Message #560

From: Jenelle Levenstein <>
Subject: Re: [MC4D] How many eyes?
Date: Sat, 13 Sep 2008 21:53:56 -0500

How many legs would a 4D creature need to walk on a 4D planet. On a 3D world
an object neads at least three legs to stand stably. Would that mean that in
order for something to stand upright in a 4D world you would need at least 4

On Sat, Sep 13, 2008 at 6:52 PM, Melinda Green <>wrote:

> Guy,
> When you talk about animals and predator/prey strategies, you are
> talking about real-world situations and not purely geometric ones, and
> the difference is everything. I suspect that the need to instantly judge
> the distance to prey as it briefly flashes past from any relative
> direction makes binocular vision important. From your natural world
> description, I think the best geometric reduction of your question is
> the minimum number of eyes needed to determine the distance to a point
> from a swivelable platform. In that one particular case I think that
> your answer of two is correct.
> -melinda
> Guy wrote:
> >
> > Thank you very much for your answer, Melinda.
> >
> > The motion parallax point is interesting but yes, it is cheating as
> > far as answering my real question is concerned!! As you guessed, it
> > was more the geometry than the psychology of perception that was
> > challenging me!
> >
> > I think you have confirmed (tell me if I’ve misunderstood you) that
> > two stationary eyes would suffice to see at least a /part/ of
> > N-dimensional space in full N-D stereo, just as in 3D reality our two
> > eyes allow us to see depth in a part of our visual field. Many
> > predators remain stock still while they observe their prey. Herons,
> > for example, stand motionless, bill poised over the water, waiting for
> > a fish to move into spearing range (they have to deal with refractive
> > depth effects too when they strike, of course!). If I understand you
> > aright, a 4D heron would indeed only need two eyes for there to be a
> > part of its visual field in full 4D, enabling it to strike with
> > accuracy within that range.
> >
> > Most animals with good binocular vision are hunters – the hunted tend
> > to have widely separated eyes pointing in different directions, like
> > rabbits. Hunters only need really accurate depth perception in a
> > limited field – namely, in the direction of the prey, for the final
> > attack. So maybe predatory animals in N dimensions would be able to
> > get away with just two eyes.
> >
> > Thanks again,
> >
> > Guy
> >
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