# What experimental techniques could be used to search for higher (macroscopically occurring) spatial dimensions?

We live in a a universe with 3 spatial dimensions and 1 time dimension. However, if we lived in a universe with 4 or more spatial dimensions, under the right conditions (such as a general lack of momentum in the 4th dimension for particles in our world), life on Earth could look entirely the same, with humanity's perceived existence merely limited to 3 spatial dimensions.

What experimental techniques (if any) could be used to search for evidence of higher spatial dimensions? Are any techniques in current use? Has there ever been any serious discussion about this in the scientific community?

I am aware of the implications of string theory and various other theories of quantum gravity, that extra dimensions can exist in various ways that are concealed from the macroscopic universe, but I specifically ask about higher dimensions occurring on a macroscopic level.

## 2 Answers

A good reference is the list of constraints on extra dimensions compiled by the particle data group

One approach is to look for violations of the inverse square law, arising from the fact that gravity can "leak" into the extra dimension. Currently, based on this type of constraint, extra dimensions are bound to be less than approximately 40 $$\mu$$m.

I specifically ask about higher dimensions occurring on a macroscopic level.

Real macroscopic dimensions of the (x,y,z) type we have modeled our three dimensional space are excluded because classical physics models are all very accurate at the level of microns, and only at nanometer scales and velocities close to the velocity of light, very high masses, other dimensions may become necessary.

(In everyday life, if an extra dimension existed, there would be inconsistencies in simple observations, for example a pendulum motion would not fit the 3 dimensional equations if part of its motion were in the extra dimension.)