Is there a size, beyond which a system cannot be considered at once?

[Mordred]

They do. In cosmology calculations we have, conformal time and cosmological time. Of which any calculation can be converted between the 3. The lightcone calculator in my signature uses proper time.

Cosmic (cosmological time) is often referred to as look back time

 

http://en.m.wikipedia.org/wiki/Cosmic_time

Conformal time coincides with the particle horizon

 

http://en.m.wikipedia.org/wiki/Particle_horizon

 

 

Then we have as well different types of distance. Proper distance conformal distance and commoving distance.

 

This article covers these in detail

 

http://www.google.ca/url?sa=t&source=web&cd=6&ved=0CCsQFjAF&url=http%3A%2F%2Farxiv.org%2Fpdf%2Fastro-ph%2F9905116&rct=j&q=proper%20time%20cosmology&ei=o4uhVOe8EpOnyATs6ICYAw&usg=AFQjCNENt8vXuRz1vhm6vF3-TawOcXsUcA&sig2=_FVL77t2rD6gMvWYoBTx7A

 

"Distance measures in cosmology" David Hogg

Grr I ya modified your last post while I was typing mine. Lol

Tar we can calculate how many photons are in the universe using the blackbody temperature of the universe and the Bose-Einstein statistics. We also know how that radiation affects expansion and universe geometry using the equation of state for radiation

http://www.google.ca/search?site=&source=hp&ei=io-hVIehAc35yQT-koDYCg&q=equation+of+state+cosmology&oq=eq&gs_l=mobile-gws-hp.1.0.41j0l4.2472.2918.0.4678.3.3.0.1.1.0.239.608.0j1j2.3.0.msedr...0...1c.1.60.mobile-gws-hp..0.3.429.3.u--EvSC4PwU

 

 

See particle physics of the Early universe under my signature chapter 3 for how to use the Bose-Eintien statistics in regards to photons

However the answers on how much of any contributor to the universes energy budget can be found here

 

http://arxiv.org/pdf/astro-ph/0406095v2.pdf"The Cosmic energy inventory

You really need to sit back and understand what we can and do calculate both in the how and why. The cosmic inventory should give you quick OMG we can calculate all of that?!!?.

 

My signature has the books and articles to assist you in learning how

SwansonT, Mordred, Strange,

 

I appreciate that the science and accepted measurements of Z and proposed volume and density calculations point to an expanding universe. My intent is not to try to prove current science wrong, but to question if the inferences make sense.

Taking a measurement and fitting it to a mathematical model is appropriate. Establishing a mathematical model thusly and seeing that measurements fit the model is good confirmation that the model is workable.

 

However, the well understood science is a somewhat similar body of knowledge that we had just a short time ago, when everybody thought the universe was slowing down its expansion. My conondrum is figuring out which pieces of information are derived from assumptions and data that was properly vetted for time and distance considerations, and uncomfortably, whether or not the time and distance assumptions made were based on knowledge and measurements taken before or after certain insights and constant adjustments were made.

 

It is not unusual to find a cyclical nature to the reasoning of time and distance, where an assumption provides the distance and time figures that are plugged into the equation from which assumptions about distance and time are inferred.

 

Like Z.

 

And now, the areas of the universe that are just now visible to us as CMB, which at the time of photon launch were 380thousand years old, are now 13.8 billion years old. Those areas are thusly two different sizes in terms of volume, the way we see them, and the way they are. Yet Strange submits that there is no universal now, as if it is not required that the universe actually be, at this current moment, larger than it appears.

 

So, with the differences in models between current physicists, and the changes in models over the years as new inferences are made and new observations made to fit into the models, and with the "difference" in models derived from what we see, as opposed to what we know to have been the case, and what we know must currrently be the case, it is hard to visualize the model that a particular scientist is using when making a particular statement or writing a particular formula that encompasses an entire system that is larger than a moment in radius.

 

Regards, TAR

Ah it wasn't a change in post just an earlier one lol. The first part of my post is in regards to how time and distance is calculated to include how it evolves

Edited December 29, 2014 by Mordred

[swansont]

SwansonT,

 

Sorry about my large mistake, missing the percentage, but energy released by suns does not stay in the galaxy for long. Maybe a hundred thousand years, but after that it is outside the galaxy. Otherwise we could not see other galaxies. So mass/energy calculations should include a time component, as some energy has left, is leaving and will leave, according to whether you are considering energy on this side of the galaxy or on the other.

 

Regards, TAR

 

Some energy leaves. But what fraction of energy leaves? Over the span of 100,000 years (which is 10,000 times shorter than the number I calculated). Tiny, isn't it? So why is steady-state not a reasonable approximation here?

[tar]

SwansonT,

 

I think steady state is a reasonable approximation for some considerations, but not necessarily for others. That is the nature of my inquiry here. When is it not appropriate to assume a steady state over an entire system that is so large as to have communication between its parts take 100,000 years?

 

Mordred,

 

I am only 5 pages into the 35 page survey you linked, and it is very good and I am learning a lot, so I will refrain from forming any conclusions at this point, but a couple questions. When the author speaks of the current epoch what is he talking about? How long is an epoch and from which point of view are we to take it? Is it from this point (Earth) that we view, or is it from a God-like position, where all items and elements in the universe are currently 13.8 billion years old, that we are considering "this" epoch to be occurring?

 

Strange,

 

From the enegy survey article is this proof that main stream scientists do what I was suggesting earlier, and it is not only puedoscientists that work the data into the equations rather than let the data establish the equations.

 

It appears that most of the

baryonic components are observationally well con-

strained, apart from the largest entry, for warm

plasma, which still is driven by the need to bal-

ance the budget rather than more directly by the

observations.

 

Regards. TAR

Thread,

 

Another notion related to this discussion occurred to me as I was reading the mass/energy survey article. As energy "goes out" from an item, does mass also have such loss? If gravity travels at the speed of light, is there a "something" that changes position as gravitation attraction is happening? And if so, should this transaction be accounted for in taking a large system into account?

 

Like on a childhood playground ride, the speed of the spinning could be adjusted by moving your body toward the outside or toward the inside. Or a ballet dancer or ice skater can slow or speed her/his spin by extending or retracting her/his arms.

 

As material is expelled by a star the wheight of a system is redistributed, but does the "act" of gravitational attraction cause any redistribution or evening out of some actual stuff (mass), analogous to photons in the exchange of electromagnetic energy?

 

Regards, TAR

Edited December 30, 2014 by tar

[Strange]

From the enegy survey article is this proof that main stream scientists do what I was suggesting earlier, and it is not only puedoscientists that work the data into the equations rather than let the data establish the equations.

 

It appears that most of the

baryonic components are observationally well con-

strained, apart from the largest entry, for warm

plasma, which still is driven by the need to bal-

ance the budget rather than more directly by the

observations.

 

Can you explain what data is being forced to fit the equations in that case? All I see is that in the absence of data (for the amount of warm plasma) it is derived from the equations. But maybe I haven't understood the point you are trying to make.

 

As energy "goes out" from an item, does mass also have such loss?

 

It is not clear what you are asking here. Obviously, as the sun or a galaxy radiate energy, they lose mass. Is that what you mean?

Also, stars throw of a "wind" of particles as well as energy. This also contributes to the mass loss. Is that what you mean?

 

If gravity travels at the speed of light, is there a "something" that changes position as gravitation attraction is happening?

 

You mean apart from the change of position of the masses that are attracted to one another? No.

 

 

Like on a childhood playground ride, the speed of the spinning could be adjusted by moving your body toward the outside or toward the inside. Or a ballet dancer or ice skater can slow or speed her/his spin by extending or retracting her/his arms.

 

This is conservation of (angular) momentum. This applies to a rotating object so as a star or galaxy loses mass it will slow its rotation. Is that what you mean?

 

 

As material is expelled by a star the wheight of a system is redistributed, but does the "act" of gravitational attraction cause any redistribution or evening out of some actual stuff (mass), analogous to photons in the exchange of electromagnetic energy?

 

Or are you talking about an equivalent of the exchange of virtual photons that mediates the electromagnetic force?

 

That would be the hypothetical exchange of virtual (and hypothetical) gravitons. But we don't have a theory of quantum gravity yet, so there isn't much to say about that. (Except they would be massless, with zero charge and spin 2.)

[Mordred]

Epochs and eras are chronological points in the universes history where there are significant changes in the dynamics. The major ones after inflation is the radiation dominent era which includes BB inflation and surface of last scattering (CMB). This is followed by the matter dominent era CMB till the universe is roughly 7.3 billion years old. At this time the cosmological constant becomes the dominent influence so we call this era the lambda dominent.

[swansont]

SwansonT,

 

I think steady state is a reasonable approximation for some considerations, but not necessarily for others. That is the nature of my inquiry here. When is it not appropriate to assume a steady state over an entire system that is so large as to have communication between its parts take 100,000 years?

 

 

When doing so introduces errors large enough to be problematic.

[tar]

Mordred,

 

Well thank you for the epoch discription. Makes sense, but seems to indicate that scientists switch readily between the hypothetical universal now, and the Earth as here and now, as I have been trying to describe on various threads, with some regular chiding about such notions coming from several sources.

 

This switch between what we see, to what we know must be the case is something I figure to be required inorder to hold a proper model of the place. I am glad to understand that this switch is already understood as required, and people know when to make the switch and how to add back between the two perspectives.

 

But this as well worries me that sometimes the required shifts of ALL components are not made in all cases. I worry for instance, when someone states something like they know how many photons there are in the observable universe, that they might be double counting, and counting the same thing once from here, and then again from the hypothetical universal now.

 

For instance as we look out at our galaxy we see only the very closest stuff within a moment of it happening. We know something is happening at Proxima now, and we know we see something happening at Proxima now, yet the two things, what we see and what we know, are separated by a couple of years. But there is only one instance of Proxima, that can be understood in two different ways, alternately, and taken together to understand the huge model that comprises both the Earth and Proxima, and understand what we see, based on what we know to be the case...but an equation or survey that includes Proxima, must be specific about which way Proxima is being considered, and such specific defined ways of viewing a thing, must be consistently applied to everything else in the survey.

 

If the difference between our here and now, and the universal now is not mentioned in the equation, how is one to know that it is being looked at properly?

 

Regards. TAR

Strange,

 

Yes, I was asking if any actual material thing was transferred during the act of gravitational attraction. Was there something over there that is now here, and was something that was here now over there? Impulse or field, or mass or energy, virtual or actual, particle or wave? Anything transferred from one place to the other. You say no, but dark matter and energy seem to be somehow related to gravitational attraction, and so far I don't think how the stuff works is very well understood.

 

If angular momentum is conserved, how do you know how much you have currently, if currently is spread out over 100 thousand years?

 

Regards, TAR

[Mordred]

That's my point the differences are incorperated into the equations. In the case of the various particle species. The number of photons per era can be determined from understanding the photons properties such as spin. Number of degrees of freedom, entropy density , etc and with use of Bose-Einstein mechanical statistics. Which covers the bosons. The Fermi-Dirac statistics covers the fermions. In each case the properties of the particles in question must be understood.

 

Chapter 3 of Early Universe particle physics covers how to apply those two formulas. In order for them to work however you also have to consider the contributions of other particles at the time period as well as consider chemical reactions.

 

This thermodynamic calculation process took centuries of research to develop. It's methods is well tested.

 

One could however calculate the number of photons using Gibbs law however the method above is more precise. Thermodynamics is a huge and vital field in understanding our universe. The FLRW metric includes the ideal gas laws for that reason.

 

http://arxiv.org/pdf/hep-th/0503203.pdf"Particle Physics and Inflationary Cosmology" by Andrei Linde

http://www.wiese.itp.unibe.ch/lectures/universe.pdf:"Particle Physics of the Early universe" by Uwe-Jens Wiese Thermodynamics, Big bang Nucleosynthesis

I've already posted the articles describing proper distance commoving distance and explained conformal and commoving time

These different distances and time relations is a part of all cosmology based calculations

The problem is most people don't realize these details as they seldom look deep enough . The best way to learn is of course thru a course. However barring that it is buying and studying good textbooks. Learning via the internet alone misses too many of the essential details. This is the reason for my site. To help fill those oft missed details

As far as textbooks go out of the 30 some odd I own. The easiest to learn cosmology from with under grad calculus is Barbara Rydens "Introductory to Cosmology". The best book on taking the complexity out of the mathematics "Roads to Reality" by Sir Roger Penrose. (The last is non model specific as he covers a wide variety of fields including string theory and ADS/CFT and QFT as well as the classical models

[Strange]

Yes, I was asking if any actual material thing was transferred during the act of gravitational attraction. Was there something over there that is now here, and was something that was here now over there? Impulse or field, or mass or energy, virtual or actual, particle or wave? Anything transferred from one place to the other.

 

In that case, the short answer is no. Nothing like that happens just because of (or as a mechanism of) gravitational attraction.

 

There are other effects such as tidal drag or gravitational waves that can cause some of the gravitational energy to be lost.

 

You say no, but dark matter and energy seem to be somehow related to gravitational attraction, and so far I don't think how the stuff works is very well understood.

 

Dark matter has mass. That's it (as far as gravitational effects are concerned). It doesn't seem to have any other relevance to your question.

 

Dark energy is whatever-it-is that is causing the apparent expansion of acceleration of expansion of the universe. One way of modelling it is as a fixed amount of energy per unit volume of space (hence the name). Again, it doesn't seem to have any relevance to the question.

 

If angular momentum is conserved, how do you know how much you have currently, if currently is spread out over 100 thousand years?

 

I'm not sure what you mean by t being "spread out" over time. Momentum (angular or linear) is a property of an object or system.

So you can measure / calculate it from orbital or rotational speed, mass and radius.

[tar]

Mordred,

 

Understood...I think. But still am not sure how such a statement as "the universe is currently expanding and that expansion is accelerating" is meant to be taken. First of all, the universe we see, with the cosmic background radiation at the furthest and quasars very far away and walls of galaxies hundreds of billions of years out, is not the way the universe currently is. The universe is not doing those things at the moment, those things are already done, and the items we see doing this and that have evolved and spun and accreted and radiated a great deal, since. In one sense, there can only be 13.8 billion year old stuff in the universe, and the state of that stuff is closer to the way we see closer stuff, than to the state that stuff very far away seems to be in. So no material or area of space is "just" becoming transparent to photons, as 280,000 year old stuff. That already happened 13.8 billion years ago. Currently, that area of space is likely in a state similar to our local cluster, in terms of how many generations of stars and such have evolved in 13.8 billion years. So how the universe currently is, would be better characterised by what we see locally, than by what we see very far away. And since the local cluster is thought to behave in a manner that indicates it is gravationally bound, then there is no reason to think that other areas of space would not "currently" be in a similar situation. This "current" that I am imagining does not seem to be the same "current" that would find the expansion of the universe accellerating. So somebody is not explaining what they mean by currently.

 

Regards, TAR

If you were to count the number of photons in a volume of local space and multiply by the estimated current volume of the total current universe, then you would have an exact number. But since the total volume of the current universe is not known, such a claim would be impossible to make. To measure particles in various epochs is misleading, as that would be an old count, and would not pertain but as precursors to the current count.

[Mordred]

The answer to that is contained in the distance measures article I posted earlier. We calculate the proper and commoving distance from the redshift. Those are the two terms you need to grasp. Commoving distance includes expansion along line of site. As Hubbles constant is only constant everywhere at a moment in time. Proper distance is the calculated distance at a point in time such as now.

 

Now as far as expansion is concerned tests are regularly done to look for variations in the expansion rate. These variations would cause anidtropies. As well as lead to a variating cosmological constant. The cosmological constant however is constant. So the reason we say expansion is accelerating is due to the increase in volume.

 

Similar to this number exercise.

 

Lets assume expansion is 100% of a given volume just for simplicity.

 

So start with two objects one Mpc apart. In one second they are now two Mpc apart, then 4 then 8,16,32,64,128,256 ... there you have accelerating expansion between two objects. However per Mpc it isn't accelerating it is still 100%.

 

Now expansion is far less than 100% it's 70 km/s/Mpc it's still constant per Mpc, but just as the 100% value it Is an exponential seperation between the same two points.

Your main problem seems to stem from the time aspects and the possibility of changing conditions. In this we have a unique advantage . In that we can look into the past to look for those variations. We can see how the universe evolves using the objects spotted in a given time period.) Unfortunately we cannot see now everywhere. However unless we can detect or determine a change in dynamics we can safely assume it's the same as it's been for the last several billion years. Or since the CMB. (Taking into consideration temperature dropping since due to an increase in volume). Which the ideal gas laws allow us to predict.)

In terms of the major influences to expansion. Baryonic matter such as stars and galaxies influence little. In fact the two major influences is dark matter and the cosmological constant.

[tar]

Mordred,

 

I think you have nailed it. My two biggest problems are with time and changing conditions. While I will give you the fact that it would be alright to assume that things everywhere, including the places and nows we can not physically witness, because of the speed of light, are galaxies and walls of galaxies and voids, and have been that kind of thing for quite a few billion years. But that means that a distant quasar we see is most probably now an area similar to our local cluster perhaps and therefore can not be counted both as a quasar and as a galaxy cluster. The count of particles and energies within a quasar is probably different than the count within a modern galaxy cluster, so one should be cautious not to count twice, and one should be particularly obvious about the fact that equations meant to describe the current universe have nothing to do with what we see, but only to do with what we imagine must be there now, for us to see it later. Or perhaps some cosmologists are talking about what we see as being presently there, in which case there might be some overlap of materials and energies as an equation starts out talking from one perspective and winds up figuring in the other.

 

In your discription above, which I appreciate, I noticed I could not determine when you were talking about the universal present, and when you were talking about the present as witnessed from here and now. If cosmologists are talking about "currently" from a god like universal now perspective, where all items are 13.8 billion years old, I wish they would state that, more clearly. If on the other hand, it is hard to tell which perspectives are being melded during any particular equation, then I think I have a point, and there may be some calculations that use an unthoughthrough combination of the two, and may not carry some "condition" properly through the entire consideration, from end to end.

 

Two for instances.

 

One, I have heard, in the discussion of red shilfts and Z that there is an area of Z that seems to be dark or unaccounted for. That is that as you look out at items older and older the Z increases 2, 3, 4, 5 and then 1000 at the CMB. What happened to all the inbetween Z. There should be, if the universe is isotropic and has a smooth and consistent history a connected trail of Zs as you look back into the history of the universe. Whole peices would not just disapear, there would be items noticable at 250 Z and 500 Z and 750 Z consistent with the evolution of the universe. And the fact that we can see the CMB now indicates to me that the universe is still clearing, at the speed of light, and what is now CMB will be visable as 1,000,380,000 year old stuff in a billion years, and the stuff behind it will be visible as 380,000 year old CMB.

 

And second for instance, is the way the local group of galaxies is considered to be gravitationally bound and not swept up in the hubble flow. That the universe "is" expanding, but space between Andromeda and MIlkly Way is not, and the space between Sun and Alpha Centuri is not, and the the space between the Sun and the Moon is not and the space between Chicago and NYC is not, and the space between my fingers is not, and the space between two water molecules in a snowflake is not, and the space between two quarks is not. So why assume the universe is "currently" expanding when nothing local and therefore more current, is expanding?

 

Regards, TAR

I made the same mistake above, when I said "as you look out at items older and older", when actually I could have said younger and younger in reference to their apparent age, or could have been thinking how old the image was, or the photons carrying the image, as they have been on their way here for, in the case of the CMB, 13.8 billion years.

 

So the older the signal, the younger the signaler, which confounds the photon count, as some photons are on their way here, from very far away, and some photons have passed by and are on their way to some other observer, that may see the photon tomorrow, if they are 1/365th of a ly in the other direction from the sender from Earth.

 

So do you count the photons as they pass, or do you count those that are on the way, or have passed us by, or that will never hit us?

Another example of what may or may not be significant. The energy contained in a volume of space filled with books and furnishings, as in the room you are in, is significantly different on a zero degree night, with no heat, and a 100 degree day with no air conditioning. Unless you are considering as your scale of significantly different energy content the difference between a volume with a black hole at the center, and the same volume centered in the middle of a void. For human purposes, the difference between a space heated to 0 degrees F and one heated to 100 degrees F is quite significant and the only difference between the two volumes (being the same room) is time, as one survey was taken in the summer during the day and the other in the winter at night.

Edited January 1, 2015 by tar

[Mordred]

You have a lot of independant questions here. So rather than try to fully answer them all I'm going to post a handy tutorial website. However the page I will post is specific to your redshift. Look at the curvature of the worldlines. The applicable relations and reasons are on this site.

http://www.astro.ucla.edu/~wright/cosmo_02.htm

 

it's a good idea to read the entire tutorial. For an intro tutorial its excellent.

 

photon and particle counts is per the same time period. It's rather complex to explain without getting extremely intense into the ideal gas laws and thermodynamics. But you do the estimates at a specific time period using the average temperature of that time period. The two statistic equations I mentioned are used. I'll dig up an example I'll try to find a simplified example. Bose Eintein statistics is a bit advanced.

This is a good training but lengthy article on statistical mathematics.

 

http://www.physics.uoguelph.ca/poisson/research/spii.pdf

 

I'm still looking for a simpler example

Here is about one of the simpler examples

http://www.google.ca/url?sa=t&source=web&cd=3&ved=0CB8QFjAC&url=http%3A%2F%2Fwww.astronomy.ohio-state.edu%2F~dhw%2FA873%2Fnotes4.pdf&rct=j&q=number%20of%20photon%20in%20the%20universe%20calculations%20%20pdf&ei=BpKlVIP1A8P3yQSVuYCoAw&usg=AFQjCNHU4o_AumJDNrn44y-WnpRazIWKuQ&sig2=M3kWLon30HDv8WewHqOhDQ

[Strange]

 

That is that as you look out at items older and older the Z increases 2, 3, 4, 5 and then 1000 at the CMB. What happened to all the inbetween Z.

 

This is because it took a long time (100s of millions of years) for galaxies to form. So there is nothing much to observe for a long time. Also, the more distant things are, the harder it is to see them and to accurately measure their red-shift.

 

 

the highest confirmed spectroscopic redshift of a galaxy is that of UDFy-38135539 ^[64] at a redshift of z = 8.6, corresponding to just 600 million years after the Big Bang.

http://en.wikipedia.org/wiki/Redshift#Highest_redshifts

[Mordred]

 

This is because it took a long time (100s of millions of years) for galaxies to form. So there is nothing much to observe for a long time. Also, the more distant things are, the harder it is to see them and to accurately measure their red-shift.

 

http://en.wikipedia.org/wiki/Redshift#Highest_redshifts

Not completely there is a point where the z rate of change has a sharper curve. If only I could post the lightcone results on my signature.

http://arxiv.org/pdf/astro-ph/0402278v1.pdf[/url

 

The results of the calculator will match the graph on page 26 of the above article

As well as the redshift graph on page 40

As you can see it's not a linear but a curved relation

Due to the formulas used

 

 

Don't quote me on this but if I recall the distance to luminosity relations is also part of the reason

Which is also why the common redshift formula everyone knows is only valid for close distances. This is mentioned in the distance measures article in my previous post by Hoggs

http://www.google.ca/url?sa=t&source=web&cd=6&ved=0CCsQFjAF&url=http%3A%2F%2Farxiv.org%2Fpdf%2Fastro-ph%2F9905116&rct=j&q=proper%20time%20cosmology&ei=o4uhVOe8EpOnyATs6ICYAw&usg=AFQjCNENt8vXuRz1vhm6vF3-TawOcXsUcA&sig2=_FVL77t2rD6gMvWYoBTx7A

Edited January 1, 2015 by Mordred

[Strange]

Not completely there is a point where the z rate of change has a sharper curve.

 

Right. Which is why there appears to be such a large "jump" from the earliest galaxies to the z of the CMB when the difference is "only" about 200 million years.

[Mordred]

One other question I wish to answer in greater detail was your concern on homogeneous and isotropy in terms of expansion. First we must be clear the rate of expansion is calculated per the time period being modelled. In the FLRW metric. The point in time being modelled is the scale factor and it includes the rate of expansion as a function of time. This correlates to the proper distance which can change over time. Vs the commoving distance which we use the CMB as a reference point.

 

From this you can see that the rate of expansion is determined at any point in time and we can account for its evolution when measuring objects in our past to our present.

 

 

http://en.m.wikipedia.org/wiki/Scale_factor_(cosmology)

 

The math relations to Z is on this page. As well as the related formulas. Surprising enough wiki does this FLRW variable justice in its coverage.

 

One thing to note on the term homogeneous many people do not understand. It is a term that depends on the area being measured.

 

Take a lake on a windy day for example. Up close and at a small volume it is obviously inhomogeneous. You can easily discern the waves Eddie's and swirls. It is obviously not uniform. However if you look at the same lake from a higher height and measure a larger area those ripples are no longer discernable. Now you can model the lake to a good approximation as being homogeneous andbisotropic.

 

Cosmology works the same way. At small scales there is numerous variations. Large scale structures, galaxies stars etc. However if you increase the measurement area those inhomogeneous regions filter out. They are no longer discernable.

 

In the FLRW metric the scale that homogeneity occurs is usually considered to be 100 Mpc. However later discoveries Sloan great wall etc, May cause us to once again increase that scale. Figures I have read suggest 130 Mpc. However I don't believe an increase has occured as of yet in the main stay.

So the fact that expansion does not affect gravitationally bound objects isn't a factor in the FLRW metrics. Those inhomogeous regions are essentially filtered out. In point of fact the FLRW metric does not work within large scale structures or within galaxies. Those inhomogeneous regions typically also have anistropies involved. Different metrics is used to model those areas. They may bear similarities to the FLRW metric however they involve modifications depending on the system being modelled.

Typically in those regions the Einstein field equations are often used. You have greater flexibility in observer relations and stress energy tensors for interactions such as gravity. The gas law trick is to model individual uniform regions seperately, then apply an imaginary boundary between two uniform regions then develop the metrics to describe the interactions between the two regions. (The boundary region).

Hope this helps

A good example of the latter method is a black hole. The event horizon is the seperation of one spacetime to another. As you can model the influence of gravity with the Einstein field equations the outer region is modelled inclusively. However you can examine the different ergosphere regions within the accretion disk seperately apply boundaries around those regions then discuss the interactions between the ergospheres seperately.

(Hint this methodology is used in most physics models to some extent. Though can add individual interaction dimensions). Good examples is ADS/CFT,QFT,particle physics and string theory

 

 

So in answer to the opening post title the answer is only limited by the data available, the ability to describe the relations involved in those data sets. Size of the region's isn't an issue. The only issue is data and understanding of that data. And how to seperate regions of interactions from regions of non interaction.

Edited January 2, 2015 by Mordred

[tar]

Mordred,

 

Thank you for your good descriptions and your links. I am just into Tamara Davis' Thesis, but have a conceptual problem with the cosmological event horizon.

 

"The cosmological event horizon separates events we are able to see at some

time, from events we will never be able to see. At any particular time the event

horizon forms a sphere around us beyond which events are forever inaccessible. An

event horizon exists if light can only travel a finite distance during the lifetime of

the universe."

 

If the areas of space that are currently viewed as CMB are currently (in the universal now, or cosmic now as Dr. Davis calls it) 46 billion lys proper distance from here, at the cosmological event horizon, that means that those areas of space are currently13.8 billion year old galaxies. Since today we see those areas of space as 380,000 year old areas, there are a great deal of events, on their way here from that area of space. The fact that we will never be able to witness an event that happens there tomorrow (in the cosmic now sense of tommorrow,) does not mean we will not see all the events that happened in that area of space between the time the place was 380,000 years old and the time it becomes 13.8 billion years old. All those events are currently on their way here. In addition, due to the stretching of space and the wavelengths of light that are traveling through it, the wavelengths of the CMB are already 1000 times their emission length. This means that a vibration of a hydrogen electron, as it fell from its energy level in a nano second will take a millionth of a second to unfold. And a second's worth of activity will take 16.7 minutes to unfold and be spread out over 186 million miles. By this conceptual visualization of the situation, that area of space might get smaller in an angular sense, as the eons and billions of years go by, but has no reason to ever disapear from view as by definition the events happening today will never reach us, and therefore what we see can only be slowed down for us, into radio waves perhaps, but cosmic waves that left that area at some point in its history would reach here as visible light. And this at some point far in our future. There is no reason to think that electromagnetic waves would not continue to reach here, from there, at the speed of light, depicting the events, albeit slowly, getting increasing closer to the 13.8 billion year mark, at longer and longer radio wavelengths, with the events appearing to be going so slowly as to appear to be still.

 

Regards, TAR

Edited January 3, 2015 by tar

[Mordred]

No problem glad to help I don't see anything inaccurate in your last statement. Looks like your getting the hang of it. Keep up the good work

Looking over it again. A couple of points. What we see is the past events ie CMB. As our time and the past progress at the same rate. We will see the progressive change in the past events of that region. Which is an earlier state progress towards our thermodynamic state. Albeit a different distant region. Since the CMB this will be the lowering of the blackbody temperature.

It's probably what you meant

Edited January 3, 2015 by Mordred

[tar]

Mordred,

 

Still have the majority of your links to read, but to the thread topic, if there are two perspectives one can take on a particular area of space where we see the CMB, one as an event that is already done 13.8 billion years ago, which we are currently witnessing, and another imaginary perspective where that area of space currently contains clusters of galaxies which we will never actually experience, the two cannot be both included in any equation, or you would get a double count of what can only be one instance of that area of space.

 

This is a clear and evident case where a double count can and should be avoided, and the universe can either be considered historical or imaginary. Unfortunately, this clear distinction is not as easily come upon when looking at the sky, where some things are burning up in our atmosphere, only a moment away, and others are planets and our moon and Sun, seconds and minutes away, and others are nearby stars a few years away, and others are distant stars in our own galaxy 100,000 years away and others are galaxies a million years away. In this view of the sky, where it is obviously present and real and not imaginary, it is difficult to immediately recognize an image as historical, and view the whole situation from the cosmic now point of view, because of the immense size of the place, and the incredible length of time that it has been around, concurrently with the immediacy and reality of the items sensed, measured and withnesses and fit into the imaginary model. Here is where I figure there must be a size at which physical events cannot be both withnessed as one event, and imagined as one event.

 

Regards, TAR

And here when considering a huge system, separated by more than a half a million miles, the equation formulated can either be representative of what is presently being withnessed, or representative of an accurate and true representation of the arrangement of matter and energy in the cosmic now. The translation between, the transform that takes one from one perspective to the other cannot be ignored, and large distances must be factored in and left in the transform and not discarded, primarily because holding a very large system as taking place at once, is not the way the universe works. The universe does not happen at the speed of thought, it happens at the speed of light.

[Mordred]

Ok let's pick an equation.

 

[latex]d{s^2}=-{c^2}d{t^2}+a{t^2}d{r^2}+{S,k}{r^2}d\Omega^2[/latex]

 

In this equation you see a value for time. You see c for speed of light to handle relativity. You see k for the curvature constant. You also see two different terms for distance. a is the scale factor (handles the expansion history)

 

This formula is used when you spot a new galaxy and you find its redshift. now we know the galaxy will not be there in our present. So where will it be?

 

This is the function of this formula to calculate its current location due to expansion. Or in its more correct usage its used to tell us the size of the universe today as opposed to what we visually see. The value k curvature constant is set at different values for flat,positive curved or negative curved.

 

Any time we spot a new object and state its distance we calculate expansion and the observer effects such as redshift as well as difference in time to obtain its proper distance or commoving distance.

 

Now the redshift of z=1089 CMB is a calculated value that corresponds to a calculated radius. In this we take into consideration luminosity to distance relations. However we know the object is no longer there so we calculate its position.

 

Thermodynamics However needs to be calculated at a specific time. So if we wish to know what properties it has at that time we must measure samples of that time. Do this for various times and keep doing it till you establish a time evolution pattern.

 

The average redshift per time period allows us to test expansion change and how it evolves. From this we can test the thermodynamic history and vice versa. Methods such stellar parallex allows us to test redshift.

 

Every measurement technique undergoes numerous tests to ensure the accuracy of the methodology. This is critical as we need to confirm the universe is flat to calculate the size of the universe using the above equation. We also need to know redshift is accurate, and the expansion history.

 

Keep in mind the ideal gas laws alone could be used to show the expansion history. However we need to account for possible intermediate changes. This is where observation and measurements of redshift is used.

 

Now as mentioned this assumes homogeneity and isotropy. The CMB and stellar data sets confirm that.

 

 

These are just a few of the steps to model a system with such a huge time change between and b.

 

PS we also never rely on any one method. Universe cosmology relies on extensive datasets. Those datasets allow the development and confidence in the formulas used.

 

Unlike most physics that model clearly seen entire processes. Cosmology doesn't have that luxury. The continuous tests and formulas allow us to overcome this obstacle.

 

Prior to WMAP every time you did a calculation of distance you had to dob it three times. Why? Well we didn't know for sure what k was in the above formula.

 

Now let's play hypothetical mayhem.

 

let's imagine we discover conclusively that the universe underwent a 2000 degree Kelvin increase in temperature for say 1 million years roughly 2 billion years ago. What does this effect.

 

 

first off it means the universe underwent either a phase change, a decrease in volume or an increase in density. Ideal gas laws.

 

In all three cases this will effect redshift as well as rate of expansion. The above formula will no longer work as is so a correction must be made. The calculations for the age of the universe must be redone. Distances of objects earlier must be recalculated . Datasets must be adjusted. All formulas that derived from the above formula must be redone.

 

wow lot of work. Glad that hasn't happened.

 

 

However that example didn't happen instead dark energy and dark matter did get confirmed.

 

If you pick up an article prior to WMAP. You will probably find the wrong metrics. The FLRW metric underwent a change to include the cosmological constant. Conformal distance based on the Hubble sphere as being the size of the observable universe is no longer valid.

 

Older textbooks sold today still have these problems. So study recent articles and textbooks

Publishing date 2000 and later should be ok

Lol you should have seen forum debates in the ,90's

Your lucky we didn't have LCDM back then. The best fit model was anyone's guess BB , quintessence, trespace, HCDM WCDM HLCDM MOND etc etc etc....many of em you can't even Google anymore

 

 

The main point Is how you limit the model. You can model the past with the present if you can collect enough data, experimentation to do so. Can the model change absolutely. Can it be disproven then yes. Can the model make predictions yes it can. LCDM does make predictions it includes past and present events. It can describe what we see , it can describe aspects such as proper distance that we don't see. So is time a limit to a model?

 

If LCDM which describes the dynamics of the universe isn't a model then what is lol.

 

 

Try to link to the calculator in my signature. Set steps to 100, then open column selections. Then press

Calculate. It will give you the expansion history of the particle horizon, the observable universe, the distance now,the distance then (proper and commoving. The redshift . Past, present and 80 billion years into the future based on our current knowledge

Forgot the recessive velocity

It also uses the Planck and WMAP datasets so you can compare the differences.

Edited January 4, 2015 by Mordred

[tar]

Mordred,

 

Thank you for the description. Sounds like my worries are mostly factored in and figured out already. However I still think there is room for inadvertant shifting between the actual present and the universal present. And I am still not sure in which present the formulae tell us that the universe is currently accelerating its expansion.

 

You say we know an object is no longer where we see it, so we calculate its position. Do we also calculate what type of object it currently is? That is, if we see CMB at 1090z we know we are looking at stuff that is so far away, we are just seeing its first photons, but there is other, closer stuff, whose first photons we saw 13 billion years ago. We are now looking at more recent photons of the close objects. Maybe only 3 years old, or 30 or 300 or 3000 or 30000 or 3 hundred thousand, or 3 million or 30 million or 300 million or 3 billion lys away. In each case the equations are different in terms of how many photons that object has already released in our direction, how many have gotten here, and how many have passed us by and are on their way to other locations. In all cases there is only one instance of said object that truely exists and is currently, in the cosmic now, releasing photons. We cannot say much about the current configuration of the universe, because it is so massive as even the closest stuff is more than a lifetime of light travel away.

 

In this situation, when we say "currently" expanding, from what vantage point, are we making this claim? What time is it, at this vantage point, and what instance of an item are we considering true, at the moment? All instances? The one we are currently witnessing? The one we are figuring might be the case we will witness in 3 years? 30 years? 3 million years?

 

I still have at least this worry. Of what value is it to know the universe is currently expanding, if the closest items we see, within a couple million lys, are not receeding from each other in the manner in which we figure the current items of the universe should be receeding from each other?

 

First of all, if the universe is expanding and this expansion is accelerating, then the closer items should be separated from each other, to a greater degree than the further away items. The local cluster, for instance should have been more densly packed a billion years ago, and even more densely packed 10 billion years ago. So far away things should not appear to be isotropic, they should appear to be more densely packed that space around here. If we figure the spacing we see, at huge distances, as similar to the spacing we see more locally then we have not accounted for the compression that should be evident in items that we see billions of lyrs away.

 

How can you fit a large portion of the universe into the same thermodynamic equation, under these conditions?

 

It is either incorrect, outdated, or inconsequencial. In all three cases, there is no way to verify, or choose a vantage point from where the thing could be considered factually correct, true or meaningful.

 

Or so is my worry.

 

Regards, TAR

P.S.

 

What does minus the square of c mean anyway? I thought a negative number times a negative number gave you a positive number. Plus if the speed of light is the speed limit of the universe, what meaning could squaring that number have?

[Mordred]

When we say the universe expansion is accelerating it is the entire observable universe.

 

However as mentioned the rate of expansion per Mpc is the same everywhere.

 

It is the recessive velocity that is accelerating. This value depends on seperation distance. I posted how that works earlier in this thread.

 

Now thermodynamics is specifically at a moment in time. To determine a specific thermodynamic state one must measure samples from the same moment in time.

[Strange]

What does minus the square of c mean anyway? I thought a negative number times a negative number gave you a positive number. Plus if the speed of light is the speed limit of the universe, what meaning could squaring that number have?

 

The use of c² in equations like this (and e=mc²) is just a conversion constant because of the units we use for measuring time and distance. If we used different units, it could just be 1.

 

You can have a negative square. For example, 4 is 2² but you can still have -4. Think of it as -1 x c², if you prefer.

First of all, if the universe is expanding and this expansion is accelerating, then the closer items should be separated from each other, to a greater degree than the further away items. The local cluster, for instance should have been more densly packed a billion years ago, and even more densely packed 10 billion years ago. So far away things should not appear to be isotropic, they should appear to be more densely packed that space around here. If we figure the spacing we see, at huge distances, as similar to the spacing we see more locally then we have not accounted for the compression that should be evident in items that we see billions of lyrs away.

 

Two things. Firstly the local galaxy cluster is held together by gravity and so is not expanding. So we can only see the expansion by looking at objects further away than that. Secondly, the acceleration is quite small so would not be noticeable as a change in spacing (we can only measure expansion and acceleration by comparing velocities).

[tar]

Lost a post somehow. Thought I answered you both with a few more questions. Oh well.

 

Main drift today, thinking about this thread, was related to human thought and perception. Kant figured that time and space were the two apriori intuitions. Steven Pinker talks of how the human mind shifts grain size making huge things one grain that can thought of in bunches of said grains.

 

Everybody has seen the movie in highschool science class where you have the atom and 10 times that the molecule and the crystal and the mitochondria and the cell and the organ the organism and the family and the neighborhood and the state and the country and the continent and the world and the solar system and local part of the galaxy and the local cluster and the wall of galaxies we are part of, and so on. The brain can handle this nicely, the grain size thing.

 

My concern, in reference to this thread is that as you get larger and larger through the above logorithmic progression, what was instantaneous, faster that we can process it, at the atom level, becomes incredibily long and drawn out on the massively huge scale of the galaxy (not even considering the even larger "local" cluster, or the distance of a type one A supernova.)

 

In this, the speed of thought, the handling of the grain size, as taking the whole picture in at once, is not really actually possible, and the required adjustments and transforms and relationships between the components of the "at once" picture, are not consistently and properly carried through, from one end of the picture, to the other, because of our inability to view the thing for 150 thousand years, and then pick a time to freeze the whole arrangement at, and view it at once.

 

Even if we were able to perform such an observation and figuring and lock down of the picture, it would be a picture of what happened 150 thousand years ago, and would not include any observations at all of what is going on currently, even at the closest star. We don't get that info until 2017.

 

Yet you figure we can figure a way to apply our observations and data to equations that can accurately portray the thermodynamic state of a system millions of lys in diameter? How?

 

Regards, TAR

At what cosmic date are we freezing said system, inorder to consider it, at once?