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The Astronomy Cafe and Back to the Astronomy Cafe

Sten Odenwald (1998, 2003)


How do astronomers know that Earth had a different rotation period long ago?
Geologists discovered sedimentary tidal deposits near ancient coastlines dating from about 750 million years ago, and the layering sequence of the sediments could be traced in the rock. By counting the layers during a particular dating sequence, they deduced that Earth was rotating about once every 18 hours. There is an article about this by astronomers from the University of Arizona in the July 5, 1996, Issue of Science. By studying the laminations in tidal sediment deposits from Utah, Indiana, Alabama, and Australia, they found that some 900 million years ago the day was only 18 hours long, and there were 481 days to the year. (45)

Was Earth almost hit by an asteroid on March 23, 1989?
Yes. There was a near miss that went unnoticed because the Moon was so bright that the asteroid was lost in the glare. The object was discovered by astronomers eight days later and cataloged as 1989 FC. . . . Had it hit, we would have had a crater bigger than the Barringer Meteor Crater in Arizona. . Many cattle and sheep would have died. (56)

What existed in space prior to the big bang?
Again, we do not know whether this question has a meaningful answer. Many cosmologists feel that it is very much like asking how many angels can dance on the head of a pin. It sounds like a sensible question, but in fact its physical basis and foundation may be utterly lacking. Einstein's theory of general relativity, our premier theory of how gravity works, tells us that in the cosmological setting the concepts of time and space did not preexist the big bang. The big bang is seen as the defining event that created space, time, matter, energy, and gravity. You cannot ask what happened before the big bang because this state was both timeless and spaceless and lacked the concepts of "before" and "place." This is serious business and not just some stupid semantic game of hopscotch played by astronomers and physicists. (125-6)

Why did nature produce a big bang at all?
We honestly do not know. The problem seems to be that we live inside the universe, and even if the big bang is an event that occurs with a probability of one chance in 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000, we who live inside this rare event will perceive it as having a likelihood of one chance in one, by the mere fact that we exist. (133)

If the universe expanded from the size of a grapefruit to the size of the solar system by 10-10 seconds after the big bang, was matter traveling faster than light?
All, the wonders of relativity! According to general relativity, it wasn't the matter that was moving faster than light but the distance between various points in space that was increasing faster than light. No matter actually made the journey from one point to another at translight speed. In general relativity, space is free to do things that matter cannot, and one of these is to cause the distances between galaxies to increase without the galaxies themselves having enough time to traverse the distance. We do not like to think of this possibility, because we never see such things happen in our nonrelativistic world, and we have never had the pleasure of developing the right intuition about it. (147)

And don't forget that the largest single constituent of the universe is empty space. Physicists and astronomers are only now beginning to understand what space is, and someday someone will write a book about this subject. (153)

What is time?
We don't really know. Physically, time is an essential parameter that we seem to need to sort out spatial configurations of matter and energy in our universe. For thousands of years, four dimensions have circumscribed how we classify and link together external events in nature. Some physicists in search of the theory of everything have suggested that, at a scale trillions of times smaller than a proton, many more dimensions are needed to mathematically sort out how particles interact and account for the various patterns seen at these scales. Like the numbers we throw away in long division to get our answer, we don't really know if the hidden dimensions in the mathematics of quantum field theory are real or just bookkeeping tricks we need to carry out our calculations with the theory. (161-2)

Although given the galaxy's current appearance, this possibility is unlikely, the supergiant star Betelgeuse in the constellation Orion may already have gone supernova, but we won't know for another 1,500 years. (163)

I find myself increasingly in the role of Scrooge, having to throw massive amounts of cold water on the speculations of several generations of Star Trek followers. I really hate this part of science popularization, because it always seems to pit science against our most cherished dreams about what the future could be like. (174)

Has anyone ever had sex in space?
Not that I have heard. Then again, who would tell? There are cryptic rumors about something called the Three Dolphins Club but no official word on whether any human experiments have ever been attempted or even sanctioned. (251)

Have you ever seen or heard something you could not explain scientifically?
Yes. In a remote canyon in Yosemite Valley near Merced Lake, California, I was fixing dinner after a long hike, when in the distance I saw a thunderstorm approaching. It never passed overhead, but the eastern horizon was pretty cloudy. Then, in the distance and seemingly out of nowhere, I heard a pair of deeply resonating, low tones, about two octaves below middle C and about a semi tone apart. The sound switched between the two tones about four times, then stopped. I imagined that winds from the storm may have excited some kind of resonance in something but could never figure out what. The effect was captivating and absolutely eerie. I did not sleep very well that night, given my penchant for an overactive imagination. (188)

It is well known that humans believe what they wish to despite any reasonable evidence, especially if what they experience meshes with some prior belief in how the world ought to work. We selectively remember events that reinforce our prejudices and ignore contrary evidence. This is why astrology is still believed to be valid by billions of people around the world, even though every study shows that it doesn't work any better than flipping a coin. (189)

Can we see any of the Apollo artifacts left on the Moon from Earth?
Not a chance. Even using the Hubble Space Telescope, with a resolution of 0.04 arc seconds, at the distance of the Moon, some 224,000 miles, you could only resolve objects 230 feet across. (193)

Is everything you see with a small telescope a part of our Milky Way galaxy?
All of the bright stars, star clusters, and nebulas in the night sky are part of the Milky Way. Only the occasional faint smudge of a galaxy, such as Andromeda, or the Magellanic Clouds can be seen beyond our Milky Way and are separate systems of stars in the universe. Quasars are starlike objects, but the brightest one is 3C273 at a magnitude of + 13, which is too faint for most amateur telescopes to see. (193)

Do I have to be another Einstein to be an astronomer?
No, but it would help when you go for tenure! Seriously, you do not have to be an Einstein in absolute terms, but the catch is that, as viewed by nonscientists, you do have to appear to be nearly as brilliant. As for any career, your skill and competency are determined by how much raw information you have been able to accumulate and the skill that you have in manipulating this knowledge. In astronomy, you have to be fully competent with a vast body of basic facts. In addition, there are [sic] an equally vast array of tools you must have at your fingertips to enable you to figure out the physics of what you are observing. This latter resource can only be acquired via the textbook and lab approach as an undergraduate and graduate student. Sadly, there are lots of people out there in the world who think they can short-circuit this learning process and get right into crafting theories of the universe. They are wasting their time, just as they would be if, after reading one page of the business section of a newspaper, they thought they could run a bank or plot the economic future of an entire country. Good intentions and enthusiasm are simply not enough currency to become a competent, professional astronomer with a shot at a long-term career. (223-4)


In 1997, astronomer Martin Rees in his popular book Before the Beginning seems to claim that he came up with this "new concept" of multiverse, but in fact this is not correct. In fact, a non-scientist came up with the term. Just as science fiction writer Arthur C. Clarke is credited with inventing geosynchronous satellites, the actual term multiverse can be credited to the work of another science fiction writer, Michael Moorcock, in his book The Sundered Worlds published by Paperback Library in 1962. Moorcock not only coined this term but also defined it in his story in a way that is identical to many of the theoretical definitions in vogue today. (23)

What existed before the big bang?
This is one of the Big Questions in modern cosmology. I think it is fair to say that we don't know for certain. (27)

Everyone eventually learns that the rotation axis of Earth is tilted 23.5 degrees to its orbit. For generations, teachers and scientists have dutifully noted this number. First calculated in the Western World by Eudoxus (400-347 B.C.), its decimal value has remained unchanged in our textbooks. (29)

Comets are a real problem, and can do nearly as much damage as asteroids. Hale-Bopp is one of the largest and is about 30 miles across. We knew about it many years before it dazzled our skies, because it was big enough to be tracked beyond the orbit of Mars. Had it been on collision course with Earth there is absolutely nothing we could have done about it. This is serious business, and the extent to which we all live on a knife-edge in relation to the devastation from these objects is very unsettling to those of us who keep track of these things. (39)

How are auroras produced?
For decades, physicists have understood the answer to this question, but text book authors, especially of grade school science books, persist in giving the wrong answer. (40)

Contrary to what you might think, when galaxies collide, it is very unlikely that even a single pair of stars would collide within the two galaxies. (137)

Did the birth of the universe violate the conservation of energy?
Yes it did. Very badly in fact. The reason this seems to fly in the face of common sense is that we have been told, mostly correctly, that energy cannot be created or destroyed. Once you measure the total energy of a system, that total stays the same as the system evolves in time. The problem we face with the universe is that this kind of definition doesn't work as well, when we have no fool proof way to actually calculate or measure this total energy. (151)

How could a quantum vacuum fluctuation produce a universe with well-ordered laws of physics, rather than complete randomness?
We don't know. It is not known just how or where the laws of physics are ultimately proscribed for our universe. One possibility is that there was/is an infinite number of alternate ways that our universe could have emerged from this quantum process. (153)

it really true that the laws of physics were randomly selected at the big bang?
We honestly do not know. Obviously for this to be a scientific statement, we will have to be able to make some kind of observation to test this proposition. No physicist or astronomer has any clue how to test such an idea; so, many physicists and most astronomers view these kinds of statements as currently beyond science. This is a polite way of saying that the idea is not scientific because it is not falsifiable, no matter what its formal basis might be either in quantum mechanics, quantum field theory, or quantum gravity theory. (153-4)

The anthropic principle says, basically, that some of the things we measure are the way they are because we are here to measure them with the values they have. (155)

What is Olbers' Paradox and how does modern cosmology resolve it?
Heinrich Olbers (1758-1840) is credited with asking in 1826 why the night sky is dark. But it is very hard to believe that he was the first human to ask this astonishingly simple question. If we live in an infinite universe, which has been around for eternity, then every line of sight in the sky should end on the surface of some distant star. The night sky should be as bright as the surface of the Sun. This "paradox" is resolved in modern cosmology because the amount of space we can observe is not infinite, and stars and galaxies have not been around long enough for all their light to reach Earth. Also, because of the expansion of the universe, the light from the most distant galaxies gets shifted into other parts of the spectrum outside the optical range, in the infrared. (159-60)

How is it possible for "nothing" to create a big bang?
This is one of those questions that may not ever have a sensible answer because we don't have theories that are powerful enough to describe the initial stages of the big bang itself. We can, at least in principal, speak meaningfully about the things that happened after the big bang, but it seems that we have nothing that we can test to give us guidance past that point. Even calling it "nothing" may not be correct. (185)

What is your main complaint about science fiction in the 21st century?
It has long since gone beyond the boundaries of science and has now become fantasy. Not even Star Trek, Babylon 5, and Stargate SG-1 make for believable reading or TV viewing based on what we know of the current universe. For example, science fiction offers us no possible future than one that also allows interstellar travel as though it were a week-long, cross-country drive. There is not one science fiction story that plausibly describes interstellar trips taking a year, or more, except perhaps the Alien movies or Lost in Space, which use cryo-sleep to freeze humans so that they sleep for years or decades. (207)

Are there sky events that should have been noticed but weren't?
The most dramatic celestial events we know about are the supernovas. In 185 A.D., there was only a single entry by Chinese observers for this dazzling star in the constellation Centaurus. G 135.4-2.3 (RCW 86) is the likely remnant of this explosion. A second supernova in 393 A.D. was also mentioned by Chinese observers within the curve of the tail of Scorpius, now identified with the young supernova remnant G 11.2-03. No other mentions of these events were found in Mediterranean or European records. The Crab Nebula supernova appeared in 1054 A.D. but was only mentioned by Chinese and Japanese observers even though its brilliance exceeded that of Venus for many months. The 1181 A.D. supernova in Cassiopeia, which formed the radio source 3C58, was also noted by Chinese and Japanese observers only. Were any supernovas seen before the 185 A.D. event? Chinese astrologers were very close observers of the heavens since 2000 B.C., but there are no records of any new "guest stars" being seen, possibly because the records are too fragmentary, or astrologers didn't pay them much attention compared to eclipses and sunspots. Meanwhile, no one has explained why European and Mediterranean civilizations between 185 and 1181 A.D. gave no indication of interest or awareness in three supernovas. (209)

If a marshmallow traveling at 99.99 percent the speed of light hit Earth, what would happen?
At this speed, special relativity says that the energy of this marshmallow equals about 100,000 terajoules. The most powerful American bomb, known as Castle/Bravo, was detonated on February 28, 1954, and released energy equivalent to an astounding 15 megatons of TNT or 84,000 terajoules. As with many uncontrolled natural phenomena, most of this energy will end up as heat, light, and sound, although there would also be tremendous ionization of the local atmosphere that would go along with this event. When you look at the energy per particle of the marshmallow, the energy is shared by 100 trillion trillion protons in the marshmallow for an average energy per particle of 10 billion volts per proton. This is more than enough energy to trigger some thermonuclear fusion and the production of gamma radiation. As for what it does when it actually impacts, it will cause a detonation equal in energy to a stony asteroid 200 yards across traveling at 20 miles/second and produce a crater nearly a mile across. (225)

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