All Posts Tagged With: "astronomy"

On May 1st, Brandon quoted a theoretical physicist, Mark Buchanan, in this blog. My curiosity was piqued, as it often is when questions of applications of physics to real-life are concerned. I had kitten pull Buchanan’s Ubiquity and Nexus from the University stacks and I dove in….

And was transfixed. Buchanan is an expert on Non-equilibrium Critical States. These are conditions where there are literally millions of different factors and interactions working on something–far too many to count and examine separately. This is a new field in theoretical physics–less than forty years old, really, and like chaos theory has only been possible to study with the advent of large-scale parallel processing and tools like Wolfram’s Mathematica.

One of the Holy Grails of geology has been earthquake prediction. Countless millions of dollars are at stake and hundreds or thousands of lives could be saved if we could know when a quake is liable to hit San Francisco, Tokyo or St. Louis. Therefore, a lot of time and effort has been expended to attempt to learn how to make accurate predictions.

They all failed. No matter what models were used, statistics recorded or physical measurements made, any predictions were useless. Some, like the false predictions of “The Big One” in the St. Louis area, caused a great deal of consternation and panic. At the same time, the scientists completely missed predicting the San Francisco earthquake of 1989.

It was too complex. An interesting discovery came out of their research, however, concerning the magnitudes of earthquakes. Current methods of recording earthquakes are accurate over about 6 or 7 orders of magnitude. This is a huge range in science–sort of the equivalent of the mass range of a shrew to a blue whale.

When one graphed the number of earthquakes versus their Richter value on the scale of 2 through 8 on a logarithmic scale, a straight line was found. This was called the Gutenberg-Richter Law. Here’s a wiki on Power Laws, for those of you who want more information about them.

This caught the interest of theoretical physicists who were interested in Game Theory, which is a method of examining real-world situations by making simple mathematical models with certain rules and then turning a computer loose with those rules and some initial conditions and seeing what happens next. They were successfuly in modelling the data by using blocks and springs with connections between them.

However, the physicists were more creative than that, as per usual. They began looking for other examples of this type of power law occurance and found them everywhere.

There are power-law relationships found in the distribution of wealth in society, how large a forest fire grows, the historical extinction of species in the earth’s biosphere over the last billion years and how many people are killed per week in historical wars.

All of the systems examined had several things in common:

1) There were large-scale (orders of magnitude) differences between the low end numbers and the high-end results of a perturbation.

2) There were uncountable numbers of factors working on the items examined.

3) It was impossible to predict what the result would be of the next perturbation of the system.

The type of system involved can best be visualized by thinking of a pile of rice grains. You add a grain at a time to the pile. Usually, nothing big happens, but every once in a while, a huge avalanche of grains occurs, changing the condition of the pile drastically.

One discovery that would be of immediate interest to you, Billy Joe, is that fluctuations in the Stock Market indexes are one of these cases. If you go back for the last eighty years and feed in the day-to-day fluctuations of the Dow Index adjusted for inflation, you find that there’s a power-law relationship between the size of the change and the number of times that it occurs.

My research in this respect is nothing new. Evidently, physicists have been watching this for some time, as these papers indicate. Assuming that the market really is a non-equilibrium critical system, one major result can be deduced:

One cannot predict the magnitude of the stock market’s change from one time period to the next on any scale.

This means that my earlier prediction in Urbanagora of a large-drop in value is utter nonsense. The laws of Physics dictate that it is impossible to predict the size of either a fall or a rise in the market, period.

Side note–everyone always talks about what a great long-term investment the Stock Market is. One of the things I found during my search is the actual, inflation-adjusted return on long-term investment over the course of the market. Can anyone guess what it is?

Now, I want to get to the last point in this article–the relationship of these systems to the Fermi Paradox. In order to do this, I need to start with Forest Fires.

Physicists found that, in spite of the uncountable factors in the spread of an individual forest fire, they were easy to model. They made a grid of squares and began having trees grow in them over a period of time. Every so often, a match would be dropped on a tree and the rules of the game said that the fire could only spread to an adjacent square.

The size of the area that burned in a given fire ended up being a power-law relationship, just as happens in real-life. They also found an interesting corrolary, however. If someone or something had a tendency to put out the fires and the number of trees available to burn increased greatly, the entire line moved upward on the graph. In other words, if you put out small fires (and perserve a lot of the trees), when you do get a fire, it has a tendency to burn a lot larger area than if you didn’t. This was demonstrated in the devestating Yellowstone fires a couple decades ago, as well as the brush fires currently burning in the LA Basin and in Florida where housing developments have precluded the small fires that used to remove brush and trees.

So, the impatient of you who are still awake are asking, “What the hell does all this have to do with Alien Civilizations?”

Here’s the deal: Let’s assume that one cannot go faster than light, as Fermi did years ago and that an alien civilization has a finite lifetime. Let’s also assume that there is a maximum distance in light-years to the nearest habitable planet that is practical for a civilization to colonize. (This is an analogue of the distance between trees exhibited in the forest-fire model.) Therefore, the size to which a civilization grows before dying out becomes a power-law distribution. As one looks out over the galaxy in the electromagnetic spectrum at any given time, one sees silence for a large part of the time, just as a park ranger in a fire tower usually sees no smoke over his forest.

From time to time, a civilization will arise and colonize a portion of the galaxy, but the area involved will not be very large (for a vast majority of the cases), so it would be unlikely to leave artifacts in our solar system, for example, just as one usually doesn’t see burned trees along the sides of roads as you drive through Colorado.

The discovery of a red-dwarf with a planet in its habitable zone adds an interesting note to this analogy, however. If you remember, during my article on Gliese 581c, I noted that the period of time that the planet would be within the habitable zone would be much larger than that of a solar-type sun.

With our Sun, our civilization appeared at about the 80% mark of habitability as far as time goes. Yellow stars come and go at a swift rate in the galaxy. However, red dwarfs are stable in the long-term. This means that as time goes on, more and more of them come into being, and continue providing a stable home base for a colony of a civilization for a long time.

This is another analogy to the forest fires becoming larger with additional trees being added to the forest.

Therefore, my solution to the Fermi Paradox is as follows:

Aliens have existed and may currently exist, but their extent of colonized worlds follow a power-law distribution. We, as observers, have a privileged postion within the history of the galaxy because the number of red-dwarf stars has not yet reached a critical value which would push the power-law line upward and encourage large, easily visible galactic empires.

Anyone have any ideas of testable observations that could disprove this hypothesis?

Tom

The world is buzzing this week about what could be called the most important discovery of the decade in astrophysics–the discovery of a planet within the habitable zone of a red dwarf star, Gliese 581. I want to talk about this and explain why it is truly important for our understanding of our role in the universe as human beings.

Let’s start, first of all, with one of my favorite physicists, Enrico Fermi. I’ve heard a lot about him over the years, especially since the head of High-Energy Physics at the university when I began as a contractor was his graduate student on the Chicago Pile Project, Al Wattenburg. Fermi was an amazing man without whom the Manhattan Project probably would not have succeeded. He’s currently best known among astronomers, though, for a characteristic way of thinking and the question that came from it.

Fermi was the king of the back-of-the-envelope calculation. He used to ask questions in his courses like, “Calculate the number of grains of sand on all of the beaches of Earth.” These came to be known as “Fermi Questions.”

Although it seems far-fetched, it is possible to solve Fermi Questions to about an order of magnitude or so by making some logical assumptions. To solve the one above, you need an order of magnitude approximation of the following items: the volume of a grain of sand, the packing efficiency of sand grains on sand beaches, the length of all the coastlines of the planet, the percentage of such coastlines with sand beaches and the average width and depth of the sand on those beaches. I’ll leave it to you engineers out in the reading audience to come up with an answer to the question if you want a break from your study for finals. Here’s a few more.

Fermi used assumptions like this to calculate the yield of the Trinity A-bomb. He stood at a safe distance with his back to the tower. When he saw the flash, he opened his hand and allowed small pieces of paper to fall from them. By the distance that they were tossed by the shockwave, he was able to calculate the power of the weapon.

He also used this method to calculate, over lunch with his graduate students, that it would take an average of 100 million years to colonize the galaxy using self-replicating machines if they could not go faster than light. This led to the famous Fermi paradox, “if this is so, there should have been 45 alien civilizations colonizing our planet by now–where are they?”

Now, we move forward about ten years to Green Bank Radio observatory, where scientists are listening for intelligent signals from alien civilizations. An astrophysicist came up with a Fermi-type question: “How many civilizations are there in the Milky Way Galaxy with whom we can communicate?” The Fermi solution to this became known as the Drake Equation.

Over the years, information has been plugged into it, getting estimates of anywhere from 10,000 to .0000001, depending on the assumptions going into it. A range this wide in a Fermi solution means that there’s not enough knowledge to make a good guess, since a Fermi solution should be reasonable within only a factor of 10 either way.

[I want to take a moment and mention that the Drake Equation is not a scientific hypothesis. A hypothesis must be verifiable by experimentation. Since that is impossible, it falls closer to a philosophical concept than a hypothesis. Michael Crichton pointed this out years ago.]

Now we get to the center of the relevance of Gliese 581c. Until this past week, we knew of exactly four rocky worlds within the habitable zone of a star at present–Venus, Earth, the Moon and Mars (with one more, Titan, that would be at the right temperature after the Sun became a Red Giant). There was absolutely no way to tell whether or not there was something completely unique that prevented such worlds from occuring in other systems.

There were many theorists that believed just that–that gas giants spiralled into their sun destroying rocky planets as they go unless something truly unusual (like the resonances in our solar system) prevented it. There were a lot of Hot Jupiters orbiting very close to their suns that seemed to endorse this view.

Gliese 581c has a typical mass for a rocky world at 5 Earth masses (abbreviated Me henceforth.) The transition between a rocky world like Earth and a gas giant is theorized to be about 10 Mes.

It also gives a new number to plug into the Fermi Question. We had not, until now, had any example of a small planet within the habitable zone of a different star. Now we do and it’s close–only about 20.5 light-years away. I did a quick calculation yesterday and if we assume that this distance is typical (a valid assumption because even though such planets could be more rare, we have a very low sampling rate within the solar neighborhood) I come up with a total estimate of 300 million rocky planets within the habitable zone of their stars outside the central third of the galaxy where the radiation from the core’s black hole and the high frequency of supernovae would be problematic.

This new planet is important because it is circling a Red Dwarf Star. Such stars have not been targets of examination in the past because they were not seen as likely candidates for life. There are billions of them in the galaxy–80% of the stellar population are Red Dwarfs. One characteristic of such stars is their extremely long lifetimes compared to other stars. Earth will have probably 5.5 billion years total in which water-based life is possible on its surface at its present distance before stellar evolution heats it beyone the boiling point of water. Gliese 581c, with a mass half that of the Sun has 5 or 6 times as long in which life could develop. In other words, we on Earth have perhaps a billion years of viabilty remaining as an ecosphere. Our equals on 581c would have over 26 billion years left for the life lottery.

Lastly, it has a Hot Jupiter inside its orbit. This means either that Hot Jupiters do not necessarily destroy rocky planets outside of their orbits as they spiral inward or that they are formed where they are currently found and do not spiral in at all.

Now, a cautionary note before we get too excited. Red Dwarfs are very different from our sun. They are cooler and dimmer and their spectrum has much less Ultraviolet light, which forms a protective ozone layer above our planet and Gliese 581 (man, we need a better name for this star and its planets now that it’s important, it’s too damn long to type each time) is what is called a “flare star.” These stars have a tendency to have much larger versions of the solar flares that our sun exhibits. Therefore, the sunward side of the planet would have a much higher dose of X-Rays than our world receives.

Why is the discovery of this new world important in a philosophical sense? Our estimated number for possible other races and civilizations has just gotten a lot larger. This reopens the Fermi Paradox for consideration, since it is proportionally more surprising that we have no evidence of other races having reached our solar system.

I’m going to have a bit of fun here at the end. I’m going to examine the parameters of the system and see if I can describe a habitable world there and what one would experience as one of its people. I am not implying that any of my conclusions are valid, merely that the science that I am employing is current.

First of all, it is highly likely that the planet is tide-locked to its sun, much as our Moon always has one side facing the Earth. This means that it has a bright-side and a dark-side. (Where’s David Gilmore when you need him?) How high Gliese would stand in the sky would depend on how close you were to the Hot Pole–the point at which the star would be overhead all the time. Gliese would appear to be about seven times larger than our sun does.

I am going to assume that the point where our planet….let’s name it Fredville, for lack of a better name….first formed was similar to where Earth formed in our solar system and that the composition of the molecular cloud was the same. Therefore, it would have a similar amount of water in its rocks and have been hit by a similar number of comets. (See why this is speculation or science-fiction? There’s way too many unknowns.)

Because of the amount of water and minerals, it would have about 70% of its surface covered with water. However, the distribution would be very different from that of the Earth. Because of the tidal effects of being so close to its star, Fredville would have a tendency to have its oceans preferentially located at the sunrise and sunset points of the planet. This would mean that the planet would have a ring of oceans completely around it, with one large continent facing the star and another one on the farside.

It was once assumed that a tide-locked planet would have its atmosphere frozen completely on the dark side. By studying Venus, which has an extremely long rotation, scientists have discovered that the atmosphere of near-locked planet circulates anyway due to differences in temperature. Venus rotates in 243 days, but its atmosphere goes completely around the planet in only 4 days. There are winds blowing off of the hotside near the equator, but the air is returned to that side by opposing prevailing winds at different latitudes. The closer you get to the Hot Pole, the higher the temperature, perhaps reaching as high as a constant 95 degrees Fahrenheit. At the sunset/sunrise lines, it’s comfortable on Fredville, and by the time you get to the Cold Pole in the middle of Farside, you’re down to Antarctic temperatures.

Most important, there’s life on Fredville. The intelligent Freddies evolved from creatures that lived in the Ring Ocean. They breathe oxygen like us, but look a lot different. When life left the ocean and crawled onto the Hotside land, the ones without shells died from the X-radiation with which Gliese regularly bombared the planet. Freddies look a lot like Earth’s hermit crabs, except that their shells are extruded. Babies are kept inside thick manufactured shells until they’ve grown their own carapace. Since the gravity on Fredville is twice that of Earth, things fall faster and it is a lot easier to be injured, so they grow up fast and tough.

On the Farside, there are different kinds of life-forms, but they’re much more primitive due to the lack of energy from the sun. They resemble Earth-like fungi and have limited vision capability. Close to the Cold Pole, there’s no life at all and it’s eternally dark except for the stars, the other planets of the system and an occasional aurora near the magnetic poles.

The Freddies have explored their planet and discovered the stars when they crossed the Ring Ocean four hundred years ago. Now that they’ve discovered astronomy, chemistry and physics they look up at the sky at the sunset line and wonder, “Is there life out there? If so, where the hell is it?”

Tom