home | index | units | counting | geometry | algebra | trigonometry & functions | calculus
analysis | sets & logic | number theory | recreational | misc | nomenclature & history | physics

Not-so-Final Answers
© 2000-2014   Gérard P. Michon, Ph.D.

The Unexplained

The most beautiful thing we can experience is the mysterious.
 Albert Einstein (1879-1955)
 The  Initial Mystery   that attends any journey is:
How did the traveler reach his starting point in the first place ?

 Louise Bogan (1897-1970)   Journey Around My Room
 I would rather have a miserable ape for a grandfather than a man
[who employs his great]  faculties and influence for the mere
purpose of introducing ridicule into a grave scientific discussion.

 Thomas H. Huxley (defending Darwin against the bishop of Oxford)
 When you have eliminated the impossible,
whatever remains, however improbable, must be the truth
.
Sherlock Holmes in  The Sign of the Four,  ch. 6   (1890)

Articles previously on this page:

Related articles on this site:


Related Links (Outside this Site)

UC Museum of Paleontology (UC Berkeley): The History of Life.
3000-Year-Old Microbes in Antarctic Lake Vida (NSF-OLPA Press Release).
 
Introduction to Epistemology by Francis Heylighen (Vrije Universiteit Brussel).
The Skeptic's DictionaryStrange Beliefs, Amusing Deceptions & Dangerous Delusions.
Science Frontiers: The Unusual & The Unexplained (bimonthly newsletter).
13 things that do not make sense.  by  Michael Brooks  (New Scientist).
Ancient Mysteries and Lost Cities in Dr. von Zuko's Mysterious Planet.
Mysteries of the Universe in MSNBC News "Science & Technology".
Anomalies and Alternative Science: Open Directory Project (DMOZ).
Science > Physics > Alternative   (Google Directory)   |   Other Links
Fortean Times   |   The Anomalist   |   SIS - Catastrophism   |   James Randi
Metrological Coincidences
 
The Highest Energy Cosmic Rays   |   The Very Highest Energy Cosmic Rays

Videos :

Origin and Evolution of Life in the Universe  by  Carl Sagan   (Cosmos, 1980)
Is Evolution Predictable?  by  Richard Dawkins  (Culham, 2012-02-28)

 
border
border

Mysteries.  The Frontiers of Science (and Beyond).


(2002-10-02)   The magnetic field of the Earth :
What's its origin?  How does it change over time?  Why?

Einstein once remarked that the origin of the Earth's magnetic field was one of the greatest mysteries of physics.

The magnetic field of the Earth is not quite dipolar, but the dipolar component is dominant.  The so-called magnetic poles of the Earth are the intersections of the dipolar line [the axis of symmetry of the field's dipolar component] with the surface of the Earth.  Curiously, the poles of magnets (including compass needles) have been named according to which magnetic pole of the Earth they would point to.  This implies that the North Magnetic Pole of the Earth has the same polarity as the south pole of a regular magnet.

There cannot be any ferromagnetism deep inside the Earth because it's too hot there:  Iron loses its usual magnetic properties at the Curie Temperature of 1043 K (about 770°C or 1418°F).  Instead, the magnetic field of the Earth may be due to some kind of dynamo effect (there's no significant magnetic field around Venus which seems to rotate too slowly to produce a similar effect).

 Come back later, we're
 still working on this one...

References:

  • Fatal Attraction
  • Ronald T. Merrill, Michael W. McElhinny, Phillip L. McFadden
    "The Magnetic Field of the Earth"   Academic Press,
    San Diego, CA © 1983, 1996, 1998.  ISBN 0-12-491246-X.
 

(2002-11-11)
How do new life structures appear?

The basic mechanisms of the evolution of species are now well understood.  Normally, the so-called gene pool of a given species is larger than the number of genes of a given member of the species.  If one gene gives a particular advantage to the survival of its bearer, it will tend to be more frequent among individuals that have survived long enough to reproduce.  The frequency of such a gene will therefore increase from one generation to the next until most members of a species carry it.  This is the idea of natural selection first advocated by Charles Darwin (1809-1882), whereas the broader idea of the evolution of species is a much older concept (known to the ancient Greeks).  If a sudden change in the environment makes a gene essential to individual survival, it may even be the case that all members of a new generation will end up carrying the life-saving gene.

This is what happens among insects when a new insecticide is massively introduced:  The so-called susceptible insects are eradicated but there may be a few resistant individuals whose descendants will multiply at an increased rate to fill the space vacated by a much higher mortality rate among the rest of the species.

The richness of the gene pool is thus essential for species to respond to new threats.  This richness is depleted when a gene is "used" in response to an actual attack (as the "better" gene completely replaces alternate choices) but the gene pool is also replenished by random mutations, which occur at a very slow rate due to rare errors in genetic duplications (which may be induced by cosmic rays, or other violent causes at the molecular level).

Even in the absence of drastic environmental changes, the above evolutionary mechanism allows species to become better adapted and/or more competitive with other species in the same niche.  Some species keep winning the survival race for millions of years, others become extinct much faster.

Quite a few drastic "inventions" have occurred in the evolution of life on this planet of ours.  Some of these are so radical that it may be hard to rule out the existence of something more potent than the above evolutionary process.  For now, however, we may have no other solution but to believe (rightly or wrongly) that, given enough time, unlikely events do occur and may help generate previously unknown innovations.  First among these mysterious innovations is the appearance of life itself from a prebiotic environment.  We discuss this in the next article;  a few other deep life mysteries are listed below:

Homochirality

All biological molecules are skewed in only one of two possible ways.  Nucleotides are righthanded, amino acids are lefthanded.  Although artificial synthesis can produce both handedness in equal proportions, only one form of glucose  (dextrose)  is produced or consumed by living organisms.

The physical laws that are relevant to chemistry do not distinguish between left and right  (only the  weak nuclear force  does that and it seems completely unable to influence the chirality of chemical reactions).  However, the dominant chirality of food would so potently favor the lifeforms can consume it that other types of lifeforms would soon be eradicated  (if they had managed to survive and evolve in a separate habitat).

Nowadays, life exists on Earth in only one type of handedness.  This is called  homochirality.  A lone organism from outer space endowed with the wrong chirality could not survive on Earth  (except in suspended animation)  for total lack of food...

Likewise, there are many examples of physical systems that evolve from symmetrical conditions into a completely antisymmetrical situation.

Proteins Synthesis

Nucleus

Sex

 Come back later, we're
 still working on this one...

Symbiosis and Endosymbiosis

Lichens are, in fact, the mutually beneficial association of two organisms a fungus (called mycobiont) and a cyanobacteria (called photobiont).

The fungus provides minerals, moisture and protection from overexposure to sunlight, whereas the photobiont is able to photosynthesize organic food from the carbon dioxide in the air, even when no other food supply is available.  This type of association is known as a symbiosis; it allows at least one of the constituents to live under conditions where it could not survive by itself.  Not all types of symbioses are mutually beneficial, but most of them are.

Note that a lichen's photobiont is often described as an alga in most introductory presentations, which are clearly unduly influenced by the fact that cyanobacteria are still called "blue-green algae" in spite of the fact that these photosynthetic prokaryotes are not algae at all...

There is an even closer form of symbiosis, called endosymbiosis, which is exemplified by all higher life forms, including you and me.  Each of our own cells harbors a number of mitochondria, which are (like blue-green algae) an elementary form of bacteria lacking a nucleus.  Human cells could not function without them, and human mitochondria only reproduce within a human cell...  However, mitochondria have their own genetic material (a single chromosome containing a circular strand of DNA) and their replication is independent from the replication of the rest of the human cell which harbors them  When a human cell divides, after replicating its nucleus, about half of the mitochondria in it will go into each new cell and they will reproduce there, as needed.  As human tissue grows, the mitochondrial population within its cells grows as well.  When a human egg is fertilized by sperm, it so happens that the male mitochondria remain in the sperm's tail, which never enters the egg.  Therefore, all mitochondria in a human embryo will be the same as the mitochondria present in the cells of the mother.

Mitochondrial DNA (often abbreviated mtDNA) is thus inherited from mother to daughter in an asexual way.  As the evolution of mtDNA is only subject to slow mutations over time, it has been shown that all human maternal lineages have died out, except one...  Therefore, all humans are descendants of a single woman (called the "mitochondrial Eve") who lived about 200 000 years ago.  She probably lived in Africa, because the mtDNA of African populations shows more variation than what is observed on other continents:  This suggests that the descendants of "Eve" lived exclusively in Africa for a long period of time before migrating to other regions.  This is the basis of what's now known as the "Out of Africa" theory.

Neanderthals became extinct (and/or were exterminated by our Cro-Magnon ancestors) about 30 000 years ago.  Mitochondrial DNA from their bones showed that their species was clearly separate from our own.  They are not our ancestors, contrary to what was previously thought, and we did not interbreed.


(2002-10-06)   Origin of Life   (Abiogenesis, Autogenesis)
When did life appear on Earth?  How?

The Solar system itself condensed in a rather short time [a few million years] out of interstellar gas and debris from nearby explosions of an earlier generation of stars, in which heavier atomic nuclei where synthesized (including some radioactive ones which have been decaying ever since).  The age of the  nucleosynthesis  of the stuff which made the Solar system can be precisely estimated from the current isotopic abundance of some key radioactive elements found on Earth and in extraterrestrial rocks.  Such methods indicate consistently that the Earth  (and the other solid bodies of the Solar system)  formed about 4.55 billion (4550 000 000) years ago, give or take 50 million years or so.

(2014-02-23)   The Earth crust formed shortly thereafter but very little of the earliest formation survived recycling.  As of today, the oldest reliably dated crystal  (by John W. Valley et al.)  is a tiny zircon grain, collected in 2001 from a rock outcrop of the Jack Hills  (Western Australia).  It's  4.4  billion years old.

The main fossil record goes back  only  to the so-called Cambrian explosion, about 600 million years ago, which marks a date when there was a burst of new life diversification, from an earlier epoch of bacterial life.  In fact, huge bacterial colonies have produced layered rocks (stromatolites) which have been found to be as much as 3.5 billion (3500 000 000) years old, in western Australia.  There are also preserved imprints of ancient bacteria in solidified mud (called microfossils) which have been found in rocks of about the same age.  This earliest fossil record indicates a degree of diversification which implies that bacterial life had already been evolving for quite a while.  This is confirmed by some older carbon deposits (dated to be about 3.85 billion years old) which show an enrichment in carbon-12, normally attributed to the presence of life forms.  On the other hand, it's unlikely that life could have appeared in the first 500 million years of the Solar system:  The young Earth was still too hot and was constantly bombarded by large asteroids (at a rate probably sufficient to sterilize its entire surface).  Therefore, life on Earth appeared 3.9 billion years ago, give or take 100 million years or so...

The early atmosphere of our planet had virtually no free oxygen in it  (resembling what's today the atmosphere of Titan).  Surprisingly enough, to the first life forms which evolved in that environment, oxygen was then a poisonous gas.  (It has been established that sulfur, not oxygen, was the key oxidizing element 2.45 billion years ago.)   Cyanobacteria This changed only at the halfway mark, about 1.8 billion years ago, when massive quantities of free oxygen finally appeared in the atmosphere, because of the ubiquitous presence of cyanobacteria (which are also known as "blue-green algae", although there are not algae at all).  The proportion of oxygen in the atmosphere went from much less than 1% to the current level of 21% or so (by volume).  Earlier life forms had to evolve into revolutionary organisms adapted to this new oxygen atmosphere.

The appearance of oxygen in the atmosphere also allowed the formation of the so-called "ozone layer".  (This is, in fact, not a "layer" at all.  The term comes from the fact that the presence of ozone throughout the upper atmosphere is traditionally measured in terms of what the thickness of an equivalent layer of pure ozone would be at sea-level.)  This important UV shield made it safe for life to move to shallow waters and, eventually, establish itself on dry land.

Before all this happened, the Earth was exclusively populated with anaerobic bacteria, called archaea (the term archaeobacteria is being deprecated).  A few of these survive to this day in oxygen-free environments, but they are so different from other living things that they form one of only three "domains" underlying our  current classification of life  ("domains" are more fundamental than "kingdoms").

 Come back later, we're
 still working on this one...

Viruses are simple infectious agents consisting of genetic material (RNA or DNA) surrounded by a capsid (a protective coat of protein).  A virus is not usually considered a life form since it cannot normally reproduce outside of the living cell it infects.  However, there does not seem to be universal agreement on this definition and viruses are sometimes considered "alive".  So are even simpler structures capable of self-replication using the same basic mechanisms as ordinary living organisms.  One of the simplest such things consists of a strand of RNA containing only 220 nucleotides and known as Spiegelman's Monster.  It was first obtained by the American microbiologist Sol Spiegelman, at the University of Illinois, by putting one of the simplest known viral forms (RNA with about 4500 nucleotides) in an environment containing free nucleotides and replicase.  Under such conditions, smaller mutants tend to replicate faster and will crowd every other viral life out of existence, until a better and smaller mutant appears.  This selective process repeats until the appearance of some minimal self-replicating RNA strand, like Spiegelman's monster, whose mutants are either too large to compete or too small to even "recognize" the replicase (which makes them effectively "sterile", so to speak)...

In 1974, the German biologist Manfred Eigen (originator of the so-called Quasispecies Model) and his coworkers ran a similar experiment, but they did not introduce a single strand of RNA into the proper uncontaminated broth.  Surprisingly enough, RNA strands appeared spontaneously which were almost as large as Spiegelman's monster (about 120 nucleotides, on average).  So, it seems that something almost alive will necessarily appear, provided the proper building blocks are put together in a relatively crude way...

In 1953, the celebrated Miller/Urey experiment proved conclusively that the most basic constituents of life (the 20 amino-acids) could indeed form spontaneously rather easily, in the presence of lightning, under the very anaerobic conditions prevalent at the surface of the young Earth.  Although this is very far from a final solution to the puzzle, this constitutes a pretty strong hint that, given enough time, some kind of broth could form naturally with all the constituents that would make the appearance of rudimentary replicating "things" more or less unavoidable.

On the other hand, the fact that the simplest "life forms" have such an apparent reproductive advantage makes one wonder why the evolution of life did not stop as soon as some random assembly of nucleotides became large enough to self-replicate.  Part of the answer is that there is more to life than replication:  The physicist Freeman Dyson has argued that the smallest self-sustaining metabolic systems must contain at least 10000 nucleotides of at least 10 different types.  This is clearly much larger than the smallest self-replicating viral "parasites" manufactured by either Spiegelman or Eigen...

Also, the favorable conditions under which such a purely reproductive advantage exists would not be expected to last long in a natural environment.  In a soup populated with doomed little monsters, there must have been some solution to the riddle, possibly in the form of a larger and more resistant mutant which was allowed to win the reproductive battle only because a slightly harsher environment did not allow anything else to multiply.  Life may thus have appeared only because of some catastrophic event which killed something that was not even alive yet.  This primordial "catastrophe" may well have been of a strange and delicate nature, though.  Could it be that a very slight change in the temperature or acidity of a warm pond brought into survival a primordial life form whose descendants are still kicking, writing and reading?  Maybe...

References


(2002-11-02)
Is there any extraterrestrial life?  Any extraterrestrial intelligence?  Anybody who could communicate with us?  Anybody who will?  Anybody who has? 
There is too much point to the wisecrack that life is extinct on
other planets because their scientists were more advanced than ours
.
John F. Kennedy  (1917-1963)

If we believe some arguments presented in the above article, life will necessarily appear under conditions that are not too different from those prevalent on the surface of the young Earth, and we must definitely give a positive answer to the first part of the question.  That's because such conditions are not so special as to prevent a repeat occurrence in each and everyone of the many planets in orbit around one of about 100 000 000 000 000 000 000 000 stars in the observable Universe, or even one of "only" 400 000 000 000 stars in our own Milky Way.

It all boils down to statistics.  A quantitative estimate was attempted in 1961 by Frank Drake (b. 1930) in the form of a formula giving the probability of existence of an advanced civilization in some random star system.  It's the product of the following factors, for which our best guessses (mostly following Carl Sagan's estimates) are indicated in square brackets:

  • [0.3] The probability that a star has a planetary system.
  • [2.0] The average number of bodies suitable for life in such a given system.
  • [0.3] The probability that life arises in a suitable environment.
  • [0.1] The probability that rudimentary life evolves into intelligent beings.
  • [0.1] The probability that intelligent beings will form a technical civilization.
  • [0.0000001] The ratio of such a civilization's lifetime to the life of the star.

All these numbers are highly speculative of course, but none is as critical as the last one, which says essentially that a technical civilization (like the one we are in the process of building) could not possibly last much more than 1000 years before it self-destructs, with little or no hope of renewal before the host star dies.  This time frame could be a gross underestimate, but it could also be quite optimistic (think about it)...  Well, if we put any trust at all in the above speculations, the probability that a random star currently harbors a technical civilization could be somewhere around 1 in 5000 000 000.  This would translate into no more than about 80 star systems harboring a technical civilization right now, in the entire Milky Way galaxy.  None of these would be expected to be anywhere within reasonable range [a few hundred light years, say] even if we have been very pessimistic with that critical last number. On the other hand, if the above is somewhat optimistic, we could even be the only "advanced" civilization in this galaxy of ours.  (We may as well discard the billions of advanced civilizations which are surely in other galaxies, because any form of contact is ruled out over intergalactical distances.)

However, there is one other interesting possibility discussed at length by the late Carl Sagan and others, which says that a sufficiently advanced civilization could have wise [green?] men in its midst who would forecast impending doom and [maybe] have the talent to convince their comrades to work unselfishly for the survival of their species and their culture.  Their advanced technology would be used to send colons to nearby suitable star systems as soon as they achieve the possibility of interstellar spaceflight.  If that's the case, it could take the colons only a few centuries to multiply on a new planet and build the resources to embark a few of their own on another successful star-hop, preciously keeping the knowledge to do so and expanding on it between hops.

Work out the math:  If this idea is sound, it must have occurred to a few of the many advanced civilizations that have been around in the past few millions years (surely, we're not the first to achieve our current state, and think about what we'll be able to do in just one more century).  Some of them must have been spawning rapidly for millions of years and hundreds or thousands of successive generations of colons.  They should be everywhere by now.  So much so that colons from many different lineages should be scouting suitable worlds like our own very regularly.  The Earth should have been colonized by a technically advanced civilization at a time when the dinosaurs where still around. Maybe even earlier.  This did not happen.  Why?

Like Carl Sagan, you may enjoy speculating about the many possible reasons which could make this scenario unlikely.  Don't let me spoil your fun.

One of many explanations, however, is that some of the above guesses for the parameters of Drake's Formula are grossly overestimated.  For example, George Wetherhill ran computer simulations in 1992 which seem to indicate that a dominant outer planet the size of Jupiter reduces by a factor of at least 1000 the probability that major bolides would hit inner planets capable of harboring life.  If major extinctions had occurred on Earth every 26 000 years instead of every 26 million years  (as the fossil record discussed next indicates)  we would not be here to discuss anything...  So, a huge outer planet like Jupiter might well be absolutely necessary.

Also, a potential life-supporting planet may well need substantial tides to enrich its coastline chemistry in order to allow the emergence of life.  A satellite like the Moon may thus be needed too...

As a result of these and other factors, it could very well be that it's only a rare galaxy that has ever harbored a civilization capable of interstellar travel.  Our Milky Way doesn't appear to be among those yet, and it may never be unless we get our own act together...

Is the Universe Full of Life?  Panel discussion hosted by  Robert Kuhn  (USC, 2008)  27 min 42 s.


(2002-12-01)   Nemesis: The Sun's lethal companion?
Is there a periodic pattern to mass extinctions of species on Earth?
Could a distant companion of the Sun ["Nemesis"] explain this?
 Apparent Period of 26 Ma

Around 1983, the two paleontologists David Raup (1933-)  and Jack Sepkoski (1948-1999)  put together what was then the largest collection of data ever assembled about the extinctions of families of marine life.  Summarizing their work with a graph similar to the one at right, they observed that the peaks in the rates of extinctions tend to occur with a period of 26 million years or so (corresponding to the arrows shown in the graph).  In fact, a set of arrows spaced about 26 millions years apart would fail to point to an extinction peak in only two cases.

This is quite puzzling, because at least two of the last three mass extinctions are firmly linked to the impact of a large asteroid crashing into the Earth.

In particular, Luis W. Alvarez (1911-1988; Nobel 1968), Walter Alvarez, Frank Asaro and Helen Michel showed beyond a reasonnable doubt, in 1979, that the extinction which wiped out the dinosaurs at the end of the Cretaceous ( 65 milion years ago) was due to the impact of a large asteroid  [dubbed Chicxulub or Chixalub ]  in the Yucátan peninsula.

A priori, major asteroid impacts would be expected to be random events, not subject to any kind of periodicity.  Most of the asteroids that could impact the Earth or other planets have already done so, when the Solar System was young.  Major impacts in the mature Solar System are rather rare.  However, it is conceivable that the sufficiently close approach of a large enough body [a star or a brown dwarf] could upset the delicate balance of solar orbits and send some asteroids into new random orbits, not yet "time-tested" for staying clear of the Earth's path.  This could significantly increase the probability of impacts for a few million years...  The observed periodicity of extinctions due to impacts could then be explained if we assume that the "large body" is, in fact, a not-too-distant companion to the Sun and that the two bodies are in a very elongated orbit around each other, with a period of about 26 million years.  Also, our reservoir of comets (the so-called Oort cloud) is very large and would undoubtedly be deeply affected by such a close approach, sending a steady shower of comets through the normally peaceful inner solar system.

Rich Muller (b. 1944) and others have dubbed "Nemesis" this hypothetical companion of the Sun, after the daughter of Night, the Greek goddess of retributive justice and inescapable divine vengeance, whose name is commonly used to denote a formidable foe and/or the source of impending doom. 

Assuming the mass of Nemesis to be much smaller than the Sun's, the "observed" period of 26 million years implies that Nemesis would be at an average distance of about 1.4 light-years (about 1/3 of the way to Proxima Centauri, the closest known star).  However, since the orbit must be a very elongated ellipse, the maximum distance of Nemesis would be almost twice as large, and the current distance would be close to that maximum, namely 2½ light-years or so.

If we take into account the mass M of Nemesis (expressed in solar masses), the above distances should be multiplied by the cube root of (1+M).  This amounts only to a 3% correction if Nemesis is 10 times less massive than the Sun, whereas distances would be 26% larger if Nemesis and the Sun have the same mass, in which [unlikely] case the maximum distance of Nemesis would be about 3½ light-years.

Little else is known about this Death Star, whose gravitational disturbances could increase periodically the probability of major destructive impacts on Earth.

Conceivably, Nemesis could also drag its own cloud of asteroids and/or comets, but they would not be as likely to impact the Earth as solar objects with disturbed orbits:  An extrasolar body passing through the Solar System has only one [minute] chance of hitting the Earth, whereas a solar object could have many similar opportunities (one per orbit, essentially)...

It has also been observed that the known extinction impacts have left iridium-enriched clay boundaries in the geological record, which have isotopic ratios matching those of the Earth's crust.  This is a very strong indication that the impacting bodies originated within the Solar System.  However, this evidence alone would be inconclusive to rule out asteroids from Nemesis, which may not be distinguishable at all from their solar counterparts, since Nemesis and the Sun could well have formed together about 4.5 billion years ago (as a single binary system).  Although the gravitational pull of passerby stars would not allow a very elongated orbit to remain stable for much more than a billion years or so, the actual orbit of Nemesis could very well have evolved from a rounder and more stable orbit into a very elongated and relatively unstable one (which could still last for another billion years, before the Sun and Nemesis drift apart permanently).

The Search for Nemesis

As a brown dwarf more than 2 light-years away, Nemesis could easily have escaped detection up until now.  Alternately, it could have been observed already but its close distance (high parallax) would not have been recognized yet.

Astronomers call "proper motion" the tiny angular speed which makes a nearby star move, over a period of years, against the background of distant objects.  Unlike most close stars, Nemesis would have a low relative speed and, therefore, low  proper motion.  At first, it could be mistaken for a distant object.

If/when a potential Nemesis candidate is found at the correct distance, its speed relative to the Sun should also be considered to establish the actual orbit.  For example, consider our closest known stellar neighbor, Alpha Centauri, which would be a suprisingly good Nemesis candidate, if it was not for its high speed relative to the Sun, which indicates that it's not even gravitationally bound to it:

Alpha Centauri (also known as Rigil Kent) is actually composed of 3 stars: a-Centauri A is 9% more massive than the Sun, and it's tightly bound to a-Centauri B, which is 10% less massive than the Sun.  The third star, Proxima, is a red dwarf (only 15% of the Sun's mass), which happens to be closer to us than any other known star.  Proxima is much younger than the other two and it may not be gravitationally bound to them.  For the sake of this argument, however, we'll assume that it is, and we shall considerer the whole thing as a single body of about 2.14 solar masses at a distance of about 4.40 light-years (according to the latest Hipparcos data for the A and B components).

An object of 2.14 solar masses which reaches a maximum distance of 4.4 light-years in a very elongated orbit would have an orbital period of about 29 million years, which is surprisingly close to the extinction periodicity we're after (anything between 26 and 35 million years would do).  However, Alpha Centauri cannot be Nemesis, because its relative speed is not nearly low enough for an object in elliptical orbit at that distance, as shown in the next paragraph.

The yearly proper motions involved are 3.7096" for the A star, 3.7241" for the B star, and about 3.7086" for their center of mass (we're ignoring Proxima in this computation).  At a distance of 4.4 light-years, this corresponds to a transverse speed of about 23.7 km/s.  In addition, the average blueshift of the light from Alpha Centauri indicates that it approaches the Sun at a radial speed of about 22 km/s, so its total speed, relative to the Sun, is about 32 km/s.  Way too fast!  If Alpha Centauri and the Sun were actually in any kind of elliptical orbit around each other, that speed should be less than 0.4 km/s (much less if they were near maximum separation, in the hypothetical case of an elongated orbit)...

On 2005-06-04, Bill Yeung wrote:
I accidentally read your writing about Nemesis online while I was setting up my robotic telescope in New Mexico.  I have to admit, after researching this project for one year, that your writing reflects very much what I have been thinking.
 
I am a Canadian amateur asteroid hunter who has discovered more than 2000 asteroids over the last few years.  I am in the process of designing a parallax survey to see whether Nemesis exists or not.

In 1986, Saul Permutter (b. 1959) earned his Ph.D. under  Richard Muller  for a doctoral dissertation entitled  An Astrometric Search for a Stellar Companion to the Sun  where he describes the search for  Nemesis.

Perlmutter went on to earn half the 2011 Nobel prize in Physics for work establishing that the Universe expands at an accelerating rate  (the other half of the prize was split between  Brian P. Schmidt  and  Adam G. Riess  for their own work on the same revolutionary topic).

Another Tentative Explanation, Without a "Death Star":

At least one other mechanism exists which could disturb periodically the outer fringes of the Solar System and increase the number of solar bolides that hit the Earth:  The Sun goes full circle around the Galaxy in about 240 million years, but it oscillates "up" and "down" through the Galactic plane with a period of only 66 million years (and an amplitude of 250 light-years on either side).  This means that the Sun traverses the Galactic plane every 33 million years or so.  Whatever drives this very oscillation [ordinary matter or exotic dark "stuff"] could be more concentrated near the midway point (which we went through about 2 million years ago) and may be causing severe gravitational disturbances in the outer Solar System with a periodicity that's roughly consistent with mass extinctions...

One problem with this Galactic explanation concerns the phase of the extinction "cycle":  We seem to be currently near a trough, not a peak...

References:

  • Nemesis Page of  Dr. Richard A. Muller  (of UC Berkeley and LBL). 
  • Online article by Lynn Yarris (Spring 1987.  LBL Research Review). 
  • Online article by Robert Roy Britt (2001-04-03.  Space.com). 
  • "Cosmic Terrorist" & "I Think I See It" by Richard Muller (1944-),
    in "The World Treasury of Physics Astronomy and Mathematics"
    Edited by Timothy Ferris.  Back Bay Books (1991).
    New York, NY.  ISBN 0-316-28133-6.   pp. 261-271. 
  • "The Solar System Has Two Suns", Chapter 6 of
    "Nine Crazy Ideas in Science" (2001) by Robert Ehrlich (1938-)
    Princeton University Press.  ISBN 0-691-09495-0.   pp. 102-121


(2002-10-02)
What are some of the latest challenges to established scientific dogma?

It is a healthy scientific practice to question established principles.

Revolutionary science may come from such challenges, but very few of them are ever successful at dethroning accepted scientific wisdom.  The promising ideas listed below may still be destined to fail, but some of them could be the seeds of new science, yet to come...

 Come back later, we're
 still working on this one...


(2002-10-05)   Gentle Debunking
What are some of the most popular unexplained things?

Man's most valuable trait is a judicious sense of what not to believe.
 Euripides (c.480-406 BC)

Some of the topics listed below have probably little or nothing to do with Science.  The media and/or the general public found them intriguing at one time or another.  Impressive human artifacts whose instruction manuals have been lost (or were never written) are bound to capture our collective imagination.  So are extraordinary natural phenomena...  Have some investigative fun but please don't take "results" too seriously...

Ancient Geodesy:

Aristotle knew that the Earth was spherical.  This much can be derived from proper interpretations of basic astronomical observations (the circular shadow of the Earth in a lunar eclipse, the changing angles of celestial bodies observed from various geographical locations, etc.).  The curvature of the ocean's surface is also obvious to any sailor who has ever watched the coastline disappear under the horizon (or to anyone on the beach who has ever observed a departing sailboat disappear hull first).  Was some cryptic kind of latitude/longitude system used by some elite of an ancient civilization?  Probably not, but we may dream:
On 2006-10-05, James Q. Jacobs wrote:       [edited summary]
Try as I might, I just couldn't get the Carl Munck people to not link to me.  I don't wish to be associated with them.  If you want to debunk my research, please do so by discussing it.
James Q. Jacobs
Anthropologist/Archaeologist

Duly noted.  Allow me to limit myself to the historical record.

Numerology in Physics:

The dimensionless constants of nature are the same in all consistent systems of physical units.  In the final theory of physics (if there is such a thing), the values of all of these are expected to be expressed purely mathematically.  There has been a plethora of guesses about what such expressions might be.  Invariably, such guesses have been invalidated by sufficiently precise new experimental measurements.  This has not stopped people from making new guesses based on the latest measurements, so we have many proposals for the following dimensionless physical constants which are not yet invalid...
  • Ratio of gravity to electrical force between electrons:   » 2.4´10-43. 
  • Sommerfeld's Fine Structure Constant:   a » 1 / 137.036. 
  • Weinberg's weak mixing angle :   qw » 28°.  [Defined here.]
  • Equivalent of the "Fine Structure Constant" for the strong force:   as » 1.
  • Various mass ratios:  muon/electron » 207, proton/electron » 1836   ...
  • ... ... More than 20 numbers from which the above can be derived. 
Another popular view is that there could be many equally consistent complete theories of physics in which selected values of dimensionless constants could be plugged in.  Such theories would describe widely different universes for widely different values of those parameters.  Only when the constants are finely tuned would the resulting universe permit the development of intelligent beings like us who would be able to wonder about a number of coincidences in the observed values.  Presumably, many "parallel" universes could "exist" in some sense, but there would not be any observers in them...  This type of argument is based on what is now known as the anthropic principle.  If the ultimate explanation for our own Universe is purely anthropic, there can't be mathematical expressions for all dimensionless constants of physics (it would still be a blessing to discover mathematical relations between some of them).

Ball Lightning

A very popular subject.  It's highly unlikely that any new physics is involved in this well-documented class of not-so-rare phenomena.  There's a vast uncharted territory out there, populated by many strange objects allowed by the most ordinary laws of physics...

Spontaneous Human Combustion (SHC)

There's no such thing as a live person spontaneously catching fire.  You have to look elsewhere for a proof of the existence of the Devil.  There have been, however, a number of documented instances of incapacitated (or dead) people who literally burned like candles when their clothing was set on fire by some heat source or open flame.  The clothing acted as a wick and body fat was the fuel.  In a few such cases, there was little or no fire damage around the poor soul and the legend was thus born of some weird phenomenon that would "spontaneously" turn a human being into ashes and smoke.

Very few chemicals are known to ignite spontaneously.  One of them is a gas once known as "phosphuretted hydrogen" (or phosphorated hydrogen) which the young French scientist Philippe-Joachim Gengembre (1764-1838) first obtained in 1783, by heating phosphorus with potassium hydroxide (KOH).

 Lavoisier
 Berthollet
  Trained as a chemist and a metallurgist, Philippe-Joachim Gengembre (1764-1838) was a pupil of Antoine-Laurent de Lavoisier (1743-1794).  He was also a protégé of the chemist Claude-Louis Berthollet (1748-1822)  of the Finance Minister Charles Gaudin, duc de Gaëte (1756-1841)  and of the archaeologist Antoine Mongez (1747-1835) who would become Director of the Mint in 1804.  Gengembre was hired in 1795 at the Mint as "Mécanicien des Monnaies".  Napoléon promoted him to "Inspecteur Général des Monnaies" in 1803.

The gas obtained by Gengembre actually consists mostly of phosphine (also called phosphane, PH) which does not ignite spontaneously below 38°C, but it also contains some diphosphine (or diphosphane, P2H) which does and may lower the autoignition point of the mixture to room temperature.  This was explained in 1845 by the French chemist Paul Thénard (1819-1884) who obtained nearly pure diphosphine from the hydrolysis of  calcium monophosphide  (itself made from tricalcium diphosphide by reaction in an excess of white phosphorus):

2 CaP  +  4 H2O     ®     2 Ca(OH)2  +  P2H4

In 1876, a patent for sea flares was awarded to a British telegraph engineer by the name of Nathaniel John Homes, who realized diphosphine from the above reaction could ignite acetylene gas produced by hydrolysis of calcium carbide:  A mixture of CaP and CaC2 produces a bright flame upon contact with water.

CaC2  +  2 H2O     ®     Ca(OH)2  +  C2H2  +  458 kJ
C2H2  +  5/2 O2     ®     2 CO2  +  H2O  +  1256 kJ

Phosphine is clearly produced in the advanced putrefaction of cadavers, and some diphosphine was found in fermentation experiments with human fecal bacteria.  Although we're not aware of any documented instance, it's thus not entirely impossible for a decaying human cadaver to ignite spontaneously, but this seems extremely far-fetched for a live person, or a recently deceased one.

Crop Circles

Why some people enjoy trampling somebody else's crop is indeed a mystery.
border
border
visits since Oct. 2, 2002
 (c) Copyright 2000-2014, Gerard P. Michon, Ph.D.