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The young centre of the Earth (2016)

arxiv.org

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Re: The young centre of the Earth (2016)

#21

Post by bluedevil2k »

stingraycharles wrote: post #10
woah wrote: post #5

How is it possible that the core is several years younger if the core and the surface have gone around the sun the same number of times?

Mass, gravity and general relativity. It’s a fascinating and very counter-intuitive at some moments, such as this. Same goes for people that stay on the moon, when they go back to earth their watches are slightly different than those on earth. GPS satellites need to be synced with earth clock periodically as well for this reason.

The GPS satellites have multiple general relativity effects on their definition of time. Since they're moving so fast, the internal clocks on the satellites move slower than Earth (about 7 microseconds a day), while the decreased gravity on the satellites causes the internal clocks to speed up compared to Earth (45 microseconds a day). Net effect is a speed up of 38 microseconds.

Also, the on-board chips are pre-programmed to take into account the relativistic effects and compensate when doing their calculations.

Re: The young centre of the Earth (2016)

#22

Post by Uhuhreally »

woah wrote: post #5

How is it possible that the core is several years younger if the core and the surface have gone around the sun the same number of times?

because spacetime is curved by mass the matter in the centres of the Earth and Sun computes at a slower rate than matter at their surfaces so that from our point of view the centres of the Earth and Sun are younger because their clocks have ticked fewer times compared to their surfaces

Re: The young centre of the Earth (2016)

#23

Post by lisper »

spuz wrote: post #17

Does the same apply to the Sun? How old is the centre of the Sun compared to its surface?

There's a little bit of smoke-and-mirrors going on here. Yes, the same effect happens on/in the sun (in fact it's even more extreme because the sun's gravitational field is much stronger than earth's). But no, it's not quite correct to say that the center of the sun -- or of the earth for that matter -- is "older" than the surface because the material in both bodies moves around. If you put a clock at the center and another synchronized clock at the surface and left them running for a few billion years and then compared them, you'd see a difference. But of course there are no such clocks. The only "clock" is the material that exists in both locations, and in all cases this material moves around over time. On earth there is some stability because heavier material sinks towards the center and more or less stays there, while lighter material floats to the surface and again more or less stays there. But the sun is made almost entirely of hydrogen and helium and that material is constantly being moved around due to convection.

Re: The young centre of the Earth (2016)

#24

Post by kstrauser »

It seems like it would be the opposite:

- If you are smack dab in the middle of the Earth, although you'd be mashed, gravitational forces should be equal in all directions and therefore cancel out to zero.

- Ergo, if you are on the surface of the Earth, gravity should make your clocks run slower than in the middle.

What am I missing that makes this untrue?

Re: The young centre of the Earth (2016)

#26

Post by Rooster61 »

woah wrote: post #5

How is it possible that the core is several years younger if the core and the surface have gone around the sun the same number of times?

In addition to the other excellent comments about general relativity, a "year" is only valid in expressing the time it takes to go around the Sun right NOW, not the entire existence of the Earth. The Earth's orbit has shifted throughout the lifetime of the solar system. A year circa 1000000 B.C. isn't the same as the year circa recorded history if we are considering it one revolution. so that number wouldn't represent the number of times it's gone around the Sun even excluding relativistic effects.

Re: The young centre of the Earth (2016)

#27

Post by Zenst »

woah wrote: post #5

How is it possible that the core is several years younger if the core and the surface have gone around the sun the same number of times?

https://en.wikipedia.org/wiki/Gravitational_time_dilation

Now a detail that really makes things more interesting is that gravity is not constant upon the surface ( https://svs.gsfc.nasa.gov/11234 ), due to mass variations. So with that, it would be interesting to work out the age difference as a surface map. Though would need to historically adjust for tectonic shifts and other effects upon the surface mass. Of course the difference won't be as large, but still, I'd dare say that a day or so, would be more than viable upon the scale of things.

Re: The young centre of the Earth (2016)

#28

Post by colechristensen »

woah wrote: post #5

How is it possible that the core is several years younger if the core and the surface have gone around the sun the same number of times?

Time isn't universal, it doesn't tick for everybody at the same rate, in fact every particle has its own unique clock.

One thing that changes how your clock flows is being in a gravity well. We have clocks which can measure it over just a few feet of height difference. Gravity isn't so much a "force" but the bending of space and time. Clocks moving differently is the result.

Re: The young centre of the Earth (2016)

#29

Post by shroom »

spuz wrote: post #17

Does the same apply to the Sun? How old is the centre of the Sun compared to its surface?

”If you want an even more stark illustration of gravity’s effect on time, take the Sun - the team calculates that the Sun’s core is around 40,000 years younger than its surface.”

https://www.sciencealert.com/earth-s-core-is-2-5-years-young...

Re: The young centre of the Earth (2016)

#30

Post by ryanmercer »

Rooster61 wrote: post #26
woah wrote: post #5

How is it possible that the core is several years younger if the core and the surface have gone around the sun the same number of times?

In addition to the other excellent comments about general relativity, a "year" is only valid in expressing the time it takes to go around the Sun right NOW, not the entire existence of the Earth. The Earth's orbit has shifted throughout the lifetime of the solar system. A year circa 1000000 B.C. isn't the same as the year circa recorded history if we are considering it one revolution. so that number wouldn't represen…

> The Earth's orbit has shifted throughout the lifetime of the solar system.

I'm by no means qualified to state this as fact but also I imagine that as we travel through space and hit random stuff in space (meteors, particles from stars, comet trails etc) we ever so slightly change our speed outside of the gravitational influences of other bodies, it would probably be incredibly small fractions of a second over centuries but it's something.

I wonder how much of an effect something like an extinction event asteroid on the speed of the earth both around the sun and on its rotation on its axis.

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