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-   -   Where does word universe originate from? (http://www.physicsforums.com/showthread.php?t=319364)

anonymoussome Jun11-09 12:08 PM

Where does word universe originate from?
 
I know this question is quite off the track but while watching a documentary I came across terms 'Universe' and 'multiverse'. Though I understand what they mean but I would like to have some knowledge about the history of these words.

What I wish to ask is that would anyone tell me that 'why do we call 'the universe' universe....i mean what does universe mean?'

and I would also like to know about the possibilities of parallel universes...about what work is being done in this field...is it just a possible interpretation or some significant discoveries have been made regarding it?

Chalnoth Jun12-09 02:25 AM

Re: Where does word universe originate from?
 
Quote:

Quote by anonymoussome (Post 2233185)
I know this question is quite off the track but while watching a documentary I came across terms 'Universe' and 'multiverse'. Though I understand what they mean but I would like to have some knowledge about the history of these words.

What I wish to ask is that would anyone tell me that 'why do we call 'the universe' universe....i mean what does universe mean?'

and I would also like to know about the possibilities of parallel universes...about what work is being done in this field...is it just a possible interpretation or some significant discoveries have been made regarding it?

Wikipedia's quite good here:
http://en.wikipedia.org/wiki/Universe

Basically, the word universe was originally understood as meaning "all that exists". The problem is that people have gotten slightly sloppy with how that is used, such that today instead of meaning "all that exists", it often means instead "everything visible" or even "everything that came from the same big bang event".

So the word universe becomes really confusing when we start talking about things very far away, or that potentially stemmed from other big bang events. Strictly speaking, all of those regions should also be considered part of the universe, and so we shouldn't say things like, "The universe started very hot and dense," not because our region didn't start that way (because it did), but instead because we don't know that our region is all that exists: there could be lots of other universe out there that we are unaware of at present, stuff that has had a very different history.

To try to manage this, many people have started to exclusively use the word "universe" not to mean all that exists, but instead to mean everything that came from our big bang event. Then people use the word "multiverse" to talk about everything else that is out there. There are multiple ways in which the word "multiverse" is used, however:

1. Different regions started by different big bang events.
2. Different regions from the same big bang events that have different low-energy laws of physics.
3. The parallel worlds of the many worlds interpretation of quantum mechanics.

So, even though it's not technically correct, I think that you can usually understand "universe" to only mean the part of all that exists which we can observe. When people talk about the beginning and fate of the universe, then, they're only talking about our little region, and typically aren't discussing what may or may not be going on outside of it, or even how much else there is out there.

Wallace Jun12-09 02:41 AM

Re: Where does word universe originate from?
 
To give you some historical context, early in the 20th century 'the Universe' effectively meant what we know call the Milky Way galaxy. People starting seeing these funny things they called 'spiral nebuale', which they eventually worked out were in fact a lot further away than the stars we can see, and similiar in strucuture to the thing we are sitting in. Originally these were called 'island iniverses' since they were other things similiar to the 'Universe' that we inhabited. After a while though, once we got familiar enough with this idea, the term 'Universe' started to mean us and all the other spiral nebuale so 'island universes' became 'galaxies'.

I strongly suspect that if we ever do become pretty sure that there are indeed whole other regions out there similiar to the one we inhabit we won't call them other Universes, but will eventually extend the meaning of the term Universe to encompass them, possibly coining a new term for what we currently call 'the Universe'. The very term 'multverse' I find to be ill posed.

TalonD Jun12-09 12:12 PM

Re: Where does word universe originate from?
 
From...

http://www.etymonline.com/


1589, "the whole world, cosmos," from O.Fr. univers (12c.), from L. universum "the universe," noun use of neut. of adj. universus "all together," lit. "turned into one," from unus "one" (see one) + versus, pp. of vertere "to turn" (see versus). Properly a loan-translation of Gk. to holon "the universe," noun use of neut. of adj. holos "whole" (see safe (adj.)).

marcus Jun12-09 12:32 PM

Re: Where does word universe originate from?
 
Quote:

Quote by anonymoussome (Post 2233185)
why do we call 'the universe' universe....i mean what does universe mean?'

Quote:

Quote by Chalnoth (Post 2234103)
Wikipedia's quite good here:
http://en.wikipedia.org/wiki/Universe

Right on! Wikipedia takes the word right back to Cicero and Lucretius, everything turned (versum) into one (uni)


Quote:

Quote by Wallace (Post 2234113)
...I strongly suspect that if ... we won't call them other Universes, but will eventually extend the meaning of the term Universe to encompass them, possibly coining a new term for what we currently call 'the Universe'. The very term 'multverse' I find to be ill posed.

I also find the counterfeit coinage "multiverse" deplorable. I hope that you are right and the term Universe (comprehensive all rolled into one, very useful idea) is extended as needed and remains inclusive of all physical existence.

Chronos Jun13-09 02:23 AM

Re: Where does word universe originate from?
 
The 'multiverse' is a fumbling attempt to differentiate the observable from the unobservable. The problem with the unobservable is . . . it is unobservable, hence scientifically irrelevant. Fairies all the way down [up?]. Whatever does eventually become observable will be automatically conferred membership in our semantic 'universe'.

Chalnoth Jun13-09 09:33 AM

Re: Where does word universe originate from?
 
Quote:

Quote by Chronos (Post 2235191)
The 'multiverse' is a fumbling attempt to differentiate the observable from the unobservable. The problem with the unobservable is . . . it is unobservable, hence scientifically irrelevant. Fairies all the way down [up?]. Whatever does eventually become observable will be automatically conferred membership in our semantic 'universe'.

I wouldn't say that. Just because stuff that lies outside our region of the universe isn't directly observable doesn't mean it isn't indirectly observable. It is well within reason, for instance, that experimentally-confirmed theories of the behavior of the universe here within our own observable region lead to definite, unambiguous predictions of the properties of what lies outside.

GiZeHy Jun13-09 09:42 AM

Re: Where does word universe originate from?
 
Quote:

Quote by Chalnoth (Post 2234103)
Wikipedia's quite good here:
http://en.wikipedia.org/wiki/Universe

Basically, the word universe was originally understood as meaning "all that exists". The problem is that people have gotten slightly sloppy with how that is used, such that today instead of meaning "all that exists", it often means instead "everything visible" or even "everything that came from the same big bang event".

everybody knows what is meant because it is defined. same with e.g. the word 'atom' and its original meaning. it would be pretty exhausting to change terms every time discoveries are supplemented or expanded.

Chalnoth Jun13-09 09:43 AM

Re: Where does word universe originate from?
 
Quote:

Quote by GiZeHy (Post 2235495)
everybody knows what is meant because it is defined. same with e.g. the word 'atom'. it would be pretty exhausting to change terms every time discoveries are supplemented or expanded.

The problem is that everybody doesn't know what is meant, because people use it for different things all the time.

anonymoussome Jun14-09 12:02 PM

Re: Where does word universe originate from?
 
So you mean that Universe is all that we know about...and as we keep on going on knowing more about new things....we will keep them including into our universe?

Chalnoth Jun14-09 12:46 PM

Re: Where does word universe originate from?
 
Quote:

Quote by anonymoussome (Post 2236783)
So you mean that Universe is all that we know about...and as we keep on going on knowing more about new things....we will keep them including into our universe?

That is a good description of how the term is used, yes. It is unfortunate that we have, for so long, assumed that all we knew about was all there was.

anonymoussome Jun14-09 01:09 PM

Re: Where does word universe originate from?
 
thanks mates.....

Chronos Jun15-09 12:55 AM

Re: Where does word universe originate from?
 
Agreed. Evidence of indirect forces must necessarily be included in our description of the observable universe. I would argue, however, no compelling evidence of external forces acting upon our universe has been offered to date.

ideasrule Jun15-09 07:24 PM

Re: Where does word universe originate from?
 
"Just because stuff that lies outside our region of the universe isn't directly observable doesn't mean it isn't indirectly observable."

I thought that most multiverses predicted by theory are not observable, even indirectly. Is this correct, or am I just ignorant?

Chalnoth Jun15-09 07:48 PM

Re: Where does word universe originate from?
 
Quote:

Quote by ideasrule (Post 2238565)
"Just because stuff that lies outside our region of the universe isn't directly observable doesn't mean it isn't indirectly observable."

I thought that most multiverses predicted by theory are not observable, even indirectly. Is this correct, or am I just ignorant?

Only direct observation can possibly be under a fundamental limitation. Indirect observation contains so many possible alternatives that you really can't place limits upon it.

Basically the way you'd indirectly observe one of these 'multiverse' theories would be to experimentally confirm a theory through a variety of independent experiments here within our region of the universe, a theory that makes clear and unambiguous predictions as to the nature of what lies outside our region. Obviously no such theory could ever say what the precise nature of that which lies outside our region is, but it could potentially say, for instance, what the statistical properties are.

Edit: I'd just like to add that to be perfectly explicit, the fundamental limitation is that no information about what lies outside our region of the universe can possibly reach us. But we can still make use of the behavior of the matter within our own region to place limits upon what may or may not exist outside what we can observe.

marcus Jun15-09 08:00 PM

Re: Where does word universe originate from?
 
Quote:

Quote by ideasrule (Post 2238565)
"Just because stuff that lies outside our region of the universe isn't directly observable doesn't mean it isn't indirectly observable."

I thought that most multiverses predicted by theory are not observable, even indirectly. Is this correct, or am I just ignorant?

You are basically correct. There are several conjectures involving regions where different laws of physics apply that are causally separate. Statements about that kind of thing involve exotic purely speculative physics and do not appear to be testable. That kind of multiverse talk is just fantasy and shouldn't be considered science, since not empirical.

But there is a serious issue which you have to keep carefully separate. What Chalnoth was talking about is very different. Please not the distinction.

Cosmology is a mathematical science which means that what is tested are mathematical models. You want them to fit data and to be simple. It is not about what you can see, it is about what you can test.

We do not have to see the whole spactime history of the universe in order to test models.

Cosmo models based on Gen Rel have to contain large regions we can not observe or else they don't work mechanically or have to be unduly complicated.
Containing unobservable regions makes is no philosophical or epistomological problem. We can test General Relativity and its expanding geometry solutions on what we can see. And cosmology now has millions of data points to fit its models to.

The model would have to be enormously more complicated if we were to pretend that regions of space and matter out beyond our range of observation do not exist. That would be silly and one probably couldn't even build such a model. To keep the model simple and to get it to work with Gen Rel (the best, essentially the only) theory of dynamic geometry we have, and one that passes the empirical tests with impressive precision---to keep it simple and get it to work---we have to assume stuff extends out beyond range.

What we are testing is the model itself, not every individual statement that can be logically derived from the model.

The model (actually now with quantum extensions of Gen Rel and quantum cosmo one can say several versions) also extends back before what we can see.
As long as a model makes prediction about stuff we can observe in the present, and can be adequately tested, it can tell us about stuff going back earlier in time. And we can talk about what went on in that blind spot.

With some new versions, inference will go back before the big bang, once those models are tested. For now we certainly back before year 380,000, even though that was when the oldest light we can see was emitted.

We can only see back to year 380,000 but we can talk reasonably about stuff going on before that. In a math science you routinely study stuff you can't see, by fitting a model to stuff you can.

And in time we will probably be able to talk about process before and leading up to the big bang or the bounce as it is called in some versions.

Working with a model that you fit to data means we can talk about stuff beyond observational horizons. It's always been this way in the mathematical sciences.

That is different from those "multiverse" fantasies where you get elaborate fairyland scenarios which do not make falsifiable predictions of stuff you can not (even in principle) observe.

ideasrule Jun15-09 08:32 PM

Re: Where does word universe originate from?
 
Quote:

Quote by Chalnoth (Post 2238590)
Edit: I'd just like to add that to be perfectly explicit, the fundamental limitation is that no information about what lies outside our region of the universe can possibly reach us. But we can still make use of the behavior of the matter within our own region to place limits upon what may or may not exist outside what we can observe.

OK, so it's not as if cosmologists can ever say "look there and you'll find a relic left behind by a different universe" in the same way that biologists can say "look at these fossils and you'll see dinosaurs once walked the earth". Instead, cosmologists have to place their trust in a theory after the theory proves itself trustworthy. I would say that falls short of what I would consider indirect evidence.

Chalnoth Jun15-09 09:00 PM

Re: Where does word universe originate from?
 
Quote:

Quote by ideasrule (Post 2238633)
OK, so it's not as if cosmologists can ever say "look there and you'll find a relic left behind by a different universe" in the same way that biologists can say "look at these fossils and you'll see dinosaurs once walked the earth". Instead, cosmologists have to place their trust in a theory after the theory proves itself trustworthy. I would say that falls short of what I would consider indirect evidence.

Well, I would go a little bit further than that, though. It is conceivable, for instance, that we can build experimental tests based upon these properties of other regions of our universe.

Here's an example (about quantum mechanics, not cosmology, but about a common 'multiverse' idea):
http://arxiv.org/abs/0809.4422

The proposal is that we obtain a very specific prediction of convergence rates based upon assuming the many worlds interpretation, a prediction that can be experimentally tested.


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