h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

if all this couldnt happen twice , how come it seems acceptable to you that it happened once???
Maybe none of this happened at all ??
LIke I've been trying to say science explains very little on the grand scale of things...
We are simple creatures .... our brains cant cope with stuff that we don't see every day.

I was talking about ET visiting us in spaceships. Not about them just being out there. And just because we can't understand anything, doesn't mean we are being visited by aliens. That would also mean dragons in the garage and all that stuff.

Anythg in the universe that can exist exists many times. Stars, planets (we now know), and even matter is common throughout the universe, and there's no reason to think that life isn't too. If there was no other life out there, then there wouldn't be any life here either.

"If there was no other life out there, then there wouldn't be any life here either."
Why?

¦M¦

As Hiker Mond said: "if all this couldnt happen twice , how come it seems acceptable to you that it happened once".

If it couldn't happen twice in such a vast universe then you would expect it not to happen once either.

Expect, maybe. That doesn't necessarily mean that it has happened twice, or will happen twice.

And after all, how do we know that it has happened once?

¦M¦

Well, if there's a million planets and the chance of life happening is a million to one shot. Then it is possible it has only happened once.

Backtracking to posting 61 (I assume you were referring to my earlier posting)

I didn't say that it couldn't happen twice. I just said that it was improbable. I'm sorry if I seemed to imply otherwise.



I think that the current explanation of the size of the universe is that it is boundless. But it appears likely (assuming that the Big Bang theory is correct) that there is a finite amount of matter (and therefore planets) out there. Therefore the argument that anything that happened once had to happen more than once does not follow through.

It is my belief that on many planets, the early "virus" stage was reached. But stability is necessary for life to exist, and this meant the evolution of a stable molecule of heredity (in Earth's case, DNA), which is unlikely (the fact that it did happen at least once, here on Earth, does not make it any less likely in absolute terms).

And I think that applying our ideas of science to extra-terrestrial affairs is perfectly valid. Obviously, there are some scientific disciplines which are exclusively Earth-based (eg human biology), but my explanation was given in terms of the chemistry of life. Matter is matter, wherever you are. We have a good understanding of how matter interacts to produce life. So humans are perfectly qualified to use the disciplmes of chemistry and physics to speculate on the nature (or lack of it) of life elsewhere.

Xanatic: As said earlier, there are around 10^21 stars in the universe. Many of our nearby stars have planets, so it is very unlikely that on 1 in 10^15 stars in the universe have planets. If the chance of life was one in a million, then there would be millions of planets with life.

MSC: Stability for life is undoubtably a rare event, but a a very large area for it to occur that it isn't unreasonable to think that it could more than just once.

So if there are, say, 10^600 planets in the universe, and the probability of life is, say, 10^600, then there is a possibility that it has only happened once.

¦M¦

1 in 1000000000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000

That's a small probablitiy, but theoretically yes. I don't life's that much of an anomoly though.

Thank you ming mang, that's what I meant. However virus is not what would happen first. Virus seems to have evolved rather late, it was bacterias and such that came first. And virus does have DNA, it really isn't much else.

Well, we can't know.

¦M¦

True.

That's OK Xanatic, I figured it was.
And viruses can't actually replicate unless they are inside a living cell.

¦M¦

Not all viruses have DNA. Some viruses (for example TMV and HIV) have RNA as their genetic material.

I apologise for my inaccuracies. Ming Mang, you are of course perfectly correct when you say that viruses can only replicate inside a living cell. Xanatic, you are correct in saying that viruses probably came later, as the result of 'rogue' DNA. Guess that's what comes of not reading the biochem. textbooks properly before making an argument!

However, virus-like particles did probably exist before cells. These were likely to have been ribozymes (catalytic RNA) inside a proteinoid microsphere. But again, given that RNA is so extremely unstable, the chances of cells actually developing were minute. Which is why I agree with both Ming Mang and Xanatic that we must give serious consideration to the idea that perhaps life did only arise on one planet (at least, I think that's the argument that was being made).

But I've read the accounts given in three textbooks and even more scientific journals since this morning, and no-one seems to agree on whether or not any of what I've said is true, which is making me feel incredibly stupid. I'm going to go away and have a good long think about all of this, and to determine what my opinions really are. Makes me glad to be specialising in life that we actually know (or can assume) does exist.

MSC

*goes off with head in hands, suffering from information overload*

LOL, don't feel stupid. There are plenty of people who wouldn't even read any textbooks before arguing. I haven't, for one.
Anyway, there is a continual debate about what is alive anyway. As far as I know, this usually involves whether viruses are alive - they cannot replicate themselves. I can't remember any other arguments about it, but there are others.

Oh - and my argument and also my view, is that we can't know whether there is other life, and can't know what the probability of it existing anywhere else.

Good luck with the thinking, anyway. Hope the calms down.

¦M¦

There is a primitive form of self-replicating protein called a prion (http://www.bbc.co.uk/h2g2/guide/A531776), the type agent that causes BSE. I don't think these are classed as alive though.

Prions aren't quite self-replicating. The cells which prions infect already contain a gene which codes for a protein which is similar to the prion. The host protein is normally produced, and is generally found in neurons. The incoming prion modifies the host cell protein either during or after synthesis, and causes a change in its folding pattern, giving it resistance to proteases and making it insoluble in water. Thus it is actually the host cell which produces more copies of the prion.

Sorry to wander from the topic of extra-terrestrial life and UFOs, but I felt the need to clarify that point.

Regarding (again) Occam's Razor: The razor does nothing to establish truth or falsity based upon simplicity. It is a method of arbitrarily eliminating numerous equally valid hypotheses based upon the number of variables involved.

For example, if one day you left your house and noticed a turtle on one side of your lawn, then returned later in the day to find the turtle on the other side of the lawn, you may propose numerous paths that the turtle took across the lawn. The path with the fewest points along the path would be a straight line. This may or may not be the correct path, but it's better to start with that hypothesis than the one that involves a circumnavigation of the globe.