| That's the energy scale where the force of gravity becomes strong enough to influence subatomic particle interactions. Currently, our model of nature at subatomic scales (the 'Standard Model') does not include gravity. This is fine for LHC energy scale, because gravity is so weak compared to the other three forces (electromagnetism, strong & weak nuclear force), that it can be ignored. The mass of quarks, electrons etc is tiny, you can make precise predictions on stuff like 'particle X will decay into particles Y & Z at this likelihood', without accommodating gravity. But at the planck energy scale, gravity is too strong to be ignored, and the Standard Model breaks down, it can't make predictions. So this is why the planck scale is where you're 100% guaranteed to see 'new physics'. https://en.m.wikipedia.org/wiki/Planck_units EDIT: think the reason gravity becomes stronger at higher energies, is because the _relativistic mass_ of particles increases with their velocity. So if you bang two electrons a&b together at nearly the speed of light, the effective mass of electron a from the frame of reference of electron b will be orders of magnitude greater than the 'rest mass of electron a'. Because strength of gravitational interaction is proportional to mass of particles involved, electron b will feel stronger gravitational pull of electron a (and vice versa). So if the electrons are traveling at planck scale speeds, the strength of gravitational interaction becomes comparable to the electromagnetic interaction between them. Then all standard model predictions of how the electrons interact goes out of the window, because SM cannot model gravity. https://en.m.wikipedia.org/wiki/Mass_in_special_relativity |