Why do galaxies rotate?

[CumbrianGadgey]

It seems to be a pointless question, but no question is pointless...except for anybody asking me if I want a pint of cider...now that doesn't need to be asked.

Basically there should be no rotation from an explosion, without external influencing forces.

After a good deal of 'Googling' it seemed that I am not the only one to question this.

The point is simple. During and after the initial big bang, there is traditionally (if I can use that term) no space or time and the embryo universe obeys the rules of physics as it expands. In an explosion without the influence of any other body or force, it follows that the universe would expand radially in all directions, like spokes supporting the inside of a ball. With nothing else to influence this radial motion, there would be no chance of spin, since no angular momentum can result from an 'explosion' originating at a point source.

This concerned me because there is rotation to be seen everywhere, even as close to home as the solar system. How can this be?

Michael Longo has shown that not only is there rotation, the majority of galaxies rotate anti-clockwise suggesting a few things to me. The first is that the rotation should not be there at all, but without it there could be no planets...bad news for us, I'd say. The second is that if there is rotation, why would one direction be favoured above another?

To answer this, Mr Longo suggests that our universe was born spinning inside some other space and was influenced by other universes within that space.

I can understand all of his logic up to the point that he says that our universe exists within another space full of universes.

At this point, I struggle. Is he suggesting that space and time within our universe had already been created by an older big-bang? If so, our universe is not technically a universe at all, but is more akin to a galaxy within a bigger construct. Worse, it contradicts all theory to date, which suggests time and space did not exist until our universe was created...maybe we are just being too arrogant here and have to assume that we came first and foremost. What really nags me about the concept is that it would not introduce angular momentum into our own system, except at a random level if one or more older expanding older universes passed through our own, because they would also expand radially.

I came to the conclusion that his idea is understandable if by our universe existing 'within another space' he is not referring to the usual four dimensions of space and time. After all, there is no mathematical limit to the number of independent axes of a matrix. A fifth, sixth or higher dimension seem reasonable. I can happily conceive of numerous universes popping into existence inextra dimension(s) and obeying the rules of physics that apply to it. Universes could then interract or collide in this dimension and introduce rotation that would not be possible in conventional 4-D physics.

Either this or the big bang theory is far from perfect and still needs to explain rotation. If you can understand my worry, what do you think? Is ours the only universe and we simply have more to learn about the big bang to explain away these inconsistencies? Or are we beginning to see that we knew even less than we thought?

Sorry, this is the sort of thing I think about!

Another good response would be to tell me to shut up and I'll keep future concerns to myself.

Cheers.

[JulianO]

Galaxies rotate basically because, in the end, the big bang wasn't complete homogeneous (meaning the same everywhere).

There were bits that were slightly more lumpy than other bits. These are the seeds of galaxies, and other stuff falls into them. However the stuff falling in has its own motion, which is rarely exactly towards the very centre, so they come in an spin around, orbiting. Wanting to go straight on but, being pulled around into a circle. They also tend to flatten preferrentially in one direction, leading to that forming the plane of rotation.

We can simulate this, quite easily. Sprinkle a big bang mix of random bis of matter, and you'll find the clump together into a galaxy and one that spins. As the galaxy contracts, the spin gets faster, so even a small spin is soon amplified.

I think its now agreed that there are about equal numbers of clockwise/counter-clockwise galaxies. This came out of some zooniverse research.

[JamesF]

I think its now agreed that there are about equal numbers of clockwise/counter-clockwise galaxies. 

Doesn't that just depend on which side you're looking from?

James

[jnb]

It's sometimes worth asking the opposite question. So instead of asking why galaxies spin ask what it would take to have no rotation in the universe. It would have required an absolutely homogenous initial condition and expansion. Now ask what is the probability of there being no random deiations whatsoever. It seems that a universe without spin would be far less probable than one with spin.

[JulianO]

Yes it does, but initially it looked like it was about a 60:40 split - which would have been interesting to explain.

On more refined study, taking out some human biases, it went to nearly exactly 50:50 I believe.

I can't find the paper though off hand.

[kirkster501]

Rather than think of the galaxy "rotating", think of the stuff that comprises the galaxy orbiting something.  That "something" is the Supermassive black hole that is thought to exist at the core of all galaxies.  Thats what I read on this subject.

[Alien 13]

I was trying to imagine the galaxy spin in the same way as water goes down a plug hole it allways spins the same direction the greater the pressure difference (the deeper the water) the faster and closer to the center it goes. Now someone in the opposite hemisphere says hold on my water is going in the other direction so who is right?, well if i could see through the earth i would notice that his spin is exactly the same as mine but we cant both be right can we?

[CumbrianGadgey]

Galaxies rotate basically because, in the end, the big bang wasn't complete homogeneous (meaning the same everywhere).

There were bits that were slightly more lumpy than other bits. These are the seeds of galaxies, and other stuff falls into them. However the stuff falling in has its own motion, which is rarely exactly towards the very centre, so they come in an spin around, orbiting. Wanting to go straight on but, being pulled around into a circle. They also tend to flatten preferrentially in one direction, leading to that forming the plane of rotation.

We can simulate this, quite easily. Sprinkle a big bang mix of random bis of matter, and you'll find the clump together into a galaxy and one that spins. As the galaxy contracts, the spin gets faster, so even a small spin is soon amplified.

I think its now agreed that there are about equal numbers of clockwise/counter-clockwise galaxies. This came out of some zooniverse research.

Is this 'Zooniverse' research more recent than July 2011? If so that supercedes what I 'knew'.

That is critical.

If that is the case it lends credence to the rest of the supposition that the original theory still holds true.

[CumbrianGadgey]

I was trying to imagine the galaxy spin in the same way as water goes down a plug hole it allways spins the same direction the greater the pressure difference (the deeper the water) the faster and closer to the center it goes. Now someone in the opposite hemisphere says hold on my water is going in the other direction so who is right?, well if i could see through the earth i would notice that his spin is exactly the same as mine but we cant both be right can we?

The rotation around the plughole is not at all the same. First and foremost it assumes that there is spin on the planet in which the plughole is situated. that in turn assumes that the planet spins, which means it forms from a revolving gas cloud. the gas cloud rotates because the early umiverse had spin. Why was that? To use an unintended pun, we come full circle. the reason that coriolis forces exist is that the universe began to spin after it was formed.

At least, that's my understanding.

[CumbrianGadgey]

Yes it does, but initially it looked like it was about a 60:40 split - which would have been interesting to explain.

On more refined study, taking out some human biases, it went to nearly exactly 50:50 I believe.

I can't find the paper though off hand.

I totally agree. If the universe developed spin through random lack of homogeniety in the initial mixture, I could accept that some spin would develop but i would also expect that out of the trillions of galaxies, the normal rules of probability would have to suggest a 50/50 split in the rotational direction of the galaxies. That's why I want to know if julianOs 'zooniverse' data is more recent than Longo's ideas of 2011 and if so, what credence lies behind the findings.

Longo suggested that the ratio was even more distorted.

Thanks for the discussion so far, folks. it seems I'm not mad to worry about these things after all.

Cheers.

[ScottS]

It's sometimes worth asking the opposite question. So instead of asking why galaxies spin ask what it would take to have no rotation in the universe. It would have required an absolutely homogenous initial condition and expansion. Now ask what is the probability of there being no random deiations whatsoever. It seems that a universe without spin would be far less probable than one with spin.

Surely everything would just collapse in on itself in that case, therefore no galaxies.

[Chris Rowland]

Chris Lintott came to our Astro Society a few years ago and talked about this.  The Zooniverse initially found a bias!  But when they presented mirror images - which would have had the rotation reversed - the bias was the other way.  It turned out to be a psychological process where people have a preference for one rotation direction. He showed us a video of the spinning ballerina, there's actually no rotation information at all but people can see it.

Once you remove the human biases galaxy rotation seems to be about 50:50.  And they inadvertently did some psychological research as well.

I'm not sure of the dates, but think it was about 2011.

Chris

[jnb]

Surely everything would just collapse in on itself in that case, therefore no galaxies.

Yes, but the point of the question is to highlight the improbability of their being no rotation

[CumbrianGadgey]

Surely everything would just collapse in on itself in that case, therefore no galaxies.

No, if the universe expanded with no spin, this does not prevent galaxies forming, or individual stars within each galaxy. what may be prevented is the formation of solar systems, because the planets forming in each gas cloud would simply get sucked back into the star. The galaxies would survive because they have momentum propelling themselves from the centre.

in one sense, you are right, whether spin exists or not. For a long time, astronomers expected that the expansion of the universe would be slowing down, and then contract back in on itself. This does not now seem to be the case and the accelerating expansion is explained by dark energy.

[CumbrianGadgey]

Yes, but the point of the question is to highlight the improbability of their being no rotation

True, but as with most debates, this one has expanded!

We can say that there will be rotation if the bang was not homogeneous. I think this is a rather big assumption, but if we accept it to explain rotation, then we would have to assume that the rotation of galaxies would be random, since the galaxies form due to random dense spots in the expanding cloud. What Michael Longo has found is that there is a bias to anti-clockwise rotation of about 7%. For galaxies to show this bias, he claims that the probability of this bias being random is around 1 in several million.

Here is his document: http://arxiv.org/ftp/arxiv/papers/0904/0904.2529.pdf

I agree with him that even a 7% bias has to be highly unlikely. If there are 500 billion galaxies or thereabouts, their rotation should be like tossing a totally unbiased coin 500 billion times and we all know that the more a coin is tossed the closer we get to 50% heads and 50% tales.

So the question remains. Is there a bias, because if there is, the traditional ideas are missing something.

[Cath]

If they didn't rotate we'd all immediately make a bee line for the central black hole. And if their is no central black hole, then their soon would be

This basically means that any not rotating galaxy doesn't get chance to form in the first place, leaving all but the rotating ones behind.

[ollypenrice]

Going back to the opening post, I don't agree with this premise;

The point is simple. During and after the initial big bang, there is traditionally (if I can use that term) no space or time and the embryo universe obeys the rules of physics as it expands. In an explosion without the influence of any other body or force, it follows that the universe would expand radially in all directions, like spokes supporting the inside of a ball. With nothing else to influence this radial motion, there would be no chance of spin, since no angular momentum can result from an 'explosion' originating at a point source.

I don't think 'radially in all drections' makes sense. It makes sense for normal explosions but in the context of a universal expansion of spacetime isn't it self contradictory? Either it expands radially or it expands (universally) in all directions. The difference is that in the BB expansion every part expands in every direction. In the case of a normal explosion, the expansion is centre-driven. The ever present danger in ruminating about the BB is thinking in terms of centre-driven explosions seen from the outside. However murderously difficult it is to do so, I think it essential to ban myself from ever imaging the universe from the outside. There isn't an outside, so any perception this gives me will be misleading.

Olly

[CumbrianGadgey]

Hey,

thanks peeps! They say you can't teach an old dog knew tricks but this one is slowly getting the hang of it.

I think part of what I struggle with is the fact that I've only really watched TV programmes on the subject in recent years and they leave me with more questions than answers, probably because the producers seem to assume that the watching public don't know a proton from an electron.

It has just dawned on me that at the 'time' of the bang, you would only need to have one imbalance in the original matter and that is the one between matter and antimatter. After that, the rest kind of follows, since vast swathes of the new universe would anhihilate each other, leaving holes all over the place.

I guess the idea about homogeniety may be compared to gas inside a football, though this may be a bit simplistic. although the gas pressure seems uniform enough to keep the ball round, locally and at a sub-microscopic level, the pressure will vary from one point of the ball to another. Cosmologists would probably be tearing their hair out, reading my childish attempts to understand the early universe!

I am still intrigued with the notion of parallel universes and a multiverse. The idea that Longo suggests of other universes interracting with our own conjures up all sorts of fascinating possibilities, whether it is true or not!

I'm happy with what you've patiently told me so far. If you want to add other points of interest, then that is okay, too, but I think my question has been answered.

Thanks again.

[ollypenrice]

Beware of footballs! In a football the gas pressure is pressing out against a surface. It has a tenedency to make the ball expand.

In a universe ( ) radiation pressure, bizarrely, is a force for contraction. This is because energy has mass equivalence and therefore generates gravity which is will provoke contraction. And a universe has no surface. Or we don't think this one does!

Olly

[CumbrianGadgey]

Beware of footballs! In a football the gas pressure is pressing out against a surface. It has a tenedency to make the ball expand.

In a universe ( ) radiation pressure, bizarrely, is a force for contraction. This is because energy has mass equivalence and therefore generates gravity which is will provoke contraction. And a universe has no surface. Or we don't think this one does!

Olly

I said it may not be the best analogy. But the pressure is caused by the presence at the inner skin of atoms. i was just trying to suggest that however evenly we imagine the molecules to be spaced in a gas, when you look closely enough they are not homogenous at all. I suppose even that analogy is not very reasonable because the molecules were introduced at pressure and pinged about off the wall and each other, so their random nature is one that was imposed on them, not one that just naturally occurred.

Drat! If I had my own way I'd have the universe beginning in a way that was easier to understand!