Dark Flow

[Chris Peterson]

What?
The universe got stretched?

Of course. It was stretched in the past and continues to be stretched now. That is fundamental to nearly all theories of cosmology. It is almost certain that the Universe is far bigger than the observable Universe (which is 93 billion ly across).

[Chris Peterson]

No . The visible universe is 13.4 billion light years . And according to the big bang, There is nothing past that time.

I can't figure out what you are trying to say. The observable Universe (a better term than "visible universe") is currently about 93 billion ly across, which corresponds to our seeing back 13.7 billion years at its edge (although in practice we don't have the technology to see that far back). The BBT tells us how old the Universe it, not how large it is.

Except, What ever this huge thing is, we can not see. Matter and huge black holes do not jump behind the horizon faster than light speed.

Most of the Universe is outside our sphere of observability, precisely because it is moving away from us faster than the speed of light. This doesn't break any rules of physics.

Don't get to focused on "this huge thing". The suggestion that it exists is very speculative, at best. There are other possibilities to explain the observed motion that don't require a great attractive mass outside the observable Universe.

[The Code]

I can't figure out what you are trying to say. The observable Universe (a better term than "visible universe") is currently about 93 billion ly across, which corresponds to our seeing back 13.7 billion years at its edge (although in practice we don't have the technology to see that far back). The BBT tells us how old the Universe it, not how large it is.

, since the source of the farther than we can observe''.


ion is more than twht?
Mark

[Chris Peterson]

So what you are saying is, the speed of expansion is more than twice the speed of light?

The speed of expansion is given as a velocity per unit distance. The farther away something is, the faster it is moving away. Once you go far enough away (in fact, to the edge of the observable Universe), space is moving away from us faster than the speed of light. If the Universe is large enough, there will be parts receding from us at many times the speed of light.

[canuck100]

So what you are saying is, the speed of expansion is more than twice the speed of light?

The speed of expansion is given as a velocity per unit distance. The farther away something is, the faster it is moving away. Once you go far enough away (in fact, to the edge of the observable Universe), space is moving away from us faster than the speed of light. If the Universe is large enough, there will be parts receding from us at many times the speed of light.

To elaborate Chris' point:

This Wikipedia graph is esseitially a copy of a graph in a 2001 Research paper on Superluminal Recession Velocities

You can read the original paper at

Superluminal Recession Velocities
Tamara M. Davis and Charles H. Lineweaver
http://arxiv.org/PS_cache/astro-ph/pdf/ ... 1070v2.pdf
Abstract.
Hubble’s Law, v = HD (recession velocity is proportional to distance), is a theoretical result derived from the Friedmann-Robertson-Walker metric. v = HD
applies at least as far as the particle horizon and in principle for all distances. Thus, galaxies with distances greater than D = c/H are receding from us with velocities greater than the speed of light and superluminal recession is a fundamental part of the general relativistic description of the expanding universe. This apparent contradiction of special relativity (SR) is often mistakenly remedied by converting redshift to velocity using SR. Here we show that galaxies with recession velocities faster than the speed of light are observable and that in all viable cosmological models, galaxies above a redshift of three are receding superluminally.

and fortunately, its abstract is pretty straightforward. The paper itself is short and easier to read than most.

From Wikipedia, the largest redshift objects (all well cited) at the time of its article:

Highest redshifts
. . .
the highest confirmed spectroscopic redshift of a galaxy is that of IOK-1,[54] at a redshift z = 6.96, corresponding to just 750 million years after the Big Bang.
. . .
The most distant observed gamma ray burst was GRB 090423, which had a redshift of 8.2.[57]

The most distant known quasar, CFHQS J2329-0301, is at z = 6.43.[58] The highest known redshift radio galaxy (TN J0924-2201) is at a redshift z = 5.2[59] and the highest known redshift molecular material is the detection of emission from the CO molecule from the quasar SDSS J1148+5251 at z = 6.42[60]
, , ,
The Cosmic Microwave Background has a redshift of more than 1,000, corresponding to an age of approximately 379,000 years after the Big Bang and a distance of more than 13 billion light years.
http://en.wikipedia.org/wiki/Redshift

This doesn't invalidate causality because what we are observing is not the state of these galaxies now but rather their state billions of years in the past. In the case of a galaxy 13 billion light years away, that information is, by definition, 13 billion light years old.

This faster than light speed motion is not straightforward motion like the speed of a rocket, though. It is due to the expansion of space itself. I'm not up on all the subtleties of that distinction.

[The Code]

ark

[makc]

Well, I don't

Here we show that galaxies with recession velocities faster than the speed of light are observable

This is a bummer for me. I guess I will have to read the article.

[canuck100]

Well, I don't

Here we show that galaxies with recession velocities faster than the speed of light are observable

This is a bummer for me. I guess I will have to read the article.

I don't really understand it either. As far as I do get it, these galaxies are in a part of space that is receding from us at greater than light speed. I don't think it means that they are like a galaxy nearby moving at greater than light speed. Furthermore, we are seeing them as they were, not as they are now. We will never see them as they are now as they have long since moved too far away for us to ever be able to observe them.

[canuck100]

If you want an even better explanation than in the paper I linked to above, there is a Scientific American article by the same authors that is on line at http://www.darkcosmos.dk/~tamarad/paper ... igBang.pdf
A few sample quotess

Misconceptions about the Big Bang
Baffled by the expansion of the universe? You're not alone. Even astronomers frequently get it wrong.
by Charles M. Lineweaver and Tamara M. Davis
. . .
Renowned physicists, authors of astronomy textbooks and prominent popularizers of science have made incorrect, misleading or easily misinterpreted statements about the expansion of the universe. Because expansion is the basis of the big bang model, these misunderstandings are fundamental.
. . .
The idea that the big bang was "small" is misleading. The totality of space could be infinite. Shrink an infinite space by an arbitary amount, and it is still infinite.
. . .
galaxies beyond a certain distance, known as the Hubble distance, recede faster than the speed of light. For the measured value of the Hubble constant, this distance is about 14 billion light-years.
Does this prediction of faster-than-light galaxies mean that Hubble's law is wrong? Doesn't Einstein's special theory of relativity say that nothing can have a velocity exceeding that of light? This question has confused generations of students. The solution is that special relativity applies only to "normal" velocities -- motion through space. The velocity in Hubble's law is a recession velocity caused by the expansion OF space, NOT a motion through space. It is a general relativistic effect and is not bound by the special relativistic limit. Having a recession velocity greater than the speed of light does not violate special relativity. It is still true that nothing ever overtakes a light beam.
. . .
The idea of seeing faster-than-light galaxies . . . is made possible by changes in the expansion rate. . . . the Hubble distance is not fixed, because the Hubble constant, on which it depends, changes with time. In models . . . that fit the . . . data . . .the Hubble constant decreases. In this way, the Hubble distance gets larger. As it does, light that was ititially just outside the Hubble distance and receding from us can come within the Hubble distance. The photons then find themselves in a region of space that is receding slower than the speed of light. Thereafter they can approach us.

and so on. A great article - worth printing out and digesting.
cheers

[THX1138]

Wow, exclamation point and a period. That is really something, imagine though matter is indeed moving away from us at a rate seemingly well above that of c we can still observe
It.
The total velocity of distant photons is not constant because it is the sum of
the distance-dependent recession velocity (vrec) and the constant peculiar velocity,
This way cool, I believe I may have a grasp on what it’s saying. Then also who gives a big darn if some “ so called great attractor “ Is much to far away to ever, ever see.”
It matters not as far as using it for some kind of reasoning that the BBT is wrong because it puts matter in and of this universe further away than the 13.7 would imply. I have never liked the BBT, but not that my opinion means squat considering I probably know less than one percent of one percent of what the most of you all do. None the less the more I read here the more it seems certain that the BBT is on the real.
Wonder what the #1 BBT hating person on this site “ Harry “ will have to say if…No not if, when he posts next here on this thread.


I never met a weapon I didn’t like. Ronald Regan ( 1989 )

[Chris Peterson]

I have never liked the BBT, but not that my opinion means squat considering I probably know less than one percent of one percent of what the most of you all do. None the less the more I read here the more it seems certain that the BBT is on the real.

Nothing better represents rational thought and intellectual honesty than accepting the weight of evidence over one's philosophical opinions.

[Bawper]

The Speed of Dark .. when Space is said to be expanding at two or three times or more the speed of light it is easy to see that darkness proceeds light, with the dark edge of the universe growing ever larger as it leaves light behind. Like I said before .. speed of dark is directly involved in non-locality. Plain and Simple. Thanks to the Mind at Maine.

[makc]

Like I said before

using which account

[Chris Peterson]

The Speed of Dark .. when Space is said to be expanding at two or three times or more the speed of light it is easy to see that darkness proceeds light, with the dark edge of the universe growing ever larger as it leaves light behind. Like I said before .. speed of dark is directly involved in non-locality. Plain and Simple. Thanks to the Mind at Maine.

There's no such thing as a "speed of dark". Locally, space does not expand faster than the speed of light. The idea of it expanding faster than light at all is just a poor attempt to phrase a physical concept in language not very well suited for that purpose. Mathematically, it is all about causality and regions of the Universe that are time-like or space-like.

It should require nothing more than common sense to recognize that if the rate of expansion increases with distance, you will get to a distance where light hasn't had time to reach us. Space does not expand faster than light- the actual expansion rate is tiny. It would be better to say that because the tiny rate of expansion increases with distance, the distant Universe is moving away from us at greater than c, which is why it is unobservable. An observer in that distant universe, of course, would see nothing unusual, and local space would be expanding at the same tiny rate we see here.

[The Code]

There's no such thing as a "speed of dark".

Does not

[Chris Peterson]

There's no such thing as a "speed of dark".

Does not the increased speed of expansion, enshroud more of the universe, faster than we can see it reaching us?

The size of the observable Universe increases with time, as well. Regardless of the ratio between what we can see and what we can't, and how it changes with time, I'd argue that "speed of dark" is a meaningless term outside of poetry. Light has a physical reality (photons); dark does not.

[The Code]

It should require nothing more than common sense to recognize that if the rate of expansion increases with distance, you will get to a distance where light hasn't had time to reach us. Space does not expand faster than light- the actual expansion rate is tiny. It would be better to say that because the tiny rate of expansion increases with distance, the distant Universe is moving away from us at greater than c, which is why it is unobservable. An observer in that distant universe, of course, would see nothing unusual, and local space would be expanding at the same tiny rate we see here.

Have another go mate. Please

[Chris Peterson]

Have another go mate. :) Please

If you have a specific question, I'll try to answer it. I don't really know how to say what I said any clearer, though. Quantitatively, the expansion rate of the Universe is given as approximately 71 km/s/Mpc; this doesn't have the same units as c, so you can't directly compare "expansion rate" to "the speed of light". You can only compare the relative speeds of two objects given some specific separation between them.

[The Code]

Quantitatively, the expansion rate of the Universe is given as approximately 71 km/s/Mpc; this doesn't have the same units as c, so you can't directly compare "expansion rate" to "the speed of light". You can only compare the relative speeds of two objects given some specific separation between them.

It should require nothing more than common sense to recognize that if the rate of expansion increases with distance, you will get to a distance where light hasn't had time to reach us. Space does not expand faster than light- the actual expansion rate is tiny. It would be better to say that because the tiny rate of expansion increases with distance, the distant Universe is moving away from us at greater than c, which is why it is unobservable. An observer in that distant universe, of course, would see nothing unusual, and local space would be expanding at the same tiny rate we see here.

[bystander]

What part of Chris Peterson wrote: Do you not understand?

It should require nothing more than common sense to recognize that if the rate of expansion increases with distance, you will get to a distance where light hasn't had time to reach us.

expansion rate x distance = speed of recession

Quantitatively, the expansion rate of the Universe is given as approximately 71 km/s/Mpc; this doesn't have the same units as c (km/s), so you can't directly compare "expansion rate" to "the speed of light". You can only compare the relative speeds of two objects given some specific separation between them.

Space does not expand faster than light- the actual expansion rate is tiny. It would be better to say that because the tiny rate of expansion increases with distance, the distant Universe is moving away from us at greater than c, which is why it is unobservable. An observer in that distant universe, of course, would see nothing unusual, and local space would be expanding at the same tiny rate we see here.

The effects of the rate of expansion are cumulative, the farther away an object is the faster it is receding. At some large distance, the apparent speed of recession exceeds c.

There is nothing inconsistent in what Chris is saying. You are just failing to understand.

[harry]

G'day Bystander

You said

The effects of the rate of expansion are cumulative, the farther away an object is the faster it is receding. At some large distance, the apparent speed of recession exceeds c.

There is nothing inconsistent in what Chris is saying. You are just failing to understand.

Hubble question his own work velocity/redshift even until the day he died.

All observations show a clustering effect and the formation of jets large and small reforming the surrounding Stars and galaxies.

I posted a link on "Loop quantum cosmology with higher order holonomy corrections" written by Dah-Wei Chiou, Li-Fang Li found in arXiv and it was banned. Directing science information to what you think regardless how informed you are is a big mistake.

[apodman]

Hubble question his own work velocity/redshift even until the day he died.

Hubble's questions were those of someone with a thorough knowledge of the subject conducting a critical examination. Do you put your questioning on a par with Hubble's as if you are an expert who can argue the subject from a knowledgeable point of view? It appears to me that your questions should be more those of a layman seeking knowledge.

[Chris Peterson]

Hubble question his own work velocity/redshift even until the day he died.

So? It was a radical new viewpoint, that many found philosophically difficult to swallow. Hubble may have had doubts, but he never came up with a better explanation. And thousands of scientists since have just further solidified the work that he began.

Hubble's doubts are irrelevant.

[harry]

G'day

You can question what ever you want or just float down mainstream.

I'm suggesting do not put all your eggs in the same bag.

A scientist looks at the various options and alternatives this is how science moves forward.

The trap is "I KNOW" and people stop looking beyond.

[Orca]

G'day

You can question what ever you want or just float down mainstream.

I'm suggesting do not put all your eggs in the same bag.

A scientist looks at the various options and alternatives this is how science moves forward.

The trap is "I KNOW" and people stop looking beyond.

With all due respect, Harry:

While I agree that we should try and remain as objective as possible in any application of scientific method, you appear to have a double standard. When it comes to questioning accepted theory, you call for open-mindedness. Yet when it comes to the theories you personally accept as reality, well, those are the facts baby, and anyone who disagrees simply hasn't read the right papers or understood the material.

If you really believed in strict empiricism you'd apply it to all theories. You'd also start from the ground up with prevailing theory and work from there, rather than simply dismissing prevailing theory if it goes against your gut feelings of "how things ought to be."