*Zeno's Paradox (actually the first of four) purports to show that motion is impossible.
If you want to walk from one point to another, you must first cross half the distance, then to cross the remaining distance, you must first cross half of the remainder, and so on.
If the distance you want to walk is 1 kilometre long, you will first reach 1/2 km from your start, then 3/4 km from your start (1/2 + 1/4), then 3/4 km (1/2 + 1/4 + 1/8), then 7/8 and so on. After you have taken N steps of the journey, you will have gone a distance equal to 1-(1/2)N kilometres. No matter how big N becomes (that is, no matter how many successive half-distances you cover), this distance will always be less than 1 and you will never arrive at your destination.
(Another permutation of Zeno's First Paradox seemingly prevents you from leaving your starting point. Before you can cross a given distance you must first cross half the distance, but before you can do that you must cross half that half-distance, ad infinitum.)
The solution I propose involves observing that Zeno's First Paradox assumes the person or object doing the moving is infinitely small, eg. a point (or a line perpendicular to the direction of travel).
Say your walking stride length is 1 metre, and for convenience the distance to your destination is 10 metres.
Using these figures, it's easy to see that it will take you 10 strides to reach your destination. Working through the paradox, to reach 10 m you must first reach 5 m, which you easily can cover in 5 strides. From this point to reach half the remainder (7.5 m from the start), you only need 3 more strides. In fact, with 3 more strides you exceed that distance. To fit with the paradox, you must reduce your stride length and keep on doing it so that you don't exceed each subsequent half-distance. And you must do so an infinite number of times in order to never reach your destination.
However, this is only possible with an object of zero size. If we started with an object with finite (positive) size, like a tortoise or a human, and measured the stride lengths from one heel to the next, at some point in our stride-length-reducing exercise the heel of a foot would exceed the length that is left to travel, so that the tortoise or human can be said to have arrived at the destination.
Interestingly, by merely changing how we measure stride-lengths in this scenario, we can illustrate the non-arrival of a zero-sized object. By measuring toe to toe rather than heel to heel, we in effect have a zero-sized object which, with ever reducing stride lengths, never arrives at its intended destination.
A funny way of describing this is that in order to 'prove' that motion is impossible using Zeno's Paradox, you must purposefully try not to reach your destination (that is, by successively reducing your stride length).
(You can perform this thought experiment using a line segment of finite size. Imagine you have a 1 metre long ruler. For the first 5 m, you 'walk' or flip the ruler end to end to cover the distance.
Then for the next 2.5 m you can flip the ruler for two-lengths, then angle the ruler so that it covers the remaining 1/2 metre without exceeding it. And so on. Over time, the final angle of the rulers gets more and more oblique as the final 'stride' distance gets progressively smaller.)
Therefore an object with a finite size can traverse a finite distance, but an object that is infinitely small cannot do the same.
This solution has a couple of interesting ramifications. The first is that since a point is infinitely small, its 'stride length' is infinitely reducible and it can satisfy Zeno's First Paradox, namely a point cannot move. Points can mark positions but they cannot traverse a finite distance.
Conversely, a moving object cannot be a point. If you observe an object travelling from one point to another, the object must have a finite size, no matter how small. Motion is a property of finiteness.
Stimulus: "The Infinite Book", by John D. Barrow. The description of Zeno's paradox above is largely drawn from pages 20-21.
kyy 2007-04-02 1542 z+10
*Note: This is version 1.1 of the solution. The first two comments below refer to version 1.0 of the solution, which published by kyy on 2006-03-21 1332 z+9.