How far can we see?

[Michael Mooney]

Modest

]On cosmic scales everything is expanding away from everything else. The simplest way to express such a thing is to put everything on a metric (or a grid, if you like), and to scale the metric. This accomplishes something very specific which I will describe.

 

If you consider a galaxy such as the Milky Way and measure the speed at which other galaxies are moving away from it then the further the galaxies are, the faster they will be moving away. That is a physical law of astronomy known as Hubble's law.

 

It is sensible to assume that our position in the universe is not special so that any other galaxy out there also has galaxies receding from it in such a way that the recession velocity increases with distance. An easy way to show this (to model it) is to use a rubber sheet (think of a piece of paper made of rubber). You can mark a bunch of dots on the sheet representing galaxies.

 

Maybe you are not yet familiar with how i see the cosmos, as re-stated yet again in post #26 of the "Bang/Crunch Revisited" thread, as follows:

 

Our cosmic event horizon is just a small bubble of visibility *within* the thickness of the "rubber" of the good old cosmic expanding balloon. This mini-cosmos within the maxi-cosmos, the Whole Balloon, is cycling through bangs and crunches even as the whole balloon keeps expanding.... *Yes*... out into the infinity of space.

...

Anyway, we can't even "see out of the rubber" (the visible cosmos) let alone see the *yes* empty space within or beyond the bubble.

Modest:

If you have 4 people each grab a corner of the sheet and stretch it apart then you have effectively modeled the manner in which galaxies move away from one another. One of those dots on the rubber sheet has every other dot moving away from it and the further the other dots are from it, the faster they move away. This is true for any dot.

 

The above is a two dimensional rubber sheet... a plane. My expanding balloon is a 3-D sphere... and the "rubber" is the "stuff" of cosmos... with a thickness containing the whole mini-sphere of visibility which is our cosmic event horizon.

So, naturally cosmos appears isotropic/homogeneous in all directions

as the whole balloon expands with our little visible cosmos as one tiny bubble in the rubber of the balloon.

Can you understand what I am saying?

The expansion of the universe is very similar. Saying "space is expanding faster than the speed of light" means that the distance between two objects on the metric is increasing faster than c. This is an inevitable conclusion given two things:

[*]The further away one galaxy is from another the greater the rate at which their distance increases.

[*]The universe is infinite in size.

 

Space is infinite emptiness. Cosmic "stuff" exists in specific locations within unbounded space.... reference balloon cosmology above.

Nothing... none of this cosmic "stuff" travels faster than light, and space is lack of 'things', emptiness... no-thing-ness, the *volume* in which stuff exists, and "it", being nothing, does not 'travel" or expand at all.

 

You're probably wondering what difference it makes if we say something is moving through space or if we say space is expanding between things. And, it indeed does make a difference which can only be revealed by measuring and understanding the apparent motion of cosmic objects. To give one example, if an object is moving away from us *through space* then we expect it to exhibit a redshift which can be calculated with and is due to special relativistic Doppler shift. If, however, space is expanding SR doppler shift will not give the correct redshift results. Cosmological redshift must be used. Wiki summarizes the difference:

 

I may introduce a very important criticism of all assumptions surrounding the redshift paradigm, but this is not the "place or time."

I am not "wondering" at all "what difference it makes if we say something is moving through space or if we say space is expanding between things."

It is my most profound understanding that space is empty volume in which all *observable/detectable* phenomena exist and move.

Space is emptiness. It has no properties... being the *void* in which things with properties exist. Space does not expand. Things move away from other things in space... emptiness/volume.

 

That quote references "the metric expansion of space" which is a good article at wikipedia. If you want to get a good understanding of just what astrophysicists mean by expanding space then that would be a good place to start.

 

I will study it at another time.... and get back to you on prevalent dissent on redshift as the basis for the "inevitable conclusions"... what you believe are indisputable "facts."

........

 

I don't think "volume" is that bad of a word to substitute for "space" in the setting of astronomy and cosmology. We could say that the volume between galaxies increases over time rather than saying the space between them increases. We would also say that the rate at which volume expands is proportional to the volume itself much in the way we would say the expansion of space between objects is proportional to the distance between them. :phones:

 

But the reason for more volume between objects over time is that they are simply moving away from each other as in the expanding balloon... not that "space itself" (as if it were an entity) is expanding.

This is your (and "expanding space theorists') fundamental misconception as i see it.

 

And don't get me started on dilating time again!;)

 

Michael

[enorbet2]

I understand what you say and yet when I look at images near and far 13,2 Gyrs I see galaxies mature and young, various forms from spiral to elliptical and so on as we see them close. In addition the images show a clustering effect proven by galaxies merging and clustering into a super cluster of clusters of galaxies.

 

Could these papers be wrong or is the Big Bang theory in question.

 

Hello Pluto

While I get it that so far the Universe seems isotropic and homogeneous when viewed on Large Scale, not to mention that the Cosmic Background Radiation is uniform to 1 part in 100,000, but are you saying you're aware of no differences in the early Universe, even at visible light frequencies?

 

Yes! and Yes! Those papers could be wrong AND the BBT is in question. I'm not yet saying they are wrong and, but as I've posted in other threads, the odds are still in favor of the Standard Model including BBT. Admittedly this is a revolutionary age in Astronomy and this could change rather quickly as more new data comes in. Renewed Hubble with COS, the awesome Herschel Space Telescope and the Planck telescope are but three that are underway as we speak that will likely have a profound impact on questions and answers.

 

BTW good to see you focusing more on redshift since it is so fundamental - if the Universe isn't expanding BBT is done. I will read the papers. Most of the links you post aren't exactly digestible in one sitting on the john (or, loo, if you prefer)

[enorbet2]

Michael

It is not a given that Space is empty since it is not yet known if it is itself discrete, especially at the Planck Scale. There are as yet deep problems correlatiing scale which seems necessary to understand why gravity is so weak let alone the full nature of the Universe. One of the major problems is formulating a theory that is background independent.

 

Quantizing the Universe » American Scientist

 

As for distance calculations this might help

 

http://en.wikipedia.org/wiki/Distance_measures_(cosmology)

 

Distance calcs may be revised sometime soon as The Planck Telescope intends to duplicate WMAP in much higher resolution. Pretty damned exciting!

[modest]

Michael, I've answered you in your Bang/Crunch Revisited thread.

 

~modest

[maddog]

I'll try to state my problem with parsimony:

 

When we look a Barnards star (for example, ~15 light years out) we see it as it was 15 years ago. When we look 1 million ly out we are looking at a scene from 1 million years ago. So I think I understand it when astronomers say that looking very far away is equivalent to looking very far into the past.

 

I've heard of telescopes that see BILLIONS of light years away. Here's my problem: the universe is only ~15 billion years old. So if we are looking at something 15 billion ly away, we are looking 15b years into the past - at that time when whatever we are looking at should've been RIGHT HERE.

 

Maybe we just can't see that far, but still, the farther we look the closer we come to the point where all mater was in the same spot. This is the paradox: the FARTHER it is away from us, the CLOSER everything sould be to everything else.

 

I'm sure I'm missing something here that someone can fill in. I'd appreciate any comment.

In your statement is the dilemma as a hidden assumption. That being the "yardstick" you

use to measure everything "from here to there". You imply it is static. As Modest has

stated in his posts to this thread, the conventional wisdom of BBT has this is not necessarily

the case. Alan Guth in 1980 published his Inflation Theory. This in essence says that

early in the BB time scale -- that yardstick went from {1 yard} to {10e6 or 10e7 Light year of yards}.

This being done so in a matter of seconds or so. Thus Space and Time being created.

In the recent period a rival Theory being VST or Variable Speed of Light Theory. Both

explain some things yet do not answer all questions (I forget the Portuguese Physicist's

name). I have not heard a definitive debunking or validating of either so far.

So if Inflation/VST were true -- Yes the Universe could be "MUCH" bigger that about

15 Billion LY in size. :hihi:

 

maddog

[enorbet2]

The name of the Portuguese theoretical physicist is Joao Magueijo and he has an interesting site here

João Magueijo's Big Bang : Science Channel

 

Perhaps more important than his VST is his early recognition of structure within WMAP. There is a linear anomaly he calls "the axis of evil" brcause it can be interpreted many ways. Most BBT advocates think it is simply due to our motion within the local group. Joao begs to differ. Cool controversy:)

 

An excellent site for questions and answers or at least info and insights is here (example specific to why we don't see a speck as we look way out)

Curious About Astronomy: When we look back to the Big Bang, why don't we see the universe as a tiny speck of matter?

 

There are also good sections on measuring distance, the size and shape of the universe there, and also here

http://en.wikipedia.org/wiki/Distance_measures_(cosmology)