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Thread: Help answer a Portal related question

  1. #1 Help answer a Portal related question 
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    Hi,

    First post so please be kind. :wink:


    There's a thread over at rllmuk forum relating to a theoretical scenario for the game Portal. Basically we can't decide whether the answer to the set up in the image is a) Fly or b) Slide and I'm hoping someone (that'll be you guys) with a bit more understanding of the laws of physics can help solve.

    http://yfrog.com/mdportalimagej

    Thanks.

    EDIT: Link to the actual thread -

    http://www.rllmukforum.com/index.php?showtopic=244036


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  3. #2  
    Moderator Moderator Janus's Avatar
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    I'll give you the only answer I can:

    It depends on how the makers of the game designed the portals. Invoking the laws of physics cannot answer your question because there are already instances in which the game ignores them for the sake of the game, so I can't tell you how the game would handle this situation.

    For an example of how the game ignores real physics consider the following example:

    You are on a platform 100 ft from the floor. There are is a portal on the platform and one on the floor. If you jump off the platform through the portal on the floor, the game would have you exit the portal on the platform with the same speed as you entered the first portal, allowing you to reach a height of 200 ft above the floor at the peak of your trajectory.

    This violates the conservation of energy.

    Your total energy standing on the platform is equal to your gravitational potential energy(GPE) plus your kinetic energy (KE). At this point, your KE=0, and your GPE is some value greater than it would be if you were standing on the floor. (found by mgh, which is your mass time the acceleration due to gravity and the difference in height)*

    When you jump from the platform and fall towards the floor you give up GPE for KE, but your total energy, GPE+KE remains the same. When you reach the first portal, Your KE will be high, but your GPE will be lower.

    If you come out of the second portal with the same KE, your total energy will have increased, as your GPE will be back to what it was before you jumped.

    If energy were conserved between portals, you should exit the second portal with just enough speed to bring you back level to the platform.

    Conversely, if you were to jump into the portal on the platform, the game would have you exit the floor portal with just enough energy to pop out on to the floor, in which case, energy will have been lost.

    The game also plays fast and free with consevation of momentum, as it allows you to enter a portal going in one direction and exit going in another (though sometimes they conserve momentum in one direction but not another.)


    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  4. #3  
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    Nice reply, thanks.

    Game mechanics aside (let's say the portals are worm holes or something), what do you think would happen in this scenario?
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  5. #4  
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    first i think the object will just slide away cause i didnt saw any amortization on the lower platform which gave no speed to gift or what ever it is.
    And if its a wormhole,gravity inside would accelerate the package and then repress it out with same speed as it entered so it wont get any speed from it when it comes out.It would end up on the other side with same speed as it entered.
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  6. #5  
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    Quote Originally Posted by blaster
    first i think the object will just slide away cause i didnt saw any amortization on the lower platform which gave no speed to gift or what ever it is.
    And if its a wormhole,gravity inside would accelerate the package and then repress it out with same speed as it entered so it wont get any speed from it when it comes out.It would end up on the other side with same speed as it entered.
    So you're saying it would fly out?
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  7. #6  
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    I have thought about this too... and if you visualize the "trampoline" analogy of spacetime/gravity that so many have used, and try visualizing a portal there, it's easy (the link has complicated terms, but the visualization is the same). http://lnns.webs.com/lnns/wormhole_graphic.jpg
    But with a 3D trampoline, wouldn't you get a 3D portal, as you got a 2D portal in the 2D trampoline? So I think a portal in our space would be a globe, and continuing the visualization, if you entered a portal at a certain latitude and longitude, as it were, you would logically exit from the same latitude and longitude on the other portal, as would happen in the 2D analogy.
    As Janus said, there would have to be some resistance somewhere to make it physically possible and not violate physics, and since we're messing with a gravity analogy, then it makes sense that the gravitational forces exerted by the portal would slow you down*. So you would remain in stasis inside a parallel space to our universe unless you pulled or pushed yourself out somehow, or if you want to make the game possible, then the gun has a machine or battery that will propel you out of the portal with a calculated equal velocity as when you entered.
    Since the walls of the portal are that of curved space, I think you would have the appearance of being inside yourself turned inside out, as you are seeing yourself from all directions.
    I like these thought experiments, and I hope my insight isn't confusing...

    *So in the trampoline, if the portal went below the surface like a tunnel, you'd get a gravity towards the portal, like a black hole, hopefully not as strong. If it went above the surface, you'd get literal antigravity, methinks, that repelled you from the portal.
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