[alancalverd (OP)]

Halc here:  Topic split from Fermi-Paradox entry in A-Z Apropos Fermi Paradox  I wasn't the one who split it, but I patched this one up a bit.

The Fermi paradox, named after Enrico Fermi, contradicts the lack of evidence of extraterrestrial civilization with the seeming high probability of it.

The argument goes roughly like this:
There's lots of stars, a good percentage with viable planets for life.
Some of that life must have evolved intelligence, interstellar travel, etc and must have populated the galaxy.
Where are they?

Taking apart the paradox requires debunking one of several assumptions made.

Maybe Earth is really unique and those conditions simply don't occur as frequently as Fermi calculated.

The argument assumes that technology is sustainable, but this is questionable since resources are limited and technology falls permanently once they are exhausted.

Maybe they're out there but are good at hiding it.  The ones that are not soon get eliminated.

If this planet is typical, life has been around for about 4.5 x 10⁹ years, but has only ever left the planet or transmitted "intelligent" signals in the last 100 years, not for very long, and is unlikely to do so again, so the probability of anyone outside detecting life other than by spectroscopy is about 1 in 4.5 x 10⁷ assuming that he had been looking at us continuously, with infinite resolution.

But if our little green man has evolved in a similar fashion to ourselves, the probability of his observation window being open simultaneously with our making a signal is about 2 x 10^-15. And the probability that he has also chosen our planet to study during that period is very, very close to zero!

Jewellers know this. Individual diamonds are sent by first-class post, because nobody is going to sift through an entire trainload of tax bills and love letters to look for one.   

[paul cotter]

Coupled with the astronomical(!) distances to the nearest habitable planet and the possibility approaches zero.

[paul cotter]

Personally I would guess that the universe is teeming with life but the distances involved preclude contact. Fantasy ideas like warp drives, Alcubierre drives, traversable wormholes and any other schemes to defeat "c" are the products of overactive imaginations. Anyway travelling at greater than c, if possible, would be extremely hazardous- hit a bit of interstellar dust and turn into an inferno with the kinetic energy released.

[Eternal Student]

Hi.

I have a picture, but cannot for the life of me figure out how to post my own picture, ...

   It really is a bit fiddly to start with.   On the sixth go, you'll get it.

Here's the official guide:

https://www.thenakedscientists.com/forum/index.php?topic=45718.msg397740#msg397740

You can, eventually work out what you need to do if you read that,  however it's not easy to understand.   After you've finally done it, then the guide will start making sense  -  so it's   OK   for a quick-reference or reminder after you've somehow managed the first time.


Here's a simplified version, with pictures, that will at least get you started:

Step 1:
   Start a reply or new post as usual.     Find the + button for  "Attachments and other options" and click it.





Click it.png (92.02 kB . 1112x633 - viewed 290 times)






Step 2:

An extra set of new things you can do will drop down.     Use the  "Browse" button,  which opens up a familiar windows "file manager" style mini-window.   Find the picture on your computer (in whatever folder you left it in) and select "Open" in that mini-window.
   Some new info will now appear right next to that browse button where you were making the forum post/reply.   It should be the name of your picture file.    Just below will be some writing such as   (Insert Attachment 0).    Here's a picture of that below:





New info and choices appear.png (39.73 kB . 1053x592 - viewed 285 times)



   Please, just leave the new information and new choices alone for a moment and actually put some ordinary text in you forum post / reply first.

---------------------------------

Step 3:
    Organise your reply / post a bit.   Move the cursor to where you want the picture to appear.
    When you've finally got the spot where you want the picture to appear, then hit that green text that said  "Insert Attachment 0".
    Sadly, the picture won't appear BUT fear not, you do get a little bit of code inserted into the forum post.  So there is some hope it will all work out in the end....
This is (almost) the code you will see in the forum post:

Code: [Select]

[ attachment=0 ]

   I had to deliberately add a space after the opening square bracket and before the closing bracket,  it shouldn't be there and you will NOT have it.   I had to add it because if I don't then this forum software will actually interpret what I've shown as some code that it must act on... so it goes looking for attachment 0 and either finds it or displays an error message.
----------------------------------

Step 4:
    What you would now like to do is  "PREVIEW" the post as usual before you post it.   Wouldn't that be just lovely?   Of course you can't.... well you can  BUT the pictures you tried to insert will just display with the message "invalid attachment".
    However, fear not, be brave and just post it anyway.    It turns out that just before posting, the forum software actually does go and do its things, collects the attachments and has them available.   It just doesn't bother to do that for the preview function.

-------------------------------------

Step 5:
     Sometimes something does go wrong....   You accidentally posted a picture of your elbow instead of a white ghost flower,   the picture is just too close to some other text.... etc.  etc.
     There is the ability to  "EDIT" or completely remove/delete a post that you have already posted.   You seem to already know how to do that.    This sort of editing is the only kind of "preview" that you have whenever pictures are inserted... so don't worry about how many times you may need to edit the post within the first 10 minutes of posting it.
    A word of caution:   As you use this feature, you will work out what the code means that was automatically inserted.   For example, if you tried to insert 3 pictures,  then you'll have code involving the tags   "attachment 0",  "attachment 1"  and "attachment 2".    The software starts counting from 0 when you first create the post.  However, after you've posted it and then go to edit it, you may find it has re-labelled the attachments,  for reasons that make sense to someone,  it might decide to start counting from 1 and not 0.   So, when you go back to edit, you need to look again at the information that appears along the bottom when you click the + button next to Attachments and other options.   You should find that all the files you originally uploaded are still there, they just might have been re-numbered.

Best Wishes.

[Halc]

If this planet is typical, life has been around for about 4.5 x 10⁹ years, but has only ever left the planet or transmitted "intelligent" signals in the last 100 years, not for very long, and is unlikely to do so again, so the probability of anyone outside detecting life other than by spectroscopy is about 1 in 4.5 x 10⁷ assuming that he had been looking at us continuously, with infinite resolution.

But if our little green man has evolved in a similar fashion to ourselves, the probability of his observation window being open simultaneously with our making a signal is about 2 x 10^-15. And the probability that he has also chosen our planet to study during that period is very, very close to zero!

Alan seems to agree with my assessment that tech is fleeting.  This is also my opinion.

Coupled with the astronomical(!) distances to the nearest habitable planet and the possibility approaches zero.

There are plenty of planets that can sustain life, so if by 'habitable', you mean that, then I disagree. They're everywhere, even in our own solar system.  Europa comes to mind.

If by 'habitable' you mean that humans can go there and step out sans life support system ('class M planet'), then sure, there might not be another one in our galaxy, but I wouldn't expect aliens to be evolved in an identical environment.
The odds of a planet being 'class M' is inversely proportional to the budget of the film depicting it.

I did look up Europa, and it indeed has free oxygen.  The radiation at the surface (from Jupiter) is probably not conducive to life, but that oxygen bleeds through the ice into the water. Any assertions I've made that oxygen on a planet necessarily means life is clearly wrong. There are other means by which it might be generated, in this case, at about the rate of a Gigagram (1000 tons) per day.

[paul cotter]

The only way we could become aware of the existence of little green men is (1) EM transmissions and (2) vehicles from such planets. I know I am going to sound like a "broken record"(if people still understand that concept?) here in that the distances involved will reduce any radio/tv or any other EM transmission to a level well below the best noise figure achievable with today's tech and these distances are only traversable in science fiction. Personally I see no paradox but then again I am no scientist.

[alancalverd (OP)]

Free oxygen is a rarity, and only exists in our atmosphere because it is exhaled as toxic waste by plants, so I would class it as a very strong indicator of life.

Halc says

There are other means by which it might be generated,

Pray tell!

[paul cotter]

According to the Wiki article water is split by radiation and the hydrogen floats off into free space, the gravity on Europa being considerably less than on earth. I don't necessarily believe everything on that site as I have in the past found errors but on the whole it is quite reliable.

[alancalverd (OP)]

Plausible.