Am 25.02.2012 12:46, schrieb Warp:
>    How about this theory:
>
>    Make one portal on the ground and the other on the ceiling right above it.
> Then take a metallic rod that's exactly the same length as the height of
> the room, pass it vertically through the portal, and then weld its ends
> (iow. the rod gets welded to itself).
>
>    Now the rod can be moved horizontally and vertically, but it cannot be
> turned around a horizontal axis (because it stops itself from being turned).
> It's effectively an infinite rod. Now let the rod go.
>
>    The rod will start falling.

Why should it? Downward motion won't put the endless rod into a state of 
lower potential energy, so it will not happen.

To the contrary, every coaxial acceleration of the rod would impose an 
ever so slight length contraction due to relativistic effects, leading 
to buildup of internal stress (and hence internal energy - not sure how 
the expert would call this type), while deceleration would reduce the 
internal stress, so deceleration is likely to happen spontaneously while 
acceleration would require external energy input (and I mean energy 
input, not just some force). So even if the rod was falling in the first 
place, given sufficient time its motion will actually /stop/.

(You /could/ force it into motion by heating it up though: As the 
material would try to expand in all directions, again internal stress 
would be induced, and as any increase in speed - whether up- or 
downwards - would reduce this stress due to length contraction, a tiny 
push /would/ eventually get it up to relativistic speed - provided the 
rod doesn't melt long before due to air friction. Or at least that's how 
the thought experiment goes - maybe there's a flaw in it as well.)

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clipka <ano### [at] anonymousorg> wrote:
> Why should it?

  Because gravity points down at all points in the rod. There is no force
in the opposite direction counteracting gravity.

  If the rod were not welded to itself, it would definitely fall (until
it collides with the borders of the portal or whatever), no? Welding it
to itself doesn't change this. (Basically the only thing the welding
achieves is that it stops the rod from tilting.)

> Downward motion won't put the endless rod into a state of 
> lower potential energy, so it will not happen.

  The rod is not literally endless. It's just that the parts that go
thrown the portal on the floor are transported to the portal on the ceiling.
(From a physics point of view this would mean that the energy required to
transport matter adds to the potential energy of said matter if the endpoint
is higher than the startpoint.)

-- 
                                                          - Warp

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I wonder how the fact that teleportation is revealed to be limited by the 
speed of light affects this, tho.

-- 
Darren New, San Diego CA, USA (PST)
   People tell me I am the counter-example.

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Am 26.02.2012 17:35, schrieb Warp:
> clipka<ano### [at] anonymousorg>  wrote:
>> Why should it?
>
>    Because gravity points down at all points in the rod. There is no force
> in the opposite direction counteracting gravity.
>
>    If the rod were not welded to itself, it would definitely fall (until
> it collides with the borders of the portal or whatever), no? Welding it
> to itself doesn't change this. (Basically the only thing the welding
> achieves is that it stops the rod from tilting.)

That's /one/ way to interpret the observable effects of gravity, but the 
force of gravity is not necessarily the /cause/ of the movement, but may 
instead be just the result of trying to /counter/ that movement. 
Remember how inertia is not caused by some force of inertia, but instead 
a force of inertia is caused by trying to counter the inertial movement.

The movement due to gravity may instead be a result of quantum 
fluctuations in the position of the object, which favor positions with 
lower potential energy.

>> Downward motion won't put the endless rod into a state of
>> lower potential energy, so it will not happen.
>
>    The rod is not literally endless. It's just that the parts that go
> thrown the portal on the floor are transported to the portal on the ceiling.
> (From a physics point of view this would mean that the energy required to
> transport matter adds to the potential energy of said matter if the endpoint
> is higher than the startpoint.)

Actually that's the one weak point of all the portal stuff: Rather than 
allowing objects to fall through without a change in speed, a real 
working portal technology would have to result in a repelling force at 
the lower portal itself, proportional to the difference in potential energy.

So no automatic "speedy thing goes in, speedy thing comes out".

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Am 26.02.2012 18:56, schrieb Darren New:
> I wonder how the fact that teleportation is revealed to be limited by
> the speed of light affects this, tho.

... or is it?

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On 2/26/2012 15:21, clipka wrote:
> Am 26.02.2012 18:56, schrieb Darren New:
>> I wonder how the fact that teleportation is revealed to be limited by
>> the speed of light affects this, tho.
>
> ... or is it?

Have you played Portal 2?

Answer: Yes, the developers say so in the commentary. :-)

-- 
Darren New, San Diego CA, USA (PST)
   People tell me I am the counter-example.

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On 2/26/2012 15:20, clipka wrote:
> The movement due to gravity may instead be a result of quantum fluctuations
> in the position of the object, which favor positions with lower potential
> energy.

That's kind of a non-answer, tho, given that the potential energy is indeed 
mass.

> Actually that's the one weak point of all the portal stuff: Rather than
> allowing objects to fall through without a change in speed, a real working
> portal technology would have to result in a repelling force at the lower
> portal itself, proportional to the difference in potential energy.

Unless you're assuming the power is not coming from the gun itself. I would 
think anything powered by a black hole could probably generate as much power 
as it needs to via hawking radiation. Certainly as much power as we've seen 
it use.

-- 
Darren New, San Diego CA, USA (PST)
   People tell me I am the counter-example.

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Le 27/02/2012 01:23, Darren New a écrit :
> Unless you're assuming the power is not coming from the gun itself.


Or, if you opened the gun, you would find a set of miniportals with
their infinite rods falling all over again and again.

That will answer "where does the infinite energy come from, for the new
portal." (now, it's a chicken & egg... how was the first portal done...
maybe with some failed experiment in time travel or space travel)

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clipka <ano### [at] anonymousorg> wrote:
> That's /one/ way to interpret the observable effects of gravity, but the 
> force of gravity is not necessarily the /cause/ of the movement, but may 
> instead be just the result of trying to /counter/ that movement. 
> Remember how inertia is not caused by some force of inertia, but instead 
> a force of inertia is caused by trying to counter the inertial movement.

  I don't understand.

  At every single point in the rod you have an acceleration downwards of
about 9.8 m/s^2 due to gravity.

  What exactly is the force in the opposite direction counteracting this?

-- 
                                                          - Warp

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Darren New <dne### [at] sanrrcom> wrote:
> Unless you're assuming the power is not coming from the gun itself. I would 
> think anything powered by a black hole could probably generate as much power 
> as it needs to via hawking radiation.

  You can't use a black hole to generate energy because you have no way
of controlling the amount of energy it produces.

  Rather ironically, the smaller the black hole, the more energy it produces
(assuming the Hawking radiation hypothesis is true) and the faster it
evaporates, and very small black holes produce enormous amounts of energy
and evaporate extremely fast.

  For example, a black hole with a mass of 200 thousand kilograms would
evaporate in just 1 second and release an amount of energy equivalent
to 5 million megatons of TNT. (The largest hydrogen bomb ever detonated
was "only" 50 megatons.)

  I haven't done the math but I assume that if you had a manageable mass
as a black hole, such as 1 kilogram, it would evaporate in microseconds
or faster (and still release a rather big amount of energy).

  In order to keep the black hole at a constant mass and producing energy
you would need to feed it matter continuously. At the rate of evaporation
of a 1-kilogram black hole I wouldn't be surprised if you had to feed it
matter faster than c in order to keep it from evaporating.

  A much larger black hole takes more time to evaporate and releases less
energy. The problem now becomes how to handle that black hole and stop it
from plummeting towards the center of the Earth. A black hole (probably)
can have an electromagnetic charge, which means you could keep it hovering
inside a magnetic field. But we are talking about millions and millions of
tons here. The magnetic field required to keep a mass of that size hovering
is probably so strong that it would melt everything around it (including
the hardware used to create the magnetic field in the first place).

  Of course with such massive black hole you also get the problem of its
gravity becoming a significant hazard factor close to it. It would have to
be kept hovering quite far away from all other objects, and in a vacuum
(else it would constantly suck atmosphere).

  Then we have the problem of what to do with the excess energy. Not only
do you have to feed the black hole a constant stream of matter to stop it
from evaporating in a multi-million-megaton explosion, but you also have
to do something with the energy that it's producing. It has to go somewhere.
And there's a lot of it. (Basically you are converting matter into pure
energy, and matter has incredible amounts of it.)

  The hazards of having such a source of energy are quite great. You only
need a small disruption in the inflow of matter and you could end up with
a runaway evaporation that you cannot stop, and which would make the Tsar
Bomba look like a firecracker.

  Also if the black hole is not kept constantly charged it could escape
the magnetic field and fall to the ground, and again it would explode
(although this time probably somewhere inside the Earth).

  And this assuming you can produce such a black hole in the frist place...

-- 
                                                          - Warp

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