introduction to the book of nature

8/9/2019 Introduction to the Book of Nature

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An Introduction To

The Book Of Nature

Bruce Nelson

October, 2009


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Introduction

The Scientific Method

Isaac Newton saw an apple fall and supposed that same force might also hold the moon in its orbit. Of all thepeople who had observed apples and the moon, he was the first to make a connection. This may seem obviouto us now, but back then, the movements of the "heavenly bodies" were prescribed by the Church. Newton hmade a daring move. But he did not stop there -- he did some calculations to check his idea that a single

universal force law could account for the motions of both the apple and the moon. He found that the forcewould have to decrease as the square of the distance and to be proportional to mass. This "Law of Gravitatiois now in every introductory physics text, and was one of the early sections in the Book of Nature. Thisillustrates the scientific method: observe, form a theory, test the theory, publish results. The reason we believNewton was correct is that we can repeat his observations and analysis to check his results.

There is no room in this scheme for anything supernatural. Many processes are monitored closely all the timand any discrepancy would not only be noticed, but possibly disastrous: Aircraft landings based on GPS readings. Automated factories, nuclear reactors, oil refineries. Pharmaceutical production, DNA analysis, MRIs. Movements of the planets and of spacecraft navigating to them.

Leon Ledermann's bookThe God Particle starts with an entertaining account of how scientific discoveries wemade, then moves to particle physics. This popular level book contains complex ideas but is not mathematic(The lurid title refers to the Higgs particle, which gives masses to particles like the electron.)

Observations and Measurements

So what observations can we make to base our theories of the universe on? Start with the night sky (preferabaway from city lights), where we can see some galaxies as well as stars and planets. The "Milky Way" is thecentral part of our galaxy, and the Andromeda galaxy is easy to see if you know where to look and what toexpect. (It is as big as the Moon, but fuzzy and dim.) Early telescopes expanded this vista tremendously,showing hundreds of fuzzy blobs, which were named "nebulae." In 1923 Edwin Hubble found that many ofthese nebulae were made up of stars and therefore were galaxies similar to our own Milky Way. Then in the l1920s Hubble found that most of the galaxies were moving away from us, the more distant ones moving fasteThis became known as "Hubble's Law." More recently, this expansion was found to be accelerating. [Prima& Abrams, p90-93; Guth, p46-51; Weinberg, p19-27, Riess & Turner]

Astronomers have come up with several ways to measure the distances of stars and galaxies. Nearby stars shtheir positions slightly as they are viewed by the Earth from opposite sides of its orbit. This is called parallaxand allows calculation of their distance from the known distance from Earth to the Sun. For greater distanceswhat is needed is a "standard candle"; i.e., an object of known brightness. For example if we know that twostars have the same brightness but one is 100 times dimmer than the other, then the dim one must be 10 timesfarther. It has been determined that Type Ia supernovae all have the same brightness; these can be seen in vedistant galaxies and have become our standard candles. [Weinberg, p19-27, Riess & Turner]

The velocity and composition of a star are determined by looking at its spectrum, just like Newton used a pristo make a rainbow from sunlight. The spectral lines allow a chemical analysis of stars, since each element hadistinctive pattern of lines and their intensity measures their relative amount. An 18th century philosopherclaimed that we could never know what the stars were made of. Actually, once scientists had measured andcataloged the spectral lines of many elements in the laboratory, it turned out to be quite routine to do that -- echemical element produces and absorbs a pattern of colors that acts as its unique fingerprint. The composition


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of glowing gas clouds can also be measured, and in this way it was determined that the visible matter was abo25% helium and 75% hydrogen, with only tiny amounts of heavier elements like carbon and oxygen. Thespectrum of a star moving away from us is shifted toward the red end, like the sound of a passing siren dropspitch as it heads away from you. (Red light is lower in "pitch" than blue.) The velocity is calculated from thamount of shift (just like a traffic cop with his radar gun.) [Guth, p46-49; Weinberg, p20-21]

The more distant galaxies are dimmer, so larger telescopes were made to collect more light. As these powerftelescopes search for the most distant galaxies, they are also looking back in time. (We see the Sun as it was

eight minutes ago, and the Andromeda galaxy as it was two million years ago.) We can now see galaxies (anquasars, which are just extremely bright galaxies) at such early times that their light shifts beyond red and intthe infrared, and telescopes must be specially designed to detect these wavelengths. (The James Webb SpaceTelescope, to be launched about 2015, will be able to see the formation of the first stars and galaxies.) Severtelescopic surveys have recorded the redshift (and hence approximate distance) of thousands of galaxies. Theshow that at early times galaxies were evenly distributed but they are now clustered into filaments and walls,with nearly empty voids in between. [Strauss]

To see even earlier times requires "telescopes" sensitive to microwaves since the original light waves havestretched (cooled) to only 2.7 degrees above absolute zero. This thermal radiation is called the CosmicMicrowave Background (CMB) and gives us a look at the universe when it was only 380,000 years old. [Hu

and White] The Universe was opaque to light before this, but neutrino and gravity wave telescopes now unddevelopment could let us see even farther back.

The Big Bang

Edwin Hubble's 1929 discovery that galaxies are receding from us at a speed proportional to distance impliedthat the universe had once been highly compressed and that we are seeing the explosion of that dense state.Such a state is well-understood from laboratory experiments; it is entirely specified by the temperature andparticle content. Friedmann's solution to Einstein's general relativity equations for a homogeneous universeprovided a description of the expansion using only Hubble's proportionality constant and the particle density.But it took a long time for these ideas to form into a proper theory that could make predictions.

In 1948, Gamov, Alpher and Herman published an expansion theory that, when adjusted to match the observabundances of chemical elements in the universe, predicted that there would be a residual microwavebackground of about 5K (5 degrees Celsius above absolute zero.) Nobody looked for this, probably becausethere were other theories that tried to explain Hubble's measurements without expansion. Fred Hoyle, EnglanAstronomer Royal, sneeringly dubbed the expansion idea the "Big Bang", and the name stuck. In 1965, Penzand Wilson, working at Bell Laboratories, were puzzled at the "excess noise temperature" they were picking in their microwave antenna. At the same time, Dicke, Peebles, Roll and Wilkinson at Princeton were preparito look for radiation their theory had predicted. Neither group knew of the other, but a common friend made connection, and their findings were quickly published. Many scientists then picked up on this, andmeasurements of the Cosmic Microwave Background (CMB) soon showed that the radiation was close to the"black body" form predicted by the theory. The competing theories could not account for this and fell into

disfavor. By 1977, the Big Bang theory had become so well established it was called the "Standard Model ofCosmology", and scientists concentrated on improving the accuracy of Hubble's constant and othermeasurements to refine the model. Steven Weinberg's bookThe First Three Minutes is a classic description.

Weinberg describes the expansion starting at a temperature of 10 billion degrees (about 1000 times hotter thathe center of the Sun), at a time about 0.01 second after the beginning. (See Riordan & Zajc for earlier timesAt that time the only particles around were electrons, neutrinos and their antiparticles, and photons, plus a tin(one part per billion) sprinkling of protons and neutrons. Friedmann's formula gave the expansion rate


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proportional to the square root of the energy density, and as the Universe expanded, it cooled. Weinberg's bofollows this cooling through the time electrons combined with their antiparticles to the temperature where theprotons and neutrons could stick together to form atomic nuclei without being blasted apart again by all thephotons. The billion-to-one ratio of photons to protons & neutrons determined which atomic nuclei were ablto form in this brief period. The predictions from the theory were 25% helium, 75% hydrogen, and 0.003%deuterium; these agreed very well with the amounts measured by astronomers. Further cooling to about 3000allowed the nuclei to hold on to electrons to form atoms, and this caused the Universe to become transparent tphotons for the first time. The result, after billions of years of cooling, is now observed as the 2.7K CMB.

Although these checks proved that the Big Bang theory accurately described the Universe, there were somethings the theory did not explain. The obvious one is what caused the "Bang." Another problem was that aperfectly smooth CMB was predicted, and this did not provide any irregularities from which the stars andgalaxies could form by gravitational collapse. The fact that the CMB on opposite sides of the sky has the samtemperature even though those parts of the Universe were never in contact is called the "Horizon Problem."And there is the "Flatness Problem", where the measured density happens to be so close to the razor edge ofstability (like a pencil balanced on its point) that some explanation is required. And finally, the age of theUniverse was predicted to be about 12 billion years, but some star clusters were thought to be more like 15billion years old (the "Age Problem".)

Inflation To The Rescue!Fortunately, a clever fellow named Alan Guth came up with a pre-bang theory called "Inflation" that solved abut the Age Problem and also provided a way to pop the entire universe out of the vacuum! The idea was thafluctuation in a previously unknown quantum field (named the "Inflaton") acted like anti-gravity and had staran exponential expansion at rate much faster than light. (Relativity is OK with this because space itself isexpanding; nothing is moving faster than light within space.) The original quantum fluctuations were thenmagnified to cosmic dimensions by the subsequent expansion and became the seeds for galaxy formation. Thuniverse expanded about 10 billion trillion times in a tiny fraction of a second; this stretched out any curvaturthus solving the flatness problem. Also, the stretching moved neighboring points to far distant parts of theuniverse: no more Horizon problem. When the Inflaton field died away, it released the huge energy that hadbeen built up; hence the Bang. (This did not violate conservation of energy since the energy released was

balanced by the negative gravitational energy.) Alan Guth's bookThe Inflationary Universe explains all this much more detail, and gives a personal account of how the Inflation theory developed from his original idea(which didn't work) with help from people like Steven Hawking. The new particle accelerator (LHC) nearGeneva, will search for particles like the Inflaton starting in 2009. (The Inflaton may be a version of the Higparticle.) In the coming decades, gravity wave telescopes may provide measurements to support (or refute) ththeory by examining the beginnings of our Universe.

In 1970, Vera Rubin measured the orbital velocities of stars in nearby galaxies and determined that the visiblmatter in them did not provide enough gravity to hold them together. An unknown kind of matter, named "DMatter", was postulated to account for this. Dark matter also turned out to be necessary for galaxy formationsince it isn't blown around by all the photons [Primack & Abrams, p144]. (It is dark because it doesn't intera

with anything except gravity.) Including Dark Matter brought the total matter density of the universe up to 3of the value predicted by the Friedmann formula for a flat geometry. [Primack & Abrams, p100-105]

The ongoing "Hubble Program" to measure speed versus distance of the most distant galaxies using our besttelescopes showed that the expansion is accelerating. This was attributed to "Dark Energy", which can easilyincorporated into Friedmann's formula since Einstein had once added such a term but had later removed it.(Interesting story there.) The Dark Energy brought the total energy density of the universe up very close to th(unstable) value for a flat geometry, just as predicted by Inflation. Dark Energy also eliminates the Age


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Problem by increasing the calculated age to about 14 billion years. (And it turned out that the oldest stars wenot as old as previously thought. [see Chaboyer])

Since Earth's atmosphere is mostly opaque to the CMB, satellites were put up to get a better look. COBEmeasured the CMB temperature to be 2.725K and showed that it had an exact (to 5 decimals) blackbodyspectrum, just as predicted. COBE detected tiny variations in the CMB temperature, and these were the rightmagnitude to start galaxy formation in the known time frame. WMAP spent five years getting a high-resolutmeasurement of CMB temperature variations. Subsequent analysis, combined with astronomical measureme

of things like the Hubble constant and element abundances, gave us accurate and consistent values for the macosmological parameters. The Universe is 13.7 billion years old, is composed of 4.6% atomic matter, 22%Dark Matter, 73% Dark Energy and 0.008% photons. The Hubble constant is 70.5 km/sec/Mpc and there are1640 million photons for every proton or neutron. The statistical characteristics of the CMB fluctuationsmatched predictions, thus providing strong support for Inflation theory. These values are uncertain by a fewpercent, but more accurate values are on the way: the Planck satellite is now up there and just starting itsmeasurement program. [Hu & White, Turner]

Stars and Galaxies Form

It was known to Newton that a gas cloud in space was gravitationally unstable: any region that was slightlydenser than its surroundings would contract and become even more dense. WMAP's analysis of the CMB

polarization showed that it took 430 million years for the first stars to light up. During this time, small densitvariations were magnified by the force of gravity, causing the gases to condense into proto-galaxies. Darkmatter was the leader in this condensation since it was only affected by gravity -- the hydrogen and heliumatoms were pushed around a lot by the photons, which were still a billion times more numerous. The stars thformed within this dark matter "halo" as the atoms radiated away the energy of their motion and sank to thecenter.

Many of the first stars were huge, over 100 times the mass of our Sun. This caused them to burn out veryquickly (for a star), in a million years or so. (Our Sun's lifetime is 10 billion years, but half of that is gonealready.) Because they were large, they ended their lives in powerful supernova explosions, which created althe higher elements and scattered them widely. The dark matter was not affected by this and it remained in

place to attract the debris back to the galaxy to form a second generation of stars. Since there was much morthan just hydrogen and helium available this time, solid planets were able to form around the new stars. Theearly galaxies collided and merged to form the galaxies we see today. Primack & Abrams give a detailed andvery readable account of galaxy formation, p141-152.

The Sun, Earth and planets formed about 4.5 billion years ago. Earth must have had a very violent birth, sincit was assembled from rocks of all sizes -- sort of a continuous meteor bombardment. It is thought that theMoon was formed when a planet the size of Mars smacked into the young Earth. The Sun was 20% coolercompared to today, but Earth must have experienced many episodes of impact heating that would likely havecooked any life that had started. Somehow it managed to hold onto its water and atmosphere through all thatWills & Bada include a good description of the formation of Earth in Chapter 3 of their book.

The Origin of Life

Life appears to have begun 3.7 billion years ago, which was only a couple of hundred million years after Eartcooled below the boiling point of water. In cosmology various theories fell by the wayside as a clear path wagradually discovered and verified. The origin of life is still in the "various theories" stage. Many partial pathto life are under investigation and being verified as they are proposed, but a complete end-to-end creation of lhas not yet been discovered. Even then, we cannot exclude the possibility of other pathways to create life.Since the original life almost certainly devoured its precursors, it may never be possible to determine exactly


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how life originated on Earth.

Wills & Bada and Hazen discuss the many theories being pursued. The most promising approach is "RNAFirst" (as opposed to "Metabolism First" and "Cell Walls First", which also have their proponents.) RNA issimilar to DNA and can carry the same genetic information. It consists of long strands of "nucleotides", eachcontaining one of the four "bases" adenine, cytosine, guanine and uracil (A, C, G and U). (DNA uses thymininstead of uracil.) Much of the reproductive machinery in a modern cell is made of RNA, so it seemsreasonable that early organisms used RNA to store its genetic information and to perform many other functio

such as catalysing chemical reactions. RNA is less stable than DNA, and its replication is less accurate, thusgenerating lots of random mutations.

RNA first is the most difficult path because of the many complex molecules that must be created from theavailable materials. A promising sequence of partial paths is as follows:

1) Geological research has identified the raw materials that life had to start with, including theatmosphere, deep ocean, volcanic vents, various mineral surfaces, etc. These are water, carbon dioxide,nitrogen, phosphate, mineral salts, hydrogen sulphide, cyanide, and various organic compounds from meteorsThere was no free oxygen.

2) Laboratory experiments starting with the raw materials have generated hundreds of organiccompounds by means of heat, electric sparks, pressure and mineral catalysts.

3) A major step was recently accomplished when John Sutherland's team created the RNA nucleotideand U from available chemicals [Ricardo & Szostak]. To have the complete RNA alphabet available, the A aG nucleotides must also be created.

4) Connect the individual nucleotides together into long strands. [Hazen, p158] This has beendemonstrated to occur on the surfaces of certain minerals, but the longer the strand, the more tightly it adhereto the mineral. It was recently discovered that the RNA strands could be released by a concentrated saltsolution. Many random RNA sequences could be generated in this way.

5) "Test Tube Evolution" has been demonstrated to create RNA strands with desired characteristics fra random mixture. (In a series of cycles, only the desirable RNA is selected by the experimenter for the nextcycle. Similar to selective breeding of animals.) What is desired is self-replication, and so far an RNAsequence has been found that can copy small parts of itself. Self-replicating RNA would be considered livingby most scientists.

6) Once some self-replicating RNA appeared on the Early Earth, Darwinian evolution would take oveto select for useful characteristics, such as cell walls (which have been shown to self-assemble from lipids inwater), protein enzymes, and new energy sources. RNA does not reproduce very accurately, so there would bplenty of variation for natural selection to work on. Eventually DNA would replace RNA for more reliable

storage of the organism's genetic instructions. [Dawkins, Carroll]

Conclusion

Many important discoveries are so recent that they are not yet in books, hence the Scientific Americanreferences. (At the professional level, preprints serve this function; see http://arXiv.org/abs/) That it all fitstogether in a unified self-consistent whole shows these are pages from the same book.

Portions of Nature's Book


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In a normal book, this would be the Bibliography. Instead, the following should be considered as some of thactual chapters of Nature's Book.

Popular: Books in this section explain important concepts without requiring much scientific knowledge. Inparticular, they are careful to avoid math! (Many authors believe that each equation in a book cuts thereadership in half.)Carroll, S. (2005)Endless Forms Most Beautiful.

Chaboyer, B., "Rip Van Twinkle"; Scientific American, May, 2001, p44-53.Dawkins, R. (1987) The Blind Watchmaker.Guth, A. (1997) The Inflationary Universe.Hawking, S. (1988),A Brief History of Time.Hazen, R. (2005) Genesis, The Scientific Quest for Life's Origin.Hogan, Kirshner & Suntzeff, "Surveying Space-time with Supernovae"; Scientific American, Jan 1999, p46-Hu & White, "The Cosmic Symphony"; Scientific American, Feb, 2004, p44-53.Lederman, L. (1993), The God Particle.Primack & Abrams (2006), The View From the Center of the Universe.Ricardo & Szostak, "Life On Earth"; Scientific American, Sept, 2009, p54-61.Riess & Turner, "From Slowdown to Speedup"; Scientific American, Feb, 2004, p62-67.

Riordan & Zajc, "The First Few Microseconds"; Scientific American, May, 2006, p34A-41.Strauss, M., "Reading the Blueprints of Creation"; Scientific American, Feb, 2004, p54-61.Turner, M., "The Universe"; Scientific American, Sept, 2009, p36-43.Weinberg, S. (1993), The First Three Minutes.Wilczek, F. (2008), The Lightness of Being.Wills & Bada (2000), The Spark of Life.(Large libraries have collections of Scientific American. Back issues can be ordered at www.sciam.com for$10.95 each, including S&H.)

Professional: The following are highly technical books, included in case you want to explore a subject indepth. They are the closest you can get to the actual Book of Nature.

Clayton, D. (1983),Principles of Stellar Evolution and Nucleosynthesis.Gilbert, S. (2006),Developmental Biology.Peacock, J. (1999), Cosmological Physics.Ridley, M. (2004), Evolution.Stryer, L. (1995),Biochemistry.Weinberg, S. (1972), Gravitation and Cosmology.

Beware of False Prophets!

There are some popular books that were written by "scientists" to promote creationism and deny evolution. Jlike in Galileo's time, the religious establishment is fighting to hold on to authority. About half the people inthe USA believe that the world was created 6000 years ago in essentially its present form; these people will

fight any new idea that threatens their beliefs, and they are frightened by evolution, fossils, and cosmology.There are also people with some scientific credentials who write books just for the money; they make a bigthing of long-settled "paradoxes" like Schrodinger's cat and Bell's Theorem and generally just rehash outwornideas. It is often hard to recognize trash like this because it is well-written and contains a lot of correct mater

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