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Thread: Question on the Universe speed limit (light ???)

  1. #1 Question on the Universe speed limit (light ???) 
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    i was just thinking of a practical example trying to find something that would be able to pass on information faster than the speed of light.

    I came up with the following, please don't go attack the post it was just a thought.

    According to relativity if the sun disappeared in a instance it would take 7/8 minutes before the earth began to leave its orbit. Hence the information that the sun is no longer there can only travel at the speed of light

    My counter is if the earth was using centrifugal forces to stay in orbit and there was an invisible string connecting the sun and the earth and that string is cut, the effect on the earths orbit would be immediate, there would be no 8 minute delay??

    Can someone explain this away, I cant be the first to think of this scenario hence i must be going wrong somewhere


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  3. #2  
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    I'm curious, where is this string you speak of???

    Any second year mechanics course will teach you that there is no such thing as centrifugal force (only centripetal in the other direction). The earth is held in place by gravity, a curvature, or well if you will, in space/time surrounding the sun. If you remove the sun, space/time will realign and get rid of the gravity well, but the information that the sun is missing will propagate out at 'only' the speed C, no faster! Since gravity and all other effects are also limited to this speed there will be noanomalous effects.

    Incidentally, if you can make the sun disappear instantaneously without other consequences, the speed of light is the least of your limitations !!


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    In simple terms the gravitational effect change due to the sun's disappearance would reach the earth at the same time as the change in radiation (sun's light loss).
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    Quote Originally Posted by MigL
    I'm curious, where is this string you speak of???

    Any second year mechanics course will teach you that there is no such thing as centrifugal force (only centripetal in the other direction). The earth is held in place by gravity, a curvature, or well if you will, in space/time surrounding the sun. If you remove the sun, space/time will realign and get rid of the gravity well, but the information that the sun is missing will propagate out at 'only' the speed C, no faster! Since gravity and all other effects are also limited to this speed there will be noanomalous effects.

    Incidentally, if you can make the sun disappear instantaneously without other consequences, the speed of light is the least of your limitations !!
    OK maybe I havent explained this clearly

    I know all about what the physics says

    I was using it as an example. I was trying to create a scenario where the information that the sun has vanished can reach us faster than the speed of light.

    the whole situation is hypothetical a sun wouldn't just vanish

    Quote Originally Posted by mathman
    In simple terms the gravitational effect change due to the sun's disappearance would reach the earth at the same time as the change in radiation (sun's light loss).
    and I know that is the case but from that its said that NOTHING can travel faster than light my question is in the scenario Iv created here the information of the sun disappearing reaches us faster than the speed of light (instantly)

    So back to my question (is it possible for information to travel faster than the speed of light, if they are directly connected, as mentioned in the above example)
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    If you had a string that long, it'd still take (longer than) 8 minutes for the release of tension to reach from one end to the other. It's the same problem as taking a light year long rod and pushing on one end.
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    Quote Originally Posted by MagiMaster
    If you had a string that long, it'd still take (longer than) 8 minutes for the release of tension to reach from one end to the other. It's the same problem as taking a light year long rod and pushing on one end.
    ok I did some reading on the light year rod scenario, its the same as the principle I was trying to put forward.

    If the rod was made of an incompressible material and a material that cannot be broken and was pushed what would happen to the end of the rod.

    (please dont now say that a material like that is impossible)

    Black holes are incompressible (lets say we had a rod that was made from something as dense as a black hole) <<< again I know its impossible just trying to look at the situation
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    Well, if you accept its impossibility, then, yes, such a rod could transmit info faster than the speed of light. All that really proves though is that such a rod couldn't exist in this universe.
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    If the rod was made of an incompressible material and a material that cannot be broken and was pushed what would happen to the end of the rod.

    (please dont now say that a material like that is impossible)

    Black holes are incompressible (lets say we had a rod that was made from something as dense as a black hole) <<< again I know its impossible just trying to look at the situation
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    Quote Originally Posted by proximityinfotech3
    If the rod was made of an incompressible material and a material that cannot be broken and was pushed what would happen to the end of the rod.

    (please dont now say that a material like that is impossible)

    Black holes are incompressible (lets say we had a rod that was made from something as dense as a black hole) <<< again I know its impossible just trying to look at the situation
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    Such a rod would allow violation of special relativity.

    That is why, as a result of special relativity, such materials are indeed impossible. There is no such thing as a rigid body in special or general relativity.

    Who said that black holes are incompressible ? Whqt do you think that even means ?
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  11. #10  
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    I'll add that if you had a rod of crazy-high, but not infinite, stiffness, you could get the transmission speed to approach the speed of light (AFAIK), but never exceed it.
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    There is always the idea of quantum entanglement. Although we do not know that it exists over large distances for you theoretical case what if we said that this string that was holding the earth to the sun was made up of entangled particles. Therefore giving instantaneous notification to the earth that the sun was gone and traveling faster than light!
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    My counter is if the earth was using centrifugal forces to stay in orbit and there was an invisible string connecting the sun and the earth and that string is cut, the effect on the earths orbit would be immediate, there would be no 8 minute delay??

    Think about it, if I cut a string in one place, it would travel down each atom until it reaches the body, lik a chain reaction. We don't notice this because it takes a very short amount of time with short strings but with one one astronomical unit long, it would take a lot longer. I'm not sure of the exact speed though
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