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Bleeding Edge

Dark Energy

by Cyrus Ance
Feb 13,2003


Bleeding Edge

First let me thank Aeon and everyone at RPGnet for giving me the chance to write Bleeding Edge. This column is a news report on science with a focus on what is happening today. I am a working scientist, experimental particle physics, and keep up on the latest results. In the last month as I have been writing columns I realize that I try to focus on breakthrough science. That is science that changes how we think about the universe or has the possibility to change our lives. Some of things I report on will prove to be false leads and disappear without much impact. Such is the nature of science, and it is important to note that the impact of break through technology is usually over estimated in the short term, and under estimated in the long term. Thus something that is apparently lost from sight or dismissed as useless can transform the world at some later time.

The columns will be annotated with footnotes, links to sources, and suggestions on further investigations. They tend to get close to the primary source when I am writing about the physical sciences, and be secondary sources when I am out of my field. Mistakes will be inevitable, and I will acknowledge whoever has found my errors, and do my best to make corrections. Suggestions or requests for future topics should be made in the responses to the columns. I have a good list to go through which should keep me busy for about a year, but good ideas are welcome. I am not going to get into dialogs, as I simply do not have the time.

What does Bleeding Edge have to do with role playing? Good question, which the editors asked when I proposed the column. At the end of each column I will provide suggestions as to how to use the new science in role playing. Most of the suggestions will obviously be for contemporary or near future genres. They tend to fall into three broad categories: enemies get secret knowledge and have to be stopped; a friend gets secret knowledge that someone wants to remain secret; and the science breakthrough is used as a MacGuffin to hide something else.

I do hope you enjoy Bleeding Edge over the coming months and let me now turn to what appears to be one of the Universe's deepest secret.

Dark Energy

Up until about five years ago physicists were feeling pretty happy about their understanding of the Universe. They thought they had quite a manageable list of the fundamental particles that are the building blocks of matter, 12 plus antimatter partners, and the fundamental forces that control their interactions, three after two had been unified in the 1970's thorugh the 1990's. There remained some mysteries including a basic explanation for the masses of the particles, the inner workings of the sun, and exactly what holds a galaxy together. There were road maps for understanding these mysteries and plausible theories to explain them without radically rewriting the entire picture. More on all of these in future columns.

One of the mysteries under active assault was the evolution of the Universe. The Big Bang as the origin of the Universe is an established fact, but the details of how the Universe got from the initial explosion to what we observe today were, and still are, not clear. One basic question is about the pace of the expansion of the Universe. When I throw a ball in the air it rises up at an ever slower rate, stops rising, and falls at increasing rate back to earth. (1) The same thing should happen to the Universe. The initial explosion is similar to me throwing the ball up. Once the Universe starts propagating only under the influence of gravity, exactly as the thrown ball in the earth's gravitational field with the Universe providing its own gravitational field, the expansion should start slowing, eventually stop, and finally contract into a Big Crunch. (2)

To study the rate of the expansion of the Universe the Hubble Space Telescope and the most powerful ground based telescopes were used to look at the distribution of supernovas, explosions of stars when they have exhausted their primary fuel, as a function of time. Supernovas probe the Universes size since they are evenly distributed and since the explosions are all essentially the same brightness. The brightness that we see here on earth is thus related to how close the supernova was. Bright ones are close, and dim ones are far away. (3) The results were shocking. (4) It seems that the expansion of the Universe is not slowing down as expected, but is in fact speeding up.

The initial reaction to this observation was to assume that there was some mistake. But shortly a competing observation of super novas and other observations of galactic clusters, and radio galaxies provided confirming evidence. (5) No one today assumes that any of these observations are flawed. (6) There is other evidence that this view of the Universe is correct that would need at least two other columns to explain and can be explored in the references.

The cause has been dubbed Dark Energy. The origin of this name will need another column. It is some form of energy that is acting counter to gravity and pushing the Universe apart. It does not fit into any known behavior of the three fundamental forces. In any case most of the Universe, using E=mc^2 to put matter and energy on equal footings, about two thirds of the total, is Dark Energy.

Thus physicists' picture of the Universe has been shattered. Most of it is something completely unexplained. There are not even plausible theories that have been advanced to explain Dark Energy. Basically it seems that empty space acts to push stuff out of it. Note that the size of this effect is very small and can only be noticed on distance scales much larger than galaxies and time scales that are significant as compared to the age of the Universe. Today trying to understand the origin of Dark Energy is one of the most important mysteries facing science.

Roleplaying Ideas

  • Mystery power source: Enemies are suddenly showing up with portable high power weapons. Their power source violates the known laws of physics. The mystery has to be solved before they strike again. They are using Dark Energy based power sources. Who invented the Dark Energy power source?
  • Alien Benefactors: To prevent the Big Crunch an advanced, enigmatic race of aliens is generating the Dark Energy field. One adventure could revolve around discovering and figuring out the operation of one of Dark Energy field generators floating in space. Alternatively the aliens could covertly turn to the players for help because someone or something is destroying their Dark Energy field generators. Who? Why? <\li>
  • The Big Chill: The Dark Energy field has recently become much stronger. It is now pushing the Universe apart so fast that within a short time stars will start to fall apart and the Universe will grow colder and colder ending in the Big Chill. Who or what caused the Dark Energy field to strengthen? How? Why?

1 - It is possible, not by a human but via other means, to throw the ball so fast that it escapes the earth's gravitational field. Similarly it is possible that the original explosion of the Big Bang was so strong that the Universe would never stop expanding.

2 - As noted in footnote (1) this is not the only possibility. It is actually more complex than only these two possibilities. It has to do with the structure of the Universe itself. There are three possibilities. The Universe could be "closed", that is like a ball in two dimensions, such that everything eventually gets back the same place and there is a Big Crunch. Space could be "flat", well like flat in two dimensions, with the Universe getting to some sort of equilibrium. Space could be "open", like a saddle shape in two dimensions, with everything getting further and further from everything else and the stars eventually fading in to a Big Chill. Whether the Universe will have a Big Crunch or Big Chill, or reach an equilibrium depends on the amount of material and energy in the Universe. There is good evidence based on observations of the Cosmic Microwave Background that space is flat. Discussion of that needs another column.

3 - This is a simplification. What is actually observed about a distant astronomical object is its redshift and its apparent brightness. The redshift tells us how fast the object is moving away from us. Explaining this is beyond the scope of this column, it is not news, but here is high school level explanation. For an object of known brightness such as certain types of supernovas and other so called standard candles, the apparent brightness gives the distance, or since we know the speed of light, the time since the supernova. Thus the supernovas give a rate of expansion of the universe, how fast they are moving away from us, as a function of the time since now. This rate of expansion is called the Hubble Constant, or has it has been renamed in the face of clear evidence that it changes with time the Hubble Parameter.

4 - The original report of the observation from early 1998 by S. Perlmutter and others can be found here. The published version of their work from 1999 can be found here.

5 - These observations of super novas, galactic clusters, and radio galaxies.

6 - For a scientific summary of the revolution see this by the always entertaining cosmologist Michael Turner. There is a recent "tell all" book by an insider, The Extravagant Universe: Exploding Stars, Dark Energy and the Accelerating Cosmos by Robert P. Kirshner, Princeton University Press (2002). There are popular explanations of Dark Energy from the SNAP satellite collaboration, they are planning a satellite based supernova observatory, and Discover. A web search of Dark Energy will result in a huge amount of material.

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What do you think?

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