Ask a physicist anything. (6)

Wiccan_Child · May 11, 2011

Doveaman said:
Was that question directed at me?

I'll wait and see how Wiccan responds. If he's wrong I'll correct him.

In my opinion, the difficulty is that viruses arguably don't metabolise - they inject their genome into a host which does the metabolising for them. They don't take in any outside resources themselves, nor do they directly replicate. So the definition ("metabolic replicators") isn't harmed, it's just that it's not clear whether viruses fit that definition.

But I'm inclined to say that yes, they are alive.

Wiccan_Child · May 11, 2011

Naraoia said:
I think you should look around the world of cellular automata. Some really simple rules lead to outcomes ranging from simple, stable patterns all the way to complex, dynamic and chaotic ones depending on your starting point. And they are fundamentally similar to neural networks in a way - in both, the future state of each cell is determined by the interaction of its present state with that of connected cells.

If a von Neuman device (these guys, right? You made me look them up ) is alive, then your definition of metabolism is so broad that it probably includes a fan.

Why would a fan count? It neither metabolises nor replicates - something living things, and von Neumann machines, do.

chris4243 · May 11, 2011

As a biologist, I can confidently say that we have no idea what "alive" means. We can't agree whether viruses are "alive" or not. I think that most of us would not consider self-replicating robots to be alive, but some might. The most precise definition for life involves the specifics of cellular Terran life and would potentially exclude many forms of what normal people would consider alien life. Then you have to consider whether something that is frozen or dessicated is alive (since it has no metabolism). Etc, etc. Is something that is "fatally wounded", possibly at the cell level, still alive? A cell without its DNA? Too many fuzzy things for the definition to be clear, and little agreement.

For the most part we focus on the specifics: metabolism, homeostasis, replication, boundary between self and non-self, DNA, RNA, protein, ATP, cell potential, etc. No need really to mention "alive" at all, except as a convenient word distinguishing three classes of states for a specific organism (alive, suspended animation, dead).

Naraoia · May 12, 2011

Wiccan_Child said:
I wonder, would a meme count as alive? It replicates, in a sense, and could be seen as metabolising...

In what sense?

Wiccan_Child said:
In my opinion, the difficulty is that viruses arguably don't metabolise - they inject their genome into a host which does the metabolising for them. They don't take in any outside resources themselves, nor do they directly replicate. So the definition ("metabolic replicators") isn't harmed, it's just that it's not clear whether viruses fit that definition.

But I'm inclined to say that yes, they are alive.

I'm not sure what you mean by "directly replicate". Viruses do often encode their own replication apparatus.

My take on the "virus" issue is that they are in the grey zone, along with even more minimalistic replicators like virusoids, viroids and prions. I don't think they are simply "alive" or "not alive". Some of them are more alive than others.

Wiccan_Child said:
Why would a fan count? It neither metabolises nor replicates - something living things, and von Neumann machines, do.

I think I misunderstood you there. When you said von Neumann devices, I didn't realise the term refers to more than cellular automata. :o "Machines" tipped me off...

Wiccan_Child · May 12, 2011

Naraoia said:
In what sense?

A meme replicates when it infects another person - there are then two versions of the meme. It varies and mutates upon replication, as although the idea is broadly passed, it's rarely passed on exactly in all its details. Chinese whispers, Arab phone, that sort of thing.

Naraoia said:
I'm not sure what you mean by "directly replicate". Viruses do often encode their own replication apparatus.

My take on the "virus" issue is that they are in the grey zone, along with even more minimalistic replicators like virusoids, viroids and prions. I don't think they are simply "alive" or "not alive". Some of them are more alive than others.

Well, a virus that can take in resources and make more of itself certainly is alive, inasmuch as anything is alive. But those viruses that replicate by disassembling inside a host cell, subverting the host to then manufacture virus parts, which then come together as new viruses... those things aren't so clearly alive.

Naraoia said:
I think I misunderstood you there. When you said von Neumann devices, I didn't realise the term refers to more than cellular automata. :o "Machines" tipped me off...

A von Neumann machine is something that a device that builds more of itself, such as a self-perpetuating pattern in the Game of Life.

(I play a game called Sword of the Stars which has a randomly occurring hit-and-run race called the Von Neumann, as they harvest system resources and make more of themselves. Scary buggers).

Naraoia · May 12, 2011

So I didn't misunderstand you after all, you do mean the cellular automata.

In honesty, you seem to be conflating metabolism and replication. Metabolism is the exchange and transformation of "stuff" between a system and its environment. Replication can be metabolism - the new copy of the system has to be made of something, after all - but if you allow the "stuff" to be as abstract as information, then I don't see how a machine that takes up electricity and uses the energy to do stuff isn't metabolising.

That game you play sounds awesomely geeky

Maxwell511 · May 13, 2011

Doveaman said:
Maxwell511, the Contributor, must be proud of his long thread. Although he seldom contributes to it.

It wasn't my thread. I just restarted it after the last got closed for some reason.

I'm not even a physicist, I'm more of a complexity scientist. Which is a such a young field we don't have a cool name for those that study it yet. How does Complexitist sound?

Maxwell511 · May 13, 2011

Wiccan_Child said:
I'm also pleased that the new thread is called (6), instead of "Ask a physicist anything. (5) (2)"!

I was also very worried about that. I think I mentioned it before the thread split.

Naraoia · May 13, 2011

Maxwell511 said:
It wasn't my thread. I just restarted it after the last got closed for some reason.

I'm not even a physicist, I'm more of a complexity scientist. Which is a such a young field we don't have a cool name for those that study it yet. How does Complexitist sound?

"Complexity scientist" is still less of a mouthful than "evolutionary developmental geneticist"!

Maxwell511 · May 13, 2011

Wiccan_Child said:
Is a falsified theory still a theory? I'd say yes, though a minority of scientists would disagree (or it might be a majority, I'm not sure).

I think the majority would agree with you.

Is Phlogiston a theory? If it was a theory at all, then yes. The evidence supporting it still exists, it's just been disproven by contradictory evidence.

So, as you ask, what happens to that supporting evidence? Well, whatever theory replaces the disproven one has to also account for that pre-existing evidence. So, the new theory, which is compatible with the old evidence, takes that evidence as its own.

All the evidence for Classical Mechanics still exists, but its successor, Quantum Mechanics, can also explain all the evidence that supports Classical Mechanics. For example, Newtonian gravity can be deduced from QM, using large-scale approximations. The Correspondence Principle states that the quantum mechanics of very large things must correspond with the classical counterpart - the mechanics of billiards, whether modelled classically or quantum mechanically, must be essentially the same.

CM has the unique exception of being more useful than its successor in some instances, so we still use it.

And the mathematics of the Caloric Theory. It is easier to make calculations on the assumption that heat is a substance that flows rather than trying to deduce things from the first principles from the Kinetic Theory.

Also Newtonian Mechanics is still extremely useful.

EDIT: Others disagree with me

It's large semantics anyway - disproven theories are rarely any interest to us.

I dislike the use of your word "disproven". While I understand that some theories can be disproven, physical theories can very rarely be disproven. They can be superseded. Please use the word "superseded" from now on. CM was not disproven it was superseded by QM. Newtonian Mechanics was not disproven it was superseded by Special Relativity, and so on.

QM did not show that CM was wrong. CM is theoretically derivable as special cases of QM. QM superseded CM, in the same manner that Maxwell's Equation superseded Ampere's Law.

Please, use the word superseded from now on. Mostly for my own sake, I will not have anything bad said about James Clerk's work. If you force my hand I will need to dedicate my life to proving that his equations are derivable from QM.

Maxwell511 · May 13, 2011

Just on this general conversation of the definition of life. Although it probably should be in another thread.

Ability to replicate cannot be a necessary factor in determining if something is alive. If this were the case then a sterile animal could not be alive. I really doubt that women that have gone through the menopause are not alive anymore.

Naraoia · May 13, 2011

Maxwell511 said:
Please, use the word superseded from now on. Mostly for my own sake, I will not have anything bad said about James Clerk's work. If you force my hand I will need to dedicate my life to proving that his equations are derivable from QM.

That made me chuckle. (You'd actually do that, wouldn't you? )

Maxwell511 said:
Just on this general conversation of the definition of life. Although it probably should be in another thread.

Ability to replicate cannot be a necessary factor in determining if something is alive. If this were the case then a sterile animal could not be alive. I really doubt that women that have gone through the menopause are not alive anymore.

Her genome still keeps replicating as long as there is cell division in her body (which is right up until she really isn't alive). And chances are she was quite capable of reproducing before menopause.

Maxwell511 · May 13, 2011

Naraoia said:
That made me chuckle. (You'd actually do that, wouldn't you? )

I probably would.

Although I am doubtful that I would get funding for it.

Her genome still keeps replicating as long as there is cell division in her body (which is right up until she really isn't alive). And chances are she was quite capable of reproducing before menopause.

So it is a weak form of the reproduction requirement that is used in biology?

One of my concerns on this is that we would have a potential problem if people were successful on producing Artificial Intelligence that could not self replicate. We could have a situation were something is self-aware but not alive. What do you think?

Naraoia · May 13, 2011

Maxwell511 said:
So it is a weak form of the reproduction requirement that is used in biology?

One of my concerns on this is that we would have a potential problem if people were successful on producing Artificial Intelligence that could not self replicate. We could have a situation were something is self-aware but not alive. What do you think?

Haha, I think that "life" is best left vaguely defined. There are so many exceptions and borderline cases that any strict definition is going to leave someone saying "but" It's not like a strict definition of life is needed for biology to function.

That said, I'm quite comfortable with the idea of self-aware non-life. Cognitive ability never figured prominently in my intuitive definition of life.

Your thoughts on AI and life ... made me think of The Bicentennial Man.

ETA: I think descent is an important, though often implicit, part of many definitions in biology. For example, if plants have a definition, it generally includes photosynthesis. Rafflesia and some other parasitic plants don't do that, but they are still considered plants because their ancestors (presumably) did.

Maxwell511 · May 14, 2011

Naraoia said:
ETA: I think descent is an important, though often implicit, part of many definitions in biology. For example, if plants have a definition, it generally includes photosynthesis. Rafflesia and some other parasitic plants don't do that, but they are still considered plants because their ancestors (presumably) did.

From a complexity stance, descent with long term memory is the only thing that matters. I mean that it matters in that it is interesting, not the definition of life. Biological systems are great at this, but it is way above our heads in trying to comprehend it.

Did you know (which of course you do because you are a geneticist, but I am using this a rhetorical device) that DNA can be analyzed so that we can tell the evolutionary relationships between different species? Even without fossils we could tell that certain species are descendants from a common ancestral species. That is amazing to me.

mzungu · May 14, 2011

Maxwell511 said:
One of my concerns on this is that we would have a potential problem if people were successful on producing Artificial Intelligence that could not self replicate. We could have a situation were something is self-aware but not alive. What do you think?

A self aware sentient artificial life form is no different to a non self replicating biological life form. Self replication is not in itself an indication of a life form.

Consider this:

A bacteria (or any suitable life form you like) is born with a mutation that precludes self replication. Of course its lineage is doomed to stop with this particular bacteria but it does not mean it is not alive!

The question of what is life; is half science and half philosophical.

If we built a positronic brain that has self awareness and sentience; But you change your mind and want to permanently switch it off. But, the Positronic brain pleads you not to switch it off (kill) because it is afraid! Will you do it? Will switching it off be considered murder?

In my opinion; Yes it would be murder. Just because it is man made does not preclude it from being alive!

Nostromo · May 14, 2011

mzungu said:
If we built a positronic brain that has self awareness and sentience; But you change your mind and want to permanently switch it off. But, the Positronic brain pleads you not to switch it off (kill) because it is afraid! Will you do it? Will switching it off be considered murder?

In my opinion; Yes it would be murder. Just because it is man made does not preclude it from being alive!

I suppose an interesting problem then would be determining that the machine was actually sentient, rather than just appearing to be.

Naraoia · May 14, 2011

Nostromo said:
I suppose an interesting problem then would be determining that the machine was actually sentient, rather than just appearing to be.

Another interesting problem is, can you appear sentient without being it? (And also, precisely what do we mean by sentience?)

Maxwell511 · May 14, 2011

Nostromo said:
I suppose an interesting problem then would be determining that the machine was actually sentient, rather than just appearing to be.

I have researched this. By research, I mostly mean that I have recently watched Terminator 2: Judgement Day.

We will know that the machine is sentient, once it starts killing us.

There will be none of this Short Circuit nonsense. I do not care how many bids for freedom Gaak makes, it is not alive.

Maxwell511 · May 14, 2011

Naraoia said:
can you appear sentient without being it?

I do this daily. It's not that hard.

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