514void

Relativity seems to allow it.

Yes, but if you have these disks on the top of a container, and the center of mass of the system is not at the center of mass of the 2 disks, then would the center of mass move towards the disks as they were spun up due to relativistic mass gain? would the system move so that the center of mass stayed at rest in an inertial frame? would transferring energy from one part to another part using AC power cause acceleration?

A) If you have a closed system with 2 disks and spin the disks in opposite directions, would the system stay at rest in an inertial frame? B) And if you tilted the disks would the system still stay at rest in an inertial frame? C) Is relativistic mass directional? If A then you could change the center of mass of a system while keeping the system at rest in an inertial frame. If (B and C) The same thing. So if A and/or (B and C), then I believe that a closed system could accelerate itself.

the energy would be transferred to the container, which would gain mass and the battery wouldn't transfer as much 'negative' momentum as it is slowed and returned to the start. win, win.

I don't see how that wouldn't work, nice one.

I read somewhere that relativistic mass as opposed to rest mass does have a direction. so to make the mass gain along a vector you would need to have the axle perpendicular to the desired force. Also you would need spinning opposing disks to cancel the net torque on the system. So spinning twin disks faster or slower would have no net force in any direction, but would gain directional mass. So could you control the speed of the disks while moving them in a system to gain a net force in a direction?

yes, in any inertial frame, the outside of a spinning disk will have relative motion to its center. does relativistic mass gain have a certain direction like length contraction? I suppose that this is known from circular particle accelerators where the directing force and accelerating force are separate.

the velocity of the rim of a spinning disk with the center being at rest in a inertial frame would always be more than the center of the disk.

If the disk was fixed at the top of the container, and it was spun up, would the center of mass move closer to the disk?

I was thinking that this could be used to accelerate spaceships. Here is the hypothisis: If i have a closed system with a disk that moved up and down, and the disk was made to spin by a motor at the top of the system and made to stop spinning at the bottom of the system, the whole system would feel a force that would accelerate it upwards. The system could have a similar disk that moved up and down but spun the opposite direction than the first to stop the whole system from spinning. I have thought about how It mightn't work, such as if you spun up the disk, would it lose translational inertia? I think no, since according to relativity, there is no preferred frame to slow down against. I understand that there would not be much translational force produced for 'non relativistic' speeds, but sensors are quite good, so this might even be experimentally testable on earth.

yer, i started writing that before you answered, then i added the bit where i said that i didn't realise that the length of space changed

so in frame A all of B's clocks would go slower... and in frame B all of A's clocks would go slower... so the paradox would grow as time elapsed? o, i didn't realise that moving clocks changed the length of space between them.

but all clocks in frame A would be syncronised, and all clocks in frame B would be syncronised so for each clock in frame A, the nearest clock in frame B would show a certain time. how would there be any difference in any B's clocks observed from frame A?

so frame B's clocks would not look syncronised? like all of frame B's clocks would show different times? that seems weird since you could check all of frame B's time from all of frame A. I would of thought that each frame would see each other frame as being syncronised. Unless there was a preferred point in space, I'm not sure if there is any mention of that in SR.

I am not sure what would happen if there were multiple lines of infinite clocks where each line of clocks was at rest in an inertial frame. each line of clocks is syncronised so that you can tell what time it is in each inertial frame from any position. I realise that in SR each inertial frame that you would see the others going slower, but wouldn't that create a paradox? a clock in inertial frame A would read the year 3000 and see a clock in inertial frame B as having the year 2000, and the clock in frame B would see the clock in frame A as having the year 1000 3000 = 1000? thats a paradox right?

The length contraction of an object was first theorised in ether theory. The length of an object can be measured by the time it takes for light to travel the length of it. (point A and point B) The ether has the speed of light going in all directions at c. If you move relative to the ether then the time for light to travel from point A to point B would be different than from point B to point A If you take the average of those measurements then you get the Lorentz factor. In experiments where length was measured by light travelling the length of a distance moving at different speeds compared to the ether, there was an expected "relative length expansion" by the lorentz factor. There was no detected "relative length expansion", so it was theorised that the actual length measured was shortened as it moved through the ether. Relativity theory took this theory and took out the ether and predicted that any object would "appear" to contract by the lorentz factor corresponding to the relative speed that object would move to an observer.