Extraterrestrial Limerick

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In The Beginning -- Bug-Eyed Monsters

Remember the flood of science fiction movies in the 50s? It ushered in wide ranging interest and speculation about aliens from other worlds, an interest that's still very much alive today.

But that speculation didn't start in the 1950s. Sci-fi serials were produced for movie houses in the 30's and 40's, and writings of Edgar Rice Burroughs considered inhabitants of Mars at the turn of the 19th century. Before that, astronomers of old could see the moon, and even with the naked eye imagine that the dark, flat areas were seas, perhaps sailed by a lunar civilization.

Mars was always a first choice for imagined aliens, once astronomy established some of its characteristics at the end of the 19th and beginning of the 20th centuries. It was found to be about 1/2 the size of earth, tilted on its axis only about a degree-and-a-half differently than earth, with a day nearly the same length as an earth day.

The Draw Of Mars

At that time of great discovery, made possible by the great refracting telescopes of the age like the massive 40 inch refractor at Yerkes Observatory, the Italian astronomer Giovanni Schiaparelli viewed what he called canali, which translates to English as channels. But some astronomers, like Percival Lowell extrapolated the idea to that of canals, which he believed were dug and used by a Martian civilization.

Some other astronomers agreed, and many drawings of the canal system were made by Lowell and others. It was also observed that during the Martian year the prominence of the canals seemed to wax and wane, possibly in relation to the melting and re-freezing of the polar ice caps. A convincing story of intelligent water use existed until well into the 20th century, though many astronomers were unconvinced.

Satellite photos sent back by the early Mars Mariner spacecraft showed no existence of canals whatsoever -- or any evidence of civilization or even life, for that matter. The photos transmitted back in the mid 1960's showed a barren planet, heavily cratered like our own desolate moon. There were polar caps to be sure, but these were found to contain more frozen carbon dioxide that water, so the belief in Martian life was dealt a severe blow.

Where Are The Aliens?

Still, belief in the existence of alien life somewhere in our galaxy remained strong. It seemed that with some 200 billion or more stars in our galaxy, there had to be life out there somewhere. Yet the absence of any real evidence caused Enrico Fermi and Michael Hart to postulate the Fermi-Hart Paradox.

Given that our galaxy is much older than earth, it seems that many other life-producing planets -- if they exist -- could be much older than earth, and have space travel capabilities perhaps millions of years more advanced than our own. But -- there is no tangible evidence that aliens have ever come to our planet to give us greeting. The Ferim-Hart Paradox basically asks: "Where are they?" And truly, we have no real evidence that alien life is out there.

The Drake Equation

Adding that to the Mars canal bust certainly deflated many wishful believers. Yet this did not dismay Charles Drake, who proposed what has become known as the Drake Equation. The Drake equation combines a string of numbers and probabilities together to mathematically predict the number of concurrent civilizations in our galaxy. The parameters in the equation are our best guess values based on current research. You can try your own predictions using the Drake equation at Little Green Men. Based on best parameter measurements, predictions range from a few to as many as 1000 concurrent civilizations existing in the Milky Way.

The Drake equation doesn't run headlong into the Fermi-Hart Paradox primarily because the equation assumes that technical civilizations do not necessarily last that long, astronomically speaking. No doubt the fact that the equation was proposed during the height of the cold war helped formulate that belief. Our current inability to solve problems without war and even agree that there is global warming certainly does nothing to stretch those conservative civilization lifetime numbers.

The Mars Viking Mission -- A Failure?

None-the-less, optimism is difficult to squash, and in the 1970's the U.S. sent two Viking spacecraft to Mars to look for life. No longer were civilizations expected, or even visible plant or animal life. The Mariner pictures pretty much put that level of optimism to rest. But there were things about Mars that Mariner did reveal that still gave hope.

The Mariner program showed evidence of ancient flood channels on Mars. Not the canals of Lowell, but long dead and dry channels that had at least at some point in the past been flooded with a lot of water. Maybe millions, perhaps billions of years ago, but still flooded with water. This suggested that at least for a few million years of its early existence, Mars had all the ingredients that should have been needed to allow life to develop. A moderate temperature, a thicker atmosphere, and liquid water.

After that period of time, things went badly on Mars, with the atmosphere thinning out, water freezing, and the surface of the planet becoming dry, dry, dry. That change apparently was so fast on astronomical time scales that complex life apparently couldn't get started. But perhaps microbial life did.

So the Mars Viking program intended to find out, with two craft at two different locations, each with the ability to perform life and organic material search experiments.

The Viking probes ran experiments to determine if Mars had current life, and if existing organic material was in the soil. You can read more about the experiments at Discovery.com. A more detailed report about the metabolic discovery test, called the Labeled Release experiment, can be found at Factoids.

The Labeled Release experiment involved feeding nutrients to a sample of Martian soil and looking for signs of metabolism. The experiment gave a resounding positive result. Of course, that result could have simply been a chemical reaction between a possible exotic Martian soil and the nutrient. So the soil was heated, and then the test was performed again. The assumption was that if microbes were causing the result, the heat would kill the microbes, and the rerun would give a negative result.

It did.

But an experiment designed to search for organics in the soil gave a negative result. A third experiment to look for signs that some introduced gases being metabolized also failed. So the conservative position to take was to assume that no life or organic material had been found on Mars.

The Rise Of The Phoenix

But then came the Mars Phoenix Mission. It landed on Mars in 2008, some 30 years after Viking. It was sent to land in the Martian arctic region to explore the water history of Mars. It found the anticipated solid evidence for water ice on the planet, but also found that the soil had perchlorate in it. This had far reaching implications about the Viking experiment ran 30 years before.

It turns out that the organic search experiment of Viking would have been contaminated if perchlorate was also in the sites of the Viking craft. And if that was the case, the Discovery.com article says that perhaps organic material was discovered on Mars by the Viking missions. Coupled with the Labeled Release experiment results, the possibility of having discovered life on Mars in the 1970's greatly increases.

Reaching Out With SETI

Which brings us to the SETI Mission. Rather than search for primitive live on other bodies of our solar system, in the 1980s SETI started searching for intelligence generated radio signals from space. The idea was that an advanced civilization may send radios messages into space in an effort to establish communications. Certainly an advanced civilization would likely at least generate radio signals for its own use. In either case, it was considered possible for properly designed radio telescopes on earth to pick up such radio signals generated from afar.

Some in the astronomical community thought that the SETI mission was a bit premature, since we were not yet sure that many earth-like planets existed. At that time, the only known planets outside of our solar system were gas giants, many far too close to their parent stars to have hospitable conditions even had they been earth-like.

But with the launch of the Kepler Mission, some of that complaint has been answered. There have been planets found that are near earth size, although those so far discovered are too close to their parent stars. But planets have been found in the life zone -- the zone where a planet may have liquid water -- though as yet those planets so far discovered are gas giants. But one promising truth has been emerging -- stars with planets are commonplace. So the idea of SETI is not far fetched.

Thus far, the SETI effort has detected no definitive indication of extraterrestrial intelligence. But there are many many stars, and even with 1000 concurrent civilizations spread among them, it could take a long time to stumble upon an alien generated radio signal. Yet, it might occur any time -- so stay tuned.

I've always been interested in the possibility of extraterrestrial civilizations, having been an avid science and science fiction reader since grade school. But like all of a similar ilk, I'm disappointed that thus far, no proof of extraterrestrial civilizations is yet in hand. I tried to sum up this anticipation and disappointment with a humorous astronomy Limerick, which I've place on a few products at my Keen Designs store, in association with Zazzle.

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Event Horizon Blues Limerick

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The humorous limerick poster at left gives a tongue-in-cheek lament of what happens if you get too near to an Event Horizon. It depicts the space-time distorting funnel of a gravity well, and a dire prediction.

So, What Exactly IS An Event Horizon

A good question, and until just a few decades ago, a good question for physicists as well. The answer in part goes all the way back to 1784, when John Mitchell published a work on the effect of gravity on light. In his published work, he described what he called a Dark Star, which was an object with such a strong gravitational field that it would prevent even light from escaping. You can read more about Dark Stars and Black Holes on the Black Hole Limerick article of my blog.

The Dark Star idea didn't gain much traction in Mitchell's time, but the concept did re-catch fire after Albert Einstein's theory of General Relativity was published. General relativity is Einstein's masterful theory of gravity, encompassing the 4-dimensional aspect of space-time. Soon after the modern gravity theory was published, ruminations of Black Holes began anew.

If you review the Black Hole Limerick article, you'll find that when a star has enough mass at the end of its life, it will collapse to a point of infinitesimal size called a singularity. This tiny point, whose properties are still largely unknown, marks the physical boundary of the remains of the star.

The Schwarzschild Radius

But there is another boundary, a bubble so to speak, the surrounds the singularity of a black hole. That boundary isn't the surface of a solid object, but a boundary marking a physical transition region. Sort of like the boundary between states of the country. There's no real physical boundary there, you can walk right across it. But it marks the non-physical divider that determines which state you are in, depending upon your position with respect to the boundary.

Thus is the meaning of the Schwarzschild Radius. It's a non-physical boundary that describes a distance from a singularity where something observable happens.

What happens at the Schwarzschild Radius?

The Schwarzschild radius is the radius beyond which light has sufficient velocity to escape the singularity. Within that radius, the escape velocity is greater than the speed of light. Any light produced by processes within that radius will not be observed by anyone outside of that radius.

Another term used to describe this region surrounding a singularity is Event Horizon.

The Event Horizon

Though the Event Horizon isn't a physical boundary, neither is it a docile place. Stars, planets, comets, asteroids, meteors, or any other objects that venture too close to the Event Horizon of a black hole won't meekly fade into oblivion as they descend through the boundary. They rather get accelerated to extreme velocities, and stripped apart by the ferocious tidal forces of the gravity well. This tearing apart of material approaching the Event Horizon produces a lot of energy. Many black holes have been discovered by the amount of x-rays produced as they viciously devour material.

Tidal Forces, You Say?

You may wonder what I mean by Tidal Force. As it pertains to black holes, it refers to the difference in level of gravitational force of a gravity well at different distances from the gravity well.

The concept applies near any gravitational field, even that of Earth. As you stand on the Earth's surface, the pull of gravity at your feet is a tiny bit more than that at your head -- depending upon your height. That difference of pull is a tiny force that tries to stretch you ever so little. But given the strength of the Earth's gravity, and the difference between about 4,000 miles and 4,000 miles plus your height, the tidal force on you produced by Earth's gravity is far too small to be of significance.

Now consider being much closer to the pull of a much more massive black hole. The difference in gravitational pull at your feet versus your head would easily be enough to pull you apart, even to dissociate the molecules of your body. That dissociation and subsequent collision of molecules traveling at extremely high velocities is what produces the bursts of energy occurring near black hole Event Horizons.

Is it all just speculation?

Not any more. Many black hole candidates have been found, and it is beginning to appear that super-massive black holes lurk in the heart of most, if not all, galaxies.

Enter The Quasar

The enigmatic Quasars were long difficult to fit into our conceptual view of the universe. They were extremely energetic, small compared to galaxies, and yet very distant according to their observed Hubble shifts. What could possibly be so small, so distant, and yet so easily observed because their enormous energy output?

It appears that quasars are essentially young galaxies, well, young when the light from them began the long journey to Earth. These young galaxies have hungry, super-massive black holes feasting ravenously on the material collected by the growing collection of stellar material. Eventually the super-massive black holes reach a point where they've devoured nearly everything within reach, and additionally the energy produced by the gorging will have pushed more distant material out of harms way.

When this stable configuration is reached, you may end up with a galaxy like ours, the Milky Way. It has a lurking black hole at its center, but the black hole is no longer involved in a feeding frenzy, as all the close material has been long since digested.

My Humorous Event Horizon Limerick

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I remember reading about the enigma of quasars some 40 years ago when I was in college, and it's been very exciting to see how that mystery and the seemingly arcane predictions of general relativity have come together. I created the Event Horizon Limerick Poster you see at the beginning of this article as a humorous way of describing the mysterious Event Horizon. The image is also available on other products like the physics t-shirt at left, at my Keen Designs store, created in association with Zazzle.

Black Hole Limerick

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Astronomy for some years now has been abuzz with speculation, information, and discoveries of Black Holes.

Black holes you say? What is a black hole?

Black hole is a term now commonly used to describe an object whose size and mass leads to the situation where the gravity of the object is so great that light cannot escape from it. The concept has been around for a long time, dating back at least to 1784, when John Mitchell published a work on the effect of gravity on light. In that work, Mitchell postulated that if a star had enough gravity, the escape velocity would be so great that light could not escape. He termed such an object a Dark Star.

So what is escape velocity?

Escape velocity is the velocity a projectile must have in order to avoid being pulled back to the planet or star of origin. Think of a bullet fired into the air. It's given an initial velocity by the blast, and gravity provides a deceleration that acts to slow that velocity, eventually stopping the projectile altogether, and reversing its direction. But if the velocity of a projectile was great enough, it would escape into space and never return. The answer is a bit different for a rocket that keeps being propelled as it departs, as the escape velocity diminishes the further a projectile gets from the star or planet.

For our humble planet, the escape velocity for a projectile fired from the surface is about 25,000 mph. Considerably faster than projectiles fired from guns, but we've managed a technology that can get rockets to reach escape velocity.

The concept of escape velocity was known clear back in John Mitchell's time. Remarkably, so was a reasonable value for the speed of light. A Danish astronomer by the name of Ole Romer made the speed of light determination in the late 1600's. He did so by meticulously observing and noting the time variation of Jupiter's moon transits. He correctly concluded that these variations were the result of a constant speed of light and the variation of distance from the Earth to Jupiter. Since the distance variation between Earth and Jupiter is so large due to their orbits, Romer was able to make accurate enough measurements to calculate a velocity of light good to 2 or 3 digits.

So Mitchell applied the velocity of light to the escape velocity calculations and concluded that stars with enough mass and small enough radius would be Dark Stars, allowing no light to escape. Not much was made of it, however, until the 20th century and Albert Einstein's formulation of General Relativity.

Radius and mass must both be considered in escape velocity calculations. The Sun, for example, obviously has a strong gravitational pull, enough to hold an entire system of planets, asteroids, and comets together. Yet clearly light escapes from the Sun, as it lights up our day. But if the mass of the Sun were compressed down to diameter of a small city, about 3.75 miles, then light would no longer be able to escape its pull. That seems a remarkably small size, given that the Sun's diameter is currently about 865,000 miles. From 865,000 miles to 3.75 miles -- is that crazy or what?

For our sun, it probably is crazy. Our sun will eventually run out of fuel and reach the end of its life, but it doesn't have enough mass to likely end up as a black hole. Our sun will end its life as a white dwarf. Don't sell your beach front property just yet, however, as that ultimate fate is billions of years away.

How Does A Star Become A Black Hole?

Stars bigger than our sun, perhaps 20 times its mass, may retain enough mass after collapsing (which blows off a lot of mass) to end up as a black hole. Here's a quick, layman description of what goes on as a star becomes a black hole.

Stars shine so brightly because of Nuclear Fusion. The pressure near the center of stars is so great that atoms cannot maintain their integrity. That is -- the nuclei orbiting electrons are so agitated by the compression energy that they cannot remain bound to the nuclei. The stripped electrons become more of an electron fluid. Without the buffering of the orbiting electron clouds, atomic nuclei (mostly hydrogen at first) are more likely to be pushed together, fusing to become helium nuclei (and more massive nuclei in later processes). This nuclear fusion gives off enormous energy, creating the light we see as stars.

A star mostly produces photons from this fusion deep in its interior, and the outward moving photons interact with the electrons of the atoms making up the remainder of the star -- many many times on their journey to the star's surface and ultimately into space. This photon interaction causes an expansive pressure, helping to keep the star from collapsing from the contracting force of gravity. Additional outward pressure is created by the rapid vibrations of the excited, high-temperature electrons in all the atoms.

A star also produces neutrinos in the nuclear furnace. Neutrinos are neutrally charged, nearly massless particles that move near the speed of light. The issue with neutrinos is that unlike the photons that interact with electrons of atoms, neutrinos are virtually inert. They move from the nuclear furnace into space with little or no interaction with the atoms making up the star. So neutrinos do not add to the necessary outward pressure needed to sustain a star against the unrelenting squeeze of gravity. Neutrinos amount to kind of an energy leak, letting some of the energy of fusion escape without helping sustain the star.

As a star ages, it uses up much of its hydrogen, then even helium fuel, causing the fusion of heavier nuclei. At this point the star's furnace becomes less stable. In addition, as the heavier nuclei are consumed during the fusion process, a higher ratio of neutrinos to photons is produced, allowing more of the energy to escape to space without helping sustain the star. So the star begins to collapse against the pressure. If the star has little enough mass, the collapse will stop at the point of producing a neutron star, where electrons are essentially squashed into atomic nuclei to combine with protons, creating a big ball that's nothing but neutrons. A neutron star is essentially a big atomic nuclei.

The neutrons of the big stellar nuclei will be vibrating wildly from the heat of gravitational contraction, creating an expansive pressure to sustain the integrity of the neutrons, and thus the neutron star -- if they can. But if the necessary vibrations of the excited neutrons should exceed the speed of light (and nothing can go faster than light), then the neutron vibrations will not produce enough outward pressure to sustain the star, and it further collapses into a singularity -- a point with infinite gravitational density. Thus, a black hole is formed.

Will all of its mass now contained in a singularity, the star's radius is well within that required to have an escape velocity greater than the speed of light. So you have a black hole, or as Mitchell described it -- a dark star.

All rather fanciful you say?

Many thought so, until the discovery of x-rays in 1964 emanating from Cygnus X-1. Try as they might, scientists could think of no source of energy other than a black hole that could provide such an intense source of radiation. Theory suggests that black holes will pull in any material that gets too close, and the absorption of the material is violent. The atoms of any such unfortunate material becomes disassociated, emanating x-rays in the process.

Since that time, many observations and measurements have been made of Cygnus X-1, and the conclusion is even more convincing that Cygnus X-1 is a black hole. But that's only the beginning. The center of our own Milky Galaxy has been found to contain a super-massive black hole. The same is true of many other galaxies. Perhaps nearly all galaxies have super-massive black holes in their centers. Black holes long predicted and now discovered are the most enigmatic objects in our universe.

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I find the subject of black holes fascinating, having read about the evolving evidence during and since college, some decades ago. I created a little science limerick about a poor, unfortunate star that happened to become a black hole, putting the concept into a compact limerick. You can see and purchase the design on a wide variety of shirts as well as posters, at Keen Designs, my online store in affiliation with Zazzle.

Dark Energy Limerick

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Up until the early 20th century, our home galaxy the Milky Way was assumed to be the extent of the entire universe. This limited view led scientists to believe that the universe had existed forever in a perpetual state, never changing its appearance. In fact, that view gave Albert Einstein reason for considerable head scratching, since his newly discovered Theory Of Relativity suggested that a perpetual state universe was not possible. The universe, according to General Relativity, must be either expanding or contracting.

Beyond The Milky Way

It wasn't until the discovery of galaxies of stars beyond the boundary of the Milky Way that the view of the universe began to drastically change. It was Edwin Hubble who made the discovery that the Milky Way was not the extent of the universe. He used the newly completed 100 inch Wilson observatory telescope to make his discovery.

But he then discovered something even more damaging to the old view of a perpetual state universe. He found that the external galaxies were all moving away from one another. This discovery suggested that in fact the universe was expanding, bringing into harmony the observed characteristics of the universe and the theory of General Relativity.

The Expanding Universe

However, that brought up another great problem. If the galaxies are all moving away from one another now, they must have been closer together at some time in the past. And the more the clock was ran backward, the closer together the galaxies would have been. It was the consideration of this inescapable conclusion that lead to the Big Bang theory.

Most cosmologists now agree that the beginning of the universe was created in a colossal Big Bang. Many observations and theoretical considerations have combined to cement this conclusion. Since the Big Bang, the scattered galaxies have all been receding from one another as the universe expands. What will happen as the universe ages has been another open question.

It was long assumed that the pull of gravity from the masses of all the stars and planets in the receding galaxies would act as a brake, slowing down the expansion. The question that remained to be answered was whether the universe expansion would win out over the mass attraction, or if the amount of mass in the universe would succeed in halting and reversing the expansion.

If the initial Big Bang explosion was big enough, theory suggested that while always slowing down because of the gravity of the mass contained in the universe, the universe would none-the-less expand forever, at an every decreasing rate. This would suggest that the Big Bang was the one and only creation event for our universe.

But if the contained mass of the universe won out, it would mean that at some point in time the expansion would cease, and then according to General Relativity, begin contracting. That led to speculation about what a contracting universe would mean. Some theorized that it would mean another Big Bang at some point, and that perhaps the universe was like a big oscillator, going through successive cycles of a creation explosion and an eventual contraction.

The problem then to solve was to determine how much mass was contained so the calculation could be made as to the ultimate fate of the universe. At first, it seemed that the amount of mass necessary to stop the expansion was tantalizingly close to the amount of mass contained in the universe. Clearly, better measurements needed to be made to determine the ultimate fate.

Enter -- Dark Matter

As the search for any hidden mass gathered momentum, the dark matter mystery arose. You can read more about the evidence for dark matter in the Does Dark Matter -- Matter? entry of this blog. The dark matter discovery indicated that there is much more dark matter in the universe than normal matter.

That suggested that if the necessary mass needed to halt and reverse the expansion of the universe was nearly provided by the amount of observed normal matter, surely adding in the mass of dark matter would tip the result. The universe seemed clearly to have enough mass within it to cause a halt to the expansion and an eventual contraction.

The Revolution -- A Speeding Up Expansion

But then, a revolutionary and unexpected discovery was made. Using the newly discovered distance-measuring candle of a certain type of nova, called a Type Ia Supernova, astronomers were able to determine with precision the distances of galaxies very far away. This precision, combined with the measurement of the distant galaxies' recession velocities, indicated that instead of slowing down, the expansion rate of the universe was actually increasing.

It was a difficult fact to absorb. For decades it had been assumed that the universe was slowing down, with the only question being if it would slow enough to reverse the expansion, or just continue slowing indefinitely but never quite stopping. Now scientists had to deal with the unexpected revelation that the universe expansion rate was actually increasing.

This revelation has led to a new cosmological concept, called Dark Energy. Dark Energy is the term used to describe the as yet still mysterious force that is causing the increasing expansion rate.

A Summarizing Limerick

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I've been interested in astronomy for most of my life, having studied it in college and since. Like everyone else who keeps up with the field, I was totally surprised by the revelation of dark energy. I've created a little science limerick that tries to capsulize the strange phenomenon. You can see it on posters, shirts, and mugs at Keen Designs, my web store created in association with Zazzle. At the top of the page you can see a poster example of the design, and below you can see a mug and shirt example with the design.

Does Dark Matter -- Matter?

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By now you've probably heard the term Dark Matter bandied about in the news and on science shows. So -- what's the big deal? What is it?

Ah, that's the rub. No one knows for sure what dark matter is. And I can imagine that you then wonder: "If no one knows what dark matter is, why do scientists even believe it exists?" A fair question, for sure.

We NEED Dark Matter

One thing is, for the universe to even have galaxies such as the one in which we blissfully live, we need dark matter, at least according to many cosmologists. We need it because the extreme high temperature caused by the Big Bang would have prevented galaxies from forming so soon after the event, had there not be something other than the mass of the observable stars withing the galaxies to draw the matter together.

We live in a rather mature galaxy, which formed within only a few billion years after the Big Bang. Without dark matter to help collect the mass together to make stars and galaxies, that could never have happened in so short a time.

But aside from such esoteric speculation, there is direct evidence of the existence of dark matter.

Indication One: Galaxy Clusters

The first direct evidence of the existence of dark matter isn't something locally observed. In fact, so far there's no locally observed evidence of the existence of some new type of elusive matter. But it has been found that galaxies are not uniformly scattered across the expanse of the universe. The galaxies seem to be strung along in streaks and clusters in an arrangement resembling the material of a sponge.

The galaxies seen in clusters are a clue to the existence of dark matter. If the mass contained in galaxy clusters was primarily contained in the observable stars within the galaxies, then the galaxies would long ago have drifted apart. There just doesn't seem to be enough observable matter in the galaxy clusters to cause them to stay together. But clearly, they do stay together. The inescapable conclusion is that there is much more matter in the galaxy clusters than is directly observable. Some kind of invisible matter that pulls on the observable matter and keeps the galaxy members of the clusters from getting away.

Indication Two: Galaxy Rotation

You've likely seen Hubble and other telescope photos of some of the great spiral galaxies. The pinwheel shape of rotating galaxies at first glance seems like a very reasonable thing. But upon closer examination, it would seem that if the rotation of stars within the galaxies are caused the the masses of the visible stars, and perhaps even a hidden black hole, then the spiral arms should be wrapped around many more times than they are. The orbital velocities of the stars as a function of their distance from the galaxy centers doesn't seem to match up well with predictions.

This strange phenomenon was studied extensively by Vera Rubin, as well as others. One popular theory for the apparent observed rotational speed anomaly is that galaxies are surrounded by a halo of dark matter, which if true, accounts for the observed rotational rates. Dark matter is not the only proposed answer for the rotational rate quandary of galaxies. Another less well accepted explanation is that our understanding of gravity may not be entirely correct, and that a better understanding of gravity on large scales might explain the galaxy rotation problem without need of dark matter.

Indication Three: Gravity Lensing

A more recent indication of the existence of dark matter is based on a prediction by Albert Einstein. He suggested that a super massive galaxy that happened to occur between Earth and an even more distant galaxy might act as a gravitational lens, with the nearer galaxy's gravity focusing the light from the more distant galaxy. This would produce an image, likely distorted, of the more distant galaxy. In fact, the gravitational lens may make possible observing a galaxy too distant to be seen otherwise.

Albert Einstein didn't necessarily believe anyone would actually observe this effect, but just that it was theoretically possible. As it happens, this effect has been observed and photographed a number of times. And the lensing appears to be of a magnitude in excess of that possible by only the mass of the visible stars in the lensing galaxies. This is evidence again for dark matter, being the added yet invisible matter that gives rise to the observed lensing effect.

My Poetic Addendum

I'm fascinated by the ongoing research and debate about dark matter. Clearly something we don't entirely understanding is involved. While some believe we need to modify our view off gravity to solve the observed problems instead of searching for some exotic form of dark matter, most cosmologists seem to believe that dark matter is the culprit.

I've had some fun trying to capsulize the dark matter enigma in a concise science limerick. You can see it below, illustrated on a coffee mug and a shirt. It's also available on posters, as shown on the image link near the top of the page. You can click on any of the images to see the range of products that carry the design, and purchase any of the products if you desire. You can see many more witty science limerick poster, mug, and shirt designs at Keen Designs, which presents my designs in association with Zazzle.

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Maxwell's Equation Physics Limerick

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So it was that in the mid 1800's, the famed Scottish physicist James Clerk Maxwell created his famous quartet of equations and defined the field of E&M, or Electricity and Magnetism. While giving concise and elegant mathematical expressions for Gauss's laws for electric charges and magnetism, he also -- in physics speak -- unified electricity and magnetism.

Unified? Whazat?

What physicists mean when they say unified is that Maxwell described the precise relationship between electricity and magnetism with the famous Maxwell's Equations. For some time, especially since the innovative experiments of Michael Faraday in the early 1800's, physicists knew that some kind of relationship existed between electricity and magnetism. Faraday discovered, for example, that a magnetic field produced around a current carrying wire in a coil would induce a current through another coil in close proximity. But the precise and predictable relationship was unknown until Maxwell defined the relationship.

Essentially, Maxwell's equations define the complex relationship between electric and magnetic fields in all circumstances, from the creation of magnetic fields by moving electrons, to the creation of current by a fluctuating magnetic field, to even the coupled electric and magnetic fields of photons. The definition of a relationship between physical phenomenon is called unification. Maxwell's discovery is so complete that now the coupling is considered a single entity called electromagnetism.

In a similar context, Abdus Salam, Sheldon Glashow and Steven Weinberg were awarded the Physics Nobel Prize for their successful effort in unifying the electromagnetic force with the nuclear weak force. The result is now referred to as the Electroweak Interaction. In this case, the problem was much more difficult to work out. Even in a high school science lab one can demonstrate the existence of a connection between electricity and magnetism, but not so for the connection between the electromagnetic force and the weak nuclear force.

The Weak Nuclear Force is involved with the radioactive decay of neutrons into protons and electrons. When a neutron decays, it emits an electron (beta decay) and becomes a proton. Because the strength of the weak nuclear force is so much less than that of the electromagnetic force, at low energy levels the two forces can be effectively treated as if they are independent. But at high energies, like that which existed shortly after the big bang, the two forces are on a more equal footing, and the relationship between the two must be known in order to understand what happens at those energy levels.

As you can imagine, this isn't the kind of science that can be accomplished in a high school physics lab. You can also see why it was over 100 years between the unification of the electric and magnetic forces and the unification of the electromagnetic and weak nuclear forces.

But what can be accomplished with even a t-shirt, poster, or mug from Keen Designs is the display of a clever encapsulation of Maxwell's discovery with a witty physics limerick. I created such a limerick, and you can get it on products like those below:

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Heisenberg Uncertainty Principle Limerick

Heisenberg Uncertainty by keendesigns
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If you've bumped into physics classes in school, at some point or another you may have encountered the mystical Heisenberg Uncertainty Principle. The first impression most students get when introduced to the Uncertainty Principle is that it describes a measurement problem, and that making measurements on sub-atomic particles is a tricky business.

In fact, measuring parameters relating to sub-atomic particles is a tricky business, and many things can't be directly measured, but only concluded by watching the results of quantum events. But the Heisenberg Principle isn't about measurement accuracy as much as it is about complementary parameters. It turns out that many of the parameters one wants to know are in a complimentary pair with another parameter. One thing the complimentary feature insures is that one cannot know with precision both parameters of a complementary pair. It isn't because they are hard to measure, but the physics of the quantum world insures that you cannot know them both with precision.

I've used the following example as a non-mathematical way to grasp the concept. Imagine that you are researching the day to day habits of bees. You want to know with as much precision as possible information about individual bee characteristics, and their normal daily behavior.

You could, for example, set up a telescope or use a pair of binoculars to observe bees from a distance as they leave and return to their hive. In this way, you would observe bees behaving quite routinely, but with pretty poor precision on the individual bees.

You could walk up and pull the top off of the beehive and see the bees with much better clarity, but now the bees in large part would be reacting to your presence, and not behaving as they were before you removed the top from the hive. So you would be trading precision of viewing the bees for the precision of observing their normal behavior. You can't seem to have it both ways. Observe normal behavior, but from a distance that precludes close examination of the individual bees, or view the bees inside of the hive directly, but with a severe impact upon the behavior you want to study.

Of course, in this technical world you could perhaps install an observing device inside the hive, and observe a monitor from a distance so as not to disrupt their normal behavior. But this is the kind of trick not possible in the quantum world.

Another example is to imagine that you're wanting to observe in great detail the markings and grooves on the faces of a cube. Imagine even further that the markings on the faces change over time, and that you suspect that the changes are in some way correlated on the different faces of the cube.

But from a distance, you can't simultaneously observe multiple faces. You can turn the cube to see one face with great detail, but the others are hidden from view (again, without any camera contrivance, which we must assume is not possible). If you turn the cube so that you can get a glimpse of two or more faces simultaneously, each will be seen foreshortened, and some of the grooves and markings may be obscured. So you can't see more than one face at a time in the greatest detail. You could consider the different faces as being complimentary in that sense.

In each of these simple and non-precise examples, you can grasp the reason why the parameters you want to observe cannot be simultaneously observed in great detail. But in the quantum world, I'm not sure if anyone quite knows why the parameters are paired in this way, they just are.

I've had fun creating a few t-shirt, mug, and poster designs that play on this mysterious aspect of quantum physics, from just some comical designs like the one at the top of the page, to the clever physic limerick featured below. You can see a number of other witty science limerick and humorous physics shirt designs at Keen Designs.

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