09 Aug 14
Originally posted by Grampy BobbyAlthough the number of planets in the universe is vast, we only know one that contains life. The main problem is that, while there are many planets, there are only a few we can see clearly enough to have some idea about the conditions on the planet.
twhitehead, my interest in this context is learning what mechanisms [for lack of a better word] make earth habitable.
See this article: http://en.wikipedia.org/wiki/Habitable_planet
10 Aug 14
Originally posted by KazetNagorraOriginally posted by KazetNagorra
Although the number of planets in the universe is vast, we only know one that contains life. The main problem is that, while there are many planets, there are only a few we can see clearly enough to have some idea about the conditions on the planet.
See this article: http://en.wikipedia.org/wiki/Habitable_planet
"Although the number of planets in the universe is vast, we only know one that contains life..."
And, may I ask, how do we know this incredible extravagance to be of the essence of the scheme with scientific certainty?
10 Aug 14
Originally posted by Grampy BobbyI don't understand your question. My statement is intended to say that we know of only one planet with life, not that we know that there is only one planet with life!
Originally posted by KazetNagorra
"Although the number of planets in the universe is vast, we only know one that contains life..."
And, may I ask, how do we know this incredible extravagance to be of the essence of the scheme with scientific certainty?
10 Aug 14
If we are talking about planets other than our own, we must also talk of life forms other than our own in which case habitability includes a much larger range. There are a number of planets and moons in the solar system that are habitable to for at least some life forms known on earth and it is difficult to rule out life forms that may be very different from those on earth and thus require a very different habitat.
The number of planets habitable to at least some earthly life form beyond the solar system is at present only possible to estimate very roughly. However, it is almost certain that the number is very large, in the order of a billion billion.
Humans have very special requirements - including the presence of plant life or something equivalent to produce oxygen - so planets suitable for human habitation without special equipment, would be much rarer.
10 Aug 14
Originally posted by KazetNagorraOriginally posted by KazetNagorra
I don't understand your question. My statement is intended to say that we know of only one planet with life, not that we know that there is only one planet with life!
"Although the number of planets in the universe is vast, we only know one that contains life..."
My error. Sorry.
10 Aug 14
Originally posted by twhiteheadSo we're only able to speculate on other organisms or material life forms anywhere else in the known universe?
If we are talking about planets other than our own, we must also talk of life forms other than our own in which case habitability includes a much larger range. There are a number of planets and moons in the solar system that are habitable to for at least some life forms known on earth and it is difficult to rule out life forms that may be very different f ...[text shortened]... xygen - so planets suitable for human habitation without special equipment, would be much rarer.
10 Aug 14
Originally posted by Grampy BobbyYes.
So we're only able to speculate on other organisms or material life forms anywhere else in the known universe?
I estimate that there are over a thousand billion billion planets in the universe. We have had a close look at exactly one. We haven't even ruled out the existence of life on our nearest neighbour Mars.
We don't yet know much about planets around other stars. We have identified quite a lot of them and know their approximate orbits and mass, and from this can estimate temperature, but not much else.
10 Aug 14
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Originally posted by twhiteheadAnd if that estimate is true and life is limited to only one in a trillion planets, there still would be a billion planets with life. At that rate, there might only be one life form per galaxy but we don't know that yet. We might have the milky way entirely to ourselves. If so, at least there won't be aliens attacking any time in the next billion years.
Yes.
I estimate that there are over a thousand billion billion planets in the universe. We have had a close look at exactly one. We haven't even ruled out the existence of life on our nearest neighbour Mars.
We don't yet know much about planets around other stars. We have identified quite a lot of them and know their approximate orbits and mass, and from this can estimate temperature, but not much else.
I keep waiting for one of the Mars rovers to image a thigh bone sticking out of a cliff somewhere. That would be a game changer, eh!
Bobby, have you gotten through my essay on vacuum yet?
10 Aug 14
Originally posted by sonhouseJust to be clear, there is a big difference between life, and intelligent life. It is likely that the former is far more common than the latter.
At that rate, there might only be one life form per galaxy but we don't know that yet. We might have the milky way entirely to ourselves. If so, at least there won't be aliens attacking any time in the next billion years.
I also do not expect aliens to attack at all. Once a civilization gets to the point that it can space travel across vast distances, there is nothing worth attacking earth for that they wouldn't already have.
And it is also important not to forget that intelligent biological life may actually typically lead to intelligent machines that replace or enslave the intelligent biological life, so we might encounter non-biological intelligent machines before we encounter biological life. Or we might be replaced by machines before any contact is made.
10 Aug 14
Originally posted by sonhouse"Bobby, have you gotten through my essay on vacuum yet?" sonhouse, as an employee in California once said to me: "Mr. Bob, please don't push me and I'll work cheaper." lol Still giving thought to your extraordinarily comprehensive reply.
And if that estimate is true and life is limited to only one in a trillion planets, there still would be a billion planets with life. At that rate, there might only be one life form per galaxy but we don't know that yet. We might have the milky way entirely to ourselves. If so, at least there won't be aliens attacking any time in the next billion years.
...[text shortened]... ere. That would be a game changer, eh!
Bobby, have you gotten through my essay on vacuum yet?
10 Aug 14
Originally posted by twhiteheadInsightful and informative. Thank you, twhitehead. -Bob
Just to be clear, there is a big difference between life, and intelligent life. It is likely that the former is far more common than the latter.
I also do not expect aliens to attack at all. Once a civilization gets to the point that it can space travel across vast distances, there is nothing worth attacking earth for that they wouldn't already have.
...[text shortened]... re we encounter biological life. Or we might be replaced by machines before any contact is made.
10 Aug 14
AOriginally posted by twhiteheadI think the real reason we don't find traces of extra-terrestrial life is because civilizations on that level come and go, as we see our civilizations come and go.
Just to be clear, there is a big difference between life, and intelligent life. It is likely that the former is far more common than the latter.
I also do not expect aliens to attack at all. Once a civilization gets to the point that it can space travel across vast distances, there is nothing worth attacking earth for that they wouldn't already have.
...[text shortened]... re we encounter biological life. Or we might be replaced by machines before any contact is made.
The problem there is the wavefront of radiation that would leave a planet indicative of advanced life, always assuming such advanced life develops like we do, finding out about electricity and later about radio waves and using them. Our wavefront now covers a sphere about 200 light years across, 100 light year radius. So that means a civilization say 10,000 light years away won't get our signal for over 9000 years.
But 9000 years is a long time for intelligent life, at least like ours. We have had countless civilizations come and go in all that time.
For instance, the ancient Babylonians apparently had electricity but their civilization died before it could advance further.
So 9000 years from now, some civilization picks up or signal but we are say, 2000 years gone by then, or we stop using radio and go to something much more advanced, like neutrino beams or something we can't even think about today.
The net result is those signals only last for 2000 years and if they send one back to us, another 9000 odd years goes by so now it is 20,000 years into our future and there is a signal if only we had the equipment to detect it.
Chances are not very good that 20,000 years from now, we will still have radio telescopes.
So it would be like ships passing in the night, neither one seeing the other, never knowing about them.
10 Aug 14
Originally posted by sonhouseI think it has more to do with the fact that we haven't looked very hard. Current technology would not pick up tv signals from another planet. In fact, we would only see a signal that was specifically directed at us at considerable cost to the civilization trying to communicate. And even that sort of signal would probably be missed. We have not yet attempted to send out any such signals to other civilizations.
I think the real reason we don't find traces of extra-terrestrial life is because civilizations on that level come and go, as we see our civilizations come and go.
As our own civilization advances we are most likely to rely more and more on terrestrial networks of optic fibre for most of our communication, and only use radio for satellites.
Where we would use high power radio signals would be if we make a base on Mars and start communicating with it. It has been suggested that we look at other planetary systems and try to intercept such interplanetary communication which would be strongest when the planets line up in our direction.
10 Aug 14
Originally posted by twhiteheadActually, our equipment is sensitive enough to at least pick up noise that would be concluded to be artificial all the way across the galaxy, assuming the equipment and the signal arrived at the same place in time and space. That's the problem. Lets assume we stop transmitting entirely say 100 years from now and switch to fiber and other techniques. That will define the width of the wavefront, 100 years in our past to 100 years in our future.
I think it has more to do with the fact that we haven't looked very hard. Current technology would not pick up tv signals from another planet. In fact, we would only see a signal that was specifically directed at us at considerable cost to the civilization trying to communicate. And even that sort of signal would probably be missed. We have not yet attemp ...[text shortened]... interplanetary communication which would be strongest when the planets line up in our direction.
So a 200 lightyear wavefront moves through the galaxy and say it passes some point, say 10,000 light years away but the equipment on an alien planet is in the development stage and it takes 100 years for that equipment to start detection studies. But our wavefront already passed them by and there is no equipment in the universe that that equipment could detect us at that point in time because we stopped using RF.
11 Aug 14
Originally posted by sonhouseThat is not the case. Our current SETI searches would not pick up stray tv or radio signals from even nearby planets let alone all across the galaxy.
Actually, our equipment is sensitive enough to at least pick up noise that would be concluded to be artificial all the way across the galaxy, assuming the equipment and the signal arrived at the same place in time and space.