[DP5Ups8o]

How could one ever know whether anything did or did not exist "out there", when all one knows is what they experience through the six senses?

See....SN 35.23: Sabba Sutta - The All
http://www.accesstoinsight.org/tipit....023.than.html

Greetings Retrofuturist

The Sabba Sutta does refer to the internal & external (eye & forms, etc,) sense media

Thus it is quite debatable that refuting "out there" has any real importance in Buddhism

"out there" is impermanent, unsatisfactory, not-self

"in here" is impermanent, unsatisfactory, not-self

"neither-here-nor-there" is also not-self

With metta

Element

[The Buddha said:]

'The six internal media should be known.' Thus was it said. In reference to what was it said? The eye-medium, the ear-medium, the nose-medium, the tongue-medium, the body-medium, the intellect-medium. 'The six internal media should be known.' Thus was it said. And in reference to this was it said. This is the first sextet.

'The six external media should be known.' Thus was it said. In reference to what was it said? The form-medium, the sound-medium, the aroma-medium, the flavor-medium, the tactile sensation-medium, the idea-medium. 'The six external media should be known.' Thus was it said. And in reference to this was it said. This is the second sextet.

Chachakka Sutta: The Six Sextets [The Buddha said:]

When there is no you in terms of that, there is no you there. When there is no you there, you are neither here nor yonder nor between the two. This, just this, is the end of stress.

Bahiya Sutta