Monday, November 24, 2008
Dark Matter Experiments
Today's New York Times features an article on some recent experimental findings that might provide evidence for the existence of dark matter. For background information on dark matter, I invite you to read one of my previous entries.
Wednesday, September 24, 2008
Friday, September 12, 2008
Physics of Usain Bolt's Sprinting
In a development that blends two of my passions -- sports and physics -- Norwegian physicists have estimated how much faster Jamaica's Usain Bolt could have run in his gold-medal and world-record 100-meter-dash performance at the recent Beijing Olympic Games, had he not slowed down toward the end.
Wednesday, September 10, 2008
Parties Celebrating LHC Opening
Last night, a number of research labs and university physics departments in the U.S. hosted parties and open houses to mark the occasion of the first beam of particles being sent through the Large Hadron Collider in Europe.
Texas Tech, where I teach in the social sciences, is one of 94 U.S. institutions participating in LHC research. Our physics department was one of those hosting an event last night, which I attended. The local newspaper did a nice article on the gathering, capturing the excitement of Texas Tech's high-energy/particle physicists.
As the bloggers at Cosmic Variance noted:
[Tuesday's] start-up is a symbolic event, not a physics event; as I understand it, the beam will only be circulating in one direction, so there won’t even be any collisions. Still, it’s a very important symbolic event! The first time the beam goes through the entire machine.
The Texas Tech gathering began with refreshments and some brief opening remarks by Sung-Won Lee, one of the physics faculty members involved with the LHC. The audience was then invited to walk around and look at various exhibits, video monitors, and computer screens, and chat individually with the physics faculty members. LHC-related pamphlets were everywhere, a couple of which I've scanned and added in collage form below (you can click on the image to enlarge it). I had some nice conversations with Dr. Lee and Dr. Richard Wigmans. After the open-house segment of the event, there were some talks by the physics faculty.
Here at Watered Down Physics, my aim is to provide non-technical descriptions of what's taking place at the LHC, among other physics concepts. The posting immediately below tells where you can find my previous LHC postings in the archives.
Texas Tech, where I teach in the social sciences, is one of 94 U.S. institutions participating in LHC research. Our physics department was one of those hosting an event last night, which I attended. The local newspaper did a nice article on the gathering, capturing the excitement of Texas Tech's high-energy/particle physicists.
As the bloggers at Cosmic Variance noted:
[Tuesday's] start-up is a symbolic event, not a physics event; as I understand it, the beam will only be circulating in one direction, so there won’t even be any collisions. Still, it’s a very important symbolic event! The first time the beam goes through the entire machine.
The Texas Tech gathering began with refreshments and some brief opening remarks by Sung-Won Lee, one of the physics faculty members involved with the LHC. The audience was then invited to walk around and look at various exhibits, video monitors, and computer screens, and chat individually with the physics faculty members. LHC-related pamphlets were everywhere, a couple of which I've scanned and added in collage form below (you can click on the image to enlarge it). I had some nice conversations with Dr. Lee and Dr. Richard Wigmans. After the open-house segment of the event, there were some talks by the physics faculty.
Here at Watered Down Physics, my aim is to provide non-technical descriptions of what's taking place at the LHC, among other physics concepts. The posting immediately below tells where you can find my previous LHC postings in the archives.
Friday, August 08, 2008
Cosmic Variance Blog Previews LHC
Cosmic Variance, a blog collaboratively run by a team of physicists, has posted a couple of articles in recent days about the Large Hadron Collider (LHC) moving closer to being operational and the prospects for what scientific discoveries might be made when its full research program gets underway.
For readers interested in non-technical background information about the LHC, I wrote an eight-part series on the topic. These writings span from May 15, 2007 to September 15, 2007; see the archives in the right-hand column of this blog, scrolling down a bit.
For readers interested in non-technical background information about the LHC, I wrote an eight-part series on the topic. These writings span from May 15, 2007 to September 15, 2007; see the archives in the right-hand column of this blog, scrolling down a bit.
Monday, August 04, 2008
Book Review: "50 Physics Ideas..."
I recently made a nice find at a bookstore's discount table, picking up a 200-page volume entitled 50 Physics Ideas You Really Need to Know, by Joanne Baker. The book actually is a quite recent release (August 2007) for it to be available at reduced price.
From Newtonian motion to contemporary topics such as the standard model of particle physics, string theory, and dark matter, 50 Ideas covers a wide range. This PDF pamphlet on the book from its publisher lists all 50 of the topics.
I've now read several of the entries. The one on Feynman diagrams is the clearest exposition I've seen of them. The (separate) entries on nuclear fission and fusion are also quite informative.
From Newtonian motion to contemporary topics such as the standard model of particle physics, string theory, and dark matter, 50 Ideas covers a wide range. This PDF pamphlet on the book from its publisher lists all 50 of the topics.
I've now read several of the entries. The one on Feynman diagrams is the clearest exposition I've seen of them. The (separate) entries on nuclear fission and fusion are also quite informative.
Sunday, July 06, 2008
Big Bang/Inflationary Cosmology VIII
To close out our series on the Big Bang and inflationary cosmology, today we discuss Alan Guth's inflation model (a similar model developed independently by Alexei Starobinsky should also be acknowledged).
As Guth writes in this MIT Physics magazine-style article, "Despite the striking successes of the big bang theory, there is good reason to believe that the theory in its traditional form is incomplete." Adds Guth:
Could the big bang have been caused by a colossal stick of TNT, or perhaps a thermonuclear explosion? Or maybe a gigantic ball of matter collided with a gigantic ball of antimatter, releasing an untold amount of energy in a powerful cosmic blast. In fact, none of these scenarios can plausibly account for the big bang that started our universe... (p. 30).
Further, as Dan Hooper writes in his book Dark Cosmos (reviewed here), "...three puzzles -- the monopole, flatness, and horizon problems -- confounded cosmologists and particle physicists" (p. 195). The major contribution of Guth's model of dramatic, early expansion of the universe (i.e., in the tiniest infinitesimal fraction of a second) is thus its ability to solve these problems that existed in the traditional Big Bang model.
To get an initial visual image of what the inflation model proposes, this diagram from NASA is very helpful. Rather than emanating outward from a single point in linear fashion (analogously to a spotlight), the universe can be seen in the NASA diagram to have widened out from the initial point very early on. Until recently, the further widening of the universe over billions of years has been relatively modest, thus yielding a timeline that looks like a wastebasket laid on its side (also see Figures 9.2, 10.3, and 10.6 in Brian Greene's book, The Fabric of the Cosmos). An "inflaton" field may be the responsible mechanism.
The first problem listed above involves what are known as magnetic monopoles. As discussed by Hooper (pp. 190-194), there exist some theories of grand unification and symmetry -- invoking Maxwell's electromagnetism -- that call for there to be charged magnetic objects (i.e., with only one pole), just as there are charged electric particles such as electrons. However, mono-polar magnets do not appear to exist. Even after breaking a magnet, each new piece will have both north and south poles.
This Wikipedia entry on Alan Guth explains his solution to this conundrum:
The reason for the missing monopoles was that the universe was so big that the density of monopoles would be very low. The “enormous number of monopoles could have risen in the inflationary universe, yet we and all other observers would find them to be observationally far rarer than snowballs in the Sahara…Inflation would spread them so thin that the average observer would expect to find only a single monopole in the entire observable universe.”
The flatness problem pertains to how amazingly perfectly the universe appears to be situated for it to exist as it does -- where any deviation could throw things askew. To use the popular "Goldilocks" analogy, the physical parameters for the shape of the universe seem to be "just right."
As John Gribbin writes in his essay Inflation for Beginners, "This is the puzzle that the spacetime of the Universe is very nearly flat, which means that the Universe sits just on the dividing line between eternal expansion and eventual recollapse." Mathematically, as described by Guth's aforementioned MIT article, the flatness problem can be characterized thusly:
Unless, however, we postulate that the mass density at one second just happened to have a value between 0.999999999999999 and 1.000000000000001 times the critical density, the theory will not describe a universe that resembles the one in which we live (p. 32).
The proposed solution is described in Guth's Wikipedia profile:
Guth realized from his theory that the reason why the universe appears to be flat was because it was fantastically big, just the same way the spherical Earth appears flat to those on its surface. The observable universe was actually only a very small part of the actual universe.
Brian Greene's balloon depictions in Figure 10.4 of The Fabric... are also helpful in understanding solutions to the flatness problem.
A third difficulty, known as the horizon problem, pertains to the extreme uniformity of the Cosmic Microwave Background. It is characterized as follows by Guth in his MIT article:
Calculations show that energy and information would have to be transported at about 100 times the speed of light in order to achieve uniformity by 300,000 years after the big bang. Thus, the traditional big bang theory requires us to postulate, without explanation, that the primordial fireball filled space from the beginning. The temperature was the same everywhere by assumption, but not as a consequence of any physical process (p. 31).
However, as noted in the Wikipedia entry:
The paradox was resolved, as Guth soon realized, by the inflation theory. Since inflation started with a far small[er] amount of matter than the Big Bang had presupposed, [there was] an amount so small that all parts would have been in touch with each other. Inflation th[e]n blew up the universe so quickly that there was no time for the essential homogeneity to be broken.
This University of Arizona document conveys the situation somewhat differently:
If the Universe just expanded in a uniform way, it would have developed large uniformities over distances where the light communication time would be too long to even them out. The observed high degree of uniformity (to about 1 part in 100,000 for the 3K radiation!) must have been locked in at an early stage and maintained since then.
I recall this idea also being discussed during an episode of the History Channel's "Universe" series, but I cannot find a transcript online.
For those interested in pursuing another concise description of the flatness, horizon, monopole, and other problems -- and their solutions -- I would recommend this University of Maryland document.
As noted above, Guth has critiqued the original Big Bang model for its reliance on assumptions rather than proposed physical processes that may have generated conditions we observe in the universe. Regarding his own model, he asserts the following in his MIT article:
The crucial property of physical law that makes inflation possible is the existence of states of matter which have a high energy density that cannot be rapidly lowered. Such a state is called a false vacuum... (p. 33).
The false-vacuum concept appears relatively complex, so I would encourage interested readers to study this section of Guth's article -- which includes some drawings -- for themselves!
Where does inflationary theory stand today, in terms of scientific acceptance?
This NASA document (different from the one cited earlier) concludes, “So inflation remains a widely accepted but unconfirmed modification to the Big Bang theory.”
As Guth writes in this MIT Physics magazine-style article, "Despite the striking successes of the big bang theory, there is good reason to believe that the theory in its traditional form is incomplete." Adds Guth:
Could the big bang have been caused by a colossal stick of TNT, or perhaps a thermonuclear explosion? Or maybe a gigantic ball of matter collided with a gigantic ball of antimatter, releasing an untold amount of energy in a powerful cosmic blast. In fact, none of these scenarios can plausibly account for the big bang that started our universe... (p. 30).
Further, as Dan Hooper writes in his book Dark Cosmos (reviewed here), "...three puzzles -- the monopole, flatness, and horizon problems -- confounded cosmologists and particle physicists" (p. 195). The major contribution of Guth's model of dramatic, early expansion of the universe (i.e., in the tiniest infinitesimal fraction of a second) is thus its ability to solve these problems that existed in the traditional Big Bang model.
To get an initial visual image of what the inflation model proposes, this diagram from NASA is very helpful. Rather than emanating outward from a single point in linear fashion (analogously to a spotlight), the universe can be seen in the NASA diagram to have widened out from the initial point very early on. Until recently, the further widening of the universe over billions of years has been relatively modest, thus yielding a timeline that looks like a wastebasket laid on its side (also see Figures 9.2, 10.3, and 10.6 in Brian Greene's book, The Fabric of the Cosmos). An "inflaton" field may be the responsible mechanism.
The first problem listed above involves what are known as magnetic monopoles. As discussed by Hooper (pp. 190-194), there exist some theories of grand unification and symmetry -- invoking Maxwell's electromagnetism -- that call for there to be charged magnetic objects (i.e., with only one pole), just as there are charged electric particles such as electrons. However, mono-polar magnets do not appear to exist. Even after breaking a magnet, each new piece will have both north and south poles.
This Wikipedia entry on Alan Guth explains his solution to this conundrum:
The reason for the missing monopoles was that the universe was so big that the density of monopoles would be very low. The “enormous number of monopoles could have risen in the inflationary universe, yet we and all other observers would find them to be observationally far rarer than snowballs in the Sahara…Inflation would spread them so thin that the average observer would expect to find only a single monopole in the entire observable universe.”
The flatness problem pertains to how amazingly perfectly the universe appears to be situated for it to exist as it does -- where any deviation could throw things askew. To use the popular "Goldilocks" analogy, the physical parameters for the shape of the universe seem to be "just right."
As John Gribbin writes in his essay Inflation for Beginners, "This is the puzzle that the spacetime of the Universe is very nearly flat, which means that the Universe sits just on the dividing line between eternal expansion and eventual recollapse." Mathematically, as described by Guth's aforementioned MIT article, the flatness problem can be characterized thusly:
Unless, however, we postulate that the mass density at one second just happened to have a value between 0.999999999999999 and 1.000000000000001 times the critical density, the theory will not describe a universe that resembles the one in which we live (p. 32).
The proposed solution is described in Guth's Wikipedia profile:
Guth realized from his theory that the reason why the universe appears to be flat was because it was fantastically big, just the same way the spherical Earth appears flat to those on its surface. The observable universe was actually only a very small part of the actual universe.
Brian Greene's balloon depictions in Figure 10.4 of The Fabric... are also helpful in understanding solutions to the flatness problem.
A third difficulty, known as the horizon problem, pertains to the extreme uniformity of the Cosmic Microwave Background. It is characterized as follows by Guth in his MIT article:
Calculations show that energy and information would have to be transported at about 100 times the speed of light in order to achieve uniformity by 300,000 years after the big bang. Thus, the traditional big bang theory requires us to postulate, without explanation, that the primordial fireball filled space from the beginning. The temperature was the same everywhere by assumption, but not as a consequence of any physical process (p. 31).
However, as noted in the Wikipedia entry:
The paradox was resolved, as Guth soon realized, by the inflation theory. Since inflation started with a far small[er] amount of matter than the Big Bang had presupposed, [there was] an amount so small that all parts would have been in touch with each other. Inflation th[e]n blew up the universe so quickly that there was no time for the essential homogeneity to be broken.
This University of Arizona document conveys the situation somewhat differently:
If the Universe just expanded in a uniform way, it would have developed large uniformities over distances where the light communication time would be too long to even them out. The observed high degree of uniformity (to about 1 part in 100,000 for the 3K radiation!) must have been locked in at an early stage and maintained since then.
I recall this idea also being discussed during an episode of the History Channel's "Universe" series, but I cannot find a transcript online.
For those interested in pursuing another concise description of the flatness, horizon, monopole, and other problems -- and their solutions -- I would recommend this University of Maryland document.
As noted above, Guth has critiqued the original Big Bang model for its reliance on assumptions rather than proposed physical processes that may have generated conditions we observe in the universe. Regarding his own model, he asserts the following in his MIT article:
The crucial property of physical law that makes inflation possible is the existence of states of matter which have a high energy density that cannot be rapidly lowered. Such a state is called a false vacuum... (p. 33).
The false-vacuum concept appears relatively complex, so I would encourage interested readers to study this section of Guth's article -- which includes some drawings -- for themselves!
Where does inflationary theory stand today, in terms of scientific acceptance?
This NASA document (different from the one cited earlier) concludes, “So inflation remains a widely accepted but unconfirmed modification to the Big Bang theory.”
Wednesday, June 18, 2008
Big Bang/Inflationary Cosmology VII
My extended series of write-ups on the Big Bang and inflationary cosmology is nearing a close. Tonight, I will write about Einstein's cosmological constant, and then later on, I'll have a piece on Alan Guth's ideas on inflation. I will sometimes use "CC" as an abbreviation for the cosmological constant, although in scientific circles it is referred to by the Greek letter lambda (Λ).
Einstein intended the cosmological constant for one purpose, then jettisoned it as a mistake after the original premise for its use was discredited. Other physicists and cosmologists later resurrected the CC, however, for use in a different context. As Dan Hooper's book Dark Cosmos explains:
Einstein... had originally introduced the cosmological constant into his equations in order to force the mathematics to provide a Universe that was static, neither expanding nor contracting. Although he later abandoned this extra term after Hubble's observations demonstrated that the Universe was in fact expanding, today it seems that perhaps he shouldn't have been so eager to throw away this extra piece of mathematics after all.
...The value of the cosmological constant originally chosen by Einstein led to a static and unchanging Universe. But with a different value, it is also possible for such a term to cause the expansion of the Universe to accelerate over time (p. 168).
Georges Lemaitre, the subject of John Farrell's book The Day Without Yesterday(which I reviewed here), was one scientist who tried to convince Einstein to put the CC to new use. In this way, the CC would fit with Lemaitre's ideas of a Big Bang and expanding universe. Writes Farrell:
In July 1947 Lemaitre wrote a letter to Einstein -- the last of their correspondence that survives -- in which he tried, once again, to persuade the founder of the general theory of relativity to reconsider his dismissal of the cosmological constant(p. 159).
[To Lemaitre and Sir Arthur Stanley Eddington, the] cosmological constant was not an arbitrary number, not a number picked out of thin air merely to balance the force of gravity. For them Λ represented something more, something physical. Lemaitre in particular began to treat the constant as the indicator of an actual force with a special role to play in an expanding universe(pp. 164-165).
Einstein's cosmological constant today is sometimes juxtaposed with the concepts of dark energy (a hypothetical entity driving the universe apart in an expansion) and vacuum (empty space) energy. Lemaitre's idea in the previous paragraph of an expansionary "force" also has some apparent similarity (to me at least) with Guth's model of inflationary cosmology, which I shall address in my next posting.
Back to our main discussion, the CC, dark energy, and vacuum energy all are proposed to account for the accelerated expansion of the universe observed in recent years.
A New York Timesarticle from just a couple of weeks ago, after describing Einstein's abandonment of the CC, notes that "...quantum physics resurrected it by showing that empty space should be foaming with energy that had the properties of Einstein’s constant." However, a problem attends this formulation: "Alas, all attempts to calculate the amount of this energy come up with an unrealistically huge number, enough energy to blow away the contents of the cosmos like leaves in a storm before stars or galaxies could form. Nothing could live there."
Thus, to fit with observable nature, the CC must be much smaller than expected. Again quoting from the Times article, "But if dark energy is the cosmological constant, it is smaller than predicted by a shocking factor of 10^60 [10 raised to the 60th power]."
University of California Riverside professor John Baez has written a piece explaining the difficulties involved in determining the energy density of the vacuum. As he discusses, within the framework of Einstein's general relativity, a few steps are needed to understand the estimation of the energy density:
"...we've known for a long time that the universe is expanding... [and] this expansion is speeding up."
"...negative pressure makes the expansion tend to speed up."
Under the necessary conditions, the vacuum "must have a pressure equal to exactly -1 times its energy density..."
"From this, it follows that if the vacuum has positive energy density, the expansion of the universe will tend to speed up! This is what people see. And, vacuum energy is currently the most plausible explanation known for what's going on. ...the basic fact that the energy density of spacetime is very close to zero is almost unarguable: for it to be false, general relativity would have to be very wrong."
Other approaches, based in quantum field theories, yield other estimates.
Noting that "the conventionally defined cosmological constant Λ is proportional to the vacuum energy density PΛ," Sean Carroll concludes that, "If the recent observational suggestions of a nonzero Λ are confirmed, we will be faced with the additional task of inventing a theory which sets the vacuum energy to a very small value without setting it precisely to zero."
Another problem cited in the Times article: "Nor is there any solid evidence yet that dark energy is or is not varying with time — if it is not constant, it cannot be Einstein’s constant."
In light of the various conundrums involving the CC, vacuum energy, and dark energy, another theory being considered by some scientists is quintessence.
Finally, if your curiosity about Einstein's cosmological constant still has not been satiated, this University of Colorado page provides a seven-part, Q&A style, rundown of important themes.
Einstein intended the cosmological constant for one purpose, then jettisoned it as a mistake after the original premise for its use was discredited. Other physicists and cosmologists later resurrected the CC, however, for use in a different context. As Dan Hooper's book Dark Cosmos explains:
Einstein... had originally introduced the cosmological constant into his equations in order to force the mathematics to provide a Universe that was static, neither expanding nor contracting. Although he later abandoned this extra term after Hubble's observations demonstrated that the Universe was in fact expanding, today it seems that perhaps he shouldn't have been so eager to throw away this extra piece of mathematics after all.
...The value of the cosmological constant originally chosen by Einstein led to a static and unchanging Universe. But with a different value, it is also possible for such a term to cause the expansion of the Universe to accelerate over time (p. 168).
Georges Lemaitre, the subject of John Farrell's book The Day Without Yesterday(which I reviewed here), was one scientist who tried to convince Einstein to put the CC to new use. In this way, the CC would fit with Lemaitre's ideas of a Big Bang and expanding universe. Writes Farrell:
In July 1947 Lemaitre wrote a letter to Einstein -- the last of their correspondence that survives -- in which he tried, once again, to persuade the founder of the general theory of relativity to reconsider his dismissal of the cosmological constant(p. 159).
[To Lemaitre and Sir Arthur Stanley Eddington, the] cosmological constant was not an arbitrary number, not a number picked out of thin air merely to balance the force of gravity. For them Λ represented something more, something physical. Lemaitre in particular began to treat the constant as the indicator of an actual force with a special role to play in an expanding universe(pp. 164-165).
Einstein's cosmological constant today is sometimes juxtaposed with the concepts of dark energy (a hypothetical entity driving the universe apart in an expansion) and vacuum (empty space) energy. Lemaitre's idea in the previous paragraph of an expansionary "force" also has some apparent similarity (to me at least) with Guth's model of inflationary cosmology, which I shall address in my next posting.
Back to our main discussion, the CC, dark energy, and vacuum energy all are proposed to account for the accelerated expansion of the universe observed in recent years.
A New York Timesarticle from just a couple of weeks ago, after describing Einstein's abandonment of the CC, notes that "...quantum physics resurrected it by showing that empty space should be foaming with energy that had the properties of Einstein’s constant." However, a problem attends this formulation: "Alas, all attempts to calculate the amount of this energy come up with an unrealistically huge number, enough energy to blow away the contents of the cosmos like leaves in a storm before stars or galaxies could form. Nothing could live there."
Thus, to fit with observable nature, the CC must be much smaller than expected. Again quoting from the Times article, "But if dark energy is the cosmological constant, it is smaller than predicted by a shocking factor of 10^60 [10 raised to the 60th power]."
University of California Riverside professor John Baez has written a piece explaining the difficulties involved in determining the energy density of the vacuum. As he discusses, within the framework of Einstein's general relativity, a few steps are needed to understand the estimation of the energy density:
"...we've known for a long time that the universe is expanding... [and] this expansion is speeding up."
"...negative pressure makes the expansion tend to speed up."
Under the necessary conditions, the vacuum "must have a pressure equal to exactly -1 times its energy density..."
"From this, it follows that if the vacuum has positive energy density, the expansion of the universe will tend to speed up! This is what people see. And, vacuum energy is currently the most plausible explanation known for what's going on. ...the basic fact that the energy density of spacetime is very close to zero is almost unarguable: for it to be false, general relativity would have to be very wrong."
Other approaches, based in quantum field theories, yield other estimates.
Noting that "the conventionally defined cosmological constant Λ is proportional to the vacuum energy density PΛ," Sean Carroll concludes that, "If the recent observational suggestions of a nonzero Λ are confirmed, we will be faced with the additional task of inventing a theory which sets the vacuum energy to a very small value without setting it precisely to zero."
Another problem cited in the Times article: "Nor is there any solid evidence yet that dark energy is or is not varying with time — if it is not constant, it cannot be Einstein’s constant."
In light of the various conundrums involving the CC, vacuum energy, and dark energy, another theory being considered by some scientists is quintessence.
Finally, if your curiosity about Einstein's cosmological constant still has not been satiated, this University of Colorado page provides a seven-part, Q&A style, rundown of important themes.
Saturday, May 24, 2008
Big Bang/Inflationary Cosmology VI (Cosmic Microwave Background III)
This entry presents the third and final installment on the Cosmic Microwave Background (CMB), all of which are part of a larger series I've been writing on the Big Bang and inflationary cosmology. Part III discusses research that followed the CMB's discovery in the early 1960s and continues to the present.
As reported in this 2003 University of Chicago news release on the WMAP research mission, images of the CMB provide a “baby picture” of the universe, "as it looked 380,000 years after the big bang, some 200 million years before any stars or galaxies had formed."
Writes Simon Singh in his book, Big Bang:
It might not be immediately obvious that observing the CMB radiation is equivalent to looking back in time, but exactly the same thing happens when astronomers observe a distant star... ...if the CMB radiation was released billions of years ago and has taken billions of years to reach us, then when astronomers eventually detect it they are effectively sensing the universe as it was billions of years ago, when it was only 300,000 years old (p. 446).
WMAP (alluded to above) and its predecessor mission, the Nobel Prize-winning COBE, were the first to find tiny variations in the CMB across different areas of space. (WMAP's images were designed to be 35 times sharper than COBE's, as seen here in comparative images of the two.)
Prior to the WMAP and COBE missions, observations of the CMB radiation showed it to be absolutely uniform and homogeneous across space (Singh, p. 447). This was problematic, because our present-day universe is obviously not absolutely uniform; some areas of space have larger and denser aggregations of matter than do other areas. In other words, there would need to have been at least some tiny variations in the CMB so that gravity could trigger accretions of matter over billions of years to produce the various kinds of astronomical objects we see today.
The Smoot Cosmology Group -- Smoot being a co-recipient of the Nobel Prize for the COBE discoveries -- discusses the importance of finding even slight non-uniformities in the CMB (scientists use the term "anisotropy" for a non-uniformity; the way I think of it, "iso" means "same," as in the word "isomorphic" which means the same shape, so the "an" in front of "iso" would signify "not the same"). According to the Smoot Group's website:
These anisotropies, or "ripples" in the temperature map, correspond to areas of various density fluctuation in the early Universe. Eventually, gravity would draw these fluctuations into even denser ones. After billions of years, these minute ripples in the early universe evolved, through gravitational attraction, into the planets, stars, galaxies, and clusters of galaxies that we see today.
Dan Hooper's book Dark Cosmos, which I reviewed previously, also provides some nice discussion of the CMB, COBE, and WMAP.
As reported in this 2003 University of Chicago news release on the WMAP research mission, images of the CMB provide a “baby picture” of the universe, "as it looked 380,000 years after the big bang, some 200 million years before any stars or galaxies had formed."
Writes Simon Singh in his book, Big Bang:
It might not be immediately obvious that observing the CMB radiation is equivalent to looking back in time, but exactly the same thing happens when astronomers observe a distant star... ...if the CMB radiation was released billions of years ago and has taken billions of years to reach us, then when astronomers eventually detect it they are effectively sensing the universe as it was billions of years ago, when it was only 300,000 years old (p. 446).
WMAP (alluded to above) and its predecessor mission, the Nobel Prize-winning COBE, were the first to find tiny variations in the CMB across different areas of space. (WMAP's images were designed to be 35 times sharper than COBE's, as seen here in comparative images of the two.)
Prior to the WMAP and COBE missions, observations of the CMB radiation showed it to be absolutely uniform and homogeneous across space (Singh, p. 447). This was problematic, because our present-day universe is obviously not absolutely uniform; some areas of space have larger and denser aggregations of matter than do other areas. In other words, there would need to have been at least some tiny variations in the CMB so that gravity could trigger accretions of matter over billions of years to produce the various kinds of astronomical objects we see today.
The Smoot Cosmology Group -- Smoot being a co-recipient of the Nobel Prize for the COBE discoveries -- discusses the importance of finding even slight non-uniformities in the CMB (scientists use the term "anisotropy" for a non-uniformity; the way I think of it, "iso" means "same," as in the word "isomorphic" which means the same shape, so the "an" in front of "iso" would signify "not the same"). According to the Smoot Group's website:
These anisotropies, or "ripples" in the temperature map, correspond to areas of various density fluctuation in the early Universe. Eventually, gravity would draw these fluctuations into even denser ones. After billions of years, these minute ripples in the early universe evolved, through gravitational attraction, into the planets, stars, galaxies, and clusters of galaxies that we see today.
Dan Hooper's book Dark Cosmos, which I reviewed previously, also provides some nice discussion of the CMB, COBE, and WMAP.
Saturday, May 10, 2008
Big Bang/Inflationary Cosmology V (Cosmic Microwave Background II)
Tonight, I present Part II on the Cosmic Microwave Background, focusing on its discovery. These entries on the CMB are part of a larger series on the Big Bang and inflationary cosmology. The prediction of the CMB (by Alpher and Herman, with Gamow) as a vestige of the Big Bang was discussed in the previous entry.
The discovery of the CMB derives from radio astronomy. In the early 1960s, the Bell Lab scientists Arno Penzias and Robert Wilson were working on some radio observations. There was a persistent noise in their observations and despite assiduous attempts by Penzias and Wilson to account for and remove the noise, it wouldn't go away. According to Simon Singh's book, Big Bang:
What the two frustrated radio astronomers had not realised was that they had stumbled into one of the most important discoveries in the history of cosmology. They were completely oblivious to the fact that the omnipresent noise was actually a remnant of the Big Bang: it was the 'echo' from the early expansion phase of the universe. This annoying 'noise' would turn out to be the most convincing evidence yet that the Big Bang model was correct (p. 429).
Penzias and Wilson were eventually put in touch with a team from nearby Princeton, Robert Dicke and James Peebles, who, it appears, were busy "re-inventing the wheel" regarding the CMB. According to Singh:
Dicke and Peebles had no idea that they were walking in the fifteen-year-old footstepts of Gamow, Alpher, and Herman. Independently and belatedly, they were re-postulating the CMB radiation (p. 431).
Among all the players in the CMB saga, the only ones to receive the Nobel Prize for it were Penzias and Wilson, in 1978 (official press release). The award to Penzias and Wilson, with no such recognition ever to CMB theorists Alpher, Herman, and Gamow, is discussed on this list of Nobel Prize controversies. Singh details the plight of Alpher, Herman, and Gamow:
When Gamow, Alpher, and Herman heard of the discovery of the CMB radiation, their joy was mixed with some bitterness. It was they who had predicted this echo of the Big Bang well before Dicke and Peebles, but they received virtually no acknowledgement for their pioneering efforts. They were not mentioned in the initial pair of papers [by Penzias and Wilson; and by Dicke and colleagues] announcing the breakthrough in the Astrophysical Journal... (p. 434).
When a journalist later asked Alpher if he had felt offended by Penzias and Wilson's failure to acknowledge his contribution, he spoke his mind: 'Was I hurt? Yes! How the hell did they think I'd feel? I was miffed at the time that they'd never even invited us down to see the damned radio telescope. It was silly to be annoyed, but I was' (p. 436).
Singh's book does, however, detail the efforts by Penzias to make contact with and publicly acknowledge the contributions of Gamow, Alpher, and Herman.
The discovery of the CMB derives from radio astronomy. In the early 1960s, the Bell Lab scientists Arno Penzias and Robert Wilson were working on some radio observations. There was a persistent noise in their observations and despite assiduous attempts by Penzias and Wilson to account for and remove the noise, it wouldn't go away. According to Simon Singh's book, Big Bang:
What the two frustrated radio astronomers had not realised was that they had stumbled into one of the most important discoveries in the history of cosmology. They were completely oblivious to the fact that the omnipresent noise was actually a remnant of the Big Bang: it was the 'echo' from the early expansion phase of the universe. This annoying 'noise' would turn out to be the most convincing evidence yet that the Big Bang model was correct (p. 429).
Penzias and Wilson were eventually put in touch with a team from nearby Princeton, Robert Dicke and James Peebles, who, it appears, were busy "re-inventing the wheel" regarding the CMB. According to Singh:
Dicke and Peebles had no idea that they were walking in the fifteen-year-old footstepts of Gamow, Alpher, and Herman. Independently and belatedly, they were re-postulating the CMB radiation (p. 431).
Among all the players in the CMB saga, the only ones to receive the Nobel Prize for it were Penzias and Wilson, in 1978 (official press release). The award to Penzias and Wilson, with no such recognition ever to CMB theorists Alpher, Herman, and Gamow, is discussed on this list of Nobel Prize controversies. Singh details the plight of Alpher, Herman, and Gamow:
When Gamow, Alpher, and Herman heard of the discovery of the CMB radiation, their joy was mixed with some bitterness. It was they who had predicted this echo of the Big Bang well before Dicke and Peebles, but they received virtually no acknowledgement for their pioneering efforts. They were not mentioned in the initial pair of papers [by Penzias and Wilson; and by Dicke and colleagues] announcing the breakthrough in the Astrophysical Journal... (p. 434).
When a journalist later asked Alpher if he had felt offended by Penzias and Wilson's failure to acknowledge his contribution, he spoke his mind: 'Was I hurt? Yes! How the hell did they think I'd feel? I was miffed at the time that they'd never even invited us down to see the damned radio telescope. It was silly to be annoyed, but I was' (p. 436).
Singh's book does, however, detail the efforts by Penzias to make contact with and publicly acknowledge the contributions of Gamow, Alpher, and Herman.
Wednesday, May 07, 2008
Big Bang/Inflationary Cosmology IV (Cosmic Microwave Background I)
As I briefly alluded to a couple of posts ago, in my series on the Big Bang and inflationary cosmology, the discovery of the Cosmic Microwave Background (CMB) played a decisive role in building support for the theory of a Big Bang and in undermining the Steady State model.
Tonight, I'd like to launch a three-part posting on the CMB. The remainder of the present piece will constitute Part I, focusing on the early theorizing about the CMB. In the coming weeks, Part II will focus on the accidental discovery of the CMB, and Part III on the more recent, high precision measurement of it.
According to Simon Singh's (2004) book, Big Bang, CMB theorizing goes back to Ralph Alpher and Robert Herman in 1948, with Alpher's mentor George Gamow also being associated. (The famous Alpher, Bethe, Gamow paper, with the name of Hans Bethe inserted primarily to make the authorship sound like the Greek letters alpha, beta, and gamma, dealt with a different issue, nucleosynthesis.)
What Alpher and Herman did was formulate ideas about the interactions of temperature, light, and states of matter (particularly one known as plasma) in the early universe. The following passages from Singh convey the main points of Alpher and Herman's theorizing:
They realised that as the universe expanded, its energy would become spread through a greater volume, so the universe and the plasma within it would steadily cool. The two young physicists deduced that there would be a critical moment when the temperature would become too cool for a plasma to exist, at which point the electrons would latch onto the nuclei and form stable, neutral atoms of hydrogen and helium. The transition from plasma to atoms happens at roughly 3,000 [degree Celsius] for hydrogen and helium, and the duo estimated that it would take 300,000 years or so for the universe to cool to this temperature. This event is generally known as recombination... (p. 330).
If the Big Bang model was correct, and if Alpher and Herman had got their physics right, then the light that was present at the moment of recombination should still be beaming its way around the universe today... In other words, the light that was released at the end of the plasma epoch should currently exist as a fossil. This light would be a legacy of the Big Bang (p. 332).
One further refinement involved accounting for the stretching of light waves in an expanding universe. "Alpher and Herman confidently predicted that the stretched Big Bang light should now have a wavelength... invisible to the human eye,... located in the so-called microwave region of the spectrum" (Singh, p. 333).
Hence the name Cosmic Microwave Background.
Brian Greene, in his 2004 book The Fabric of the Cosmos, presents an even more vivid account of how one can imagine the CMB:
If your eyes could see light whose wavelength is much longer than that of orange or red, you would not only be able to see the interior of your microwave oven burst into activity when you push the start button, but you would also see a faint and nearly uniform glow spread throughout what the rest of us perceive as a dark night sky (p. 226).
Given the importance of the CMB prediction for testing the theory of a Big Bang, and what seems like an intrinsically interesting idea in its own right, one would think that Alpher and Herman's suggestion would have sparked immediate attempts to detect the CMB. But, as Singh notes, "Unfortunately, Alpher and Herman were completely ignored. Nobody made any serious effort to search for their proposed CMB radiation" (p. 333).
How the CMB was ultimately discovered will be the topic of my next entry...
Tonight, I'd like to launch a three-part posting on the CMB. The remainder of the present piece will constitute Part I, focusing on the early theorizing about the CMB. In the coming weeks, Part II will focus on the accidental discovery of the CMB, and Part III on the more recent, high precision measurement of it.
According to Simon Singh's (2004) book, Big Bang, CMB theorizing goes back to Ralph Alpher and Robert Herman in 1948, with Alpher's mentor George Gamow also being associated. (The famous Alpher, Bethe, Gamow paper, with the name of Hans Bethe inserted primarily to make the authorship sound like the Greek letters alpha, beta, and gamma, dealt with a different issue, nucleosynthesis.)
What Alpher and Herman did was formulate ideas about the interactions of temperature, light, and states of matter (particularly one known as plasma) in the early universe. The following passages from Singh convey the main points of Alpher and Herman's theorizing:
They realised that as the universe expanded, its energy would become spread through a greater volume, so the universe and the plasma within it would steadily cool. The two young physicists deduced that there would be a critical moment when the temperature would become too cool for a plasma to exist, at which point the electrons would latch onto the nuclei and form stable, neutral atoms of hydrogen and helium. The transition from plasma to atoms happens at roughly 3,000 [degree Celsius] for hydrogen and helium, and the duo estimated that it would take 300,000 years or so for the universe to cool to this temperature. This event is generally known as recombination... (p. 330).
If the Big Bang model was correct, and if Alpher and Herman had got their physics right, then the light that was present at the moment of recombination should still be beaming its way around the universe today... In other words, the light that was released at the end of the plasma epoch should currently exist as a fossil. This light would be a legacy of the Big Bang (p. 332).
One further refinement involved accounting for the stretching of light waves in an expanding universe. "Alpher and Herman confidently predicted that the stretched Big Bang light should now have a wavelength... invisible to the human eye,... located in the so-called microwave region of the spectrum" (Singh, p. 333).
Hence the name Cosmic Microwave Background.
Brian Greene, in his 2004 book The Fabric of the Cosmos, presents an even more vivid account of how one can imagine the CMB:
If your eyes could see light whose wavelength is much longer than that of orange or red, you would not only be able to see the interior of your microwave oven burst into activity when you push the start button, but you would also see a faint and nearly uniform glow spread throughout what the rest of us perceive as a dark night sky (p. 226).
Given the importance of the CMB prediction for testing the theory of a Big Bang, and what seems like an intrinsically interesting idea in its own right, one would think that Alpher and Herman's suggestion would have sparked immediate attempts to detect the CMB. But, as Singh notes, "Unfortunately, Alpher and Herman were completely ignored. Nobody made any serious effort to search for their proposed CMB radiation" (p. 333).
How the CMB was ultimately discovered will be the topic of my next entry...
Thursday, April 10, 2008
Physics of Baseball Demonstrations
Here's another little break from my ongoing series on the Big Bang and inflationary cosmology. The following online article provides a visually rich set of demonstrations on the physics of baseball.
Sunday, March 30, 2008
Big Bang/Inflationary Cosmology III
Getting back to my series on the Big Bang and inflationary cosmology, I'd like to devote the third entry to what for many years was the leading scientific alternative to big bang theory, the Steady State model. Championed by Fred Hoyle, and colleagues Thomas Gold and Hermann Bondi, the Steady State model proposed "a universe that was expanding but which was still truly eternal and essentially unchanging," in the words of Simon Singh's book Big Bang (p. 341).
As noted in the above quote, the Steady State researchers accepted cosmological findings of an expanding universe. To keep the density of galaxies throughout the universe stable over time, even though the universe's expansion would drive existing galaxies further and further apart from each other and thus dilute the concentration of galaxies, required some unorthodox theorizing. According to Singh (p. 345), Gold suggested a process that:
...counteracted the thinning effect of the expansion and resulted in no overall change. This was the idea that the universe compensated for its expansion by creating new matter in the growing gaps between the receding galaxies, so that the overall density of the universe would remain the same.
The proposed constant density in an expanding universe is illustrated graphically here. Singh's Figure 86 on page 346 is also helpful.
The movie Dead of Night, in which events happen but everything at the end of the film turns out to be the same as at the beginning, is said to be an inspiration for Hoyle and colleagues' Steady State model.
Spontaneous creation of new matter, of course, appears to violate the foundational concepts of conservation of mass and of energy.
Georges Lemaitre, the early big bang theorist who was profiled in John Farrell's book, The Day Without Yesterday (which I reviewed here), among others, appears to have found the deviation from the conservation laws objectionable. Writes Farrell (p. 155):
Lemaitre did not agree with the steady state, either. For one thing, although he understood the reason for the theory's violation of the conservation of energy in order to pop hydrogen atoms out of nothingness to stabilize the eternal universe, and that it might be explained by quantum mechanics, he did not see why this one modification of the conservation laws should be singled out -- and not others as well. If conservation of energy should be altered for the sake of fitting a theory, for example, why stop there? Why not modify the other principles if they are not convenient to the theory?
Ultimately, the discovery of the Cosmic Microwave Background, which I will discuss in my next posting, decisively tipped the scales in favor of the Big Bang, as opposed to the Steady State model. Although Hoyle's view of the universe was discredited, it should be noted that his research on stellar nucleosynthesis remains well-respected; his exclusion from the Nobel Prize on the topic is listed among the great controversies in Nobel Prize awards (and non-awards).
As noted in the above quote, the Steady State researchers accepted cosmological findings of an expanding universe. To keep the density of galaxies throughout the universe stable over time, even though the universe's expansion would drive existing galaxies further and further apart from each other and thus dilute the concentration of galaxies, required some unorthodox theorizing. According to Singh (p. 345), Gold suggested a process that:
...counteracted the thinning effect of the expansion and resulted in no overall change. This was the idea that the universe compensated for its expansion by creating new matter in the growing gaps between the receding galaxies, so that the overall density of the universe would remain the same.
The proposed constant density in an expanding universe is illustrated graphically here. Singh's Figure 86 on page 346 is also helpful.
The movie Dead of Night, in which events happen but everything at the end of the film turns out to be the same as at the beginning, is said to be an inspiration for Hoyle and colleagues' Steady State model.
Spontaneous creation of new matter, of course, appears to violate the foundational concepts of conservation of mass and of energy.
Georges Lemaitre, the early big bang theorist who was profiled in John Farrell's book, The Day Without Yesterday (which I reviewed here), among others, appears to have found the deviation from the conservation laws objectionable. Writes Farrell (p. 155):
Lemaitre did not agree with the steady state, either. For one thing, although he understood the reason for the theory's violation of the conservation of energy in order to pop hydrogen atoms out of nothingness to stabilize the eternal universe, and that it might be explained by quantum mechanics, he did not see why this one modification of the conservation laws should be singled out -- and not others as well. If conservation of energy should be altered for the sake of fitting a theory, for example, why stop there? Why not modify the other principles if they are not convenient to the theory?
Ultimately, the discovery of the Cosmic Microwave Background, which I will discuss in my next posting, decisively tipped the scales in favor of the Big Bang, as opposed to the Steady State model. Although Hoyle's view of the universe was discredited, it should be noted that his research on stellar nucleosynthesis remains well-respected; his exclusion from the Nobel Prize on the topic is listed among the great controversies in Nobel Prize awards (and non-awards).
Saturday, January 26, 2008
Scientific American: "The Future of Physics"
The February 2008 issue of Scientific American, now out on the newsstands, features a special series (with top billing on the cover) entitled "The Future of Physics." The series, consisting of three primary articles that together run for about 20 pages, focuses on the upcoming particle/high energy experiments that will take place at the Large Hadron Collider in the next year or so, and beyond. (I, myself, wrote an eight-part series on the LHC for this blog last year, spanning from the opening essay in May to the concluding piece in September; earlier postings can be accessed via the archives to this blog.)
The first article of the new Scientific American series ("The Discovery Machine") focuses on the engineering aspects of physically constructing the LHC. Two areas I found of interest were the detailed description of the detector systems and how they are designed to winnow down the incredible avalanche of data to the occurrences of greatest potential importance to scientists; and a summary of the malfunctions that have occurred in testing the LHC and have caused delays in the official opening of the facility.
The second article ("The Coming Revolutions in Particle Physics") focuses on the scientific aspects of what physicists expect (or at least hope) to find at the LHC. One historical development discussed in the article, which I don't recall ever learning about before, is how some of the key ideas of electroweak symmetry breaking (i.e., how the electromagnetic and weak forces diverged after being unified) were inspired by superconductivity research. This article is accompanied by nice colorful charts providing overviews of the Standard Model of particle physics, the "hierarchy problem," and "Five Goals for the LHC."
Finally, the third article ("Building the Next-Generation Collider") discusses the proposed successor to the LHC, the International Linear Collider (a website set up to provide basic information on the proposed ILC is available here). This article focuses both on the engineering of building the ILC and how it would complement the LHC scientifically.
The ILC is just a hypothetical entity at this point. What country it would be built in, and how its estimated cost of many billion dollars would be funded, remain to be seen. Also, the richness of scientific yield from the LHC (or relative lack thereof) may affect the prospects for the ILC. In any case, the article estimates that research at the ILC -- if it ever gets underway -- would not take place until sometime in the decade of the 2020's.
The first article of the new Scientific American series ("The Discovery Machine") focuses on the engineering aspects of physically constructing the LHC. Two areas I found of interest were the detailed description of the detector systems and how they are designed to winnow down the incredible avalanche of data to the occurrences of greatest potential importance to scientists; and a summary of the malfunctions that have occurred in testing the LHC and have caused delays in the official opening of the facility.
The second article ("The Coming Revolutions in Particle Physics") focuses on the scientific aspects of what physicists expect (or at least hope) to find at the LHC. One historical development discussed in the article, which I don't recall ever learning about before, is how some of the key ideas of electroweak symmetry breaking (i.e., how the electromagnetic and weak forces diverged after being unified) were inspired by superconductivity research. This article is accompanied by nice colorful charts providing overviews of the Standard Model of particle physics, the "hierarchy problem," and "Five Goals for the LHC."
Finally, the third article ("Building the Next-Generation Collider") discusses the proposed successor to the LHC, the International Linear Collider (a website set up to provide basic information on the proposed ILC is available here). This article focuses both on the engineering of building the ILC and how it would complement the LHC scientifically.
The ILC is just a hypothetical entity at this point. What country it would be built in, and how its estimated cost of many billion dollars would be funded, remain to be seen. Also, the richness of scientific yield from the LHC (or relative lack thereof) may affect the prospects for the ILC. In any case, the article estimates that research at the ILC -- if it ever gets underway -- would not take place until sometime in the decade of the 2020's.
Saturday, January 19, 2008
Big Bang/Inflationary Cosmology Part II
As the second essay in my series on inflationary cosmology, I would like to discuss the phenomenon of redshifts in the visible spectrum of astronomical bodies, which has allowed scientists to infer that such bodies are moving away from us.
This Wikipedia page offers an illustrative -- and colorful -- diagram of how "Absorption lines in the optical spectrum of a supercluster of distant galaxies" is redshifted away from the Sun. The same Wikipedia page notes that, among other mechanisms:
Another cause of redshift is the expansion of the universe, which explains the observation that the redshifts of distant galaxies, quasars, and intergalactic gas clouds increase in proportion to their distance from the earth. This mechanism is a key feature of the Big Bang model of physical cosmology.
Another webpage, this time from the Exploratorium, discusses the Doppler Effect and presents an analogy between the sound of a police car's siren and light waves (along with some nice graphics):
Like sound, light is a wave that can be described in terms of its frequency, the number of wave peaks that pass by each second. Just like a cosmic police car, a star zooming toward you has its light waves squeezed together. You see these light waves as having a higher frequency than normal. Since blue is at the high-frequency end of the visible spectrum, we say the light from an approaching star is shifted toward blue, or blueshifted.
Likewise, if a star is zooming away from you, any light it emits gets stretched. You see these stretched-out light waves as having a lower frequency. Since red is at the low-frequency end of the visible spectrum, we say that light from a receding star is shifted toward red, or redshifted.
A naive, layperson question that occurred to me is how we know the movement of galaxies and other objects away from us represents the expansion of the universe, rather than the movement of these objects into what was previously existing, empty space in the universe.
While not (apparently) addressing my exact question, Brian Greene's 2004 book, The Fabric of the Cosmos, explains the basis for why the universe must be expanding:
Just as the gravitational pull of the earth implies that a baseball popped high above the catcher must either be heading farther upward or must be heading downward but certainly cannot be staying put (except for the single moment when it reaches its highest point), [Alexander] Friedmann and [Georges] Lemaitre realized that the gravitational pull of the matter and radiation spread throughout the entire cosmos implies that the fabric of space must either be stretching or contracting, but that it could not be staying fixed in size (p. 230).
This Wikipedia page offers an illustrative -- and colorful -- diagram of how "Absorption lines in the optical spectrum of a supercluster of distant galaxies" is redshifted away from the Sun. The same Wikipedia page notes that, among other mechanisms:
Another cause of redshift is the expansion of the universe, which explains the observation that the redshifts of distant galaxies, quasars, and intergalactic gas clouds increase in proportion to their distance from the earth. This mechanism is a key feature of the Big Bang model of physical cosmology.
Another webpage, this time from the Exploratorium, discusses the Doppler Effect and presents an analogy between the sound of a police car's siren and light waves (along with some nice graphics):
Like sound, light is a wave that can be described in terms of its frequency, the number of wave peaks that pass by each second. Just like a cosmic police car, a star zooming toward you has its light waves squeezed together. You see these light waves as having a higher frequency than normal. Since blue is at the high-frequency end of the visible spectrum, we say the light from an approaching star is shifted toward blue, or blueshifted.
Likewise, if a star is zooming away from you, any light it emits gets stretched. You see these stretched-out light waves as having a lower frequency. Since red is at the low-frequency end of the visible spectrum, we say that light from a receding star is shifted toward red, or redshifted.
A naive, layperson question that occurred to me is how we know the movement of galaxies and other objects away from us represents the expansion of the universe, rather than the movement of these objects into what was previously existing, empty space in the universe.
While not (apparently) addressing my exact question, Brian Greene's 2004 book, The Fabric of the Cosmos, explains the basis for why the universe must be expanding:
Just as the gravitational pull of the earth implies that a baseball popped high above the catcher must either be heading farther upward or must be heading downward but certainly cannot be staying put (except for the single moment when it reaches its highest point), [Alexander] Friedmann and [Georges] Lemaitre realized that the gravitational pull of the matter and radiation spread throughout the entire cosmos implies that the fabric of space must either be stretching or contracting, but that it could not be staying fixed in size (p. 230).
Tuesday, January 01, 2008
Big Bang/Inflationary Cosmology Part I -- Book Review: "The Day Without Yesterday"
Happy New Year! To get 2008 off to a bang, I will be kicking off a series on the big bang and the expanding universe (also known as "inflationary cosmology"). An excellent way to do so, in my view, is by reviewing John Farrell's 2005 book, The Day Without Yesterday: Lemaitre, Einstein, and the Birth of Modern Cosmology.
As noted in the title, the book is about Georges Lemaitre (1894-1966), a Belgian astrophysicist (Ph.D. from MIT) and priest. It is Lemaitre who, with some later modifications by others, laid the groundwork for the modern big bang theory of an expanding universe, at a time when there was widespread belief among scientists in a static universe.
A few weeks ago, I had seen an episode of the History Channel series, The Universe, which introduced me to Lemaitre for the first time. Shortly thereafter, I found The Day Without Yesterday in a bookstore, and it seemed to be a perfect way for me to expand my knowledge from what I had seen in the documentary.
With access to letters and photographs from the Lemaitre and Einstein archives, Farrell weaves, to my mind, the perfect blend of scientific exposition and personal story. The duality of Lemaitre's scientific and theological commitments is discussed somewhat, toward the end of the book, and the overwhelming sense is that he kept the two quite separate. At a little over 200 pages, the book is a quick read, easily capable of being finished in a few sittings.
As the book conveys, Lemaitre's ideas stemmed from his thoughtful responses to Einstein's general relativity and Willem de Sitter's initial elaborations on Einstein's theory. In fact, Farrell quotes one of Einstein's letters to Lemaitre, as follows (p. 169):
"I doubt that anybody has so carefully studied the cosmological implications of the theory of relativity as you have."
Further, as the book discusses, development of the big bang theory from roughly 1925-1950 went through at least three stages:
First, having learned of data from astronomical observations suggestive of receding objects, Lemaitre introduced the idea of an expanding universe. Writes Farrell:
It's important to note here that Lemaitre was not yet interested in discussing a temporal beginning of the cosmos in any sense of the term, as has often been inaccurately stated in many books about twentieth-century cosmology. His 1927 paper suggested an expansion of the universe beginning from an initial static Einstein state -- not a big bang, not an explosion of matter from nothing (p. 90).
As a second stage, quoting from Farrell (p. 91), Lemaitre's "further theory of a primeval atom, or initial cosmic origin, would come later, once he realized the physical deficiencies of beginning with Einstein's model."
Third, Lemaitre predicted that there would be a physical residue of the initial expansion of the universe, but his version consisted of a "cold" process of radioactive decay, involving cosmic rays. A later alternative by George Gamow and colleagues, involving a "hot explosion" and the cosmic microwave background as the residue, along with the eventual detection of the background, ended up providing major support for the big bang theory (Farrell, pp. 101-109, plus Chapter 7).
One other topic from Farrell's book that is worth noting is the argument about sociological factors playing a large role in what types of theories the scientific community would find acceptable at any given time (back in October 2005, I reviewed a book titled Constructing Quarks, which dealt with similar issues).
Focusing on Einstein's seeming obsession with preserving the idea of a static universe -- even going so far as to insert a "cosmological constant" into his equations to ensure such -- Farrell offers the following observation:
It's somewhat odd to see in retrospect how conservatism and hesitation manifest themselves in the history of science... Perhaps because of the general nature of this conservatism, it's unfair to ask why Einstein was content to plug the cosmological constant into his equations -- in reaction to their clear suggestion that the universe as a whole could not be static. Einstein was preceded by generation after generation of thinkers who believed the same thing (pp. 52-53).
As this series continues, future topics I plan to discuss include redshifts, Hoyle's steady-state theory, the cosmic microwave background, the cosmological constant, and Guth's inflationary cosmology.
As noted in the title, the book is about Georges Lemaitre (1894-1966), a Belgian astrophysicist (Ph.D. from MIT) and priest. It is Lemaitre who, with some later modifications by others, laid the groundwork for the modern big bang theory of an expanding universe, at a time when there was widespread belief among scientists in a static universe.
A few weeks ago, I had seen an episode of the History Channel series, The Universe, which introduced me to Lemaitre for the first time. Shortly thereafter, I found The Day Without Yesterday in a bookstore, and it seemed to be a perfect way for me to expand my knowledge from what I had seen in the documentary.
With access to letters and photographs from the Lemaitre and Einstein archives, Farrell weaves, to my mind, the perfect blend of scientific exposition and personal story. The duality of Lemaitre's scientific and theological commitments is discussed somewhat, toward the end of the book, and the overwhelming sense is that he kept the two quite separate. At a little over 200 pages, the book is a quick read, easily capable of being finished in a few sittings.
As the book conveys, Lemaitre's ideas stemmed from his thoughtful responses to Einstein's general relativity and Willem de Sitter's initial elaborations on Einstein's theory. In fact, Farrell quotes one of Einstein's letters to Lemaitre, as follows (p. 169):
"I doubt that anybody has so carefully studied the cosmological implications of the theory of relativity as you have."
Further, as the book discusses, development of the big bang theory from roughly 1925-1950 went through at least three stages:
First, having learned of data from astronomical observations suggestive of receding objects, Lemaitre introduced the idea of an expanding universe. Writes Farrell:
It's important to note here that Lemaitre was not yet interested in discussing a temporal beginning of the cosmos in any sense of the term, as has often been inaccurately stated in many books about twentieth-century cosmology. His 1927 paper suggested an expansion of the universe beginning from an initial static Einstein state -- not a big bang, not an explosion of matter from nothing (p. 90).
As a second stage, quoting from Farrell (p. 91), Lemaitre's "further theory of a primeval atom, or initial cosmic origin, would come later, once he realized the physical deficiencies of beginning with Einstein's model."
Third, Lemaitre predicted that there would be a physical residue of the initial expansion of the universe, but his version consisted of a "cold" process of radioactive decay, involving cosmic rays. A later alternative by George Gamow and colleagues, involving a "hot explosion" and the cosmic microwave background as the residue, along with the eventual detection of the background, ended up providing major support for the big bang theory (Farrell, pp. 101-109, plus Chapter 7).
One other topic from Farrell's book that is worth noting is the argument about sociological factors playing a large role in what types of theories the scientific community would find acceptable at any given time (back in October 2005, I reviewed a book titled Constructing Quarks, which dealt with similar issues).
Focusing on Einstein's seeming obsession with preserving the idea of a static universe -- even going so far as to insert a "cosmological constant" into his equations to ensure such -- Farrell offers the following observation:
It's somewhat odd to see in retrospect how conservatism and hesitation manifest themselves in the history of science... Perhaps because of the general nature of this conservatism, it's unfair to ask why Einstein was content to plug the cosmological constant into his equations -- in reaction to their clear suggestion that the universe as a whole could not be static. Einstein was preceded by generation after generation of thinkers who believed the same thing (pp. 52-53).
As this series continues, future topics I plan to discuss include redshifts, Hoyle's steady-state theory, the cosmic microwave background, the cosmological constant, and Guth's inflationary cosmology.
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