[annie123 (OP)]

Re whether there is life on other planets, how would it be recognised/defined? Only according to earth criteria? Is it possible that what might be viewed as inorganic here actually has properties which could be construed as those of life? (An astronomer told me yesterday that some dust particles have been described as having life characteristics.)If this and other aberrations or departures from our norms are true,which i would think very likely especially at quantum levels, then how would anyone know if something on another planet was alive?

[grizelda]

It depends where you set the bar. If there were such things as UFO's, the technology and knowledge they use would be so advanced (faster than light travel and all) that they would probably consider there was no life on this planet. From our perspective, atoms join in crystals and molecules which undergo processes and form patterns and, Bob's your uncle, we have life.

[solaris]

It depends on how you define life. Is an atom alive or not? It obviously possesses some rudimentary characteristics of life. For example, it interacts with its environment, with light, with other atoms, just like other life forms would do on their levels. We constantly expect to find some other human like creatures living on Earth like planets, at the same time failing to see the life that is manifesting on different levels in front of our eyes.

[Pikaia]

The definition of life is really just a matter of semantics, and various ways of defining life have been proposed:

http://en.wikipedia.org/wiki/Life#Biology

Take your pick!

[annie123 (OP)]

it's the definnition that's my problem - that's why I asked the question, because one could argue that anything with matter is a manifestation of energy but what we understand as living things is very limited although expression of energy is surely what people would also regard as life. And since life is so hard to define - or contain within words, then so is death or not living, so immortality is a natural condition at the smallest levels of existence although not in the gross corporal manifestations of anything detectable to us. I know one starts to get metaphysical but even there the boundaries between science and metaphysics are ofeten blurred. As for testing whether life exists, in the scientific mode, i really wonder how that can happen if there is no accepted understanding of what living means.And so back to other planets - and I was't thinking of little green men etc.

[yor_on]

Why would they want to talk with us?

We make a mess out of most everything we touch, and being 'modern' just seem to make our messes more far-reaching. Either they would avoid us I think or exterminate us as a threat to the planet

And yes, I think I'm joking, at least I hope I am.

[Soul Surfer]

Here is a simple definition of a basic living thing. It must be able to perform all of these tasks.

It extracts materials and energy from its environment (feeds itself)
It can (to a limited extent) repair damage to its structure, grow and develop.
It can replicate itself either by fission into two or more similar organisms or by the generation of "seeds"  that can in the right conditions develop and grow into a mature organism.
It contains all the information needed to perform these tasks within itself with the one exception that reproduction may require the association of two (or more ) substantially similar organisms  (sexual reproduction).

There is a possible argument that solids crystallising out of a solution could display most of these properties but I know of no cases where crystals deliberately split in two or shoot off micro crystals to seed their environment without external disturbance, because the energy flows would not work that way.

There are of course many other attributes that are useful but not absolutely essential.
For example
The ability to sense its environment and move to the most suitable location.
The ability to defend itself from predators
and so on.

The definition of "intelligent life" is of course much more difficult

An obvious one is toolmaking but many animals and birds do that.
Probably the most telling is the use records outside of the physical structure of the organism to pass information on to future generations.

[Bill S]

SS, I wonder about your use of the word "deliberately".  Would you say that bacteria, for example, do things deliberately?

Annie, have you read Michael Brooks "13 Things That Don't Make Sense"?  It covers a lot of the issues that are raised by your OP.

[annie123 (OP)]

I will try to get the book  - 13 things.
To SS - A mule doesn't reproduce yet it would be recognised as being alive.There are bacteria that don't fit other criteria.
I just read a book by Ed Regis - What is Life - 2008 - where he goes into it the best I have seen so far. His conclusion , to date, is that life is embodied metabolism. He also looks at death of course, which is necessary and what bothered me in the first place to think about this since i don't want to be disposed of if I'm not dead. Brain death is not necessarily physical death etc etc. And what about dimensions of life we don't know about that could still be operating and not measurable by instruments that could cause us to be aware of things being done to us even though we appeared dead. Incidentally, i was glad to see some doctors anaesthetise patients when retrieving organs because they are taken when the person is still showing physical signs of 'life' and this was one stipulation i wanted put in my instructions if I became a donor. Lynn Margulis and her son Dorian Sagan have written about this too and I shall get to them.

[moonstroller]

If there was other intelligent life on other planets, that were capable of greater than light travel or light travel in the least. They would have had to conquer one of the basic battles between technology and the primitive desire to survive. If we had the capability to develop a fusion reactor. We would probably blow the whole earth to kingdom come because their would be someone who would just have to push the button. The only thing that keeps us from blowing ourselves up with atomic bombs is the high cost of refining military grade fuel and the idea that those who are well acquainted with the destructive force of such weapons keep a close eye out for violators.

So with super technology, the life forms would have had to conquer their individual desires and emotions to the point that they could utilize the super technology in a way that it would not hurt other life forms. Such life forums would find our species to be very vulgar, and self-destructive. They would not want to socialize with us or enlighten us in the use of super technology. They would, I believe have an interest in keeping apprised of what we are doing and where we are on the road of technological advancement.

Then again, it could be that there is no life form that has ever made it beyond the line that borders super-tech. Maybe our destiny, like the destiny of other life forms before us it to blow ourselves up with super-tech.

I know this. I don't like to hang around with people in other countries who allow themselves to have bombs and machine guns or to allow children to play with such things. I know it from friends in other countries that having your child die in a bomb or gun accident is very common. I try to stay away from such people because I'm afraid of them. Perhaps other life forms are afraid of our violent tendencies and don't want us to know they exist.

I will tell you this. If there is no other life out there in space, it's an awful waste of space.

[moonstroller]

It depends where you set the bar. If there were such things as UFO's, the technology and knowledge they use would be so advanced (faster than light travel and all) that they would probably consider there was no life on this planet. From our perspective, atoms join in crystals and molecules which undergo processes and form patterns and, Bob's your uncle, we have life.

Really, if it was that easy, wouldn't we be seeing more Bobs made out of rocks, etc jumping around? Is there a force that inhabits matter and makes it animated? When someone dies, all those atoms and molecules suddenly become non animated and your entire value to life can be measured by your weight.

There must be some kind of "life force". DNA is nothing but a code. DNA exists in things that are no longer alive. It is not DNA that gives us life.

Life is a device that can draw energy from it's environment and use that energy to grow and/or animate. Life is a combination of inamamated material and..... some kind of force or energy that likes intelligence.

[grizelda]

http://hyperphysics.phy-astr.gsu.edu/hbase/biology/enercyc.html#c1

[Madidus_Scientia]

It depends where you set the bar. If there were such things as UFO's,

Of course there is, not every object that's ever flown has been identified.

the technology and knowledge they use would be so advanced (faster than light travel and all) that they would probably consider there was no life on this planet. From our perspective, atoms join in crystals and molecules which undergo processes and form patterns and, Bob's your uncle, we have life.

How do you think a race gains knowledge? Through science, through studying everything they can, like us. So a race with such technology would be in the habit of studying anything and everything they can, and Earth would be a pretty major field site of study.

[yamo]

I think life is a symbol we use to describe the world around us.  It is like green, or three, or cold.  If so then life is what we say it is.  The universe around us is whether we say it is alive or not.  Three pebbles exist but three does not.

[moonstroller]

It depends where you set the bar. If there were such things as UFO's,

Of course there is, not every object that's ever flown has been identified.

the technology and knowledge they use would be so advanced (faster than light travel and all) that they would probably consider there was no life on this planet. From our perspective, atoms join in crystals and molecules which undergo processes and form patterns and, Bob's your uncle, we have life.

How do you think a race gains knowledge? Through science, through studying everything they can, like us. So a race with such technology would be in the habit of studying anything and everything they can, and Earth would be a pretty major field site of study.

Only true is they survived.

That's my point.