Why don’t aliens reply to the radio signals astronomers broadcast into space? Why should they? They don’t need to contact us and ask for directions to our planet so they can save our world or send tourists here. The aliens are already here - we’re just not advanced enough to be able to detect them. They’ve been constantly visiting and giving everybody a helping hand for as long as the planet has existed. But the best place to hide something from humans is right in front of them - so we know nothing of their presence. There are two ways the aliens could remain totally undetectable for many, many thousands of years.

The first method is to follow cosmology’s Holographic Principle and lose their 3rd dimension. This principle, which first gained attention in the late 1990s, was initially proposed by physicists Leonard Susskind and Gerard ‘t Hooft, with major contributions to its development from string theorist Juan Maldacena. It proposes that the universe is a three-dimensional image projected onto a two-dimensional surface. What happens if one word is changed so it reads “projected from a 2D surface”? The binary digits mentioned in the last paragraph as the most fundamental composition of particles could be used to encode the 2D Mobius strip and the information in the Mobius might be the first step in forming the 3D appearance of objects, similar to DNA containing the blueprint for proteins. If trillions of Mobius strips create a photon and trillions of pairs of strips form a graviton, the interaction of photons and gravitons can (as Einstein suggested in a 1919 paper) form the mass of elementary particles. The aliens would be as 2 dimensional as the image of a person or object in a mirror. Actually, they’d be perfectly 2D, having no depth or height at all (not even the minute 3rd dimension of a one-atom-thick substance like graphene).

The second method would be to exist without any physical form. Beings such as this would have no need for a planet or moon to live on but could exist in spacetime itself. Either they’d never have been on a planet or may have lived on one in a material body for a relatively brief century before transitioning to residence in the building blocks of space-time. This is possible because the components of those building blocks appear to be binary digits aka base 2 mathematics. The photons and gravitons composing space-time possess Electric Dipole Moment - each particle has both positive and negative electric charge which can completely cancel to make the photon and graviton neutral. The charges also produce the binary digits of 1 and 0 which give Artificial Intelligence to sufficiently advanced AIs or humanoid robots. This means the universe and all its parts could have, has always had, and will always have, artificial intelligence. If our human ego can accept that our natural intelligence is really artificial, conscious beings inhabiting spacetime could really exist and have a vastly expanded mind that adopts the infinite perspective produced by viewing everything in all of space and all of time. Such an event is not at all absurd if a future theory of Quantum Gravity doesn’t merely unite quantum mechanics and general relativity but goes on to later unite everything in space and time, on microscopic and macroscopic (indeed, all) levels. These beings would have abandoned the extremely limited, and possibly destructively negative, lifestyle resulting from views restricted to an individual world and might be referred to as Artificially Noological, Ghostly, Extraterrestrial Lifeforms.