Does the Acceleration of the Universe Change?

[falcon32]

"But my point is that you cannot argue that extra energy has not been added to the universe."

Of course I can...that is incorrect.

"... In the Integrated Sachs-Wolf effect, we clearly see a photon blueshifted...quite literally, energy has been added to it.''"

You mean the frame of observation has changed slightly.

Why not think about 'the energy that has been added' in one entity as coming from cooling of
the universe as it expands?

But of course all this is rather incomplete reasoning...Where did all "the energy that has been added" to the recent Oklahoma tornadoes come from?? Do you think there was energy added to Earth's atmosphere??

I might have phrased my last post a little too succinctly. Now not to be facetious, but do I think energy is being added to Earth's atmosphere? Every day the Sun shines (those 1400 watts/m² come in handy now and then)!

Hmm, thinking of a blueshifted photon as cooling from the Universe's expansion is good alternative way to look at this situation -- thanks! However, this would demand that it takes energy to expand the Universe...something I find quite natural, since it is accelerating against gravity, but something that others do not like for their own reasons.

But I still think this is a bit of a paradox.
Suppose you have three experimenters, all with watches that have been synchronized. Experimenter A stays in our Milky Way galaxy, the other two, B and C -- having identical scientific equipment -- travel out to the Andromeda galaxy, and position themselves at the base points of an isosceles triangle, with A being at the apex. The triangle base is wide enough so that B is very far away from Andromeda, and therefore any gravitational effect on photons he shines will be negligible.
But C's triangle leg passes just to the right of Andromeda's black hole (from A's perspective), so that it experiences the maximum gravitational effect (note that any photons C shines will undergo gravitational lensing, and therefore, from his perspective, he must aim a little to his left in order to hit A; likewise B must back up just a bit so that the two paths are still of equal length. So the total geometry closely approximates a triangle, but is not).
Now then, at a predetermined time, both B and C fire light beams at A. Both will travel exactly the same distance. However, the Sachs-Wolf effect will very slightly blueshift C's photons. B's will remain unaffected.
Now since both light beams were created with exactly the same apparatus, and traveled exactly the same distance, why does one have more energy than the other?

 

[falcon32]

Awesome marcus, looking into the links and thanks

 

[marcus]

Falcon, if you are interested in acceleration of the geometric expansion process maybe you should learn (very easy and quick) ability to make charts of it with the standard cosmic model. Try this:
open http://www.einsteins-theory-of-relativity-4engineers.com/LightCone7/LightCone.html
click "set sample chart range"
click "column definition and selection" which gives a menu and deselect everything but Time, Hubble radius, Distance_then, and "a' R_0".
This last thing is actually the EXPANSION SPEED OF A SAMPLE DISTANCE plotted over time, so you can see it decline at first, until around year 7 billion, and then gradually build up. Acceleration is not very dramatic so the build-up is not very dramatic but at least you can get a handle on it.

Then press "calculate". That will give a table with four columns: Time, Hubble radius, Distance of past lightcone at that time, and growth speed of the sample distance (as a multiple of the speed of light)

Then if you go back and click on the "chart" button and AGAIN press "calculate" you will get a chart with blue, red, and gold curves plotted over time.

blue is Hubble radius (the size of distance that is expanding at speed c)
red is D_then, the distance to a photon which is coming towards us and will get here today (but then continues on into future, away from us)
gold is the expansion speed of a sample distance (the chosen distance is one which for definiteness is equal to the Hubble radius 14.4 billion ly at present, you have to pick some distance to have a definite speed since the speed depends on the size of distance).

When you have the "column selection" menu open you mostly just UNCHECK the items you don't want which happen to be checked as the DEFAULT.
So you uncheck "scale factor" for example. Another time you might want it and leave it checked.
BUT THE sample speed item labeled "a'R_0" you actually have to CHECK because it is not part of the default and will not appear unless you explicitly indicate you want it.
I think if you do actually open the "column" menu you will see what I mean. Checking that is what will get you the gold curve plotted.
It is not all that dramatic, as I say, but it does show how the growth speed of a generic distance changes over time, and the minimum speed around year 7 billion.
All distances have the same speed profile shape, just proportioned to their size.

 

[Naty1]

Now not to be facetious, but do I think energy is being added to Earth's atmosphere? Every day the Sun shines (those 1400 watts/m2 come in handy now and then)!

And every day it radiates away that energy...well, sometimes a bit more, sometimes a bit less...the former are cooling periods the latter warming periods...

talk about facetious...just don't leave this discussion thinking that I have said the heat lost with cosmological expansion powers the Sachs Wolfe...I have no idea about all those very complicated relationships...for all we know maybe there is a some gain or loss of energy...I
don' t think we have observational evidence one way or the other...

 

[Mordred]

You may find this article on Sach-Wolfe effect of interest.

http://arxiv.org/abs/0801.4380

though on the technical side there is some good information within it

 

[falcon32]

And every day it radiates away that energy...well, sometimes a bit more, sometimes a bit less...the former are cooling periods the latter warming periods...

talk about facetious...just don't leave this discussion thinking that I have said the heat lost with cosmological expansion powers the Sachs Wolfe...I have no idea about all those very complicated relationships...for all we know maybe there is a some gain or loss of energy...I
don' t think we have observational evidence one way or the other...

Tongue in check, I'm never serious when I joke, my friend. And you have every right to redefine your stance, there are many mysterious things in this Universe, part of why I love learning. Thanks to all who contributed to this thread, I've learned allot and will continue to do so with the information you've provided.

 

[Naty1]

Mordred: I scanned the paper linked in your post #35...lots of the detail I don't understand...terminology not all that clear to me...
If you have any specific comments...your 'good information'...I'd be interested...

I checked the conclusions and found these comments:

... there is no indication of an evolving dark energy density. By combining
these results with other cosmological data, we find a generally consistent picture of the behaviour of the Universe, which is converging towards the ΛCDM model although
the uncertainties remain considerable.

which are reassuring, but nothing unexpected...

What would have been an indication of evolving dark energy density??

 

[Mordred]

A large chunk of that paper is calibration data. In other words removal of other factors to arrive at a dataset to work from. Section vI is where they go into looking for the Sach-Wolf effect.

Sach-Wolf effect occurs in the case of integrated Sach-Wolf when photons pass through a time varying gravitational well.
This particular form is from last scattering and essentially
present time observer.
If factors such as DE and curvature vary during the period between emmision and receiving of the photons. This would cause variations in redshift. similar to how expansion does but for a
different cause.
There are a forms of Sach-Wolf non integrated(normal) and integrated described above

http://www.astro.ucla.edu/~wright/Sachs-Wolfe.html

Ned Wright describes the two better than I can.

 

[Mordred]

You may find this technical paper handy as well. I haven't fully read it however its showing the Sach-Wolfe effect in regards to the newly released Planck data

http://arxiv.org/abs/1303.5079