What constraints and criteria define life?

[kant]

I once watched a tv program on the possibility of alien life. The program intrigued me in the possibility that life as we know it might not be as limited. Some possibilities that entertained me are: 1) alien life might not need DNA to transfer traits to the next generations. 2) They might be gas, or a smell( to us). 3) might take advantage of the "strong force", and live on the surface of a neutron star 4) they might not be detachable by our eyes, because of "longer wavelength"( don t know).. blah blah.. etc...



Any comments?
Are there necessary constraits to life?
Are there some criterion for life?
What are the possibilities? and limitations?

 

[DaveC426913]

1) alien life might not need DNA to transfer traits to the next generations.

It likely won't have DNA, though it will have something that serves a similar purpose.

2) They might be gas, or a smell( to us).

Well ... it's pretty difficult to have a metabolism if you get blown away on every wind...

3) might take advantage of the "strong force", and live on the surface of a neutron star

The trouble here is that there are a limited set of ways that things can happen. On the other hand, carbon is an extremely flexible atom, combining in near infinite variety with hydrogen. This is what lays the foundation for the fabulously complex building blocks that make up life.

Carbon, oxygen and hydrogen are not just elements picked at random from the periodic table. There are a host of very compelling reasons to use them as building blocks of complexity. They stand head and shoulders above other choices.

And that's not merely bias because I'm carbon-based. Everything in the universe must operate from the same periodoc table. i.e. the fundamentals are a given.

4) they might not be detachable by our eyes, because of "longer wavelength"( don t know).. blah blah.. etc...

Well, if they're made of matter, they'll be detectable. If they're made of energy, they'll be detectable - at least by instruments.

Are there necessary constraits to life?
Are there some criterion for life?
What are the possibilities? and limitations?

Water is another excellent substance that stands head and shoulders above other chemicals for life. It is not just any old molecule. There's virtually nothing else like it in the universe.


This is not to say that forms of life will NOT exist without C O and H, but it is suggesting a very high probability that any life we do find will be organic. It's just the way the universe is built.

 

[Ivan Seeking]

It has been suggested that silicon could be used instead of carbon. Note by the position in the period table that it has the same basic properties as carbon.

You may remember that Star Trek played with this idea in the original series - a rock beast was killing people in a mining complex in order to protect her eggs.

 

[TRCSF]

Using something different than DNA- seems fine to me. I've read early organisms used RNA before DNA came around.

Gaseous organisms- seems ridiculous for already mentioned reasons.

"smell" organisms? Does the person who suggested this understand how the sense of smell works?

organisms on neutron stars- There's a good novel on the subject, "Dragon's Egg" by Robert Forward. He also wrote a book on life on Pluto, that one stunk.

organisms with "longer wavelength" and thus undetectable by us. Stuff of pulp fiction, not that there's a problem with that. Some flowers have patterns that can only be seen in UV. We can still see the flowers.

organisms that are silicon based- The reason this is popular in sci fi is because silicon is in the same column as carbon, thus a writer might expect silicon to behave similarly to carbon. Actually, silicon behaves quite a bit differently and I'd think quite unsuited for life. For example, the by-product of oxidative respiration is CO2, a gas that's easily eliminated from the body. SiO2, on the other hand, is a solid.

 

[Ivan Seeking]

organisms that are silicon based- The reason this is popular in sci fi is because silicon is in the same column as carbon, thus a writer might expect silicon to behave similarly to carbon. .

This is simply not true. The idea has been around for a long time, and I'm sure that a little searching would produce some scholarly papers on the subject - how current they may be, I have no idea.

Also, you may recall that the position of the elements on the chart was first determined by the chemical properties of each element and not an understanding of electron shells. IIRC, the key point is that Si can bond to one, two, three, or four other atoms simultaneously.

 

[Ivan Seeking]

I got some hits that look appropriate but most require a subscription.
http://scholar.google.com/scholar?hl=en&lr=&q="silicon+based+life"&btnG=Search

 

[TRCSF]

This is simply not true. The idea has been around for a long time, and I'm sure that a little searching would produce some scholarly papers on the subject - how current they may be, I have no idea.

Also, you may recall that the position of the elements on the chart was first determined by the chemical properties of each element and not an understanding of electron shells. IIRC, the key point is that Si can bond to one, two, three, or four other atoms simultaneously.

Actually groups 14 and 15 are noted for having widely different chemical properties compared to the same group, compared to, say, the alkali metals, halogens, and nobel gases.

With group 14 you've got the nonmetal carbon, the metalloid silicon, and the metals lead and tin. You wouldn't say lead is chemically similar to carbon, would you?

You can have tetravalent silicon sure, but you can also have hypervalent silicon, and as I mentioned above, the nature of the bonds is quite different.

Feel free to link scholarly articles on silicon based organisms.

 

[DaveC426913]

Yeah about that silicon - can it form long chains like carbon can?

 

[Ivan Seeking]

Feel free to link scholarly articles on silicon based organisms.

Well, as I said, there seem to be quite a few but they require subscriptions.

Silicon-based life is discussed as the possibility of another type of life

http://www.csa.com/partners/viewrec...cid=A9512691AH&q=&uid=787421757&setcookie=yes

Decades of radio astronomical detection of interstellar molecules have provided an empirical probe into speculations about silicon-based life, as a rich interstellar carbon chemistry has been revealed without comparable silicon analogues.

http://adsabs.harvard.edu/cgi-bin/n...amp;db_key=AST&data_type=HTML&format=

From the search quote

Then there is the possibility of silicon-based life (silicon, like carbon, can form four bonds) at temperatures above 1600?C, at which sili- cates are liquid

http://links.jstor.org/sici?sici=0006-3568(198107%2F08)31%3A7%3C537%3ALBE%3E2.0.CO%3B2-E

Conceivably a silicon-based life form would find the temperature and atmosphere of Venus congenial, and of Earth execrable

http://scholar.google.com/scholar?q="silicon+based+life"&hl=en&lr=&start=20&sa=N

including silicon-based life forms, a possibility still under discussion today. ...

http://www3.interscience.wiley.com/cgi-bin/abstract/112134553/ABSTRACT

etc. etc. etc.
I still haven't seen any for free, but as you can see, I didn't invent the idea

...and I should add that I'm in no position to defend it. I was simply passing along some information.

 

[Ivan Seeking]

If you hated that one, you will loath this:



Lisa Randall
http://www.physics.harvard.edu/people/facpages/randall.html

was interviewed on Coast to Coast AM tonight. She is a theoretical physicist who specializes in "model building" for the most advanced theories in physics; in pursuit of a complete theory of physics.

She suggested that there might be life in higher dimensions based on laws of chemistry completely foreign to our known, 3+1 dimensional part of the universe. As a physicist who specializes in higher dimensions, she thinks this might be possible -life unique to other dimensions - in the most speculative sense of course.