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The AEL Goes AudioVisual (Astrophysics)
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EndlesslyRocking



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Mick Harper wrote:
As you know, Applied Epistemologists can only proceed by observed facts (o.n.o.) so we take as our text the last time the Pole shifted. Which was during the Indian Ocean tsunami.

I found this remark in a book today (in the context of considering whether or not people could have seen stars during the eclipse in Athens in 431 BC):

A recent event seemed to undermine the reliability of the [assumptions regarding Athens]: the huge Asian earthquake that triggered the deadly tsunami on Boxing Day 2004. According to Richard Gross, a geophysicist with NASA's Jet Propulsion Laboratory in California, a shift of mass towards the Earth's centre during the quake caused the planet to move one-millionth of a second faster and tilted its axis at the poles by 2.5 centimetres.
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Mick Harper
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In: London
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Yes, all this sort of stuff is most gratifying. For years I had to put up with people telling me that the mass of the earth was so gynormous that any theories that proposed terrestrial forces could effect it had to be ruled out of court immediately. Then the first big(gish) thing that came along (the tsunami in this case) proved very much the contrary.

Nearly as gratifying as when I was being earnestly assured on all sides that my proposal that water in quite small volumes would trigger earthquakes was an error-of-scale. Then we discovered that the lake caused by the Hoover Dam triggered earthquakes as it filled up. How people apologised. Not.
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DPCrisp


In: Bedfordshire
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Bear in mind, though, that they're saying the axis/Earth tilted by 2 ten-millionths of a degree: not that the position of the pole shifted with respect to geography. I don't think they measured it either.
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Mick Harper
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I remember we discussed it at the time on the other site and 'they' said it was the Pole that moved and they did say by how much. I then scaled it up from a tsunami to something a bit bigger and arrived at the correct ballpark.

'Course I'm not saying that I trust any ballparks in this particular sport but the AE point is that when paradigms are in play, errors of scale are quite likely to be held by orthodoxy. For instance we never resolved at the time of the Treasure Hunt whether a gyroscopic earth is so unbelievably stable that it would require something truly cosmic to shift it, or so unbelievably finely balanced that any old terrestrial tremor might effect it. But along came the tsunami and orthodoxy was obliged to shift hurriedly from the "nothing can move it" position to the "Did ya see that, begorrah, whodabelievedit?" camp.
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DPCrisp


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But along came the tsunami and orthodoxy was obliged to shift hurriedly from the "nothing can move it" position to the "Did ya see that, begorrah, whodabelievedit?" camp.

Leave it aht. There's nothing to see: no one measured a 1 inch movement of the Pole. The orthodox position has always been (something like) "we know how to do mechanics on rotating bodies... angular momentum is conserved... the moment of inertia was affected like so by a huge chunk of sea bed moving this much, which means there must be another 2 ten-millions of a degree in the wobbling of the axis."

We can only go by what was reported, of course, but even if they mean the axis permanently tilted by that amount, they are still not having to change camps: the tilt is continuously susceptible to influences to such-and-such known extents.

I think they are talking about the orientation of Earth, rather than the position of the Pole (the Equator, the Prime Meridian...) with respect to surface geography.


we never resolved at the time of the Treasure Hunt whether a gyroscopic earth is so unbelievably stable that it would require something truly cosmic to shift it, or so unbelievably finely balanced that any old terrestrial tremor might effect it.

What does your intuition tell you, Mick? You experience inertia in a car journey, being pushed into the seat, restrained by the belt, pushed sideways in a curve... It's all about forces being transmitted through this and that.

Imagine what you're asking of a Pole-Shift-with-respect-to-geography. Ben Nevis only goes in circles because it's stuck to the rest of Scotland, which is stuck to... which is stuck to... which is stuck to... which is stuck to Ben Nevis... To shift the Pole to Ben Nevis would require it to stop going at 600 miles an hour round a 14,000 mile circle and spin on the spot instead. The current Pole must do the opposite. Every point in and on Earth must be pushed into a new trajectory.

The principles are calculable in exactly the same way for a toy gyroscope and for Earth, but what do you think the forces are like for the latter?

I can't quantify it either. I'm not even sure that any internal forces could achieve it. (Compare: the location of a system is given as the location of its centre of gravity; because of the equal-and-opposite reaction thing, no amount of shuffling things within the system can change it's position; that's what "within the system" means. Only an external force will move the CoG and I suspect the axis is treated in the same way for a rotating system: only an external force can move the axis with respect to the body. And an external force sufficient to move the axis without changing the orbit as well would be peculiar indeed. I think the same goes for permanently reorienting the whole body/planet/axis: even with external forces you get precession and stuff rather than a finite change in alignment. Pole "Shift" might not be applicable under any natural circumstances.)
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Mick Harper
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The orthodox position has always been (something like) "we know how to do mechanics on rotating bodies... angular momentum is conserved... the moment of inertia was affected like so by a huge chunk of sea bed moving this much, which means there must be another 2 ten-millions of a degree in the wobbling of the axis."

You're always so trusting, Dan. All I can say is that I spent twenty years being completely assured that the earth was mega-stable. Science just doesn't understand the physics of large bodies. What they know is the physics of small bodies and then they scale it up and, yes, doubtless there are a few people who claimed it to be unstable and this is what is wheeled out when the unstable position looks to be true. But uniformitariansim ruled before then, believe me. The earth couldna move. The constantly shifting earth will be seamlessly embraced in its turn.

We can only go by what was reported, of course, but even if they mean the axis permanently tilted by that amount, they are still not having to change camps: the tilt is continuously susceptible to influences to such-and-such known extents.

Well clearly then they have spent the last several decades showing the effect of plate tectonics on the shifting axis....oh, woops, they seem to have forgotten to do this...

I think they are talking about the orientation of Earth, rather than the position of the Pole (the Equator, the Prime Meridian...) with respect to surface geography.

It's true I get thoroughly confused in most matters of spatial geometry (I think I'm a girl deepdown) but frankly I don't give a rat's arse. As long as I can shift the globe around that'll do for me.

What does your intuition tell you, Mick? You experience inertia in a car journey, being pushed into the seat, restrained by the belt, pushed sideways in a curve... It's all about forces being transmitted through this and that.

That's right and it's why I could never understand why my elders-and-betters seemed never to take car journeys.

Imagine what you're asking of a Pole-Shift-with-respect-to-geography. Ben Nevis only goes in circles because it's stuck to the rest of Scotland, which is stuck to... which is stuck to... which is stuck to... which is stuck to Ben Nevis... To shift the Pole to Ben Nevis would require it to stop going at 600 miles an hour round a 14,000 mile circle and spin on the spot instead. The current Pole must do the opposite. Every point in and on Earth must be pushed into a new trajectory.

Yes, that's about it. Keep working at the detailed scenarios while I sketch out the big picture.
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DPCrisp


In: Bedfordshire
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As long as I can shift the globe around that'll do for me.

No it won't: you need the hot and cold bits to move around.
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Rocky



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There is proof in fossils of trees that the days used to be only 18 hours long and so the Earth used to rotate 487 times a year, because the moon used to be closer and it looked bigger in the sky. Eventually, the moon will stop moving away from the Earth and when that time comes, the Earth would be tidally locked to the moon like the moon is to the Earth.


- At AE, is this statement believed?
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Chad


In: Ramsbottom
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Rocky wrote:
There is proof in fossils of trees that the days used to be only 18 hours long and so the Earth used to rotate 487 times a year, because the moon used to be closer and it looked bigger in the sky. Eventually, the moon will stop moving away from the Earth and when that time comes, the Earth would be tidally locked to the moon like the moon is to the Earth.


- At AE, is this statement believed?


Rocky, I really could do with finding out more about this. Would you care to share the source? ... Pretty please!
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Ishmael


In: Toronto
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Rocky wrote:
- At AE, is this statement believed?


I don't believe the Earth ever rotated in just 18 hours.

There is no proof of this in tree fossils. Some features observed in tree fossils may evidence that notion, but a simpler explanation may yet account for that same evidence. We shall see.
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Rocky



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Chad wrote:
Rocky, I really could do with finding out more about this. Would you care to share the source? ... Pretty please!


Here's the source: http://answers.yahoo.com/question/index?qid=20081114103927AAGnvNq

Sorry about that. Sometimes I misjudge whether anyone would be interested in the source or not.
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Rocky



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Ishmael wrote:
There is no proof of this in tree fossils. Some features observed in tree fossils may evidence that notion, but a simpler explanation may yet account for that same evidence. We shall see.


Yes, and if the change had been gradual wouldn't there be evidence that days used to be 19.5 hours, 22.1 hrs, ..., etc?
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Brian Ambrose



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Any evidence that in the past the earth rotated much faster than now is useful support for the idea that the Earth was once much smaller. Interesting that the source says the Earth rotated faster because the moon was closer. I wonder why. But I do agree that the moon will eventually stop moving away from the Earth (and was therefore closer in the past), and that the Earth will become tidally locked to it.
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Komorikid


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Ish wrote:

I don't believe the Earth ever rotated in just 18 hours


This not a statement of fact but belief.

There is no proof of this in tree fossils.


No proof that you are willing to accept.

Some features observed in tree fossils may evidence that notion, but a simpler explanation may yet account for that same evidence.


It's amazing that someone who professes such unorthodox thought can use such orthodox statements when a pet theory is at stake.

It is not just tree fossils that evidence a variable rotation rate in the past but geological studies of marine bi-valves, corals, stromatolites etc. It can also be inferred from the current rotation anomaly.

The Earth's rotation has never been constant. It is affected by the Moon's drag and the increase in gravity that has also happened since the time of the dinosaurs.

You didn't know that Gravity is not constant?

How do you think 40-80 ton sauropods actually walked around on the earth back then?

The African elephant is the largest possible terrestrial animal, given its body weight and biometric structure that can exist under the present gravity on Earth. And even it has limitations (slopes it can traverse and ability to stand from a laying position).

It is gravitationally impossible for dinosaurs to have existed and flourished with the present gravitation environment we experience.

Gravity and therefore rotation has changed.
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Grant



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Komorikid wrote
How do you think 40-80 ton sauropods actually walked around on the earth back then?

And just as strange, how did pterosaurs use membranes to build 20 foot wings when today the largest creature with a membraneous wing is a bat?

Maybe the Earth fluctuates in diameter. Before the dinosaurs it was small, and the largest creatures were about the size of a horse. Then it expanded and the gravity reduced to 80% of its present level allowing the dinosaurs to grow so big. Since then it has been contracting (or oscillating?).
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