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Knock, knock. Who's there? Looks like nobody's in.

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#1 DaveC2042

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Posted 18 June 2019 - 05:55 PM

Interesting report on the search for ET coming up with another blank.

https://www.theguard...s-of-alien-life

Important context is that this was a search of stars within 160 light years of us, a miniscule distance in the scheme of things.

So it is not really about whether there is life out there somewhere, but more about whether there is any close enough to meet.

#2 Astroman007

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Posted 18 June 2019 - 05:59 PM

An interesting perspective, though one I smile at.

 

Look a little closer? Take that as you will.


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#3 TOMDEY

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Posted 18 June 2019 - 07:26 PM

That brings up an interesting related >>>

 

Not that long ago, Lowell and others were substantially-convinced that technological ~people~ were living on Mars... now! That turned out to be over the top optimistic. My opinion is that our current state of true Goldilocks exoplanets, within even detectable range... is probably equally-optimistic. I'm sure they are out there... but far apart... too far to expect to discover, with our current (and future) technologies. As they say... ~Space is a big place!~

 

Regarding "The Space-Aliens are here!!!" --- just zero evidence for that, as in absolute zero.    Tom

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#4 DaveC2042

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Posted 18 June 2019 - 08:41 PM

A few rough numbers on scale.  (Happy for people to point out any errors.)

 

Assuming a Milky Way 175,000ly across and 2,000ly thick, we have a volume of 4.8 x 10^13 ly2.  Against this our 160ly radius search sphere is 80,0000 ly2.  So we have covered around 0.0000002% of just our own galaxy in this search.

 

Now for getting to something 100ly away.

 

The fastest we have ever made something go is around 70,000m/s - a small satellite in solar orbit.  This is 0.02% of the speed of light.  This gets us there in around 400,000 years.  And the kinetic energy at that speed is 2.5 x 10^9 J per kilogram, much of which we got from chucking it down the sun's gravitational well, which is the opposite of what we'd need to do to leave.

 

Suppose we wanted to get there in, say, 400 years - this is much longer than I credit humanity with being able to plan for, but hey.  This would require us to get something up to 25% of the speed of light.  I calculate the energy required as 3 x 10^15 J per kilogram.  6 orders of magnitude higher.  For a ton-sized craft which might just be manned, that's 3 x 10^18 J.  That's getting up towards a full percent of total annual global energy consumption.

 

I love the research and would be delighted if we ever found evidence someone else is out there.  But it is a needle in a haystack, and we probably won't be visiting each other.



#5 BillP

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Posted 19 June 2019 - 05:30 PM

love the research and would be delighted if we ever found evidence someone else is out there.  But it is a needle in a haystack, and we probably won't be visiting each other.

 

I agree.  If, for some reason, life were limited to only Earth-like planets, then the needle gets even smaller.  Based on our actual data on exoplanets found and those in the goldilocks zone, it is only about 5% of the exoplanets found that meet the criteria.  And that criteria does not further limit to planets with suitable atmospheres, planets that are geologically stable, planets orbiting stars that are stable, stars in stable parts of their local neighborhoods.  So the needle gets a lot smaller again.  And when you further limit to life that has actually evolved into industrial/technological status, way smaller still.  Then factor in how likely is any industrialized civilization able to exist before they are snuffed out by either themselves or nature?  So the needle gets microscopic really that any communicating civilization that would lend itself to detection is even still in existence.  Could very well be that in something the size of a galaxy that no two industrialized/technological communicating civilization ever exist in the same time frame!  And even if they did, given the cesspool that Earth is with trillions upon trillions of different bacteria and viruses, "visiting" would be very much out of the question.  So doubt anything past a phone call would be acceptable unless you are interested in risking an extinction-level biological event just for the sake of a visit so you can shake hands.



#6 Sketcher

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Posted 21 June 2019 - 12:55 AM

. . . and we assume that ET is going to be sending out radio transmissions (a potentially very short-lived practice by our own civilization) that radiate out in all directions (very wasteful in energy consumption by any so-called intelligent civilization) that would be recognizable (to us) as being of intelligent origin.  Seriously?

 

We always make the same mistakes -- never really learning our lessons:  Just how smart is it to assume that ET would be neither any less technologically advanced than us nor any more technologically advanced than us?

 

It wasn't that long ago that it was suggested that we set fire to large (patterned) expanses of our forests in an attempt to send a message to the intelligent Martians when our planets were closest to one another.

 

Somebody needs to start thinking "outside the box".



#7 BillP

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Posted 21 June 2019 - 10:58 PM

It wasn't that long ago that it was suggested that we set fire to large (patterned) expanses of our forests in an attempt to send a message to the intelligent Martians when our planets were closest to one another.

 

Somebody needs to start thinking "outside the box".

 

The problem with either looking for radio signals or visual signals, or producing them for others, is that it will take forever really.  If others are looking for intelligence from Earth and using transmitted signals as the method, well then anyone further than about 100 LY from us will see a radio dark and lifeless place.  On the idea of sending visual signals I guess we can assume that perhaps we had enough gas lamps around some major cities in the 1800's that those lamp lights might have shown something distinctive from space on the night side of the planet?  So that extends us out to about 200 LY for showing another civilization there is something going on here.  Bottom line is that basically any relatively new industrial civilization, whether us or someone else, could easily exist but we and they would never know if we live more than a few hundred light years apart, which I think would be most likely.



#8 llanitedave

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Posted 23 June 2019 - 01:48 AM

I agree.  If, for some reason, life were limited to only Earth-like planets, then the needle gets even smaller.  Based on our actual data on exoplanets found and those in the goldilocks zone, it is only about 5% of the exoplanets found that meet the criteria.  And that criteria does not further limit to planets with suitable atmospheres, planets that are geologically stable, planets orbiting stars that are stable, stars in stable parts of their local neighborhoods.  So the needle gets a lot smaller again.  And when you further limit to life that has actually evolved into industrial/technological status, way smaller still.  Then factor in how likely is any industrialized civilization able to exist before they are snuffed out by either themselves or nature?  So the needle gets microscopic really that any communicating civilization that would lend itself to detection is even still in existence.  Could very well be that in something the size of a galaxy that no two industrialized/technological communicating civilization ever exist in the same time frame!  And even if they did, given the cesspool that Earth is with trillions upon trillions of different bacteria and viruses, "visiting" would be very much out of the question.  So doubt anything past a phone call would be acceptable unless you are interested in risking an extinction-level biological event just for the sake of a visit so you can shake hands.

5% is really not such a bad number.  And even if the other requirements take it down to 1%, that's still a billion living planets in the galaxy.

 

Of course technology changes everything, and the Drake equation doesn't tell us anything abut how many of these living planets might have civilizations on them.  I agree that the number is most likely very, very small.  But "small" is something we can't enumerate right now, anything between zero and a hundred is essentially equally small.



#9 Sandy Swede

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Posted 26 June 2019 - 12:55 PM

On one hand, it seems reasonable to assume that of all the exoplanets in our galaxy alone there would exist intelligent life on a select few in their star's1 habitable zone.  But we see what happens when the Drake Equation with realistic assumptions is applied to what started out as a large number.  On the other hand, however, the distances and hence, time, involved in communication between advanced civilizations are so great as to statistically rule out contact.  Could these constrains manifest as a virtual 'quarantine'?  And if so, does it exists for reasons which may be forever beyond our ken?

 

I am 70.  My interest lies in witnessing humans reach Mars before I shuffle off this mortal coil.  I don't believe that I, or even my grandchildren, will witness Contact.

 

1. I used the singular possessive case because I deem it highly unlikely that habitable zones exist in multiple star systems.  Could be wrong, though.


Edited by Sandy Swede, 26 June 2019 - 12:56 PM.


#10 llanitedave

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Posted 26 June 2019 - 03:54 PM

On one hand, it seems reasonable to assume that of all the exoplanets in our galaxy alone there would exist intelligent life on a select few in their star's1 habitable zone.  But we see what happens when the Drake Equation with realistic assumptions is applied to what started out as a large number.  On the other hand, however, the distances and hence, time, involved in communication between advanced civilizations are so great as to statistically rule out contact.  Could these constrains manifest as a virtual 'quarantine'?  And if so, does it exists for reasons which may be forever beyond our ken?

 

I am 70.  My interest lies in witnessing humans reach Mars before I shuffle off this mortal coil.  I don't believe that I, or even my grandchildren, will witness Contact.

 

1. I used the singular possessive case because I deem it highly unlikely that habitable zones exist in multiple star systems.  Could be wrong, though.

Many multiple star systems are widely separated enough so that stable planetary orbits can exist within their habitable zones.  There may be some disruption during the formation process that prevents those orbits from being filled in the first place, but I would think that even that's not a problem for widely separated binaries.

 

The close binaries would certainly be problematic.




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