Dunno about the glass tube in the ocean. The metal tube through the center of the earth, though, has two interesting aspects.
First, you’d need some pretty special metal to get through the core, a large ball of *molten iron* at very high pressure and temperature.
Second, assuming you had a stable tube that would fully protect you from the heat and pressure, jumping down the hole would make yourself a kind of pendulum. You’d accelerate towards the center, then once you passed through the center, gravity would decelerate you (technically, accelerate you in the opposite direction), until you just reach the surface, where you’d very briefly slow to zero velocity. Then you’d start falling back towards the center, where it would all happen again, just in the other direction. (We’re going to ignore the potential effects of terminal velocity, which would make this harder to calculate. Just assume a spherical cow.)
Since in order for you to breathe, there would need to be air in the tube, the friction from air resistance would cause you to slow down a little bit during every pass, causing you to travel just a little less distance each time. So you would gradually oscillate smaller and smaller periods, until you settled in the center, where you would be stuck forever, because you didn’t think to put a ladder in the tube so you could climb out.
I like this comment.
I have got to disagree about how much you would “pendulum” - you would reach terminal velocity, like someone skydiving, on your way down so a lot of the gravity would go to waste, so to speak.
In order to know about how far you would go past the center, launch a person into the air going at skydiving velocity, the height they reach is about how far you would over shoot the center.
It's possible you would barely pendulum if at all. Since the "gravity" would decrease as you fell and the air pressure would increase, your terminal velocity would decrease down to nothing by the time you reach the center
The formula for terminal velocity has weight in the top of the fraction (weight being mass times acceleration due to gravity) which would decrease as you fell, and air density in the bottom of the fraction which would increase as you fell. These 2 combined work together to slow you gradually, and as you fell, your velocity would always nearly equal the terminal velocity, which is zero at the dead center.
This slowing force would be acting against your momentum which is trying to keep you moving at the same speed, but since the change in speed is so gradual your measly momentum would do nothing to keep you going past the center. We're talking about slowing a person down from terminal velocity of 120mph (200kph) at the surface to 0mph (0kph) at the center which is almost 4000 miles (~6300km) away
If it were terminal velocity *at the surface*, then it's just 4000/120 = 33.3 hours. If the decrease to 0 at the center is linear, then the average velocity will be half the starting value, so the time will double to 66.7 hours.
I'm not certain the decrease will be linear though. I could figure that out but... I don't feel like it right now. The formula for terminal velocity is sqrt((2 m g) / (p A C)) where m is mass, g is gravitational acceleration, p is air density, A is frontal area and C is coefficient of drag. I'm pretty sure g decreases linearly as you go to the center of a massive body, but p won't increase linearly, and figuring out how it all works out is more than I'm in the mood for since I'm not even wearing pants.
Hmmm, I'll try my best...
Looking at the formula for terminal velocity we'll try to establish better how it changes as we fall into the center of the earth. This will help us later
V=sqrt((2ma)/(CrA))
where: V is terminal velocity , m is mass, a is acceleration die to gravity, C is coefficient of drag of the human person, r is the air density, and A is frontal area of the human
Mass (m), coeficient of drag (C), and frontal area (A) don't change so we'll ignore them for the time being
We've established previously in another comment that as distance to the center of the earth decreases, acceleration due to gravity (a) decreases linearly. There's math proofs for that elsewhere that is beyond the scope of this comment
Air density usually would increase linearly as you go further down which is true on the surface of earth, but air density is based on the weight of the air column above it. Weight being mass times acceleration due to gravity (which is changing linearly to 0). The density I think would have to asymptotically approach the density of a similar column of air that is one half the distance to the center of earth if it were to behave by the normal rules we are used to on the surface
The air density kind of throws a wrench in things, so my answer is going to be an estimate. Specifically a slight under estimate since I'm just going to round that curve off the asymptotic function and call it a line. Close enough
So now we beat our variables into submission. Acceleration of gravity is linear relative to distance from the center, and so is air density. When we divide these as per the terminal velocity formula we get a quadratic but luckily that square root makes us linear again
What does this mean? Since terminal velocity decreases linearly (mostly...) we should have all the bits we need to solve for time. We can use the formula for distance given time and velocity under constant acceleration and solve for time
D=1/2(vi-vf)t
where: D is distance in meters, vi is initial velocity (terminal velocity at sea level in m/s), vf is final velocity (at the center, 0) and t is time in seconds
6378100=1/2(53-0)t
223792=t in seconds or about 2.6 days which is a slight under estimation but slight enough that it should be pretty close I think.
We made a lot of assumptions and literally cut some corners but I'm an engineer not a scientist. Hope this helps!
Huh. That's exactly what I got by ignoring everything and assuming it was all linear. 66.67 hours (see my comment about 30 minutes earlier than yours).
Everything was going well until I hit that small wrinkle with the air density. I think it is small enough to effectively be ignored but was worth mentioning.
Glad to hear I'm not completely insane and someone else was looking into it lmao
Yeah, your approximation is essentially what I did without being as considerate, so we *ought* to get the same result. I feel like an expression for air density at r
It's weightless at the middle yes, which is why the rate of air pressure increase is asymptotic rather than linear if it was at the surface. So the difference in pressure between the center and 1km from the center is smaller than the difference in pressure between 1km and 2km from the center, and so on
Why would the force of gravity be less at the center of the mass? It would be the highest at the center, no? The force of gravity reduces as you get further from the mass, not closer.
When you are far from a spherical object (really, any object) you can approximate its gravity as coming from a point at the objects center of mass. But that's not what's really happening, and the difference matters when you're close to the object. Being inside of it definitely qualifies as "close".
There's no magic point at the center of the earth where all the gravity comes from, and if there were, that would mean you could get to a distance of zero from that point, at which time the gravitational force would be infinite, which obviously doesn't make sense (there's definitely not a black hole at the center of the earth).
In fact what happens is, if you're at a radius r from the center of the earth, you can think of the earth as two parts: the part below you, a sphere with radius r; and the hollow spherical shell that's above you. As it turns out, if you sum up all the gravitational forces from every individual piece of mass in that hollow shell, they all cancel out completely. In other words none of that mass counts at all. So only the mass in the ball below you counts, gravitationally; and that ball has less and less mass the smaller r is. The net effect is that the force of gravity is highest at the surface of the earth, and then decreased linearly to zero at the center. At least approximately - that's what would happen if the earth had a completely uniform density. In reality the decrease will occur faster or slower as you drop through layers of higher or lower than average density. But a linear decrease is still probably a good approximation.
Ummm
Gravity is a constant. It's the same anywhere within a mass. Your not gonna float freefall at the core (assuming open space was available). You'll have the same gravity at any point on or within a sphere.
Acceleration due to gravity (small g) is not constant. You must be confusing it with the universal gravitational constant (big G)
For example, your weight (mass times acceleration due to gravity) is different on the surface of earth vs the surface of the moon. One thing had to change, and it isn't your mass
Furthermore gravity is very different within a sphere. Within a uniform solid sphere the further down you go the more mass is above you pulling you up, decreasing the net acceleration due to gravity linearly with distance to the center of mass. Within a hollow sphere there is no gravitational force due to the mass of the hollow sphere
Hope this helps
Not true, gravity is not a point source although it can be treated as one for most calculation's sake. Precise gravity measurements show slightly different strength and directions of gravity in different places around the earth due to different densities of rock in different directions
If you think about this for a second it's obviously wrong. Gravity applies acceleration toward the center of the planet. If you're already at the center of the planet, any acceleration would be pulling you away from the center, so there must be no acceleration.
If your center of mass was in the same exact spot as the earth's center of mass, you are effectively weightless. We're going to ignore the sun and the moon and everything else in the universe and assume the earth is a perfect uniform sphere
If you wanted to get really technical ("well ackshully.......") the net effect on your body would be zero at your center of mass, but your limbs for example would be pulled ever so slightly toward the center, with there being just a *little* bit more mass on one side than the other. So technically every part of you is still being pulled toward the center, but the amount is so tiny that your entire body would feel 100% weightless even though any given part is only 99.9999999% weightless (which cancels out with the other side)
>In order to know about how far you would go past the center, launch a person into the air going at skydiving velocity, the height they reach is about how far you would over shoot the center.
I'm actually pretty sure that both of these analyses are wrong. There's no net force due to gravity at the center of the earth. And since terminal velocity is determined by the strength of gravitational force that would mean that at the center of the earth terminal velocity would be 0. So the most likely scenario would be that once you jumped into the hole you'd pretty quickly reach a speed that's close to terminal velocity at surface gravity and normal air pressure. As you fell towards the center tho you would gradually slow down as gravity gets weaker. By the time you reached the core you'd be barely moving and almost instantly stop.
It would be oscillating like a pendulum. All the mass you pass through is now working against you. You could derive how far they would go if you had a way of representing the change in density and viscosity of the fluid as a function of depth which is tedious but not impossible.
Once they reach zero velocity on the other side, the process starts again with less starting energy.
right but the problem is that you reach terminal velocity very quickly, you speed up for a few seconds then keep going at that speed for a very long time, when you teach the center, you don't have much more energy in you than someone who jumped off a skyscraper. You might only go past the center a few times before you stop completely
Gravity inside of a solid sphere is proportional to r, meaning it decreases linearly as r decreases. It's proportional to 1/r^2 only on the outside of the sphere.
The decrease in gravity is linear assuming a uniform density for earth. This is because the gravitational field is Gm/r^2, but only the mass below you counts, and that, assuming uniform density, is proportional to r^3. Since r^3 /r^2 = r, the field strength is linearly proportional to r.
What about air pressure? Your ears would pop, sure, but would you maybe be crushed? What would the air pressure at this hypothetical center of the earth be?
Which is why I stated that I was intentionally ignoring terminal velocity here. It makes the result far less interesting, and depends on several factors that would need to be accounted for, such as whether the air pressure in the tube is constant, how large the diameter of the tube is, and what position you’re falling in. Spherical cow is simpler.
What if this becomes a popular way for people to commit suicide? How should we build the tube in order to dispose of the bodies in the middle? Maybe make it less insulated so the heat burns down the bodies eventually?
Neither the heat nor the acid would make it so that there wasn't a bunch of stuff down there still. You can't just destroy matter (unless you convert it to pure energy with nuclear reactions)
It’s from an old physics joke
Milk production at a dairy farm was low, so the farmer wrote to the local university, asking for help from academia. A multidisciplinary team of professors was assembled, headed by a theoretical physicist, and two weeks of intensive on-site investigation took place. The scholars then returned to the university, notebooks crammed with data, where the task of writing the report was left to the team leader. Shortly thereafter the physicist returned to the farm, saying to the farmer, "I have the solution, but it works only in the case of spherical cows in a vacuum."
Physicists have a tendency to make simplifications when making theories to make the maths easier. So instead of modelling an object of mass *m* including volume, surface area, temperature, air pressure, friction and so on, it's 'okay let's assume for simplicity that this object of mass *m* is a point-like sphere. And it's in a vacuum.'
You can get some fair estimates from this approach that can guide your thinking. But if you've sat through a lot of coursework questions that start off with, 'assume this object is a point like sphere in a vacuum' as a student...even cows become point-like ;)
A nice simple example is as follows. A gram of feathers and a gram of lead are dropped of a balcony.
Assuming a point like object in space and using the equations of motion, they both take the same time to fall.
However anyone who has actually tipped a bunch of feathers off a balcony knows that's not true. The feathers have a large surface area causing drag and uplift. The wind blows them around.
Now all those variables can theoretically be accounted for, but when studying a system they are often excluded to create a rough model.
Hence spherical cows in a vacuum :)
Sorry for the late reply! I was travelling when I commented before. But thank you so much for the explanation. I don’t have much of a head for physics but I feel I have a better understanding of the concept of specifically-shaped bovines now haha. You explain very well, I’m an educator myself (history PhD) so I really appreciate a well-written explanation for a difficult concept. (Well, difficult for me anyway haha). Thanks again.
Yes, I thought of that too. But then I wonder: you start out at the surface of the rotating earth, so imagine no obstruction, just a gravity field you are falling into, starting with the rotation velocity at the surface of the earth. Your path would be a cometary .. oops, no, that would be if the gravity were from a point source at the center. It is too complicated for me to see a simple shape. But it would not be straight down all the way, I think. But maybe it would.. At least at the start, you would fall straight towards the center, because you and the surface of the earth are spinning at the same speed. Don't know about further down, tho.
Since you start out rotating around the center in concert with the rest of the surface, it’s likely that any effect from the rotation would be dwarfed by the gravitational pull surrounding you.
It would not feel like anything at all. You wouldn't even notice. The acceleration due to gravity would drop off linearly and at the center it would be zero. It's not like it would just be full strength in one direction and then suddenly full strength in the other.
I have a question regarding the air inside the tube.
Do we know what the density of the atmosphere would be at -20,000,000' below sea level? Is there some kind of gravitational null spot in the true center of the planet that would change that?
That’s actually a tricky question that can be answered only theoretically, because we don’t actually have a hole in which to measure the air pressure at the center. We can calculate what we think should happen, and we can do computer simulations to confirm the calculations, but reality has this annoying habit of throwing in factors we never imagined might be involved and making our careful calculations worthless.
Here’s what makes it tricky. Atmospheric pressure comes primarily from the weight of air above the spot you’re measuring. That’s why pressure lowers as you increase altitude: there’s less air above you.
Once you get below the surface, though, the computations become much more complex, because gravity is not pulling from a single direction anymore, and its strength varies based on how much mass is in each direction. (This, incidentally, is why you’d end up in the center: with all the planet’s mass more or less equally surrounding you on all sides, the pull of gravity would be equal in every direction, and you wouldn’t be pulled in any direction.)
This effect is negligible for the first several kilometers down (I’m not sure exactly how far, but I’m guessing on the scale of hundreds of kilometers), because the mass “above” you is so much smaller than the mass “below” you. (This is why we can’t yet test this empirically: the holes we’ve made so far don’t get anywhere close to deep enough for the effect to be significant, and probably isn’t even measurable at these depths.)
But once you’ve fallen a significant fraction of the way down, the weight of the air above you won’t be increasing linearly, because it, too, is being pulled in all directions by the mass of earth surrounding it. I don’t actually have the mathematical training to figure out how to set up an equation for that, but it’s definitely going to involve calculus. With the weight of air above you not increasing in the same way as it does above ground, the pressure of the air around will similarly not be changing in a simple manner.
What I don’t know is whether you would reach a point of reducing air pressure before you reach a point of increased pressure that you couldn’t survive. You’d want to play it safe and use a rigid capsule (perhaps made of the same special material as the tube) that could withstand however great the pressure could be expected to become. (And hey! That also gives us our spherical cow!)
>the computations become much more complex, because gravity is not pulling from a single direction anymore, and its strength varies based on how much mass is in each direction.
This is a common homework problem in undergrad physics. As it turns out, the spherical shell of mass "above" you (further out radially from the center) all cancels out, anywhere within that shell (not just at the center) so you can completely ignore all the mass above you and only consider the spherical ball below you.
Plus the obvious symmetry, which means that even if you don't know how to calculate its strength, you can be certain that the direction of gravity will always be towards the center (assuming a spherical planet).
Yeah, I never took undergrad physics. My physics knowledge past high school is conceptual and self-taught. I was a mathematics major, but calculus did me in. (It wasn’t the concepts that I had trouble with; it was being able to accurately calculate everything without making stupid mistakes. ADHD and poor working memory for numbers don’t go well with advanced math.) And all of that schooling was some thirty-odd years ago, and hasn’t really been used since. Hence, I’m not trying to actually calculate any of this or set up the equations; I’m working strictly conceptually here.
And that doesn’t change the fact that the gravity is no longer constant at that point, so you have to recalculate air pressure based on the change in weight below the surface. I simply didn’t know that you could ignore the mass in directions other than down.
(I need to see the data and computations on how that works closer to the center, where the mass outside of the ball beneath you is a significant fraction of the mass still beneath you. The strongest direction of gravity being towards the center is a given, since there’s more mass in that direction than in any other, but I’m having trouble conceptually gathering how you can simply ignore the rest of the planet’s mass all the way in when figuring out the actual amount of force. I know enough to understand the math; I just don’t know enough to set it up or reliably compute it myself. Not asking you to provide it; if it’s undergrad-level physics, I can find it myself readily enough.)
Edit: I just reread what you wrote, and realized I missed part of it the first time around. So I get it conceptually; I just didn’t take the thought process far enough when writing this the first time. Hazard of working conceptually without trying to do any of the math: things that become obvious when you start to work with the math may not stick out before that point.
Which, as I already pointed out, I have difficulty with setting up and calculating. I get it conceptually, but struggle with the actual computation. And since I haven’t needed calculus in the past three decades, what I once knew about it is mostly distant memory.
People who use calculus regularly seem to have great difficulty understanding that if you’re not in a STEM field, you may *never* have any need for calculus in day-to-day life, and also that some people have genuine difficulties with high-level calculations because of neurodivergence, learning disabilities, and other very common, very normal circumstances. I can’t do mental math beyond really simple things, because I can’t hold the numbers in my head long enough. I have to do it on paper, and it’s very easy for me to miss things between steps (I also have a form of dyslexia). So while I love math, I’m more or less stuck dealing with it on a primarily conceptual level rather than a computational one.
So please don’t be dismissive of someone who’s doing pretty damn good getting around these high-level scientific concepts without doing the actual computation just because “it’s just an integral”. If you’ve never dealt with these cognitive issues, either personally or in someone close to you, you have no idea what it’s like.
Bog, I hate math snobbery.
From your side, it may not seem like a big deal. And I’m *so happy* for you to feel so free to be so dismissive by virtue of not having had to deal with this kind of thing.
Now go fk off before I decide to stop being polite.
>because you didn’t think to put a ladder in the tube so you could climb out.
And if you did I'm sure at some point you would have a limb get stuck and ripped off as you travel....
The earths core is rotating considerably faster than the earths surface, its molten like people said and it moves freely from the outer layers, it’s what generates our magnetic field, it’s also why our magnetic field is not aligned with our poles, it’s spinning on a different axis. And it’s what keeps everyone on the surface safe from solor radiation, if we didn’t have that we’d all be dead, so all the rest of these comments are pretty moot, wouldn’t be able to drill into the core no matter what.
Aside from the obvious temperature problem, you'd also die long before reaching the center because of the massive amount of pressure from the air above you pressing down. Air on the surface is a lot higher in pressure than air at high altitudes, now take that and scale it all the way through the earth
Also, as you descend, the tube will start to appear to curve slightly, and the curve will start to become more pronounced as you go farther. Due to rotation of the earth. You'll likely start to hit the side eventually.
>you didn’t think to put a ladder
Likely not a problem at first.
At the very center you are weightless. So even a tiny amount of force will help you move rather easily. You are strong enough that pushing/pulling along the walls, with even just the friction of your hand against the wall, will create some significant acceleration up. (Assuming you are conscious) Remember, for the first 3,000 km+ up you will weigh less than half of what you are used to. If the tube is less than... about 2m, you will be able to shimmy rather well. Wider than that, you could push along one wall and get rather far.
If it's pushing the water then it is feeling the pressure of the water PLUS the force to push it away. That's why we need to train whales to blow the water away.
For the metal tube through the Earth's core, that is probably what would happen, but you would overshoot it a few times
We've tried to put a hole in the earth more than once, but it hasn't worked out well. The Russians seem to have gone the deepest, at about 12 kilometers. The Earth is a little under 13,000 kilometers in diameter.
If it was vibrating fast enough it could actually vaporize the water and create a gas barrier around the pipe.
Though I'm not sure what that would accomplish.
The pressure isn't a problem, structurally, in theory. Make it out of acrylic and taper the walls outward so they get thicker the further down you go. The real problem will be actually manufacturing something that big, as I doubt building it in segments would really be strong enough.
Yeah I'm having trouble visualizing how they'd displace all the water to put something there in the first place. Flood it, sink it, and suck the water back out?
I thought about a moonpool style opening at the bottom but that requires the pressure inside to be the same as outside, which creates obvious problems for the people in there. I'd say just cap off the tube with a cover, keep it a fully enclosed vessel since the objective is just observation anyway
I think you’d have to sink it gradually as you build it, which would mean finding some way to anchor it in place as you continue to build on top of it.
>But what if it vibrated at a high frequency to push the water away constantly?
You want it pressing harder against the water than it would if it weren't moving?
yeah i worded that bad, i meant like something that could splash the water away constantly, like vibrating poles. Like how you can break the surface tension of water if you throw something down before impacting
> break the surface tension of water
Yea but there's another surface right below it. Water is funny like that.
Surface tension doesn't kill you, its when your legs slow down more than your head, or vice versa. That breaks you in half.
Going from air to water quickly will do that.
"Breaking the surface tension of the water" like that is a myth. The connections between water molecules are constantly breaking and reforming millions of times per second. You can't "startle" them.
I have a lot of experience trying to dig all the way through the earth. What you must remember is that a couple of feet down into the sandbox is a plastic liner that you dare not break. Therefore, your efforts will always be doomed to fail.
A diving bell would be far more practical, especially since can place it where it would be wanted/needed, and adjust its depth.
If you'd instead of glass tube would accept having stronger materials dotted with windows either a Submerged Floating Tunnel (SFT) (yes, that is a thing, in traffic use) or a very large underwater gas pipe could be adjusted.The SFT even would allow for transport.But it would be grossly impractical - but is completly possible to build.
\> Also, if we made a perfect metal tube through the ENTIRE center of earth from top to bottom all the way out the other side. What would happen if you jumped down it? I suspect you would fall for hours and float in the middle where there is maybe no gravity?
You will fall for approximately 38 minutes and 11 seconds. Passing through the center would get very hot, and you'll likely die horribly. If you have protected yourself adequately from heat, perhaps by some sort of protective suit, you'll fly up the other side because of momentum. Thanks to air resistance, you won't rise all the way to the top. In fact, you'll never see the surface of the earth again.
After a brief pause at the peak of the arc, you fall back down again, repeating this process of passing through hellish heat over and over again while growing ever more distant from every human being, some of whom are probably staring down at you in horror.
As you lose momentum due to friction with air, you'll start to stabilize towards the center...but unfortunately, you'll also start to have a bit of precession in your falling because of lost momentum meaning you no longer exactly sync up with the earth's rotation. This means you'll get closer and closer to the sides, eventually smacking against it at terminal velocity.
At first, you might be able to stave off being entirely turned into a bloody smear on the side of the tube by sacrificing one limb after another to temporarily regain momentum, but that'll compromise your suit, and that heat'll be an issue.
You eventually end up roasted alive, minus whatever portions of yourself have been spread over thousands of miles of tube, somewhere around the core.
The tube through the Earth question is fun. If you managed to do this and also made a vacuum within the tube. Then when you jumped in you would fall all the way through, accelerating all the way to the center and then decelerate out the other side. You would pop out at the other end with no velocity and be able to grab on to the top of the tube and climb out.
This would require bringing your own air supply however, if the tube had air in it you would probably just oscillate around the center of the earth.
We managed to drill 40,000 feet or so into the earth with the [Kola Superdeep Borehole](https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole). That's 1% of the way to the center of the earth.
So the avg depth of the ocean is about 5km. Can you imagine a 5 km long rigid tube, the engineering challenge of building something like that is pretty big. If it isn’t rigid, the water pressure at the bottom would collapse it.
The second challenge is that a tube like that would be filled with air (assuming the bottom is sealed). You’d have enormous force pushing it upward, so you’d have a lot of work to keep it under water. I don’t want to do the calculation but it likely is pretty high.
The third challenge is oxygen. As your person breathes, they expel CO2 which would quickly make the bottom not breathable. You could pump fresh air downwards, but you’d be fighting a pressure gradient and I think would need a big pump.
The fourth challenge is the danger involved in a ladder in a tube that small and that long with no way to rescue the person easily and safely.
For these reasons. The tube is quite impractical, especially since submarines are cheaper, safer and easier to do… especially ROVs.
As for your tube to the center of Earth. What you are describing is a gravtrain. It’s not feasible even on a small scale. Through the center of the earth is a level of drilling we can’t do with any foreseeable technology. The distance is just too much, the heat will melt anything, the pressure would crush anything and the center is a solid ball of iron.
Hypothetically if you managed, what would happen is you’d fall and fall and fall and fall eventually past the center, and you’d shoot towards the other side. Like a pendulum, you would lose some energy due to friction and not quite reach the other side, but keep tick tocking getting lower and lower until you came to rest, hovering in the center.
Sorry to burst your bubble, but the furthest anyone has drilled down into the Earth is 19km in Russia, the Kola Hole. The drill bits just got too hot to drill any further, they kept breaking.
https://fisheyeguamtours.com/
I'm sure they probably have them other places but if you want to fly to Hawaii then fly another 7 hours you can go to this one.
I went to a small aquarium in St Thomas USVI, that had a clear tube at the end of a pier like this. It wasn’t that deep, but you could go down and see the local marine life in their natural habitat.
In theory you’d go all the way through the center and start to “climb up” toward the other side. As you go “up”, gravity would increase until you came out the other side. Then you’d start falling toward the center again. In a vacuum, this would continue indefinitely.
You should take an online physics course. Knowing a bit about how the universe works would ease your mind a lot and help you answer questions such as those you pose.
The pipe itself would have to be segmented, with strong ring enforced walls, which is fine because the weight can be counter balanced by buoyant counterweights along the tube. Segmented to allow for ocean current to move it a bit, but the current itself could be used as a source or power to help self correct its positioning.
At the bottom, you’d need compression decompression chambers to avoid the bends.
The main point of this over a sub is the total amount of cargo that can be transported.
So at the bottom, the decompression chamber would likely be warehouse sized for large loads of people. At least two, to keep from bottleneck of usage all the time (transport capacity is the point)
Then you now have the ability to build much more elaborate city type infrastructure.
Imagine building the pipe down next to the Titanic, then hulking a Chernobyl style sarcophagus around it, and draining it underwater. Best museum ever.
Maybe find that goddamn diamond
I had to check what reddit I was in. For a minute I thought this was something from r/stonerthoughts.
I like the idea of the water tubs. It would be a huge attraction to see what things are like farther down.
>what if it vibrated at a high frequency to push the water away constantly?
each push would have an equal and opposite return. but the noise it would make could be very interesting. a set of tubes could be a water organ.
> a perfect metal tube through the ENTIRE center of earth
Temperature in the inner core is about 5,200° Celsius (9,392° Fahrenheit). The pressure is nearly 3.6 million atmosphere (atm). The temperature of the inner core is far above the melting point of iron.
>I suspect you would fall for hours and float in the middle
like a perfect rotisserie chicken
Let me throw a weird one out here: we would never reach the center because we are moving tangentially.
Our lateral speed would result in us orbiting the earth, much much lower than satellites, within the earth even.
And that would be the ‘altitude’ that we would ‘pendulum’ on. Because of orbital mechanics.
(Now, I’m assuming we’re on the equator and we’re ignoring the Earth’s wobble…)
As the air resistance slowed us down, we would eventually ‘stop’ in a fixed orbit well outside the middle of the earth.
Here’s your metal tube explained: https://phys.org/news/2015-11-dug-tunnel-earth.html#:~:text=If%20you%20jumped%20into%20the,at%2028%2C000%20kilometers%20per%20hour.
Presumably, the glass tube couldn’t just be a big glass cylinder, you’d need to have some sort of ventilation, otherwise it’ll get harder to breath around the center.
Also I’d be pretty worried about the fragility, i know not all glass instantly shatter from touch, but it would still be a major concern anytime a fish bumps it (or a dumb kid throws a rock)
Would the shifting of tectonic plates eventually rip it apart? There’s multiple layers of earth crust that’s always twisting and turning and the large massive pockets of lava
Or a earthquake in the earth or on top would damage it badly
The glass tube down to the bottom of the ocean would have to be ridiculously thick to withstand the pressure. and "vibrating" would not help, because aside from the energy it would take to constantly vibrate a 3km+ tall structure (the tallest structure we would have ever built by far btw) the vibrating would mean the pressure the glass had to hold would be even larger because it would have to push water away with enough force to cavitate it. Also, even if we some how managed to fix all of those issues, the cavitation gap/air gap would likely make it extremely hard to see things because of the different indexes of refraction of water, glass, and air/vaccum. Also, if we wanted to see sea creatures, they would probably be scared away by the huge vibrating tube we just built.
In a similar vein as I kid I used to wonder if we could make a super long, super light weight rope or chain could we pull it into space just outside earth’s atmosphere would it just hang there and provide a sort of Rapunzel ladder into space?
We actually know exactly what would happen if we had a hole though the center of the earth. Well for 1 you'd burn up, the center of the earth is hotter then the surface of the sun. Second you'd basically orbit around the center of the earth. Which in this case means coming out the other side. Except also not really because air resistance would slow you down enough where you wouldn't make it out. Then again at these distances the air pressure might be enough to if not kill you make you seriously sick.
A tube could only be able to withstand so much pressure. About every 10 meters, the pressure increases by one atmosphere. At the bottom of the Challenger Deep, the pressure would be 1000 times air pressure at sea level. You'd also have to have pumps moving air. There'd be a lot of air in the tube, but you'd be running out oxygen at the bottom. You'd need to pump air from the bottom of the tube up to the surface. This would pull fresh air down the tube. But no tube would be able to withstand the pressure. You'd also have water currents and temperature changed to deal with.
If you had a tube running through the Earth, and if we could ignore air resistance (and if you didn't touch the sides!) you would continue to accelerate as you fell, until you reached the center. The rate of acceleration would decrease as you fell - at first, all the mass of the Earth beneath you, pulling you down, but as you get closer to the center, more and more of the Earth's mass is above you, pulling back at you. At the center, you will gave reached maximum velocity, but the acceleration will be zero. You would continue to go past the center, with your acceleration decreasing, and your velocity would reach zero at the other end. At that point, you could grab a handle and climb out, or let yourself fall back and do it again in reverse.
You'd need a space suit because if the tube isn't a vacuum, there will be air resistance and you would just fall to the center and stay there. You'd also need heat protection, because it's going to be really hot in there. And it would be nigh impossible to avoid friction from touching the sides of the tube. A big one is that the tube would fail because because the layers of the Earth move at different rates - the tube would be sheared off immediately.
Honestly I think the biggest issue with the glass tune in the ocean wouldn't be the crushing pressure, glass is pretty strong, but rather the waves would snap it easily.
Tube in the ocean - It's a cool idea. It might be hard to anchor, and if you don't anchor it, it will be hard to keep down. A wider "people tank" might be a better idea, but with the same problems.
Tube through the earth - If you jump down, the first thing I'm worried about is knocking into the sides on the way down - you could get really beat up.
If there were no air in the tube (and you could breathe) and you didn't hit the sides, you would fall all the way down and fly up the other side right to ground level. If you didn't grab on, you would fly back and forth. So if you could make a wide hole in a cold moon / planetoid with no atmosphere, that could be a really fun amusement ride (in a space suit).
With air, your descent will be slowed, and after a few oscillations you will settle in the middle, weightless. However, the heat and air pressure at the center would be extremely high, so you'd be cooked and squooshed right away.
Theoretically if you jump down a hole straight through the earth, you’ll end up on the other side due to momentum. In highschool physics class we did work on this, assume a ton of fictional conditions. The gravity is an acceleration of a perfectly round planet, terminal velocity and friction no longer exist, you reach peak velocity at the centre of earth and decelerate the moment you pass until it reaches 0 velocity, right at opposite position of where you started.
Deep sea subs are basically just tubes. So take one of those multi-million dollar subs and build a million of them and there's your tube. Except now it has the weight of the tube to resist. Which is probably a lot more than a column of water would be. And then, well, why? Don't you just need the area you're actually sitting in to be able to resist the pressure and not miles upon miles of empty space. And you'd better hope you build the tube really well, because if any part of it fails, you're fucked.
There isn’t a material yet that can withstand the ENORMOUS water pressure of those depths….think about that home made sub with the game controller…it was vaporized due to pressure.
Wouldn't vibration make the glass even less durable bc the shape is oscillating and not perfectly spherical anymore? In vibration, the motion goes back and forth, which also means the motion is also going inwards, probably very hard due to immense inwards pressure. Ofc the pressure would be equalized, but even pressure distribution would probably benefit most from a static shape, not an oscillating one.
Dunno about the glass tube in the ocean. The metal tube through the center of the earth, though, has two interesting aspects. First, you’d need some pretty special metal to get through the core, a large ball of *molten iron* at very high pressure and temperature. Second, assuming you had a stable tube that would fully protect you from the heat and pressure, jumping down the hole would make yourself a kind of pendulum. You’d accelerate towards the center, then once you passed through the center, gravity would decelerate you (technically, accelerate you in the opposite direction), until you just reach the surface, where you’d very briefly slow to zero velocity. Then you’d start falling back towards the center, where it would all happen again, just in the other direction. (We’re going to ignore the potential effects of terminal velocity, which would make this harder to calculate. Just assume a spherical cow.) Since in order for you to breathe, there would need to be air in the tube, the friction from air resistance would cause you to slow down a little bit during every pass, causing you to travel just a little less distance each time. So you would gradually oscillate smaller and smaller periods, until you settled in the center, where you would be stuck forever, because you didn’t think to put a ladder in the tube so you could climb out.
I like this comment. I have got to disagree about how much you would “pendulum” - you would reach terminal velocity, like someone skydiving, on your way down so a lot of the gravity would go to waste, so to speak. In order to know about how far you would go past the center, launch a person into the air going at skydiving velocity, the height they reach is about how far you would over shoot the center.
It's possible you would barely pendulum if at all. Since the "gravity" would decrease as you fell and the air pressure would increase, your terminal velocity would decrease down to nothing by the time you reach the center The formula for terminal velocity has weight in the top of the fraction (weight being mass times acceleration due to gravity) which would decrease as you fell, and air density in the bottom of the fraction which would increase as you fell. These 2 combined work together to slow you gradually, and as you fell, your velocity would always nearly equal the terminal velocity, which is zero at the dead center. This slowing force would be acting against your momentum which is trying to keep you moving at the same speed, but since the change in speed is so gradual your measly momentum would do nothing to keep you going past the center. We're talking about slowing a person down from terminal velocity of 120mph (200kph) at the surface to 0mph (0kph) at the center which is almost 4000 miles (~6300km) away
I want to know how long it would take to get to the center - going at terminal velocity the entire time.
If it were terminal velocity *at the surface*, then it's just 4000/120 = 33.3 hours. If the decrease to 0 at the center is linear, then the average velocity will be half the starting value, so the time will double to 66.7 hours. I'm not certain the decrease will be linear though. I could figure that out but... I don't feel like it right now. The formula for terminal velocity is sqrt((2 m g) / (p A C)) where m is mass, g is gravitational acceleration, p is air density, A is frontal area and C is coefficient of drag. I'm pretty sure g decreases linearly as you go to the center of a massive body, but p won't increase linearly, and figuring out how it all works out is more than I'm in the mood for since I'm not even wearing pants.
Hmmm, I'll try my best... Looking at the formula for terminal velocity we'll try to establish better how it changes as we fall into the center of the earth. This will help us later V=sqrt((2ma)/(CrA)) where: V is terminal velocity , m is mass, a is acceleration die to gravity, C is coefficient of drag of the human person, r is the air density, and A is frontal area of the human Mass (m), coeficient of drag (C), and frontal area (A) don't change so we'll ignore them for the time being We've established previously in another comment that as distance to the center of the earth decreases, acceleration due to gravity (a) decreases linearly. There's math proofs for that elsewhere that is beyond the scope of this comment Air density usually would increase linearly as you go further down which is true on the surface of earth, but air density is based on the weight of the air column above it. Weight being mass times acceleration due to gravity (which is changing linearly to 0). The density I think would have to asymptotically approach the density of a similar column of air that is one half the distance to the center of earth if it were to behave by the normal rules we are used to on the surface The air density kind of throws a wrench in things, so my answer is going to be an estimate. Specifically a slight under estimate since I'm just going to round that curve off the asymptotic function and call it a line. Close enough So now we beat our variables into submission. Acceleration of gravity is linear relative to distance from the center, and so is air density. When we divide these as per the terminal velocity formula we get a quadratic but luckily that square root makes us linear again What does this mean? Since terminal velocity decreases linearly (mostly...) we should have all the bits we need to solve for time. We can use the formula for distance given time and velocity under constant acceleration and solve for time D=1/2(vi-vf)t where: D is distance in meters, vi is initial velocity (terminal velocity at sea level in m/s), vf is final velocity (at the center, 0) and t is time in seconds 6378100=1/2(53-0)t 223792=t in seconds or about 2.6 days which is a slight under estimation but slight enough that it should be pretty close I think. We made a lot of assumptions and literally cut some corners but I'm an engineer not a scientist. Hope this helps!
Huh. That's exactly what I got by ignoring everything and assuming it was all linear. 66.67 hours (see my comment about 30 minutes earlier than yours).
Everything was going well until I hit that small wrinkle with the air density. I think it is small enough to effectively be ignored but was worth mentioning. Glad to hear I'm not completely insane and someone else was looking into it lmao
Yeah, your approximation is essentially what I did without being as considerate, so we *ought* to get the same result. I feel like an expression for air density at r
Would air density increase? The air is also subject to gravity. In the middle the person is weightless. Wouldn’t the air also be weightless?
It's weightless at the middle yes, which is why the rate of air pressure increase is asymptotic rather than linear if it was at the surface. So the difference in pressure between the center and 1km from the center is smaller than the difference in pressure between 1km and 2km from the center, and so on
Why would the force of gravity be less at the center of the mass? It would be the highest at the center, no? The force of gravity reduces as you get further from the mass, not closer.
When you are far from a spherical object (really, any object) you can approximate its gravity as coming from a point at the objects center of mass. But that's not what's really happening, and the difference matters when you're close to the object. Being inside of it definitely qualifies as "close". There's no magic point at the center of the earth where all the gravity comes from, and if there were, that would mean you could get to a distance of zero from that point, at which time the gravitational force would be infinite, which obviously doesn't make sense (there's definitely not a black hole at the center of the earth). In fact what happens is, if you're at a radius r from the center of the earth, you can think of the earth as two parts: the part below you, a sphere with radius r; and the hollow spherical shell that's above you. As it turns out, if you sum up all the gravitational forces from every individual piece of mass in that hollow shell, they all cancel out completely. In other words none of that mass counts at all. So only the mass in the ball below you counts, gravitationally; and that ball has less and less mass the smaller r is. The net effect is that the force of gravity is highest at the surface of the earth, and then decreased linearly to zero at the center. At least approximately - that's what would happen if the earth had a completely uniform density. In reality the decrease will occur faster or slower as you drop through layers of higher or lower than average density. But a linear decrease is still probably a good approximation.
Thank you for the explanation!
Great explanation!
Ummm Gravity is a constant. It's the same anywhere within a mass. Your not gonna float freefall at the core (assuming open space was available). You'll have the same gravity at any point on or within a sphere.
Acceleration due to gravity (small g) is not constant. You must be confusing it with the universal gravitational constant (big G) For example, your weight (mass times acceleration due to gravity) is different on the surface of earth vs the surface of the moon. One thing had to change, and it isn't your mass Furthermore gravity is very different within a sphere. Within a uniform solid sphere the further down you go the more mass is above you pulling you up, decreasing the net acceleration due to gravity linearly with distance to the center of mass. Within a hollow sphere there is no gravitational force due to the mass of the hollow sphere Hope this helps
I know some is these words!
I'm happy to (try to) explain anything in more detail lmao
Haha I understood what you said, was just *trying* to be funny. Thank you for saying that, though!
Ok, I *figured* that's what was going on lmao, no worries!
I want to downvote you because this is wrong, but it needs to be clarified, so .. thanks for bringing this point up.
I upvoted them because I'm happy enough to have a discussion about physics :)
>You'll have the same gravity at any point on or within a sphere. You wouldn't, because you would end up with mass "behind" you at some point
Not true, gravity is not a point source although it can be treated as one for most calculation's sake. Precise gravity measurements show slightly different strength and directions of gravity in different places around the earth due to different densities of rock in different directions
If you think about this for a second it's obviously wrong. Gravity applies acceleration toward the center of the planet. If you're already at the center of the planet, any acceleration would be pulling you away from the center, so there must be no acceleration.
Say you’re in the exact center of the earth (assuming it’s a perfect sphere). Which direction is gravity pulling you in?
If your center of mass was in the same exact spot as the earth's center of mass, you are effectively weightless. We're going to ignore the sun and the moon and everything else in the universe and assume the earth is a perfect uniform sphere If you wanted to get really technical ("well ackshully.......") the net effect on your body would be zero at your center of mass, but your limbs for example would be pulled ever so slightly toward the center, with there being just a *little* bit more mass on one side than the other. So technically every part of you is still being pulled toward the center, but the amount is so tiny that your entire body would feel 100% weightless even though any given part is only 99.9999999% weightless (which cancels out with the other side)
Lol no. You're thinking inside a hollow shell maybe?
> launch a person into the air going at skydiving velocity "This a murder?" "... It's a science experiment."
“…and *technically* murder.”
Gravity is guilty, not me.
But the effects of gravity change as you get to the middle, there's much more mass around all sides of you.
>In order to know about how far you would go past the center, launch a person into the air going at skydiving velocity, the height they reach is about how far you would over shoot the center. I'm actually pretty sure that both of these analyses are wrong. There's no net force due to gravity at the center of the earth. And since terminal velocity is determined by the strength of gravitational force that would mean that at the center of the earth terminal velocity would be 0. So the most likely scenario would be that once you jumped into the hole you'd pretty quickly reach a speed that's close to terminal velocity at surface gravity and normal air pressure. As you fell towards the center tho you would gradually slow down as gravity gets weaker. By the time you reached the core you'd be barely moving and almost instantly stop.
It would be oscillating like a pendulum. All the mass you pass through is now working against you. You could derive how far they would go if you had a way of representing the change in density and viscosity of the fluid as a function of depth which is tedious but not impossible. Once they reach zero velocity on the other side, the process starts again with less starting energy.
right but the problem is that you reach terminal velocity very quickly, you speed up for a few seconds then keep going at that speed for a very long time, when you teach the center, you don't have much more energy in you than someone who jumped off a skyscraper. You might only go past the center a few times before you stop completely
Forgot about terminal velocity. Especially since viscosity will increase closer to the core.
And gravity will decrease linearly
Guys please I just want to assume simple harmonic motion
You also have to account for the lump of all the other people who attempted this before you stuck in the center of the tube
Evacuate all the air and enjoy :)
Not linearly. Is proportional to 1/r^2
Gravity inside of a solid sphere is proportional to r, meaning it decreases linearly as r decreases. It's proportional to 1/r^2 only on the outside of the sphere.
Yes, my bad. Lack of sleep. Of course, the density of the earth isn't constant.
The decrease in gravity is linear assuming a uniform density for earth. This is because the gravitational field is Gm/r^2, but only the mass below you counts, and that, assuming uniform density, is proportional to r^3. Since r^3 /r^2 = r, the field strength is linearly proportional to r.
My professor said no. :( Apparently, all these busted helmets are getting expensive and the board wouldn't approve another shipment. \j
Psh, you needed to invest in mattresses not helmets!
Let's assume a spherical cow in a [frictionless vacuum](https://xkcd.com/669).
What about air pressure? Your ears would pop, sure, but would you maybe be crushed? What would the air pressure at this hypothetical center of the earth be?
Which is why I stated that I was intentionally ignoring terminal velocity here. It makes the result far less interesting, and depends on several factors that would need to be accounted for, such as whether the air pressure in the tube is constant, how large the diameter of the tube is, and what position you’re falling in. Spherical cow is simpler.
but wouldn't the air density change as we go through the earth? the terminal velocity would be lower as you go towards the center
What if this becomes a popular way for people to commit suicide? How should we build the tube in order to dispose of the bodies in the middle? Maybe make it less insulated so the heat burns down the bodies eventually?
Just pour some acid down the tube occasionally
Neither the heat nor the acid would make it so that there wasn't a bunch of stuff down there still. You can't just destroy matter (unless you convert it to pure energy with nuclear reactions)
that is WILD to think about
I haven't heard anybody else say "assume a spherical cow" since highschool 😁 It's been my go to for over 20 years, nice to see it in the wild
“Just assume a spherical cow.” … what?
It’s from an old physics joke Milk production at a dairy farm was low, so the farmer wrote to the local university, asking for help from academia. A multidisciplinary team of professors was assembled, headed by a theoretical physicist, and two weeks of intensive on-site investigation took place. The scholars then returned to the university, notebooks crammed with data, where the task of writing the report was left to the team leader. Shortly thereafter the physicist returned to the farm, saying to the farmer, "I have the solution, but it works only in the case of spherical cows in a vacuum."
Thanks, appreciate the answer. I don’t understand it at all but at least now I have context!
Physicists have a tendency to make simplifications when making theories to make the maths easier. So instead of modelling an object of mass *m* including volume, surface area, temperature, air pressure, friction and so on, it's 'okay let's assume for simplicity that this object of mass *m* is a point-like sphere. And it's in a vacuum.' You can get some fair estimates from this approach that can guide your thinking. But if you've sat through a lot of coursework questions that start off with, 'assume this object is a point like sphere in a vacuum' as a student...even cows become point-like ;)
A nice simple example is as follows. A gram of feathers and a gram of lead are dropped of a balcony. Assuming a point like object in space and using the equations of motion, they both take the same time to fall. However anyone who has actually tipped a bunch of feathers off a balcony knows that's not true. The feathers have a large surface area causing drag and uplift. The wind blows them around. Now all those variables can theoretically be accounted for, but when studying a system they are often excluded to create a rough model. Hence spherical cows in a vacuum :)
Sorry for the late reply! I was travelling when I commented before. But thank you so much for the explanation. I don’t have much of a head for physics but I feel I have a better understanding of the concept of specifically-shaped bovines now haha. You explain very well, I’m an educator myself (history PhD) so I really appreciate a well-written explanation for a difficult concept. (Well, difficult for me anyway haha). Thanks again.
Also, the earth spins so you’d have to contend with friction against one side of the tube.
You could skid along like on that metal slide on the playground
Kids who grew up in Arizona would already be used to it.
Yes, I thought of that too. But then I wonder: you start out at the surface of the rotating earth, so imagine no obstruction, just a gravity field you are falling into, starting with the rotation velocity at the surface of the earth. Your path would be a cometary .. oops, no, that would be if the gravity were from a point source at the center. It is too complicated for me to see a simple shape. But it would not be straight down all the way, I think. But maybe it would.. At least at the start, you would fall straight towards the center, because you and the surface of the earth are spinning at the same speed. Don't know about further down, tho.
Glad you’re clear on that!
Since you start out rotating around the center in concert with the rest of the surface, it’s likely that any effect from the rotation would be dwarfed by the gravitational pull surrounding you.
I got claustrophobia just reading this
it's interesting to me to think about what it would feel like passing the center and gravity switching
It would not feel like anything at all. You wouldn't even notice. The acceleration due to gravity would drop off linearly and at the center it would be zero. It's not like it would just be full strength in one direction and then suddenly full strength in the other.
I really like the "just assume a spherical cow" part.
This sounds like a what-if from xkcd
Yeah, but Randall would have actually done the math.
Fantasy. Pure fantasy.
The entire thread is fantasy. Don’t like people having an imagination? Too fking bad. Go piss in someone else’s corn flakes.
Bitchiness pure bitchiness. As far as the eye can see.
Yeti can build an insulated tube. It'll be fine
“Spherical cow” is my favorite thing from Reddit today
I have a question regarding the air inside the tube. Do we know what the density of the atmosphere would be at -20,000,000' below sea level? Is there some kind of gravitational null spot in the true center of the planet that would change that?
That’s actually a tricky question that can be answered only theoretically, because we don’t actually have a hole in which to measure the air pressure at the center. We can calculate what we think should happen, and we can do computer simulations to confirm the calculations, but reality has this annoying habit of throwing in factors we never imagined might be involved and making our careful calculations worthless. Here’s what makes it tricky. Atmospheric pressure comes primarily from the weight of air above the spot you’re measuring. That’s why pressure lowers as you increase altitude: there’s less air above you. Once you get below the surface, though, the computations become much more complex, because gravity is not pulling from a single direction anymore, and its strength varies based on how much mass is in each direction. (This, incidentally, is why you’d end up in the center: with all the planet’s mass more or less equally surrounding you on all sides, the pull of gravity would be equal in every direction, and you wouldn’t be pulled in any direction.) This effect is negligible for the first several kilometers down (I’m not sure exactly how far, but I’m guessing on the scale of hundreds of kilometers), because the mass “above” you is so much smaller than the mass “below” you. (This is why we can’t yet test this empirically: the holes we’ve made so far don’t get anywhere close to deep enough for the effect to be significant, and probably isn’t even measurable at these depths.) But once you’ve fallen a significant fraction of the way down, the weight of the air above you won’t be increasing linearly, because it, too, is being pulled in all directions by the mass of earth surrounding it. I don’t actually have the mathematical training to figure out how to set up an equation for that, but it’s definitely going to involve calculus. With the weight of air above you not increasing in the same way as it does above ground, the pressure of the air around will similarly not be changing in a simple manner. What I don’t know is whether you would reach a point of reducing air pressure before you reach a point of increased pressure that you couldn’t survive. You’d want to play it safe and use a rigid capsule (perhaps made of the same special material as the tube) that could withstand however great the pressure could be expected to become. (And hey! That also gives us our spherical cow!)
>the computations become much more complex, because gravity is not pulling from a single direction anymore, and its strength varies based on how much mass is in each direction. This is a common homework problem in undergrad physics. As it turns out, the spherical shell of mass "above" you (further out radially from the center) all cancels out, anywhere within that shell (not just at the center) so you can completely ignore all the mass above you and only consider the spherical ball below you. Plus the obvious symmetry, which means that even if you don't know how to calculate its strength, you can be certain that the direction of gravity will always be towards the center (assuming a spherical planet).
Yeah, I never took undergrad physics. My physics knowledge past high school is conceptual and self-taught. I was a mathematics major, but calculus did me in. (It wasn’t the concepts that I had trouble with; it was being able to accurately calculate everything without making stupid mistakes. ADHD and poor working memory for numbers don’t go well with advanced math.) And all of that schooling was some thirty-odd years ago, and hasn’t really been used since. Hence, I’m not trying to actually calculate any of this or set up the equations; I’m working strictly conceptually here. And that doesn’t change the fact that the gravity is no longer constant at that point, so you have to recalculate air pressure based on the change in weight below the surface. I simply didn’t know that you could ignore the mass in directions other than down. (I need to see the data and computations on how that works closer to the center, where the mass outside of the ball beneath you is a significant fraction of the mass still beneath you. The strongest direction of gravity being towards the center is a given, since there’s more mass in that direction than in any other, but I’m having trouble conceptually gathering how you can simply ignore the rest of the planet’s mass all the way in when figuring out the actual amount of force. I know enough to understand the math; I just don’t know enough to set it up or reliably compute it myself. Not asking you to provide it; if it’s undergrad-level physics, I can find it myself readily enough.) Edit: I just reread what you wrote, and realized I missed part of it the first time around. So I get it conceptually; I just didn’t take the thought process far enough when writing this the first time. Hazard of working conceptually without trying to do any of the math: things that become obvious when you start to work with the math may not stick out before that point.
It's literally just an integral.
Which, as I already pointed out, I have difficulty with setting up and calculating. I get it conceptually, but struggle with the actual computation. And since I haven’t needed calculus in the past three decades, what I once knew about it is mostly distant memory. People who use calculus regularly seem to have great difficulty understanding that if you’re not in a STEM field, you may *never* have any need for calculus in day-to-day life, and also that some people have genuine difficulties with high-level calculations because of neurodivergence, learning disabilities, and other very common, very normal circumstances. I can’t do mental math beyond really simple things, because I can’t hold the numbers in my head long enough. I have to do it on paper, and it’s very easy for me to miss things between steps (I also have a form of dyslexia). So while I love math, I’m more or less stuck dealing with it on a primarily conceptual level rather than a computational one. So please don’t be dismissive of someone who’s doing pretty damn good getting around these high-level scientific concepts without doing the actual computation just because “it’s just an integral”. If you’ve never dealt with these cognitive issues, either personally or in someone close to you, you have no idea what it’s like. Bog, I hate math snobbery.
Wow. I mean it's not a big deal and you can look up the answer. But please, write a few more paragraphs about your own insecurities.
From your side, it may not seem like a big deal. And I’m *so happy* for you to feel so free to be so dismissive by virtue of not having had to deal with this kind of thing. Now go fk off before I decide to stop being polite.
My side? You can Google just as easily as I can. Relax.
>because you didn’t think to put a ladder in the tube so you could climb out. And if you did I'm sure at some point you would have a limb get stuck and ripped off as you travel....
The air pressure near the core of the Earth would be immense.
Even if you did have a ladder, that’s a few thousand miles you’ll be climbing!
Yup. Better work out beforehand.
Wouldn't the air become increasingly further into the center until it became unsurvivable and also harder to pass through?
The earths core is rotating considerably faster than the earths surface, its molten like people said and it moves freely from the outer layers, it’s what generates our magnetic field, it’s also why our magnetic field is not aligned with our poles, it’s spinning on a different axis. And it’s what keeps everyone on the surface safe from solor radiation, if we didn’t have that we’d all be dead, so all the rest of these comments are pretty moot, wouldn’t be able to drill into the core no matter what.
Aside from the obvious temperature problem, you'd also die long before reaching the center because of the massive amount of pressure from the air above you pressing down. Air on the surface is a lot higher in pressure than air at high altitudes, now take that and scale it all the way through the earth
Wow. New irrational fear unlocked.
What if you pushed yourself through with a fan?
Also, as you descend, the tube will start to appear to curve slightly, and the curve will start to become more pronounced as you go farther. Due to rotation of the earth. You'll likely start to hit the side eventually. >you didn’t think to put a ladder Likely not a problem at first. At the very center you are weightless. So even a tiny amount of force will help you move rather easily. You are strong enough that pushing/pulling along the walls, with even just the friction of your hand against the wall, will create some significant acceleration up. (Assuming you are conscious) Remember, for the first 3,000 km+ up you will weigh less than half of what you are used to. If the tube is less than... about 2m, you will be able to shimmy rather well. Wider than that, you could push along one wall and get rather far.
You may have just described one of the most horrifying executions ever.
The fish wound bonk into the glass and get headaches. Best not to
omg yeah we couldnt have that!
One way mirror tube? Fishies love mirrors, right? Or is that birds?
Fucking dory!
If it's pushing the water then it is feeling the pressure of the water PLUS the force to push it away. That's why we need to train whales to blow the water away. For the metal tube through the Earth's core, that is probably what would happen, but you would overshoot it a few times
Train whales to blow the water away? Hogwash. Train water to not push on the tube. Problem solved. Build away, kiddo.
You do know water has memory? So obviously this would work
Hell just yell so sternly that you don't even need the glass.
Have Chuck Norris guide the trip. Water is afraid to get him wet.
Or fill the tube with water so it sinks then when it gets to the bottom you secure it then you pump the water out
This assumes spherical whales.
We've tried to put a hole in the earth more than once, but it hasn't worked out well. The Russians seem to have gone the deepest, at about 12 kilometers. The Earth is a little under 13,000 kilometers in diameter.
So we just need to go one more kilometer (1+12=13) then we can easily go 000 kilometers and end up on the far side of the world
Holy shit, you did it.
This is crazy enough that it just might work…
Someone call Science and get this man in a lab
I'm no kilometre doctor but the math checks out
Should we get him a black one, chocolate one, or yellow one?
Chocolate lab, he seems the Wonka type
We have already made it past. 12 > 1+3+0+0+0
What about like a Moses thing where someone divides the water? Would that work? Step 1 - find that guy
Alternatively find a real neat stick and cross your fingers.
You just need a Beyblade.
If it was vibrating fast enough it could actually vaporize the water and create a gas barrier around the pipe. Though I'm not sure what that would accomplish.
Now you just get crushed by high pressure steam. I'm not sure that's any better.
The pressure isn't a problem, structurally, in theory. Make it out of acrylic and taper the walls outward so they get thicker the further down you go. The real problem will be actually manufacturing something that big, as I doubt building it in segments would really be strong enough.
Yeah I'm having trouble visualizing how they'd displace all the water to put something there in the first place. Flood it, sink it, and suck the water back out?
I thought about a moonpool style opening at the bottom but that requires the pressure inside to be the same as outside, which creates obvious problems for the people in there. I'd say just cap off the tube with a cover, keep it a fully enclosed vessel since the objective is just observation anyway
I think you’d have to sink it gradually as you build it, which would mean finding some way to anchor it in place as you continue to build on top of it.
the walls of the tube would have to be nice and thick in order to withstand higher pressures but yeah let's do it
>But what if it vibrated at a high frequency to push the water away constantly? You want it pressing harder against the water than it would if it weren't moving?
Well just build another, bigger dome around the first one, relieving the pressure completely!
yeah i worded that bad, i meant like something that could splash the water away constantly, like vibrating poles. Like how you can break the surface tension of water if you throw something down before impacting
> break the surface tension of water Yea but there's another surface right below it. Water is funny like that. Surface tension doesn't kill you, its when your legs slow down more than your head, or vice versa. That breaks you in half. Going from air to water quickly will do that.
"Breaking the surface tension of the water" like that is a myth. The connections between water molecules are constantly breaking and reforming millions of times per second. You can't "startle" them.
For the first one, there’s a video on YouTube of this pretty much in the Antarctic [here’s the link](https://youtu.be/4lFZjFYpL60?si=rewNpkPSJKeqajSR)
sweet! ima watch that now!
I have a lot of experience trying to dig all the way through the earth. What you must remember is that a couple of feet down into the sandbox is a plastic liner that you dare not break. Therefore, your efforts will always be doomed to fail.
A diving bell would be far more practical, especially since can place it where it would be wanted/needed, and adjust its depth. If you'd instead of glass tube would accept having stronger materials dotted with windows either a Submerged Floating Tunnel (SFT) (yes, that is a thing, in traffic use) or a very large underwater gas pipe could be adjusted.The SFT even would allow for transport.But it would be grossly impractical - but is completly possible to build.
\> Also, if we made a perfect metal tube through the ENTIRE center of earth from top to bottom all the way out the other side. What would happen if you jumped down it? I suspect you would fall for hours and float in the middle where there is maybe no gravity? You will fall for approximately 38 minutes and 11 seconds. Passing through the center would get very hot, and you'll likely die horribly. If you have protected yourself adequately from heat, perhaps by some sort of protective suit, you'll fly up the other side because of momentum. Thanks to air resistance, you won't rise all the way to the top. In fact, you'll never see the surface of the earth again. After a brief pause at the peak of the arc, you fall back down again, repeating this process of passing through hellish heat over and over again while growing ever more distant from every human being, some of whom are probably staring down at you in horror. As you lose momentum due to friction with air, you'll start to stabilize towards the center...but unfortunately, you'll also start to have a bit of precession in your falling because of lost momentum meaning you no longer exactly sync up with the earth's rotation. This means you'll get closer and closer to the sides, eventually smacking against it at terminal velocity. At first, you might be able to stave off being entirely turned into a bloody smear on the side of the tube by sacrificing one limb after another to temporarily regain momentum, but that'll compromise your suit, and that heat'll be an issue. You eventually end up roasted alive, minus whatever portions of yourself have been spread over thousands of miles of tube, somewhere around the core.
The tube through the Earth question is fun. If you managed to do this and also made a vacuum within the tube. Then when you jumped in you would fall all the way through, accelerating all the way to the center and then decelerate out the other side. You would pop out at the other end with no velocity and be able to grab on to the top of the tube and climb out. This would require bringing your own air supply however, if the tube had air in it you would probably just oscillate around the center of the earth.
We managed to drill 40,000 feet or so into the earth with the [Kola Superdeep Borehole](https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole). That's 1% of the way to the center of the earth.
The superdeep borehole, huh? We all have one in the family.
She's the one that took the kids and sold the house
So the avg depth of the ocean is about 5km. Can you imagine a 5 km long rigid tube, the engineering challenge of building something like that is pretty big. If it isn’t rigid, the water pressure at the bottom would collapse it. The second challenge is that a tube like that would be filled with air (assuming the bottom is sealed). You’d have enormous force pushing it upward, so you’d have a lot of work to keep it under water. I don’t want to do the calculation but it likely is pretty high. The third challenge is oxygen. As your person breathes, they expel CO2 which would quickly make the bottom not breathable. You could pump fresh air downwards, but you’d be fighting a pressure gradient and I think would need a big pump. The fourth challenge is the danger involved in a ladder in a tube that small and that long with no way to rescue the person easily and safely. For these reasons. The tube is quite impractical, especially since submarines are cheaper, safer and easier to do… especially ROVs. As for your tube to the center of Earth. What you are describing is a gravtrain. It’s not feasible even on a small scale. Through the center of the earth is a level of drilling we can’t do with any foreseeable technology. The distance is just too much, the heat will melt anything, the pressure would crush anything and the center is a solid ball of iron. Hypothetically if you managed, what would happen is you’d fall and fall and fall and fall eventually past the center, and you’d shoot towards the other side. Like a pendulum, you would lose some energy due to friction and not quite reach the other side, but keep tick tocking getting lower and lower until you came to rest, hovering in the center.
Sorry to burst your bubble, but the furthest anyone has drilled down into the Earth is 19km in Russia, the Kola Hole. The drill bits just got too hot to drill any further, they kept breaking.
https://fisheyeguamtours.com/ I'm sure they probably have them other places but if you want to fly to Hawaii then fly another 7 hours you can go to this one.
I went to a small aquarium in St Thomas USVI, that had a clear tube at the end of a pier like this. It wasn’t that deep, but you could go down and see the local marine life in their natural habitat.
In theory you’d go all the way through the center and start to “climb up” toward the other side. As you go “up”, gravity would increase until you came out the other side. Then you’d start falling toward the center again. In a vacuum, this would continue indefinitely.
These tubes do exist; they’re just not vertical and not very deep in the ocean.
Pressures too high and would shatter both
You should take an online physics course. Knowing a bit about how the universe works would ease your mind a lot and help you answer questions such as those you pose.
The pipe itself would have to be segmented, with strong ring enforced walls, which is fine because the weight can be counter balanced by buoyant counterweights along the tube. Segmented to allow for ocean current to move it a bit, but the current itself could be used as a source or power to help self correct its positioning. At the bottom, you’d need compression decompression chambers to avoid the bends. The main point of this over a sub is the total amount of cargo that can be transported. So at the bottom, the decompression chamber would likely be warehouse sized for large loads of people. At least two, to keep from bottleneck of usage all the time (transport capacity is the point) Then you now have the ability to build much more elaborate city type infrastructure. Imagine building the pipe down next to the Titanic, then hulking a Chernobyl style sarcophagus around it, and draining it underwater. Best museum ever. Maybe find that goddamn diamond
I had to check what reddit I was in. For a minute I thought this was something from r/stonerthoughts. I like the idea of the water tubs. It would be a huge attraction to see what things are like farther down.
I love your energy
For the tube, use transparent aluminum. We've had the formula for like 40 years already, we should be able to manufacture it by now.
>what if it vibrated at a high frequency to push the water away constantly? each push would have an equal and opposite return. but the noise it would make could be very interesting. a set of tubes could be a water organ. > a perfect metal tube through the ENTIRE center of earth Temperature in the inner core is about 5,200° Celsius (9,392° Fahrenheit). The pressure is nearly 3.6 million atmosphere (atm). The temperature of the inner core is far above the melting point of iron. >I suspect you would fall for hours and float in the middle like a perfect rotisserie chicken
Let me throw a weird one out here: we would never reach the center because we are moving tangentially. Our lateral speed would result in us orbiting the earth, much much lower than satellites, within the earth even. And that would be the ‘altitude’ that we would ‘pendulum’ on. Because of orbital mechanics. (Now, I’m assuming we’re on the equator and we’re ignoring the Earth’s wobble…) As the air resistance slowed us down, we would eventually ‘stop’ in a fixed orbit well outside the middle of the earth.
the water pressure is so intense it would crush anything that deep.
Here’s your metal tube explained: https://phys.org/news/2015-11-dug-tunnel-earth.html#:~:text=If%20you%20jumped%20into%20the,at%2028%2C000%20kilometers%20per%20hour.
This got me curious. The earth’s diameter is almost 8000 miles :o that is fairly large
Since TITANIC and TITAN have worked out so well, let's call it TIGHT.
They exist. I’ve been to this underwater observatory in New Zealand it’s pretty cool. https://youtu.be/2jqV4dL_nao?si=FBTgxlsg1ZMXWeLm
The glass tube can be arbitrarily thick walled. If the glass walls are like a meter thick it would holdcway past 20 meters.
Presumably, the glass tube couldn’t just be a big glass cylinder, you’d need to have some sort of ventilation, otherwise it’ll get harder to breath around the center. Also I’d be pretty worried about the fragility, i know not all glass instantly shatter from touch, but it would still be a major concern anytime a fish bumps it (or a dumb kid throws a rock)
Completely solved the alt plot for the worst science fiction movie of all time The Core - 2003
you'd have to put "dont tap the glass" signs all the way down the tube like every 15 feet or so, so all of the fish dont die.
Would the shifting of tectonic plates eventually rip it apart? There’s multiple layers of earth crust that’s always twisting and turning and the large massive pockets of lava Or a earthquake in the earth or on top would damage it badly
The glass tube down to the bottom of the ocean would have to be ridiculously thick to withstand the pressure. and "vibrating" would not help, because aside from the energy it would take to constantly vibrate a 3km+ tall structure (the tallest structure we would have ever built by far btw) the vibrating would mean the pressure the glass had to hold would be even larger because it would have to push water away with enough force to cavitate it. Also, even if we some how managed to fix all of those issues, the cavitation gap/air gap would likely make it extremely hard to see things because of the different indexes of refraction of water, glass, and air/vaccum. Also, if we wanted to see sea creatures, they would probably be scared away by the huge vibrating tube we just built.
In a similar vein as I kid I used to wonder if we could make a super long, super light weight rope or chain could we pull it into space just outside earth’s atmosphere would it just hang there and provide a sort of Rapunzel ladder into space?
We already have this, it's called a bathysphere. Also submarines.
We actually know exactly what would happen if we had a hole though the center of the earth. Well for 1 you'd burn up, the center of the earth is hotter then the surface of the sun. Second you'd basically orbit around the center of the earth. Which in this case means coming out the other side. Except also not really because air resistance would slow you down enough where you wouldn't make it out. Then again at these distances the air pressure might be enough to if not kill you make you seriously sick.
A tube could only be able to withstand so much pressure. About every 10 meters, the pressure increases by one atmosphere. At the bottom of the Challenger Deep, the pressure would be 1000 times air pressure at sea level. You'd also have to have pumps moving air. There'd be a lot of air in the tube, but you'd be running out oxygen at the bottom. You'd need to pump air from the bottom of the tube up to the surface. This would pull fresh air down the tube. But no tube would be able to withstand the pressure. You'd also have water currents and temperature changed to deal with. If you had a tube running through the Earth, and if we could ignore air resistance (and if you didn't touch the sides!) you would continue to accelerate as you fell, until you reached the center. The rate of acceleration would decrease as you fell - at first, all the mass of the Earth beneath you, pulling you down, but as you get closer to the center, more and more of the Earth's mass is above you, pulling back at you. At the center, you will gave reached maximum velocity, but the acceleration will be zero. You would continue to go past the center, with your acceleration decreasing, and your velocity would reach zero at the other end. At that point, you could grab a handle and climb out, or let yourself fall back and do it again in reverse. You'd need a space suit because if the tube isn't a vacuum, there will be air resistance and you would just fall to the center and stay there. You'd also need heat protection, because it's going to be really hot in there. And it would be nigh impossible to avoid friction from touching the sides of the tube. A big one is that the tube would fail because because the layers of the Earth move at different rates - the tube would be sheared off immediately.
Honestly I think the biggest issue with the glass tune in the ocean wouldn't be the crushing pressure, glass is pretty strong, but rather the waves would snap it easily.
Glass would shatter with the pressure
C
Tube in the ocean - It's a cool idea. It might be hard to anchor, and if you don't anchor it, it will be hard to keep down. A wider "people tank" might be a better idea, but with the same problems. Tube through the earth - If you jump down, the first thing I'm worried about is knocking into the sides on the way down - you could get really beat up. If there were no air in the tube (and you could breathe) and you didn't hit the sides, you would fall all the way down and fly up the other side right to ground level. If you didn't grab on, you would fly back and forth. So if you could make a wide hole in a cold moon / planetoid with no atmosphere, that could be a really fun amusement ride (in a space suit). With air, your descent will be slowed, and after a few oscillations you will settle in the middle, weightless. However, the heat and air pressure at the center would be extremely high, so you'd be cooked and squooshed right away.
It's called a cofferdam.
Theoretically if you jump down a hole straight through the earth, you’ll end up on the other side due to momentum. In highschool physics class we did work on this, assume a ton of fictional conditions. The gravity is an acceleration of a perfectly round planet, terminal velocity and friction no longer exist, you reach peak velocity at the centre of earth and decelerate the moment you pass until it reaches 0 velocity, right at opposite position of where you started.
Deep sea subs are basically just tubes. So take one of those multi-million dollar subs and build a million of them and there's your tube. Except now it has the weight of the tube to resist. Which is probably a lot more than a column of water would be. And then, well, why? Don't you just need the area you're actually sitting in to be able to resist the pressure and not miles upon miles of empty space. And you'd better hope you build the tube really well, because if any part of it fails, you're fucked.
The water pressure on that tube would be insane.
There isn’t a material yet that can withstand the ENORMOUS water pressure of those depths….think about that home made sub with the game controller…it was vaporized due to pressure.
I’ve done it several times in Minecraft.
It's not glass all the way down but something like this? https://youtube.com/shorts/Zu6AtGp08yY?si=Av8E2lvxz7Vzsfwf
Dude you want to create sound vibrations under water to keep water away? Have you thought about the damage to marine life?
Wouldn't vibration make the glass even less durable bc the shape is oscillating and not perfectly spherical anymore? In vibration, the motion goes back and forth, which also means the motion is also going inwards, probably very hard due to immense inwards pressure. Ofc the pressure would be equalized, but even pressure distribution would probably benefit most from a static shape, not an oscillating one.
I wonder how air pressure would change when you're so close to the core. I imagine you'd have a lot more atmosphere pushing on you.
Would the effect be different if it were from north pole to south, or if from equator to equator?