The Fermi Paradox: Where are they?

Any discussions of the size of the universe will lead to the Fermi Paradox: given the enormous numbers of stars and the billions of years of existence of the universe, it seems obvious that life must have evolved zillions of times, and advanced space-faring civilizations can't be too uncommon. So where are they?

Consider our own Milky Way galaxy, with roughly a trillion stars. If only one out of a thousand stars has planets that develop life as we know it (as happened to the Earth quite early, some 4 billion years ago), and only one out of a thousand of those managed to develop complex life (as began on Earth about 500 million years ago), and only one out of a thousand of those developed intelligent life with a technological civilization, then there should still be a thousand such civilizations in the Milky Way. Where are they?

Also note that our sun is relatively young at 4.6 billion years. The oldest stars in the Milky Way are some 13 billion years old. Time for a little digression.

Man is an aggressive species. That may well be the case for all technological civilizations, as the humble are likely to huddle and die instead of expand and thrive. If we assume that mankind successfully moves into space (such as our own asteroid belt and cometary halo--see Our homes, the Comets), it is likely--nay, inevitable--that mankind will slowly advance into the cosmos in spite of the speed of light. It may take hundreds of years for a self-sufficient mobile comet to travel from our sun's environment to another star, but there they will find more comets. Room to grow, resources to thrive.

If we assume that only one interstellar colony is founded every hundred years by the inhabitants of Sol's Oort cloud, and then after a hiatus of a thousand years, each of the new star systems begins it own replication, slowly, one colony every hundred years, then humanity will still sweep over the entire galaxy, occupying the cometary halos of all of the stars in the Milky Way in only five or ten million years.

This is a tiny span of time in geologic terms, and a blink of the eye in the life of the universe. How could it not have happened, thousands of times already? That is the essence of the Fermi Paradox.

We see zero evidence of other life, let alone technological civilizations, present or past. The SETI (Search for Extra-Terrestrial Intelligence) project has searched the skies since 1960 with zero tangible results. We have found zero evidence that alien intelligences have visited the Earth in the past, and of course no evidence that they are here now.

Are there alternative explanations? Of course. Perhaps they wish to stay hidden (a non-interference doctrine). Perhaps their technology is so advanced that we can't recognize it, or simply works in a way we aren't looking for. Perhaps the scale of their lifespeed or technology is such that we can't recognize it (nanobots, or perhaps they only appear for a millisecond every millenia). Perhaps they are from an ocean world and we should be looking miles beneath the surface where they maintain a lab. Water worlds should be much more common than Earth-like worlds--see Earthlike Planets.

And perhaps they are computers, not terribly interested in mere, slow, organic life, and their presence will be obvious once we speed up our perceptions and intelligence by a few orders of magnitude.

In some ways, the alternatives are frightening. The odds of us being the first technological civilization in the galaxy seem remote. That leaves the likelihood that life is precious and rare, or that the universe is a very dangerous place and we will soon succumb to the odds. Supernova, gamma-ray bursters, enormous black holes in every galaxy spewing deadly torrents of radiation, supervolcanoes, solar flares, not to mention planet-busting asteriods, all pose threats to civilization and life itself.

Or still worse, there is a chance that intelligence is the opposite of a survival characteristic. Perhaps we are dooming ourselves by squandering our resources, changing the ecology of the planet, or will effect the same result by blowing ourselves up. Perhaps every time intelligence appears, some idiot invents a super-bug which destroys all life, or creates advanced computers which eliminate all competing intelligent life. Or perhaps there is some simple experiment that every intelligent species eventually tries that destroys their home planet.

It may only be a matter of time.

Humanity's Prison: The Speed of Light

Did you read my blog post Humanity versus the Universe? The universe is huge. Unbelievably huge. And we can't visit, humanity is stuck near hear for the foreseeable future.

The biggest problem appears to be God, who has decreed, "Thou shalt not exceed the speed of light." Maybe she has a good reason, like keeping us from messing up the rest of her universe, but I'm still frustrated.

Ignoring problems of energy and conservation of momentum for the moment (see Inventions: Likely, Possible, and Damn!), interstellar travel simply takes too much time. Even local travel is slow. Assuming a 1-gravity acceleration, our own Oort cloud takes a year or more to reach. With today's technology, the Oort cloud is decades or centuries away. Other stars? The closest is a five-year journey even with our near-magical 1-G space drive. There are two-dozen stars within a dozen light-years, and five-dozen within about 16 light-years. Real travel times will be roughly the distance in years plus one.

One convenient factoid: one gravity of acceleration is approximately one light-year per year per year, and thanks to time dilation the perceived travel times roughly follow non-relativistic rules (as long as we don't care to return to home). A year of 1-G acceleration gets you close to the speed of light, and a second year gets you a little closer to c, but time passes that much slower (equivalently, the distance to your destination appears to shrink). So we can, in principle, travel considerable distances in the span of a human lifetime. Hundreds of light-years.

But even our Milky Way galaxy is large, roughly 100,000 light-years across, 30,000 LY to the core.

If we want to visit another galaxy, it gets worse. Andromeda (our nearest large neighbor and the furthest naked-eye object in the sky) is fully 2 million LY away.

It is difficult to imagine a civilization spanning travel times of years or decades, let alone millennia. I can imagine humanity spreading across the galaxy, perhaps eventually heading for other galaxies in our Local Group, millions of years hence. And that will lead to another post, on the Fermi Paradox. But there's another problem.

Let me correct my comment about humanity spreading to the stars: I see no way for humanity to do that, because it will be our descendants, who are not likely to think of themselves as human. The time frames and distances are so vast that interbreeding is completely impossible: we will have evolved into many species, all alien to each other, likely with less in common than homo sapiens has with Neanderthal.

So our remote, non-homo-sapiens descendants will inherit the universe. I hope. I'm still afraid that our computers will own the future, leaving us behind (see The Technological Singularity).

So here's hoping that God is just hiding the keys to the universe until we learn to behave well, to not soil our home, and to get along with others. Then once we've proven ourselves, she'll let us learn about practical wormholes, or warp drives, or hyperspace travel. While she's at it, perhaps we'll learn the secrets to gravity control, cheap, unlimited energy, and ways around those pesky problems of conservation of energy and momentum.

At least as a science fiction writer I can make all those problems vanish with a wave of my literary wand. Poof!

Humanity versus the Universe

Have I mentioned that one of my hobbies is cosmology? I enjoy pondering the ultimate big picture: how big is the universe, how did it start, how will it end, and why is it like it is?

For today's post, I thought I'd describe just how big the universe appears to be. It is likely very much larger than the Observable universe, that part close enough to us that the evidence of it is visible. Another way of saying that is, how far back in time can we see? The age of the universe is currently estimated at 13.7 billion years, so we can, in principle, see light emitted 13.7 billion years ago in all directions. However, that light came from matter moving away from us, so scientists estimate that the current size of the observable universe is about 46 billion light-years in all directions.

But that is just the physical size of the portion we can, in principle, see. And it is by far empty space. The galaxies and stars are the visible part.

A better question is how many stars are in the observable universe? After all, stars are what we see in the night sky, stars (or rather the solar systems around them) are where life must evolve, and stars are likely where humanity will always congregate.

I have two ways of describing the size of the visible universe (the number of stars) in terms that some of us might comprehend.

THE HAND METHOD: Go to the beach, and pick up a handful of sand. Choose an average size grain. Imagine that our entire solar system is represented by that single grain of sand.  How many grains of sand does it take to be equivalent to a Universe full of solar systems? A bucket full? A cubic yard? A dump truck full?

The actual answer is astounding. Take all of the sand in places like Daytona Beach and Waikiki, larger places like Florida and the deserts of California, Nevada and Arizona, and throw in the really big deserts like the Sahara. Australian, Arabian, and Gobi, all of them combined. Then add the rest of it, the off shore sand of buried beaches.  If our sun is a single grain of sand, then the universe is equivalent to all of the sand on the entire planet Earth. 

THE EYEBALL METHOD: My screen background is the Hubble Ultra Deep Field image, where nearly every visible spec is yet another galaxy. Look at the image, which reveals about 10,000 galaxies, each much like our own Milky Way.

How big of a piece of the sky is in that Hubble image? Take a dime out of your pocket or purse. Hold it at arms length. No, that's too big. You see where it says "IN GOD WE TRUST" under President Roosevelt's chin?  Take a tiny drill, and drill out the center of the "O" in "GOD". Now hold the dime at arm's length, and look through that hole.

The Hubble Space Telescope sees 10,000 galaxies through that hole. 

If your arms are much longer than average, you might have to drill out the entire "O" instead of just the center. And remember, most galaxies are a bit smaller than the Milky Way which contains about a trillion suns (a heaping cubic yard of sand in the earlier example). But a hundred billion stars in an average galaxy, times 10,000 galaxies in that tiny fraction of the sky works out to a hell of a lot of stars.

Are you feeling a bit insignificant yet?

Population Unlimited

In a previous post, I considered some of the limits on the human population here on Earth. Now I'd like to discuss two things: the problems with trying to limit population growth, and how we can exceed the recognized limits.

At present, we expect the Earth's human population to stabilize at roughly 10 billion by 2040 or 2050. This estimate is based on a continuing reduction in the birth rate, which has been trending down, especially in the wealthier countries and in China which has legislated one child per family. The Earth can likely sustain that population, although with even more ecological impacts than at present. Several times that could likely be supported with severe impact on ecosystems. Note that population growth estimates wary wildly, and that low fertility rates in North America, Europe, Japan, and Australia may have dire consequences. See http://en.wikipedia.org/wiki/World_population.

There is a major problem with reducing the birth rate: not everyone will go along, and in the long term, those who are against population limits will have more children and will own the future. Those of us who choose to have fewer children than average are doomed to extinction. In the long term, our descendents will be those who are driven to reproduce. Hopefully, that will somehow include some significant proportion of intelligent people, as the alternative is a dumbing down of humanity. Do you know anyone who accidentally got pregnant?

Significantly, the recent human doubling time is short, currently about forty years. This is much higher than in the distant past, when much higher fertility rates were balanced by much higher death rates from disease and starvation.

A global conflict between wealthy, low population regions and poor, high population ones seems unavoidable. The have-nots will want to take from the haves. And they'll outnumber us.

There is hope: the intelligent and wealthy can choose to move into space where there are no short-term resource limitations on population growth. Some will. Those who remain on Earth may face ecological catastrophes, food wars, and other side effects of growing populations and dwindling resources.

In the long run, that is the only possible future of humanity. If we're stuck on Earth, we are doomed to die, or stagnate, at best. Perhaps something better will evolve and replace us. But we'll be dead.

In a convention speech back around 1980, Larry Niven said (and I'm paraphrasing here), "Humanity will reach the stars. It may not be the United States, or Europe, or any of today's leading nations. It may not be for hundreds of years. For if we don't move into space soon, our resources will become too limited for us to afford it. To deflect those resources would cause people to suffer, to die. But some day, some dictator will decide to spend a fraction of his resources not on some of his people, but rather on the future. Perhaps he will doom tens of millions of people to starvation, but he will fund a space program, and he will seed the planets and the stars with his descendents. And the far future won't give a damn about the millions of people his decisions killed; rather he will be remembered as the father of man in space, the greatest leader of all time."

What are the (relatively) cheap and readily found resources in space?

Asteroids and comets. A single 1-kilometer diameter comet contains enough resources to support a million wealthy people people for longer than we've tamed fire (this may require taming fusion, a higher form of fire).

How many comets are available? Some staggering statistics:

• There are perhaps 500-1000 easily reached near-Earth 1-kilometer-wide asteroids.
• There are an estimated 1,000,000 asteroids in the main belt at least 1km in diameter. Most of these are rich, carbonaceous chondrites, full of the stuff of life. Perhaps 5% are nickel-iron.
• There are an estimated 1,000,000 satellites 1km or larger in the Jovian Trojans (L4 and L5), 60 degrees ahead and behind Jupiter in its orbit around the sun, and their composition is closer to a comet, being mostly ices. Comets may have an ideal composition from a life support viewpoint.
• There are an estimated 10,000,000 cometoids in Neptune's Trojan orbits that are 1km or larger
• The Kuiper Belt (30-50 au from the sun) holds:
• an estimated 100,000 comets larger than 100km
• and 100,000,000 comets larger than 10km
• and likely billions more larger than 1km
• The Oort Cloud (out to about 100,000au, or half way to Proxima Centauri) holds:
• an estimated 1,000,000 comets larger than 100km
• It holds 1 billion comets larger than 10km
• and the Oort Cloud probably holds at least 1 trillion comets that are 1km or larger

This is an immense amount of livable space - easily room for a billion times the current human population, and this without leaving the vicinity of Sol!

 

Note that the Milky Way Galaxy holds perhaps a trillion times that many comets. All this without mining planets, or stars. Without destroying any ecosystems.

The Earth would make a very nice zoo, however. We should definitely save it. For old times sake.