of the particles known today, with no underlying structure being probed. The aforementioned timespan might be shortened by observing the GUT scale through a radical development in accelerator physics, or by a non-accelerator observational technology, such as examining tremendously high energy cosmic ray events, or another, yet undeveloped technology. Alternatives to the desert exhibit particles and interactions unfolding with every few orders of magnitude increase in the energy scale. MSSM desert With the Minimal Supersymmetric Standard Model, adjustment of parameters can make the grand unification exact. This unification is not unique. Such exact gauge unification is a generic feature of supersymmetric models, and remains a major theoretical motivation for developing them. Such models automatically introduce new particles ("superpartners") at a new energy scale associated with the breaking of the new symmetry, ruling out the conventional energy desert. They can, however, contain an analogous "desert" between the new energy scale and the GUT scale. Mirror matter desert Scenarios like the Katoptron model can also lead to exact unification after a similar energetic desert. If the known neutrino masses are due to a seesaw mechanism, the new heavy neutrino states must have masses below the GUT scale in order to produce the observed O(1 meV) masses, thereby falsifying the desert hypothesis. Evidence As of 2019, the LHC has excluded the existence of many new particles up to masses of a few TeV, or about 10x the mass of the top quark. Other indirect evidence in favor of a large energy desert for a certain distance above the electroweak scale (or even no particles at all beyond this scale) includes: The absence of any observed proton decays, which has already ruled out many new physics models that can produce them up to (and beyond) the GUT scale. Precision measurements of known particles and processes, such as extremely rare particle decays, have already indirectly probed energy scales up to 1 PeV (106 GeV) without finding any confirmed deviations from the Standard Model. This significantly constrains any new physics that might exist below those energies. Research from experimental data on the cosmological constant, LIGO noise, and pulsar timing, suggests it's very unlikely that there are any new particles with masses much higher than those which can be found in the standard model or the Large Hadron Collider. However, this research has also indicated that quantum gravity or perturbative quantum field theory will become strongly coupled