very distant galaxies VDGs

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very distant galaxies VDGs

Postby hyksos on February 24th, 2019, 3:03 pm 

Our current theories of the cosmos predict that there is "metric expansion" driving all galaxy clusters away from each other. The recession velocity of a distant galaxy grows with distance, so that more distant galaxies appear more red-shifted. In the equations that describe this "scaling" of recession velocity (per megaparsec) is a constant that determines how strong this effect is, called the Hubble Constant.

Current theories dictate that the Big Bang was not a localized event that unfolded in space -- like an explosion located in space. (We assume) that space was always infinite, and that discussions of scale are relative comparisons with the current "observable universe". The entire universe was not squashed into a space the volume of a grapefruit. Rather, the observable universe was. More precisely, the spherical volume that circumscribes the observable universe was metrically compressed to a sphere of grapefruit size.

A consequence of the above dogmas is that there do actually exist galaxies that are extremely far away from us. Taken literally, we can state that for any positive real number, r , there will likely exist a galaxy that is r meters away from the Milky Way.

Now we get to the fun part: Because for any r > 0.0 , there is a galaxy r meters away. Recession velocity scales with r, so there must exist a galaxy that is receding away from us at the speed of light, c. In every case, cosmologists will park the discussion there and end it. Those galaxies receding at those speeds could never be detected by us, because the light they emit will "never" reach us. Further, there must also be galaxies that recede from us at a velocity that exceeds c. Those galaxies are the topic of this article : very distant galaxies or VDGs

V.D.G.
Define VDG as a galaxy so distant that it is being metrically-expanded away from us at a speed that is substantially larger than c. v >> c. Cosmologists throw their cards on the table and declare that they don't matter, because we could never see them. They are "forever cut off" from us. Then the conversation fizzles there and every goes home.

Not today. Let's talk about those galaxies receding away from us at v >> c.

Pretend we could detect them somehow, in a platonic sense. If we could measure VDGs, I assert that we would see them progressing backwards in time. The stars in them would appear to be collecting light and becoming more massive. Planets would disintegrate into thin accretion disks and dust which would fly away from their host star. If there were black holes there, they would appear to spit out matter that circles away from them and forms into objects around them. I concur that we "couldn't see them because light can't reach" , which is fine.

Nevertheless, I find myself haunted by the prospect that VDGs are out there some where and they are progressing backwards in time in a very real way. We "cant see them". Fine. Right. But still : if they are there, then their clocks are (in a platonic sense) running backwards from ours. We may have all the numbers we need to quantify how far away the closest VDGs are. The calculation could be done on the back of a napkin.
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Re: very distant galaxies VDGs

Postby TheVat on February 24th, 2019, 3:28 pm 

>5 gpc? (16 gly)
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Re: very distant galaxies VDGs

Postby bangstrom on February 24th, 2019, 5:39 pm 

hyksos » February 24th, 2019, 2:03 pm wrote:

(We assume) that space was always infinite, and that discussions of scale are relative comparisons with the current "observable universe". The entire universe was not squashed into a space the volume of a grapefruit. Rather, the observable universe was. More precisely, the spherical volume that circumscribes the observable universe was metrically compressed to a sphere of grapefruit size.


I think your comment in the quote above varies from the conventional understanding of the cosmos but, if you are implying that the standard model does not hold up under close examination, I would agree to that.

The part that I find inconsistent with the standard model is the view that the universe is infinite. The universe is considered to be an expanding but finite volume of spacetime and all of that spacetime was once confined to the volume of a sphere the size of a grapefruit which included all of spacetime and all of matter both visible and invisible. It was what Timothy Ferris calls “the whole shebang.” That is, if we could step outside the early universe and view it from the perspective of our present day, expanded universe, the entire universe would be within that grapefruit sized sphere including everything visible and invisible and all of space itself. There would be nothing (no space, no time and no beyond) anything within that sphere.

The implication of a finite view of the universe is that the universe is not expanding into preexisting space, on the contrary, it is space itself that expanding from within. The distant galaxies are not ‘moving away’ from us or any common center. It is space between us and the distant galaxies that is expanding giving us the illusion that the galaxies are ‘moving away’ from us with true recessional velocities. This is a much different scenario where distances appear to be increasing because space is expanding rather than the galaxies actually “moving away” through space.

The view from the distant galaxies is that we are ‘moving away’ from them and the view from the VDG’s is that we are the ones moving away at v>>c with clocks running backwards in time. Also, in Riemann curved space, this means the same galaxies that appear moving away from us are simultaneously moving towards us and the VDG’s are moving towards us at v>c and blue shifting as they approach. Of course, we can’t see the VDG’s either coming or going.
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Re: very distant galaxies VDGs

Postby davidm on February 24th, 2019, 7:01 pm 

bangstrom » February 24th, 2019, 3:39 pm wrote:The part that I find inconsistent with the standard model is the view that the universe is infinite. The universe is considered to be an expanding but finite volume of spacetime and all of that spacetime was once confined to the volume of a sphere the size of a grapefruit which included all of spacetime and all of matter both visible and invisible. It was what Timothy Ferris calls “the whole shebang.” That is, if we could step outside the early universe and view it from the perspective of our present day, expanded universe, the entire universe would be within that grapefruit sized sphere including everything visible and invisible and all of space itself. There would be nothing (no space, no time and no beyond) anything within that sphere.


This is not, to my understanding, correct. Here is the correct explanation.

As to what Hyksos wrote, I think everything you say here is correct, except for your conclusion. The backward-in-time aspect to superluminal signaling that is forbidden by SR does not, so far as I know, apply to the metric expansion of space, which is not in the purview of SR. In any case, as you note, we can never see or experience anything outside the observable universe (Hubble volume) so this whole line of reasoning seems moot to me. “Platonic sense” seems to have no meaning. Maybe I’m missing something in your chain of reasoning? To put it another way, what you are talking about seems to entail the very thing that SR forbids: That to observe VDGs, those beyond the observable universe, light from them would have to travel faster than c, overcoming the metric expansion of space — which of course is what does not and cannot happen.
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Re: very distant galaxies VDGs

Postby bangstrom on February 25th, 2019, 1:16 am 

davidm » February 24th, 2019, 6:01 pm wrote:
This is not, to my understanding, correct. Here is the correct explanation.

My understanding of the UCLA quote is that it deals with the expansion of the visible part of the universe within the much greater metric expansion of space.

More recent Big Bang scenarios don’t have the universe contracted to a point but something close to a point- more like the size of a grapefruit- as if it makes a difference. No matter what the radius, the Big Bang radius includes all of what we term the “universe” and not just the visible part. It is the “whole shebang” that is expanding from within.

The UCLA quote explains how the observable part of the Universe is expanding in sync with the general expansion so we see a greater distance between galaxies and a decline in galactic densities but not a greater number of visible galaxies.

davidm » February 24th, 2019, 6:01 pm wrote:

To put it another way, what you are talking about seems to entail the very thing that SR forbids: That to observe VDGs, those beyond the observable universe, light from them would have to travel faster than c, overcoming the metric expansion of space — which of course is what does not and cannot happen.


In theory, the galaxies are moving away from us faster than c so naturally we can’t see them and no one is claiming that we can.

The expansion of space appears to us as a slowing of time as galactic distances from the Earth increase which we observe as a redshift. In theory, the passage of time should appear to come to a stop when the galaxy has a recessional velocity of v=c. For VDG’s with v>>c, time should appear to be running in reverse if we could see them-which we can’t. There is no signaling either way between Earth and VDG’s so this is speculation about metric expansion far beyond SR. I think Hyksos is right about this possible time reversal.
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Re: very distant galaxies VDGs

Postby davidm on February 25th, 2019, 10:33 am 

Oh, goodness, this subject has piqued my curiosity, so I did some research. It turns out that things are more complicated and fascinating than I had thought, and it’s always nice to learn something new!

It turns out that we can see objects outside the Hubble volume — objects superluminal with respect to us! This is because the Hubble volume itself is expanding at an accelerating rate, and eventually this volume “catches up” with the light previously in a space expanding superluminally with respect to us, and now that light is in space expanding subluminally with respect to us, and eventually that light reaches out eyes! So we can see objects traveling faster than the speed of light with respect to us. Discussion here.
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Re: very distant galaxies VDGs

Postby TheVat on February 25th, 2019, 11:01 am 

Do you mean we can see objects that were formerly traveling faster than C wrt us? I.e. that are now within the cosmic event horizon?
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Re: very distant galaxies VDGs

Postby davidm on February 25th, 2019, 12:32 pm 

Here is the answer. I. had been wrongly conflating the Hubble volume with the cosmic event horizon. Live and learn! :)
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Re: very distant galaxies VDGs

Postby TheVat on February 25th, 2019, 2:43 pm 

Yeah, that's how i had learned it a few years ago, that the Hubble radius can move beyond a particle.. As that remarkably clear wiki says, it's easy to conflate HV and CEH. It drives home the point that the HV is not the entire universe that can be known. And the CH is about the present, while the CEH is about the future and any possible observation at any future time. Makes my head ache.
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Re: very distant galaxies VDGs

Postby hyksos on February 27th, 2019, 1:10 am 

I didn't think we would have to go back to the drawing board to establish definitions. But yeah,..,so..

Observable Universe
This is a spherical volume of space with the Milky Way at the center. The radius of this region is determined by the age of the universe. Free-moving light has had 13.7 billion years to travel from the edge of this region to us. We cannot see beyond this region simply because there has not been enough time. The radius, r expands at exactly 1 light year per year. This expansion is a mental time-keeping device on a chalkboard, unrelated to metric expansion.

Special Relativity
Electromagnetic radiation ('light') does not travel locked to a stationary background. Further, all observers see light propagating at a constant speed regardless of their relative or local motions. A consequence is that an object in motion will progress through time slower than one at rest. In other words "its clock slows down". This effect is physically real according to S-R, and not a mere "optical illusion". More importantly, the clock in the moving frame will run slower even when it does not emit nor receive light.

Space is infinite
Max Tegmark holds a plastic beach ball with the CMBR on its outside. He holds it up and says,
Tegmark wrote:"This is the observable universe."

Tegmark gestures at the outside of the ball, and continues,
Tegmark wrote:"Nobody could reasonably claim that space somehow STOPS at this boundary. There will exist galaxies and other things outside this region that we cannot yet see because their light has not reached us yet."


I fear we have people in this thread contending that (1) Time dilation requires the exchange of light between comoving frames. (it doesn't) (2) That space somehow stops at some mystical boundary centered around the Milky Way. (it doesn't)


The assertion stands. For any given positive real r , there will be a galaxy at that distance r meters away. For sufficiently large r , that galaxy will be receding away from us at a velocity v >> c.
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Re: very distant galaxies VDGs

Postby bangstrom on February 27th, 2019, 2:25 am 


Are you saying space is infinite in the flat Euclidean sense or in the sense of Riemann geometry where space is finite but curved in giant geodesics?
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Re: very distant galaxies VDGs

Postby davidm on February 27th, 2019, 12:04 pm 

hyksos » February 26th, 2019, 11:10 pm wrote:
I fear we have people in this thread contending that (1) Time dilation requires the exchange of light between comoving frames. (it doesn't) (2) That space somehow stops at some mystical boundary centered around the Milky Way. (it doesn't)


I don't know who you think is saying the above. Certainly I am not




The assertion stands. For any given positive real r , there will be a galaxy at that distance r meters away. For sufficiently large r , that galaxy will be receding away from us at a velocity v >> c.


Yes, and as a matter of fact, as has been shown, we CAN see objects receding from us FTL, when the expanding Hubble sphere catches up with the light emitted by the FTL galaxy. And, when we see that light, no time reversal is displayed by the superluminal object, as you seem to suggest is what we should see.
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Re: very distant galaxies VDGs

Postby hyksos on March 1st, 2019, 7:05 pm 


I have 4207.6 Mpc is the distance to those galaxies receding at c. i.e. 4.208 gpc. Our napkin calcs pretty much match.

vr = H0*D
D = vr/H0
D {Mpc} = vr {km/sec} / H0 {km/sec/Mpc}
D {Mpc} = 299792.458 {km/sec} / 71.25 {km/sec/Mpc}
D = 4207.6 Mpc

There could be some wiggle room on H0.
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Re: very distant galaxies VDGs

Postby hyksos on March 1st, 2019, 7:19 pm 

Yes, and as a matter of fact, as has been shown, we CAN see objects receding from us FTL, when the expanding Hubble sphere catches up with the light emitted by the FTL galaxy. And, when we see that light, no time reversal is displayed by the superluminal object, as you seem to suggest is what we should see.

Alright, last November we got a color image of galaxy GN-z11. Rumor is that galaxy is 9800 Mpc away. We need only 4208 Mpc to reach those galaxies receding at FTL velocity. GN-z11 is certainly receding far faster than light, but we have an image.

At the time GN-z11 emitted the light that formed our image, it was a measly 11.1 billion light years away. Metric expansion has since hoisted it to its current giga-parsec range.

Q: Was GN-z11 receding at FTL at the time in which it emitted the light we see?

(...another napkin calc is needed)
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Re: very distant galaxies VDGs

Postby bangstrom on March 2nd, 2019, 3:12 pm 

The expansion of the universe is a scaling effect where distances expand while time quickens in such a way that c remains a constant ratio so that the measured distance of a light year remains the same over time. If we could go far back in time by several billion years we should find that early universe was never any smaller than what it is measured to be today.
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Re: very distant galaxies VDGs

Postby TheVat on March 2nd, 2019, 7:07 pm 

Bangs,

Not quite sure what you mean by the scaling effect. Is there a link to this that provides more illustration of the concept?
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Re: very distant galaxies VDGs

Postby hyksos on March 3rd, 2019, 12:28 am 

Although others have told me we already have imaged galaxies that were receding at 4*c at time of emission.

This following article suggests that it is inevitable that we would eventually see such an image arrive to earth.

https://en.wikipedia.org/wiki/Ant_on_a_rubber_rope
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Re: very distant galaxies VDGs

Postby bangstrom on March 3rd, 2019, 3:18 am 

TheVat » March 2nd, 2019, 6:07 pm wrote:Bangs,

Not quite sure what you mean by the scaling effect. Is there a link to this that provides more illustration of the concept?


I don’t know of a link that explains the scaling effect in quite the same way but it follows from the conventional explanations for cosmological redshifting. The galaxies are not being driven apart by any vector force sending them scattering from a common center of origin like some gigantic explosion. Instead, the galaxies remain in relatively the same positions while space itself expands in all directions between them. This is illustrated by the ‘old buttons on a balloon example’ where the buttons remain in the same relative positions while the skin of the balloon expands uniformly increasing their distances from each other. Another illustration using the example of what happens to the raisins in a rising loaf of raisin bread applies even better because it works in 3D space.

The same cosmological expansion that expands space between the galaxies also expands the wavelengths of light between the galaxies, and the larger the distance from Earth to the VDG, the longer time the emitted light waves have traveled through expanding space, the higher their measured cosmological redshift. The expansion of space expands the length of light waves as light becomes ‘stretched out’ and it also expands distances measured in light units such as light years or the observable distance we can see into space. As space expands, the length of a light year expands proportionally so the radius of the universe measured in light years remains constant over time even though the density of galaxies is decreasing.
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