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Why Haven't Aliens Contacted Us Yet? (Fermi Paradox)

I recommend the novel 'Space' by Stephen Baxter re. the Fermi Paradox!
 
Baxter's main answer to the Fermi Paradox in Space is that advanced civilisations get periodically wiped out by gamma-ray bursts.
There are two problems with that idea; firstly the model he was using for gamma-ray bursts was an old model, specifically two neutron stars colliding; the current explanation for the most luminous GRBs is actually a very large kind of supernova. Short GRBs of the kind described by Baxter probably wouldn't be frequent or energetic enough to sterilise a galaxy; and long GRBs are directional, so they would only sterilise a narrow band of a galaxy.

My second objection is that a suitably advanced civilisation could prepare for, and survive, a GRB of either kind, if only by digging refuges deep inside a number of moons or planets.

(Apart from that, Space is one of my favorite books, by the way...)
 
If we are talking in terms of going from Point A to Point B by any conventional means of propulsion, interstellar voyages are pretty much impractical. If Earth is being visited, its visitors have almost certainly mastered some shortcuts - whether those are wormholes or another type of interdimensional secret passage. This idea actually fits the available evidence a bit better. UFOs tend to appear and disappear without the continuous flight paths we would expect from a craft as we would understand it.

S
 
Maybe the reason that aliens haven't found us is that we don't exist yet.
 
bazizmaduno said:
Maybe the reason that aliens haven't found us is that we don't exist yet.
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i'll drink to that! :_pished:
 
bazizmaduno said:
Maybe the reason that aliens haven't found us is that we don't exist yet.
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Yes, but then they and us would get into the whole "ok, prove to me you don't exist' argument. Which does my head in. :p
 
Sorry folks - I shall try and be serious.

It is the case that stellar distances are immense; but time has been around for a while as well. There's the "infinite number of monkeys...for an infinite amount of time" issue. Maybe there's been enough aliens and enough time for them to have visited us, and passed on elsewhere. It's also possible they're still here.

There are indeed tens of thousands of UFO reports - some of which come from reputable sources, e.g. Jimmy Carter for example. Some of which can be rationally explained; some of which might be explained; some of which, it would seem, cannot. Not only do 'reports' of aliens and UFOs occur in modern times, but also in the more historical record. Folklore and legend record strange tales of all manner of weird beasties and events. I think there's enough circumstantial evidence to suggest...

Could it not also be a human need for there to be 'something' else that exists out there, and, alas, there isn't.

For me, there IS life out there in the sweping expanse of the Universe; though I cannot honestly say I've ever (knowingly) met an alien. If I ever do, I just hope I have some beer-money in my pocket, and there's a close by, welcoming and comfortable hostelry with a decent pint.
 
For us to be found requires not only intelligent life on other planets, but intelligent life far more technologically advanced than us, which reduces the options somewhat.

Bearing in mind what we are doing to our planet, maybe we will never get that clever, and maybe other life can't either for the same reason?

That further reduces the options

I'm not holding my breath or hoovering the lounge in readiness.
 
If life developed on our cosmic neighbor-worlds at approximately the same time it did here and evolution proceeded apace the neighborhood may be teeming with intelligent civilizations complaining "Why don't alien races ever visit us?" and "When are we going to invent a stardrive so we can go visiting?"
 
If life developed on our cosmic neighbor-worlds at approximately the same time it did here
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That isn't very likely, however.

To have an Earth-like planet may require a solar system which resembles ours; the number and size of planets in a solar system seems to depend to a certain extent on the metallicity of the star at the centre. Too little metallicity and there are not enough planets; too much and giant planets form, which tend to migrate inward and may disrupt the rest of the planets in that system.

Over time the metallicities of new-formed stars have been increasing, as more and more supernovae pump metals into the interstellar medium; stars with similar metal ratios to the Sun tend to be a little older than our star, so presumably a large number of solar systems which resemble our own are a little older than our own system.

This would suggest that a number of advanced civilisations may have developed before ours; as much as a billion years or two ago, in fact. Plenty of time to explore the galaxy.
 
Try this, just for a speculation:

Life is unique to the planet Earth.

But every solar system, and perhaps even every planet, contains something just as unique and just as wonderful as Life.
 
eburacum,

Am I correct in thinking that in 'Space', SETI would be unsuccessful through a combination of humans being late developers in the galaxy and the majority of the earlier intelligences learning that it was a good idea to not advertise their presence? e.g. the dinosaurs might have had a chance of hearing something, but not us?
 
or maybe theyve been and had a look
similar to us say investigating penguins

we study but dont see the need to communicate,why would they bother is a more apt question

it all leads back to the "we are the centre of the universe"mentality
 
From the index of this book:

Peter Ulmschneider
Intelligent Life in the Universe
From Common Origins to the Future of Humanity

9.7 The Fermi Paradox: Where are the Extraterrestrials? . . . . . . . 222
9.7.1 They do not Exist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
9.7.2 Technically, a Visit is not Possible . . . . . . . . . . . . . . . . . . 223
9.7.3 They are Nearby, but have not been Detected . . . . . . . . 224
9.8 The Zoo Hypothesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226

I think those are the main theories of alien absence.
 
Another possibility is that there're plently of aliens, but the eras where they're capable of interstellar travel and exploration but rarely overlap with other civilizations or culture capable of understanding them.

That is the aliens could have been, colonized the galaxy and for whatever reason become extinct and vanished in deep time...perhaps were're the next wave...perhaps something in another star system just thinking that coming out of the water might be worth a shot...
 
yet another is that we are some kind of petri dish

they have created an experiment ,which we are it.


and they plan to sit back and observe,just like an ant colony
 
TinFinger said:
or maybe theyve been and had a look
similar to us say investigating penguins

we study but dont see the need to communicate,why would they bother is a more apt question
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Personally, I'd be proud to talk to penguins.
 
Greenglow said:
eburacum,

Am I correct in thinking that in 'Space', SETI would be unsuccessful through a combination of humans being late developers in the galaxy and the majority of the earlier intelligences learning that it was a good idea to not advertise their presence? e.g. the dinosaurs might have had a chance of hearing something, but not us?
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That is part of the solution; the 'Big Bad Wolf' scenario you could call it. Perhaps most civilisations don't advertise their existence in case they attract the wolves down upon their heads.
But mostly the idea in Stephen Baxters's Space was that any advanced civilisation has a limited lifespan, because they are likely to be wiped out by a gamma-ray burst (or perhaps some other disaster) before they can colonise the whole galaxy.

Baxter also mentions resource depletion: an advanced civilisation will quite quickly reach a limit to growth once they have used all the resources in a solar system; they would be forced to expand, but that expansion would be limited to the speed of light. This would lead to a central region of any expanding civilisation where growth is no longer possible.
 
Quite a depressing thought... what if we are the most advanced civilisation in the galaxy. Why must they be more advanced then us?
 
Why would another civilisation be more advanced than us?
A matter of chance.
If we encounter a lifebearing planet we could expect to find it at any stage of development; we can roughly gauge how long those stages would last by looking at our own planet's prehistory.
For three and a half billion years life was almost all single cells on our world; for much of that time there was not much free oxygen either. Half a billion years ago there was an explosion of multicellular forms, then a few hundred million years later life came out on land. Only in the last ten thousand years has there been a civilisation with cities and metalworking; only in the last hundred years has this civilisation had air and space travel, nuclear power and computers.

Civilisations at the same level as ours would be very uncommon, civilisations less advanced than ours would be quite uncommon.
But our history has not yet ended; an advanced civilisation might last for another ten thousand years, or a million, or a billion. If so then almost all the civilisations we will ever meet will be far in advance of our own.
Unless, as Baxter suggested, some catastrophe consistently befalls other, more advanced civilisations.
 
The gamma-ray burster hypothesis used by Baxter is examined in this paper by James Annis (pdf file)

but bear in mind this paper was wriiten eight years ago, and the study of gamma-ray bursts has moved on since then.
 
rjmrjmrjm said:
Quite a depressing thought... what if we are the most advanced civilisation in the galaxy.
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I know what you mean. I was so depressed years ago to learn that dinky little Cincinnati has the world's largest Music Hall and one of the world's greatest Zoos. Because I'd previously assumed that if this is what we have, greater metropoli must have REALLY HUGE music halls and zoos.
 
Nassim Taleb has posted on Facebook about the Fermi paradox. He is not very concise, but I think he means:
- If you look at our own civilization then we'll most likely destroy ourselves before we invent interstellar travel.

https://www.facebook.com/pages/Nassim-Nicholas-Taleb/13012333374?fref=nf
The Fermi Paradox and the Hubris Hypothesis.
The great Enrico Fermi proposed the following paradox. Given the size of the universe and evidence of intelligent life on Earth making it non-zero probability for intelligent life elsewhere, how come have we not been visited by alliens? "Where is everybody?", he asked. No matter how minute the probability of such life, the size should bring the probability to 1. (In fact we should have been visited a high number of times: see the Kolmogorov and Borel zero-one laws.)

Plenty of reasons have been offered; a hypothesis is that:
+ With intelligence comes hubris in risk-taking hence intelligent life leads to extinction.
+ As technology increases, misunderstanding of ruin by a small segment of the population is sufficient to guarantee ruin.

Think how close humanity was to extinction in the 1960s with several near-misses of nuclear holocausts. Think of humans as intelligent enough to do genetic modifications of the environment with GMOs but not intelligent enough to realize that we do not understand complex causal links. Many like Steven Pinker are intelligent enough to write a grammatical sentence but not intelligent enough to distinguish between absence of evidence and evidence of absence. We are intelligent enough to conceive of political and legal systems but let lobbyists run them. Humans are like children intelligent enough to unscrew a computer but not enough to avoid damaging it. And we are intelligent enough to produce information but unable to use it and get chronically fooled by randomness in some domain (even when aware of it in other domains). +
Acknowledgments: I thank Alessandro Riolo.
 
Ooh, the burn, Steven Pinker!

(Not that I necessarily disagree, mind you. Not that Steven Pinker is stupid, but unfortunately he may be the best of a bad lot.)
 
eburacum said:
That is part of the solution; the 'Big Bad Wolf' scenario you could call it. Perhaps most civilisations don't advertise their existence in case they attract the wolves down upon their heads.
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The problem I have with the Big Bad Wolf scenario is that it calls for a combination of far-sightedness and paranoia. When Marconi first broadcast a radio message, how many people then foresaw the potential for attracting the attention of a malign extra-terrestrial civilisation? Does anyone know when that idea was first mooted on Earth? I'd put money on it being post-1945 at the earliest. So presumably any civilisation that invents radio communication will have a few years, if not decades, of it being sprayed willy-nilly into the ether before it is stopped, if stopped it is - it's not like any broadcasters on this planet seem particularly bothered by the thought. Now, I'm a linguist not a physicist, but there's no way of bringing those waves back once they're out there, is there?

<tl:dr> I don't think the reason why we have yet to intercept alien broadcasts is because they are deliberately shielding them.
 
Krepostnoi said:
The problem I have with the Big Bad Wolf scenario is that it calls for a combination of far-sightedness and paranoia. When Marconi first broadcast a radio message, how many people then foresaw the potential for attracting the attention of a malign extra-terrestrial civilisation? Does anyone know when that idea was first mooted on Earth? I'd put money on it being post-1945 at the earliest.
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1897.

https://en.wikipedia.org/wiki/The_War_of_the_Worlds
 
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