Archive for the 'science' Category

Spectroscopy and Quantum Leap

October 20, 2008

In a recent article on the Big Bang, I mentioned the method of spectroscopy twice without explaining what it is or how it works. Although the art of spectroscopy was accurately used long before it’s mechanisms were fully explained, I think that it is both helpful and interesting to consider spectroscopy alongside its quantum mechanical workings.

One of the basic tenets of quantum physics is that an atom of any chemical element is only capable of particular levels of kinetic energy unique to that element. It is important to remember here that electrons, like photons, behave both like particles and like waves. We know that there is a direct relationship between an electron’s frequency and the amount of energy that it contains. Because of the wave nature of electrons, most paths that an electron could take around nucleus are forbidden, as they would cause the electron to catch up with itself and cancel itself out. This means that only specific frequencies/energy levels are allowed for an electron of any particular element.

A hydrogen atom, for instance may have -13.6 electron volts (eV), -3.4eV, -1.5eV, etc. An atom in normal circumstances has a tendency toward its lowest possible level of kinetic energy, known as its ground state. Any time an atom has more kinetic energy than its ground state energy, it is considered to be in an excited state. When an atom is in an excited state, it releases a precise amount of energy in the form of electromagnetic radiation in order to return to a more “comfortable”, lower kinetic energy state. This rapid change in energy is known as a quantum leap. Again, we know that there is a direct relationship between energy and frequency, so all this means that when an atom in an excited state returns to it’s ground state, it releases a photon of a very specific frequency, which our eyes interpret as color, allowing us to learn the chemical makeup of a substance by analyzing the light that it emits. You can test this for yourself by sprinkling table salt over a flame. You will see specs of yellow in the flame, a result of the chemical properties of sodium. This phenomenon is known as emission spectroscopy. When the light from a hot, low-density gas is shown through a prism, an emission line spectrum results (see figure 1). Each chemical element has it’s own “spectral fingerprint”. Neon atoms emit red light while mercury emits a bluer light, accounting for the color of light you expect to see from neon and mercury light fixtures.

Figure 1 - The emission spectrum of hydrogen.  Each line of color in the spectrum represents

Figure 1 - The emission spectrum of hydrogen.

Next we’ll consider absorption spectroscopy, which is the inverse of emission spectroscopy. When light with a complete spectrum (figure 2) is shone through a prism, absorption spectroscopy can be used to identify the chemical composition of the atoms in between the light source and the observer. The electrons of the atom will only absorb photons of the particular frequencies that will result in another allowed level of kinetic energy particular to that element. The result is a nearly continuous spectrum with dark lines representing the frequencies of light that were absorbed (figure 3). Note that the emission lines for hydrogen (figure 1) line up perfectly with the absorption lines for hydrogen (figure 3). Absorption spectroscopy allows us to learn the chemical makeup of the atmospheres of stars by analyzing the dark lines in the spectrum that they emit.

Figure 2 - A continuous spectrum

Figure 2 - A continuous spectrum

Figure 3 - The absorption spectrum of hydrogen

Figure 3 - The absorption spectrum of hydrogen

Finally, I’ll take a second to relate this all back to the Big Bang. What Hubble noticed when observing the absorption spectra from distant galaxies is that the easily identifiable spectral lines were shifted toward the red end of the spectrum as in figure 4. Hubble interpreted this as the Doppler effect, or the change in frequency and wavelength of a wave for an observer moving relative to the source of the waves. Hypothetically, had the spectral lines been shifted toward the blue end of the spectrum, scientists might have concluded that distant galaxies were moving closer to us.

Understanding quantum leap and spectroscopy in relation to galactic redshift is one of many things that allows me to appreciate the wealth of observational support for the Big Bang Theory of cosmology.

Figure 4 - Redshift of hydrogen

Figure 4 - Redshift of hydrogen

Faith in Science

August 31, 2008

When discussing religion with believers, I often encounter the accusation that science is just another religion, complete with dogma, blind faith, etc. This is a misguided idea. Science is set apart from religion in that it is verifiable by everyday experience. It is also fluid in the sense that scientific facts are falsifiable and theories are subject to change according to the most current observations. Religion, on the other hand is static and considered infallible. Believers are expected to have faith not just in the absence of supporting evidence, but also when the evidence blatantly contradicts the religious tenets.

Someone who considers the validity of any scientific principle has the benefit of being able to verify the claim to their satisfaction. Anyone can retrace the logical steps of any successful theory or repeat any successful experiment and see the results for themselves, but this is not always practical. Because scientific theories and experiments have the tendency to be too complicated and labor intensive for the average person to experience for themselves, many people do take scientific principles on faith alone.

But what is the nature of that faith? I have faith that if I jump off of the side of the cliff, I will fall down and probably be killed. This faith is not blind, it is established from prior evidence—my daily experience with gravity, that one time I threw a rock off of a cliff and watched it bounce violently down, and stories I have heard of tragedies involving bodies and cliffs. I haven’t personally experienced falling off of a cliff, so I do have to have faith regarding the end result, but it isn’t a great degree of faith. It would take a lot more faith to believe that when I jumped off of the cliff I would be miraculously unharmed, that there would be some sort of divine intervention, like a host of angles sent to protect me.

Similarly a person unfamiliar with physics and math would have to take it on faith that the Theory of General Relativity explains that gravity is the result of a curve in space-time. There is a compromise to be made here. Even though it is counter intuitive and confusing, anyone can open a book or two and learn about the theory along with its proofs. They can learn that many physicists and mathematicians have repeated and confirmed Einstein’s calculations. They can also learn that the effects of General Relativity can be viewed during a solar eclipse when a straight beam of light coming from a distant star appears to curve as space itself curves due to the mass of the sun. They can learn that the theory even has practical implications, for example the fact that we have to account for the principles of General Relativity when coordinating signals to and from satellites in space. Suddenly something that was taken on faith alone, that was considered abstract and beyond comprehension, becomes something understandable and something that makes sense logically.

I personally find this second-hand evidence sufficient proof for General Relativity because it follows a logical progression. I am satisfied with the observations of others because of the structure and nature of the scientific process. In order for a theory to be accepted as the scientific consensus it must pass the rigors of peer-review. This means that I can be assured that something like General Relativity isn’t just accepted by a few scientists, but by the vast majority of the scientific world. Virtually everyone who is able to understand Einstein’s calculations agrees with them. But I don’t have to be satisfied with the observations of others. I could get a PhD in physics and learn how to do the calculations myself.

When someone goes around touting their belief in Relativity, Big Bang Cosmology, or the Theory of Evolution by Natural Selection without fully grasping the evidence for these phenomena, they are taking a leap of faith and are indeed no better off then their religious counterparts. The difference between religion and science is that, where science is concerned, nothing has to or should be taken on faith.

Co-written by orDover and cross-posted at The Art of Skepticism

The Big Bang

August 31, 2008

Where did the Universe come from? How old is time? By the early twentieth century, these questions seemed beyond the scope of human knowledge. That the universe was eternal and unchanging seemed the only sensible viewpoint as there was no observational evidence to suggest otherwise. The Big Bang Theory offers a remarkably different view of an ever-expanding Universe. According to this bizarre theory, the entire universe, all matter, energy, space and time, were condensed in to a single point smaller than a pinhead, and, several billion years ago, it began a violent expansion that is still occurring today. This is truly an extraordinary claim and would be very difficult to believe without extraordinary evidence to support it.

In order to understand why the evidence for the Big Bang Theory is so compelling, we would do well to find what makes a strong scientific theory. The most well phrased definition of “theory” that I’ve ever heard or read is from Stephen Hawking’s best-selling book A Brief History of Time: “A theory is a good theory if it satisfies two requirements. It must accurately describe a large class of observations on the basis of a model that contains only a few arbitrary elements, and it must make definite predictions about the results of future observations.” Let’s move forward with an overview of some of the key evidence for the Big Bang Theory and see how it holds up to Hawking’s criteria.

The Expanding Universe

One of the revolutionary implications of Albert Einstein’s remarkably successful General Theory of Relativity was that the Universe was an extremely unstable place. According to the theory, gravity acts between every bit of matter in the cosmos and, if left unchecked, should cause the Universe collapse in on itself. While the rest of the theory had been vindicated time and again, this collapse was clearly not an accurate description of the Universe that we lived in. Einstein’s theory needed some force to counter gravity in order to fit observation. Rather than accept the possibility of an expanding Universe that his theory seemed to suggest, Einstein altered his equations with what would become known as the cosmological constant.

Mathematician Alexander Friedmann, however, posed three unique solutions to Einstein’s equations, each describing a Universe that was expanding from a primeval state. While Friedmann’s proposed expansion had the effect of counterbalancing gravity, his theory had two major setbacks: 1) It challenged the scientific orthodoxy of the time, which had always perceived the Universe as static, and 2) It did not agree with observation as expansion is not noticeable in “small” systems, such as solar systems and galaxies, and observational data of anything beyond the Milky Way was scarce.

Astronomer Edwin Hubble

Friedmann’s solutions would remain in obscurity until they were corroborated by the observations of astronomer Edwin Hubble. Using the method of spectroscopy, Hubble showed that the light from distant galaxies was being shifted toward the red (lower energy) end of the electromagnetic spectrum. Hubble interpreted this as the Doppler effect, which Wikipedia describes as “the change in frequency and wavelength of a wave for an observer moving relative to the source of the waves.” In other words, high-energy light waves from galaxies millions of light years away from us were being “stretched” in to lower energy light waves on their way to us. Hubble had documented the expansion of the Universe!

This first observational evidence in support of the Big Bang Theory changed the way we thought of the Universe, inviting cosmologists to use the theory to explore questions that had previously escaped the grasp of science.

The Abundance of Elements

One of the cosmic mysteries that eluded scientists in the decades before the Big Bang Theory took foot was the uneven distribution of chemical elements throughout the Universe. Again by the method of spectroscopy, it had been established that hydrogen, the lightest of the elements, is by far the most abundant, consisting of over ninety percent of all of the atoms in the universe. Helium, the second lightest element, is a distant second consisting of about nine percent of all atoms. This means that all of the remaining chemical elements consisted of only one thousandth of a percent of all of the atoms in the universe.

Nuclear Physicist George Gamow

In the nineteen-forties, nuclear physicists George Gamow and Ralph Alpher attempted to explain the processes of nuclear synthesis during the early stages of the Universe within the framework of the Big Bang model. Gamow knew that the Friedman theory supported by Hubble’s observations implied an extremely hot and dense early Universe. Working forward from this primeval state using painstaking calculations, Gamow and Alpher found that the Big Bang Theory predicted that there should be approximately one helium nucleus for every ten hydrogen nuclei, mirroring observations of astronomers.

While their findings were nothing short of a triumph for the Big Bang Theory, Gamow and Alpher found that they could not explain the synthesis of heavier elements in the conditions of the early Universe. This discrepancy was later resolved when Fred Hoyle posed stellar nulceosynthesis as a mechanism for the formation of elements heavier than helium, which I’ll discuss in a future post. The Big Bang Theory was proving to be very good at describing existing astronomical observations, but had failed to make any scientific predictions that could be tested.

Cosmic Microwave Background Radiation

All of the nuclear synthesis that Gamow and Alpher described happened in the first few minutes of the Universe. Afterwards, the Universe was cooled down to a point where nuclear synthesis was no longer possible, but was still so hot that electrons could not attach themselves to the newly formed hydrogen and helium nuclei. During this period, which lasted more than 300,000 years, the abundance of free-floating electrons prevented the free travel of the gamma rays that permeated everything. The Universe continued to expand and cool, eventually to the point that electrons could join with the nuclei, forming hydrogen and helium atoms. With no haze of electrons to block their path, the gamma rays were free to travel across the Universe.

Based on this model, Gamow and Alpher along with fellow physicist Roger Herman, predicted that this abundance of gamma rays would still permeate the Universe in our time, but because the waves would seem to be “stretched” by the familiar phenomenon known as redshift, they would be microwaves when they reached us in the Twentieth Century. More specifically, Alpher and Herman predicted that the temperature of this background radiation should be approximately 5 Kelvin.

Fifteen years passed before anyone detected the Cosmic Microwave Background Radiation (CBR), but it was finally discovered in 1964 by two physicists working for Bell Labs, Arno Penzias and Robert Wilson. The reality of the CBR matched prediction almost exactly in that it was an all pervading radiation, equally measurable from any direction. Alpher and Herman had even gotten the approximate temperature right (the actual temperature of the CBR is 2.70 Kelvin as opposed to the 5 Kelvin predicted).

The fulfillment of the prediction of the CBR was a momentous triumph for the Big Bang Theory. Not only was the CBR a very precise prediction, but it is also yet another strange observation of the Cosmos that can be explained by the Big Bang and the Big Bang alone.

Microwave Imaging of the CBR from the WMAP Sattelite

Microwave Imaging of the CBR from the WMAP Sattelite

There are still quite a few holes in the Big Bang Theory. It cannot be used to predict what occurred in the first few moments of the Universe because at those extreme temperatures and pressures the laws of physics as we know them break down. Also, we are only in the speculative stage regarding the question of why there is an abundance of matter over antimatter in the Universe. While questions like these seem to be beyond the grasp of the Big Bang model, history has shown us that it is a mistake to consider anything to be outside the reach of science.

My knowledge on these topics relies heavily on a few resources not cited above including Big Bang by Simon Singh, and Origins by Neil Degrasse Tyson. I strongly recommend these books for further reading.

Knowledge

August 17, 2008

As it is the aim of this blog to explore the extent of what we humans know about our universe, our world, and ourselves, I thought it would be appropriate to begin with a discussion about the nature of knowledge itself. Before we address how we know what we know, let us first ask how we know that we know what we know.

Bertrand Russell, Philosopher

Bertrand Russell, Philosopher

At the outset, it seems that there are three ways that one can gain knowledge of an event: first hand perception, written and verbal communication and logical deduction. In an effort to economize our discussion, we can ignore communication for the time being, as first hand perception of an event is a prerequisite for the communication of knowledge of that event. Similarly, in order to apply the rules of logic to the data that we gather from our surroundings, we must first gather that data. Thus we can say comfortably that all of our knowledge is based on the perceptions of individuals.

That said, it is often argued that the flaws inherent to individual perception negate any possibility of true empirical knowledge. If all of our knowledge and experience of the universe is the product of our senses, and our perceptions are nothing but chemical events in the brain, then isn’t it possible that the external world doesn’t exist anywhere but in our minds? Hallucinations, which to some degree are experienced by all people, are perceptual events with no stimuli external to the brain. Is it possible that the whole of human experience is a grand hallucination? I don’t think so.

First of all, that entire line of reasoning is founded solely on the cognitive sciences, which, in turn, are based entirely on perceptions and hence deemed unreliable by the very same line of reasoning. Therefore, the hypothesis cannot support itself.
If followed to it’s logical end, this system of thought seems to deny the existence of matter, energy, space, time and the forces of nature. After all, we can only become aware of these characteristics of the universe through our senses. This leaves us not only with no stimuli for our brains to perceive, but also with no brains to perceive them with.

The alternative is a more sensible, materialistic theory of cognition. If you are an average, healthy person you probably find that your five senses are generally in agreement. For instance, if you are standing on the side of the road at a bus stop and you see a bus approaching, you have probably come to expect to hear the engine of the bus as it gets closer and, as it stops next to you, you may even be able to smell the exhaust before you climb inside. The more our senses agree about a common phenomenon, the more confidence we ascribe to our assessment of that phenomenon.

Our senses provide information about matter and the way that it interacts with space and time, and we generally observe that similar configurations of matter and energy tend to behave in similar ways. This allows us to make predictions about how matter will behave in certain situations. For example every time I drop a rubber ball over a hard surface, the ball falls to the ground and bounces. We also apply this logic to other human beings when we assume that because they have similar sense organs to us, they must also be capable of providing accurate reports of their surroundings.

We live in a world of individual percepts, both those of our own and those of others that we become aware of through communication. This does not conclusively prove that there is no world beyond our perceptions. It does, however, mean that if such a world does exist than it is utterly beyond our reach and will remain, as it should, forever in our imaginations. We haven’t proven beyond a shadow of a doubt that our universe is not illusory, only that we may as well not doubt what we commonly call “reality”, because it’s the only reality we have.