Size of the universe
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01-07-2013, 03:43 PM
RE: Size of the universe
Thanks, Jeffasaurus.

Expansion kind of helps, but BOOM. My head just exploded. What exactly is it that is expanding? See, in your Cityville analogy, I know what's expanding: the road. So the road is expanding while I'm driving on it. It's a little absurdist, but I can picture it. It's like two people at an airport walking away from each other, but each is on a people-mover/conveyor belt.

My head hurts.
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01-07-2013, 04:06 PM
RE: Size of the universe
(01-07-2013 03:43 PM)TwoCultSurvivor Wrote:  Thanks, Jeffasaurus.

Expansion kind of helps, but BOOM. My head just exploded. What exactly is it that is expanding? See, in your Cityville analogy, I know what's expanding: the road. So the road is expanding while I'm driving on it. It's a little absurdist, but I can picture it. It's like two people at an airport walking away from each other, but each is on a people-mover/conveyor belt.

My head hurts.

here is a visual that might help. Think of a volcanic island where the center is pushing the edges out. You begin walking away from your friend and behind you there is an ever increasing island growing.

(31-07-2014 04:37 PM)Luminon Wrote:  America is full of guns, but they're useless, because nobody has the courage to shoot an IRS agent in self-defense
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01-07-2013, 04:07 PM
RE: Size of the universe
(01-07-2013 03:24 PM)ridethespiral Wrote:  
(01-07-2013 03:08 PM)Chas Wrote:  Looking in any direction in the universe is looking back in time.

There is no center to look toward.

I'm not sure I follow? Do we not point our telescopes toward the point of the big bang to observe the early radiation patterns of the universe? I get that there is no matter there anymore and that all galaxies are moving away from each other (or at least the various local clusters are moving away from each other) at an ever increasing rate. Looking at Andromeda I'm looking back 2.5 million years, as Andromeda is relatively close (and actually on a collision course with the milkyway), but yes anywhere I look I am seeing what was....The sun will die 8 minutes before I know about it, etc.

Space itself is expanding, all things moving away from all other things.

A 2-dimensional metaphor is the surface of a polka-dotted balloon that is being inflated. All of the dots would get further from each other, and the further they were apart, the faster they would move apart.

The background microwave radiation from the Big Bang comes from every direction.

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01-07-2013, 04:12 PM
RE: Size of the universe
(01-07-2013 03:40 PM)TwoCultSurvivor Wrote:  Part of the reason I ask all this is, if a criticism of creation is that light from distant stars takes x number of years to reach earth, and that is inconsistent with the age of the earth as calculated by Biblical chronology, how do WE (atheists) account for our ability to see stars and galaxies that are so far away that the universe is not even old enough for the light from those galaxies to have reached us yet?

We don't. We cannot observe galaxies further than 13.7 billions light-years away.

The universe is larger than the observable universe.

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01-07-2013, 04:28 PM
RE: Size of the universe
Is that right? I thought we could.
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01-07-2013, 04:41 PM
RE: Size of the universe
(01-07-2013 03:24 PM)ridethespiral Wrote:  I'm not sure I follow? Do we not point our telescopes toward the point of the big bang to observe the early radiation patterns of the universe? I get that there is no matter there anymore and that all galaxies are moving away from each other (or at least the various local clusters are moving away from each other) at an ever increasing rate. Looking at Andromeda I'm looking back 2.5 million years, as Andromeda is relatively close (and actually on a collision course with the milkyway), but yes anywhere I look I am seeing what was....The sun will die 8 minutes before I know about it, etc.

Not exactly. We can't point 'towards' the big bang. It's in every direction, because it began as a singularity. We moved 'away' (poorly defined here, but it's as good a word as any) in one direction (as it were), and everything else is moving in slightly different directions.
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01-07-2013, 04:49 PM
RE: Size of the universe
I'm not really sure where to start explaining this.

Distance and time (as we understand them on an intuitive level) have no meaning on a relativistic scale.

What we see is the photons which reach us. By studying them carefully we can make guesses about what state things were in when they were emitted.

The background radiation - what we 'see' as the best evidence of the big bang - is in every direction because it began at one point and spread out essentially equally. Matter, because of its gravity, and a non-uniform distribution which is still not well understood, clumps - into galactic superclusters, down to stars and planets.

We say things are 'x billion light years away' because that is how far we think the photons have travelled. We measure this by comparing intensity to known sources (closer sources' distances can be corroborated in other ways, which are then extrapolated for distant objects). That means, in a certain (not strictly apt!) sense, that they are also 'x billion years old'. Because photons travel at the speed of light, and they have covered that distance, it's kind of convenient to think of them as that same age.

The farthest/oldest things we see are those which share their origin in the singularity of the big bang but which have since travelled close enough to us that we may still observe them. The expansion of the universe itself may be close to, or even exceed, the speed of light. This means that something on the far 'side' of a universe will not be visible to us (ever) - because the distance the light has to cover is increasing faster than it is able to cover it. This is why we conclude the 'universe' to be more than just what is actually observable.
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01-07-2013, 05:44 PM
RE: Size of the universe
(01-07-2013 01:39 PM)TwoCultSurvivor Wrote:  Can someone help me understand this? It's huge. Not interested in an appeal to religion as part of the answer.

If the Big Bang was under 14 billion years ago, how is it that there are stars and galaxies that we can observe that are more than 28 billion light years away? First off, the light hasn't had enough time to reach us. Secondly, how did we have enough time to get that far away from each other. Wouldn't we each have to be traveling faster than light to achieve this?

I'm confident science has the explanation. I'm not confident of my ability to understand it. Dr. Cooper? Dr. Hofstadter? Anyone?

This is a pretty good interactive flash demo as the the sheer size of the universe. It goes all the way down from a single string and the quantum foam of space time all the way up to the (assumed) size of the universe and the size of the known universe. Also, it's a lot of fun to use!

http://htwins.net/scale2/

To answer your question about the age and distance of stars and galaxies. The light we receive we can age and determine which direction the object is moving by means of redshift. For example, if we know that the light from some galaxy in the cosmos is 9.2 billion years old and only appears in the infrared spectrum, we can determine its moving away from us at a pretty fast rate (>80% the speed of light). Since the light originated 9.2 billion years ago and the speed of light is constant at 300,000 km/sec and the target is moving away from us at ~0.8c the total distance between us and that cosmic object is (9.2E9 years) x (9.3E15 km/year) + (0.8)*(9.3E15km/year)*(9.2E9 years) from Earth at our present time. This factors in both the distance that the light took to reach us and the relative velocity of the object in space to arrive at the final distance.

Hope that helps.

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01-07-2013, 06:11 PM (This post was last modified: 01-07-2013 06:17 PM by ridethespiral.)
RE: Size of the universe
(01-07-2013 04:07 PM)Chas Wrote:  Space itself is expanding, all things moving away from all other things.

Got that.

(01-07-2013 04:07 PM)Chas Wrote:  A 2-dimensional metaphor is the surface of a polka-dotted balloon that is being inflated. All of the dots would get further from each other, and the further they were apart, the faster they would move apart.

I get that too.

(01-07-2013 04:07 PM)Chas Wrote:  The background microwave radiation from the Big Bang comes from every direction.

I get that the radiation is dispersed, it makes up all the static on TV/radio if I understand correctly, what I don't get is how we obtain this image of the early universe unless we can point our telescopes toward the origination point of the universe:

[Image: cosmic_microwave_background_radiation_large.jpg]

Are you guys saying we can see this no matter what direction we look in?

Does space and time not exist beyond the skin of the balloon, does light not travel across the interior? How do we observe galaxies on the other other side of the balloon? Or is that all gravitational lensing?

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01-07-2013, 06:35 PM
RE: Size of the universe
(01-07-2013 06:11 PM)ridethespiral Wrote:  Are you guys saying we can see this no matter what direction we look in?

Yes, because that particular phenomenon originated in the singularity (as we all did!) but remained uniformly distributed (that's... not a good characterization, but it'll do) since then - in other words, it is equally 'spread out' in any direction we look.

Not that direction as such means much... The farther 'away' we look, the farther back in time (kind of!), and so in every direction we eventually 'see' back to an earlier time as well. The background radiation is the constant, uniform remnant of that earlier time, so it is everywhere. If that makes sense.

(01-07-2013 06:11 PM)ridethespiral Wrote:  Does space and time not exist beyond the skin of the balloon, does light not travel across the interior? How do we observe galaxies on the other other side of the balloon? Or is that all gravitational lensing?

See, the balloon is not really a very good analogy. There is no 'inside' the balloon. It is a two-dimensional universe with a closed topology. Our 'actual' universe is macroscopically three-dimenionsal, and its curvature is unknown.

The light, in that analogy, is likewise confined to the outer surface.

The thing is, we don't observe galaxies on the other side. We only suppose that they probably exist. We can only see so far in one direction - as far as the expansion of the universe has allowed said distant light to reach us. That is, looking out is looking back, and we can't look back earlier than the beginning, thus we can't look out further than that limit. We have literally no idea what is happening in the unobservable regions. Strictly speaking we cannot even say they exist - but we assume the immediate post-big-bang state was relatively uniform, and spread out relatively uniformly - which would result in areas beyond our detection.
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