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Topic: Time in physics

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	Time - Wikipedia, the free encyclopedia
		Time is also a matter of significant social importance, having economic value ("time is money") as well as personal value due to an awareness of the limited time in each day and in our lives.
		Time is currently one of the few fundamental quantities (quantities which cannot be defined via other quantities because there is nothing more fundamental known at present).
		However, some aspects of time use are relatively stable over long periods of time, such as the amount of time spent traveling to work, which despite major changes in transport, has been observed to be about 20-30 minutes one-way for a large number of cities over a long period of time.
	en.wikipedia.org /wiki/Time (2013 words)

	Time [Internet Encyclopedia of Philosophy]
		If physical time, psychological time, and biological time are three different kinds of time, then three answers are required to the question "What is time?" and some commentary is required regarding their relationships, such as whether one is the most fundamental.
		Spacetime is four-dimensional and a continuum, with time being a distinguished, one-dimensional sub-space of this continuum.
		Proper time along a worldline in 4-d spacetime is the time elapsed by an object having that worldline, as shown on an ideal clock having the same worldline.
	www.utm.edu /research/iep/t/time.htm (15898 words)

	Chapter 8. On the Idea of Time in Physics. Einstein, Albert. 1920. Relativity: The Special and General Theory
		It is clear that this definition can be used to give an exact meaning not only to two events, but to as many events as we care to choose, and independently of the positions of the scenes of the events with respect to the body of reference 1 (here the railway embankment).
		Under these conditions we understand by the “time” of an event the reading (position of the hands) of that one of these clocks which is in the immediate vicinity (in space) of the event.
		This assumption is a physical hypothesis about the law of propagation of light; it must certainly be fulfilled if we are to maintain the law of the constancy of the velocity of light in vacuo.
	www.bartleby.com /173/8.html (730 words)

	Time in physics - Unipedia (Site not responding. Last check: 2007-10-10)
		The sun was the arbiter of the flow of time, but time was known only to the hour, for millennia.
		The use of the pendulum, ratchets and gears allowed the towns of Europe to create mechanisms to display the time on their respective town clocks; by the time of the scientific revolution, the clocks became miniaturized enough for families to share a personal clock, or perhaps a pocket watch.
		Cosmological arrow of time - distinguished by the expansion of the universe.
	www.unipedia.info /Time_in_physics.html (1732 words)

	Time - Time Travel
		Time travel is the concept of traveling forward and backward to different points in time, much as we do through space.
		The assumption that time travel or superluminal communications is impossible allows one to derive interesting results such as the no cloning theorem, and how the rules of quantum mechanics work to preserve causality is an active area of research.
		Time, and the apparent movement of time, is connected to the number 12 - which is 1+2 =3 - or third dimension.
	www.crystalinks.com /timetravel.html (3083 words)

	Space Time Mass Home Page (Site not responding. Last check: 2007-10-10)
		The estimated equivalent mass of space-time (density) is calculated to be approximately one to 1000 times the mass of one electron per cubic meter.
		The simple proof to this theory is Comprised of all the present scientific observations and calculations of modern astronomy and physics, which dictate the existence of some kind of dark matter or massive neutrinos.
		According to him (and the science of that time) air has no mass or pressure.(since air goes to infinity!!, any mass or pressure would crush everything!!) The wind, heat, cold, birds' ability to fly, and sound were all explained by levitation force, heat force, etc., which were all inaccurate.
	www.space-time-mass.com (510 words)

	NIST Physics Laboratory home page
		Electron and Optical Physics: develops measurement methods and associated technology for determining electron and photon interactions with matter.
		is responsible for the standards of time and frequency; and since length is now derived from the second, develops optical frequency standards.
		conducts research in atomic and chemical physics, precision measurement, and laser and optical physics.
	physics.nist.gov (149 words)

	[No title]
		Time as we experience it has two outstanding features: it is unidirectional, and it is non-homogeneous.
		Absolute time, for Newton, is somewhat like a Platonic universal; it is time as it would be for God, who "is everywhere present; and by existing always and everywhere, he constitutes duration and space....God is the same God, always and everywhere.
		Intervals of time, however, are part of the definition of velocity, and velocity in turn is part of the definition of energy.
	www.ucs.mun.ca /~davidt/TimePhys.html (4135 words)

	Time Travel and Modern Physics
		It is ironic that time travel should lead generically not to contradictions or to constraints (in the normal region) but to underdetermination of what happens in the time travel region by what happens everywhere else (an underdetermination tied neither to a probabilistic dynamics or to a free edge to space-time).
		In the time travel case there is no such causal story to be told: there simply has to be some pre-established harmony between the global space-time structure and the matter distribution on some space-like surfaces.
		Thus the reason why the global time travel properties of the counterfactual space-time have to be significantly different from the actual space-time is not that there are problems with metric singularities or alterations in the metric that force significant global changes when we go to the counterfactual matter distribution.
	plato.stanford.edu /entries/time-travel-phys (12645 words)

	Time
		Other issues concerning the topology of time include (i) whether time is branching or non-branching, (ii) whether time is open or closed, (iii) whether there can be two or more disconnected time streams, (iv) whether time has an intrinsic direction, and (v) whether time is dense or continuous or neither.
		The question of whether there could be time without change has been debated by philosophers since the days of Plato and Aristotle, and has traditionally been thought to be closely tied to the question of whether time exists independently of the events that occur in time.
		On this view, time is like an empty container into which events may be placed; but it is a container that exists independently of whether or not anything is placed in it.
	plato.stanford.edu /entries/time (5523 words)

	MKaku.org \| Articles \| “The Physics of Time Travel” (Site not responding. Last check: 2007-10-10)
		That may have made great fiction, but physicists have always scoffed at the idea of time travel, considering it to be the realm of cranks, mystics, and charlatans, and with good reason.
		One stubborn problem with time travel is that it is riddled with several types of paradoxes.
		According to Einstein, time was more like a river, which meandered around stars and galaxies, speeding up and slowing down as it passed around massive bodies.
	www.mkaku.org /articles/phys_time_travel.shtml (1439 words)

	Time in Physics (Site not responding. Last check: 2007-10-10)
		The time and place of our birth is fixed, not subject to our will, but we hope to influence the conditions of our death.
		Time is a river which sweeps me along, but I am the river; it is a tiger that devours me, but I am the tiger; it is a fire that consumes me, but I am the fire.
		This is beautifully mirrored in the modern, scientific view of time, where connection to the largest and earliest structures in the universe generates the asymmetry between past and future.
	www.lightlink.com /vic/tricycle_final.html (2601 words)

	Time Travel Paradoxes
		First, we might think that entropy could be reversed by time travel, so that forms of matter would be restored to that state they would have been at the earlier period.
		Every instance of time travel generating an infinite number of alternative universes might be thought to violate Ockham's Razor, especially since the idea that an alternative universe could be generated in the first place has disturbing consequences for the metaphysics of identity.
		But without them, time travel, that would allow for the sort of temporal loop in which the paradoxical and impossible watch of Somewhere in Time becomes possible, is itself impossible.
	www.friesian.com /paradox.htm (1328 words)

	Specularium A Site exploring the hypothesis of Three-Dimensional Time - Rebel Physics, an Introduction.
		A decade ago I became convinced, from my researches in another field, that time must have a richer structure than that offered by the single dimension that we commonly ascribe to it.
		The overwhelming majority of alternative theories in physics attack only a limited number of the interpretations of observations which constitute the paradigm of the Standard Models of Cosmology and Particle Physics.
		Whilst the hypothesis of 3 dimensional time remains unfalsified, I intend to devote my time to exploring its implications in parapsychology and starship design, neither of which have much of a chance within the standard models.
	www.specularium.org (234 words)

	"The Nature of Time: Geometry, Physics & Perception"
		Although underlined by physics, substantial space is also given to novel and unorthodox ideas from other branches of science.
		Volume 95 of the NATO Science Series II: Mathematics, Physics and Chemistry, Kluwer Academic Publishers, Dordrecht - Boston - London.
		An electronic copy of the poster of the workshop is also available.
	www.astro.sk /~msaniga/nato_arw (233 words)

	Sci-Fi Science - Time Travel, Aliens, Hyperdrive Systems, Dr Who (Site not responding. Last check: 2007-10-10)
		As a small group of professional scientists we thought it would be a good idea to create a fun website to explore the true science underlying popular science fiction.
		The site is split into two parts, the serious discussion of the science behind common science fiction themes, such as time travel etc and a fun part, such as why we got interested in science and what we consider to be the greatest Sci-Fi films ever made.
		Wherever you are if you want the serious stuff click on an Einstein and for the fun stuff click on a Dalek.
	freespace.virgin.net /steve.preston/Time.html (108 words)

	Time Travel in Flatland? (Site not responding. Last check: 2007-10-10)
		Abbott wrote Flatland before the unified picture of space and time emerged in early 20th century mathematics and physics.
		Einstein's General Theory of Relativity is much simpler in Flatland (plus time), so that is where we'll start exploring what it means to travel in time.
		In one time and two space dimensions, the Einstein equation is almost too simple, but the results are not!
	www.theory.caltech.edu /people/patricia/lctoc.html (237 words)

	Space-Time Physics Ph 1bc (Site not responding. Last check: 2007-10-10)
		Click here to find out how to get it fast.
		On the left is a graph of "space", in each experiment you will see objects moving through space here.
		Press the reset button to reset all variables and enable the velocity scrollbar.
	www.its.caltech.edu /~phys1/java/phys1/Einstein/Einstein.html (280 words)

	A Walk Through Time
		The Evolution of Time Measurement through the Ages
		Time and Frequency Division (for additional information on time services and standards)
		Online: May 1995 - Last update: April 30, 2002 - cns
	physics.nist.gov /GenInt/Time/time.html (39 words)

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