Milky Way Is Being Pushed Across the Universe (cnn.com)

dryriver quotes a report from CNN: Our home galaxy, the Milky Way, is being pushed across the universe by a large unseen force, according to new research. Although it may not seem like a friendly gesture, the newly discovered Dipole Repeller is actually helping our galaxy on its journey across the expanding universe. Researchers have known that the galaxy was moving at a relative speed for the past 30 years, but they didn't know why. "Now we find an emptiness in exactly the opposite direction, which provides a 'push' in the sense of a lack of pull," said Brent Tully, one of the study authors and an astronomer at the Institute for Astronomy in Honolulu. "In a tug-of-war, if there are more people at one end, then the flow will be toward them and away from the weaker side." But this is no aimless journey of motion. Researchers have long believed that our galaxy was attracted to an area rich with dozens of clusters of galaxies 750 million light-years away, called the Shapley Concentration or Shapley Attractor. "We found a flow pattern reminiscent of streams of water that are organized by gravity to run downhill," Tully said. "In detail, we played a mathematical trick by inverting the sense of gravity to see where flows would terminate in this altered case. Flows ended at our Dipole Repeller."

Comments

Hm

[backslashdot]

If I understood this right they are calling the lack of attraction, repulsion. There's no negative force, or dark energy style shit involved. Shouldn't they call it a non-attractor unless they show active repulsion? If I drop an object and it moves towards the ground I am not going to say my hand repelled it.

Re:Hm

[ShanghaiBill]

If I understood this right they are calling the lack of attraction, repulsion.

Yes, you understood it right. They also provide the analogy of a tug-o-war rope being "repulsed" by the end with fewer people tugging on it. That is the stupidest analogy I have heard all day. The rope, of course, is not being "pushed" and neither is the galaxy.

Re:Hm

[Anonymous Coward]

If I understood this right they are calling the lack of attraction, repulsion. There's no negative force, or dark energy style shit involved. Shouldn't they call it a non-attractor unless they show active repulsion? If I drop an object and it moves towards the ground I am not going to say my hand repelled it.

That is the wonderful thing about maths. Math can be both fun and insightful for a great number of things beyond simply 'describing reality'.

You may say "This has 60% of some quantity" but that doesn't mean it in'ts equally true to say "This lacks 40% of some quantity" simply because you don't wish to describe it that way.
So long as the percentages add up to 100, both statements are true.

You are also making two very big mistakes in your assumptions, one of which I am going to fault you for.

One, math does not need to be restricted to describing reality.
You remind me of people that say "Computers should only exist to do X, and you are *wrong* for making software for any other purpose"

Two of course is - stop putting words in other peoples mouths! And shame on you for doing so!
These people never once claimed their math represents reality, and never claimed there is any such thing as a force of repulsion being proved here. You quite literally made that up and attributed that factually wrong statement as something they claimed.

In this case they are using the math as a little game. Reverse your point of view and focus on the other side of the equation just purely to see what happens.
After they did so, they were able to show not where gravity is pulling things, but where those things were prior to being pulled, thus showing more detail on the path they have traveled.

The really interesting thing that came out of this is when they pretended the math was correct and actually looked through a telescope to the place in space indicated as the start of the trip for our galaxy.
They noticed that, in reality, more galaxies than just ours are moving away from this point.

This provides insight that wasn't thought to be looked for previously.

Not only are there large clumps of mass gravitational pulling things to them, but there are also large areas with little to no mass they are being pulled away from.
It has always been thought that galaxies are 'born' in high mass galactic clusters and flung out by forces such as super novas and such.
We now have observational evidence this isn't always the case, which we did not have before.

Being just a starting point for what to observe, clearly there are few if any conclusions beyond that we can draw from this, but we now have a better idea of places to look that very well may be more interesting than previously assumed.

Maybe after checking the observations nothing comes of this, and this was just some strange coincidental anomaly that came out of the math for these two runs of numbers.
Maybe it will turn out this will be a useful method to trace back the path of galaxies in more detail than we had before.

But when you have trillions upon trillions of things in space to pick to look at, anything that can raise something to a higher priority instead of simply choosing at random is worth while.
And whatever criteria you used to choose does not need to be some mathematical proof of a deeper explanation of reality, it's only requirement is pointing us in a direction to look that has some, any, amount of meaning behind it above just rolling the dice.

Re:Hm

[Baloroth]

Attractor and repeller are, in this case, being used as very technical terms to describe the behavior of those regions of space in the velocity field of the universe. Neither the repeller nor attractor needs to actually be exerting any physical force at all.

Re:"Helping our galaxy on its journey"

[Black Parrot]

What does this even mean in a non-teleological universe?

"We're moving in the direction gravity is pulling us."

It's the most powerful force in the universe...

[Zaatxe]

... love!

Re:It's the most powerful force in the universe...

[tigersha]

You know why Hurricanes are named after women? When they arrive they are all wet and wild and when they leave they take your house, your card and everything else.

So much for your theory then.

Re:Beware the Cosmic Drain!

[Joce640k]

"Now we find an emptiness in exactly the opposite direction, which provides a 'push' in the sense of a lack of pull," said Brent Tully, one of the study authors and an astronomer at the Institute for Astronomy in Honolulu. "In a tug-of-war, if there are more people at one end, then the flow will be toward them and away from the weaker side."

But ... that doesn't mean the weaker team is 'pushing', does it?

(facepalm)

Re:"... distances of ~20,000kms1 or more" ???

[AthanasiusKircher]

This is what I read from the original article. To my very limited ability to understand, it seems that "Km s-1" is a speed, not a distance.

You may want to read up on the Hubble constant. When talking about large distances in the universe, there is no direct way to measure them. Instead, we measure red shift. Red shift is used to calculate velocity. Velocity is used to calculate distance. There are various assumptions at each stage of calculations.

And then there are other complexities about what you actually mean by "distance." Astronomers have various ways to calculate it, but it's complicated by relativistic effects, not to mention the problem of how to talk about distance in relationship to things where you only know where they were by light that left millions or billions of years ago. So, are you talking about distance "then" or "now" or something else? And there's the fact that space is actually expanding over time, so are you talking about "proper" distance or comoving distance. And your calculated "distance" could depend on the exact cosmological model you're using and assumptions about the future development of the universe.

To avoid some of those complications, it's more accurate to report the actual measurement you're taking when talking about "distance," which is redshift. Or you could go one step further and calculate the Hubble velocity based on the redshift, while ignoring the complications of "distance" mentioned above. That's what is being done here -- and it's quite common in astronomical literature. If you had bothered to read to the end of the second paragraph, you'll discover they actually explain this: "The Cosmicflows-2 dataset of galaxy distances provides reasonably dense coverage to R ~= 10,000 km s-1 (distances are expressed in terms of their equivalent Hubble velocity)."

I agree with you that it would probably have been clearer to people unfamiliar with this usage to put that explanation after the very first use of the Hubble velocity as distance... I assume they probably just didn't want to do that because stylistically it clutters the very first sentence of their article.