illustration (attribution, if any possible, is at the end of the article)
Many have marvelled at the recent images of Pluto, but some interested in Buddhism have concluded that « if we can design and send scientific tools that send back pictures, pictures that we all share and comment on, then surely Pluto is real and 'objective', not just a 'subjective' dream… therefore karma isn't real. »
This unfortunately is a misunderstanding of karma and of the nature of reality.
While karma is 'individual', individuality itself merely is an appropriation mechanism (gplus.wallez.name/KZRPUvkHpLg), making some streams of consciousness 'mine'.
To consider that interacting/interdependent streams of consciousness (e.g. sharing and discussing the 'same' Pluto) are contradictory with the individuality of karma is erroneous: karma is hard to track, its unfolding is hard to predict, precisely because of the multitude of interactions! However, no matter how complex the web of streams is, one can always pick a few streams and —quite arbitrarily— announce (and believe) "these are mine / these are me". It makes the 'self' an illusion, a sign of ignorance, but it doesn't contradict the individualisation of karma: it simply makes the individualisation a result of ignorance, a consequence of appropriating, of seeking a separate existence in the midst of a continuum. [It also makes Liberation possible, by ungrasping the cognitive error].
There's even more fundamental problem with the materialistic perspective though. It's the very assumption that it's the same Pluto we're all sharing!
Karma refers to (individual) tendencies, notably 'appropriative' tendencies: how we appropriate, make some experiences 'ours' while being blind to others (or even denying them, making them "not ours"), etc. Nothing under the Sun tells you that my perception of Pluto is the same as yours… and therefore which 'objective' Pluto do we share?
We're exchanging about a concept, but even this concept may be interpreted differently (not only because of varying degrees of knowledge but also because of varying interests: from the same knowledge at a given moment, one person might look forward the next developments in e.g. mineralogy while another person might lose interest because e.g. there's no sign of life).
There's inter-dependence and we probably share more than a name ('Pluto')… but there's little 'objective' about it: the 'more' that we share is a lot more linked to the shared conversation we had through time, the "scientific consensus" we made, than to any essential trait we could pinpoint. And there's no warranty that we'll continue the conversation (precisely because our 'interests' might diverge). Maybe there's more than a shared conversation, but it's still impossible to find something that would be 'objective' without mediation of the 'subjective' mind (gplus.wallez.name/j3k3QS2ELnY), something that would have an essence (not only have one, but have it perceived by all directly and without prejudices, preferences or personal biases).
To make the point more intelligible, if need be, one might rely on more common experiences.
Some people drive without fear at speeds that frighten others (be it because they know more —e.g. know the brakes are not designed for such extreme conditions— or because they know less —e.g. one fears to push the vehicle to its limits, limits that a very experienced professional driver might handle comfortably).
Some people experience vertigo, others don't, in the 'same' context.
Some people might find a house reassuring and cosy, others might feel the 'same' house 'haunted' and oppressive.
The 'same', simple interaction (e.g. a hug) might be a blessing to someone in need of affective support, and a nightmare to someone who went through abuse.
Sharing doesn't make the 'subjective' disappear: individual karma is even perfectly compatible with sharing the delusion of an objective world that one might define purely in materialistic terms (without realising that each one involved 'understands' —appropriates— the terms differently).
The above is compatible with interpreting the Buddhist realms as psychological metaphors: realms are not separate from each others, all beings share the 'same' reality, the 'same' web of inter-dependences, but they appropriate it differently and what is perceived as nectar to those 'in' god's realms appear as poison to those 'in' hells.
Sharing a reality doesn't mean this reality may be completely described purely in materialistic terms, and doesn't means its existence is 'objective.'
It doesn't mean either that materialistic models are utterly useless or pointless: a simple model might be very useful, it might empower us to make predictions (up to a point, but enough to take responsibility and act) but utility doesn't imply the model is complete or even true (cf. Newtonian gravitation, which proved useful but very wrong outside a narrow range of conditions).
Hence a Middle Way (neither essentialism nor nihilism…)!