Idk if to put biology or planetary science so ye.
In: Biology
I would like to note something others missed.
Our definition of life isn’t really that well defined. Like humans are considered life. So are bacteria. But your average person considers something living so long it has consciousness. A biologist might tell you that life needs to be able to reproduce its cells on its own. By this definition viruses aren’t really life. But someone might consider viruses as living organisms.
I really like fantasy novels. I read mostly the high-level fantasy ones. High-level fantasy would be something like I solo leveling, Starcraft, etc. These novels definitely can give some inspiration about possible ways life can exist. Think of the Swarm from Starcraft. Although each zerg can be considered a living organism there is a special situation. The Swarm itself is a living organism with subconscious consciousness. So we have a living “organism” that exists in the form of pan-consciousness.
We also can’t really explore or define well enough consciousness. Like what are the criteria to distinguish between something being conscious or not? I should note that research projects like neuralink might allow us to have a new look at consciousness and our subjective Ego/Will.
So defining life a bit better as well as consciousness is really important.
It doesn’t have to and we have theories about finding single cell organisms on the Methane seas under the ice sheets of Titan.
But with complex life it’s pretty likely that it needs similar conditions to earth. First and foremost because carbon is one of the most available things out there and it is incredibly at forming bonds with other atoms. Others like Silicium or Selen might be also atoms for it but much less available. Sure there might be a fluke galaxy out there where those two elements are rather common but right now there is no indication for it.
Laws of physics, they are similar around the galaxy and in regions were the go crazy like black holes life of any kind is unlikely to form. Other than that you need some amount of gravity on planets to hold the atmosphere in which ever composition, probably some decent magnetic field against the worst radiation from the local star and some form of energy, most likely the local star but a huge molten core might also do the trick. But it needs some form of stability which extreme seismic active planets don’t seem to have.
For complex life you also likely need a food chain, because it’s unlikely that conscious life will spring out of nowhere. So you need develop from simple to complex.
Is it possible for life to forgo some or all of these, well maybe. But it seems unlikely, and given that the universe is only becoming less hostile to life in general (e.g., less super novae, less gamma ray burst, right star sizes, etc.), we cannot know for sure but can deduct from the laws of physics and go from there.
We don’t know how to look for life that isn’t like our own. So we look for life like our own because, although chances are slim, it’s the best chance we can get.
Because for life to start, the conditions are pretty specific.
And chemistry is strict.
So sure a creature can evolve to survive extreme environments but those same environments wouldn’t allow the initial sparks of life to happen.
So for the most part we should focus our search on places like earth.
Carl Sagan had some though on this topic around 1980. [https://www.youtube.com/watch?v=uakLB7Eni2E](https://www.youtube.com/watch?v=uakLB7Eni2E) The life forms in the video are still earth-like but it does encourage thinking out of the box
Hi!
Great question.
There are a few things to consider.
#Energy issues
The first is very unforgiving – we call it **thermodynamics or energy issues**.
When there is **too much energy** (say inside a sun) there is little chance of any physical substance staying organized in that high energy, chaotic environment.
When there is **too little energy** (say far from a sun and far from geologically produced heat) there is nothing to drive the chemical reactions that we think are needed for living.
#Chemistry issues
All the life we know of is based largely on the interesting chemistry of Hydrogen, Oxygen and Carbon. These are mostly in the form of water and organic (carbon based) molecules.
We can imagine that chemistry not based on these (inorganic chemistry) might be possible as a living system, but we have not yet seen it. We do have some life forms that get their energy by reducing iron or sulfur or other inorganic chemistry but the creature itself is carbon based.
In 2018, Michael Wall wrote a book [Out There: A Scientific Guide to Alien Life, Antimatter, and Human Space Travel](https://annas-archive.org/md5/601a84b2a78a885fb736c6ee8116bdf6) that is worth reading.
By mass our universe is 75% hydrogen, 23% Helium, 1% Oxygen, 0.5% carbon and all the rest of the periodic table making up the 0.5% left over. (Remember that Hydrogen and helium have the lightest mass, so them making up 98% of the universe by mass is a big deal.)
This suggests that Hydrogen and Oxygen and carbon should be major players in any form of life based on their abundance. Helium is the least chemically reactive element. Helium is unlikely to react in any conditions where we expect life to thrive.
#Earth – our only example
The physics of our location seems rare.
* We have a magnetosphere that blocks cosmic radiation so we are protected from that. DNA and other bits important to our kind of life require this.
* We have abundant liquid water. That is a big deal. Life on earth is all about chemistry in a water solution. We have cell membranes that keep water in, and keep water out. We are absolutely dependent of water for life.
* We have a narrow temperature range where we can survive. Using the Kelvin scale, (0C = 273K) it is hard for human life to thrive below 273k or above 320k.
* Most life also does not do well in hard vacuum, or at high pressures. The only life we know of seems adapted for or created for earth like conditions.
Everything else everyone is saying, but also do you remember in the 80s/90s when there was all kinds of sci-fi about silicone life forms on other planets? The reason that became the next most popular base element is because silicone has similar properties and forms the same kind of bonds as carbon. The reason we don’t really take it seriously is because, even if it was possible to form life from silicone, it would be very heavy and unable to form long complex chains. It might support simple life occuring naturally, but it’s very unlikely that it could support complex life. Carbon just seems the be the perfect element for complex life forms.
You are 5. Why are you asking these things. Go pick boogers and wonder about their origins.
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