Is it bad to kill your children? Absolutely not! (Relatively, perhaps!) The Carthaginians, for example, every now and again would sacrifice the odd child to the god Moloch. They thought it was a good thing to do, a noble and sacred act, in some circumstances. It's hard to define good and bad in absolute terms, but the Afghan bandit, Abdel Khader Khan, makes a pretty good stab at it.
According to Khader -- the character in Gregory David Roberts' novel, Shantaram -- physicists believe the universe is moving toward greater complexity, referred to as the "tendency toward complexity". Khader defines "bad"/"wrong"/"evil" as anything that opposes the tendency toward complexity, and "good"/"right" as anything that furthers or enhances the tendency*.
What I like about Khader's definition is that it's clear and unambiguous, with minimal scope for subjectivity or opinion. But the problem is that the universe is NOT moving towards greater complexity. In fact, it's moving towards greater simplicity, as expressed in the Second Law of Thermodynamics. [Despite this problem, Khader's definition can be rescued and rehabilitated (more on that later). For now, back to the Second Law.]
Simplifying the technical jargon, under the Second Law the universe is moving towards greater and greater disorder (entropy/randomness):
Entropy is the thermodynamic property toward equilibrium / average / homogenization / dissipation...(Wikipedia)One of the implications of the Second Law is "the heat death of the universe":
...in which the universe has diminished to a state of no thermodynamic free energy and therefore can no longer sustain motion or life. (Wikipedia)Other scenarios of the fate of the universe also point to greater simplicity, not complexity. If the universe keeps expanding, for example, ultimately there'd be so much empty space between the galaxies and stars that you'd be hard-pressed to find any matter at all, even if you were a god.
Under the Second Law, Khader's definition is dead, but ironically, under the same law it can be resurrected, thanks to all the anti-Second-Law engines in the universe.
Every living thing is an anti-Second-Law engine. Every creature, every organism is an island of order in the ocean of disorder that is the universe. Living things create and maintain order as they go about the business of life. But there's a price to pay. To maintain themselves in good order and avoid death, living creatures need energy (among other things). And we all get energy from the environment. Plants get it from the sun. Herbivores get it by eating plants. Carnivores get it by eating other herbivores and carnivores.
The point is that living things maintain themselves (in good order) by sucking in order/energy from outside themselves. So, discarding Khader's definition but retaining his methodology enables us to define "good" as anything that optimises the overall (universe-wide) smooth running of anti-Second-Law engines, and "bad" as anything that fails to optimise the overall (universe-wide) smooth running of anti-Second-Law engines.
In other words, a thing is "good" if it promotes or enhances life, "bad" if it destroys or constrains life.
The definition includes "optimise" and "universe-wide" to cater to those situations involving choices only between "bad" options, eg when the killing of one person enables thousands to live.
And lastly, some terminological sleight-of-hand that integrates Khader's definition within a pantheistic framework: if we define Life as "ordered complexity" then the "good" is that which maximises ordered complexity across the entire universe, and the "bad" is that which minimises ordered complexity across the entire universe.
In those terms, existence is "better" than non-existence because there can be no ordered complexity if nothing existed at all.So "isness" is by definition "good", and the fact that there is a universe at all is a very encouraging sign!
*eg page 550, published by Abacus in 2004, reprinted 2012.
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