25 ms·
The young centre of the Earth (2016)
- madengr 7y agoWhat's the deepest core sample; 10 km? I assume isotope dating is no where near accurate enough to see the difference.
- distant_hat 7y ago10 kms would not show any effect at all. The difference in gravity would be too low and mixing in the crust high.
- danbruc 7y agoEven if it were accurate enough, I think plate tectonics moves the crust around enough such that one would have a hard time finding a piece of rock that has been more or less always in the same depth. And I have no idea how static the core is, maybe even it undergoes some mixing process over long enough periods of time.
- dredmorbius 7y agoIf there are any such stable deep-crust locations, they're most likely located under a continental location rather than oceanic, if my understanding is correct. Ocean basins reform at a higher rate (and hence: are more-recently-exposed crust) than continental plates. The very oldest regions are two locations, presently in South Africa and Australia, previously joined, dating back several billions of years. The Jack Hills region in Australia has been dated to 4.4 billions of years (the Earth itself is 4.5 billion): https://www.nationalgeographic.com/news/2014/2/140224-oldest-crust-australia-zircon-science/ https://www.nationalgeographic.com/news/2014/2/140224-oldest... A region presently under Greenland was dated to 3.8 billion years, in 2007: https://www.newscientist.com/article/dn11438-oldest-chunk-of-earths-crust-ever-found/ https://www.newscientist.com/article/dn11438-oldest-chunk-of... The Nuvvuagittuq Greenstone Belt, near Hudson Bay, Canada, has been dated to between 3.7 and 4.3 billion years old: https://en.wikipedia.org/wiki/Nuvvuagittuq_Greenstone_Belt https://en.wikipedia.org/wiki/Nuvvuagittuq_Greenstone_Belt All of these are surface rock. My thought is that drilling from these locations might find very old subsurface structures as well. Though whether any relativistic time dilation could be observed is hard to say.
- girishso 7y ago12 km to be precise, of the earth’s 6000 odd km radius. That’s all we could accomplish in entire human history. https://www.smithsonianmag.com/smithsonian-institution/ask-smithsonian-whats-deepest-hole-ever-dug-180954349/ https://www.smithsonianmag.com/smithsonian-institution/ask-s...
- woah 7y agoHow 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?
- bityard 7y agoGeneral Relativity
- wlesieutre 7y agoParent comment is making a joke about “year” as a unit measuring how many times you go around the sun. Less time has passed for the core per relativity, but is it not the same number of years? The more official definition of years defines it in terms of days, which break down further to SI’s rigorously defined second as the base unit of time. But it’s still weird to think about.
- bladedtoys 7y agoUnless the second is defined on a Hubble flow co-moving observer, it's ill-defined enough to be ambiguous by at least 2 years out of 4 billion.
- wlesieutre 7y agoYes, you wouldn't be able to measure it accurately, but it's nonetheless a static amount of time unrelated to the Earth's orbital period. I'm not an astrophysicist, but I'd guess the Earth's orbital period isn't quite the same as when the planet first formed either. So using today's defined measurement of "years", the planet's age and the number of times it's been around the sun might not match up at the surface either. The impact that formed the moon must have changed our velocity a bit, right? And the sun has been losing mass (into energy via fusion) since it first formed.
- furyofantares 7y agoThat explains how it can be ...does the conversion... 75 megaseconds younger, but the whole of the earth modulo ejected material like spacecraft should be the same number of _years_ old.
- dashesyan 7y agoThere's a "yo momma" joke just waiting to be made here...
- keanebean86 7y agoAccording to General relativity your mom is actually more attractive compared to other mothers...
- gumby 7y agoThis only works because the core is denser than the surface. (hint: imagine the limit case where the earth were a hollow sphere)
- nyc640 7y agoThey calculated the 1.5 years assuming a homogenous Earth (equal density throughout), so this is not true. The 2.5 years is calculated using a more realistic density distribution for the Earth.
- pdonis 7y ago> imagine the limit case where the earth were a hollow sphere If it were a hollow sphere with the same total mass as our actual Earth, as measured from the outside, then clocks everywhere inside the hollow sphere would run slow relative to clocks just on the outer surface of the sphere, by roughly the same amount as clocks at the center of the actual Earth. The "clock rate" in the interior of the sphere's material would decrease a lot faster, per unit distance down from the outer surface, than it does in our actual Earth, because the material of the hollow sphere would have to be a lot denser than the material of our actual Earth, in order to have the same total mass.
- gumby 7y agoWhat is the force of gravity at any point in such a sphere? So what does GR have to say?
- lalaithion 7y agoThe force of gravity is 0. But the potential of gravity is higher than on the outside, so clocks run slower.
- pdonis 7y ago> the potential of gravity is higher than on the outside, so clocks run slower Correction: the potential of gravity is lower inside the sphere than outside, so clocks run slower.
- nyc640 7y agoHere is a more accessible explanation for those (like me) who are unfamiliar with the maths: https://www.sciencealert.com/earth-s-core-is-2-5-years-younger-than-its-crust-thanks-to-the-curvature-of-space-time https://www.sciencealert.com/earth-s-core-is-2-5-years-young...
- civilian 7y agoFrom that article: > 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. Wow!
- p1esk 7y agoWhat about the center of a black hole? Is it younger than the surface?
- zamadatix 7y agoBlack holes are a singularity. They have an even horizon but it's not really a surface of an object it's just a place in space where certain conditions occur. What happens underneath that horizon (and in the singularity) isn't solidly known.
- Filligree 7y agoThe question is slightly ill-formed. I understand why you'd ask it, but there are a couple of possible answers, none of which work directly. - No, because a black hole has nothing underneath the event horizon. (This is true from the perspective of anyone outside it, at least to a first approximation. Gravity is affected by curvature, and whatever might be in the centre cannot be the cause of the event horizon, except historically, but the event horizon is stable in itself. It's a self-sustaining cascade of space-time.) - Mu, because once you pass the event horizon the extreme warping of space-time turns "inwards" into "future", making the centre of the hole a point in time, not space. This makes it difficult to determine what the question is asking. - Maybe, because singularities probably don't exist. There should be something in the centre, which might evolve over time. It might just be a faster-than-light cascade of space-time, though. We still can't answer your question, because we don't know how to accurately model the 'singularity'. (As anything other than a singularity, and that's essentially just the math giving up.)
- redblacktree 7y ago> self-sustaining cascade of space-time I am in awe of these words and fail to understand them in equal parts.
- qubex 7y agoThe way I usually explain it is that gravity is a form of energy, and that energy has mass, and that at the event horizon the energy of the gravity is exactly sufficient to maintain the gravity itself, basically becoming a self-powering loop of gravitational energy.
- spuz 7y agoDoes the same apply to the Sun? How old is the centre of the Sun compared to its surface?
- lisper 7y agoThere'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.
- Kutta 7y agoThere is no convection in the core of the sun. It is plausible that material has mostly stayed there since the formation of the sun.
- lisper 7y agoHeh, you're right. TIL.
- dredmorbius 7y agoWhat form(s) of motion are there, if any, according to theory? (I'll presume ... direct observations ... are limited.)
- pdonis 7y ago> 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 Correction: "younger", not "older".
- kstrauser 7y agoIt 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?
- deleted 7y ago[deleted]
- ajkjk 7y agoIt's not the gravitational force that determines the relative passage of the time but the gravitational potential, which can be much higher despite not experiencing any force.
- kstrauser 7y agoOh, interesting. Thanks for the clarification!
- blix 7y agoThe gravitational forces at the center do cancel out, but the important term for this effect is not the sum of forces but the gravitational potential, essentially the energy gained/lost by moving from deep space to the given location. Force is the derivative of this potential, so the abscence of forces in the center indicates an extremum.
- hirundo 7y ago> Comments: Published version, apart from minor editing (e.g. corrections of 'center' to 'centre') > Journal reference: Eur.J.Phys. vol. 37, 035602 (2016) If Brexit occurs, Britain will no longer be a European nation, and therefore the European Journal of Physics will no longer be obliged to accept "centre" as the standard spelling of "center", right?
- pmontra 7y agoThe UK will no longer be a European Union country but it will definitely keep being European. And I guess Ireland has a "centre" too.
- tasssko 7y agoWe will most certainly still be a European nation. Just not a member of the European Union. We are still located on the European continent. Its spelled centre.
- hirundo 7y ago“Some years ago I opined that London was not really an English city any more. Since then, virtually all my friends from abroad have confirmed my observation So there must be some truth in it.” -- John Cleese In that sense, perhaps London remains a European city while still the capital of a not really European nation.
- anonymfus 7y agoEuropean Physical Society which produces this journal is unrelated to EU, national physical societies have its membership directly without involvement of their countries' governments. IOP Publishing which publishes this journal is based in UK. "IOP" in "IOP Publishing" is Institute of Physics which is also based in UK. Equating being "a European nation" with EU membership is surely a trolling.
- mechatrocity 7y agoCentre is the standard for all English countries except the US, no? We use centre in Canada
- bregma 7y agoIt's all a wibbly-wobbly, timey-wimey big BIG ball of string.
- tomxor 7y ago> The pedagogical value of this discussion is to show students that any number or observation, no matter who brought it forward, must be critically examined. Excellent, I hope this value is also encouraged more in schools now than when I was there.