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# 4D Physics?

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Hi all, I''ll admit outright that I aint a physics inclined person. Physics and network programming are about the only two areas I try to hide from But I was pondering game physics the other day... Was wondering about collision. So you have a bunch of vertices and planes that makes up a bunch of geometry that you calculate collisions and then responsese. great. But, has anyone ever done ''4D'' collsion - that is, taking in the velocity (the fourth ''d'' being time?) of an object into account? such that, surely its possible to work out given suitable constant speeds its possible to work out in one foul swoop when/where an object collides? Is this already done? Have I just "worked out" something thats bog-standard in middleware physics engines? Just curious really... regards, Jack

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What would be the purpose of such a thing?

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sounds like using swept volumes for collision.

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I hate it when people call time a dimension. it''s a universal mesurement. the only mesurements, are size, time and position, however position can be derived from size.

at anyrate, what you would want to do is find the intersection point between two delta v graphs. the best way to do this is the N dimensional colum major vector method (other wise known as the hard way of solving algebra problems.)

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There are a number of situations in which time can be considered a fourth dimension. Relativity comes to mind.

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everything measurable and representable with one number, has one dimension. everything measurable and representable with 3 numbers had 3 dimensions.

time is a one-dimensional thing. question is, is it a dimension independent of space, or not? relativity sais no.

there are just that tons of people that try to IMAGINE time as a 4th space-dimension. and this is wrong, of course. you can''t walk in direction of time, or rotate around in it, or such. at least, not in the same way (or you would not recept it in the same way), as in the 3 space dimensions.

If that''s not the help you''re after then you''re going to have to explain the problem better than what you have. - joanusdmentia

davepermen.net

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I think collision projections that take time into account are fairly standard, if your using a series of instantaneous checks then you will eventually start getting objects passing through one another etc, you can of course account for this in various ways but projecting through time is a much nicer approach.

I'm not sure whether it is quicker to perfrom the collision tests over time or build a hull to contain the objects movement. For example a sphere moving through time will map to a losenge used in an instantaneous check, however using time you get the advantage of the exact point at which the collision occurs.

[edited by - Rdf on March 26, 2004 12:16:50 PM]

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Swept volumes is the closest to 4d(3d+time) collision detection.

If you want to work out 4d space collision detection, please do. It would make a helluva conference paper.

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quote:
Original post by davepermen
there are just that tons of people that try to IMAGINE time as a 4th space-dimension. and this is wrong, of course. you can''t walk in direction of time, or rotate around in it, or such. at least, not in the same way (or you would not recept it in the same way), as in the 3 space dimensions.

may i argue, that actually:
1) You "walk" in time always , however only in one direction...
2) you rotate in coordinate axis x time axis plane, each time you start moving relatively to something (transition from/into inertial reference frame, or so-called boost)
of course, 4d physics is different from 3d physics, and the things we really feel are connected with 3 dimensions, but this is only because we never mooved too fast, i presume...

C++ RULEZ!!!

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it does''nt matter how fast you move, you can never feel or see a difference in the speed of time. rember that einstien guy? yah, remeber what he said about relitivity, and how time was completly and totaly relative to your point of reference? yah...

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