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1121 lines
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FREQUENTLY ASKED QUESTIONS ON SCI.PHYSICS - Part 2/2
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Item 12.
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Which Way Will my Bathtub Drain? updated 24-JAN-1993 by SIC
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-------------------------------- original by Matthew R. Feinstein
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Question: Does my bathtub drain differently depending on whether I live
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in the northern or southern hemisphere?
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Answer: No. There is a real effect, but it is far too small to be relevant
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when you pull the plug in your bathtub.
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Because the earth rotates, a fluid that flows along the earth's
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surface feels a "Coriolis" acceleration perpendicular to its velocity.
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In the northern hemisphere low pressure storm systems spin counterclockwise.
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In the southern hemisphere, they spin clockwise because the direction
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of the Coriolis acceleration is reversed. This effect leads to the
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speculation that the bathtub vortex that you see when you pull the plug
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from the drain spins one way in the north and the other way in the south.
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But this acceleration is VERY weak for bathtub-scale fluid
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motions. The order of magnitude of the Coriolis acceleration can be
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estimated from size of the "Rossby number". Coriolis accelerations are
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significant when the Rossby number is SMALL.
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So, suppose we want a Rossby number of 0.1 and a bathtub-vortex
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length scale of 0.1 meter. Since the earth's rotation rate is about
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10^(-4)/second, the fluid velocity should be less than or equal to
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2*10^(-6) meters/second. This is a very small velocity. How small is it?
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Well, we can take the analysis a step further and calculate another, more
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famous dimensionless parameter, the Reynolds number.
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The Reynolds number is = L*U*density/viscosity
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Assuming that physicists bathe in hot water the viscosity will be
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about 0.005 poise and the density will be about 1.0, so the Reynolds Number
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is about 4*10^(-2).
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Now, life at low Reynolds numbers is different from life at high
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Reynolds numbers. In particular, at low Reynolds numbers, fluid physics is
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dominated by friction and diffusion, rather than by inertia: the time it
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would take for a particle of fluid to move a significant distance due to an
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acceleration is greater than the time it takes for the particle to break up
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due to diffusion.
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Therefore the effect of the Coriolis acceleration on your bathtub
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vortex is SMALL. To detect its effect on your bathtub, you would have
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to get out and wait until the motion in the water is far less than one
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rotation per day. This would require removing thermal currents, vibration,
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and any other sources of noise. Under such conditions, never occurring in
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the typical home, you WOULD see an effect. To see what trouble it takes
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to actually see the effect, see the reference below. Experiments have been
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done in both the northern and southern hemispheres to verify that under
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carefully controlled conditions, bathtubs drain in opposite directions due
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to the Coriolis acceleration from the Earth's rotation.
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The same effect has been accused of responsibility for the
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direction water circulates when you flush a toilet. This is surely
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nonsense. In this case, the water rotates in the direction which the pipe
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points which carries the water from the tank to the bowl.
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Reference: Trefethen, L.M. et al, Nature 207 1084-5 (1965).
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********************************************************************************
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Item 13.
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Why are Golf Balls Dimpled? updated 14-May-1992 by SIC
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--------------------------- original by Craig DeForest
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The dimples, paradoxically, *do* increase drag slightly. But they
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also increase `Magnus lift', that peculiar lifting force experienced by
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rotating bodies travelling through a medium. Contrary to Freshman physics,
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golf balls do not travel in inverted parabolas. They follow an 'impetus
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trajectory':
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* *
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* *
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(golfer) * *
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* * <-- trajectory
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\O/ * *
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| * *
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-/ \-T---------------------------------------------------------------ground
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This is because of the combination of drag (which reduces
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horizontal speed late in the trajectory) and Magnus lift, which supports
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the ball during the initial part of the trajectory, making it relatively
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straight. The trajectory can even curve upwards at first, depending on
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conditions! Here is a cheesy diagram of a golf ball in flight, with some
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relevant vectors:
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F(magnus)
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^
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F(drag) <--- O -------> V
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\
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\----> (sense of rotation)
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The Magnus force can be thought of as due to the relative drag on
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the air on the top and bottom portions of the golf ball: the top portion is
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moving slower relative to the air around it, so there is less drag on the
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air that goes over the ball. The boundary layer is relatively thin, and
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air in the not-too-near region moves rapidly relative to the ball. The
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bottom portion moves fast relative to the air around it; there is more drag
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on the air passing by the bottom, and the boundary (turbulent) layer is
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relatively thick; air in the not-too-near region moves more slowly relative
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to the ball. The Bernoulli force produces lift. (alternatively, one could
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say that `the flow lines past the ball are displaced down, so the ball is
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pushed up.')
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The difficulty comes near the transition region between laminar
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flow and turbulent flow. At low speeds, the flow around the ball is
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laminar. As speed is increased, the bottom part tends to go turbulent
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*first*. But turbulent flow can follow a surface much more easily than
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laminar flow.
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As a result, the (laminar) flow lines around the top break away
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from the surface sooner than otherwise, and there is a net displacement
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*up* of the flow lines. The magnus lift goes *negative*.
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The dimples aid the rapid formation of a turbulent boundary layer
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around the golf ball in flight, giving more lift. Without 'em, the ball
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would travel in more of a parabolic trajectory, hitting the ground sooner.
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(and not coming straight down.)
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References: Perhaps the best (and easy-to-read) reference on this effect is
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a paper in American Journal of Physics by one Lyman Briggs, c. 1947.
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Briggs was trying to explain the mechanism behind the `curve ball' in
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baseball, using specialized apparatus in a wind tunnel at the NBS. He
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stumbled on the reverse effect by accident, because his model `baseball'
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had no stitches on it. The stitches on a baseball create turbulence in
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flight in much the same way that the dimples on a golf ball do.
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********************************************************************************
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Item 14.
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Why do Mirrors Reverse Left and Right? updated 11-JUN-1992 by SIC
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--------------------------------------
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The simple answer is that they don't. Look in a mirror and wave
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your right hand. On which side of the mirror is the hand that waved? The
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right side, of course.
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Mirrors DO reverse In/Out. The further behind you an object is,
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the further in front of you it appears in the mirror. Imaging holding an
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arrow in your hand. If you point it up, it will point up in the mirror.
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If you point it to the left, it will point to the left in the mirror. But
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if you point it toward the mirror, it will point right back at you. In and
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Out are reversed.
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If you take a three-dimensional, rectangular, coordinate system,
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(X,Y,Z), and point the Z axis such that the vector equation X x Y = Z is
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satisfied, then the coordinate system is said to be right-handed. Imagine
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Z pointing toward the mirror. X and Y are unchanged (remember the arrows?)
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but Z will point back at you. In the mirror, X x Y = - Z. The image
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contains a left-handed coordinate system.
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This has an important effect, familiar mostly to chemists and
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physicists. It changes the chirality, or handedness of objects viewed in
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the mirror. Your left hand looks like a right hand, while your right hand
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looks like a left hand. Molecules often come in pairs called
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stereoisomers, which differ not in the sequence or number of atoms, but
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only in that one is the mirror image of the other, so that no rotation or
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stretching can turn one into the other. Your hands make a good laboratory
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for this effect. They are distinct, even though they both have the same
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components connected in the same way. They are a stereo pair, identical
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except for "handedness".
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People sometimes think that mirrors *do* reverse left/right, and
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that the effect is due to the fact that our eyes are aligned horizontally
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on our faces. This can be easily shown to be untrue by looking in any
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mirror with one eye closed!
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Reference: _The Left Hand of the Neutrino_, by Isaac Asimov, contains
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a very readable discussion of handedness and mirrors in physics.
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********************************************************************************
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Item 15.
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What is the Mass of a Photon? updated 24-JUL-1992 by SIC
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original by Matt Austern
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Or, "Does the mass of an object depend on its velocity?"
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This question usually comes up in the context of wondering whether
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photons are really "massless," since, after all, they have nonzero energy.
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The problem is simply that people are using two different definitions of
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mass. The overwhelming consensus among physicists today is to say that
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photons are massless. However, it is possible to assign a "relativistic
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mass" to a photon which depends upon its wavelength. This is based upon
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an old usage of the word "mass" which, though not strictly wrong, is not
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used much today.
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The old definition of mass, called "relativistic mass," assigns
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a mass to a particle proportional to its total energy E, and involved
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the speed of light, c, in the proportionality constant:
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m = E / c^2. (1)
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This definition gives every object a velocity-dependent mass.
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The modern definition assigns every object just one mass, an
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invariant quantity that does not depend on velocity. This is given by
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m = E_0 / c^2, (2)
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where E_0 is the total energy of that object at rest.
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The first definition is often used in popularizations, and in some
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elementary textbooks. It was once used by practicing physicists, but for
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the last few decades, the vast majority of physicists have instead used the
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second definition. Sometimes people will use the phrase "rest mass," or
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"invariant mass," but this is just for emphasis: mass is mass. The
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"relativistic mass" is never used at all. (If you see "relativistic mass"
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in your first-year physics textbook, complain! There is no reason for books
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to teach obsolete terminology.)
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Note, by the way, that using the standard definition of mass, the
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one given by Eq. (2), the equation "E = m c^2" is *not* correct. Using the
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standard definition, the relation between the mass and energy of an object
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can be written as
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E = m c^2 / sqrt(1 -v^2/c^2), (3)
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or as
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E^2 = m^2 c^4 + p^2 c^2, (4)
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where v is the object's velocity, and p is its momentum.
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In one sense, any definition is just a matter of convention. In
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practice, though, physicists now use this definition because it is much
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more convenient. The "relativistic mass" of an object is really just the
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same as its energy, and there isn't any reason to have another word for
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energy: "energy" is a perfectly good word. The mass of an object, though,
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is a fundamental and invariant property, and one for which we do need a
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word.
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The "relativistic mass" is also sometimes confusing because it
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mistakenly leads people to think that they can just use it in the Newtonian
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relations
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F = m a (5)
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and
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F = G m1 m2 / r^2. (6)
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In fact, though, there is no definition of mass for which these
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equations are true relativistically: they must be generalized. The
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generalizations are more straightforward using the standard definition
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of mass than using "relativistic mass."
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Oh, and back to photons: people sometimes wonder whether it makes
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sense to talk about the "rest mass" of a particle that can never be at
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rest. The answer, again, is that "rest mass" is really a misnomer, and it
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is not necessary for a particle to be at rest for the concept of mass to
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make sense. Technically, it is the invariant length of the particle's
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four-momentum. (You can see this from Eq. (4).) For all photons this is
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zero. On the other hand, the "relativistic mass" of photons is frequency
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dependent. UV photons are more energetic than visible photons, and so are
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more "massive" in this sense, a statement which obscures more than it
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elucidates.
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Reference: Lev Okun wrote a nice article on this subject in the
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June 1989 issue of Physics Today, which includes a historical discussion
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of the concept of mass in relativistic physics.
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********************************************************************************
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Item 16.
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updated 4-SEP-1992 by SIC
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Original by Bill Johnson
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How to Change Nuclear Decay Rates
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---------------------------------
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"I've had this idea for making radioactive nuclei decay faster/slower than
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they normally do. You do [this, that, and the other thing]. Will this work?"
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Short Answer: Possibly, but probably not usefully.
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Long Answer:
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"One of the paradigms of nuclear science since the very early days
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of its study has been the general understanding that the half-life, or
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decay constant, of a radioactive substance is independent of extranuclear
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considerations." (Emery, cited below.) Like all paradigms, this one is
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subject to some interpretation. Normal decay of radioactive stuff proceeds
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via one of four mechanisms:
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* Emission of an alpha particle -- a helium-4 nucleus -- reducing
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the number of protons and neutrons present in the parent nucleus
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by two each;
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* "Beta decay," encompassing several related phenomena in which a
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neutron in the nucleus turns into a proton, or a proton turns into
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a neutron -- along with some other things including emission of
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a neutrino. The "other things", as we shall see, are at the bottom
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of several questions involving perturbation of decay rates;
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* Emission of one or more gamma rays -- energetic photons -- that
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take a nucleus from an excited state to some other (typically
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ground) state; some of these photons may be replaced by
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"conversion electrons," of which more shortly; or
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*Spontaneous fission, in which a sufficiently heavy nucleus simply
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breaks in half. Most of the discussion about alpha particles will
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also apply to spontaneous fission.
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Gamma emission often occurs from the daughter of one of the other decay
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modes. We neglect *very* exotic processes like C-14 emission or double
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beta decay in this analysis.
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"Beta decay" refers most often to a nucleus with a neutron excess,
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which decays by converting a neutron into a proton:
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n ----> p + e- + anti-nu(e),
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where n means neutron, p means proton, e- means electron, and anti-nu(e)
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means an antineutrino of the electron type. The type of beta decay which
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involves destruction of a proton is not familiar to many people, so
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deserves a little elaboration. Either of two processes may occur when this
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kind of decay happens:
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p ----> n + e+ + nu(e),
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where e+ means positron and nu(e) means electron neutrino; or
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p + e- ----> n + nu(e),
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where e- means a negatively charged electron, which is captured from the
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neighborhood of the nucleus undergoing decay. These processes are called
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"positron emission" and "electron capture," respectively. A given nucleus
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which has too many protons for stability may undergo beta decay through
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either, and typically both, of these reactions.
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"Conversion electrons" are produced by the process of "internal
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conversion," whereby the photon that would normally be emitted in gamma
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decay is *virtual* and its energy is absorbed by an atomic electron. The
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absorbed energy is sufficient to unbind the electron from the nucleus
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(ignoring a few exceptional cases), and it is ejected from the atom as a
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result.
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Now for the tie-in to decay rates. Both the electron-capture and
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internal conversion phenomena require an electron somewhere close to the
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decaying nucleus. In any normal atom, this requirement is satisfied in
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spades: the innermost electrons are in states such that their probability
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of being close to the nucleus is both large and insensitive to things in
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the environment. The decay rate depends on the electronic wavefunctions,
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i.e, how much of their time the inner electrons spend very near the
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nucleus -- but only very weakly. For most nuclides that decay by electron
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capture or internal conversion, most of the time, the probability of
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grabbing or converting an electron is also insensitive to the environment,
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as the innermost electrons are the ones most likely to get grabbed/converted.
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However, there are exceptions, the most notable being the
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the astrophysically important isotope beryllium-7. Be-7 decays purely
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by electron capture (positron emission being impossible because of
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inadequate decay energy) with a half-life of somewhat over 50 days. It has
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been shown that differences in chemical environment result in half-life
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variations of the order of 0.2%, and high pressures produce somewhat
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similar changes. Other cases where known changes in decay rate occur are
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Zr-89 and Sr-85, also electron capturers; Tc-99m ("m" implying an excited
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state), which decays by both beta and gamma emission; and various other
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"metastable" things that decay by gamma emission with internal conversion.
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With all of these other cases the magnitude of the effect is less than is
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typically the case with Be-7.
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What makes these cases special? The answer is that one or another
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of the usual starting assumptions -- insensitivity of electron wave
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function near the nucleus to external forces, or availability of the
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innermost electrons for capture/conversion -- are not completely valid.
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Atomic beryllium only has 4 electrons to begin with, so that the "innermost
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electrons" are also practically the *outermost* ones and therefore much
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more sensitive to chemical effects than usual. With most of the other
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cases, there is so little energy available from the decay (as little as a
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few electron volts; compare most radioactive decays, where hundreds or
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thousands of *kilo*volts are released), courtesy of accidents of nuclear
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structure, that the innermost electrons can't undergo internal conversion.
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Remember that converting an electron requires dumping enough energy into it
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to expel it from the atom (more or less); "enough energy," in context, is
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typically some tens of keV, so they don't get converted at all in these
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cases. Conversion therefore works only on some of the outer electrons,
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which again are more sensitive to the environment.
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A real anomaly is the beta emitter Re-187. Its decay energy is
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only about 2.6 keV, practically nothing by nuclear standards. "That this
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decay occurs at all is an example of the effects of the atomic environment
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on nuclear decay: the bare nucleus Re-187 [i.e., stripped of all orbital
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electrons -- MWJ] is stable against beta decay and it is the difference of
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15 keV in the total electronic binding energy of osmium [to which it decays
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-- MWJ] and rhenium ... which makes the decay possible" (Emery). The
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practical significance of this little peculiarity, of course, is low, as
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Re-187 already has a half life of over 10^10 years.
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Alpha decay and spontaneous fission might also be affected by
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changes in the electron density near the nucleus, for a different reason.
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These processes occur as a result of penetration of the "Coulomb barrier"
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that inhibits emission of charged particles from the nucleus, and their
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rate is *very* sensitive to the height of the barrier. Changes in the
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electron density could, in principle, affect the barrier by some tiny
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amount. However, the magnitude of the effect is *very* small, according to
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theoretical calculations; for a few alpha emitters, the change has been
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estimated to be of the order of 1 part in 10^7 (!) or less, which would be
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unmeasurable in view of the fact that the alpha emitters' half lives aren't
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known to that degree of accuracy to begin with.
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All told, the existence of changes in radioactive decay rates due
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to the environment of the decaying nuclei is on solid grounds both
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experimentally and theoretically. But the magnitude of the changes is
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nothing to get very excited about.
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Reference: The best review article on this subject is now 20 years old: G.
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T. Emery, "Perturbation of Nuclear Decay Rates," Annual Review of Nuclear
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Science vol. 22, p. 165 (1972). Papers describing specific experiments are
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cited in that article, which contains considerable arcane math but also
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gives a reasonable qualitative "feel" for what is involved.
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********************************************************************************
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Item 17. original by David Brahm
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Baryogenesis - Why Are There More Protons Than Antiprotons?
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-----------------------------------------------------------
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(I) How do we really *know* that the universe is not matter-antimatter
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symmetric?
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(a) The Moon: Neil Armstrong did not annihilate, therefore the moon
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is made of matter.
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(b) The Sun: Solar cosmic rays are matter, not antimatter.
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(c) The other Planets: We have sent probes to almost all. Their survival
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demonstrates that the solar system is made of matter.
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(d) The Milky Way: Cosmic rays sample material from the entire galaxy.
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In cosmic rays, protons outnumber antiprotons 10^4 to 1.
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(e) The Universe at large: This is tougher. If there were antimatter
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galaxies then we should see gamma emissions from annihilation. Its absence
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is strong evidence that at least the nearby clusters of galaxies (e.g., Virgo)
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are matter-dominated. At larger scales there is little proof.
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However, there is a problem, called the "annihilation catastrophe"
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which probably eliminates the possibility of a matter-antimatter symmetric
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universe. Essentially, causality prevents the separation of large chucks
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of antimatter from matter fast enough to prevent their mutual annihilation
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in in the early universe. So the Universe is most likely matter dominated.
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(II) How did it get that way?
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Annihilation has made the asymmetry much greater today than in the
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early universe. At the high temperature of the first microsecond, there
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were large numbers of thermal quark-antiquark pairs. K&T estimate 30
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million antiquarks for every 30 million and 1 quarks during this epoch.
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That's a tiny asymmetry. Over time most of the antimatter has annihilated
|
|
with matter, leaving the very small initial excess of matter to dominate
|
|
the Universe.
|
|
|
|
Here are a few possibilities for why we are matter dominated today:
|
|
|
|
a) The Universe just started that way.
|
|
Not only is this a rather sterile hypothesis, but it doesn't work under
|
|
the popular "inflation" theories, which dilute any initial abundances.
|
|
b) Baryogenesis occurred around the Grand Unified (GUT) scale (very early).
|
|
Long thought to be the only viable candidate, GUT's generically have
|
|
baryon-violating reactions, such as proton decay (not yet observed).
|
|
c) Baryogenesis occurred at the Electroweak Phase Transition (EWPT).
|
|
This is the era when the Higgs first acquired a vacuum expectation value
|
|
(vev), so other particles acquired masses. Pure Standard Model physics.
|
|
|
|
Sakharov enumerated 3 necessary conditions for baryogenesis:
|
|
|
|
(1) Baryon number violation. If baryon number is conserved in all
|
|
reactions, then the present baryon asymmetry can only reflect asymmetric
|
|
initial conditions, and we are back to case (a), above.
|
|
(2) C and CP violation. Even in the presence of B-violating
|
|
reactions, without a preference for matter over antimatter the B-violation
|
|
will take place at the same rate in both directions, leaving no excess.
|
|
(3) Thermodynamic Nonequilibrium. Because CPT guarantees equal
|
|
masses for baryons and antibaryons, chemical equilibrium would drive the
|
|
necessary reactions to correct for any developing asymmetry.
|
|
|
|
It turns out the Standard Model satisfies all 3 conditions:
|
|
|
|
(1) Though the Standard Model conserves B classically (no terms in
|
|
the Lagrangian violate B), quantum effects allow the universe to tunnel
|
|
between vacua with different values of B. This tunneling is _very_
|
|
suppressed at energies/temperatures below 10 TeV (the "sphaleron mass"),
|
|
_may_ occur at e.g. SSC energies (controversial), and _certainly_ occurs at
|
|
higher temperatures.
|
|
|
|
(2) C-violation is commonplace. CP-violation (that's "charge
|
|
conjugation" and "parity") has been experimentally observed in kaon
|
|
decays, though strictly speaking the Standard Model probably has
|
|
insufficient CP-violation to give the observed baryon asymmetry.
|
|
|
|
(3) Thermal nonequilibrium is achieved during first-order phase
|
|
transitions in the cooling early universe, such as the EWPT (at T = 100 GeV
|
|
or so). As bubbles of the "true vacuum" (with a nonzero Higgs vev)
|
|
percolate and grow, baryogenesis can occur at or near the bubble walls.
|
|
|
|
A major theoretical problem, in fact, is that there may be _too_
|
|
_much_ B-violation in the Standard Model, so that after the EWPT is
|
|
complete (and condition 3 above is no longer satisfied) any previously
|
|
generated baryon asymmetry would be washed out.
|
|
|
|
References: Kolb and Turner, _The Early Universe_;
|
|
Dine, Huet, Singleton & Susskind, Phys.Lett.B257:351 (1991);
|
|
Dine, Leigh, Huet, Linde & Linde, Phys.Rev.D46:550 (1992).
|
|
|
|
********************************************************************************
|
|
Item 18.
|
|
|
|
TIME TRAVEL - FACT OR FICTION? updated 25-Nov-1992
|
|
------------------------------ original by Jon J. Thaler
|
|
|
|
We define time travel to mean departure from a certain place and
|
|
time followed (from the traveller's point of view) by arrival at the same
|
|
place at an earlier (from the sedentary observer's point of view) time.
|
|
Time travel paradoxes arise from the fact that departure occurs after
|
|
arrival according to one observer and before arrival according to another.
|
|
In the terminology of special relativity time travel implies that the
|
|
timelike ordering of events is not invariant. This violates our intuitive
|
|
notions of causality. However, intuition is not an infallible guide, so we
|
|
must be careful. Is time travel really impossible, or is it merely another
|
|
phenomenon where "impossible" means "nature is weirder than we think?" The
|
|
answer is more interesting than you might think.
|
|
|
|
THE SCIENCE FICTION PARADIGM:
|
|
|
|
The B-movie image of the intrepid chrononaut climbing into his time
|
|
machine and watching the clock outside spin backwards while those outside
|
|
the time machine watch the him revert to callow youth is, according to
|
|
current theory, impossible. In current theory, the arrow of time flows in
|
|
only one direction at any particular place. If this were not true, then
|
|
one could not impose a 4-dimensional coordinate system on space-time, and
|
|
many nasty consequences would result. Nevertheless, there is a scenario
|
|
which is not ruled out by present knowledge. It requires an unusual
|
|
spacetime topology (due to wormholes or strings in general relativity)
|
|
which has not not yet seen, but which may be possible. In this scenario
|
|
the universe is well behaved in every local region; only by exploring the
|
|
global properties does one discover time travel.
|
|
|
|
CONSERVATION LAWS:
|
|
|
|
It is sometimes argued that time travel violates conservation laws.
|
|
For example, sending mass back in time increases the amount of energy that
|
|
exists at that time. Doesn't this violate conservation of energy? This
|
|
argument uses the concept of a global conservation law, whereas
|
|
relativistically invariant formulations of the equations of physics only
|
|
imply local conservation. A local conservation law tells us that the
|
|
amount of stuff inside a small volume changes only when stuff flows in or
|
|
out through the surface. A global conservation law is derived from this by
|
|
integrating over all space and assuming that there is no flow in or out at
|
|
infinity. If this integral cannot be performed, then global conservation
|
|
does not follow. So, sending mass back in time might be alright, but it
|
|
implies that something strange is happening. (Why shouldn't we be able to
|
|
do the integral?)
|
|
|
|
GENERAL RELATIVITY:
|
|
|
|
One case where global conservation breaks down is in general
|
|
relativity. It is well known that global conservation of energy does not
|
|
make sense in an expanding universe. For example, the universe cools as it
|
|
expands; where does the energy go? See FAQ article #1 - Energy
|
|
Conservation in Cosmology, for details.
|
|
|
|
It is interesting to note that the possibility of time travel in GR
|
|
has been known at least since 1949 (by Kurt Godel, discussed in [1], page
|
|
168). The GR spacetime found by Godel has what are now called "closed
|
|
timelike curves" (CTCs). A CTC is a worldline that a particle or a person
|
|
can follow which ends at the same spacetime point (the same position and
|
|
time) as it started. A solution to GR which contains CTCs cannot have a
|
|
spacelike embedding - space must have "holes" (as in donut holes, not holes
|
|
punched in a sheet of paper). A would-be time traveller must go around or
|
|
through the holes in a clever way.
|
|
|
|
The Godel solution is a curiosity, not useful for constructing a
|
|
time machine. Two recent proposals, one by Morris, et al. [2] and one by
|
|
Gott [3], have the possibility of actually leading to practical devices (if
|
|
you believe this, I have a bridge to sell you). As with Godel, in these
|
|
schemes nothing is locally strange; time travel results from the unusual
|
|
topology of spacetime. The first uses a wormhole (the inner part of a
|
|
black hole, see fig. 1 of [2]) which is held open and manipulated by
|
|
electromagnetic forces. The second uses the conical geometry generated by
|
|
an infinitely long string of mass. If two strings pass by each other, a
|
|
clever person can go into the past by traveling a figure-eight path around
|
|
the strings.
|
|
|
|
GRANDFATHER PARADOXES:
|
|
|
|
With the demonstration that general relativity contains CTCs,
|
|
people began studying the problem of self-consistency. Basically, the
|
|
problem is that of the "grandfather paradox:" What happens if our time
|
|
traveller kills her grandmother before her mother was born? In more
|
|
readily analyzable terms, one can ask what are the implications of the
|
|
quantum mechanical interference of the particle with its future self.
|
|
Boulware [5] shows that there is a problem - unitarity is violated. This is
|
|
related to the question of when one can do the global conservation integral
|
|
discussed above. It is an example of the "Cauchy problem" [1, chapter 7].
|
|
|
|
OTHER PROBLEMS (and an escape hatch?):
|
|
|
|
How does one avoid the paradox that a simple solution to GR has
|
|
CTCs which QM does not like? This is not a matter of applying a theory in
|
|
a domain where it is expected to fail. One relevant issue is the
|
|
construction of the time machine. After all, infinite strings aren't
|
|
easily obtained. In fact, it has been shown [4] that Gott's scenario
|
|
implies that the total 4-momentum of spacetime must be spacelike. This
|
|
seems to imply that one cannot build a time machine from any collection of
|
|
physical objects, whose 4-momentum must be timelike unless tachyons exist.
|
|
Similar objections apply to the wormhole method.
|
|
|
|
TACHYONS:
|
|
|
|
Finally, a diversion on a possibly related topic.
|
|
|
|
If tachyons exist as physical objects, causality is no longer
|
|
invariant. Different observers will see different causal sequences. This
|
|
effect requires only special relativity (not GR), and follows from the fact
|
|
that for any spacelike trajectory, reference frames can be found in which
|
|
the particle moves backward or forward in time. This is illustrated by the
|
|
pair of spacetime diagrams below. One must be careful about what is
|
|
actually observed; a particle moving backward in time is observed to be a
|
|
forward moving anti-particle, so no observer interprets this as time
|
|
travel.
|
|
|
|
t
|
|
One reference | Events A and C are at the same
|
|
frame: | place. C occurs first.
|
|
|
|
|
| Event B lies outside the causal
|
|
| B domain of events A and C.
|
|
-----------A----------- x (The intervals are spacelike).
|
|
|
|
|
C In this frame, tachyon signals
|
|
| travel from A-->B and from C-->B.
|
|
| That is, A and C are possible causes
|
|
of event B.
|
|
|
|
Another t
|
|
reference | Events A and C are not at the same
|
|
frame: | place. C occurs first.
|
|
|
|
|
| Event B lies outside the causal
|
|
-----------A----------- x domain of events A and C. (The
|
|
| intervals are spacelike)
|
|
|
|
|
| C In this frame, signals travel from
|
|
| B-->A and from B-->C. B is the cause
|
|
| B of both of the other two events.
|
|
|
|
The unusual situation here arises because conventional causality
|
|
assumes no superluminal motion. This tachyon example is presented to
|
|
demonstrate that our intuitive notion of causality may be flawed, so one
|
|
must be careful when appealing to common sense. See FAQ article # 6 -
|
|
Tachyons, for more about these weird hypothetical particles.
|
|
|
|
CONCLUSION:
|
|
|
|
The possible existence of time machines remains an open question.
|
|
None of the papers criticizing the two proposals are willing to
|
|
categorically rule out the possibility. Nevertheless, the notion of time
|
|
machines seems to carry with it a serious set of problems.
|
|
|
|
REFERENCES:
|
|
|
|
1: S.W. Hawking, and G.F.R. Ellis, "The Large Scale Structure of Space-Time,"
|
|
Cambridge University Press, 1973.
|
|
2: M.S. Morris, K.S. Thorne, and U. Yurtsever, PRL, v.61, p.1446 (1989).
|
|
--> How wormholes can act as time machines.
|
|
3: J.R. Gott, III, PRL, v.66, p.1126 (1991).
|
|
--> How pairs of cosmic strings can act as time machines.
|
|
4: S. Deser, R. Jackiw, and G. 't Hooft, PRL, v.66, p.267 (1992).
|
|
--> A critique of Gott. You can't construct his machine.
|
|
5: D.G. Boulware, University of Washington preprint UW/PT-92-04.
|
|
Available on the hep-th@xxx.lanl.gov bulletin board: item number 9207054.
|
|
--> Unitarity problems in QM with closed timelike curves.
|
|
|
|
********************************************************************************
|
|
Item 19.
|
|
|
|
Gravity and the Radiation of Charged Particles updated 24-JAN-1993 by SIC
|
|
---------------------------------------------- original by Kurt Sonnenmoser
|
|
|
|
Here as some answers to three oft-asked questions about the Equivalence
|
|
Principle and the radiation of charged particles in a gravitational field
|
|
according to GR. Remember that the behavior of charged particles in strong
|
|
gravitational fields is a matter of theory only - the effects are incredibly
|
|
small and have never been subject to direct experimental test. To make
|
|
matters worse, there is some disagreement among the experts as to the
|
|
predictions of GR in some cases - the mathematics is difficult and rigorous
|
|
proofs are not always available.
|
|
|
|
A) DOES THE GRAVITATIONAL FIELD OF A STATIC MASSIVE BODY CAUSE
|
|
RADIATION FROM A CHARGED PARTICLE AT REST ON ITS SURFACE?
|
|
(Or: "According to the Equivalence Principle, the electron on my
|
|
desk should radiate!")
|
|
|
|
Answer: No, it doesn't. Reason: Static situation --> no magnetic
|
|
fields --> vanishing field energy current, i.e. no radiation. The
|
|
Equivalence Principle only leads you to the conclusion that if you
|
|
put the particle on the bottom of an accelerated elevator in gravity
|
|
free space, you will observe no radiation (in the reference frame of
|
|
the elevator).
|
|
|
|
It is not trivial to show that the magnetic field vanishes for
|
|
a static charged particle in a gravitational field. EM fields do
|
|
not behave trivially in a curved spacetime. For example, the electric
|
|
field of a stationary point charge in a static gravitational field is not
|
|
a simple Coulomb field. However, it can be shown that the magnetic
|
|
field does vanish. [I do not have a literature reference for this
|
|
statement. Suggestions are welcome - Ed.]
|
|
|
|
B ) DOES A CHARGED STABLE PARTICLE IN FREE FALL IN THE GRAVITATIONAL
|
|
FIELD OF A MASSIVE BODY RADIATE? (Or: "According to the Equivalence
|
|
Principle, my electron should not radiate if it falls to the
|
|
ground!")
|
|
|
|
Answer: Yes, it does. Reason: It's like with any accelerated motion
|
|
of a charged particle: The acceleration causes "kinks" in the field
|
|
lines that propagate with the velocity of light and carry off
|
|
energy. This energy comes from the orbital energy of the particle
|
|
and not from its mass. As before, trying to apply the Equivalence
|
|
Principle is misleading: the free falling particle is only _locally_
|
|
equivalent to one at rest in gravity free space, but in order to
|
|
calculate the energy radiated off, you can integrate the energy
|
|
flux of the electromagnetic field over a sphere going to infinity
|
|
(in a fixed reference frame), which is, of course, not a local
|
|
procedure. The Equivalence Principle only tells you that if you go
|
|
very close to the particle, you see no radiation.
|
|
|
|
Caveat: It is not clear, despite the heuristic argument given
|
|
above, that this is a settled question. Our net experts have not
|
|
come up with a reference for a proof. This question is probably
|
|
best considered an open research question.
|
|
|
|
C) DOES A UNIFORMLY ACCELERATED CHARGE RADIATE? (Or: "Ok, let's forget
|
|
about the Equivalence Principle! What happens globally?")
|
|
|
|
Answer: David Boulware [Ann.Phys. 124, 169-188 (1980) ("Radiation
|
|
from a Uniformly Accelerated Charge")], for example, has shown that a
|
|
uniformly accelerated charge in gravity-free space does in fact radiate
|
|
(contrary to earlier beliefs, e.g. of Pauli), but also that it is
|
|
_not_ globally equivalent to a charge at rest in a static
|
|
gravitational field. More specifically, there are regions of
|
|
space-time where there is no coordinate frame in which the
|
|
accelerated charge is at rest and the gravitational field static. So
|
|
there is no contradiction to the fact that charges at rest in a
|
|
gravitational field do not radiate.
|
|
|
|
********************************************************************************
|
|
Item 20.
|
|
|
|
The Nobel Prize for Physics (1901-1992) updated 29-Nov-1992 by SIC
|
|
---------------------------------------
|
|
|
|
The following is a complete listing of Nobel Prize awards, from the first
|
|
award in 1901. Prizes were not awarded in every year. The description
|
|
following the names is an abbreviation of the official citation.
|
|
|
|
1901 Wilhelm Konrad Rontgen X-rays
|
|
1902 Hendrik Antoon Lorentz Magnetism in radiation phenomena
|
|
Pieter Zeeman
|
|
1903 Antoine Henri Bequerel Spontaneous radioactivity
|
|
Pierre Curie
|
|
Marie Sklowdowska-Curie
|
|
1904 Lord Rayleigh Density of gases and
|
|
(a.k.a. John William Strutt) discovery of argon
|
|
1905 Pilipp Eduard Anton von Lenard Cathode rays
|
|
1906 Joseph John Thomson Conduction of electricity by gases
|
|
1907 Albert Abraham Michelson Precision metrological investigations
|
|
1908 Gabriel Lippman Reproducing colors photographically
|
|
based on the phenomenon of interference
|
|
1909 Guglielmo Marconi Wireless telegraphy
|
|
Carl Ferdinand Braun
|
|
1910 Johannes Diderik van der Waals Equation of state of fluids
|
|
1911 Wilhelm Wien Laws of radiation of heat
|
|
1912 Nils Gustaf Dalen Automatic gas flow regulators
|
|
1913 Heike Kamerlingh Onnes Matter at low temperature
|
|
1914 Max von Laue Crystal diffraction of X-rays
|
|
1915 William Henry Bragg X-ray analysis of crystal structure
|
|
William Lawrence Bragg
|
|
1917 Charles Glover Barkla Characteristic X-ray spectra of elements
|
|
1918 Max Planck Energy quanta
|
|
1919 Johannes Stark Splitting of spectral lines in E fields
|
|
1920 Charles-Edouard Guillaume Anomalies in nickel steel alloys
|
|
1921 Albert Einstein Photoelectric Effect
|
|
1922 Niels Bohr Structure of atoms
|
|
1923 Robert Andrew Millikan Elementary charge of electricity
|
|
1924 Karl Manne Georg Siegbahn X-ray spectroscopy
|
|
1925 James Franck Impact of an electron upon an atom
|
|
Gustav Hertz
|
|
1926 Jean Baptiste Perrin Sedimentation equilibrium
|
|
1927 Arthur Holly Compton Compton effect
|
|
Charles Thomson Rees Wilson Invention of the Cloud chamber
|
|
1928 Owen Willans Richardson Thermionic phenomena, Richardson's Law
|
|
1929 Prince Louis-Victor de Broglie Wave nature of electrons
|
|
1930 Sir Chandrasekhara Venkata Raman Scattering of light, Raman effect
|
|
1932 Werner Heisenberg Quantum Mechanics
|
|
1933 Erwin Schrodinger Atomic theory
|
|
Paul Adrien Maurice Dirac
|
|
1935 James Chadwick The neutron
|
|
1936 Victor Franz Hess Cosmic rays
|
|
1937 Clinton Joseph Davisson Crystal diffraction of electrons
|
|
George Paget Thomson
|
|
1938 Enrico Fermi New radioactive elements
|
|
1939 Ernest Orlando Lawrence Invention of the Cyclotron
|
|
1943 Otto Stern Proton magnetic moment
|
|
1944 Isador Isaac Rabi Magnetic resonance in atomic nuclei
|
|
1945 Wolfgang Pauli The Exclusion principle
|
|
1946 Percy Williams Bridgman Production of extremely high pressures
|
|
1947 Sir Edward Victor Appleton Physics of the upper atmosphere
|
|
1948 Patrick Maynard Stuart Blackett Cosmic ray showers in cloud chambers
|
|
1949 Hideki Yukawa Prediction of Mesons
|
|
1950 Cecil Frank Powell Photographic emulsion for meson studies
|
|
1951 Sir John Douglas Cockroft Artificial acceleration of atomic
|
|
Ernest Thomas Sinton Walton particles and transmutation of nuclei
|
|
1952 Felix Bloch Nuclear magnetic precision methods
|
|
Edward Mills Purcell
|
|
1953 Frits Zernike Phase-contrast microscope
|
|
1954 Max Born Fundamental research in QM
|
|
Walther Bothe Coincidence counters
|
|
1955 Willis Eugene Lamb Hydrogen fine structure
|
|
Polykarp Kusch Electron magnetic moment
|
|
1956 William Shockley Transistors
|
|
John Bardeen
|
|
Walter Houser Brattain
|
|
1957 Chen Ning Yang Parity violation
|
|
Tsung Dao Lee
|
|
1958 Pavel Aleksejevic Cerenkov Interpretation of the Cerenkov effect
|
|
Il'ja Mickajlovic Frank
|
|
Igor' Evgen'evic Tamm
|
|
1959 Emilio Gino Segre The Antiproton
|
|
Owen Chamberlain
|
|
1960 Donald Arthur Glaser The Bubble Chamber
|
|
1961 Robert Hofstadter Electron scattering on nucleons
|
|
Rudolf Ludwig Mossbauer Resonant absorption of photons
|
|
1962 Lev Davidovic Landau Theory of liquid helium
|
|
1963 Eugene P. Wigner Fundamental symmetry principles
|
|
Maria Goeppert Mayer Nuclear shell structure
|
|
J. Hans D. Jensen
|
|
1964 Charles H. Townes Maser-Laser principle
|
|
Nikolai G. Basov
|
|
Alexander M. Prochorov
|
|
1965 Sin-Itiro Tomonaga Quantum electrodynamics
|
|
Julian Schwinger
|
|
Richard P. Feynman
|
|
1966 Alfred Kastler Study of Hertzian resonance in atoms
|
|
1967 Hans Albrecht Bethe Energy production in stars
|
|
1968 Luis W. Alvarez Discovery of many particle resonances
|
|
1969 Murray Gell-Mann Quark model for particle classification
|
|
1970 Hannes Alven Magneto-hydrodynamics in plasma physics
|
|
Louis Neel Antiferromagnetism and ferromagnetism
|
|
1971 Dennis Gabor Principles of holography
|
|
1972 John Bardeen Superconductivity
|
|
Leon N. Cooper
|
|
J. Robert Schrieffer
|
|
1973 Leo Esaki Tunneling in superconductors
|
|
Ivar Giaever
|
|
Brian D. Josephson Super-current through tunnel barriers
|
|
1974 Antony Hewish Discovery of pulsars
|
|
Sir Martin Ryle Pioneering radioastronomy work
|
|
1975 Aage Bohr Structure of the atomic nucleus
|
|
Ben Mottelson
|
|
James Rainwater
|
|
1976 Burton Richter Discovery of the J/Psi particle
|
|
Samual Chao Chung Ting
|
|
1977 Philip Warren Anderson Electronic structure of magnetic and
|
|
Nevill Francis Mott disordered solids
|
|
John Hasbrouck Van Vleck
|
|
1978 Pyotr Kapitsa Liquifaction of helium
|
|
Arno A. Penzias Cosmic Microwave Background Radiation
|
|
Robert W. Wilson
|
|
1979 Sheldon Glashow Electroweak Theory, especially
|
|
Steven Weinberg weak neutral currents
|
|
Abdus Salam
|
|
1980 James Cronin Discovery of CP violation in the
|
|
Val Fitch asymmetric decay of neutral K-mesons
|
|
1981 Kai M. Seigbahn High resolution electron spectroscopy
|
|
Nicolaas Bleombergen Laser spectroscopy
|
|
Arthur L. Schawlow
|
|
1982 Kenneth G. Wilson Critical phenomena in phase transitions
|
|
1983 Subrahmanyan Chandrasekhar Evolution of stars
|
|
William A. Fowler
|
|
1984 Carlo Rubbia Discovery of W,Z
|
|
Simon van der Meer Stochastic cooling for colliders
|
|
1985 Klaus von Klitzing Discovery of quantum Hall effect
|
|
1986 Gerd Binning Scanning Tunneling Microscopy
|
|
Heinrich Rohrer
|
|
Ernst August Friedrich Ruska Electron microscopy
|
|
1987 Georg Bednorz High-temperature superconductivity
|
|
Alex K. Muller
|
|
1988 Leon Max Lederman Discovery of the muon neutrino leading
|
|
Melvin Schwartz to classification of particles in
|
|
Jack Steinberger families
|
|
1989 Hans Georg Dehmelt Penning Trap for charged particles
|
|
Wolfgang Paul Paul Trap for charged particles
|
|
Norman F. Ramsey Control of atomic transitions by the
|
|
separated oscillatory fields method
|
|
1990 Jerome Isaac Friedman Deep inelastic scattering experiments
|
|
Henry Way Kendall leading to the discovery of quarks
|
|
Richard Edward Taylor
|
|
1991 Pierre-Gilles de Gennes Order-disorder transitions in liquid
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|
crystals and polymers
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1992 Georges Charpak Multiwire Proportional Chamber
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|
********************************************************************************
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Item 21.
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Open Questions updated 13-OCT-1992 by SIC
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-------------- original by John Baez
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While for the most part a FAQ covers the answers to frequently
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asked questions whose answers are known, in physics there are also plenty
|
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of simple and interesting questions whose answers are not known. Before you
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set about answering these questions on your own, it's worth noting that
|
|
while nobody knows what the answers are, there has been at least a little,
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|
and sometimes a great deal, of work already done on these subjects. People
|
|
have said a lot of very intelligent things about many of these questions.
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|
So do plenty of research and ask around before you try to cook up a theory
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|
that'll answer one of these and win you the Nobel prize! You can expect to
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|
really know physics inside and out before you make any progress on these.
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|
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|
The following partial list of "open" questions is divided into two
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|
groups, Cosmology and Astrophysics, and Particle and Quantum Physics.
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|
However, given the implications of particle physics on cosmology, the
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|
division is somewhat artificial, and, consequently, the categorization is
|
|
somewhat arbitrary.
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|
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|
(There are many other interesting and fundamental questions in
|
|
fields such as condensed matter physics, nonlinear dynamics, etc., which
|
|
are not part of the set of related questions in cosmology and quantum
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|
physics which are discussed below. Their omission is not a judgement
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|
about importance, but merely a decision about the scope of this article.)
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|
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|
Cosmology and Astrophysics
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|
--------------------------
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|
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|
1. What happened at, or before the Big Bang? Was there really an initial
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|
singularity? Of course, this question might not make sense, but it might.
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|
Does the history of universe go back in time forever, or only a finite
|
|
amount?
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|
|
|
2. Will the future of the universe go on forever or not? Will there be a
|
|
"big crunch" in the future? Is the Universe infinite in spatial extent?
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|
|
|
3. Why is there an arrow of time; that is, why is the future so much
|
|
different from the past?
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|
|
|
4. Is spacetime really four-dimensional? If so, why - or is that just a
|
|
silly question? Or is spacetime not really a manifold at all if examined
|
|
on a short enough distance scale?
|
|
|
|
5. Do black holes really exist? (It sure seems like it.) Do they really
|
|
radiate energy and evaporate the way Hawking predicts? If so, what happens
|
|
when, after a finite amount of time, they radiate completely away? What's
|
|
left? Do black holes really violate all conservation laws except
|
|
conservation of energy, momentum, angular momentum and electric charge?
|
|
|
|
6. Is the Cosmic Censorship Hypothesis true? Roughly, for generic
|
|
collapsing isolated gravitational systems are the singularities that might
|
|
develop guaranteed to be hidden beyond a smooth event horizon? If Cosmic
|
|
Censorship fails, what are these naked singularities like? That is, what
|
|
weird physical consequences would they have?
|
|
|
|
7. Why are the galaxies distributed in clumps and filaments? Is most of
|
|
the matter in the universe baryonic? Is this a matter to be resolved by
|
|
new physics?
|
|
|
|
8. What is the nature of the missing "Dark Matter"? Is it baryonic,
|
|
neutrinos, or something more exotic?
|
|
|
|
Particle and Quantum Physics
|
|
----------------------------
|
|
|
|
1. Why are the laws of physics not symmetrical between left and right,
|
|
future and past, and between matter and antimatter? I.e., what is the
|
|
mechanism of CP violation, and what is the origin of parity violation in
|
|
Weak interactions? Are there right-handed Weak currents too weak to have
|
|
been detected so far? If so, what broke the symmetry? Is CP violation
|
|
explicable entirely within the Standard Model, or is some new force or
|
|
mechanism required?
|
|
|
|
2. Why are the strengths of the fundamental forces (electromagnetism, weak
|
|
and strong forces, and gravity) what they are? For example, why is the
|
|
fine structure constant, which measures the strength of electromagnetism,
|
|
about 1/137.036? Where did this dimensionless constant of nature come from?
|
|
Do the forces really become Grand Unified at sufficiently high energy?
|
|
|
|
3. Why are there 3 generations of leptons and quarks? Why are there mass
|
|
ratios what they are? For example, the muon is a particle almost exactly
|
|
like the electron except about 207 times heavier. Why does it exist and
|
|
why precisely that much heavier? Do the quarks or leptons have any
|
|
substructure?
|
|
|
|
4. Is there a consistent and acceptable relativistic quantum field theory
|
|
describing interacting (not free) fields in four spacetime dimensions? For
|
|
example, is the Standard Model mathematically consistent? How about
|
|
Quantum Electrodynamics?
|
|
|
|
5. Is QCD a true description of quark dynamics? Is it possible to
|
|
calculate masses of hadrons (such as the proton, neutron, pion, etc.)
|
|
correctly from the Standard Model? Does QCD predict a quark/gluon
|
|
deconfinement phase transition at high temperature? What is the nature of
|
|
the transition? Does this really happen in Nature?
|
|
|
|
6. Why is there more matter than antimatter, at least around here? Is
|
|
there really more matter than antimatter throughout the universe?
|
|
|
|
7. What is meant by a "measurement" in quantum mechanics? Does
|
|
"wavefunction collapse" actually happen as a physical process? If so, how,
|
|
and under what conditions? If not, what happens instead?
|
|
|
|
8. What are the gravitational effects, if any, of the immense (possibly
|
|
infinite) vacuum energy density seemingly predicted by quantum field
|
|
theory? Is it really that huge? If so, why doesn't it act like an
|
|
enormous cosmological constant?
|
|
|
|
9. Why doesn't the flux of solar neutrinos agree with predictions? Is the
|
|
disagreement really significant? If so, is the discrepancy in models of
|
|
the sun, theories of nuclear physics, or theories of neutrinos? Are
|
|
neutrinos really massless?
|
|
|
|
The Big Question (TM)
|
|
---------------------
|
|
|
|
This last question sits on the fence between the two categories above:
|
|
|
|
How to you merge Quantum Mechanics and General Relativity to create a
|
|
quantum theory of gravity? Is Einstein's theory of gravity (classical GR)
|
|
also correct in the microscopic limit, or are there modifications
|
|
possible/required which coincide in the observed limit(s)? Is gravity
|
|
really curvature, or what else -- and why does it then look like curvature?
|
|
An answer to this question will necessarily rely upon, and at the same time
|
|
likely be a large part of, the answers to many of the other questions above.
|
|
|
|
********************************************************************************
|
|
Item 22. updated 15-OCT-1992 by SIC
|
|
|
|
Accessing and Using Online Physics Resources
|
|
--------------------------------------------
|
|
|
|
(I) Particle Physics Databases
|
|
|
|
The Full Listings of the Review of Particle Properties (RPP), as
|
|
well as other particle physics databases, are accessible on-line. Here is
|
|
a summary of the major ones, as described in the RPP:
|
|
|
|
(A) SLAC Databases
|
|
|
|
PARTICLES - Full listings of the RPP
|
|
HEP - Guide to particle physics preprints, journal articles, reports,
|
|
theses, conference papers, etc.
|
|
CONF - Listing of past and future conferences in particle physics
|
|
HEPNAMES - E-mail addresses of many HEP people
|
|
INST - Addresses of HEP institutions
|
|
DATAGUIDE - Adjunct to HEP, indexes papers
|
|
REACTIONS - Numerical data on reactions (cross-sections, polarizations, etc)
|
|
EXPERIMENTS - Guide to current and past experiments
|
|
|
|
Anyone with a SLAC account can access these databases. Alternately, most
|
|
of us can access them via QSPIRES. You can access QSPIRES via BITNET with
|
|
the 'send' command ('tell','bsend', or other system-specific command) or by
|
|
using E-mail. For example, send QSPIRES@SLACVM FIND TITLE Z0 will get you
|
|
a search of HEP for all papers which reference the Z0 in the title. By
|
|
E-mail, you would send the one line message "FIND TITLE Z0" with a blank
|
|
subject line to QSPIRES@SLACVM.BITNET or QSPIRES@VM.SLAC.STANFORD.EDU.
|
|
QSPIRES is free. Help can be obtained by mailing "HELP" to QSPIRES.
|
|
|
|
For more detailed information, see the RPP, p.I.12, or contact: Louise
|
|
Addis (ADDIS@SLACVM.BITNET) or Harvey Galic (GALIC@SLACVM.BITNET).
|
|
|
|
(B) CERN Databases on ALICE
|
|
|
|
LIB - Library catalogue of books, preprints, reports, etc.
|
|
PREP - Subset of LIB containing preprints, CERN publications, and
|
|
conference papers.
|
|
CONF - Subset of LIB containing upcoming and past conferences since 1986
|
|
DIR - Directory of Research Institutes in HEP, with addresses, fax,
|
|
telex, e-mail addresses, and info on research programs
|
|
|
|
ALICE can be accessed via DECNET or INTERNET. It runs on the CERN library's
|
|
VXLIB, alias ALICE.CERN.CH (IP# 128.141.201.44). Use Username ALICE (no
|
|
password required.) Remote users with no access to the CERN Ethernet can
|
|
use QALICE, similar to QSPIRES. Send E-mail to QALICE@VXLIB.CERN.CH, put
|
|
the query in the subject field and leave the message field black. For
|
|
more information, send the subject "HELP" to QALICE or contact CERN
|
|
Scientific Information Service, CERN, CH-1211 Geneva 23, Switzerland,
|
|
or E-mail MALICE@VXLIB.CERN.CH.
|
|
|
|
Regular weekly or monthly searches of the CERN databases can be arranged
|
|
according to a personal search profile. Contact David Dallman, CERN SIS
|
|
(address above) or E-mail CALLMAN@CERNVM.CERN.CH.
|
|
|
|
DIR is available in Filemaker PRO format for Macintosh. Contact Wolfgang
|
|
Simon (ISI@CERNVM.CERN.CH).
|
|
|
|
(C) Other Databases
|
|
|
|
Durham-RAL and Serpukhov both maintain large databases containing Particle
|
|
Properties, reaction data, experiments, E-mail ID's, cross-section
|
|
compilations (CS), etc. Except for the Serpukhov CS, these databases
|
|
overlap SPIRES at SLAC considerably, though they are not the same and may
|
|
be more up-to-date. For details, see the RPP, p.I.14, or contact:
|
|
For Durham-RAL, Mike Whalley (MRW@UKACRL.BITNET,MRW@CERNVM.BITNET) or
|
|
Dick Roberts (RGR@UKACRL.BITNET). For Serpukhov, contact Sergey Alekhin
|
|
(ALEKHIN@M9.IHEP.SU) or Vladimir Exhela (EZHELA@M9.IHEP.SU).
|
|
|
|
(II) Online Preprint Sources
|
|
|
|
There are a number of online sources of preprints:
|
|
|
|
alg-geom@publications.math.duke.edu (algebraic geometry)
|
|
astro-ph@babbage.sissa.it (astrophysics)
|
|
cond-mat@babbage.sissa.it (condensed matter)
|
|
funct-an@babbage.sissa.it (functional analysis)
|
|
hep-lat@ftp.scri.fsu.edu (computational and lattice physics)
|
|
hep-ph@xxx.lanl.gov (high energy physics phenomenological)
|
|
hep-th@xxx.lanl.gov (high energy physics theoretical)
|
|
lc-om@alcom-p.cwru.edu (liquid crystals, optical materials)
|
|
gr-qc@xxx.lanl.gov (general relativity, quantum cosmology)
|
|
|
|
To get things if you know the preprint number, send a message to
|
|
the appropriate address with subject header "get (preprint number)" and
|
|
no message body. If you *don't* know the preprint number, or want to get
|
|
preprints regularly, or want other information, send a message with
|
|
subject header "help" and no message body.
|
|
|
|
********************************************************************************
|
|
END OF FAQ |