What makes the universe spin

According to the first principle, every local reference frame of space-time is Minkowskian and the laws of physics are the same in all local reference frames. The second principle allows us to actually identify between elementary particles and irreducible representations of the symmetry groups of nature. Now, since elementary representations of the rotation group are classified by the spin, then elementary particles carry spin.

There is a subtlety in this description, in that the representations of the rotation group correspond only to integer spin and as we know half integer spin exists in nature also.

This issue was also addressed by Wigner, who generalized the correspondence between elementary particles and representations to projective representations as well see for example Wigner's collected works. The projective representations of the rotation group correspond to half integer as well as integer spin. I think that the simplest way to answer this question is to state the apposite.

To have no angular momentum in 0g is nearly impossible. Besides vacuum random spin is the most difficult problem in space. The momentum need not be oriented in any particular direction and need not be transferred at any particular point.

Let us take a rod that is situated in free space as our body. This rod may be bombarded with all sorts of objects that transfer momentum to it. If momentum is transferred to the body at any point other than the com, rotation takes place.

If we want pure translation, we'll have to strike the rod at exactly the center of mass. Since transferring momentum at exactly the center of mass is impossible since there will always be an error in measuring where the center of mass is , there will always and inevitably be rotation of the body when an impulse is given to it.

Therefore, most extended masses in the universe such as planets and stars have some amount of rotation. The earth, for example, collided with another planet long ago, due to which it rotates about its own axis even today. Say you have two masses moving in opposite directions but not head-on.

You know that gravity acts between them. As they move closer, they will curve in towards each other due to gravity. This curving-in causes a centrifugal force to act on either of them. For some configuration of this two-mass system i. In galaxies, the same thing happens. Initially, as the galaxy forms, many gas molecules start to rotate in the same way as above.

This initial angular momentum is conserved as more and more gas molecules accumulate in this galaxy, and thus it retains this rotation. The solar system also forms the same way, and the matter forms clumps and coalesce to form planets and so on.

I'm not exactly sure whether this applies for the angular momentum but I know it is true for the spin.. When things condense they begin to rotate or their existing rotation is accelerated.

This can easily be seen in the form of neutron stars, and as an example from here on earth, a tornado. In the case of the neutron star, it spins rapidly, but before its collapse, it was slowly rotating. This is because, as the collapse happens the particles inside of the star condense and therefore the whole star condenses, resulting in accelerated rotation.

I'm not exactly certain but I believe that the angular momentum is a result of the spin and the effect it has on the surrounding matter. Planets spin when it moves about a central mass. This is because spin and orbital angular momentum are related. Hence, any orbiting planet must spin in order to be in equilibrium and stay in its stable orbit. This relation is shown in a paper published in Astrophysics and Space Science, V.

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Learn more. In any region of space you look, about half should be spinning in a clockwise direction, and about half anticlockwise. In , a study of 15, galaxies found that there was a small bias in rotation.

Because of the relatively small sample size, the evidence was somewhat weak. But this week a paper was presented at the th American Astronomical Society meeting, which showed an even stronger bias.

The study looked at , galaxies and their measured rotations. With the larger sample size, it found not only a rotational bias but also some of its cosmological properties. For one, the bias seems to get stronger with greater redshift. At ever-larger scales the bias is harder to ignore. This supports the idea that the universe as a whole has an axis of rotation.

Interestingly the cosmic axis seems to align with the so-called cold spot of the cosmic microwave background. Instead, the bias has a more complicated multipole structure. All that said, there does seem to be something strange going on. While that might not seem like a big deal, it has huge implications for our cosmological models. Future measurements of the polarization of the CMB may improve in the next few decades, but the new data is unlikely to challenge the previous findings.

While the result that the universe is not rotating is certainly a relief for the cosmologists who had based their models on this assumption, it also gives us an interesting perspective on our place in the universe.

Originally published on Live Science. Mara Johnson-Groh is a contributing writer for Live Science. She writes about everything under the sun, and even things beyond it, for a variety of publications including Discover, Science News, Scientific American, Eos and more. Mara has a bachelor's degree in physics and Scandinavian studies from Gustavus Adolphus College in Minnesota and a master's degree in astronomy from the University of Victoria in Canada.

Live Science. Mara Johnson-Groh.