**Ask a monkey a physics question thread**

[OngBonga]

I wonder if there's anything I can possibly say that will make you believe that the only thing the Plank length tells us is that our model stops working in the limits of the very very tiny. It makes no predictions.

I wonder when it will dawn on you that the Planck length is more than just a length!

https://www.youtube.com/watch?v=bjVfL8uNkUk&t=2s

Maybe Arvin can explain better than I can. Skip to 6 minutes if you don't want to be patronised.

He is at pains to point out that we simply do not know what happens at sub-Planck scales. However, it's not a question of measurement accuracy, it's a fundamental limit at which our models stop working. Our 4-dimensional model of the universe doesn't work at sub-Planck scales. That means length as we understand has absolutely no meaning. It's not a math trick, no more than c or g are math tricks. It's a fundamental constant of nature.

If an object is perfectly rigid, then it cannot experience length contraction

I need to think this one through!

[MadMojoMonkey]

He is at pains to point out that we simply do not know what happens at sub-Planck scales. However, it's not a question of measurement accuracy, it's a fundamental limit at which our models stop working. Our 4-dimensional model of the universe doesn't work at sub-Planck scales. That means length as we understand has absolutely no meaning.

That doesn't mean anything at all about the physics below those scales. It's just a statement about human ignorance or the limitations of models.

It's not a math trick, no more than c or g are math tricks. It's a fundamental constant of nature.

I need to think this one through!

c and G are not math tricks. They're constants you have to go out and measure. There's no predictive model of what those values *should* be, there's only the busywork of actually doing the science and measuring them.

Google the Buckingham Pi method.
Google other "Planck" units. Like Planck energy, etc. All found by the same method as the Planck Length, but whether or not they tell us anything about the universe is not guaranteed.