4 ms·

I actually think that alien life won't be very alien at all. Given that the laws of physics are constant throughout the universe/s in question, I think they're

by araneae 17y ago

I actually think that alien life won't be very alien at all. Given that the laws of physics are constant throughout the universe/s in question, I think they're probably very similar. Why? Well, DNA and RNA are self replicators that, to the best of our knowledge, arose independently. Given that the emergence of self-replicators is improbable to begin with, it's even more improbable that two different types of self-replicators arose that are so similar to each . This probably means that there is some about the way natural laws are shaped that means that certain types of self-replicators are more probable than others; and those that use heterocyclic aromatic organic compounds as code fall under this category. What about other aspects of life? All large forms of life are modular; that is, composed of many smaller but similar types. It's likely that alien life will follow this basic structure as well, because it's much easier to evolve that way. Evolving a larger body without modularity requires fundamental changes in structural composition which may be difficult to achieve with incremental changes. The temptation with exploratory thinking is to deliberately think as much outside the box as you can. Doing so is good, but it's not always correct.

ubernostrum 17y ago
Given that the laws of physics are constant throughout the universe/s in question That actually turns out to be a pretty big given, and there's some evidence that the "laws" as we know them are contingent and could be subject to variation across different regions of the universe. Of course, those regions are in principle unobservable by us, but if it can vary on a large scale it'd be rash to rule out variation on a smaller scale.
- rglovejoy 17y ago
  Not really. What you are describing might happen on a bad episode of Star Trek TNG (Q changes the gravitational constant, for example), but in reality stuff that happens on a planet orbiting a distant star are not going to be all that different than what happens here on Earth. Chemical bonds work the same way in Sunnyvale as they do in the Oort Cloud or in a galaxy billions of light years away. We know this by studying the spectra of the light coming from these places. At the chemical level, I do not anticipate that extraterrestrial life would be very different than that found here. Water is a terrific solvent and is liquid at a wide range of temperature. Unlike methane and ammonia, its molecules are dipoles (one end is more positive and the other more negative), which makes it easy for it to form hydrogen bonds and a strong surface tension at the surface. Carbon and Oxygen are both fairly abundant. They are formed during the carbon-cycle of aging stars (3 He -> C, 4 He -> O). I have read SF stories that tell of creatures that breathe Florine or are Silicon-based, but these are pretty far-fetched. Florine is a lot rarer than Oxygen, and though it is more electro-negative than O, because of this it is likely to stay locked up in rocks than remain in the atmosphere. Silicon has the same number of valence electrons as Carbon does, but the bonds that it forms are at a higher energy state (n=3, vs. n=2 for C). This means that it is hard for Si to form double or triple covalent bonds; this is something C can do very easily. For a more detailed discussion on this subject, see: http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry#Silicon_biochemistry http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemis...
rriepe 17y ago
Expanding on this is the concept of panspermia, life spreading across worlds on its own. For all we know, the building blocks of life could be older than the Earth itself. So, aside from playing by the same rules, different forms of life on different planets could actually have the same ancestors.
Eliezer 17y ago
> DNA and RNA are self replicators that, to the best of our knowledge, arose independently Citation needed.
- xel02 17y ago
  I can give a counter citation. The RNA World Hypothesis states that RNA was the first self-replicating nucleic acid that arose. http://en.wikipedia.org/wiki/RNA_world_hypothesis http://en.wikipedia.org/wiki/RNA_world_hypothesis Note that DNA is NOT a self-replicator. It requires ribozymes (RNA + Proteins) to actually replicate. To my knowledge there has not yet been a enzyme made of DNA (thermodynamically it's favoured structure is not catalytic).
  - nudded 17y ago
    to my knowledge this is what happens when DNA is replicated: they take the tangled dna string thats inside the core of a cell, it is transported outside of that core and then some enzyme copies the DNA but it replaces the T protein with a U (could be another one). This is then called RNA. Why do they do this? well the T protein is very vulnerable. By replacing it, they can now safely transport the rna to the place where they're duplicated.
    - xel02 17y ago
      What you are trying to describe is transcription, the process of reading a DNA template to produce a RNA transcript. This is done in the nucleus for eukaryotes, and in the nucleoid for prokaryotes (which don't have a nucleus). RNA Polymerase is the protein that synthesizes mRNA (from the DNA template) and the nitrogenous base Uracil (U) is used in place of Thymine (neither are proteins). In fact Uracil is less stable that Thymine and the hypothesis is that DNA uses Thymine due to its lower rate of point mutation. (Note I mean less stable in the sense that it can be mutated more easily due to functional groups).

by araneae 17y ago

ubernostrum 17y ago

Given that the laws of physics are constant throughout the universe/s in question That actually turns out to be a pretty big given, and there's some evidence that the "laws" as we know them are contingent and could be subject to variation across different regions of the universe. Of course, those regions are in principle unobservable by us, but if it can vary on a large scale it'd be rash to rule out variation on a smaller scale.

rglovejoy 17y ago
Not really. What you are describing might happen on a bad episode of Star Trek TNG (Q changes the gravitational constant, for example), but in reality stuff that happens on a planet orbiting a distant star are not going to be all that different than what happens here on Earth. Chemical bonds work the same way in Sunnyvale as they do in the Oort Cloud or in a galaxy billions of light years away. We know this by studying the spectra of the light coming from these places. At the chemical level, I do not anticipate that extraterrestrial life would be very different than that found here. Water is a terrific solvent and is liquid at a wide range of temperature. Unlike methane and ammonia, its molecules are dipoles (one end is more positive and the other more negative), which makes it easy for it to form hydrogen bonds and a strong surface tension at the surface. Carbon and Oxygen are both fairly abundant. They are formed during the carbon-cycle of aging stars (3 He -> C, 4 He -> O). I have read SF stories that tell of creatures that breathe Florine or are Silicon-based, but these are pretty far-fetched. Florine is a lot rarer than Oxygen, and though it is more electro-negative than O, because of this it is likely to stay locked up in rocks than remain in the atmosphere. Silicon has the same number of valence electrons as Carbon does, but the bonds that it forms are at a higher energy state (n=3, vs. n=2 for C). This means that it is hard for Si to form double or triple covalent bonds; this is something C can do very easily. For a more detailed discussion on this subject, see: http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry#Silicon_biochemistry http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemis...

rriepe 17y ago

Expanding on this is the concept of panspermia, life spreading across worlds on its own. For all we know, the building blocks of life could be older than the Earth itself. So, aside from playing by the same rules, different forms of life on different planets could actually have the same ancestors.

Eliezer 17y ago

> DNA and RNA are self replicators that, to the best of our knowledge, arose independently Citation needed.

xel02 17y ago
I can give a counter citation. The RNA World Hypothesis states that RNA was the first self-replicating nucleic acid that arose. http://en.wikipedia.org/wiki/RNA_world_hypothesis http://en.wikipedia.org/wiki/RNA_world_hypothesis Note that DNA is NOT a self-replicator. It requires ribozymes (RNA + Proteins) to actually replicate. To my knowledge there has not yet been a enzyme made of DNA (thermodynamically it's favoured structure is not catalytic).
- nudded 17y ago
  to my knowledge this is what happens when DNA is replicated: they take the tangled dna string thats inside the core of a cell, it is transported outside of that core and then some enzyme copies the DNA but it replaces the T protein with a U (could be another one). This is then called RNA. Why do they do this? well the T protein is very vulnerable. By replacing it, they can now safely transport the rna to the place where they're duplicated.
  - xel02 17y ago
    What you are trying to describe is transcription, the process of reading a DNA template to produce a RNA transcript. This is done in the nucleus for eukaryotes, and in the nucleoid for prokaryotes (which don't have a nucleus). RNA Polymerase is the protein that synthesizes mRNA (from the DNA template) and the nitrogenous base Uracil (U) is used in place of Thymine (neither are proteins). In fact Uracil is less stable that Thymine and the hypothesis is that DNA uses Thymine due to its lower rate of point mutation. (Note I mean less stable in the sense that it can be mutated more easily due to functional groups).