Size of distant galaxies.

[BlameTheEx]

I just got the following reply to a question that has been interesting me for some time:

_______________________________________________________________________

> ---------- Forwarded message ----------

> Date: Wed, 13 Oct 2004 06:05:13 -0400

> From: [email protected]

> To: [email protected]

> Subject: Ask an Astronomer question

>

> Question:

>   The universe of the most distant galaxies observed was much smaller,

> but that earlier universe is observable in all directions. That means a

> small universe is stretched over a large field of vision. Presumably

> that means those early galaxies must be visually larger than their

> distance would suggest, but as their light is dissipated over the

> current universe, their magnitude should be as expected.

>

> Is my logic correct here, and do observations back it?

 

Your logic is correct.  However, I'm not sure that observations are really

good enough to confirm this.  Attempts to measure the expansion of the

universe by measuring the apparent length scale of galaxies have generally

not been very successful because the population of galaxies has evolved

over time.  It's thought that mini-galaxies accreted to form the galaxies

that we see today, so how do we compare the apparent size of galaxies in

the distant past to the apparent size of galaxies in the present when the

two kinds of galaxies are not really the same?  There are other problems,

like the fact that it's not always trivial to estimate the amount of dust

along the line of sight between us and a distant galaxy.  Dust makes the

galaxy dimmer, and can make it appear to be smaller than it actually is.

 

So while the effect that you describe almost certainly happens (unless our

understanding of the expansion of the universe is seriously out of whack),

I can't point to a particular set of observations as "proof".

 

Chris Springob

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Ok People. Any ideas as to how to work out how big or bright a distant galaxy actually is, rather than how it appears? We are talking about very large discrepancies here. At minimum I think a galaxy with a red shift of 6 should be about 7 times larger in diameter than distance should make it. This is a chance to finally prove, or disprove, the expanding universe theory conclusively.

[Bo]

if i'm not mistaken, your observation would only alter our notion of diameters of galaxies. the ideas of inflation arise from much more large-scale structure; that we can measure.

 

Bo

[Freethinker]

Originally posted by: Bo

if i'm not mistaken, your observation would only alter our notion of diameters of galaxies. the ideas of inflation arise from much more large-scale structure; that we can measure.

 

Bo

 

Bo:

 

Blame has tried since day one to pretend the universe is not expanding. He ahs grapsed at anything he can find to claim so. When asked for actual details, when the articles he supplies don't make it, he ignores the requests and complains to management.

 

Good luck getting any facts from him as proof.

[BlameTheEx]

Bo

 

Um. I am a tad confused. What Idea of inflation? What is it exactly that can't be measured?

 

Sorry, but your reply was too short for me to understand.

[wepe]

Hey, i just had a thought about the universe and how it all started as i was reading this forum.

 

Ok, so we have a visible universe, which means, light from distances beyond our visible universe hasn’t reached us yet so we cant see them. DUH! Ok so if we say that there was a big bang and every thing started from that point, which really is the mid-point of the universe, because everything first occured at taht point. then how does it make sense that light hasn’t reached us yet. I will explain this better as we go down. think of the initial big bang explosion. when every thing gets dispersed across the universe from the explosion (big bang), the light will travel alot faster then the matter that is being dispersed from the explosion, so lets say over the billions of years, gravity has changed and pulled matter together to form these celestial figures, like all the stars and earth and such. Ok so the paradox with this 'big bang theory’ is, how could matter (such as you and me) be this far out, and yet we cant see light from the mid-point of the universe. Look what I’m saying is everything is goofed up, we should be able to see where the big bang occurred because the initial light (being light from the big bang) should have LOOONG surpassed where we are now, BECAUSE, we are made of matter and matter doesn’t travel as fast as light does. IM SORRY IF THIS ISNT CLEAR.

 

IM STANDING PROOF THAT IF WE CAN’T SEE THE POINT WHERE THE BIG BANG OCCURED THEN THERE WAS NO BIG BANG. There had to have been some other way this all came to be.

[Freethinker]

Originally posted by: wepe

DUH! Ok so if we say that there was a big bang and every thing started from that point, which really is the mid-point of the universe, because everything first occured at taht point... when every thing gets dispersed across the universe from the explosion (big bang)...

 

IM STANDING PROOF THAT IF WE CAN’T SEE THE POINT WHERE THE BIG BANG OCCURED THEN THERE WAS NO BIG BANG. There had to have been some other way this all came to be.

Your confusion is based on a lack of understanding of the BB. In your description, you have some fixed point where the BB happened in an existing Universe and then matter from the BB spread "dispersed across the universe". In your approach the Universe already existed. This is your first error. The universe as we know it did not exist BEFORE the BB. So your explanation is wrong.

 

Further, since the universe did not exist, matter did NOT "dispersed across the universe" after the BB. The universe itself expanded, is expanding. Everything in the Universe is moving away from everything else at speeds slower than Light.

 

I hope this clears up your confusion.

[Freethinker]

Originally posted by: BlameTheEx

Um. I am a tad confused.

Nothing new there.

What Idea of inflation?

Inflation for Beginners

http://www.biols.susx.ac.uk/home/John_Gribbin/cosmo.htm

What is it exactly that can't be measured?

Interesting question. Especially since it has nothing to do with Bo's answer. He said things CAN be measured.

Sorry, but your reply was too short for me to understand.

Even longer ones seem to give you the same problem. His response is basically the same one you have received from others, such as myself, in your claims about galaxy SHAPES. You could never succesfully respond to those either.

Originally posted by: Bo

your observation would only alter our notion of diameters of galaxies.

Exchange Shapes with diameters and it's the same thing.

Originally posted by: Bo

the ideas of inflation arise from much more large-scale structure; that we can measure.

So show where the SIZE of distant galaxies is a problem for an expanding universe.

 

Or perhaps go back and prove where SHAPE is one, first?

[BlameTheEx]

wepe

 

My apologies for not defining the big bang theory under discussion.

 

The main contender, and the one under discussion, is not one of a point source of matter exploding into an already large (or infinite) universe. That version is, as you point out, easily disproved.

 

I was referring to the version where both matter AND space started as a point, and expanded out together. In this version there is no edge to space, and never was. The matter was ALWAYS more or less evenly distributed over the entire universe. Perhaps space expanded, and the matter went along for the ride, so to speak.

[Bo]

blame wrote:

Um. I am a tad confused. What Idea of inflation? What is it exactly that can't be measured?

 

hmm you're right, my use of the word inflation was actually wrong even what i meant was in reply to your remark: "This is a chance to finally prove, or disprove, the expanding universe theory conclusively"

the ideas of the expanding universe did not arise from the size of the galaxies, but from their relative speeds. so that is the realy realy large scale structure. the big bang model arised when Hubble measured that all galaxies/stars/whatever are receding away from us. on the small scale this would indeed imply that galaxies, far enough away would look larger then that they are, but unfortunatly -since galaxy evolution is hardly understood- it is (for now!) extremely difficult to use these measurements (measurements of the size of galaxies) to determine the expansion of the universe.

hmm a thought that comes to my mind here:

the dark matter theorem was introduced because the rotationspeed of a galaxy at certain distences from its centre was not in accordance with its total mass. maybe your ideas can have a crucial meaning in this context.

 

wepe wrote more or less about something that is commonly called the 'horizon problem'.

simply said: everything was together at one small point, then it blasted away, so causal contact was lost, and now we see those distand stars again. This problem is solved by the theory of inflation. Inflation means a very short time directly after the big bang, the universe expanded with a HUGE speed. (basicly much faster then the speed of light, but since the light moved along with the expansion, nothing is violated here). So after inflation all matter was widely spread through the universe, and lost all causal contact, until the time that the light from one star again reaches another star. (see eg http://superstringtheory.com/cosmo/cosmo3.html for a trip through the big bang)

 

Bo

[BlameTheEx]

Bo

 

Great minds think alike.

 

I too was wondering if Galaxy rotational speed would be a fair indicator.

 

Here is a copy of the reply I sent to Chris Springbob:

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I can see that magnitude is not going to help much. How about thickness of spectral lines? There must be some sort of upper limit to the spin speed of components of a mini galaxy.

 

Assuming that then most distant galaxies observable have a red shift of 6, I would guess that their diameter is about 7 times smaller than observed. A lot smaller than that if the predicted early hyper inflation is correct.

 

Still, assuming 7, to get the same rotational velocity the density would have to be 7 to the power of 2.5. In short, rotational velocity is a pretty good measure of mass. This mini galaxy optically stretched, would have to have a mass of about 38% of expected, but a density of about 130 times expected.

 

If these galaxies do have similar rotational speeds to current galaxies, and similar apparent diameter, then clearly they are not much less massive, but must be an awful lot denser. Accumulation of smaller galaxies into larger ones can't really be much of an explanation. Could small galaxies evolve to become that much less dense, with so little increase in mass?

 

Once again it is quite likely my logic is at fault, so I would appreciate your help.

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I still don't quite understand why this doesn't work out as an excellent test of the Expanding Universe version of the BB. If there isn't a distortion of size how can it be right? If there is, can you think of a plausible alternative theory that would also produce this distortion? I can't.

 

At the very least Chris Sprinbob's remark seems fair:

 

"So while the effect that you describe almost certainly happens (unless our understanding of the expansion of the universe is seriously out of whack),....."

 

Would it not be interesting to check if our understanding of the expansion of the universe is seriously out of whack?

 

Regarding The cause of this dark matter theorem. Presumably size distortion was assumed (It is such an obvious result of an expanding universe). Would the data also be consistent with a universe of no size distortion and no, or much less, dark matter?

[Aki]

Freethinker, please remember that this is only a light scientific discussion and we are all here to learn. No personal remarks are needed.

And maybe everyone participating in this thread should remember to read the FAQ.

 

Since this is my first official post as a moderator, I'm still learning to do the job, I'm open to suggestions/comments.

By the way Freethinker, I'm not picking on you or anything, I just think you went over the line a little bit.

 

Thanks

[Tormod]

Originally posted by: BlameTheEx

I still don't quite understand why this doesn't work out as an excellent test of the Expanding Universe version of the BB. If there isn't a distortion of size how can it be right? If there is, can you think of a plausible alternative theory that would also produce this distortion? I can't.

 

Blame,

 

I don't understand the response you got from Chris S. Like Bo wrote, the inflation happened immediately after the Big Bang, and - crucially - it lasted for a *very brief period of time*. It is believed to have happened at 10^^-32 seconds at which point the universe grew by a factor of 10^^50.

 

The universe at this point in time only consisted of energy and perhaps proto-particles, but there was no such thing as galaxies (or even normal matter).

 

So the inflationary theory cannot be tested by observation of remote galaxies. They did not form until long after the extremely brief period of inflation.

 

Here is one source: http://csep10.phys.utk.edu/astr162/lect/cosmology/inflation.html

 

Would it not be interesting to check if our understanding of the expansion of the universe is seriously out of whack?

 

Yes - but the period of inflation and the expansion of the universe are not necessarily related. We can have expansion without inflation.

[BlameTheEx]

Tormoid

 

Ok Its a bit complicated. The inflation did NOT happen just after the Big Bang. It started with the Big Bang, and still continues. An easy mistake to make. You are confusing it with the supposed hyperinflation that was immediately after the BB. I say supposed because while theories require it, there is no compelling direct evidence. I am not convinced that a BB without hyperinflation is impossible. Anyway, that is what your link is referring to. After that short period of hyperinflation the universe settled down to expanding at much the same rate as it is now, or at least so the BB theory goes.

 

 

Edit

 

Hang on a moment. Is this just a semantics problem? I would say there is no difference between the meaning of "inflation" and "expansion" in this context.

[Tormod]

No, the "inflation" was what you refer to as "hyperinflation". The "expansion" is a result of the origin of the universe, and has gone one ever since. The expansion might eventually become a contraction if the universe is closed, but the inflation cannot be reversed.

[Tormod]

To make it more clear what I mean: Inflation caused a giant universe to form from the big bang. Expansion is the subsequent growth of this universe at macro levels (ie, galaxies dont grow but the space between them is stretching.

 

Here is a rather heavy but interesting read on the topic of a finite vs infinite universe regardless of the inflation (and the role of a hot vs a cold big bang). If you read what Hawking writes here it seems he uses the term inflation to also include the current expansion. So I guess there are many opinions on this matter.

 

http://www.hawking.org.uk/lectures/inflate.html

[BlameTheEx]

I just got a reply to my last letter to Chris Springob:

 

 

OK.  I looked into it some more, and found that maybe there *is* some

observational evidence for this.  Go to this URL:

 

http://www.astr.ua.edu/keel/galaxies/obscosmo.html

 

and look for the section that begins with "The angular diameter - redshift

test".  You see a plot there of the *expected* apparent size at different

redshifts for different cosmological models.  The text suggests that there

may be observational evidence to back this up ("This effect may be in part

responsible for the large apparent sizes of very-high-redshift radio

galaxies").  But looking up those references to dig up exactly what the

observations would be too time-consuming for a busy grad student like

myself who is just doing this on a volunteer basis. 

 

If you're interested, you may want to email Bill Keeo, whose website I

found this on.  I would presume that he knows more about this and would be

able to explain it in more detail.

 

Chris Springob

[wepe]

reply to freethinker, then what made the universe start. that first initial bb. if thats what the bb claims then how does that make any sense at all?