Why can’t we get smaller than the plank length?
In: Physics
We can’t get anywhere close to planck length with our current technology.
Googling says that the smallest distance that we have measured is 10^(−18) m. Planck length is 10^(⁻35) m.
But this has nothing to do with “planck length being the smallest possible distance”. Planck length is not the smallest possible distance. It doesn’t really have any real physical meaning behind it.
There is a bit of problem with our theories not working at such scale (the equations resolve to nonsense) but the problem is that we don’t have theory for quantum gravity yet. Not some fundamental meaning of planck length.
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So what is planck length then?
Planck length is one of the planck units. They were made to be used to make math easier.
In SI units speed of light is 299792458 m/s. Big number.
In planck units speed of light is 1 planck length/planck time. When doing calculations “1” is one of the easiest numbers to have!
Many other common numbers of physics also reduce to “1” in planck units. Wikipedia lists some of them https://en.wikipedia.org/wiki/Planck_units
Additionally the planck units are defined straight from physical constants making them more universal.
As a theoretical, of course you could. You could have a half Planck, right? Theoretically, you can divide any number in half… in reality, though, we don’t do that.
In practice, it’s meant to represent the smallest feasible distance. It’s the distance light travels in a Planck unit of time, which is the smallest unit of measurable time. With these values, we can have the smallest divisors to work on quantum mechanics and other very small maths.
It’s a real thing, but for most of us, it’s used as the “infinitely small” distance or time.
We don’t know if “we can get smaller” because our understanding of causality stops making much sense on that scale. We don’t know if that means that there is no smaller scale or if that is just the limiting point of our current knowledge base.
Things can get smaller than the plank length. That’s just the limit that “Macro physics” gives way to quantum mechanics. QM starts taking over and Heisenburg’s uncertainty principle means we can’t accurately measure distances anymore.
Unifying those two systems would be a neat trick. People have been working on it.
Not really sure what you mean by “get smaller than” but if you mean “why is the plank length considered the smallest possible (physical size) unit of anything?” then the answer is two-fold. One – our understanding of physics stops at the plank length – anything smaller just doesn’t “work” in our formulae. Two – to measure something (anything at all), we need to detect it. We detect things by bouncing particles off them (e.g., we see a car because photons bounce off the car and strike our retinas in the back of our eyes). To see/detect smaller and smaller things, we need to use more energetic particles. This is because more energetic particles have smaller wavelengths, and we cannot detect things smaller than the wavelength of whatever we’re using for detection. The plank length comes into play because if we try to detect something smaller than the plank length, we need to use particles so energetic that they will become black holes (mini black holes, but black holes nonetheless). That is, cramming that much energy into that small a space causes gravitational collapse, which means no detection at that scale is possible.
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