this post was submitted on 26 Mar 2024
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Zeno's Paradox, even though it's pretty much resolved. If you fire an arrow at an apple, before it can get all the way there, it must get halfway there. But before it can get halfway there, it's gotta get a quarter of the way there. But before it can get a fourth of the way, it's gotta get an eighth... etc, etc. The arrow never runs out of new subdivisions it must cross. Therefore motion is actually impossible QED lol.
Obviously motion is possible, but it's neat to see what ways people intuitively try to counter this, because it's not super obvious. The tortoise race one is better but seemed more tedious to try and get across.
So the resolution lies in the secret that a decreasing trend up to infinity adds up to a finite value. This is well explained by Gabriel's horn area and volume paradox: https://www.youtube.com/watch?v=yZOi9HH5ueU
If I remember my series analysis math classes correctly: technically, summing a decreasing trend up to infinity will give you a finite value if and only if the trend decreases faster than the function/curve
x -> 1/x.Great. Can you give me example of decreasing trend slower than that function curve?, where summation doesn't give finite value? A simple example please, I am not math scholar.
So, for starters, any exponentiation "greater than 1" is a valid candidate, in the sense that 1/(n^2), 1/(n^3), etc will all give a finite sum over infinite values of n.
From that, inverting the exponentiation "rule" gives us the "simple" examples you are looking for: 1/βn, 1/β(βn), etc.
Knowing that
βn = n^(1/2), and so that 1/βn can be written as 1/(n^(1/2)), might help make these examples more obvious.Hang on, that's not a decreasing trend. 1/β4 is not smaller, but larger than 1/4...?
From 1/β3 to 1/β4 is less of a decrease than from 1/3 to 1/4, just as from 1/3 to 1/4 is less of a decrease than from 1/(3Β²) to 1/(4Β²).
The curve here is not mapping 1/4 -> 1/β4, but rather 4 -> 1/β4 (and 3 -> 1/β3, and so on).
Turns out the resolution to that paradox is that our universe is quantized, which means there's a minimum "step" that once you reach will probabilistically round up or down to the nearest step. It's kind of like how Super Mario at extreme float values will snap to a grid.
Wait, isn't space and time infinitely divisible? (I'm assuming you're referencing quantum mechanics, which I don't understand, and so I'm genuinely asking.)
Disclaimer: not a physicist, and I never went beyond the equivalent to a BA in physics in my formal education (after that I "fell" into comp sci, which funnily enough I find was a great pepper for wrapping my head around quantum mechanics).
So space and time per se might be continuous, but the energy levels of the various fields that inhabit spacetime are not.
And since, to the best of our current understanding, everything "inside" the universe is made up of those different fields, including our eyes and any instrument we might use to measure, there is a limit below which we just can't "see" more detail - be it in terms of size, mass, energy, spin, electrical potential, etc.
This limit varies depending on the physical quantity you are considering, and are collectively called Planck units.
Note that this is a hand wavy explanation I'm giving that attempts to give you a feeling for what the implications of quantum mechanics are like. The wikipΓ©dia article I linked in the previous paragraph gives a more precise definition, notably that the Planck "scale" for a physical quantity (mass, length, charge, etc) is the scale at which you cannot reasonably ignore the effects of quantum gravity. Sadly (for the purpose of providing you with a good explanation) we still don't know exactly how to take quantum gravity into account. So the Planck scale is effectively the "minimum size limit" beyond which you kinda have to throw your existing understanding of physics out of the window.
This is why I began this comment with "space and time might be continuous per se"; we just don't conclusively know yet what "really" goes on as you keep on considering smaller and smaller subdivisions.
The paradox holds in an infinitely dividable setting. Take the series of numbers where the next number equals the previous one divided by 2: {1, 1/2, 1/4, 1/8, 1/16...}. If you take the sum of this infinite series (there is always a larger factor of two to divide by) you are going to get a finite result (namely 2, in this instance). So for the real life example, while there is always another 'half' of the distance to be travelled, the time it takes to do so is also halved with every iteration.
I had success talking about the tortoise one with imaginary time stamps.
I think it gets more understandable that this pseudo paradox just uses smaller and smaller steps for no real reason.
If you just go one second at a time you can clearly see exactly when the tortoise gets overtaken.
Came to say the same thing. Zeno's paradoxes are fun. π
Lol. It pretty much just decreases the time span you look at so that you never get to the point in time the arrow reaches the apple. Nothing there to be "solved" IMHO