Density of Space

[gre]

Is space-time alone thought to have density? Would areas of space with higher gravity be considered more dense?

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Merged post follows:

Consecutive posts merged

I guess I could ask the same question about mass as well... Is it possible that an object's (mass) density increases in areas of higher gravity? Not from the actual force of gravity on the object, but from an effect similar to red/blue shifting.

Edited April 16, 2009 by gre
Consecutive posts merged.

[Mr Skeptic]

What would you measure the density of space as? Volume over volume?

[gre]

What would you measure the density of space as? Volume over volume?

 

Probably not.

 

But what is the exact cause of frequency/wavelength shifting phenomena? Gravity seems to be the cause of gravitational red/blue shifting, and relative velocity between objects seems like the cause of the doppler effect. But what is the "common denominator" between these effects?

[gre]

Just curious, is it possible gain any insight into the relationship between the Doppler shift and gravitational red/blue shift by setting the observer's wavelength equal to each other in the following equations?

 

gravitational redshift: w.e + w.e * z = w.o

 

w.e = wavelength from emitter

w.o = wavelength at observer

z = spectral line displacement from redshift: z = (G*m) / (c^2 * r)

 

doppler shift: w.e / (1 - v / c) = w.o

 

v = relative velocity between observer & emitter (negative when objects are moving towards each other, positive when objects move apart)

c = speed of light

 

(w.e + w.e * z) = (w.e / (1 - v / c))

 

so,

 

z = (1 / (1 - (v/c))) -1

 

If v is positive, then z is negative

If v is negative, then z is positive

 

Is this right, or is something goofed up?

Edited April 20, 2009 by gre

[ajb]

What would you measure the density of space as? Volume over volume?

 

Yes, I think you could get a meaningful density that way.

 

Let [math](M,g)[/math] be the (pseudo) Riemannian manifold under examination. Then think about the ratio of the invariant measure on this manifold and the canonical measure on a Euclidean space.

 

Hint, this is related to the Ricci tensor.

[gre]

oops,

 

For gravitational/velocity redshifts (v must be positive):

 

w.e + (w.e * z) = (1 / (1 - (v/c))) - 1

 

so, z = (1 / (1 - v/c)) - 1

 

For gravitational/velocity blueshifts (v must be negative):

 

w.e / (1 + z) = w.e / (1 - (v/c))

 

so, z = (1 - (v/c)) -1

 

 

If the relative velocity between parting objects (redshift) exceeds c, then z is negative. What is negative z? Error?

[Quetzalcoatl]

Is space-time alone thought to have density? Would areas of space with higher gravity be considered more dense?

---

Merged post follows:

Consecutive posts merged

I guess I could ask the same question about mass as well... Is it possible that an object's (mass) density increases in areas of higher gravity? Not from the actual force of gravity on the object, but from an effect similar to red/blue shifting.

 

In GR, the metric defines the intrinsic curvature, not extrinisic. I usualy think of that as space-time density, intead of a curved "shape" in a hyper-space. The metric, which measures distance between every two infenetismal points, differs from one point to another. So some places are denser in space-time coordinates than others. And that's gravity. So I totaly agree with u!

 

But when u say "space-time alone", u must remember that this curvature has a source (the stress-energy tensor), so it might be that we can't speak of space with varied densities, without a source for this variation. They are always acompanied by mass/energy.

 

Now that I think about it, gravitational waves could also cause this, even though they don't apear in the standard stress-energy tensor...

[jackson33]

I wonder if the question were asked, 'does the Universe have density?', would any answers have changed? Then my follow up question would be, has this density then changed under BBT 14 BY? The obvious answer should be, YES...

 

 

Is space-time alone thought to have density? Would areas of space with higher gravity be considered more dense?

 

Isn't this backwards...Since gravity or GR curvature is caused/result of mass, wouldn't anyplace with concentrated mass naturally have the most gravity and voids with little or no mass have no gravity. Seems that's what has caused voids in the first place.

 

ajb; It's thought around 14 BYA matter (Hydrogen/Helium/Lithium) first formed, shortly after into the original stars, in turn producing the other elements.

 

Windhorst's galaxy (the most distant measured redshift galaxy) has a red shift of 2.39, or 84 percent the speed of light.

..

http://www.encyclopedia.com/doc/1P2-8073057.html

 

Using this figure (only), what would your ball park estimate for a U diameter 14 BYA and today. My figures are a rough 6 BLY and 252 BLY, understanding expansion is not thought to have been constant. I would argue that but not material to my question. Said another way, I placed Windhorst's galaxy 2.5 BLY from where the current earth exist at the time, if the same unit we currently observe....

 

Back to the OP, then the U with no additional atoms (mass) was confined to an area (density) of one size compared to todays whatever area, though thought much greater. If you take this back further to a singularity, whether bumped or some natural original expansion cause, density of whatever that was to to days should be to extremes. Matter is simply a composition of atoms into elements or into an object, all of which is limited to that original total.

[Martin]

Jackson, you are quoting something from a NEWSPAPER BACK IN 1998.

...

http://www.encyclopedia.com/doc/1P2-8073057.html

 

The date encyclopedia.com gives is August 1, 1988. But their accuracy is terrible. It is probably August 1, 1998.

(Windhorst reported a 2.39 redshift radio galaxy in 1997 http://arxiv.org/abs/astro-ph/9712099 )

 

So a non-professional who didn't have a clue what she was doing lifted something from the Boston Globe of August 1, 1998 to obtain raw content for encylopedia.com

 

Please try to use professional writing as sources and check the date when the thing was written. Recent, like 2005 or later, is better. In any case after 1998 when the new parameters from the Hubble Space Telescope were published.

 

Your Boston Globe encyclopedia.com article goes like this:

In the constellation Hercules, an estimated

13

billion light years away, astronomer Rogier Windhorst of Arizona State University has discovered the most distant known "near normal" galaxy. A near normal galaxy reveals itself to astronomers only as a faint radio source. This one is 10 million times too faint to be seen with the naked eye.

 

Windhorst's galaxy has a red shift of 2.39, or

84

percent the speed of light, higher than any of its type previously identified. Red shift, caused as the motion of a distant object shifts its light toward the red end of the electromagnetic spectrum, is...

 

That is their salespitch come-on and after that, to read more, they want you to pay.

 

They say that redshift 2.39 means distance 13 billion lightyears and recession speed of 0.84 c.

Those numbers are completely coo-coo. Would you like to get the real numbers corresponding to z = 2.39?

 

Google "cosmos calculator". Put in the current best estimate parameters:

0.25, 0.75, 74

(that means .25 for matter, .75 for dark energy, 74 for the Hubble rate.)

Then put 2.39 in the redshift box and press calculate.

 

You will get that the distance to the object now is 18.45 billion lightyears (not 13). And the recession rate now is 1.39 c (not 0.84).

 

If you are interested in the distance and recession rate back when the object emitted the light we are now receiving, it gives that too. The distance then was 5.44 billion lightyears and the recession rate was 1.33 c.

 

The light travel time was 10.61 billion years. (The calculator tells you the age of the U when the light was emitted and when it was received so to get travel time you just subtract 13.39 - 2.78 = 10.61)

 

The numbers are approximate, you can round off.

 

The hard data here is the redshift z = 2.39. I doubt that represents the farthest anything, and it isn't clear what "normal" means. Nowadays people see galaxies way past z = 5. Some in the range 6-7 and even a few z > 7.

 

The point is not these particular numbers. It's just that encyclopedia.com can't be trusted. They only give a taste, then they want money. They don't give links to professional sources.

And it is easy to get better quality more up to date stuff. Wikipedia is not bad on a lot of things. At least it sometimes gives references to profession writing, some of which are live links.

Edited June 2, 2009 by Martin

[jackson33]

Martin; Rogier Windorst, has a remarkable history in this area, knew the name and used that one figure (mentioned) to explain my rather approximate estimations. It was neither the point of that post or was his work material. I would suggest the individual your attacking is quite reputable, if that was your point. If me, fine and why a used question marks in that reply. I was asking, not informing.

 

http://hubblesite.org/newscenter/archive/releases/1992/1992/21/image/a/

http://arxiv.org/abs/astro-ph/0406438http://en.wikipedia.org/wiki/Rogier_Windhorst

 

Rogier Windorst (Arizona State University) William Keel (University of Alabama) and NASA Download full size image

Observations with NASA's Hubble Space Telescope (HST) have given a tantalizing glimpse of the time soon after galaxies formed, suggesting that these huge Systems of stars formed over a wider span of time than once believed. Posted on: 05 Feb, 2005

http://www.redorbit.com/images/gallery/hubble_space_telescope/hst_images_compact_young_radio_galaxy/18/727/index.html

 

 

 

Was going to PM you on an issue, but feel you deserve a more formal show of appreciation. You efforts on behalf of a young man the other day, made his day, probably his month. I understood the efforts, reading each of your post to him and am highly impressed with your interest in this case, not always having followed your post, at least under 'Martin'....My hat's off to you, for what it's worth and my personal thanks...

[Martin]

Jackson, thanks so much for the kind words.

 

About Windhorst, I hope I didn't say anything critical of him! He wrote this technical paper in 1997:

http://arxiv.org/abs/astro-ph/9712099

 

It didn't say any of the stuff that I was criticising. The professional article was fine---just gave the redshift figure 2.39. I would guess the boo-boos came from the Boston Globe August 1998 journalist (as far as I can tell, you have to pay to see the whole article).

And then someone from encyclopedia.com grabbed the newspaper article.

I would guess harvesting for content to put in their pay-per-view encyclopedia, which could be a job assigned to untrained people. So then it shows up 11 years later and it's kind of confusing and has large numerical discrepancies.

 

So what worries me is how unreliable information gets churned up. Windhorst can hardly be faulted, he is probably a great guy, he is rather the victim of journalism plus encyclopedia.com steam-shovel approach to acquiring content. That's my take anyway. Didn't research it. Just an impression.

 

So far, although I've seen stuff in Wikipedia I didn't like, I would guess it is the best general source of astrononomy information. It's a problem, the quality of what we get on the web. Takes some filtering. I also have found good articles at something by a David Darling. Maybe we should pool our favorite sources.

David Darling ( http://www.daviddarling.info/ ) might be half crackpot/sci-fci nut, for all I know. But I've gotten useful up-to-date info from his "encyclopedia of science". Just a small sample so I can't vouch for his whole output. I find I keep going back most often to Wikipedia.

then there are the academic outreach sites like Einstein Online and also UC Berkeley has one.

Edited June 3, 2009 by Martin