rotation speed of the universe? edit
I have been wondering the possible rotation of the universe for quite some time. The subject hasn't been discussed in any literature I've come across with, although it seems like quite non-trivial and possibly interesting.
I guess it would be notoriously difficult - if not outright impossible - to carry out such measurements. There's no reference points, obviously - d'uh! Without reference, it's the same as standing in a closed box. We can't distinguish movement from being "stationary", nor can we distinguish gravity from acceleration.
Based on the red shift and studies on other subjects, we have an estimate on the expansion speed of the universe. However, not knowing the mass of the universe, we can't tell what kind of circular orbital speeds we should expect at any distance from the centre. If the universe is expanding, however, we can be sure that the universe is not on a circular - but perhaps on an elliptic orbit around itself at the moment.
What might matter more, is the beginning of the "orbit". If a object is throwed away from a surface of a gravitational body, it will either experience an orbit that intersects with the body, or an escape orbit. If all the parts of the universe were on such an colliding orbit, eventual collapse would be imminent. However, artificial satellites sent from the surface of the earth are able to maintain (near) circular orbits, not intersecting the surface of the planet. This is possible because the payload and the fuel are accelerated in opposite directions after leaving the surface of the earth.
Likewise, universe might be on a non-self-intersecting orbit around itself, non-collapsing, yet not infinitely expanding - if there is significant difference in orbital angular speed in different parts of the universe. Now I'm not saying anything on whether or not such different orbits would or would not intersect. However, the energy for making that difference would have come from somewhere. I'm not saying that it has, just not ruling out that it couldn't have. Total angular momentum of the universe must have been preserved since the big bang, although differences in part of it could have emerged. Anyways, I'm going too far from the real question..
What is the current status on the study of this subject? Is the universe rotating, non-rotating, or is it an open question, or is either possibility just "assumed" out of convenience? Can we only make an equation that show the dependence of expansion speed on the angular speed and the mass of the universe, or is there base for the estimation of some single parameters?
- If true, this theory would put a whole new spin on the universe. :-) StuRat 04:12, 31 July 2006 (UTC)
Uh, I guess those were questions, rather than a question. Anyways, as usually, I'd just love to hear your answers (and discussion). Thank you. 193.166.173.23 12:32, 28 July 2006 (UTC) Oh, it's as if my session timed out while I wrote down this minor question, or I was never logged in. Santtus 12:34, 28 July 2006 (UTC)
Oh, and I have to add to the story before letting anyone answer. If the estimate on the mass of the universe is based on assumption of non-rotation, obviously the universe would have a larger mass should it actually be rotating, in order to give the same appearance of phenomena for us poor humans, who are doomed to wander in here without any outside physical references whatsoever. *sigh* Santtus 12:41, 28 July 2006 (UTC)
- There was a recent article in New Scientist relating to the universe rotating. The online version (which you have to pay for) is here [1]. JMiall 13:04, 28 July 2006 (UTC)
- Blah, I subscribed to the magazine, but apparently I'd have to wait for the first issue to be delivered and use a printed code in the postal delivery to enable my online content. So you nice folks at Wikipedia have still a good 3-4 weeks of time to discuss this before I recieve my "spoilers" from the postal service ;) Eh, this might be of interest to a wider audience than those willing to subscribe to a premium service.. Santtus 14:13, 28 July 2006 (UTC)
- I would have thought the question was meaningless (considering no point of reference outside the universe), so I await sight of the New Scientist article with interest.--Shantavira 14:47, 28 July 2006 (UTC)
- It would be meaningful, even though no outside reference could be established. Given the lack of other meaningful explanations, the disparity between calculated mass and the observed gravity could be properly attributed to non-zero rotation of the measured body. Santtus 15:37, 28 July 2006 (UTC)
- I would have thought the question was meaningless (considering no point of reference outside the universe), so I await sight of the New Scientist article with interest.--Shantavira 14:47, 28 July 2006 (UTC)
- Rotational speed can be measured. Rotation imparts a centrifugal force on the object being rotated. This force is greater the faster the rotation and can be measured. So align such an object with an object on both sides of the universe and measure how fast it rotates. Thus the rotational speed of the object can be determined, and how fast it is moving closer or futher away can also be measured by red shift. Thus the speed and direction of the object can be determined.
- Yeah, why not joggle with the universe while we're at it. It would just be much more convenient not to extend a measurement device for such a great distance. So obviously we'll have to contend with earth-bound measurements.. or anyways, measurements on distances insignificant compared to that of the diameter of the observable universe. The problem is that we have no solid medium in the universe where we would attach those measurement devices into ;P Santtus 15:32, 28 July 2006 (UTC)
- Basically, you are saying that outward momentum from a central point is due to centrifugal force and therefore evidence of rotation. Right?? If something like a big bang sent everything outward in a straight line with no spinning, you would still have outward momentum. --Kainaw (talk) 15:30, 28 July 2006 (UTC)
- Obviously he would have the universe-long measurement device free-floating in universe, not "attached" to anything like planets that would be moving fast away from the centre ;) Yes it would take quite a bit time to set up such a device, and even more so to get any readings from the device. Maybe it didn't even have to be very long. Still, I believe we're gonna get results faster by using what we have on earth and in vicinity. Santtus 15:43, 28 July 2006 (UTC)
- If you ment that, I dont think that expanding is by itself any indication of rotation. Santtus 15:46, 28 July 2006 (UTC)
- Basically, you are saying that outward momentum from a central point is due to centrifugal force and therefore evidence of rotation. Right?? If something like a big bang sent everything outward in a straight line with no spinning, you would still have outward momentum. --Kainaw (talk) 15:30, 28 July 2006 (UTC)
- I'm not entirely sure what you are getting at, but if the basic issue is: "Does the total angular momentum of the observable universe = 0?", then that is at least an approachable question. One obvious observation is that any large scale rotation would give rise to anisotropy in the universe, with a natural direction defined by the axis of rotation, just as the equator and poles of the Earth move differently with respect to the Earth's rotation. Such anisotropy might have observable implications that could been sought for in WMAP or SDSS. Also, if we are just talking about angular momentum conservation from some initial non-zero value, then that would have to be accomplished by ordinary gravitational forces, when would tend to concentrate mass in a plane perpendicular to the axis of rotation, just as galaxies collapse into rotating disks. Dragons flight 15:53, 28 July 2006 (UTC)
- I believe the idea that the Universe is rotating was originally put forward by Godel. It is a meaningful question as a reference point is only required for uniform motion. The current thinking is that the Universe is not rotating as (it is thought) the rotation would produce observable change in the cosmic microwave background. This has not been seen.
The suggestion by Dragons flight that the angular momentum be zero is I think a reference to the intrinsic angular momentum (spin). The net spin of all the individual particles in the Universe is zero.
Another reason cosmologists find the idea of a rotating Universe distasteful is that it would mean there would be a 'special place' in the Universe and therefore contravene the cosmological principle.
- I believe the idea that the Universe is rotating was originally put forward by Godel. It is a meaningful question as a reference point is only required for uniform motion. The current thinking is that the Universe is not rotating as (it is thought) the rotation would produce observable change in the cosmic microwave background. This has not been seen.
I've been thinking about this question for many years now. It's a good point that a rotating Universe would collapse into a disk like shape. On the other hand, obviously a special state of zero rotation must exist, since if you take a spinning object and define a coordinate system fixed to it, you will see different physical behavior of objects in that system. Every still-standing particle will experience a force pulling it outward from the center of the coordinate system. Isn't that somehow similar to the accelerated pace of the expansion of the Universe that has been observed? I know an acceleration caused by rotation would have a preferred direction, but do we know yet if the acceleration of the Universe is uniform? What if there is a rotation of the Universe but it is so small that it didn't have time to form a disc shape yet. I know, if such a hypothetical rotation would have been there at the beginning, it would have been much faster then because the Universe was much smaller. I guess that's what you refer to with differences in the cosmic microwave background. But what if the rotation only developed later on, so the total angular momentum would increase only at a later time. I know the idea of a non-constant angular momentum sounds weird, but so does that of the forces leading to a big bang at all, too.
Anyway, it's remarkable how little this topic is being discussed, I hope someone will come up with a comprehensive explanation of it someday.
Thomas
The problem is the universe maybe much vaster than we realize. The Universe may have a diameter of 100-200 or more billion light years, but we can only see out to the 13 billion light year limit due to when that is where we see the earliest galaxies anything beyond that point red shifts into the x-ray length. There is a theory that it was not a Big Bang, but a two branes colliding in string theory that would produce something that looks like a Big Bang. How vast this would be is unknowable. Our Universe may just be a tiny part of the whole and if it does rotate It would affect Red shift. The object at the end of a string is moving much faster than a the string in your hand ergo the object at the edge of our Universe would have to be red shifted more, since you are using the Earth as the center point. The latest finding also show that our region of space is moving faster than other region and no need for dark energy if that is the case. It has been hard to even pin down the exact age that we can see out. So rotational rates at this point would be a guess at best.