The Definitional Dilemma: How precisely should we define 'life' and 'intelligence'? Is this definition crucial for our identification of extraterrestrial visitors?

Hey, this is a huge question, a classic topic that sci-fi fans and scientists have debated for decades. It might seem "philosophical," but it's actually very practical, directly related to how we search for extraterrestrial life and how we'd identify it if we ever encountered it.

Let's break it down and discuss it in simpler terms.

1. The Conundrum of Defining "Life"

Why is it so hard to define "life"?

Simply put, because we only have one sample: Earth life. It's like you've only ever seen apples your whole life, and then you're asked to define "fruit." You might say: "Fruit is round, red, grows on trees, and tastes sweet and crisp." But then someone brings you a banana, and your definition completely falls apart.

Our definition of life is based on this "apple" (Earth life).

How do we usually define life? (The biology textbook version)

Generally, life is thought to have several characteristics:

Metabolism: Needs to "eat," "breathe," and "excrete," exchanging energy and matter with its environment.
Growth and Development: Grows from small to large, or changes in form.
Reproduction: Can replicate itself, producing offspring.
Response to Stimuli: If you poke it, it moves (or reacts in some other way).
Heredity and Variation: Offspring resemble parents but are slightly different, allowing for "evolution."
Composed of Cells: This is the basic unit of Earth life.

What's wrong with this definition?

Big problems.

Fire also fits several of these criteria: it "consumes" fuel, "grows," can "reproduce" (sparks flying), and reacts to environmental changes (like wind). But no one would say fire is alive.
Viruses are awkward; they can't metabolize or reproduce on their own, needing to "parasitize" other cells to live. Are they life? Scientists are still debating this.
Extraterrestrial life might not follow our script at all. Who says life must be carbon-based? Perhaps there's silicon-based life living on high-temperature planets, breathing gases we've never heard of. Who says life needs water? Maybe in the methane oceans of Titan, there are "methane organisms." They might not be composed of cells but rather some form of crystal or energy.

So, a broader, more fundamental definition might be: Life is a system capable of maintaining internal order (reducing entropy) and undergoing self-replication and evolution. But this definition is too abstract for the average person to use for identification.

2. The Conundrum of Defining "Intelligence"

If defining "life" is hard mode, then defining "intelligence" is hell mode. We haven't even fully figured out human intelligence, let alone that of other animals on Earth.

What do we usually consider "intelligence"?

Using and manufacturing tools
Complex language and communication abilities
Logical reasoning and problem-solving skills
Self-awareness (knowing 'I' exist, recognizing oneself in a mirror)
Abstract thinking (contemplating philosophy, mathematics, art, etc.)
Emotions and empathy

What's wrong with this definition?

Again, big problems.

Animal intelligence: Crows use twigs to fish for insects, dolphins have their own "dialects," and elephants experience sadness. Their intelligence differs from ours, but can you say they are "unintelligent"?
Artificial Intelligence (AI): Modern AI can beat all humans at chess, and it can draw and write poetry quite convincingly. But does it have "self-awareness"? Does it "understand" what it's doing? Or is it just a super complex computational program?
Forms of extraterrestrial intelligence: We subconsciously imagine "intelligence" as an individual "brain." But why couldn't alien intelligence be a "collective intelligence"? For example, all plants on a planet forming a unified consciousness network, where a single tree is "dead," but the entire forest is a super-brain. Or like an ant colony, where a single ant is unintelligent, but the entire colony exhibits astonishing wisdom.
Unrecognizable intelligence: Perhaps some form of alien intelligence has a completely different way of thinking and exists in different dimensions. They might communicate in ways we can't perceive (e.g., neutrinos, gravitational waves), and their "thoughts" might just be meaningless background noise to us. We're like ants; even if humans are discussing quantum mechanics right next to them, the ants would be completely unable to understand that this is an "intelligent" activity.

3. Is This Crucial for Identifying Alien Visitors?

The answer is: Absolutely crucial!

How we define "life" and "intelligence" directly determines what methods we use and where we look for extraterrestrials.

Determines our "search methods"
- If we believe "life" = water-dependent carbon-based organisms, then we'll focus our resources on searching for "habitable planets" similar to Earth. This might cause us to miss peculiar life forms existing in extreme environments.
- If we believe "intelligence" = uses radio, then we'll use massive radio telescopes to listen for suspicious signals in the universe, like the SETI program. But if aliens have long since abandoned such inefficient communication methods, switching to quantum entanglement or some other advanced technology, then our listening would be like waiting for carrier pigeons in the age of high-speed rail—we'd never get a message.
Determines whether we can "recognize" them
- Imagine an alien probe arriving on Earth. It might not be the metallic spacecraft we envision, but rather something that looks like a "cloud," or a self-replicating "gel." If we rigidly stick to the idea that "machines should have screws and casings," we might not recognize it at all.
- Now imagine a highly intelligent being arriving on Earth, completely uninterested in humans, only here to study Earth's volcanic activity. To us, it might just appear as a "strange rock" because it doesn't communicate with us or display "intelligent" behavior. We might miss the opportunity to interact with it, or even inadvertently destroy it.

Conclusion

Rigid definitions are our biggest obstacle in searching for and identifying extraterrestrial life/intelligence.

We shouldn't be looking for an "alien" that fits our preconceived notions, but rather for "anomalies" in the universe—phenomena that are difficult to explain with existing laws of physics and chemistry. For example, a planet with an unusually complex atmospheric composition that couldn't be naturally formed; or a point in the universe emitting highly regular, unnatural energy patterns.

Ultimately, when we face extraterrestrial visitors, the real challenge might not be how advanced their technology is, but how limited our cognitive frameworks are. We need to maintain an absolutely open mind, ready for all our definitions of "life" and "intelligence" to be completely overturned.