Size of the universe
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02-07-2013, 09:39 AM
RE: Size of the universe
(02-07-2013 09:29 AM)TwoCultSurvivor Wrote:  Chas, I'm sorry I keep ignoring you on this point, but it appears you are mistaken. I am WAY out of my league in trying to explain it, but I would not have asked the question if I had not already determined that we can, in fact, see things that are farther away.

Let me invite you to read this article (and if others here take issue with this article, please feel free to weigh in. I don't want to become an expert or anything. I just want to grasp it on some level so that it makes sense.

http://en.wikipedia.org/wiki/Observable_universe

I believe you are not understanding this article.
  • We cannot see light older than 13.7 billion years - it couldn't have arrived if it is older.
  • The observable universe has, therefore, a radius of 13.7 billion years.
  • Objects whose light we see are now further away than what we observe. That is, their proper distance is now greater than their observed distance.
  • The universe is larger than the observed universe.

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Science is not a subject, but a method.
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02-07-2013, 09:47 AM
RE: Size of the universe
(02-07-2013 09:39 AM)Chas Wrote:  
  • We cannot see light older than 13.7 billion years - it couldn't have arrived if it is older.
  • The observable universe has, therefore, a radius of 13.7 billion years.

Weeeel - we detect photons, which, to us, seem to have travelled 13.7 billion light years. Therefore they seem to have been travelling for 13.7 billion years.

Neither of these things is anything but an artifact of perception.

(02-07-2013 09:39 AM)Chas Wrote:  
  • Objects whose light we see are now further away than what we observe. That is, their proper distance is now greater than their observed distance.
  • The universe is larger than the observed universe.

There is no such things as 'proper' distance.
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02-07-2013, 09:57 AM
RE: Size of the universe
(02-07-2013 09:47 AM)cjlr Wrote:  
(02-07-2013 09:39 AM)Chas Wrote:  
  • We cannot see light older than 13.7 billion years - it couldn't have arrived if it is older.
  • The observable universe has, therefore, a radius of 13.7 billion years.

Weeeel - we detect photons, which, to us, seem to have travelled 13.7 billion light years. Therefore they seem to have been travelling for 13.7 billion years.

Neither of these things is anything but an artifact of perception.

(02-07-2013 09:39 AM)Chas Wrote:  
  • Objects whose light we see are now further away than what we observe. That is, their proper distance is now greater than their observed distance.
  • The universe is larger than the observed universe.

There is no such things as 'proper' distance.

For the first time I will pretty much have to disagree with your entire post.

Astronomers use the concept of proper distance, as well as comoving distance. I was trying to keep my response simple.

Perception has nothing to do with the underlying reality - that is a philosophical cesspool of shitty understanding.

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02-07-2013, 10:03 AM
RE: Size of the universe
(02-07-2013 09:57 AM)Chas Wrote:  For the first time I will pretty much have to disagree with your entire post.

Astronomers use the concept of proper distance, as well as comoving distance. I was trying to keep my response simple.

Perception has nothing to do with the underlying reality - that is a philosophical cesspool of shitty understanding.

Perhaps I phrased it poorly. Proper distance and time are indeed relativistic concepts. They have very little to do with any intuitive definition of those same concepts.

That all perception is limited has no bearing on the accuracy of our conclusions about our observations, which for all intents and purposes are absolutely certain.
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02-07-2013, 10:05 AM
RE: Size of the universe
Thanks, Chas!

I think I hit on the same thing you said, but coming at it from a different direction.

Remember how I said galaxy X is farther away, but when we speak of its distance from us, we are projecting its distance based on how far it must have moved from us by now, but the light we're seeing is from when it was much closer to us?

Hang on, a piece of my brain just popped out of my head and landed in the break room. Be right back.
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02-07-2013, 10:10 AM
RE: Size of the universe
(02-07-2013 10:05 AM)TwoCultSurvivor Wrote:  Thanks, Chas!

I think I hit on the same thing you said, but coming at it from a different direction.

Remember how I said galaxy X is farther away, but when we speak of its distance from us, we are projecting its distance based on how far it must have moved from us by now, but the light we're seeing is from when it was much closer to us?

Depends on the context. When we are talking about observing, we are usually talking about the observed distance which is the distance the object was at when it emitted the light we observe.

Quote:Hang on, a piece of my brain just popped out of my head and landed in the break room. Be right back.

I hate when that happens. Drinking Beverage

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02-07-2013, 10:23 AM
RE: Size of the universe
(02-07-2013 10:10 AM)Chas Wrote:  
(02-07-2013 10:05 AM)TwoCultSurvivor Wrote:  Thanks, Chas!

I think I hit on the same thing you said, but coming at it from a different direction.

Remember how I said galaxy X is farther away, but when we speak of its distance from us, we are projecting its distance based on how far it must have moved from us by now, but the light we're seeing is from when it was much closer to us?

Depends on the context. When we are talking about observing, we are usually talking about the observed distance which is the distance the object was at when it emitted the light we observe.

The distance the light has travelled between us is what we call distance. That is neither the distance as it was when the light was emitted, nor the present distance (that's "when" and "present", mind).

The oldest things we observe, indeed, occupied very nearly the same point as the matter constituting us at the time they emitted the light we now observe (the beginning of time). They are what is/was 'close' enough to us that they have not been pushed, by expansion, beyond the range of our observation.
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02-07-2013, 11:52 AM
RE: Size of the universe
(02-07-2013 07:53 AM)Chas Wrote:  
(02-07-2013 07:46 AM)Humakt Wrote:  OK, watched that, everything is moving away from each other, but if everything is moving away from a central point (the detonation point) then the circumference of the universe would be getting bigger, thus the area of the universe would also be increasing, thus the observable result would that the distance between point would increase.

But, from what I understand of stuff, that makes sense. However, I dont get how there isnt a center somewhere from which this expansion is happening. If the is no center, how is it we can hold to the idea that the universe is expanding from the point of origin?

Try this page.

Thx Chas, thats a baby step forward in my understanding. One question, I have the observable universe is limited by age and C, so 14 10x9 LYs. Is the universe we've currently observed that size in radius or has occlusion or some other factor limited the distance we've observed?

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02-07-2013, 12:05 PM
RE: Size of the universe
(02-07-2013 08:01 AM)Logisch Wrote:  
(02-07-2013 07:46 AM)Humakt Wrote:  OK, watched that, everything is moving away from each other, but if everything is moving away from a central point (the detonation point) then the circumference of the universe would be getting bigger, thus the area of the universe would also be increasing, thus the observable result would that the distance between point would increase.

But, from what I understand of stuff, that makes sense. However, I dont get how there isnt a center somewhere from which this expansion is happening. If the is no center, how is it we can hold to the idea that the universe is expanding from the point of origin?

I think you may be fundamentally misunderstanding sort of how the universe is from a larger perspective. I think people imagine the big bang happening from a central point, and then everything sort of stems out specifically from this central point. This is easy to do because we're used to learning that things revolve around other things, or seeing things stemming out from the center of other things.

The big bang should really be called "the big expansion" because it wasn't an explosion and then matter just spattered out from that central point. Instead, it was a very rapid and exponential expansion of space itself. Since it was an expansion of space, it continues expanding everywhere. So really, the center is an irrelevant thing to contemplate Wink





Does your brain hurt yet? I know mine did when I started contemplating this stuff.

So rather than a tap filling up from a central point and the volume of space expanding, its more like an ever expanding shower head, with the size of the holes remaining constant so as it expands more holes pour in more space?

The one thing is if the universe is still expanding does that mean the big bang is still happening now?

Lastly, big bang seems like a woefully inexact if not misleading thing to call it.

Everlasting ooze seems to fit better.

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02-07-2013, 12:16 PM
RE: Size of the universe
(02-07-2013 12:05 PM)Humakt Wrote:  So rather than a tap filling up from a central point and the volume of space expanding, its more like an ever expanding shower head, with the size of the holes remaining constant so as it expands more holes pour in more space?
Consider
It's... kind of, er, nothing like either.

We can visualize a two-dimensional universe expanding in every direction. There's not really a way to extend that to three dimensions.

(02-07-2013 12:05 PM)Humakt Wrote:  The one thing is if the universe is still expanding does that mean the big bang is still happening now?

Just so.

(02-07-2013 12:05 PM)Humakt Wrote:  Lastly, big bang seems like a woefully inexact if not misleading thing to call it.

Everlasting ooze seems to fit better.

At this point we're probably stuck with it.

But 'bang' is a way cooler term than 'ooze'. What kind of self-respecting theory uses the word 'ooze'?
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