Space station in spin makes artificial gravity, but why exactly?

[SkyWalker]

THIS IS QUITE A CHALLENGE...

A space station in spin will make artificial gravity, this is the way we can live in space according to sci-fi. (e.g. So you can walk on the inside of the circle of the circular spinning ship and have artificial gravity)

But now think relativity:
You can also think that the ship is not spinning, only the universe around it is spinning. So the ship AND all of its objects inside are standing still, but the entire universe around it is in spin relative to the ship.
OK? Got that picture in your mind? Now ask this question from that picture in your mind: Then why does a spinning universe around a ship-standing-still have gravity as an effect inside of the ships circular wall?

i cant answer this question, i see pitfalls everywhere, need help.

I first thought that it happens because the objects inside of the spinning ship want to keep going straight, but the floor is bending/accelerating into the circular spin and thus pushing the objects into the floor. But that is also not an answer, because then one needs to define straight, but straight does not exist in relativity, something can only be straight relative to something else. So thats a no-go.
The other reason is that I just painted a picture that all objects inside the ship and the ship itself are just standing still, it is only the universe which is spinning relative to it. Why would a spinning universe create gravity inside the ship?

I am confused, don't see why. Do you guys have a theory that can explain this phenomenon of gravity through spin, which is still holds in my relativity "picture"?

 

[Duxwing]

You're right, the spinning universe doesn't make any gravity; the force created by the spinning is centrifugal force.

-Duxwing

 

[SpaceYeti]

You're making a contradiction. The rest of the universe is in spin relative to the station, but then you ask why things inside have false gravity when it's the universe that's spinning... well, because inside the space station, it's the space station that's spinning within the universe, creating centripetal force. You're trying to look at what's happening from two different places.

 

[Cognisant]

If the space station were motionless everything inside would be weightless, now if the station starts spinning the objects inside wouldn't be magically attracted to the floor but the air inside would be drawn along with the station's motion which in turn would compel objects to likewise be drawn into the motion and as they speed up their momentum makes them appear to be attracted to the "ground".

If a circular space station had a single long room with a flat floor and a ball floating above that floor, as the station moves the ball would appear to go flying down this hallway (when in actual fact it's the hallway that's moving, not the ball) but it would slow down and as it slows down it would sink to the floor and start rolling, and continue rolling until friction changes the ball's frame of reference to that of the station, although not perfectly mind you, if you ran one way down the hallway both yourself and the all would become heavier and if you ran the other way both yourself and the ball would become lighter, because you're either accelerating or decelerating yourself relative to the universal frame of reference.

 

[Etheri]

How is the way in which your question is posed any diffrent from the 'blind lift', in which you do not know if you're in a gravity field or accelerating in space?

General relativity, there's gravity and acceleration act alike.

 

[Cognisant]

How is the way in which your question is posed any diffrent from the 'blind lift', in which you do not know if you're in a gravity field or accelerating in space?

What if gravity is exactly that, that over time it is not gravity that pulls us down, instead we are accelerating through some kind of gravity-spatial dimension and it is or momentum that's holds us down?

Lol, don't worry I'm joking.

 

[PhoenixRising]

This is kind of a personally developed hypothesis based on General Relativity and the Lorentz transformation:

Movement creates both time and gravity. The closer to light speed you travel, the slower time passes for you and the heavier objects become. This would indicate that time and gravity are effects of the velocity of matter.

If the space station is standing still relative to the movement of massless particles, then there will be no gravity and time will move a bit faster (as it does for satellites outside of the earth's atmosphere), since the movement of massless particles relative to the station is ~0 mps:186,282 mps. If you increase the spin of the station to, say, a quarter of the speed of light, then time will slow down just a bit and gravity will be present.

 

[Cwestiwn]

The relativistic idea that you can say that you're stationery and rest of the universe is moving only applies in inertial frames (where you're not accelerating or decelerating) since there is no test you can do in such frames to establish whether it's you that's moving, or everything else.

The space station requires a constant centripetal acceleration to keep it spinning, thus it is a non-inertial frame. In a non-inertial frame you an test for "imaginary" forces like the Coriolis force or the centrifugal force that creates the artificial gravity on the space station and thus establish that it is in fact you that's moving, and not the universe. So in this case you can't actually think of the station as motionless and the universe spinning.

 

[Proletar]

Wait, what?

If the universe was to rotate around the still space-station, that would be insane. Take a star 1 000 light years away from the space-station. If the station (which is to say the universe) was to rotate 360 degrees in ten seconds, the star would have to travel 628 light years per second. Furthermore, if the universe was to gravitate towards this space-station, it would have to be incredibly heavy. Like a supermassive space-station made of super-massive black holes.

Conclusion; the space-station rotates, not the universe around it.

 

[SkyWalker]

I have thought about it from a lot of aspects, but I still don't get it.

Unless the universe around the station "counts more" because it is heavier (e.g. more mass counts more)???

otherwise one should be able to reverse the viewpoint as in my example "the ship is still, but the universe is spinning around it".

other idea i had was: the ship is actually in orbit of something (thus constantly falling and missing earth, in case of orbiting earth), maybe the fall of the orbit is used as some kind of reference frame to which the ship is spinning. and thus the difference between the fall and the spin is creating the centrifugal force?

 

[SkyWalker]

You're right, the spinning universe doesn't make any gravity; the force created by the spinning is centrifugal force.

-Duxwing

In defense:

I didn't say anywhere that centrifugal force creates actual gravity, I said it creates artificial gravity, e.g. the effect of gravity.

And yes, I agree that centrifugal force is different from gravity according to "modern science", but thats only an assumption in our primitive theories by the way! Gravity and centrifugal force might be connected somehow, like someone above also mentioned, since it intuitively makes sense.

 

[redbaron]

1. What are you smoking?

2. Where do I get it?

 

[Etheri]

The relativistic idea that you can say that you're stationery and rest of the universe is moving only applies in inertial frames (where you're not accelerating or decelerating) since there is no test you can do in such frames to establish whether it's you that's moving, or everything else.

The space station requires a constant centripetal acceleration to keep it spinning, thus it is a non-inertial frame. In a non-inertial frame you an test for "imaginary" forces like the Coriolis force or the centrifugal force that creates the artificial gravity on the space station and thus establish that it is in fact you that's moving, and not the universe. So in this case you can't actually think of the station as motionless and the universe spinning.

This is true. You're not working in an inertial frame, but a rotating one, thus physics as you were thought them do not apply. There is a constant centripetal acceleration.

In defense:

I didn't say anywhere that centrifugal force creates actual gravity, I said it creates artificial gravity, e.g. the effect of gravity.

And yes, I agree that centrifugal force is different from gravity according to "modern science", but thats only an assumption in our primitive theories by the way! Gravity and centrifugal force might be connected somehow, like someone above also mentioned, since it intuitively makes sense.

You're right, the spinning universe doesn't make any gravity; the force created by the spinning is centrifugal force.

-Duxwing

Gravity works towards the space station, centrifugal, by definition and by name, always works away from the space station. Mind if I ask how you're comparing forces that work in a diffrent direction? I'm quite certain you're looking for a centripetal force which keeps you on the station and curving along with it, not a centrifugal force that will be happy to throw you off.

 

[SkyWalker]

Aha "curving along with it"? That is only if you are not relativistic, that only holds if you say the rest of the universe is (kind of) still, and only the ship is spinning. I turn things around, and then the default explanation doesn't hold, this is the root of the problem. And although I wish it was, your reply is no answer to that problem.

 

[Etheri]

Aha "curving along with it"? That is only if you are not relativistic, that only holds if you say the rest of the universe is (kind of) still, and only the ship is spinning. I turn things around, and then the default explanation doesn't hold, this is the root of the problem. And although I wish it was, your reply is no answer to that problem.

Have you read the rest? You can't apply regular physics because your referance frame is spinning. You can't just randomly say 'lets look at it from this POV and see if it all still holds up'.

 

[Lostwitheal]

The trouble is that the space station spinning whilst the rest of the universe is still, and the rest of the universe spinning and the space station having no rotation are actually the same thing.


http://en.wikipedia.org/wiki/Mach%27s_principle

 

[ProxyAmenRa]

The space station spins around a centroid. The rest of the universe has nothing to do with the space station spinning. Though, space time is dragged behind spinning objects.

 

[Jah]

are you remembering about inertia ?


(newton comes in handy here, no need to go all the way with relativity yet)

 

[SkyWalker]

Have you read the rest? You can't apply regular physics because your referance frame is spinning. You can't just randomly say 'lets look at it from this POV and see if it all still holds up'.

My "reference frame of the ship" is NOT spinning. (at least in the way I painted the picture)

My "reference frame of the universe" is spinning. yes.

And by the way: That is quite similar on Earth itself. Except that our Earth model is 3D and our ship model is 2D. This gives me the chills, there is something so obviously similar here, but i cant grasp it. What I do see is that we see centrifugal force as 2D and we see gravity as 3D. So gravity (compared to centrifugal force / 2D artificial gravity) might be something like a spin in multiple directions (3D). This goes something along the line as: Earth might be actually hollow and spherical at the same time. (hollow as in a 3D centrifugal force, us living on the inside, or spherical as in conventional gravity, us living on the outside) It might be all the same in the end. Just depends on the way you look at the spacetime bend.

 

[Reluctantly]

I'd say the trick to solving your paradox is to find a way where the space station acts on the universe and the universe acts on the space station, simultaneously.

In other words, I guess the question might be "If A moves relative to B, does that imply that B moves relative to A as well?" Perhaps, it's the only way to eliminate the paradox.

 

[Jah]

Hmm... ok,
here's a thing.

Relatively you're also making the entire universe spin in relation to you.
This means you've acceleration (centripetal force) which bends space-time (imagine it's like this; everytime you have an acceleration this bends spacetime (you probably know the visualization of space-time as a membrane, where gravity is a like placing a weight on that membrane).


The centripetal force is upwards towards the center of your station. kinda opposite to the one you'd get from gravity, but that's beside the point, these are quite different, (in that centripetal force is a so-called pseudo-force or a fictitious force (if I remember correctly) )

anyway, Since you have an acceleration there (F = m A ) you have a "weight" upon the space-time membrane, which means a couple of things;

Your time will be affected and light will look different (since it enters a gravity-field, even an induced one like this) speed up a little, -look up gravitational effect,
and you will be able to walk around along the inside of the space station.



now there are very noteable differences between this and the earth. (you all probably have some reference to Halo (the games) where the protagonists are stationed originally on a Space-station shaped like a Halo )

On earth, you have a massive massive object, where if you take the entire earth and make a spherical surface around it, you have can make a Surface field and run your Gaussian integrals (basically you'll be calculating the flux here, but pretty much the same principles)
you'll end up with a center point of the entire mass, which will be kinda like the sum of the drag the entire mass has along the surface of that sphere you made.

in the space station, you'll also have this, just make it donut-shaped instead of spherical , imagine a field around the entire thing, and you'll get a similar center-point as the one you got with the Earth, except the force exerted from this point will be much much smaller due to the lack of mass.


Good thing is, your station is spinning, so it induces it's own field of gravity, simply by the fact that it constantly alters your inertia (p = mv) and the alterations to this is found by derivation ( p' = m v' = m a = F )


and we're back at the spinning station.

technically it seems like any other gravity-field, when you're standing on terra firma, but if you'd climb a ladder on your space-station, the gravity would actually become stronger in the higher strata. (since it moves faster)





But yes, one of the weirdest elements of Einstein are that you're actually Bending SpaceTime in exactly the same way as it would if you stood on a massive object, by sitting on an object which is accelerated. (This is also the one usually explained using the Elevator, in Einstein's explanations)

 

[pjoa09]

I don't know.

I will try to feed the discussion using Jahs stuff.

Being in a falling elevator versus standing in a still elevator with the building that it is within rising.

The other way around doesn't seem to work.

 

[Jah]

that's... curious.

but yeah, the elevator parable/paradox that einstein used was that there is no difference for you, in any way whatsoever, if you're standing in an elevator that's stationary on Earth (that is, within a field of gravity) and if that elevator is accelerated upwards at roughly 10 m/s^2 (if you don't like approximations, or want to argue, just pretend I'm using a number which is exactly the gravitational value on the surface of the earth. )

we can extend that one also to include that your elevator is standing on a space-station which is rotating.


The point isn't that it's an Elevator, but that it is a Closed Box, which people are familiar with standing in.


It doesn't matter what the acceleration is, whether it's from being near a massive object, or being pulled through space by a choir of angels, or if it's from standing in an interstellar tumble-dryer and experiencing the centripetal acceleration... the effects are the same, and you'll experience them the same way.



The whole discussion was started around an imaginary universe where you're not connected or in relation to that which is outside you... kinda like arguing that you didn't move within the car even though the cops pulled you over for speeding.

It's not about which frame you see the world from, but about the Change in the relation between the two frames. (i.e. the universe and your center of mass)

Even though you aren't "moving" in relation to the space station, and from your point of view you're standing still on the surface of whatever shape it's in, you still have an inertia in regards to the universe that is Space-time, and because you stand on something spinning;
The inertia Changes. (inertia is your mass and your velocity.)
Change in inertia means the change in your velocity.
change in velocity we call acceleration.
gravity is another form of acceleration.
gravity and "other" acceleration are indistinguishable for the subject/object.
thus you will observe the same phenomena as from gravity, albeit your "up" will be towards the donut-center, and not away from the larger mass.

 

[SkyWalker]

yes true, we must see the problem as the relative difference between the 2 viewpoints. I was just reversing the viewpoint around to the other side, to say: they should both be possible at the same time (e.g. dont forget the other viewpoint).

is it just me or... if one is accelerated upwards, then one would increase ones gravity with that acceleration! because the original gravity is also still there, otherwise "up" has no meaning???

 

[Sorlaize]

Just use magnetic boots on your space station. done.

 

[SkyWalker]

Just use magnetic boots on your space station. done.

that would suck, such boots would drive me crazy

p.s. The one that solves this challenge will get a one night free in my future space hotel, plus free late check-out so you don't have to hurry in the morning. If its a really good answer I'll even arrange you a girl (or boy, whatever you fancy).

 

[Velo]

p.s. The one that solves this challenge will get a one night free in my future space hotel, plus free late check-out so you don't have to hurry in the morning. If its a really good answer I'll even arrange you a girl (or boy, whatever you fancy).

Well, now that you've made it worthwhile, it's time to chime in and attempt to win a free night at the future space hotel.

but yeah, the elevator parable/paradox that einstein used was that there is no difference for you, in any way whatsoever, if you're standing in an elevator that's stationary on Earth (that is, within a field of gravity) and if that elevator is accelerated upwards at roughly 10 m/s^2 (if you don't like approximations, or want to argue, just pretend I'm using a number which is exactly the gravitational value on the surface of the earth. )

So far, so good. We can't tell if we and the elevator/box are in a gravitational field or if we are all undergoing LINEAR acceleration.

we can extend that one also to include that your elevator is standing on a space-station which is rotating.


The point isn't that it's an Elevator, but that it is a Closed Box, which people are familiar with standing in.


It doesn't matter what the acceleration is, whether it's from being near a massive object, or being pulled through space by a choir of angels, or if it's from standing in an interstellar tumble-dryer and experiencing the centripetal acceleration... the effects are the same, and you'll experience them the same way.

Oops, here we've gone astray. Angular acceleration from spinning does not equal linear acceleration. With some simple experiments, we can distinguish between being in a gravitational field versus being in the interstellar tumble-dryer.

So, how do we tell? First, I produce my handy frictionless, magnetic-bearing, dragless gyroscope, which I keep handy at all times for just this occasion. Once it is spinning at a sufficiently high rate with the axis pointing straight up (as far as we can define up), we simply watch the axis of the gyroscope. If we are in a gravitational field or undergoing LINEAR acceleration, we won't see anything happening. The gyroscope spins without changing its spin axis orientation.

However, if we are being tumble-dried, then we will see the orientation of the gyroscope start to change as our massive spaceship rotates. Call it precession, wobble, or whatever you like (perhaps conservation of angular momentum), but we will definitely notice that the gyroscope's alignment will change from our perspective.

"But wait," you might say. "What if you forgot the gyro? Then what, smart guy?"

OK, now we move to the backup experiment. I bring out the spring-loaded plunger and pinball from an old, broken-down pinball machine that I have in the event of having lost the gyroscope in an unfortunate poker game. We repeatedly launch the pinball in horizontal (to us) directions, each time aligning with a different angular reference we've noted on the floor. We carefully track the flight of the ball in each instance. We find that the ball does not trace the perfect parabolic arc that we would expect in a normal gravitational field. Instead, the ball seems to travel away from the expected path ever so slightly, and the magnitude of the error depends upon the direction that the ball was launched.

Egads, man (or woman), we've just discovered the Coriolis effect, and we're inside a giant spinning appliance.

In short, we can distinguish between linear acceleration and angular acceleration, but we can't distinguish between linear acceleration and gravity.

 

[Lostwitheal]

yes true, we must see the problem as the relative difference between the 2 viewpoints. I was just reversing the viewpoint around to the other side, to say: they should both be possible at the same time (e.g. dont forget the other viewpoint).

is it just me or... if one is accelerated upwards, then one would increase ones gravity with that acceleration! because the original gravity is also still there, otherwise "up" has no meaning???

You seem rather preoccupied with being able to turn this situation on it's head. My post above explains why the distinction is meaningless in terms of the effect.