>> More fully: Some formulations of string theory suggest that the
>> universe has as many as 11 spatial dimensions. The obvious question is
>> then "so why can't I see any of them?", and the only answer anybody
>> has come up with is "well, maybe they're really tiny..."
>
> That one is easy. Simply because our eyes can only see in 2d. We can
> perceive 3d images because of the stereoscopic effect of having 2 eyes.

That doesn't explain why visible objects around us only move in 3 
dimensions. If there were more dimensions and we should somehow only 
"see" 3 of them, we should see objects constantly zipping into and out 
of the 3D slice we can perceive.

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On 26/07/2013 8:47 PM, Orchid Win7 v1 wrote:
>>
>
> That doesn't explain why visible objects around us only move in 3
> dimensions. If there were more dimensions and we should somehow only
> "see" 3 of them, we should see objects constantly zipping into and out
> of the 3D slice we can perceive.


Why would they move in the other dimensions, if they are only moved in 
our three or four?
What force would move them?

-- 
Regards
     Stephen

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On 26/07/2013 08:57 PM, Stephen wrote:
> On 26/07/2013 8:47 PM, Orchid Win7 v1 wrote:
>>>
>>
>> That doesn't explain why visible objects around us only move in 3
>> dimensions. If there were more dimensions and we should somehow only
>> "see" 3 of them, we should see objects constantly zipping into and out
>> of the 3D slice we can perceive.
>
>
> Why would they move in the other dimensions, if they are only moved in
> our three or four?
> What force would move them?

Why would they *not* move in the other dimensions? Why would all forces 
just happen to be perpendicular to those dimension?

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On 26/07/2013 9:58 PM, Orchid Win7 v1 wrote:
>
> Why would they *not* move in the other dimensions? Why would all forces
> just happen to be perpendicular to those dimension?

I thought I had said, why would a force be applied to them?
If they are dimensions that not much happens in.

-- 
Regards
     Stephen

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Orchid Win7 v1 <voi### [at] devnull> wrote:
> > That one is easy. Simply because our eyes can only see in 2d. We can
> > perceive 3d images because of the stereoscopic effect of having 2 eyes.

Perceiving three-dimensional space is not related to stereoscopic vision.
It helps, but it isn't what makes it three-dimensional perception.

> That doesn't explain why visible objects around us only move in 3 
> dimensions. If there were more dimensions and we should somehow only 
> "see" 3 of them, we should see objects constantly zipping into and out 
> of the 3D slice we can perceive.

Talking about slices is, as I see it, nonsensical. A camera doesn't see
a "slice" of the three-dimensional space. It sees a *projection*, which
is a completely different thing. If there were a fourth dimension that's
like the other three, we would likewise see a three-dimensional projection
of it, not a slice.

Anyway, according to general relativity, spacetime *is* four-dimensional,
and everything actually moves in the fourth dimension all the time.
Moreover, the reason why gravity (seemingly) accelerates objects is
because of this movement in 4-dimensional spacetime. (The spacetime is
curved, which is what causes the apparent acceleration. In reality it's
not acceleration but inertia.)

So, technically speaking, when you drop an object, you are seeing movement
in the fourth dimension (or, more precisely, the effects of the curvature
of spacetime, from which we see a 3-dimensional projection, which is what
causes us to perceive it as accelerating motion, even though in reality
it's just inertial motion. It's a similar idea as how a railroad seems
to converge at the horizon in a photograph.)

-- 
                                                          - Warp

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On 7/26/2013 3:43 PM, Warp wrote:
 >
> Anyway, according to general relativity, spacetime *is* four-dimensional,

Slight quibble: The 4d-spacetime stuff was already in special 
relativity.  General relativity added gravity into the mix, but the 
theory of 4d (Lorentzian) spacetime was there already.

What you say is of course technically correct since general relativity 
includes special relativity as a sub-case, but I think it's cleaner to 
separate the two for the purposes of talking about the 4th dimension in 
general.

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Kevin Wampler <nob### [at] nowherenet> wrote:
> On 7/26/2013 3:43 PM, Warp wrote:
>  >
> > Anyway, according to general relativity, spacetime *is* four-dimensional,

> Slight quibble: The 4d-spacetime stuff was already in special 
> relativity.  General relativity added gravity into the mix, but the 
> theory of 4d (Lorentzian) spacetime was there already.

> What you say is of course technically correct since general relativity 
> includes special relativity as a sub-case, but I think it's cleaner to 
> separate the two for the purposes of talking about the 4th dimension in 
> general.

But since the question was "why don't we see objects moving the fourth
dimension", talking about GR was more illustrative because according
to it, the apparent acceleration caused by gravity is in fact caused by
movement in the fourth dimension (and the nonlinearity of spacetime.)

-- 
                                                          - Warp

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On Fri, 26 Jul 2013 21:47:00 +0200, Orchid Win7 v1 <voi### [at] devnull> wrote:

>>> More fully: Some formulations of string theory suggest that the
>>> universe has as many as 11 spatial dimensions. The obvious question is
>>> then "so why can't I see any of them?", and the only answer anybody
>>> has come up with is "well, maybe they're really tiny..."
>>
>> That one is easy. Simply because our eyes can only see in 2d. We can
>> perceive 3d images because of the stereoscopic effect of having 2 eyes.
>
> That doesn't explain why visible objects around us only move in 3  
> dimensions. If there were more dimensions and we should somehow only  
> "see" 3 of them, we should see objects constantly zipping into and out  
> of the 3D slice we can perceive.

Hmm yes. I'll have to throw that theory out the window...

-- 
-Nekar Xenos-

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On Fri, 26 Jul 2013 23:42:23 +0200, Stephen <mca### [at] aolcom> wrote:

> On 26/07/2013 9:58 PM, Orchid Win7 v1 wrote:
>>
>> Why would they *not* move in the other dimensions? Why would all forces
>> just happen to be perpendicular to those dimension?
>
> I thought I had said, why would a force be applied to them?
> If they are dimensions that not much happens in.
>
Come to think of it. If there are other dimensions, not much is happenning  
there because we don't see any effects of more dimensions

-- 
-Nekar Xenos-

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On Sat, 27 Jul 2013 00:43:51 +0200, Warp <war### [at] tagpovrayorg> wrote:

> Orchid Win7 v1 <voi### [at] devnull> wrote:
>> > That one is easy. Simply because our eyes can only see in 2d. We can
>> > perceive 3d images because of the stereoscopic effect of having 2  
>> eyes.
>
> Perceiving three-dimensional space is not related to stereoscopic vision.
> It helps, but it isn't what makes it three-dimensional perception.
>
>> That doesn't explain why visible objects around us only move in 3
>> dimensions. If there were more dimensions and we should somehow only
>> "see" 3 of them, we should see objects constantly zipping into and out
>> of the 3D slice we can perceive.
>
> Talking about slices is, as I see it, nonsensical. A camera doesn't see
> a "slice" of the three-dimensional space. It sees a *projection*, which
> is a completely different thing. If there were a fourth dimension that's
> like the other three, we would likewise see a three-dimensional  
> projection
> of it, not a slice.
>

I imagined it this way:
Imagine a swimming pool with the water surface as a 2d universe. The  
beings in this universe cannot see anything that is not the water surface.  
When you step into the water they perceive first small circular  
shapes(your toes) merging into a oval shape, etc. The don't see a  
projection of your 3d body, they see a slice.
So I assume that we (3d beings) would only be able to see a 3d slice of a  
4d object.

> Anyway, according to general relativity, spacetime *is* four-dimensional,
> and everything actually moves in the fourth dimension all the time.
> Moreover, the reason why gravity (seemingly) accelerates objects is
> because of this movement in 4-dimensional spacetime. (The spacetime is
> curved, which is what causes the apparent acceleration. In reality it's
> not acceleration but inertia.)
>
> So, technically speaking, when you drop an object, you are seeing  
> movement
> in the fourth dimension (or, more precisely, the effects of the curvature
> of spacetime, from which we see a 3-dimensional projection, which is what
> causes us to perceive it as accelerating motion, even though in reality
> it's just inertial motion. It's a similar idea as how a railroad seems
> to converge at the horizon in a photograph.)
>

What if time could have more dimensions? That would be interesting. A  
being in 2-dimensional time could see back and forth in our 1d time.

-- 
-Nekar Xenos-

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