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Elfin

A fatal flaw in relativity

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Can someone please explain what's wrong with this, because as I understood it, the theory of relativity states that there is no difference whatsover between observing a moving object from a stationary one, and the other way round. If this is the case, then there is no difference in saying that the earth rotates on its axis in 24 hours, and that the entire universe rotates around the earth in 24 hours.

Diameter of observable universe: 93 billion light years (http://en.wikipedia.org/wiki/Observable_universe).

Circumference of observable edge of universe is therefore: 292.02 billion light years (Pi x diameter).

Rotational speed of observable edge of universe from the point of view of the earth is therefore 292.02 billion light years per 24 hours, which is 12.1675 billion light years an hour (292.02 billion divided by 24).

Since the speed of light is a mere 671 million miles an hour (http://en.wikipedia.org/wiki/Speed_of_light) this means that from the point of view of the earth, the observable edge of the universe, with all its billions of galaxies and all the rest, is travelling at about 18 times the speed of light (12.1675 billion divided by 671 million = 18.133383).

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Hmm...

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Woops just realised I made a gross error in that last statement and confused light years with miles. An easy mistake to make...

Since a light year is 5.878625 trillion miles (http://en.wikipedia.org/wiki/Light_year), the true figure is that the edge of the universe is travelling at 105.81525 trillion times the speed of light (18 times 5.878 625 trillion). Is that right? Sounds quite large.

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Oy, took me a second to understand. I believed, at least in my layman terms of physics, that the speed of light limit only affects matter and energy actually moving, whilst the universe appears to rotate around Earth from our point of view, its not actually moving in such a way. Therefore no laws of physics are actually being violated.

However I'm certainly no physicist, if there are any who'd like to correct me, then feel free.

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Elfin, please get your facts right before you take on Einstein. But i like the fact that you have a brain and you are not afraid to use it. ;)

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Can someone please explain what's wrong with this, because as I understood it, the theory of relativity states that there is no difference whatsover between observing a moving object from a stationary one, and the other way round. If this is the case, then there is no difference in saying that the earth rotates on its axis in 24 hours, and that the entire universe rotates around the earth in 24 hours.

Diameter of observable universe: 93 billion light years (http://en.wikipedia....rvable_universe).

Circumference of observable edge of universe is therefore: 292.02 billion light years (Pi x diameter).

Rotational speed of observable edge of universe from the point of view of the earth is therefore 292.02 billion light years per 24 hours, which is 12.1675 billion light years an hour (292.02 billion divided by 24).

Since the speed of light is a mere 671 million miles an hour (http://en.wikipedia..../Speed_of_light) this means that from the point of view of the earth, the observable edge of the universe, with all its billions of galaxies and all the rest, is travelling at about 18 times the speed of light (12.1675 billion divided by 671 million = 18.133383).

You are sort of correct but you must understand that it does not make sense to state that the universe is revolving around the earth. If you look at the relative motion of all the galaxies in the universe, the sun, the earth, etc. it is much easier to understand in terms of the earth rotating, and revolving around the sun, etc.

Also, relativity states that nothing can go faster than the speed of light relative to anything else. For example if you are travelling at 90% the speed of light relative to the earth, and an object is travelling in the exact opposite direction at 90% the speed of light relative to the earth, common sense says that relative to you, the other object should be travelling at 180% the speed of light! This is not possible! So what is going on? Well it turns out that time actually changes to bring the objects back under the speed of light. Time is relative also and at great speeds it is time that changes to keep the universe working like clockwork and keep the speed of light the speed limit. So to answer your question common sense would state that the edge of the universe is moving faster than the speed of light relative to the rotation of the earth, but in actuality time itself speeds up or slows down to prevent that from happening.

Now there are many unknowns here, such as is there even an edge to the universe? Nobody knows, Also the exact size of the universe is not known.

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Posted (edited)

I was about to type out a long answer but Einsteinium got most of it.

The basic error in your assumption is that the Earth is the center of anything. That same error was committed by many in the past and all were proven wrong.

Edited by questionmark
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Posted (edited)

I was about to type out a long answer but Einsteinium got most of it.

The basic error in your assumption is that the Earth is the center of anything. That same error was committed by many in the past and all were proven wrong.

I'm not assuming that at all. I'm using a famous relativistic maxim, that your point of observation is irrelevant. There should be no difference, therefore, in saying that the earth revolves on its axis in 24 hours, and that the universe revolves around the earth in 24 hours. It would work the same on any other planet or revolving body. E.g. imagine you're on a merry-go-round. The entire universe therefore revolves around you in a few minutes.

Edited by Elfin
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There is a very good sci-fi book that explains some of this for lay-people. Tau Zero by Poul Anderson

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I'm not assuming that at all. I'm using a famous relativistic maxim, that your point of observation is irrelevant. There should be no difference, therefore, in saying that the earth revolves on its axis in 24 hours, and that the universe revolves around the earth in 24 hours. It would work the same on any other planet or revolving body. E.g. imagine you're on a merry-go-round. The entire universe therefore revolves around you in a few minutes.

It does not make sense though to state that the universe is revolving around you. Just consider the gravitational attraction necessary to cause the entire universe to revolve around you, the forces required just are not there. The earth would have to be the most massive black hole in the universe to put it lightly to even consider this. You have to consider everything, forces and motion are intertwined and one does not make sense without the other. If you consider forces, mass, inertia, etc. in your thinking then no it does not make sense to think of it this way. Rotational motion is a little different than linear motion which is what is usually talked about in the context of relativistic motion.

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I'm not assuming that at all. I'm using a famous relativistic maxim, that your point of observation is irrelevant. There should be no difference, therefore, in saying that the earth revolves on its axis in 24 hours, and that the universe revolves around the earth in 24 hours. It would work the same on any other planet or revolving body. E.g. imagine you're on a merry-go-round. The entire universe therefore revolves around you in a few minutes.

From the point of view of either of the two points that may be true. However, in order to get a more accurate observation, one would have to observe both points from a third "neutral" position, and observe the movement relative to each other. When a car moves past a parked car, the parked car appears to whiz by from the perspective of the moving car, however, a pedestrian on the sidewalk could see that one car is moving and the other isn't. Same principle would apply even on a cosmic scale.

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The theory of relativity tells us that there is no preferred frame of reference, when observing the motion of one object with respect to another. If Earth were at the center of a universe that was revolving around it, the velocity of a distant point in that universe would be zero, with respect to the center of the Earth, the supposed point around which the universe revolves. If the relative velocity is zero, there is no exceeding of light speed.

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All this time I thought that I was the center of the universe, with my wife spinning circles around me.

Dang. :passifier:

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@ Elfin...

You subject question and it's answer is rather complex, as there are inherent "unknowns"

However, you might find this site www.physicsforums.com to be assistive.

Should you go there please let us know what you find as a possible answer. Some of their experts and Mods are VERY high end.

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It does not make sense though to state that the universe is revolving around you. Just consider the gravitational attraction necessary to cause the entire universe to revolve around you, the forces required just are not there. The earth would have to be the most massive black hole in the universe to put it lightly to even consider this. You have to consider everything, forces and motion are intertwined and one does not make sense without the other. If you consider forces, mass, inertia, etc. in your thinking then no it does not make sense to think of it this way. Rotational motion is a little different than linear motion which is what is usually talked about in the context of relativistic motion.

So the basic maxim of relativity, that you it doesn't matter from which point you view things, isn't actually true?

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From the point of view of either of the two points that may be true. However, in order to get a more accurate observation, one would have to observe both points from a third "neutral" position, and observe the movement relative to each other. When a car moves past a parked car, the parked car appears to whiz by from the perspective of the moving car, however, a pedestrian on the sidewalk could see that one car is moving and the other isn't. Same principle would apply even on a cosmic scale.

There is no "neutral" position in relativity.

Edited by Elfin

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@ Elfin...

You subject question and it's answer is rather complex, as there are inherent "unknowns"

However, you might find this site www.physicsforums.com to be assistive.

Should you go there please let us know what you find as a possible answer. Some of their experts and Mods are VERY high end.

It seems a bit out of my league. The only unknown, as far as I am aware, is that the universe might be even bigger, or perhaps even infinite, which would only compound the problem.

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If you truly want an answer, I'd go ask this on physicsforums as pallidin suggested. Many of the site's members are quite knowledgeable in their fields and you would most certainly learn the answer.

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It's interesting how no one has actually provided an answer to this, apart from some vague assertions, completely unencumbered by evidence, that time itself changes. But let's just think about this for a moment. If the outer reaches of the known universe are travelling round, relative to the earth, at about 100 trillion times the speed of light (as the maths tells us they are), but from the point of view of the earth, they can never go faster than the speed of light, then the earth must be at the centre of a vast, ever increasing spiral of light waves, building up inexorably at a rate of 100 trilliion revolutions to 1, all the time.

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physicsforums has a forum specifically for general and special relativity. Ask your question there.

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I asked it here, in the hope of getting an answer here. I'm not going to join a whole other forum dedicated to a subject I have only a tengential interest at best, just to ask one question.

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It's interesting how no one has actually provided an answer to this, apart from some vague assertions, completely unencumbered by evidence, that time itself changes. But let's just think about this for a moment. If the outer reaches of the known universe are travelling round, relative to the earth, at about 100 trillion times the speed of light (as the maths tells us they are), but from the point of view of the earth, they can never go faster than the speed of light, then the earth must be at the centre of a vast, ever increasing spiral of light waves, building up inexorably at a rate of 100 trilliion revolutions to 1, all the time.

Time itself has been observed to slow down relative to an objects velocity and distance from a gravity well. In fact, modern gps satellites are programed to take this change into account. My best hypothesis is that we'd see the edge of the universe rotate until eventually it seems to go at a steady rate at near the speed of light. However we would be seemingly unaffected, as time for us would appear to be going at its present rate. To an outside observer, we'd probably moving very slowly relative to them.

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It seems a bit out of my league. The only unknown, as far as I am aware, is that the universe might be even bigger, or perhaps even infinite, which would only compound the problem.

If you fold the universe in half a centre can be concieved ... to do this the universe would have to be finite... or motionless.

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Rereading your OP, I think perhaps that you are confusing the lack of absolute reference frame with your thought that there is no difference between observing a moving object from a stationary object.

If I recall about the reference frames, what it more accurately means is that if there are two observers, A and B, and one is moving and the other is not, neither one can determine which of them is the one moving. Or if both are moving, neither one can determine their velocity or that of the other, only the sum of their velocities. If there was another external frame of reference, such as a third observer, then the velocities could be determine.

It is not that there is no difference between observing a moving object from a stationary object or vice versa, but more accurately neither can determine which one is moving, or at which velocity if both are.

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This kind of reminds me of Mach's principle:

You are standing in a field looking at the stars. Your arms are resting freely at your side, and you see that the distant stars are not moving. Now start spinning. The stars are whirling around you and your arms are pulled away from your body. Why should your arms be pulled away when the stars are whirling? Why should they be dangling freely when the stars don't move?

http://en.wikipedia.org/wiki/Mach%27s_principle

Also Godel metric, which is a solution to Einstein's theory of relativity in which the universe is rotating, causing closed timelike curves which allow time travel. An observer that travels on a trajectory in spacetime along this curve may return to an event before his departure.

Also, what you see depends on which direction you look relative to the universe's rotation.

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