Dark Energy’s Role in Cosmology and Semis
Semiconductor engineers, the makers of today’s tiniest integrated circuits that power our electronic world, know about the realm of the very small. Leading edge chip designers and manufacturers work with transistor structures that are a mere 10 nm wide and shrinking ever smaller. For reference, a hydrogen atom – one of the smallest of atoms – has a diameter of about 0.1 nm. In other words, a mere 100 hydrogen atoms occupy about the same length as 1 modern transistor. (Later it will become clear why I chose a hydrogen atom for reference.)
The world of nano-sized electronic circuits obey the laws of quantum mechanics, which are based on Einstein’s postulates of quantum physics. But what if something is fundamentally wrong with Einstein’s theories, especially as they apply to larger gravitational forces? This challenge to Einstein’s theories is not coming from the quantum world but from its big brother, namely, cosmology – the study of the universe, from stars to distant galaxies. By studying distant supernovae through the orbiting Hubble Space Telescope, cosmologists have found that the universe is now expanding faster than in the very distant past. This means that the universe has not been slowing due to gravitational forces as was expected. Rather, it has been expanding since its inception from the Big Bang. But what is causing the acceleration of the universe’s expansion? What does it have to do with Einstein and, indirectly, with semiconductor engineers?
The answer to these and other related questions was at the heart of a talk by renowned cosmologist Alex Filippenko, who spoke at a recent Institute for Science, Engineering and Public Policy (ISEPP) event (Figure 1 below). Filippenko’s talk, titled, “Dark Energy and the Runaway Universe,” drew a large audience to Portland’s Arlene Schnitzer Concert Hall. The high attendance was noteworthy because it occurred on Nov 2, 2010, the same night as the return on a very contentious set of national mid-term elections.
Those in attendance enjoyed a well spent evening. Although the subject matter was complex, Filippenko’s talk was anything but dark and somber. Instead, this lively speaker peppered his discussion with fascinating conjectures while tossing a Newtonian apple as a visual aid. To keep the audience awake, he occasionally injected a bit of comic relief, such as acknowledging the general public’s confusion between cosmology and cosmetology, the later being the study of hair styles and facials.
Dark Energy, Dark Matter
Although Filippenko’s talk was both entertaining and enlightening, his main goal was to discuss the existence of dark energy and dark matter. Both of these sinister sounding concepts arose as a way to explain this counterintuitive finding that the expansion of the universe is accelerating instead of slowing down. Theorists have created three possible explanations for the accelerated expansion.
First, the expansion might be due to a cosmological constant that fills all space with a constant energy density. Interestingly, this idea was proposed and then discarded by Einstein in his original theory on gravity. Secondly, perhaps the empty areas of space are really filled with some strange kind of energy fluid whose density can vary in time and space. Lastly, some theorists speculate that there might be something wrong with Einstein’s gravitational theories.
Nobody knows for certain which explanation is correct. But they have collectively decided to call the solution – whatever it turns out to be – “dark energy.”
Dark energy is a form of energy that exists in all space and increases the rate of expansion of the universe. According to calculations by cosmologists, 74% of the universe is comprised of dark energy. Another vaguely descriptive entity known as “dark matter” makes up 22 percent of the universe. What is dark matter? In theory, it is real matter, not anti-matter. The idea of dark matter was created to explain discrepancies in the mass of galaxies, clusters of galaxies and the entire universe.
Indeed, both of these dark terms are used as theoretical “place holders” to help reconcile the measured shape of all space with the total amount of matter in the universe. This means that normal matter such as people, Portland, politicians, planets and everything else (the “etc.” in Figure 2 below) make up only a very small fraction of the Universe. Remember, the existences of dark energy and matter are needed to reconcile the measured geometry of space with the total amount of matter in the universe.
Filippenko’s lecture, including a question and answer session, lasted for almost 2 hours. In the end, he noted that “the wise, betting man would say that the universe will either expand forever or for an extremely (finite) long time. Nevertheless, it might collapse back upon itself.” This statement led into a philosophical observation that the famous poet Robert Frost must have known about these two possibilities. Either the universe would re-collapse, becoming hot, dense and compressed to end in fire. Or that the universe would eternally expand, becoming ever darker, more dilute and colder.
Fire and Ice – by Robert Frost
Some say the world will end in fire,
Some say in ice.
From what I’ve tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To say that for destruction ice
Is also great
And would suffice.
Questions at the Table
In the dinner that followed the public lecture (Figure 3 below), I asked Filippenko several questions. First, most of his findings and data seemed to come from the use of extremely powerful optical telescopes for the observation of very distant galaxies and clusters of galaxies. But what about use of radio telescopes, such as the one at Arecibo, PR? (see “Computational Powerhouse Hidden In Island Jungle”)
He was quick to point out the complementary role in cosmology that is played by radio telescopes, such as the capability to measure the 21cm hydrogen line (HI). This term refers to the electromagnetic radiation spectral line (1420.4 MHz) that is created by a change in the energy state of neutral hydrogen atoms. The HI spectral line is important in radio astronomy since it can penetrate large clouds of interstellar cosmic dust which would interfere with the visible light needed by traditional optical telescopes.
After answering this question, he noted that aging telescopes and laboratories – such as those at Arecibo – are casualties of our nation’s misplaced budgetary priorities. He was not shy in tackling such questions about the need for science from the audience, stating that all scientists must be able to defend the tax dollars that they receive. But that the cost of science, when compared to other expenditures, is very reasonable for the return.
He made several interesting observations during a brief dinner presentation. Most noticeably to me was that the angular diameter of the Moon is about the same as the angular diameter of the Sun (about 1/2 degree). This is why the Moon completely covers the disc of the Sun during a solar eclipse. However, in our expanding universe, the distance between the Moon and the Earth is slowing increasing over time. Thus, the angular diameter of the Moon is decreasing. In about 600 million years, the Moon will no longer cover the Sun completely and not total eclipses will occur. “We live in that vary narrow window of cosmological time (about 1 billion years) in which the Moon-Sun eclipses are perfect in size,” explained Filippenko.
Earlier in the evening, he had issued a challenge to everyone in the room to be cosmic observers of the “Path of Totality” in 2017. The path of totality, which can be up to 200 miles wide, represents the Moon’s shadow that is traced on the Earth during a total solar eclipse. The event in 2017 will occur in North America, visible from parts of southern Oregon.
It didn’t occur to me until my drive home that the last total solar eclipse in America occurred in 1979. As a young undergraduate physics student at Oregon State University, I observed the eclipse just barely outside the Path of Totality. Still, the darkening landscape that resulted from the Sun’s disappearance behind the Moon was a haunting memory that stays with me still.
Cosmology and Semiconductors
Let me return to my opening question: What is the connection between an expanding universe, the possible failure of Einstein’s theories and semiconductor engineering? The answer lies in the study of quantum gravity, a field of theoretical physics that attempts to unify the very small with the very large. Quantum mechanics explains behavior of the very small, for objects no larger than molecules. General relativity works for the world of the very large, for bodies such as collapsed stars. But what happens if the explanation for a paradoxically expanding universe invalidates key portions of Einstein’s postulates in quantum physics? If so, then our understanding of both worlds may collide into chaos.
Maybe cosmologists will discover the answer by further studies of very distant and ancient galaxies. Or maybe semiconductor engineers will find an explanation as they push the boundaries of integrated circuits beyond the atomic level. Either way, it promises to be an exciting time for science and engineering.