How is space expanding ?

[Martin]

...

My own posts should also be marked in some way' date=' not because I am against the mainstream but for I am still trying to understand and learn what the mainstream are.

...[/quote']

 

that sounds like a good agenda.

start by getting an idea of what the consensus view of working cosmologists is----then differ with it in whatever way you wish,

at least you have some understanding of what you disagree with!

 

an up-to-date not-too-mathematical overview by a top cosmologist

Thanu Padmanabhan has come out with one of these surveys of cosmology for general audience, that a senior cosmologist may do every now and then.

http://arxiv.org/abs/gr-qc/0503107

Understanding Our Universe: Current Status and Open Issues

T. Padmanabhan

To appear in "100 Years of Relativity - Space-time Structure: Einstein and Beyond", A.Ashtekar (Editor), World Scientific (Singapore, 2005); 30 pages; 4 figures

 

"Last couple of decades have been the golden age for cosmology. High quality data confirmed the broad paradigm of standard cosmology but have thrusted upon us a preposterous composition for the universe which defies any simple explanation, thereby posing probably the greatest challenge theoretical physics has ever faced. Several aspects of these developments are critically reviewed, concentrating on conceptual issues and open questions. [Topics discussed include: Cosmological Paradigm, Growth of structures in the universe, Inflation and generation of initial perturbations, Temperature anisotropies of the CMBR, Dark energy, Cosmological Constant, Deeper issues in cosmology.]"

 

earlier articles by another world-class cosmologist, Charles Lineweaver, who knows how to write clearly for general audience

 

Lineweaver classic article "Inflation and the CMB"

http://nedwww.ipac.caltech.edu/level5/March03/Lineweaver/Lineweaver_contents.html

 

here is the abstract, which has a link to a more legible PDF copy

http://lanl.arxiv.org/abs/astro-ph/0305179

 

Another great article by Lineweaver and one of his graduate students Tamara Davis. It helps you get out of some common misconceptions about the bigbang and expanding universe. This was a 2003 article and it pre-figures the recent 2005 article by the same authors in the Scientific American.

http://arxiv.org/abs/astro-ph/0310808

 

Lineweaver SciAm sidebars:

from the Lineweaver and Davis article in March 2005 SciAm

http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=0009F0CA-C523-1213-852383414B7F0147

 

this was a feature article "Misconceptions about BigBang"

It had some sidebars which were pictorial diagrams with a question together with right and wrong answers explained.

 

http://www.sciam.com/media/inline/0009F0CA-C523-1213-852383414B7F0147_p39.gif

What kind of explosion was the big bang?

 

http://www.sciam.com/media/inline/0009F0CA-C523-1213-852383414B7F0147_p40.gif

Can galaxies recede faster than light?

 

http://www.sciam.com/media/inline/0009F0CA-C523-1213-852383414B7F0147_p42.gif

Can we see galaxies receding faster than light?

 

http://www.sciam.com/media/inline/0009F0CA-C523-1213-852383414B7F0147_p43.gif

Why is there a cosmic redshift?

 

http://www.sciam.com/media/inline/0009F0CA-C523-1213-852383414B7F0147_p44.gif

How large is the observable universe?

 

http://www.sciam.com/media/inline/0009F0CA-C523-1213-852383414B7F0147_p45.gif

Do objects inside the universe expand, too?

 

====================

just so we dont lose track of this, here is

SPYMAN'S QUESTION

 

"So could someone give me an "mainstream" answer to this question ?

If space is stretching then how can space bring the matter with it, space has no friction ?

Or is it the other way around, matter is moving away from us very fast and stretches the space behind them ?

With matter I mean other galaxies moving away from us with what looks like higher speed than light."

 

that's worth discussing!

 

I cant distinguish between my personality and my body (I have no "mind" or "soul" that is distinct from my brain and the rest of me). If I distinguished logically between my mind and my body, then I would get into logical tangles.

 

the Western physics tradition from Aristotle up thru Leibniz, up to newton, did not distinguish space as anything different from RELATIONSHIPS AMONG MATERIAL OBJECTS. space was the sum of spatial relationships like between, next to, inside, outside, proximity relations....

 

Carlo Rovelli in his book Quantum Gravity goes thru the history of this. Newton, after a lot of agonizing, introduced the idea of an Absolute Space which was existing independent of matter, of its own accord, and was to him like the Mind of God, or as Newton said "sensorium of God". So newton created this existential split between matter and space.

that was about 1680.

 

then around 1915 Einstein healed the split and got rid of the separately existing absolute space, space is (again, like for Leibniz and Aristotle) simply the relations between things. spacetime is the relations between events.

 

it is not easy to understand, especially for us who have been infected with newton's absolute space idea for 300 years. it is still dominant in much of basic physics and engineering (almost, you could say, everywhere outside

gen rel and cosmology)

there are some nice quotes from Einstein about this. (I am not talking about 1905 moving observer stuff, this is deeper than Special Relativity which still has an absolute space concept but the symmetries have been modified. In 1915 with General Relativity Einstein got rid of space as a separate entity.)

Rovelli's book chapter 2 has the Einstein quotes and sources.

[Spyman]

So now' date=' to your question...

 

You ask, if space is expanding, how does it "grip the material" and pull the center of mass of the material with it.

 

Did I understand your question right?[/quote']Yes, either it can "grip the material" and how or not.

 

If the matter is not "moving" and space has no friction then gravity should win, whatever speed of expansion and distance, because there wouldn't be any force against it.

 

So logically either the matter is moving or space has friction or it is an illusion.

Since the speeds involved are higher than light the moving sounds impossible.

With friction comes the "ether" which also seems impossible.

If light is slowing down and creates this illusion, then the speed of light is not constant.

[Spyman]

that sounds like a good agenda.

start by getting an idea of what the consensus view of working cosmologists is----then differ with it in whatever way you wish' date='

at least you have some understanding of what you disagree with![/quote']

That was a lot of links, Thanks, I will read them all but it will take some time.

[Martin]

That was a lot of links, Thanks, I will read them all but it will take some time.

 

I dont want you to read them all. You know how to pick what you need to read. I wanted to give you a choice.

 

Stick around here and ask questions. If you spend all your time at home reading we wont ever get to talk.

[Martin]

the philosopher Descartes thought that the mind and the body were two different entities

 

and he had great deal of trouble locating the "hook" that connected them

and he finally decided that the connection point where the mind plugged in to the body was this little node inside the brain called the "pineal gland"

 

nowadays we do not make a sharp distinction between mind and body like he did, so we can chuckle at Descartes.

but we make other false distinctions and then have to struggle and go through contortions to get things reconnected, so probably in the future they will laugh at us

 

there does not have to be any "friction" or any "hook" so that space will take matter with it.

[Spyman]

the philosopher Descartes thought that the mind and the body were two different entities

 

and he had great deal of trouble locating the "hook" that connected them

and he finally decided that the connection point where the mind plugged in to the body was this little node inside the brain called the "pineal gland"

 

nowadays we do not make a sharp distinction between mind and body like he did' date=' so we can chuckle at Descartes.

but we make other false distinctions and then have to struggle and go through contortions to get things reconnected, so probably in the future they will laugh at us[/quote']Maybe I misinterpreter, but reading between the lines this sounds a lot like what Cadmus said.

You are separating matter from space. Space is not a container for matter. Space is the matter.

Is this correct and mainstream ? or is there a difference I don't notice ?

There has to be some connection between matter and space like between the mind and the brain but that is not what I am asking about, of course since I am the novice here, it might be the same thing in the end...

 

there does not have to be any "friction" or any "hook" so that space will take matter with it.

I qouted a part from one of the links You gave to further explain what I mean and are asking about:

A good analogy is to imagine that you are an ant living on the surface of an inflating balloon. Your world is two-dimensional; the only directions you know are left, right, forward and backward. You have no idea what "up" and "down" mean. One day you realize that your walk to milk your aphids is taking longer than it used to: five minutes one day, six minutes the next day, seven minutes the next. The time it takes to walk to other familiar places is also increasing. You are sure that you are not walking more slowly and that the aphids are milling around randomly in groups, not systematically crawling away from you.

 

This is the important point: the distances to the aphids are increasing even though the aphids are not walking away. They are just standing there, at rest with respect to the rubber of the balloon, yet the distances to them and between them are increasing. Noticing these facts, you conclude that the ground beneath your feet is expanding.

If the ant should decide to do something about his longer walks and tied one of the aphids to a rope which he tied in the other end to his home. The rope represents gravity and if there is no friction on the surface of the balloon then the aphid would stay within a fixed radius to the home, whatever rate of inflation of the balloon, if there is friction then depending on which is strongest the rope might also streatch and the aphid gets further away.

I just can't understand how this is supposed to happen in the Universe without somecind of friction ???

If the light from distant galaxies reatches us then so must their gravity which would stop the expansion if there is no friction. (Except for their local speed which must be lower than light if GR is to be correct.)

Also in the end of the article it is mentioned that if the expansion continues to accelerate at higher and higher rates then eventually the ground between our feets will literally get ripped apart all the way down to atoms and particles. Surely there must be some force involved to do this and so strong it is more like "hooks" than "friction".

[Martin]

these are good questions. I dont know where the ant and aphid parable came from maybe I gave you a link I hadnt read thoroughly, or maybe it is from Cadmus

 

I havent read Cadmus post thoroughly either (theres too much to read in the world)

 

I have tried to listen to what I recognize as the mainstream view and can kind of echo things

 

galaxies and clusters of galaxies dont expand because they are gravitationally bound

 

(like the rope you imagined using to tether the aphid)

 

but being gravitationally bound is a question of degree, there is a gray area, not all black and white

 

expansion is very slow, so most structures we see can adapt to it, they just get slightly larger than they would be otherwise, like a planet that is just a hair too far out for the speed it is going, and then the tendency to fall together just cancels the rate of expansion-----they are in equilibrium---they have adapted to expansion rate and they remain bound structures.

 

large clusters of galaxies that we see are calculated to be gravitationally bound, at least at current rates of expansion, and will keep their pattern or structure, and of course all smaller structures are bound (gravitationally and also solid objects even more strongly by other bonds)

 

BUT there are some very tenuous structures which are probably being very slowly disassembled. clusters of galaxies that are so loose and wispy and amorphous that one wouldnt even want to call them clusters... but its not all black or white.

 

so the ultimate nitty gritty in this business is being able to calculate or do a computer simulation to study various apparent structures (already hard to define rigorously what a structure is, or a pattern) and see what is gravitationally bound enough to be around for the foreseeable and what is going to dissolve.

 

I dont like those sensationalist "big rip" scenarios but that is carrying this sort of analysis to the extreme with imagining a severe "dark energy" acceleration of expansion.

I also dont feel comfortable with projections way way far in the future because we dont understand the universe well enough to be confident of a given model in the very long run. So, for me, trying to look ahead 100 billion years makes me giddy and i dont do it.

 

the kind of expansion I think people see is extremely gentle and nonthreatening and I dont like scare stories, but it is true that expansion can cause some weakly bound things to disperse

[Martin]

about the impossibility of partitioning between space and matter

since you are determined to focus on the mainstream view

we really need some quotes from Einstein

(from the mainstream horse's mouth)

 

I know where to find them in the 2nd chapter of Rovelli's book "Quantum Gravity" that came out last year, but have been too lazy.

 

you can download a draft version free from Rovelli's website

just go to google and say "rovelli"

 

BUT YOU CAN'T COPY AND PASTE, it will not work

 

when you find the quotes from Einstein and the other stuff that you want in rovelli's book you have to transcribe it by hand

(the draft must have been entered in such a way that people could see it but not copy and paste) I finally went and bought the hardcopy book

[Guest pattarkutty]

though i have not done extensive research on this, this is what i feel.

if we consider the rate of expansion of the universe, what u r saying is that the objects closer r not expandind as fast as expected. this u say is because the galaxies and other things are bound and still smaller structures bound by other forces.

but since the rate of change of distances is again proportional to the initial magnitude of their spacing, i belive these anomalies to be due to the wrong experimental calculations and that once the true measurments r known, we can be confident about the actual changes to be made in the theory.

[Spyman]

I dont want you to read them all. You know how to pick what you need to read. I wanted to give you a choice.

 

Stick around here and ask questions. If you spend all your time at home reading we wont ever get to talk.

I did read them all anyway, interesting, but due to my level of knowledge and partly language translations, I must confess than it was a lot I couldn't understand.

 

But the main focus of the articles seemed to be on supporting the current measurements of the expansion, Big Bang theory and Inflation theory. I couln't find any facts about how the expansion takes place, just that it does and how it appears to us.

 

BTW One of the links seems to go to an exact replica of one of the others.

[Spyman]

these are good questions. I dont know where the ant and aphid parable came from maybe I gave you a link I hadnt read thoroughly, or maybe it is from Cadmus

Your link.

Lineweaver SciAm sidebars:

from the Lineweaver and Davis article in March 2005 SciAm

http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=0009F0CA-C523-1213-852383414B7F0147

[Spyman]

but being gravitationally bound is a question of degree, there is a gray area, not all black and white

My question still stands: How can the expansion defeat the gravity in the gray area ?

 

I know that if strong enough it of course can and that the force of gravity from very distant galaxies is very very small, but still to defeat that the force must have a "grip". Any force must have a direction, strengh, source and a point where it acts.

[Spyman]

about the impossibility of partitioning between space and matter

since you are determined to focus on the mainstream view

we really need some quotes from Einstein

(from the mainstream horse's mouth)

 

I know where to find them in the 2nd chapter of Rovelli's book "Quantum Gravity" that came out last year' date=' but have been too lazy.

 

you can download a draft version free from Rovelli's website

just go to google and say "rovelli"

 

BUT YOU CAN'T COPY AND PASTE, it will not work

 

when you find the quotes from Einstein and the other stuff that you want in rovelli's book you have to transcribe it by hand

(the draft must have been entered in such a way that people could see it but not copy and paste) I finally went and bought the hardcopy book[/quote']

I am not "determined" to focus on the mainstream view, any view that can convince me of it's possibility is interesting, like I said I try to be openminded.

But it is also important to know if the view is mainstream or not, why and way not.

 

I have downloaded "Quantum Gravity" in PDF-format from Carlo Rovelli's website - very large 4 737 kB and 347 pages - I will search through it for interesting parts that I am able to understand.

 

I don't know how to copy and paste in PDF's but it should be possible someway. It is not secured by any copy-protecting software since there is no problems to print it out.

[Spyman]

though i have not done extensive research on this' date=' this is what i feel.

if we consider the rate of expansion of the universe, what u r saying is that the objects closer r not expandind as fast as expected. this u say is because the galaxies and other things are bound and still smaller structures bound by other forces.

but since the rate of change of distances is again proportional to the initial magnitude of their spacing, i belive these anomalies to be due to the wrong experimental calculations and that once the true measurments r known, we can be confident about the actual changes to be made in the theory.[/quote']You "feel" both the measurments and theories to be wrong ???

[Guest pattarkutty]

sure...can u point to one absolute theory? any theory for that is supposed to be an approximation of reality, bacause there r millions of unaddressed and unaccounted phenomenas. and these experimental setups in most of the cases atleast depend on other theories mildly. so what u have is a setup with a little amount of error used to test a theory with another amount of error . so where do u end up asking questions is something u should think. well u can never say that we have a full proof perfect theory

at a completely error free setup. but it is thought that we r reaching perfection from stage to stage. but i think that unless there is a perfect scale of correctness against which things can be measured, i really doubt we'll ever find truth. so both experiments and theories r wrong and will remain so, but the only benifit of pursue is that one can quench his curiosity with all that.

[Spyman]

sure...can u point to one absolute theory? any theory for that is supposed to be an approximation of reality' date=' bacause there r millions of unaddressed and unaccounted phenomenas. and these experimental setups in most of the cases atleast depend on other theories mildly. so what u have is a setup with a little amount of error used to test a theory with another amount of error . so where do u end up asking questions is something u should think. well u can never say that we have a full proof perfect theory

at a completely error free setup. but it is thought that we r reaching perfection from stage to stage. but i think that unless there is a perfect scale of correctness against which things can be measured, i really doubt we'll ever find truth. so both experiments and theories r wrong and will remain so, but the only benifit of pursue is that one can quench his curiosity with all that.[/quote']

Okay, I understand Your "feelings", but I don't share them.

[Martin]

...

 

I have downloaded "Quantum Gravity" in PDF-format from Carlo Rovelli's website - very large 4 737 kB and 347 pages - I will search through it for interesting parts that I am able to understand.

...

 

For me some interesting parts are the non-math parts of chapter 2

 

for example parts of section 2.4 deal with the different possible ideas of time (described in words)

and other parts of chapter 2 deal with the history of how, in the years 1912-1915 einstein gradually came (with many doubts) to the conclusions about space and time in his 1915 theory

 

also there is one page right near the beginning, that was illuminating for me:

it is in the section 1.1.3 of chapter 1, the section called

"The Physical Meaning of General Relativity"

 

in the hardcopy version I have it is page 9

in the draft you may notice two numberings, one is pages in the PDF file, and the other is the numbering actually on the page-----which is different because it starts with Roman numeral i, ii, iii, iv, .... etc

 

we should make a list of "good parts" of Rovelli

 

another good part is around a short quote from Einstein in section 2.3.2

 

"...the requirement of general covariance takes away from space and time the last remnant of physical objectivity..."

 

 

Spyman, if you find any pages in the draft that you want to flag or "bookmark", please post them! (in fact I cannot say right now what are the PDF-file page numbers for my favorite passages, so a list like this would be handy for me to use in recommending Rovelli pages to people using the draft copy, so I have a personal reason for asking)

[Johnny5]

Martin, there is a purple picture at the very beginning of Rovelli's online book, what is that? Does it have any relationship to LQG?

[Martin]

Martin, there is a purple picture at the very beginning of Rovelli's online book, what is that? Does it have any relationship to LQG?

 

hi J5, I was just looking at the hardcopy, which I own, it doesnt have it.

 

I may be able to get an answer though (but not in a hurry so dont hold breath! )

[Spyman]

Spyman, if you find any pages in the draft that you want to flag or "bookmark", please post them! (in fact I cannot say right now what are the PDF-file page numbers for my favorite passages, so a list like this would be handy for me to use in recommending Rovelli pages to people using the draft copy, so I have a personal reason for asking)

I have not had the time to read through this yet, but if I find something interesting I will "flag" it for You.

 

Anyway the reason for "copy & paste" not working is that the text is saved as/in image-format, thus "copy & paste" to paint or photoshop works well. I don't know if that info will do You any good but You should be able to paste a picture of the quote You want to show.

[island]

Hi, I'm the new guy...

 

This is a new take on an old theory:

 

Einstein's static vacuum:

 

http://www.astro.ucla.edu/~wright/cosmo_constant.html

 

In order to make a real particle from Einstein's vacuum, you'd have to condense enough vacuum energy to achieve positve matter density over a fininte region of space.

 

What happened to the vacuum when you did that?...

[Spyman]

This is a new take on an old theory:

 

Einstein's static vacuum:

 

http://www.astro.ucla.edu/~wright/cosmo_constant.html

 

In order to make a real particle from Einstein's vacuum' date=' you'd have to condense enough vacuum energy to achieve positve matter density over a fininte region of space.

 

What happened to the vacuum when you did that?... [/quote']Interesting link, Thanks.

 

However it doesn't answere my question:

If space is stretching then how can space bring the matter with it' date=' space has no friction ?

Or is it the other way around, matter is moving away from us very fast and stretches the space behind them ?

With matter I mean other galaxies moving away from us with what looks like higher speed than light.[/quote']

 

The vacuum got filled with matter ?

[island]

Interesting link' date=' Thanks.

 

However it doesn't answere my question:[/quote']

 

I think that it does if you study it, since negative pressure increases as the vacuum expands.

 

The vacuum got filled with matter ?

 

Yes, but the vacuum is growing.

[Guest edicius]

I thought it was from our point of view the matter is moving away at an accelerated rate in all directions...

Is this an optical illusion or are we in the center ???

And if this is an optical illusion then way can't the expansion also be an illusion ?

 

AFAIK matter is receding from both us and the center of the universe. This is because the matter furthest from the centre of the universe has the greatest kinetic energy and that closest has the least.

 

Following this logic through it would appear that all matter is receding regardless of your perspective (i.e. earth, the centre of the universe, the andromeda galaxy etc.).

 

Hope this helps clarify things

[SpaceTime]

The viewpoint that the universe is expanding may not need to be the case at all, it may be an illusion created by our universal motion.

 

This is similar to optically looking through a telescope, if you look through the correct way everything looks magnified, turn it around and everything looks smaller than it is.

 

Space-time is the carrier of all light and gravity can create a lense effect for light.

 

Maybe looking in the direction of where we came from, everything seems to come from a single point, and when we look into the direction of where we are going maybe everything looks infinately large.

 

This viewpoint is more likely to be realistic than, the viewpoint where we all miraculously exploded out of a pinhead. For this reason my mind still remains open in this area.

 

Maybe space-Time is not expanding but just in motion, giving us the illusion of an expanding universe.

 

I am interested in you comments..

 

Signed

SpaceTime