Expanding Universe

[ErnieM]

Suppose we find two galaxies whose galactic planes are parallel to the Milky Way galactic plane. Further suppose that all three galaxies are roughly the same class, type and mass and have the same intrinsic directional spin. Can we than assume that all three galaxies are travelling in space at the same or close to the same direction and speed and therefore any separation between these galaxies is caused by the expansion of space. Measuring this rate of separation over a period of time will yield an expansion rate. The closer these galaxies are the more accurate are the measurements.

[Chris Peterson]

Suppose we find two galaxies whose galactic planes are parallel to the Milky Way galactic plane. Further suppose that all three galaxies are roughly the same class, type and mass and have the same intrinsic directional spin. Can we than assume that all three galaxies are travelling in space at the same or close to the same direction and speed and therefore any separation between these galaxies is caused by the expansion of space.

No. The orientation and other characteristics of galaxies are independent of each other.

Measuring this rate of separation over a period of time will yield an expansion rate. The closer these galaxies are the more accurate are the measurements.

In practice, there is no way to measure changes in rate, or measure the rate at all by direct observation of distance. Doing either of these would require thousands or millions of years of observation.

[ErnieM]

Chris wrote:

No. The orientation and other characteristics of galaxies are independent of each other.

Are you saying all galaxies are distinct and unique, that not two galaxies have enough similar properties that makes them to appear traversing space in the same direction and speed? Or that we have not found any yet. Is it for lack of trying, lack of incentive, lack of technologies or all of the above?

Chris wrtoe:

In practice, there is no way to measure changes in rate, or measure the rate at all by direct observation of distance. Doing either of these would require thousands or millions of years of observation.

Then what does my recent traffic ticket means when the officer cited me for exceeding the posted speed limit? Are traffic radar readings not based on direct observation of distances? Is it not through direct observation that astronomers are in agreement that the Andromeda galaxy is in a collision path with the Milky Way? Again, is this "no way" means lack of trying, lack of incentive, lack of technologies or all of the above?

[BMAONE23]

Traffic Radar is a technology that requires that the measuring device and the object being measured are in close proximity. Using similar technology on our closest large neighbor, Andromeda, would take 4.5 million years for the radar signal to be transmitted from the source, reflect of the object and return to the measuring device.

[rstevenson]

Are you saying all galaxies are distinct and unique, that not two galaxies have enough similar properties that makes them to appear traversing space in the same direction and speed?

Galaxies don't need to be similar in size or appearance to be travelling in more or less the same direction. Gravity will cause that effect equally for everything in the vicinity. Our nearest neighbour galaxies -- the LMC and SMC -- are little puff balls by comparison with the Milky Way, while Andromeda, the other heavy-weight in our neighbourhood, is very similar to our Milky Way. Yet we're all moving in more or less the same direction. There's a thread around here somewhere which discusses that rather mysterious motion.

Your original supposition about the three similar galaxies doesn't pertain. As Chris said (and he, unlike I, knows what he's talking about) there's no known connection between shape, orientation, galactic plane and direction of travel. Picture the very early universe, from which all these galaxies have evolved, as a very turbulent place and I think you'll see that any galactic similarities can only be coincidental.

Rob

[Chris Peterson]

Are you saying all galaxies are distinct and unique, that not two galaxies have enough similar properties that makes them to appear traversing space in the same direction and speed?

Certainly, there are galaxies that are parts of clusters, and which, when observed from our perspective, are moving more or less together. In fact, they are orbiting one another, and their center of mass is moving with respect to us. But I don't see how you can use the existence of such galaxy clusters to make useful measurements along the lines you suggest.

Then what does my recent traffic ticket means when the officer cited me for exceeding the posted speed limit? Are traffic radar readings not based on direct observation of distances?

No, they are not. They measure velocity directly, using Doppler shift of a reflected microwave signal. That's similar to the way we measure the velocity that other galaxies are moving with respect to us: we look at the Doppler or relativistic frequency shift of reference optical or radio sources in those galaxies. That gives us the speed along the axis between us, but not the distance (although for cosmological distances, there's a presumed relationship between the two, such that knowing the speed allows us to infer the distance- albeit with a fair bit of uncertainty).

Of course, you could build a ranging radar that would directly give the distance to a nearby car. But that technology couldn't possibly work for getting the distance to a nearby galaxy. And consider this: the motion of galaxies is very small (typically a few hundred km/s) compared with their distance (typically millions or billions of light years). So measuring the distance to these galaxies is a bit like using a radar to measure continental drift. You can do it, but only by making measurements over many years. In the case of galaxies, making direct measurements of their motion would require observations over millions of years.

Is it not through direct observation that astronomers are in agreement that the Andromeda galaxy is in a collision path with the Milky Way?

Astronomers are not in agreement in that matter. By direct observation of the radial velocity, we know that our two galaxies are getting closer together. But we don't know the transverse component of the velocity, so it's far from certain the galaxies will collide. There is no way currently available to determine that with certainty.

[Chris Peterson]

Galaxies don't need to be similar in size or appearance to be travelling in more or less the same direction. Gravity will cause that effect equally for everything in the vicinity. Our nearest neighbour galaxies -- the LMC and SMC -- are little puff balls by comparison with the Milky Way, while Andromeda, the other heavy-weight in our neighbourhood, is very similar to our Milky Way. Yet we're all moving in more or less the same direction.

Our center of mass is moving with respect to distant objects, but the individual galaxies that make up the Local Group are, in fact, orbiting around each other semi-chaotically. We are like a cloud of gnats flying around: the cloud has a distinct, ordered movement, but the individual gnats are all over the place inside that cloud.

[Beyond]

Ahh, THAT's why galaxies collide. No way to control the gravity of their situation, like nats do.

[Ann]

Chris wrote:

Our center of mass is moving with respect to distant objects, but the individual galaxies that make up the Local Group are, in fact, orbiting around each other semi-chaotically. We are like a cloud of gnats flying around: the cloud has a distinct, ordered movement, but the individual gnats are all over the place inside that cloud.

Apart from being an excellent description of the relative movements of galaxy clusters and their individual galaxies, the metaphor is really quite poetic.

Thanks, Chris "Stratford" Peterson!

Ann

[Beyond]

Nats, poetic Hmm... How do i love thee Let me 'swat' the ways. Well, i guess they're poetic, sort of.

[ErnieM]

Ann wrote:

Chris wrote:

Our center of mass is moving with respect to distant objects, but the individual galaxies that make up the Local Group are, in fact, orbiting around each other semi-chaotically. We are like a cloud of gnats flying around: the cloud has a distinct, ordered movement, but the individual gnats are all over the place inside that cloud.


Apart from being an excellent description of the relative movements of galaxy clusters and their individual galaxies, the metaphor is really quite poetic.

And how do these clouds of gnats move with respect to each other within their respective super clusters? Does the universe has a center of mass? Approximately, where is it?

[Chris Peterson]

And how do these clouds of gnats move with respect to each other within their respective super clusters? Does the universe has a center of mass? Approximately, where is it?

There is nothing to suggest the the Universe as a whole has a center of mass. On a large scale, the Universe is essentially homogeneous, and since it is apparently unbounded, that means that there is no center of mass. There are certainly local density variations, ranging up to superclusters, and these influence how objects in their regions behave.

A supercluster doesn't significantly affect the motion of galaxies within a cluster, only the net motion of the cluster itself. At a smaller scale, this is like saying that the Milky Way doesn't affect the motion of the planets around the Sun, even though it controls how the entire Solar System is moving through the galaxy.

[bystander]

Does the universe has a center of mass? Approximately, where is it?

http://asterisk.apod.com/viewtopic.php?f=30&t=25300

[rstevenson]

... There's a thread around here somewhere which discusses that rather mysterious motion.

What I was thinking of was Dark Flow, which is not germane to the OP's original question, I think.

Rob

[bystander]

... There's a thread around here somewhere which discusses that rather mysterious motion.

What I was thinking of was Dark Flow, which is not germain to the OP's original question, I think.

http://asterisk.apod.com/viewtopic.php?f=31&t=23239

[ErnieM]

From the link posted by bystander:

Data from exploding stars contradicts earlier study pointing to the possible existence of a sibling universe

In 2008, a research team led by a NASA scientist announced a startling discovery: Clusters of galaxies far apart from one another appeared to be traveling in the same direction.(1)

The findings contradicted the standard model of the universe, which predicts that, as a whole, mass within our universe should flow randomly, in all directions, relative to the background radiation of the cosmos.

The one-way "dark flow" that the NASA-led group discovered created a mystery. What could account for the unexpected motion? Maybe another universe existed beyond the bounds of ours, dragging our stars ever closer through the pull of gravity.

Chris wrote:

There is nothing to suggest the the Universe as a whole has a center of mass. On a large scale, the Universe is essentially homogeneous, and since it is apparently unbounded, that means that there is no center of mass. There are certainly local density variations, ranging up to superclusters, and these influence how objects in their regions behave.

It is inconceivable to imagine a "universe" before the big bang that only dark matter existed clumping together by the force of "gravity". The super massive explosion of the big bang and the subsequent events that followed gave rise to our "universe" of visible large galaxy structures including the dark matter inferred to surround galactic size structures (and larger). It is also inconceivable to imagine that the explosion is not homogeneous and large chunks and clumps of dark matter were ejected outside of the edge of the resulting super massive fireball(s?). The fireball(s) stopped and the universe cooled off and the ejected dark matter clumped back together outside the edged of " our universe" exerting the "dark gravity" on themselves (dark matter) as well as the structures within the universe giving "space within the universe" to appear as expanding.
Put another way, the halo of dark matter around galaxies provide the extra mass needed for their observed/inferred motions. The mass of dark matter outside the edge of the "observable" universe provide the gravitational energy to "expand" the said universe.

Chris wrote:

A supercluster doesn't significantly affect the motion of galaxies within a cluster, only the net motion of the cluster itself. At a smaller scale, this is like saying that the Milky Way doesn't affect the motion of the planets around the Sun, even though it controls how the entire Solar System is moving through the galaxy.

What then contributes to the net motion (irrespective of the speed) of a super cluster relative to the other clusters and super clusters? The cluster combined mass and the effect of gravity binding them together! As such, would this not be the theoretical center of mass/gravity of the universe?

[Chris Peterson]

It is inconceivable to imagine a "universe" before the big bang that only dark matter existed clumping together by the force of "gravity".

There is no reason to think that there was dark matter present before the Big Bang. For that matter, there is no reason to think there was anything before the Big Bang, or that the concept of "before" even means anything in that context.

The super massive explosion of the big bang and the subsequent events that followed gave rise to our "universe" of visible large galaxy structures including the dark matter inferred to surround galactic size structures (and larger). It is also inconceivable to imagine that the explosion is not homogeneous and large chunks and clumps of dark matter were ejected outside of the edge of the resulting super massive fireball(s?).

The Big Bang was not an explosion. It produced no fireball, and was not an energetic event that ejected anything. The Big Bang was the formation of the Universe by expansion. Certainly, no existing theory suggests that material could somehow be ejected from the Universe. The Universe is everything... it has no outside.

Put another way, the halo of dark matter around galaxies provide the extra mass needed for their observed/inferred motions. The mass of dark matter outside the edge of the "observable" universe provide the gravitational energy to "expand" the said universe.

You are comparing apples to oranges. Again, there is no theory or supporting observation to support what you suggest. Indeed, there is already perfectly good and well supported theory which explains the expansion of the Universe.

What then contributes to the net motion (irrespective of the speed) of a super cluster relative to the other clusters and super clusters? The cluster combined mass and the effect of gravity binding them together! As such, would this not be the theoretical center of mass/gravity of the universe?

All of these things are acted upon gravitationally by other things. So it is hardly surprising to see interactions between them. I don't see how this has any implications for a universal center of mass. Keep in mind that elements of the observable Universe are currently observed to be moving in response to things currently outside both our observable Universe and outside the current observable Universe of what we study.

[The Code]

ErnieM wrote:It is inconceivable to imagine a "universe" before the big bang that only dark matter existed clumping together by the force of "gravity".


There is no reason to think that there was dark matter present before the Big Bang. For that matter, there is no reason to think there was anything before the Big Bang, or that the concept of "before" even means anything in that context.

The super massive explosion of the big bang and the subsequent events that followed gave rise to our "universe" of visible large galaxy structures including the dark matter inferred to surround galactic size structures (and larger). It is also inconceivable to imagine that the explosion is not homogeneous and large chunks and clumps of dark matter were ejected outside of the edge of the resulting super massive fireball(s?).


The Big Bang was not an explosion. It produced no fireball, and was not an energetic event that ejected anything. The Big Bang was the formation of the Universe by expansion. Certainly, no existing theory suggests that material could somehow be ejected from the Universe. The Universe is everything... it has no outside.

Put another way, the halo of dark matter around galaxies provide the extra mass needed for their observed/inferred motions. The mass of dark matter outside the edge of the "observable" universe provide the gravitational energy to "expand" the said universe.


You are comparing apples to oranges. Again, there is no theory or supporting observation to support what you suggest. Indeed, there is already perfectly good and well supported theory which explains the expansion of the Universe.

Unless of course If your name happens to be Roger Huh ? Isn't the standard model a theory only ? A theory that is under threat by the said "Dark Flow" . Makes me wounder How they are going to patch this one up....

http://bagotbooks.wordpress.com/2010/09 ... stitution/

tc

[Chris Peterson]

Unless of course If your name happens to be Roger Huh ? Isn't the standard model a theory only ? A theory that is under threat by the said "Dark Flow" .

Dark flow isn't threatening to substantially alter existing cosmological theory. And what does "theory only" mean? Everything we know about nature is described by "theory only"- some theories with more support, some with less, but theories all.

[bystander]

Isn't the standard model a theory only ?

http://asterisk.apod.com/viewtopic.php?t=25623

[The Code]

Unless of course If your name happens to be Roger Huh ? Isn't the standard model a theory only ? A theory that is under threat by the said "Dark Flow" .

Dark flow isn't threatening to substantially alter existing cosmological theory. And what does "theory only" mean? Everything we know about nature is described by "theory only"- some theories with more support, some with less, but theories all.

According to the Standard Model The "Dark Flow" should not be there. And you need to add another Universe to understand what is causing it... And does that mean Another Universe out side ours ? Isn't that meaningless ? I get the feeling The Standard Model's "Time" is running out..

tc

[Chris Peterson]

According to the Standard Model The "Dark Flow" should not be there. And you need to add another Universe to understand what is causing it... And does that mean Another Universe out side ours ? Isn't that meaningless ? I get the feeling The Standard Model's "Time" is running out..

That is not true. There is no major contradiction between dark flow and the standard model. People have proposed multiple explanations for dark flow (including the possibility that it doesn't even exist) that are consistent with the standard model, such as gravitational forces exerted in the past by material now outside the observable Universe. Furthermore, people have proposed minor modifications to the standard model which allow for large scale, localized motion.

I think you fail to understand how science works, and fail to appreciate the history of modern science, if you think that major theories are likely to be overturned by new observations. In fact, these theories are generally well developed and well supported, but not entirely complete. It's far more likely that observations will lead to a term or two being tweaked than a wholesale rejection of current cosmological theory.

[Ann]

My colleague Arnost, who teaches science and math, claims that when science calls something a "theory", then it is basically a proven fact.

A "hypothesis" is another thing altogether. It's just an idea that someone has got. Let's assume, for example, that someone posits the idea that the Moon is really made of cheese. Now, that's a bad hypothesis, since astronauts have already visited the Moon and brought back samples, which turned out not to be made of cheese at all. So that is a hypothesis which has already been proven false.

There is a Grecian-Roman myth which says that baby Heracles (Hercules in Latin) suckled the goddess Hero (Juno in Latin), who was not his mother. When Hera noticed what was going on, she angrily tore the baby away from her breast, sending her own milk flowing out in a large arc all over the sky. This goddess' milk became the "Milky Way". The idea that the misty "band" across the sky is really milk from a deity can be described a hypothesis. It is, of course, a hypothesis that hasn't stood the tests of science. It remains a (disproved) hypothesis and has never become a theory.

Ann

[Chris Peterson]

My colleague Arnost, who teaches science and math, claims that when science calls something a "theory", then it is basically a proven fact.

That is certainly not true... not even approximately.

A "hypothesis" is another thing altogether. It's just an idea that someone has got.

A scientific hypothesis is an explanation for some observation which is testable, but untested. A scientific theory is an explanation for some observation which has been, to some degree, tested. Theories range in quality from barely tested and likely to be discarded or substantially altered (e.g. string theory) to massively tested and effectively factual (e.g. general relativity).

[The Code]

The Code wrote:According to the Standard Model The "Dark Flow" should not be there. And you need to add another Universe to understand what is causing it... And does that mean Another Universe out side ours ? Isn't that meaningless ? I get the feeling The Standard Model's "Time" is running out..


That is not true. There is no major contradiction between dark flow and the standard model. People have proposed multiple explanations for dark flow (including the possibility that it doesn't even exist)

Quote : Studies have shown that clusters of galaxies gathering together in an explicable way. These clusters are conglomerations of about a thousand galaxies and they all follow a mysterious galactic movement. A totally unseen force discovered in 2008 . NASA has checked a catalog of different galaxy clusters and they found that all these clusters, regardless where they were in the sky, are all converging to one side of the universe. The force that is pulling these galaxies must be outside the observable universe, researchers conclude. NASA’s Goddard Space Center considered that this could be the effect of a sibling universe or a region of space-time fundamentally different from the observable universe. Ladies and gentlemen, welcome to the concept of a Multiverse.
There has been a struggle to explain the unexplainable. A theory called inflation posits that the universe we see is just a small bubble of space-time that got rapidly expanded after the Big Bang. There could be other parts of the cosmos beyond this bubble that we cannot see. For now, the standard model remains unchanged. It tells us how the universe began and how energy forms, how gravity created planets and stars, etc. It already describes a lot. But, the truth is that it could be completely wrong.

http://decodingcegep.com/2011/08/05/dar ... he-cosmos/

I think you fail to understand how science works, and fail to appreciate the history of modern science, if you think that major theories are likely to be overturned by new observations. In fact, these theories are generally well developed and well supported, but not entirely complete. It's far more likely that observations will lead to a term or two being tweaked than a wholesale rejection of current cosmological theory.

Quote : The theory might suggest that we are living in one of these universes. Alexander Kashlinsky, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, said: “At this point we don’t have enough information to see what it is, or to constrain it. We can only say with certainty that somewhere very far away the world ? is very different than what we see locally. Whether it’s ‘another universe’ or a different fabric of space-time we don’t know.“

Me
Oh I understand Chris, I understand they had a little problem with How galaxies spin, Inside and out side spinning at the same rate, So they dropped a huge amount of Dark Matter in the equation and now its ok. I also understand, while using the Standard Model, I cant explain why the universe seems to be expanding at an accelerated rate. So again, A little Dark Energy worked wonders. Only to be told that the Dark Energy has no effect on 2.5 billion light years of space ?

Our Cluster of galaxies is included in this equation. Is there a little paradox in all this ? If we cant see what ever is the cause for this, because light has not had time to reach us, then how do we account for the 2 million MPH speed, thousands of clusters, over a distance of 2.5 billion light years are traveling towards it ?

My colleague Arnost, who teaches science and math, claims that when science calls something a "theory", then it is basically a proven fact.

They'd make good in sales....

tc