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Author Topic: Does the Universe Spin ?..well..does it ?  (Read 7387 times)

Offline neilep

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Does the Universe Spin ?..well..does it ?
« on: 12/05/2006 14:43:52 »
If I were to stand on my record player (remember those ?) and turn it on I would spin ! (assuming I'm as light as a fly)

The world spins, the galaxy spins...

Why does the Universe NOT spin ?...or does it ?....Why will it never spin ?...or will it ?

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« Last Edit: 12/05/2006 14:54:37 by neilep »


 

Offline Hadrian

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Re: Does the Universe Spin ?..well..does it ?
« Reply #1 on: 12/05/2006 15:08:11 »

Would that imply it was in something? It is not so I would imagine the answer is no.  
 



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Re: Does the Universe Spin ?..well..does it ?
« Reply #2 on: 12/05/2006 15:29:33 »
It would also imply that the universe has a centre.  I am not aware of their being any observable centre (or absolute periphery) of the universe.



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Offline neilep

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Re: Does the Universe Spin ?..well..does it ?
« Reply #3 on: 12/05/2006 15:35:50 »
Doesn't everything have a centre ?..

Ok...hypothetically then..if one could freeze the Universe into a Universal Ice cube...would it not stand to reason that it would have a centre ?

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Re: Does the Universe Spin ?..well..does it ?
« Reply #4 on: 12/05/2006 16:02:54 »
quote:
Originally posted by neilep
Doesn't everything have a centre ?..

Ok...hypothetically then..if one could freeze the Universe into a Universal Ice cube...would it not stand to reason that it would have a centre ?



It depends upon its shape.

Does the surface of the Earth have a centre (not the bulk of the Earth, only its surface).

Ignoring anomalies, such mountains and oceans, and that the Earth is not a perfect sphere; and thus assuming the Earth was a perfect and smooth sphere, then every point on its surface could be an equal centre (i.e. any point upon which you stand on the surface of the sphere, you will see exactly the same peripheral view, and no point would be any more special than any other).

If, like a sphere, the universe was a closed surface, then there need be no centre to it.

Ofcourse, the Earth does spin, but it is the solid 3 dimensional bulk of the Earth that spins, not the 2 dimensional surface of the Earth (i.e. the centre of the spin actually exists outside of the plane that is the surface).

Whether, even if the universe exists as a closed surface, it nonetheless exists on a superstructure of a more open geometry, and that open geometry having a centre, is another question.

Ofcourse, it might simply be that the universe does have a centre, but it is so far away, that light from that centre could never possibly reach us, and so the centre is away from any part of the visible universe.  It may even be that the universe appears so flat and symmetric because we can only see the minutest fraction of the totality that is there.




George
« Last Edit: 12/05/2006 16:10:11 by another_someone »
 

Offline Hadrian

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Re: Does the Universe Spin ?..well..does it ?
« Reply #5 on: 12/05/2006 16:20:32 »

Please explain to me even if it had a centre what force could act on it to make it spin. What would it be spinning relative to?  



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another_someone

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Re: Does the Universe Spin ?..well..does it ?
« Reply #6 on: 12/05/2006 17:42:04 »
quote:
Originally posted by Hadrian
Please explain to me even if it had a centre what force could act on it to make it spin.



Not sure that this is relevant.

Once an object is set spinning, it will maintain a rotational inertia just as one has linear inertia when an object travels in a straight line.

What caused the universe to spin in the first place would rather depend upon what caused the universe to exist.

quote:

 What would it be spinning relative to?  



This is a more interesting question.

From a purely geometric perspective, rotation should be relative to something.  On the other hand, it should therefore follow that if one cannot observe that which one is in rotation relative to, one should not know one is in rotation.  Thus, if you were 10 meters underground, you should not be aware that the Earth was rotating around its axis.  In fact, if you are 10 meters underground, you can detect the rotation of the Earth by use of very large ring lasers – so clearly, the rotation of the Earth is perceptible even without being able to observe any external reference point.



George
 

Offline Hadrian

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Re: Does the Universe Spin ?..well..does it ?
« Reply #7 on: 12/05/2006 19:00:21 »

It may well not be relative as I well out of my dept here. But I was thinking that under present understanding of the expansion of the universe what could have accounted for any such rotation.  I was also thinking that such a rotation was subject to the existences of dimensions outside the universe.






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Offline Soul Surfer

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Re: Does the Universe Spin ?..well..does it ?
« Reply #8 on: 17/05/2006 14:51:51 »
I think that we discussed this some months ago but I haven't been able to find the topic

The universe is generally agreed to be expanding and has expanded from a very small size. If the universe was spinning as fast as it could be when it was very small,  the conservation of angular momentum would make it spin very slowly now.

As to whether it is possible to detect the rotation of the whole universe. This is an interesting question and astronomers have looked seriously to see if they could find any rotation or any other irregularities in the visible universe.

Consider our galaxy, we cannot see it rotating but can inferr that it is, by looking at the average radial velocities of stars and clouds of neutral hydrogen gas in different directions.  We can also see similar effects in other disc shaped galaxies like ours.  If there was any net rotation or difference in our whole univese it would appear in the average velocities of lots of galaxies or the cosmological microwave background radiation but no great anomalies have been detected altough there are a couple of small anomalies that may relate to an overall structure symmetry but this is subject to question.

The concept of inflation has been introduced partially to explain this great unifomity in the visible universe.  If we can only see a tiny part of the whole of the big bang it is much less likely that the bits we can see will vary very much

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Re: Does the Universe Spin ?..well..does it ?
« Reply #9 on: 17/05/2006 19:45:41 »
quote:
Originally posted by Soul Surfer

I think that we discussed this some months ago but I haven't been able to find the topic

The universe is generally agreed to be expanding and has expanded from a very small size. If the universe was spinning as fast as it could be when it was very small,  the conservation of angular momentum would make it spin very slowly now.

As to whether it is possible to detect the rotation of the whole universe. This is an interesting question and astronomers have looked seriously to see if they could find any rotation or any other irregularities in the visible universe.

Consider our galaxy, we cannot see it rotating but can inferr that it is, by looking at the average radial velocities of stars and clouds of neutral hydrogen gas in different directions.  We can also see similar effects in other disc shaped galaxies like ours.  If there was any net rotation or difference in our whole univese it would appear in the average velocities of lots of galaxies or the cosmological microwave background radiation but no great anomalies have been detected altough there are a couple of small anomalies that may relate to an overall structure symmetry but this is subject to question.

The concept of inflation has been introduced partially to explain this great unifomity in the visible universe.  If we can only see a tiny part of the whole of the big bang it is much less likely that the bits we can see will vary very much



All of this is fine, as far as it goes, but if rotation is purely a matter of external observation, then how is it possible for laser ring gyroscopes to measure the Earth's rotation without having sight of the sky?

http://www.wettzell.ifag.de/LKREISEL/G/LaserGyros.html
quote:

Large Laser Gyroscopes for Monitoring Earth Rotation


Objectives


Today, Earth rotation parameters are routinely obtained using the geodetic space techniques VLBI (Very Long Baseline Interferometry), SLR (Satellite Laser Ranging), GPS (Global Positioning System) und DORIS (Doppler Orbitography by Radiopositioning Integrated on Satellite). Technical progress over the last decades resulted in a precision of recently 0.01 milliseconds in length of day and 0.1 milliarcseconds in pole coordinates. The common principle is the relative measurement of rotation by observing reference points, stars or satellites, outside the rotating Earth. All these techniques require global networks and structures for the observation and data handling, which are coordinated by the international services IVS, ILRS, IGS and IDS.
The absolute measurement of rotation using inertial rotation sensors is a completely different approach. Mechanical gyros measuring the coriolis force are by far not sensitive enough to detect Earth rotation variations. Instruments measuring the centrifugal acceleration as a part of the total gravity vector, gravimeters and tiltmeters, are basically sensitive to Earth rotation variations, but even the excellent resolution of superconducting gravimeters of 10-11 g is not sufficient to resolve short-period Earth rotation variations. In contrast, laser gyroscopes use the Sagnac effect, whereas the small wavelength of the laser light allows an extreme high resolution. An adequate sensitive laser gyroscope attached to the Earth gives us instantaneous access to the spin of the Earth and the orientation of its axis. For the determination of the complete rotation vector, three linear independent laser gyroscopes are required.


Installation and Environment


The "G" ring laser is operating at the Fundamentalstation Wettzell (Bavaria). It is resting on a polished granite table being embedded in a 90 t concrete monument. The monument is attached to a massive 2.7 m diameter concrete pillar, which is founded on crystalline bedrock 10 m below the former surface. A system of concrete rings and isolation material shield monument and pillar from lateral deformations and heat flow. The instrument is protected against external influences in a subsurface installation, where a passive thermal stability is reached by a 2 m alternating layer of styrofoam and wet clay, and a 4 m earth mound. A lateral entrance tunnel with 5 isolating doors and a separate control room minimize thermal perturbations. After 2 years of thermal adaptation, the average temperature reached 12.2 deg with seasonal variations of less than 0.6 deg.





George
 

Offline PrajnaDhyana

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Re: Does the Universe Spin ?..well..does it ?
« Reply #10 on: 17/05/2006 20:15:37 »
One can use Einstein's Theory of Relativity (which has so much evidence to show it's right that we really should call it a Law now) to answer this question.

But first, some definitions.  In order to say that something is spinning we have to have something else to compare it too.  For example we can say the the Earth is spinning because we can compare it to say the moon and see a difference in angular momentum.  So we can say that the Earth is spinning relative to the moon.

The Universe is defined as everything that exists.  Not just the planets, gases, dust etc that floats around, but space and time itself are part of the Universe.

So, in order to say something is spinning we need something to compare it too.  The Universe is everything in existence.  Do you see the problem here?  

Without having anything to compare the Universe with, you can't say it's spinning.  What would it be spinning relative too?  The same thing could be said about whether it has a center or not.  The idea of an infinitely large object having a center is meaningless. You would have to be able to find where it ends in order to find the center.  Since it's infinite, you can never find the edges, they're simply aren't any.  The only way to find a center would be to step outside of the Universe, which isn't possible since anywhere you could go would, by definition, be part of the Universe.

On a semi-related note, when people talk about the Universe expanding they often picture the “edges” of the Universe moving outward similar to blowing up a balloon.  However, since the Universe doesn't have edges that isn't an accurate picture of what is happening.  When scientists talk about an expanding Universe they mean every single point throughout the Universe is expanding.  The distance between you and the computer screen you are reading this on is getting larger and larger every instant.  The reason you don't notice is that you and the computer screen are also getting larger and larger at the same rate.   So relative to each other, there is no perceivable change.  To understand that a bit easier, think of an astronaut orbiting the earth in the space shuttle. In order to stay in orbit they are moving around the Earth at about 25,000 miles per hour.  But from the astronaut's point of view, the shuttle and everything in it is stationary relative to him.  Since he and the shuttle have the same relative motion, the astronaut can't tell whether he is moving or not without looking out the window.  Since everything in the Universe is expanding at the same rate, there is no “window” for us to look out and thereby see the expansion.

As for the question: “All of this is fine, as far as it goes, but if rotation is purely a matter of external observation, then how is it possible for laser ring gyroscopes to measure the Earth's rotation without having sight of the sky? “

You can measure the Earth's rotation relative to the gyroscope.  And if that wasn't confusing enough, without having sight of the sky it's equally valid to say that the gyroscope is turning and the Earth is stationary.  :)
 

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Re: Does the Universe Spin ?..well..does it ?
« Reply #11 on: 17/05/2006 22:05:05 »
quote:
Originally posted by PrajnaDhyana
However, since the Universe doesn't have edges



Do we know this for a fact, or is this merely supposition?

Since we can only see up to about 13 x 10^9 light years in any direction, do we actually know for a fact what is beyond that range?

quote:

You would have to be able to find where it ends in order to find the center.



This is mostly, but not totally true.

You know that the number zero is exactly halfway between negative and positive infinity, and you can know this even without ever being able to physically approach infinity.

If you can demonstrate that you are closer or further away from an edge, then you can find a centre even without actually proving where the edge is (e.g. if you can find a universal force that decreases as you get farther from the centre, then you have no need to find where the force stops existing simply to show that a point is the centre of the universe – ofcourse, we do not know of any such force existing, but can you show that such a force cannot exist?).

Ofcourse, the word 'centre' can have many meanings.  Centre can refer to a point that is equidistant from all the edges, or it could refer to a centre of mass (which would be the same only if the mass is uniformly distributed when viewed on a large scale), or the centre when measured in some other way.

In many ways, it might reasonably be said that we are at the centre of the universe, at least insofar as we are at the centre of the observable universe, since the universe can be seen for an equal distance in all directions, the distance being that distance which light could have travelled since the birth of the universe.

quote:

The distance between you and the computer screen you are reading this on is getting larger and larger every instant.  The reason you don't notice is that you and the computer screen are also getting larger and larger at the same rate.



This is not consistent with anything that I understand about universal expansion.

If everything was expanding at the same rate, then we would never notice any expansion anywhere in the universe.  Yet, the reason we do perceive the universe to expand is because the distance between ourselves and distant galaxies is apparently increasing.  This would not be apparent if our own size was also increasing.

quote:

As for the question: “All of this is fine, as far as it goes, but if rotation is purely a matter of external observation, then how is it possible for laser ring gyroscopes to measure the Earth's rotation without having sight of the sky? “

You can measure the Earth's rotation relative to the gyroscope.  And if that wasn't confusing enough, without having sight of the sky it's equally valid to say that the gyroscope is turning and the Earth is stationary. :)



But, in a laser gyroscope, there are no moving parts except the light itself.

Even if this was not the case, the scenario you describe would imply an arbitrary rotation that is dependent upon the setup of the gyroscope; but it so happens that the laser gyroscope is measuring the rotation that is very close to that measured by astronomical observation, and so the value is clearly not arbitrary.



George
« Last Edit: 17/05/2006 22:40:23 by another_someone »
 

Offline Soul Surfer

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Re: Does the Universe Spin ?..well..does it ?
« Reply #12 on: 17/05/2006 23:10:01 »
The earth rotates once in one day and is as you say well within the range of inertial navigation systems like laser gyros.  Our part of the galaxy rotates once in about 250 million years.  The whole universe if it is rotating will take many times this period to rotate.

As I explained earlier it it quite possible to measure rotational velocities on an object without an outside source of reference because a galaxy or the universe as a whole is not a rigid body and rotates under the influence of its self gravitation.

Remember also that the rotational velocity of the earth is approximately 1000 mph at the equator

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another_someone

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Re: Does the Universe Spin ?..well..does it ?
« Reply #13 on: 18/05/2006 00:49:44 »
quote:
Originally posted by Soul Surfer

The earth rotates once in one day and is as you say well within the range of inertial navigation systems like laser gyros.  Our part of the galaxy rotates once in about 250 million years.  The whole universe if it is rotating will take many times this period to rotate.

As I explained earlier it it quite possible to measure rotational velocities on an object without an outside source of reference because a galaxy or the universe as a whole is not a rigid body and rotates under the influence of its self gravitation.

Remember also that the rotational velocity of the earth is approximately 1000 mph at the equator

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My apologies, I had misread what you had written.



George
 

Offline PrajnaDhyana

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Re: Does the Universe Spin ?..well..does it ?
« Reply #14 on: 18/05/2006 04:27:51 »
quote:
Do we know this for a fact, or is this merely supposition?


Well, personally I don't think we can really know anything as a fact.  However I can say that a number of experiments have been done and all the evidence so far seems to indicate that this is true.

quote:
You know that the number zero is exactly halfway between negative and positive infinity, and you can know this even without ever being able to physically approach infinity.


At first glance this seems a perfectly reasonable statement.  But what do you say we take it out for a test drive and see how it handles in the curves?

“ You know that the number zero is exactly halfway between negative and positive infinity”  Ok, lets think about that.  There are an infinite amount of number between zero and negative infinity.    There are also an infinite amount of number between zero and infinity.  So this seem like a perfectly legitimate statement.  But now I say this:

“The number 1,256,984.3578 is the exactly halfway between negative and positive infinity.”  Ok, lets think about that one.  There are an infinite amount of numbers between 1,256,984.3578 and infinity.  There are also an infinite amount of number between 1,256,984.3578 and infinity.  So this seems like a perfectly legitimate statement.  

In fact, you can say this about any number you can think of, since there will always be an infinite amount of numbers before and after it.

The same could be said about any point in space.  Since there is an infinite amount of space in every direction from me, I could say that I am the center of the Universe.  But you could say that the Andromeda galaxy is the center of the Universe and it would be just as valid, since there would be an infinite amount of space in every direction from it.  You can say this about any point in space.

The problem arises from thinking that “infinity” is a specific thing that we can look at, that it exists “out there somewhere.”   By definition you can never get to infinity, so it doesn't really exist per sey.  Trying to define something in relation to infinity is nonsensical.  It would be like saying “42 plus green equals tomorrow”.  While you can say the words, they are nonsensical in meaning.  

quote:
But, in a laser gyroscope, there are no moving parts except the light itself.

Even if this was not the case, the scenario you describe would imply an arbitrary rotation that is dependent upon the setup of the gyroscope; but it so happens that the laser gyroscope is measuring the rotation that is very close to that measured by astronomical observation, and so the value is clearly not arbitrary.



What you are measuring is the motion of the light relative to the Earth.  The motion is still being measured by comparing the relation of  one object to another in a common frame of reference.   But since there is nothing “outside” of the Universe, there is nothing to compare the Universe too.  How can it be moving if there is no frame of reference to measure that movement against?  What would it be moving in?  Anything you can find to measure it against, or for it to be moving in, would, by definition, be part of it. And therefore not outside of it.  

Saying "the Universe is moving" is the same as saying "41 plus green equals tomorrow".  You can say the words, but they are nonsensical in meaning.  

quote:
If everything was expanding at the same rate, then we would never notice any expansion anywhere in the universe. Yet, the reason we do perceive the universe to expand is because the distance between ourselves and distant galaxies is apparently increasing. This would not be apparent if our own size was also increasing.


Think of it as an illusion caused by a combination of the distances involved and the way light moves.

Astronomers where amazed to find data showed that some galaxies where moving away from us faster than the speed of light. Knowing that this wasn't possible they investigated more to find out what was causing it to appear that way. The culprit turned out to be the expansion of the universe.
As the light was traveling towards the Earth, the distance it had to travel was getting larger and larger as the universe expanded. Not only were the galaxies traveling away from us with their own speed, but the actual space they were in was getting farther and father away due to the expansion of space between the galaxy and us. Think of two dots drawn on an uninflated balloon. As you blow up the balloon and the rubber stretches, the dots get further apart, even though they are stationary on the surface of the balloon.
The Combination of the speed the galaxies were moving through space with the "speed" of the Universe's expansion produced the illusion that the galaxies were traveling faster than light. An example is an airplane flying in the jet stream. The plane is moving at 525 mile per hour on it's own. But the air in which it is flying is also moving at 200 mph. So even thought the plane is only moving at 525mph relative to the air around it, compared to the ground it's moving at 725mph, or faster than the speed of sound. (I've actually done this on a flight from Tokyo to Seattle.)

On a personal note: Thanks for your reply.  You made very good points and I enjoyed thinking about them while I was grocery shopping.  I look forward to hearing any other thoughts you might have  on this topic.  Frankly I would love it if you could come up with something to show me that I am incorrect.  I hope that doesn't come off as arrogant, it's not meant to be.  This is just a topic that has fascinated me for many years and I have studied it extensively.  So any new insights you might give me would be wonderful.  

« Last Edit: 18/05/2006 04:29:57 by PrajnaDhyana »
 

another_someone

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Re: Does the Universe Spin ?..well..does it ?
« Reply #15 on: 18/05/2006 12:13:05 »
quote:
Originally posted by PrajnaDhyana
quote:
You know that the number zero is exactly halfway between negative and positive infinity, and you can know this even without ever being able to physically approach infinity.


At first glance this seems a perfectly reasonable statement.  But what do you say we take it out for a test drive and see how it handles in the curves?

“ You know that the number zero is exactly halfway between negative and positive infinity”  Ok, lets think about that.  There are an infinite amount of number between zero and negative infinity.    There are also an infinite amount of number between zero and infinity.  So this seem like a perfectly legitimate statement.  But now I say this:

“The number 1,256,984.3578 is the exactly halfway between negative and positive infinity.”  Ok, lets think about that one.  There are an infinite amount of numbers between 1,256,984.3578 and infinity.  There are also an infinite amount of number between 1,256,984.3578 and infinity.  So this seems like a perfectly legitimate statement.  

In fact, you can say this about any number you can think of, since there will always be an infinite amount of numbers before and after it.




Indeed, no matter where you take the 'centre point' there will be an infinite number either side of the centre, but are all centres equal?  No they are not.  Are all infinite sets equal? No they are not.

If you have two sets of numbers, set A and set B.

You can say that all numbers in set A map onto numbers in set B because you have a function, negation, which will provide a one to one mapping between the sets.  Thus the sets are both of the same size.

Ofcourse, you might argue that rather than simply using negation to map the two sets, you could map them with a more complex function of A = 1,256,984.3578 - B.  Except, that in the first example (i.e.  A = -B), every element with A will map to another element within A using the function A0 = 1/A1,  and also B0 = 1/B1, whereas in the second mapping, A0 = 1/A1 will no longer always be true, because some values of 1/A will resolve into values in set B, while one value (where A = 0) will not resolve into a value in either set.

quote:

The same could be said about any point in space.  Since there is an infinite amount of space in every direction from me, I could say that I am the center of the Universe.  But you could say that the Andromeda galaxy is the center of the Universe and it would be just as valid, since there would be an infinite amount of space in every direction from it.  You can say this about any point in space.



Probably, but not necessarily.

A gravitational field extends for infinity, and yet has a centre, because it is not uniform.

Your statement is only true if space is both infinite and uniform.

In one sense, both we and Andromeda are indeed the centre of our own respective observable universes, but that is a consequence of the limitation of observation rather than a feature of the shared universe (i.e. someone living in Andromeda would be able to see some small part of the universe that we cannot, and visa-versa).

quote:

quote:
But, in a laser gyroscope, there are no moving parts except the light itself.

Even if this was not the case, the scenario you describe would imply an arbitrary rotation that is dependent upon the setup of the gyroscope; but it so happens that the laser gyroscope is measuring the rotation that is very close to that measured by astronomical observation, and so the value is clearly not arbitrary.



What you are measuring is the motion of the light relative to the Earth.  The motion is still being measured by comparing the relation of  one object to another in a common frame of reference.   But since there is nothing “outside” of the Universe, there is nothing to compare the Universe too.  How can it be moving if there is no frame of reference to measure that movement against?  What would it be moving in?  Anything you can find to measure it against, or for it to be moving in, would, by definition, be part of it. And therefore not outside of it.  

Saying "the Universe is moving" is the same as saying "41 plus green equals tomorrow".  You can say the words, but they are nonsensical in meaning.



As Ian (Soul Surfer) pointed out, rotation does create radial motion, and it does this because rotation is not steady linear motion, but in fact is continuous acceleration (i.e. the rim of a rotating object is constantly accelerating towards its centre).  One consequence of this is the oblate  shape of the Earth, that bulges out around the equator because of the outward force caused by the absolute rotation of the Earth.  If the rotation was relative, and not absolute, then the shape of the Earth would have to look different to different observers, and a geostationary satellite (which sees no apparent rotation of the Earth) should perceive the Earth as a perfect sphere (aside from the surface topology).

quote:

Think of it as an illusion caused by a combination of the distances involved and the way light moves.

Astronomers where amazed to find data showed that some galaxies where moving away from us faster than the speed of light. Knowing that this wasn't possible they investigated more to find out what was causing it to appear that way. The culprit turned out to be the expansion of the universe.
As the light was traveling towards the Earth, the distance it had to travel was getting larger and larger as the universe expanded. Not only were the galaxies traveling away from us with their own speed, but the actual space they were in was getting farther and father away due to the expansion of space between the galaxy and us. Think of two dots drawn on an uninflated balloon. As you blow up the balloon and the rubber stretches, the dots get further apart, even though they are stationary on the surface of the balloon.
The Combination of the speed the galaxies were moving through space with the "speed" of the Universe's expansion produced the illusion that the galaxies were traveling faster than light. An example is an airplane flying in the jet stream. The plane is moving at 525 mile per hour on it's own. But the air in which it is flying is also moving at 200 mph. So even thought the plane is only moving at 525mph relative to the air around it, compared to the ground it's moving at 725mph, or faster than the speed of sound. (I've actually done this on a flight from Tokyo to Seattle.)

On a personal note: Thanks for your reply.  You made very good points and I enjoyed thinking about them while I was grocery shopping.  I look forward to hearing any other thoughts you might have  on this topic.  Frankly I would love it if you could come up with something to show me that I am incorrect.  I hope that doesn't come off as arrogant, it's not meant to be.  This is just a topic that has fascinated me for many years and I have studied it extensively.  So any new insights you might give me would be wonderful.  



I have very little problem with the above, excepting a few with your balloon example.

The problem with the balloon example is the question of the observer.

If I stand back from the balloon, and stand with a measure in my hand, then as the balloon is blown up, I can measure the distance between the dots, and demonstrate that they are getting further apart.

But, if I myself was a part of the surface of the balloon, then as the balloon increases in size, so will I, and so will the measuring device I hold.  This is consistent with the argument you state regarding the computer screen expanding as I do, and is fine of itself.  The problem is that with this you do not explain why one would be able to measure an increase in the increase distance between galaxies, but not measure the distance between you and the computer screen.  The clear implication must be that the nature of the space between you and the computer screen must be behaving differently from the space between you and a distant galaxy.  In other words, the space between you and the computer screen is not increasing, because the local forces are strong enough to overcome the expansion of space, but distant objects that are not so strongly bound, are indeed being forced apart by the expansion of space.



George
 

Offline DocN

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Re: Does the Universe Spin ?..well..does it ?
« Reply #16 on: 18/05/2006 17:01:36 »
Only if you would have seem this reply before you posted your question.
Doc

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Offline PrajnaDhyana

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Re: Does the Universe Spin ?..well..does it ?
« Reply #17 on: 18/05/2006 20:29:20 »
quote:
As Ian (Soul Surfer) pointed out, rotation does create radial motion, and it does this because rotation is not steady linear motion, but in fact is continuous acceleration (i.e. the rim of a rotating object is constantly accelerating towards its centre). One consequence of this is the oblate shape of the Earth, that bulges out around the equator because of the outward force caused by the absolute rotation of the Earth. If the rotation was relative, and not absolute, then the shape of the Earth would have to look different to different observers, and a geostationary satellite (which sees no apparent rotation of the Earth) should perceive the Earth as a perfect sphere (aside from the surface topology).


Relativity shows us that the Earth does in fact look different to different observers.  The reason the Earth doesn't look like a perfect sphere from the point of view of the geostationary satellite is because although the satellite is stationary relative to the Earth, it can still “see” the rest of the Universe.  Being able to “see” the rest of the Universe allows it to “know” that the Earth is spinning at a certain speed relative to the rest of the Universe.  If you could somehow magically make everything else in the Universe vanish so that only the satellite and the Earth were left, then the Earth would appear as a perfect sphere from the satellite's point of view.  Everything in the Universe is relative to everything else.

Skeptical?   There is loads of scientific evidence to support this.  (Which is why we really should call it the Law of Relativity.)  I will give you an example of one way this was proven by scientists that weren't even trying to prove it:

About a decade or so ago some scientists were doing an experiment to study neutrinos.  Neutrinos are sub atomic particles that interact with matter extremely weakly.  This allows them to pass through huge amounts of matter with ease.  Millions of them pass  through the Earth as if it weren't there every second.  Every now and then a neutrino will hit an atom at  just the right angle for it to interact.  The experiment was set up to detect  these so the scientists could see just how many occur.    They set up huge detectors deep inside coal mines so that the mile or so of rock would block everything except the neutrinos.
Now, the vast majority of neutrinos that pass  through the Earth are created in the Sun by processes  that are very well understood.  These processes have been studied and tested extensively and we are confident that we have a very accurate model of them.  So the scientists used this understanding to make a prediction of how many neutrinos they would detect.  The took into account the thickness of the atmosphere and the thickness of the rock between the detector and the sun (since a few neutrinos would be blocked by them).  They came up with a prediction that they felt was very accurate and expected the number of detections to very close to it.  I don't remember the precise number so for the sake of this example I will use the totally arbitrary number of 5 detections a day.  
So they set up the experiment and let it run.  When they looked at  the data they were shocked to see that the actual number of neutrinos detected by the experiment was in fact 20 (again, a totally arbitrary number on my part just for illustration purposes.)  They went over their numbers and couldn't find any reason for the discrepancy.  As I said, they knew that the number of neutrinos produced by the sun was accurate.  They double and triple checked their math for the predicted detections and it was accurate as well.  So where did the discrepancy come from?
Then one of them remembered that neutrinos are moving very, very fast.  Like in the neighborhood of 99.999999999 % the speed of light.  Relativity says that as you move faster, space contracts.  So while the atmosphere from our point of view is some 60 miles thick, how thick is it from a neutrino's point of view?  They did the relativistic math and found that  for an object moving at 99.999999999%  the speed of light the atmosphere would be only 2 inches thick.
Going back to their calculations for how many neutrinos would be detected, they ran them again seeing how many would be detected if the atmosphere was only 2 inches thick.  
Low and behold, the answer was 20.  Exactly the number they detected.  

From our point of view the atmosphere is 60 odd miles thick.  But from the neutrino's point of view the atmosphere is only 2 inches  thick.  Both are equally true, which one you see depends on your point of view.  The appearance of the Earth is relative to the observer.  (I should also point out that the thickness and shape of the Earth would also be different from the neutrino's point of view.  It would be squashed down as if it had been stepped on.)

quote:
The problem is that with this you do not explain why one would be able to measure an increase in the increase distance between galaxies, but not measure the distance between you and the computer screen. The clear implication must be that the nature of the space between you and the computer screen must be behaving differently from the space between you and a distant galaxy. In other words, the space between you and the computer screen is not increasing, because the local forces are strong enough to overcome the expansion of space, but distant objects that are not so strongly bound, are indeed being forced apart by the expansion of space.


Are you saying that the laws of nature are different in different parts of the Universe?  After all, wouldn't the “local forces” at work between me and my laptop also be functioning in those distant galaxies?   From their point of view they are local and we are the ones that are very far away.

The reason that the distance between us and distant galaxies appears to be increasing is because it is increasing.  But it's not because of the expansion of the Universe.  It's because of plain old boring linear motion.  Our galaxy and those galaxies are moving relative to each other, in this case away from each other.  So the distances between us are increasing.  
If I get up and walk away from my laptop, the distance between us will increase due my angular momentum in the framework of the Universe.  At the same time, due to the expansion of the Universe the volume of space that I and the laptop occupy and the distance that I take in each step is increasing.  But since they are increasing at exactly  the same rate, I can't detect it as there is no relative change.  We can't see the expansion of the Universe because we don't have anything that is not expanding to compare it with.

quote:
A gravitational field extends for infinity, and yet has a centre, because it is not uniform.


From a relativistic stand point you could not say that the gravitational field has a center.  Again, you can't have a center if you don't have an edge to measure it against.  The best you could do would be to say that there is a point in the field that has a higher measurable value than other points in the field, from our point of view.   You could arbitrarily call this point the center, but it would be a meaningless statement on a Universal scale.  You could say that it's the center of the field in regards to the visible Universe, but that would only be true relative to our point of view.  Someone a trillion light years away would have a different “visible Universe” and would say that we were wrong, the point we are calling the center would be closer to one of the “edges” from their point of view.   Of course from the gravity source's point of view it's the center of the Universe, just as from my point of view I am.  It's all completely relative.

quote:
while one value (where A = 0) will not resolve into a value in either set.


Is that enough to define it as the “exact center”?
« Last Edit: 18/05/2006 20:31:52 by PrajnaDhyana »
 

Offline Sandwalker

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Re: Does the Universe Spin ?..well..does it ?
« Reply #18 on: 19/05/2006 02:13:22 »
Cosidering the start of and the perceived expansion of the alpha point/singularity, Can it not be said that every point in the universe is the centre, (God I know i'm the centre of mine).


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Re: Does the Universe Spin ?..well..does it ?
« Reply #18 on: 19/05/2006 02:13:22 »

 

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