It's because they are ideas. This table is here. My arms are on
   it. Is there a guarantee that the table is here and my arms are
   here? No.

   I can get 10,000 people to say the table is here and my arms are
   here. Is there a guarantee that it's so? No.

   If I asked the moon if my arms and table were here, and the moon
   was nearsighted, it would say, "What table? What arms?"

   If I asked a photon if my arms and table were here, no matter
   *how* good the photon's vision was, it wouldn't see my arms or
   the table. They're too big for it to notice in the same forms as
   we do.

   In short, they're physical and undeniable ONLY for species that
   happen to be of the right size, shape, cognitive capacities,
   needs, physicality that is similar to us, which includes
   macroscopic life on earth.

   Go to smaller or larger scales though, and the rules change.

   The undeniability comes from the relative density of things to
   our species' abilities.

   It's not that the table and my arms aren't here: They are. But
   that's because my reality conforms to my abilities and needs.

   It doesn't mean that I "create" reality per se. Reality is here.
   Yet, our ability to perceive it is always going to be limited to
   our cognitive abilities.

   Therefore, it can be argued that all physical processes are
   ideas.

   Being ideas doesn't mean they're not real. it just means that
   our abilities are always going to be limited and locked into a
   certain perspective of the Universe. Since no alien life forms
   are not forthcoming, it's all we have to work with for now.