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Researchers Say The Aliens Are Silent Because They Are Extinct (theconversation.com)
HughPickens.com writes: The Conversation reports that according to research by Dr. Charles Lineweaver and Dr. Aditya Chopra, a plausible solution to Fermi's paradox is near universal early extinction of life on exoplanets, which they have named the Gaian Bottleneck. "The universe is probably filled with habitable planets, so many scientists think it should be teeming with aliens," says Chopra. "The mystery of why we haven't yet found signs of aliens may have less to do with the likelihood of the origin of life or intelligence and have more to do with the rarity of the rapid emergence of biological regulation of feedback cycles on planetary surfaces." According to the researchers, most early planetary environments are unstable. To produce a habitable planet, life forms need to regulate greenhouse gases such as water and carbon dioxide to keep surface temperatures stable. About four billion years ago, Earth, Venus and Mars may have all been habitable. However, a billion years or so after formation, Venus turned into a hothouse and Mars froze into an icebox. Even if wet rocky Earth-like planets are in the "Goldilocks Zone" of their host stars, it seems that runaway freezing or heating may be their default fate. Large impactors and huge variation in the amounts of water and greenhouse gases can also induce positive feedback cycles that push planets away from habitable conditions. The difference on Earth may be that as soon as life became widespread on our planet, the earliest metabolisms began to modulate the greenhouse gas composition of the atmosphere. "The emergence of life's ability to regulate initially non-biological feedback mechanisms could be the most significant factor responsible for life's persistence on Earth, conclude Lineweaver and Chopra. "Even if life does emerge on a planet, it rarely evolves quickly enough to regulate greenhouse gases, and thereby keep surface temperatures compatible with liquid water and habitability."
In space, a snail can exceed the speed of sound.
- Don't do what I do, it's probably not healthy nor safe. -
One thing to bear in mind is that life here existed in the form of anaerobic bacteria for a staggeringly long time. Photosynthesis began as a way to split hydrogen sulphide into useful hydrogen ions and a useless waste product of elemental sulphur, which was also usefully inert. Early photosynthesis therefore didn't require much in the way of biochemical sophistication to operate; the waste sulphur is where some large sulphur deposits originated.
That changed with a mutation which let the photosynthesis split not hydrogen sulphide, but water into useful hydrogen and (to anaerobic bacteria) highly toxic and dangerous oxygen. That initially wasn't all that big a problem to early water-splitters; the oceans they were in were rich in iron-II salts which readily absorbed oxygen to become insoluble iron-III salts (this is where the banded iron rock formations come from).
Everything changed when most of the iron-II in solution in the early earth's oceans was used up. Oxygen levels slowly rose, and virtually all bacterial species either adapted or went extinct. Oxygen is toxic to most bacteria.
I would hypothesise that most alien worlds either never make the switch from anaerobic atmosphere to aerobic one, or fail to establish a homeostatic oxygen-nitrogen atmosphere quickly enough and effectively enough to become self-regulating.
Unfortunately, these geek acronyms tend to be English-specific. Some others you will encounter here:
RTKBA - Right to keep and bear arms;
TEOTWAWKI - The end of the world as we know it;
DYKWIA - "Do you know who I am?"
SJW - Social justice warrior
You are underestimating just how massive an amount of deep time 65-million years was.
What would a radioactive waste storage look like in a 100M years? Ridiculously stable. Dry. Sealed from elements. Even if it literally just disintegrated in place, the odd mix and ratios of remaining isotopes at the site, surrounded by solid geologically stable rock millions of years older... would clearly suggest something unnatural.
Or perhaps a lego mini-fig -- tey'll soon outnumber humans after all.
http://xkcd.com/1281/
Surely bunches of those highly stable bits of plastic will find themselves some place safe to hide... preserved in amber, or tarpits, or trapped in some glacier, at the bottom of the ocean, or in a salt mine... there are billions of them, so probably all of those things will happen.
And we have things like modern jewelry. Laser engraved diamonds, set in platinum bands. Stored inside fire proof safes... some which would end up buried in stable places... even bunkers. What's 65 million years going to do to that?
Secondly - your argument is flawed because that's not how time works, time is relative and doesn't happen at a constant rate. Planets that rotate their stars slower have physically existed longer than ones that move slower. So two planets around the same star, in different orbits, which orbit in the same timeframe, that formed together at the same time - the outer one will be significantly younger because time slows down as you speed up. It may be a matter of seconds per rotation - but there's been many billions of rotations for those to add up.
Ok... so lets put some figures into those numbers ... say 11 seconds for "a matter of seconds". And how about 4.6 billion for for "many billions" as that's the age of our solar system measured from earth's perspective at least.
11 seconds x 4.6 billion rotations = 1603 years. I don't think we need to worry too much about relative ages of the planets.
This is, actually, one reason why - if there is life on Io or Europa - that life is likely to be "bacterial" rather than fishes - those moons circle a massive planet, any life there has had significantly less time to evolve than life on earth has had. No, I don't feel like doing the math to figure out how much.
You really think its going to be billions of years though? I'm pretty skeptical. Maybe you should do the math.
Well, except for the fact that most such signals would originate from very close to massive radio-noise transmitters (aka stars), and it's estimated that our listening technology probably wouldn't be able to detect a perfect twin of our civilization through the noise from more than a few light-years away. So there's *maybe* a small handful of the closest stars where we *might* be able to detect "ambient" signals from. Further than that, and they would have to be transmitting far more powerfully than we do.
The one exception is high-power military radar, which is often orders of magnitude stronger, and would be correspondingly easier to detect, but wouldn't necessarily appear to be an intelligent signal.
Also, while you're quite right about the time coordinating issue, you need to dial down your numbers a bit. From 10 billion light-years away an entire galaxy appears as barely a tiny smudge, if that, using our most sensitive detectors. Unless they were somehow blinking most of the stars in their galaxy in unison (as observed from Earth, which would require a very directional signal synchronized across tens of thousands of years), we wouldn't pick up even a hint of a signal.
Sadly, for now our technology is pretty much limited to listening for civilizations from relatively close within our own galaxy intentionally trying to contact us.
On the bright side we've been sending a pretty strong signal that our planet harbors life, or at least is something pretty unusual, for many millions of years. Just as we're beginning spectrographically analyze the atmospheres of exoplanets that pass between us and their sun, aliens residing close to Earth's orbital plane can do the same - and given the volatility of free oxygen, the concentrations of it in our atmosphere should make it clear that something very unusual is happening here.
--- Most topics have many sides worth arguing, allow me to take one opposite you.