Gravity and extra dimensions
The hierarchy problem
If gravitons are real, they can be created in particle collisions. The catch is that they'd still be undetectable, at least directly, before almost immediately slipping into some other dimension. Physicists think they can nab gravitons indirectly as they vanish from our three dimensions by observing small regions of unbalanced energy and mass in particle collision products. Inferring a graviton's existence is better than nothing.Einstein's general theory of relativity tells us that space can expand, contract, and bend. Now if one dimension were to contract to a size smaller than an atom, it would be hidden from our view. But if we could look on a small enough scale, that hidden dimension might become visible again. Imagine a person walking on a tightrope. She can only move backward and forward; but not left and right, nor up and down, so she only sees one dimension. Ants living on a much smaller scale could move around the cable, in what would appear like an extra dimension to the tightrope-walker.