The definition of life is one of the most famously difficult definitions in all of philosophy. There are many definitions. For example, science has a descriptive definition for life:
- Homeostasis: regulation of the internal environment to maintain a
constant state; for example, sweating to reduce temperature
- Organization: being structurally composed of one or more cells — the basic units of life
- Metabolism: transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic
matter (catabolism). Living things require energy to maintain
internal organization (homeostasis) and to produce the other
phenomena associated with life.
- Growth: maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its
parts, rather than simply accumulating matter.
- Adaptation: the ability to change over time in response to the environment. This ability is fundamental to the process of evolution
and is determined by the organism's heredity, diet, and external
- Response to stimuli: a response can take many forms, from the contraction of a unicellular organism to external chemicals, to
complex reactions involving all the senses of multicellular
organisms. A response is often expressed by motion; for example, the
leaves of a plant turning toward the sun (phototropism), and
- Reproduction: the ability to produce new individual organisms, either asexually from a single parent organism or sexually from two
Of course, there is no particular rule which says everyone abides by this definition.
An interesting subjective answer would be that a robot is "alive" when you believe it is alive. This resolves a remarkable number of questions, but leaves the pesky subjectivity in place -- whether or not something is alive is a question people can disagree on if this definition is used.
Of course, if the issue is that you felt sorry for the robot, you can always reframe the problem and make sure the robot does not deserve your compassion because it is evil.