ISSN:0031-9228    

DOI:10.1063/1.2810614

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2810615

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2810617

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2810618

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Any Lorentz‐invariant local field theory must obey theCPTtheorem. That is to say, the theory must be invariant under thecombinedoperations of charge conjugation, parity inversion and time reversal, even though we know that these symmetries, taken one at a time, can be violated in elementary‐particle processes. It follows that particles and their antiparticles must have identical masses and equal magnetic moments (of opposite sign).

ISSN:0031-9228    

DOI:10.1063/1.2810619

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Would you believe that this is our own Milky Way? It is not an artist's conception of what the Galaxy might look like to an outside observer, but rather a near‐infrared image of the inner reaches of the Milky Way, produced by the diffuse Infrared Background Experiment aboard the Cosmic Background Explorer satellite. COBE has been in Earth orbit since November. (SeePHYSICS TODAY, March, page 17.)

ISSN:0031-9228    

DOI:10.1063/1.2810620

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Water, gasoline, pancake syrup, mucus, salad oil, cornstarch‐and‐water paste, Silly Putty, liquid dishwashing soap, egg white, glycerin, Vaseline, ketchup, model airplane glue, paint, toothpaste—this motley list of substances seems to defy scientific classification. Water, gasoline, salad oil and glycerin are clearly liquids. The other substances, strictly speaking, are also liquids, since they all flow on the application of stress. But the name “liquid” hardly captures the variety of behavior in these substances. The substances differ from one another in their mechanical responses almost as much as they differ from solids. In the first place, they differ enormously from one another in viscosity, the quantitative measure of a liquid's flow response. Furthermore, many of them have striking properties whose description requires variables besides viscosity. Syrup becomes sticky as it dries. Liquid dishwashing soap has the same consistency as syrup, but it does not become sticky on drying. Mucus, egg white and model airplane glue are springy and rubbery. Silly Putty and cornstarch paste flow on a tilted surface but shatter like a brittle solid on sudden impact. Dishwashing soap in water easily forms masses of long‐lived foam. Even the simplest flow properties of toothpaste are qualitatively unliquid‐like: It comes out of its tube as a plug rather unlike an ordinary liquid, which flows fastest in the middle of the opening.

ISSN:0031-9228    

DOI:10.1063/1.881249

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Science, like life itself, often poses questions whose answers are so sophisticated and indefinite that one must either rely on the opinion established by the majority or refer to some article of “faith” rather than deductive knowledge. “Where does randomness come from?” “How does order arise from disorder?” These are perhaps the oldest questions of this kind. Anyone who has thought about the principles governing nature has surely faced such questions. Everyday life, as well as conventional learning in physics, has almost persuaded us that complex, irregular and intricate behavior is possible only in very complex systems and that the study of some of these very complex systems may be beyond the scope of physical theory. The vast multitude of molecules in a bottle filled with gas or a crowd of infuriated fans reacting to the news that a football match has been canceled suddenly, are both examples of complex systems. In such systems we usually fail to relate cause and effect uambigously—that is, we cannot predict the behavior of the system in detail and therefore conclude that it is random. Of course, there is always the hope that it might be possible to eliminate such seeming randomness and unpredictability if one had more precise knowledge about the system. Would having a detailed knowledge of the interaction among the elements of a complex system and comprehensive and precise information about their initial states allow one to make precise predictions about the system's behavior at large times, so that the system will not appear to be random? The answer is yes only if one believes in Laplacian determinism, which was one of the earliest dogmas of science.

ISSN:0031-9228    

DOI:10.1063/1.881250

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

It was 3:40 am Pacific daylight time, 25 August 1989. I had watched with fascination a video display of Voyager 2's radio signal after the spacecraft had passed through Neptune's thick atmosphere, and for the last 90 minutes I had been attempting to nap in a sleeping bag on the floor of my office at JPL. My computer had just awakened me with a reminder that the first of 23 high‐resolution pictures of Neptune's moon Triton was about to appear on the small monitor on my desk. The adjacent office was crowded with a dozen or so of my coworkers excitedly anticipating the same pictures. The first image appeared on my screen; boisterous cheering simultaneously erupted from next door. All thoughts of sleep fled, and for the next two hours I, along with dozens of other Voyager personnel and millions of interested onlookers around the world, exulted in the amazing scenes being transmitted by a small robot more than 4.4 billion km (4.1 light‐hours) away. Humanity was seeing for the first time the surface features of the most distant moon in our solar system.

ISSN:0031-9228    

DOI:10.1063/1.881251

出版商:AIP    

年代:1990

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.2810621

出版商:AIP    

年代:1990

数据来源: AIP