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Author Topic:   Question About the Universe
GDR
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Posts: 4240
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 2.0


(1)
Message 1 of 373 (506827)
04-29-2009 3:46 PM


I'm having a tough time understanding this.

This story just came out recently.

Star 13 Billion Light Years Away

I'm told that the universe is about 13 billion years old, and here we have a star that is observed by us to be 13 billion light years away.

1/ Doesn't this mean that what we are now seeing is that star as it was at a time very shortly after the Big Bang?

2/ I also understood that there is an "event horizon" because of the expansion of the universe that has moved galaxies beyond our ability to perceive them. However here we have a star that has been here since nearly T=0 and we're still able to view it. Why is that?

3/ Using the penny on the balloon analogy shouldn't this mean that we are looking virtually all the way around the balloon, (the universe), and if we looked in another direction that we could see the same star very much closer?

I'm only suggesting this as a topic of discussion for my own information. I don't pretend to have the knowledge to actually debate it.


Replies to this message:
 Message 3 by RDK, posted 04-29-2009 6:39 PM GDR has not yet responded
 Message 4 by cavediver, posted 04-29-2009 6:45 PM GDR has responded
 Message 6 by Blue Jay, posted 04-29-2009 11:45 PM GDR has responded

    
AdminNosy
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From: Vancouver, BC, Canada
Joined: 11-11-2003


Message 2 of 373 (506839)
04-29-2009 6:21 PM


Thread moved here from the Proposed New Topics forum.
  
RDK
Junior Member (Idle past 2622 days)
Posts: 26
From: Ann Arbor, Michigan
Joined: 11-23-2008


Message 3 of 373 (506842)
04-29-2009 6:39 PM
Reply to: Message 1 by GDR
04-29-2009 3:46 PM


First of all, let's do a little math. The current consensus on the age of the universe is somewhere around 13.73 billion years, with an error margin of about 120 million years.

What's important to keep in mind is the vastness of time periods we're talking about. While 120 million years may seem like small change when comparing it to the total age of the universe, realize that a lot can happen in the way of cosmological evolution during the course of 120 million years.

This is from your article itself:

TheStar.com writes:

"We now have the first direct proof that the young universe was teeming with exploding stars and newly born black holes only a few hundred million years after the Big Bang," he said.

Seeing as how a billion (1,000,000,000) is one thousand million (1,000,000), this gives plenty of time for this star to have appeared sometime after the Big Bang.

In any case, someone else on this forum can probably explain it with greater detail than I can. Cosmology isn't my forte; I'm a biology major. ;)

Edited by RDK, : No reason given.

Edited by RDK, : No reason given.


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cavediver
Member (Idle past 996 days)
Posts: 4129
From: UK
Joined: 06-16-2005


(1)
Message 4 of 373 (506844)
04-29-2009 6:45 PM
Reply to: Message 1 by GDR
04-29-2009 3:46 PM


Hi GDR,

1/ Doesn't this mean that what we are now seeing is that star as it was at a time very shortly after the Big Bang?

Yes (on the order of several hundred million years after the BB)

2/ I also understood that there is an "event horizon" because of the expansion of the universe that has moved galaxies beyond our ability to perceive them. However here we have a star that has been here since nearly T=0 and we're still able to view it. Why is that?

We are seeing the "star" before the cosmological expansion carries it over the cosmological horizon. If we continue to observe it over time, we will see it receed and redden to the point that it fades from view.

3/ Using the penny on the balloon analogy shouldn't this mean that we are looking virtually all the way around the balloon, (the universe), and if we looked in another direction that we could see the same star very much closer?

No - even if the Universe is closed as in the balloon analogy, this is on a scale unimaginably larger than the distance to the "star", because of inflation. In an inflated closed universe, the observable universe is a tiny fraction of the whole universe.

Edited by cavediver, : No reason given.


This message is a reply to:
 Message 1 by GDR, posted 04-29-2009 3:46 PM GDR has responded

Replies to this message:
 Message 5 by GDR, posted 04-29-2009 7:37 PM cavediver has responded

  
GDR
Member
Posts: 4240
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 2.0


Message 5 of 373 (506851)
04-29-2009 7:37 PM
Reply to: Message 4 by cavediver
04-29-2009 6:45 PM


cavediver writes:

Yes (on the order of several hundred million years after the BB)

Stephen Hawking write that after 1,000 million, (an American billion), years after the BB "Clusters of matter form quasars, stars and proto-galaxies". If as RDK says, the universe is 13.87 billion years old, wouldn't this make it among the very first stars to be formed?

cavediver writes:

We are seeing the "star" before the cosmological expansion carries it over the cosmological horizon. If we continue to observe it over time, we will see it receed and redden to the point that it fades from view.

cavediver writes:

No - even if the Universe is closed as in the balloon analogy, this is on a scale unimaginably larger than the distance to the "star", because of inflation. In an inflated closed universe, the observable universe is a tiny fraction of the whole universe.

As I understand it, we are seeing the light that left that star 13 billion years ago even though, from our perspective, that star has since that time inflated beyond the cosmological horizon. If then, we can look out into space and see things as they were 13 billion ago then what is left to have inflated beyond our ability to perceive?


This message is a reply to:
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Replies to this message:
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Blue Jay
Member (Idle past 50 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 6 of 373 (506871)
04-29-2009 11:45 PM
Reply to: Message 1 by GDR
04-29-2009 3:46 PM


Expansion and the Movement of Light
Hello, GDR.

I'm not even going to pretend I can answer your question. Rather, I'm going to add to it, to make it more confusing. :)

If the universe has been expanding since the Big Bang, wouldn't this mean that a star 13 billion lightyears away was less than 13 billion lightyears away at a time closer to the Big Bang?

So, would it still have taken the light 13 billion years to get here from there?
Or, if it was 10 billion lightyears closer at the time of its formation, would the light have reached here 10 billion years earlier?


-Bluejay/Mantis/Thylacosmilus

Darwin loves you.


This message is a reply to:
 Message 1 by GDR, posted 04-29-2009 3:46 PM GDR has responded

Replies to this message:
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GDR
Member
Posts: 4240
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 2.0


Message 7 of 373 (506875)
04-30-2009 12:39 AM
Reply to: Message 6 by Blue Jay
04-29-2009 11:45 PM


Re: Expansion and the Movement of Light
Hi Bluejay

I believe, that although the star would have been closer in the past it doesn't change the fact that the light from that star that was recently viewed left it 13 billion years ago. I would imagine that if we could see that star as things are right now it would likely have burned itself out, but if it still existed it would be much further away than 13 billion light years.


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Blue Jay
Member (Idle past 50 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 8 of 373 (506900)
04-30-2009 9:16 AM
Reply to: Message 7 by GDR
04-30-2009 12:39 AM


Re: Expansion and the Movement of Light
Hi, GDR.

GDR writes:

I believe, that although the star would have been closer in the past it doesn't change the fact that the light from that star that was recently viewed left it 13 billion years ago.

If the expansion of the universe is slower than the speed of light, shouldn't it have been able to shave off at least a little bit of the transit time?


-Bluejay/Mantis/Thylacosmilus

Darwin loves you.


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Replies to this message:
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onifre
Member (Idle past 303 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 9 of 373 (506959)
04-30-2009 2:05 PM
Reply to: Message 8 by Blue Jay
04-30-2009 9:16 AM


Re: Expansion and the Movement of Light
Hi Bluejay,

If the expansion of the universe is slower than the speed of light, shouldn't it have been able to shave off at least a little bit of the transit time?

The space in between galaxies is expanding at a rate that is faster than light speed. That does not mean that the objects in space are traveling at a rate faster than lightspeed, in fact, they are barely moving at all - in comparison to (c).

That's why eventually we won't be able to see objects that we could once see, their light will not be able to reach us since the space between us and them, so to speak, is expanding at a rate faster than that of (c).

... as I understand it.

- Oni

Edited by onifre, : No reason given.


"I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks

"I never knew there was another option other than to question everything"--Noam Chomsky


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onifre
Member (Idle past 303 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


(1)
Message 10 of 373 (506961)
04-30-2009 2:11 PM
Reply to: Message 5 by GDR
04-29-2009 7:37 PM


Hi GDR,

In an attempt to better help me understand it too, I'll try to answer this so if I get it wrong cavediver will be able to correct my understanding of it as well.

If then, we can look out into space and see things as they were 13 billion ago then what is left to have inflated beyond our ability to perceive?

What is left to "inflate beyond our ability to see it" is what we can currently see.

With time, billions of years of course, from our point in space, we will not be able to see anything more than the clusters near us. Everything else will be out of our "sight" due to the expansion rate being faster than light can travel.

... as I understand it.

- Oni


"I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks

"I never knew there was another option other than to question everything"--Noam Chomsky


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cavediver
Member (Idle past 996 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 11 of 373 (506964)
04-30-2009 2:19 PM
Reply to: Message 5 by GDR
04-29-2009 7:37 PM


If as RDK says, the universe is 13.87 billion years old, wouldn't this make it among the very first stars to be formed?

Aboslutely - unless we have something very wrong!

As I understand it, we are seeing the light that left that star 13 billion years ago even though, from our perspective, that star has since that time inflated beyond the cosmological horizon.

Not "inflated" - inflation is reserved for what happened in the first 10-34sec of the Universe - but "carried by the expansion of the Universe" would be fine.

If then, we can look out into space and see things as they were 13 billion ago then what is left to have inflated beyond our ability to perceive?

I'm not sure I understand your question. Most of the Universe has never been visible to us and never will. This "star" was relatively very close to us for it to be visible at all.


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cavediver
Member (Idle past 996 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 12 of 373 (506965)
04-30-2009 2:29 PM
Reply to: Message 6 by Blue Jay
04-29-2009 11:45 PM


Re: Expansion and the Movement of Light
If the universe has been expanding since the Big Bang, wouldn't this mean that a star 13 billion lightyears away was less than 13 billion lightyears away at a time closer to the Big Bang?

Yes - much much closer. If you imagine the sphere on the sky centred on us with surface so far away that it contains this star, the actual surface area of that sphere is relatively quite small - much smaller than many of the concentric spheres that are much closer to us! Think of standing on the North Pole, and being surrounded by the lines of latitude. The Arctic Circle is obviously smaller than the Tropic of Capricorn, and the Equator, but by the time we reach the Tropic of Cancer, the surrounding circles are growing smller, down past the Antarctic Circle and finally we reach the South Pole as a point.


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cavediver
Member (Idle past 996 days)
Posts: 4129
From: UK
Joined: 06-16-2005


(1)
Message 13 of 373 (506967)
04-30-2009 2:35 PM
Reply to: Message 8 by Blue Jay
04-30-2009 9:16 AM


Re: Expansion and the Movement of Light
If the expansion of the universe is slower than the speed of light

Doesn't make sense. Expansion is measured in how much distance appears in so much time in so much existing distance. So, 10m/sec per km is an expansion rate. Every second, any distance of 1km becomes 1.01km. This is not a speed or velocity. You could say that across 1km, space is expanding at 10m/sec and you'd sort of have a point. Is this faster than light? Of course not. But what about this same expansion across 5x108km? Across that distance, you could say that space is expanding at 5x109m/sec, which is significantly faster than light. Any uniform expansion rate, over a sufficient distance, creates a "superluminal" expansion.


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 Message 8 by Blue Jay, posted 04-30-2009 9:16 AM Blue Jay has responded

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Blue Jay
Member (Idle past 50 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 14 of 373 (506969)
04-30-2009 2:50 PM
Reply to: Message 13 by cavediver
04-30-2009 2:35 PM


Re: Expansion and the Movement of Light
Hi, Cavediver.

cavediver writes:

Any uniform expansion rate, over a sufficient distance, creates a "superluminal" expansion.

Okay. So, is the expansion rate uniform, or close enough to it to get away with saying it is?

It also seems that, if each kilometer is thought of as expanding over a period of time, wouldn't much of the expansion between us and the other star be happening behind the light as it traveled? To my mind, this means that any light we're seeing didn't actually travel the entire distance from there to here.

Am I leaving something out?
It seems like I'm making it harder than it needs to be. :(


-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.


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Perdition
Member (Idle past 590 days)
Posts: 1593
From: Wisconsin
Joined: 05-15-2003


Message 15 of 373 (506973)
04-30-2009 3:36 PM
Reply to: Message 14 by Blue Jay
04-30-2009 2:50 PM


Re: Expansion and the Movement of Light
It also seems that, if each kilometer is thought of as expanding over a period of time, wouldn't much of the expansion between us and the other star be happening behind the light as it traveled? To my mind, this means that any light we're seeing didn't actually travel the entire distance from there to here.

I think it's the opposite. The expansion behind the light doesn't affect the light itself, so we don't see it. The expansion in front of the light, however, makes it travel longer than it would have to without any expansion, meaning the star was closer when the light was released than the total distance the light actually has to travel to reach us.


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