I know it’s only theoretical, but why couldn’t something be just slightly smaller?
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So if you fit enough stuff into a small enough space you’ll create a blackhole. This is because black holes don’t have to be really massive like more than the Sun, they just have to have more mass than that volume of space can “handle”.
So, if you tried to measure a distance smaller than that you’d have to put something into it to bounce of it (things are measured by bouncing something with energy…. which is like everything…… off of it……. whether that’s a photon, an electron, whatever). The problem is that if you did that whatever you fit in that space to measure it would be have enough mass on that scale to create a blackhole.
So smaller distances are possible, you just can’t measure them.
It’s a combination of several fundamental constants. Specifically the speed of light, Planck’s constant, and the gravitational constant G. If you combine these three constants in a certain way, you get a length, a very very small length, and that is the smallest length where light and gravity have the properties we see that they do.
It’s not known if it truly is the smallest scale, only that our laws of physics break down at scales that small.
Planck length and Planck time are not the *smallest possible* distance/time, they are the smallest distance/time *at which our understanding of physics still holds*.
The Planck length is about 10^-20 times the diameter of a proton, so its obscenely small. Its speculated that interactions at this scale will be dominated by quantum gravity which we really don’t have any model for yet so you can’t really apply our physics at this scale.
The Planck length is wayyyy below the point where you can call anything a “particle”, they’re manifestations of wavefunctions and its just brain hurty from here. An electron is 10^-18 meters and the Planck length is 10^-35 meters so consider the scale of an electron relative to a meter stick, now blow that electron up to be a meter wide, the Plank length is as tiny relative to an electron as an electron is to a meter stick
Important thing to learn from the Planck length – if you are reading physics news from a general news site, its wrong. At least get it from a tech news site which some basic physics background
With plank length it’s believed it’s physically impossible to measure anything smaller than that.
For example to measure something using light the wavelength of light needs to be shorter than the thing you’re measuring (this is how they fit more data on a BluRay disc than a DVD btw, by using a shorter wavelength laser so they can use a thinner data track and fit more tracks on the disc).
Shorter wavelengths of light need more energy to create though. So if you do the calculations on trying to create a laser with a wavelength of less than Planck length you’d find your photons would have so much energy that they would instantly form miniature black holes and disappear…
The Planck length is an *emergent* property of the laws of physics as we know them today. In other words, there are several pieces of experimental evidence that demonstrate the discretization of energy levels. They don’t “prove” that the Planck length is the smallest distance. Rather, the theoretical physics we have which aligns with those experiments points to this being true, regardless.
The best way I’ve seen it described is that a Planck length is the shortest possible distance that can *theoretically* be measured. If you were to have something smaller than a Planck length you wouldn’t be able to know it was smaller than a Planck length. From the point of view of our current understanding of the laws of physics, if something were smaller it would either not be detectable or would appear to be a Planck length.
Since it is derived from constants, if someone were to come along and prove that one of the constants is wrong, we could end up with a smaller length to replace it.
Our current understanding of the laws of physics break down at dimensions below Planck scale so we classify that as the smallest measurable distance. Of course you can say half a Planck but we really don’t know what goes on at that scale.
Here is my favorite way to visualize just how small a Planck length is. Theoretically you could fit more cubic meters into the known observable universe than you could fit cubic Planck lengths into a cubic meter.
One part of the answer is that our models for understanding of fundamental physics (i.e., relativistic quantum field theory, including the Standard Model) rely on spacetime being flat, or at least flat to a good approximation. In this context, “flat” means basically close enough to what intergalactic space looks like that the difference doesn’t matter, in contrast to near the event horizon of a small black hole, where spacetime is very warped.
What warps spacetime is the presence of energy in some form (usually mass — i.e., the warping of spacetime which is how gravity works). But fundamental particles have mass and energy, and the energy is related to the wavelength through Planck’s constant and the speed of light — E = h c / lambda — at least approximately.
So when you have really small distances being relevant, that means you have really high energies, and that means that ends up meaning that space is warped on a level that is no longer negligible at the distances you are talking about. So the very assumptions that we build relativistic quantum mechanics on no longer work.
To elaborate a little further: The Planck length can be thought of as the wavelength of a photon such that if you convert that photon’s energy into a point mass, the orbital speed at a radius of that wavelength is the speed of light. The actual equations give some factors of small integers and pi and so forth, but the order of magnitude works out.
The reason you can just combine G, h, and c to get this length is because of a strategy of getting approximate answers to physics problems through dimensional analysis — factor out all the dimensionful quantities (in this case, G, h, and c) and you are left with some math equation you need to solve, where the answer is probably close-ish to 1, and so the stuff you factored out is close to your answer. Since you are looking for a length, it *has* to be proportional to sqrt(hG/c^(3)).
It’s not.
It’s the wavelength at which the uncertainty derived from lights distortion on space (due to gravity) becomes larger than the wavelength itself, which is the limit of precision for lower energies (wavelength decreases with increasing energy). This makes it impossible to further increase precision without first decoding the distortion. It might be the limit of resolution even with a complete understanding of gravity, but that’s speculation. However, it’s not the smallest possible distance as things can move less than a planck length, it just can’t be confirmed experimentally without making some advancement in our understanding gravity.
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