{c}
{tag=Unsolved physics problem}
{title2=GUT}
{wiki}

<electroweak interaction> + <strong interaction>.

Appears to be an <unsolved physics problem>. TODO why? Don't they all fit into the <Standard Model> already? So why is strong force less unified with electroweak, than electromagnetic + weak is unified in electroweak?


Grand Unified Theory

{tag=Hall effect}
{tag=Physics experiment without a decent modern video}
{title2=theorized 1975}
{title2=observed 1978}
{wiki}

Quantum version of the <Hall effect>.

As you increase the <magnetic field>, you can see the <Hall resistance> increase, but it does so in discrete steps.

\Image[https://upload.wikimedia.org/wikipedia/commons/3/38/Rhoxy.jpg]
{title=<Hall resistance> as a function of the applied <magnetic field> showing the <Quantum Hall effect>}
{description=As we can see, the blue line of the <Hall resistance>  TODO material, temperature, etc. It is unclear if this is just }

Gotta understand this because the name sounds cool. Maybe also because it is used to define the <fucking> <ampere in the 2019 redefinition of the SI base units>.

At least the experiment description itself is easy to understand. The hard part is the physical theory behind.

TODO <videos of all key physics experiments>[experiment video].

The effect can be separated into two modes:
* <Integer quantum Hall effect>: easier to explain from first principles
* <Fractional quantum Hall effect>: harder to explain from first principles
  * <Fractional quantum Hall effect for \nu = 1 m>: <1998 Nobel Prize in Physics>
  * <Fractional quantum Hall effect for \nu \ne 1 m>: one of the most important <unsolved physics problems> as of 2023

\Video[https://www.youtube.com/watch?v=UNyNjZeG1wc]
{title=Integer and fractional quantum Hall effects by Matthew A. Grayson}
{description=Presented 2015. This dude did good.}


Ciro Santilli @cirosantilli 34

 Incoming links: Unsolved physics problem