bound by the speed of light is unknowable was false. I would like to see math that claims we can (or could in the future) see beyond light and transmit information beyond light speed. If you can't provide that then how can you possibly insinuate that it's wrong?

BTW, research doesn't go blindly into something that is clearly not possible (for example seeing beyond light speed).

Neverfly
2008-Sep-25, 03:16 PM
No. You claimed that my saying anything outside the "horizon" bound by the speed of light is unknowable was false. I would like to see math that claims we can (or could in the future) see beyond light and transmit information beyond light speed. If you can't provide that then how can you possibly insinuate that it's wrong?

BTW, research doesn't go blindly into something that is clearly not possible (for example seeing beyond light speed).

You're nitpicking over Nothing Lepton. Let it go already.

ETA: If I say the Universe is 46 Billion light years- are you going to jump down my throat too? What about if I say Infinite but Bounded?

jlhredshift
2008-Sep-25, 03:21 PM
No. You claimed that my saying anything outside the "horizon" bound by the speed of light is unknowable was false. I would like to see math that claims we can (or could in the future) see beyond light and transmit information beyond light speed. If you can't provide that then how can you possibly insinuate that it's wrong?

BTW, research doesn't go blindly into something that is clearly not possible (for example seeing beyond light speed).

my bold:

I claimed nor insinuated any such thing. I did not say blind conjecture. I suggest that maybe you are reading more into my statement than what I said. I will restate my thought: we do not know what advancements may occur in the future that may allow an extension of our knowledge in this area. Since it is the unknown future of which I speak it has no bearing on your correct statement of today about the horizon.

Lepton
2008-Sep-25, 03:23 PM
my bold:

I claimed nor insinuated any such thing. I did not say blind conjecture. I suggest that maybe you are reading more into my statement than what I said. I will restate my thought: we do not know what advancements may occur in the future that may allow an extension of our knowledge in this area. Since it is the unknown future of which I speak it has no bearing on your correct statement of today about the horizon.

No I am not. you claimed my statement was wrong and I asked you to back it up with mathematics. You haven't yet you keep insisting I was wrong. Either prove it or simply retract your unsupported claim.

NEOWatcher
2008-Sep-25, 03:29 PM
No I am not. you claimed my statement was wrong...
Let me make my support for jlhredshift known.
You said it was unknowable. I see that as a statement that cannot be proven because you would have to prove a negative.
Now; if you implied "currently" in your statement, that is an entirely different matter.
We just don't know, how do we know what is not known in the future?

jlhredshift
2008-Sep-25, 03:30 PM
No I am not. you claimed my statement was wrong and I asked you to back it up with mathematics. You haven't yet you keep insisting I was wrong. Either prove it or simply retract your unsupported claim.

Please quote the statement where I said you were wrong.

Lepton
2008-Sep-25, 03:31 PM
Please quote the statement where I said you were wrong.
Read your own posts. Now I will ask you once and for the last time either back up your claim with math or retract your claim. If you do neither, the only way I see to end this is by putting you on ignore.

jlhredshift
2008-Sep-25, 03:33 PM
Read your own posts. Now I will ask you once and for the last time either back up your claim with math or retract your claim. If you do neither, the only way I see to end this is by putting you on ignore.

What claim?

Lepton
2008-Sep-25, 03:34 PM
What claim?

Ignore it is.

jlhredshift
2008-Sep-25, 03:35 PM
Ignore it is.

Have a nice day.

Jeff Root
2008-Sep-25, 04:24 PM
It would be very strange if the limits of the Universe coincided with the
limits of what we can see.

We know that the Universe is vastly larger than what we can see. At a
minimum, the matter which emitted the cosmic background radiation that
we see is now about 46 billion light-years away. Analysis of temperature
variations in the CMBR indicate that it must be far, far larger than that.

The Universe may be infinite. However, the Big Bang must have involved
a finite amount of matter/energy, even if it was absurdly, unimaginably big.
Clearly it was all in causal contact at the start of the Big Bang, some
13.7 billion years ago. That couldn't be if it were infinite. However, that
says nothing about the possibility of other Big Bangs, or smaller Bangs,
elsewhere in a larger, perhaps infinite metauniverse within which our
finite Universe resides.

-- Jeff, in Minneapolis

Lepton
2008-Sep-25, 04:29 PM
It would be very strange if the limits of the Universe coincided with the
limits of what we can see.

Yes but what is observable is limited by a "horizon" due to the speed of light.

nauthiz
2008-Sep-25, 04:39 PM
Can you show mathematically how it is possible to see beyond the travel time of light?

Those dark flow (http://www.bautforum.com/astronomy/79221-more-dark-stuff-dark-flow.html) folks may have figured out a way to at least gather observational evidence about things beyond our cosmic horizon.

alainprice
2008-Sep-25, 04:42 PM
The Universe may be infinite. However, the Big Bang must have involved
a finite amount of matter/energy, even if it was absurdly, unimaginably big.
Clearly it was all in causal contact at the start of the Big Bang, some
13.7 billion years ago. That couldn't be if it were infinite. However, that
says nothing about the possibility of other Big Bangs, or smaller Bangs,
elsewhere in a larger, perhaps infinite metauniverse within which our
finite Universe resides.

-- Jeff, in Minneapolis

How is this clear?

Just because we define a horizon to our observable universe doesn't mean objects we see near this limit aren't affected by matter we can not yet see. We can in theory observe matter indirectly by its gravitation influence and possible the other forces.

Our horizon is just that, OUR horizon. It is not an end all stat to the matter we can observe.

edit: Nauthiz beat me to the punch.

John Mendenhall
2008-Sep-25, 04:54 PM
Ahem, gentle folk, perhaps some more decorum?

To the OP, this sounds like a homework assignment. Yes? No? Personally, I don't care if it is, but there are folks on the forum who do, and won't answer questions if it is.

Your questions about size come up often. You can check old threads, or the FAQ section, or other teaching sites.

Briefly, the visible universe is about 27.4 billion light years in extent and 13.4 billion years in age. There are parts of the universe that are unreachable,, that are moving away at greater than c, the speeed of light. It's probably infinite, or at least unbounded. This is all based on the big bang theory, which is quite well supported by observation. And it's also flat to within 2% to 3% over cosmological distances, i.e., no extra dimensions, no hidden spaces, etc. It also has no center, does not spin, and the laws of physics are the same everywhere.

There's enough in the above paragraph for a lifetime career as a physicist or astronomer. Have fun. Keep posting. Ignore the squabble that went on above, you now know that even adults disagree.

nauthiz
2008-Sep-25, 04:59 PM
If the large-scale structure of the universe is spherical, it may actually be smaller than the 46 billion light years in any direction that we can see. If that's the case, then the most distant galaxies we can see might actually another view of closer galaxies: one image for light taking the short path around the universe, another image for light taking the long way around.

nauthiz
2008-Sep-25, 05:03 PM
Briefly, the visible universe is about 13.7 billion light years in extent and age.
Only if we assume the universe is static. If the theory that the universe is expanding is correct, then the distance to the horizon is actually about 46 billion light years.

speedfreek
2008-Sep-25, 06:11 PM
The universe is currently 13.7 billion years old.

The CMBR photons that we currently detect were emitted when the universe was only around 379,000 years old. Those photons were around 42 million light years away when they were emitted.

Those CMBR photons took a little under 13.7 billion years to reach us due to the expansion of the universe. The coordinate that those CMBR photons were emitted from is estimated to have receded from us, due to that expansion, to a current distance of around 46 billion light-years.

The most distant galaxy we have detected, in terms of light travel time, is a galaxy with a redshift a little under z=7. That galaxy was around 3.6 billion light-years away when it emitted the light we are now seeing. It emitted that light only around 800 million years after the Big-Bang, some 12.9 billion years ago. That galaxy is estimated to be around 29 billion light-years away by now.

The most distant galaxies we have detected, in terms of proper distance when the light we are seeing was emitted, is a galaxy at the Hubble distance, where the expansion of the universe leads to an apparent recession at the speed of light. These galaxies have a redshift of around z=1.4 and they were around 5.7 billion light-years away when they emitted the light we detect. They emitted their light 9 billion years ago and are now estimated to be around 13.7 billion light-years away.

astromark
2008-Sep-25, 07:29 PM
For me one of the most intriguing questions of astronomy is this;' How big?' 'How old?'
Jeff Root and John Mendenhall and Speedfreak have offered you the accepted view...
To argue the Semantics of this is pointless as we can not know what we can not see. Only to offer this... Trust in those who are doing the work.
' Finite,' yes because if there was a great expansion from a singularity then it had a starting point. It can only be finite in mass content.
' Unbound,' yes because the expansion is accelerating into infinity. So the understanding is, At this time. ' Finite and unbound.'

Jeff Root
2008-Sep-25, 07:33 PM
To the OP, this sounds like a homework assignment. Yes? No?
A homework assignment asking how big the Universe is? What class
would that be for? Science fiction writing?

Briefly, the visible universe is about 27.4 billion light years in extent
and 13.4 billion years in age.
It appears that you edited this after nauthiz commented on it.

The figure of 27.4 billion light-years is the sum of the distance light
from the decoupling era has traveled to reach us from one direction
plus the distance it has traveled from the opposite direction. That
sum doesn't have any significance. It is a distance that doesn't
correspond to anything real. The matter which emitted that light
was only about 42 million light-years away from our current location
at the time it emitted the light, and is now some 46 billion light-years
away from our current location. As speedfreek says.

-- Jeff, in Minneapolis

John Mendenhall
2008-Sep-25, 08:39 PM
The figure of 27.4 billion light-years is the sum of the distance light
from the decoupling era has traveled to reach us from one direction
plus the distance it has traveled from the opposite direction. That
sum doesn't have any significance. It is a distance that doesn't
correspond to anything real. The matter which emitted that light
was only about 42 million light-years away from our current location
at the time it emitted the light, and is now some 46 billion light-years
away from our current location. As speedfreek says.

-- Jeff, in Minneapolis

Yes, yes, and yes to various estimates for the size of the universe. The OP's
questions sound to me like an honors science class homework. I just picked an easy to understand value for the size. 13.7 in all directions gives 27.4. diameter. Of course, the value after expansion for what we see should currently be 40 +, but I expect the OP to dig that out independently from the references. I'm don't want to do the whole homework assignment, if it is one, but I don't mind aiming the OP in the right direction.

Regards, John M.

jlhredshift
2008-Sep-26, 02:40 AM
Yes, yes, and yes to various estimates for the size of the universe. The OP's
questions sound to me like an honors science class homework. I just picked an easy to understand value for the size. 13.7 in all directions gives 27.4. diameter. Of course, the value after expansion for what we see should currently be 40 +, but I expect the OP to dig that out independently from the references. I'm don't want to do the whole homework assignment, if it is one, but I don't mind aiming the OP in the right direction.

Regards, John M.

first: Thank you NEOWATCHER and NEVERFLY

I don't think we have to fear that we are answering the homework question. It will be whatever the teacher decides is correct from whatever source that teacher chooses. This is a question that IMHO will be debated for a good deal of time yet. Trying to discern galactic motion out at the edge to determine what effect possibly unseen mass is having could extend our knowledge.

Lepton
2008-Sep-26, 03:38 AM
Let me make my support for jlhredshift known.
You said it was unknowable. I see that as a statement that cannot be proven because you would have to prove a negative.
Now; if you implied "currently" in your statement, that is an entirely different matter.
We just don't know, how do we know what is not known in the future?

1+1=2. It will be 2 tomorrow, next month, next year and the same until eternity. Gee, I told the future, maybe I should apply for the million dollar challenge.

Neverfly
2008-Sep-26, 04:29 AM
1+1=2. It will be 2 tomorrow, next month, next year and the same until eternity. Gee, I told the future, maybe I should apply for the million dollar challenge.

Irrelevant.
The mathematics will not necessarily change. But that has nothing to do with how future discoveries may enhance our ability to measure what is out there.

It is to that which jlhredshift refers- Nothing he said was ATM in any way.

Nor can anyone back up such a statement mathematically- Your demand was absurd.
The dispute is strangely ridiculous Lepton and it would be a large help if you reviewed what was actually said and tried to learn how to relax a bit.
I've been learning it too- so it's not like I'm singling you out.

first: Thank you NEOWATCHER and NEVERFLY
You owe me two chocolate chip cookies.

Ari Jokimaki
2008-Sep-26, 05:29 AM
What is the point of conjecturing about something unknown and unknowable?
Opening post was jpvoid's first post here, and you come in with this rude remark. What is the point with that?

It is perfectly legitimate to ask what our current cosmological models say about the size of the universe. Scientists do that all the time. If the model says universe is infinite for example, it has consquences to our understanding of the universe at the beginning and at the present. You don't believe me? Check out these scientific papers (which are just few examples of large amount of papers on the subject):

Extending the WMAP Bound on the Size of the Universe - Shapiro Key et al. (2006) (http://arxiv.org/abs/astro-ph/0604616)
The Most Probable Size of the Universe - McInnes (2005) (http://arxiv.org/abs/hep-th/0509035)
Nonlocal Quantum Gravity and the Size of the Universe - Reuter & Saueressig (2003) (http://arxiv.org/abs/hep-th/0311056)
The Age and Size of the Universe - van den Bergh (1995) (http://adsabs.harvard.edu/abs/1995JRASC..89....6V)
Observability of the size of the universe - Abe (1989) (http://adsabs.harvard.edu/abs/1989PhLB..229..202A) (I have access only to the abstract but this paper seems to claim that size of the universe is observable in principle)

I also agree with jlhredshift in that we don't know if this question is "unknowable". In my opinion, claiming that something is unknowable is religion, not science.

astromark
2008-Sep-26, 06:08 AM
Its good to see the work being done on this... and just maybe we should not ever close this thread, for more knowledge will change our view of this absolute uncertainty. There is always more to learn. Conceptual understanding is more important than the numbers, In my humble opinion...

jlhredshift
2008-Sep-26, 11:40 AM
I also agree with jlhredshift in that we don't know if this question is "unknowable". In my opinion, claiming that something is unknowable is religion, not science.

In case someone doesn't know, I study the history of science. Many times an impasse of knowledge has structured scientific thought for long periods of time; and the thought in place would be considered "mainstream". Then, literally, a breakthrough would occur that I find analogous to a speciation event after a mass extinction. Microscopic discovery of bacteria, macroscopic observation of the moons of Jupiter, radiometric dating (age of the Earth), magnetic reversals (plate tectonics), and DNA, are all examples of breakthroughs and of course there are many more. In my view as long as Humankind has breath, advances will continue to be made, it is our way. The impossible just takes a little longer (not my quote; if someone happens to know who actually said that first in print, let me know.) (And, fresh cookies are on the table, everyone is welcome; no exceptions)

NEOWatcher
2008-Sep-26, 12:01 PM
Opening post was jpvoid's first post here, and you come in with this rude remark. What is the point with that?
Yes; that made me mad too. jpvoid is asking a legitimate question, there are mainstream ideas out there and those were all shot down in one sweeping opinion.
I wouldn't mind if someone says there are popular ideas that ____, but I think ____. At least it gives the person something to go by.

jpvoid - I hope you return and weren't put off by this. I think it is a valid question, and from some of the good comments here, you can see there are plenty of ways of looking at it.

And; if it's a homework assignment? Who cares as long as there's a test at the end. That's when it will show if it was the easy way out.

Neverfly - Is one of those cookies mine, or do I have to beg for 2 myself?

Lepton
2008-Sep-26, 12:49 PM
Opening post was jpvoid's first post here, and you come in with this rude remark.Rude remark? The question mark at the end should have let you know it wasn't a remark you were responding to but a question. Actually your remark was the rude one.

Neverfly
2008-Sep-26, 02:02 PM
Neverfly - Is one of those cookies mine, or do I have to beg for 2 myself?

(And, fresh cookies are on the table, everyone is welcome; no exceptions)

Gotta beg for milk.

Ross PK81
2008-Sep-26, 03:22 PM
Something going on forever just doesn't seem logical, infact infinity itself just doesn't seem logical, except in maybe one or two cases, that I wont bother mentioning.

nauthiz
2008-Sep-26, 03:34 PM
Having a discrete border doesn't seem logical either.

Speculating too much on the concievability of either option is probably getting dangerously close to questions like "Why is there something rather than nothing?"

Neverfly
2008-Sep-26, 03:37 PM
Something going on forever just doesn't seem logical, infact infinity itself just doesn't seem logical, except in maybe one or two cases, that I wont bother mentioning.

It's funny.
I both agree and disagree.
I agree that I would be hard pressed to consider the Universe itself to be Infinite and Unbounded.

However, the Universe rarely conforms to what we might think is logical.

My own personal image of the Universe is almost like a bubble. Like bacteria in a drop of water. An expanding drop of water that's 46 billion light years heading thataway...

Ross PK81
2008-Sep-26, 04:32 PM
Having a discrete border doesn't seem logical either.

Speculating too much on the concievability of either option is probably getting dangerously close to questions like "Why is there something rather than nothing?"

I think about that a lot too. And also, how the hell am I 'aware'?

Jeff Root
2008-Sep-26, 05:13 PM
I have said before that some people cannot imagine an infinite Universe,
and so prefer to think of the Universe as finite. Others cannot imagine a
finite Universe, and so prefer to think of the Universe as infinite. And yet
others cannot imagine the Universe as either infinite or finite. Some of
them like to think of it as a paradox. Some find the idea so spooky that
they don't want to think about it. Some study the question to try get
an answer.

When I replied to John Mendenhall's suggestion that "this sounds like
a homework assignment" with:

A homework assignment asking how big the Universe is? What class
would that be for? Science fiction writing?
I said that because science homework generally asks questions which
can be answered correctly. The question "How big is the Universe?"
is not a question which can be answered correctly. The teacher might
be able to grade the answer in terms of how thoughtful and articulate
it is, but not in terms of whether it is right or not.

When I read the string of posts from Lepton at the start of this thread,
I was going to criticize both his opinion of the limits of knowledge and
his totally senseless attack on jlhredshift, but I decided that doing so
would detract from my message to the original poster, so let it go.
But, me too. Lepton made wild interpretations of jlhredshift's posts,
completely unsupported by what jlhredshift actually said.

-- Jeff, in Minneapolis

NEOWatcher
2008-Sep-26, 05:16 PM
The teacher might
be able to grade the answer in terms of how thoughtful and articulate
it is, but not in terms of whether it is right or not.
Especially if this is poetry class. :whistle:

Neverfly
2008-Sep-26, 05:19 PM
Especially if this is poetry class. :whistle:
Wordsmithing.:neutral:

Spaceman Spiff
2008-Sep-27, 03:41 AM
Try this (http://en.wikipedia.org/wiki/Observable_universe). You'll like it.

astromark
2008-Sep-27, 06:30 AM
jlrredshift; :)Fresh cookies... thanks, Ain't the web a great place.

This train of thinking is defeatist. The idea that we should not answer a question that we can not answer correctly...wow, I would never go striding in. Not like I am so well informed or know much more than a ninth grader. Most of us contribute with some regard for science. I do not take lightly the responsibility I see to empower the young with knowledge. I would dare suggest that as the primary reason for contributing. Out of ignorance does come the bad astronomer. Now I am well aware that at no point did anyone say we should not add our tuppence worth. As I am and will do...:)can I win the poetry quiz, please please please.
N.B. do not eat cookies at bed time. look what happens.:(

Neverfly
2008-Sep-27, 09:03 AM
There is nothing wrong with late night snacking.

http://www.toymania.com/columns/spotlight/images/s1gremlinstitle.jpg
Maybe the Universe is not big enough...

astromark
2008-Sep-27, 11:53 AM
There is nothing wrong with late night snacking.

http://www.toymania.com/columns/spotlight/images/s1gremlinstitle.jpg
Maybe the Universe is not big enough...

Well thats the first time I have had this happen... tried that link and got " FORBIDDEN "
Which is in itself odd. I will look for a back door. Not one to give up so easy... Where's my coffee and croisants...:);)

Understanding the universe is a big ask... There are those that have made this their life's work. While for most of us ( me anyway ) the quest for the what and how and even when is all just a little part of the greater study of life and astronomy. This does not cheapen the want to know. Excepting I may never is still OK. Just not as satisfying.

Neverfly
2008-Sep-27, 01:07 PM
Well thats the first time I have had this happen... tried that link and got " FORBIDDEN "

Yes, it is odd... I posted the link in img tags.
It should just show up...

It's just a picture depicting the Gremlins from the 80's movie.

First Scope
2008-Sep-27, 06:48 PM
Should we mention the views of John Dobson here?

The Student may be a monk?

First Scope
2008-Sep-28, 07:24 PM
Jeez,

I thought for sure I would get tore up over that one LOL

I guess the universe must be Alive and is Re-incarnating through black holes?

jlhredshift
2008-Sep-29, 01:23 PM
Last night the History channel "reported" that the size of the Universe is "156 bly". I wonder if Kaku or Rees gave them that number?

P.S. Milk and coffe always available at the farm.

speedfreek
2008-Sep-29, 05:49 PM
The History Channel was repeating a common misconception about the conclusions made in the paper:

Extending the WMAP Bound on the Size of the Universe (http://arxiv.org/abs/astro-ph/0604616)

We think the observable universe has a radius of 46 billion light years and thus a diameter of 92 billion light-years. But the question arose as to whether the overall topology of the universe might "wrap around", meaning that if the whole universe were small enough and light had been able to circumnavigate it, we might be looking at the same regions of space when we look in opposite directions!

If that were the case, our diameter of 92 billion light-years might contain repeated regions of space, and the whole universe might actually be smaller than we think! So a group of scientists analysed the CMBR data for any indication of repeating patterns in different areas (a "matching circle" analysis) and found none.

They were able to say with confidence that at least 78 billion of our 92 billion light-years diameter observable universe was comprised of unique space, so the whole universe must have a diameter of at least 78 billion light-years.

Unfortunately, early in the media reporting of these results, someone inferred that the 78 billion light-years figure represented a radius, and doubled it to a 156 billion light-year diameter erroneously.

See here (http://en.wikipedia.org/wiki/Observable_universe#Misconceptions) for this and other misreported figures for the size of the universe.