5 ms·

I think something is being poorly explained, because that's a lot - a very big lot - of angular momentum that's got to go somewhere or come from somewhere.

deleted 4y ago
[deleted]
mcdonje 4y ago
So, I think the headline is a little misleading. The article talks about the core spinning in relationship to the earth's spin. So, the disputed claim is that it has been spinning faster than the earth, and it's going to be spinning slower than the earth. It's not stopping or reversing. As for what would cause it to slow down or speed up with relationship to the speed of the planet's spin, they just say "magnetic and gravitational forces", whatever that means.
sliken 4y ago
Well keep in mind that it's not the rotation that's stopping, or reversing. So far there's debate, but the data supports the core is spinning 0.1 degrees per year faster or slower. Other researchers think it's changes in the surface of the core (not the rotation). What we do know is that earthquakes show waves that travel slightly faster or slower than we'd expect if the core's rotational speed was constant with the rest of the planet. But overall it's nearly in the noise compared to the other energies involved. The flows involved are turbulent and move like fluids, but at the pressures and viscosties involved they change rather slowly. Some models show it switching from slightly faster (0.1 degrees per year) to slightly slower ever 35 years or so.
- luxuryballs 4y ago
  if the waves don’t behave how we expect maybe we just don’t understand how we should expect them to behave, it seems like a lot of assumptions have to be made in order to make any broad conclusions from such readings
  - sliken 4y ago
    Sure, it's under heavy debate. While the idea or the planet spinning at different speeds weird to think about, the physics do work out. After all not like the atmosphere spins at exactly the same speed as the planet. Why should the core of the planet in a pool of magma spin at exactly the same rate? The discussed difference is only 0.1 degrees per year, on the surface of the planet that's only 7 miles. So what's under the surface today might be 7 miles different in a year. The movement that deep is quite a bit less than 7 miles since the circumference at that depth is much less. Additionally it's not rock and dirt at that depth, but a liquid magma with an average speed of a foot a day is not too surprising. Humans think of these things as constant, but the length of the day and the distance of the moon are changing because tides are transferring rotational energy of the earth into the moon. Said forces aren't directly impacting the spin of the core, so it might well be catching up and oscillating around the speed of the earth's rotation every 35 days.
someweirdperson 4y ago
Maybe earth is a cat. They can flip themselves around while in the air without exchanging momentum with anything.
rolenthedeep 4y ago
Not a geophysicist so I'm just spitballing: the earth's magnetic field is mainly generated by the motion of the liquid outer core. I think the hypothesis here is that the magnetic field is exerting some force on the inner core causing it to slow or speed up. But yes, there is an absolutely absurd amount of energy in this scenario. On the scale of "let's stop the moon spinning" big. Even at the scale of slowing from one degree of rotation per year to zero degrees over a few decades, it's a lot of energy. And that's not even counting all of the other energy drains in this system, like turbulence between the outer and inner cores from rotating at different rates, or the magnetic field of the inner core fighting the outer core. The amount of energy involved is just absolutely bonkers.

deleted 4y ago

[deleted]

mcdonje 4y ago

So, I think the headline is a little misleading. The article talks about the core spinning in relationship to the earth's spin. So, the disputed claim is that it has been spinning faster than the earth, and it's going to be spinning slower than the earth. It's not stopping or reversing. As for what would cause it to slow down or speed up with relationship to the speed of the planet's spin, they just say "magnetic and gravitational forces", whatever that means.

sliken 4y ago

Well keep in mind that it's not the rotation that's stopping, or reversing. So far there's debate, but the data supports the core is spinning 0.1 degrees per year faster or slower. Other researchers think it's changes in the surface of the core (not the rotation). What we do know is that earthquakes show waves that travel slightly faster or slower than we'd expect if the core's rotational speed was constant with the rest of the planet. But overall it's nearly in the noise compared to the other energies involved. The flows involved are turbulent and move like fluids, but at the pressures and viscosties involved they change rather slowly. Some models show it switching from slightly faster (0.1 degrees per year) to slightly slower ever 35 years or so.

luxuryballs 4y ago
if the waves don’t behave how we expect maybe we just don’t understand how we should expect them to behave, it seems like a lot of assumptions have to be made in order to make any broad conclusions from such readings
- sliken 4y ago
  Sure, it's under heavy debate. While the idea or the planet spinning at different speeds weird to think about, the physics do work out. After all not like the atmosphere spins at exactly the same speed as the planet. Why should the core of the planet in a pool of magma spin at exactly the same rate? The discussed difference is only 0.1 degrees per year, on the surface of the planet that's only 7 miles. So what's under the surface today might be 7 miles different in a year. The movement that deep is quite a bit less than 7 miles since the circumference at that depth is much less. Additionally it's not rock and dirt at that depth, but a liquid magma with an average speed of a foot a day is not too surprising. Humans think of these things as constant, but the length of the day and the distance of the moon are changing because tides are transferring rotational energy of the earth into the moon. Said forces aren't directly impacting the spin of the core, so it might well be catching up and oscillating around the speed of the earth's rotation every 35 days.

someweirdperson 4y ago

Maybe earth is a cat. They can flip themselves around while in the air without exchanging momentum with anything.

rolenthedeep 4y ago

Not a geophysicist so I'm just spitballing: the earth's magnetic field is mainly generated by the motion of the liquid outer core. I think the hypothesis here is that the magnetic field is exerting some force on the inner core causing it to slow or speed up. But yes, there is an absolutely absurd amount of energy in this scenario. On the scale of "let's stop the moon spinning" big. Even at the scale of slowing from one degree of rotation per year to zero degrees over a few decades, it's a lot of energy. And that's not even counting all of the other energy drains in this system, like turbulence between the outer and inner cores from rotating at different rates, or the magnetic field of the inner core fighting the outer core. The amount of energy involved is just absolutely bonkers.