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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] nowhere net> 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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On 27/07/2013 7:27 PM, Nekar Xenos wrote:
> 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
But what if we do see effects but don't see that they are effects?
--
Regards
Stephen
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On Sat, 27 Jul 2013 20:39:07 +0200, Stephen <mca### [at] aolcom> wrote:
> On 27/07/2013 7:27 PM, Nekar Xenos wrote:
>> 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
>
>
> But what if we do see effects but don't see that they are effects?
>
True.
I read something yesterday. Apparently according to calculations the have
to be at more than 2 more dimensions.
--
-Nekar Xenos-
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On 27/07/2013 7:47 PM, Nekar Xenos wrote:
> On Sat, 27 Jul 2013 20:39:07 +0200, Stephen <mca### [at] aolcom> wrote:
>
>> On 27/07/2013 7:27 PM, Nekar Xenos wrote:
>>> 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
>>
>>
>> But what if we do see effects but don't see that they are effects?
>>
>
> True.
> I read something yesterday. Apparently according to calculations the
> have to be at more than 2 more dimensions.
>
I think that there may be a little bit of:
"To get these calculations to work, we need at least two more
dimensions." N.B. No smiley. ;-)
--
Regards
Stephen
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On 7/27/2013 11:17 AM, Warp wrote:
>
> 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.)
>
A fair enough point.
Not really sure that I agree with your characterization of GR, as I
don't see how GR involves more "movement in the 4th dimension" than SR.
For the purposes of the current conversation it's probably not
relevant though.
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Nekar Xenos <nek### [at] gmailcom> wrote:
> 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.
That would require an actual physical volume that cuts our vision. What
would that physical volume be?
--
- Warp
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