The Cosmic Landscape (61 page)
6
The momentum of an object is defined to be its velocity multiplied by its mass.
7
The symbol for Planck’s constant is the letter
h
and its numerical value is 6.626068 × 10
–34
m
2
kg/ s. Here,
m, kg,
and
s
stand for
meter, kilogram,
and
second.
8
The term
quantum
(used as a noun) is somewhat more general than
photon
.
Quantum
refers to any discrete packet of energy while
photon
is the more specific term referring to electromagnetic energy. Thus one could say that the photon is the quantum of electromagnetic radiation.
9
Brian Greene,
The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory
(New York: Norton, 2003).
10
Whether it works for the study of the mind is a contentious issue. My own view is that the behavior of animate matter is subject to the same Laws of Physics as inanimate matter. I know of no evidence to the contrary. On the other hand, the phenomenon of consciousness has yet to be fully explained by reductionist science.
11
In addition to writing
Poor Richard’s Almanack
and signing the Declaration of Independence, Benjamin Franklin was one of the outstanding scientists of the eighteenth century.
12
The electrostatic force is also known as the Coulomb force.
13
The term
fine structure
has to do with the details of the atomic spectrum of hydrogen. The fine structure constant first made its appearance in the theory of the hydrogen spectrum.
14
Bohr’s response was, “Einstein, don’t tell God what to do.”
15
The existence of the strange-quark has a minor effect on the properties of nucleons, but the others are of no importance.
16
Brother Rabbit to Yankees.
17
Thirty is an absolute minimum that does not include the numerical parameters that are required for cosmology or for various extensions of the Standard Model. Including these additional constants, their number easily grows to more than one hundred.
18
Spectral lines are discussed in chapter 4.
1
Actually, Magellan never did arrive back in Europe. He was killed in the Philippines. But some of his crew did manage to circumnavigate the globe, thus proving that it was a sphere.
2
One hundred inches sounds like a modest size for a telescope, but it refers only to the diameter of the light-gathering mirror not the overall size of the instrument. In fact the Mount Wilson telescope was the largest in the world until the 200-inch Mount Palomar telescope was completed, in 1949.
3
The third term preferred by the press is
dark energy.
4
John D. Barrow and Frank J. Tipler,
The Anthropic Cosmological Principle
(Oxford: Oxford University Press, 1986).
5
Sorry for the anachronism; the idea of a galaxy didn’t exist yet in 1900.
1
See chapter 8 for an explanation of the navigator’s fear of supersymmetry.
2
An Mev is a tiny unit of mass used by elementary-particle physicists. Approximately five times ten to the twenty-ninth (5 × 10
29
) Mevs is equal to one kilogram.
3
A number of people were involved in the theoretical discovery of the Higgs field. In addition to Peter Higgs of Great Britain, Robert Brout and Françoise Englert of Belgium were among the earliest to realize its necessity.
4
So important that the physicist Leon Lederman wrote a book about it, which in a moment of overenthusiasm he titled:
The God Particle.
(Lederman might have called his book
The God Field.
I suppose
The God Particle
has a better ring to it.)
5
The name CERN is an acronym for “Conseil Europeen pour la Recherche Nucléaire.”
6
Even in the case of the weather, there is a notion of energy. The energy of all the molecules in a cubic meter of atmosphere depends on the temperature and pressure. Thus, we could add a concept of altitude to the weather Landscape. It would of course have nothing to do with ordinary altitude.
7
Keep in mind that in one full cycle an oscillation starts at zero, increases, decreases through zero to negative values, and then increases back to zero. The electric and magnetic fields will pass through zero twice in a single wavelength.
8
While the universe is at the top of the mountain, the vacuum energy causes the universe to expand as if there were a cosmological constant. The expansion causes a kind of friction called cosmic friction.
1
These remarks about simplicity are intended to apply only to the engineer/ mathematician/ physicist’s kind of simplicity. I hold no opinions about simplicity and complexity in music, poetry, or any other artform.
3
Apparently not everyone agrees. Walt Whitman wrote:
4
The five Platonic solids are the only polyhedra (three-dimensional analogs of polygons) whose faces are all identical polygons. The tetrahedron, octahedron, and icosahedron are all fashioned from triangles. The cube and dodecahedron are made of squares and pentagons, respectively.
5
This remark was written in the spring of 1994, but by the time I completed writing
The Cosmic Landscape
a year later, the vultures had descended in force.
6
See chapter 5 for an explanation of dark matter.
1
The boat has to be moving slower than the velocity of the surface waves.
2
To observably change color the lemon would have to move with a significant fraction of the speed of light.
3
The term
Hubble constant
is somewhat misleading, since it changes with time. Long in the past the Hubble constant was much larger than it is today.
4
The shape, of course, refers to the surface of the figure.
5
For the moment I am completely ignoring the possibility that there is a cosmological constant. As we will see, a cosmological constant can significantly alter the conclusions.
6
Don’t confuse dark matter with dark energy.
Dark energy
is another term for vacuum energy.
7
Luminosity is a measure of the rate at which an object gives off energy in the form of light. The luminosity of an electric lightbulb is measured in watts. If two objects have the same luminosity, the closer of them will appear brighter. By measuring the apparent brightness of the photographic images of Type I supernovae, their distance from us can be determined.
8
Plasma
is just another word for gas that has had its atoms ionized. In other words, some of the electrons have been torn free of the nucleus and are free to wander through the gas, unattached to atoms.
9
The picture shows a one-dimensional landscape, but the real thing is multidimensional. Think of the illustration as a one-dimensional slice through a much more complicated multidimensional Landscape. An analogy would be a one-dimensional road passing over hills and valleys in a two-dimensional Landscape.
1
The story was previously published in
The New Scientist
(November 1, 2003).
2
This theme will be taken up again in chapter 7 in the context of String Theory.
3
A more technically correct description is that pions—particles composed of quarks and antiquarks—transmit the force between nucleons. If the masses of the up- and down-quarks were larger, the mass of pions would also increase. This would have the effect that the nuclear force would be drastically modified.
4
When I say elements I am usually referring to the nucleus. The binding of electrons to the nucleus took a lot longer.
5
Hydrogen is the simplest of the elements. Its nucleus is a single proton.
6
There is debate over just how sensitive the existence of carbon is to the various constants. Some people would put it in the range of a couple of percent. Others, Steven Weinberg among them, would put the number at roughly 10 or 15 percent. But all would agree that some fine-tuning is needed to ensure an abundant supply of carbon.
7
It is called the gauge hierarchy problem, and no universal agreement on its solution has been reached.
8
By the time I finished writing
The Cosmic Landscape,
Dine became one of the chief supporters of the view that some features of nature are likely to be environmental and can be understood only from an anthropic perspective. Banks remains skeptical.
9
The difference between twenty billion and ten billion years is not important for our discussion. If the proton lifetime were ten billion (10
10
) years, that would mean that one proton out of ten billion would decay every year. If we then multiply this by the 10
28
protons in your body, the number that would decay in one year is 10
28
/ 10
10
= 10
18
.
10
Lest anyone get the idea that Smolin and I are enemies, this is not at all the case. In fact Smolin is a good friend for whom I have a great deal of admiration. Nevertheless, our opinions on this particular topic are strongly at odds.
11
See chapter 7.
1
Antiquarks are, of course, the antiparticle twins of quarks. They can be thought of either as particles in their own right or as quarks going backward in time.
2
The prefix
bary
means “heavy” in Greek. When the names were first coined, the nucleons and their close relatives were the heaviest known particles. Meson indicates something in the middle. Mesons are lighter than nucleons but a good deal heavier than the electron.
3
Fishnet diagram
was the term used by Nielsen.
4
This can be confusing because electrons and photons have a property called spin. But the spin of an elementary particle is not due to the kind of rotational motion that a basketball, a wad of dough, or a hadron can have. In particular, the spin of an electron can never be changed: it is always one-half of Planck’s constant. A basketball or hadron can be spun up to increase its angular momentum.
1
Electrons, muons, tau particles, and neutrinos are all examples of particles that physicists call leptons. The term simply refers to fermions that do not have strong interactions like quarks.
2
These are, of course, the whimsical names that particle physicists invented for the various properties of particles that were discovered during a forty-year period ending in the early 1970s.
3
The revolution that Einstein completed in 1905 was the molecular theory of matter. In his paper on Brownian Motion, he established beyond a doubt that molecules existed and determined just how big and numerous they are.
5
Placing a magnet under a sheet of paper and then sprinkling iron filings on the sheet allows the lines of force to be easily seen. The filings line up along the field lines and form filaments.
1
According to nineteenth-century physics, the ether was the hypothetical elastic material that fills all space. I always picture it as colorless Jell-O. Light was supposed to be vibrating wiggles in the ether. It was expected in the nineteenth century that anyone moving relative to the ether would find that the velocity of light was altered by the observer’s motion.
2
Rutherford bombarded gold atoms with alpha particles (helium nuclei), and from the deflection of the alpha particles, he deduced that the atom contained light electrons orbiting a tiny, heavy nucleus. This was the first modern particle physics experiment.
3
Abraham Pais,
Niels Bohr’s Times: In Physics, Philosophy, and Polity
(Oxford: Oxford University Press, 1991).
4
This was known from the absorption spectrum of atoms: once again nineteenth-century physics.
5
Quantum Electrodynamics was plagued by serious mathematical inconsistencies. The rules of calculation led to infinite answers that made no sense. A temporary cure, called
renormalization,
was cooked up in the 1950s. But it wasn’t until Kenneth Wilson developed a deeper theory in the early 1970s that the problems were resolved.
6
Chen Ning Yang and Robert Mills independently worked out non-abelian gauge theory one year after Pauli’s work. The only reason for not including it in my history is that Yang and Mills were partly motivated by certain empirical facts about nuclei that were not known until long after my cutoff date of January 1, 1900.
1
Rabi commented about the newly discovered muon (a particle similar to the electron but two hundred times heavier), “Who ordered that?” No doubt he was referring to the seeming arbitrariness of the elementary particles.
2
KKLT stands for Kachru Kallosh Linde and Trivedi. Shamit Kachru, Renata Kallosh, and Andrei Linde are professors at Stanford University. Sandip Trivedi is a professor at the Tata Institute, in India.
1
The populated Landscape is entirely familiar to cosmologists such as Linde, Vilenkin, and Guth, who have embraced it or something like it for many years.
