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Post Info TOPIC: Space-time


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Special relativity
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Einsteins famous tenet of special relativity that time slows down on a moving clock has been verified 10 times more precisely than ever before. The result comes from physicists in Germany and Canada, who have timed the ticking of lithium ions as they hurtle around a ring at a fraction of the speed of light.
Sit two clocks side by side and, if they are accurate, they will always show the same time. But if one clock is moving rapidly, it will appear to an observer standing next to the stationary clock to be ticking too slowly. This time dilation effect, which was predicted by Einstein in his special theory of relativity in 1905, has been verified many times first to within 1% of predictions in an experiment by Herbert Ives and G R Stilwell in 1938, and more recently by comparing the times of atomic clocks on Earth with those of orbiting global-positioning-system (GPS) satellites.

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Posts: 131433
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Time dilation
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Time, as we all know, is relative: good experiences seem to fly by, whereas bad ones seem to drag on forever.

"After two hours, I looked at my watch. I found that 17 minutes had gone by"  - reviewer of  a Wagnerian opera.

In 1905, Albert Einstein wrote his own treatise on the relativity of time, famously theorising that time speeds up or slows down according to how fast an object is moving in relation to another object.
Thus, according to his hypothesis, a clock which is in motion ticks more slowly than an identical clock which is at rest -- a phenomenon that Einstein called time dilation.

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RE: Space-time
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Posts: 131433
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Why our time dimension is about to become space-like
It dont get much weirder than this. The universe is about to lose its dimension of time says a group of theoretical astrobods at the University of Salamanca in Spain. And they got the evidence to prove it.
The idea comes from the study of braneworlds: the thinking that the universe we see around us is a 4-dimensional cosmos called a braneworld embedded in a multidimensional universe. The signature of our universe is the number of space and time-like dimensions it has: in our case we got 3 space-like dimensions and one time-like dimension. Its what astrobods call a Lorentzian universe. So far so good: lots of astronutters think the same thing.
But our universe may not always have been like this. Some theorists think it may once have had a Euclidean signature meaning that all the dimensions were space-like. Now Marc Bars Mars and a few pals in Spain say that the Universes signature might be about to flip from Lorentzian to Euclidean. In other words, our dimension of time is about turn space-like.

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Title: Is the accelerated expansion evidence of a forthcoming change of signature?
Authors: Marc Mars, José M. M. Senovilla, Raül Vera

We show that regular changes of signature on brane-worlds in AdS bulks may account for some types of the recently fashionable sudden singularities. Therefore, the fact that the Universe seems to approach a future sudden singularity at an accelerated rate of expansion might simply be an indication that our braneworld is about to change from Lorentzian to Euclidean signature. Both the brane and the bulk remain fully regular everywhere. We present a model in which the weak and strong energy conditions hold on the brane, in contrast with the standard cosmologies leading to the analogous kinematical behaviour, with a diverging Hubble factor.

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Cosmological Constant
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Title: The Cosmological Constant is Probably Zero, and a Proof is Possibly Right
Authors: Zhong Chao Wu
(Version v2)

Hawking proposed that the cosmological constant is probably zero in quantum cosmology. Duff claimed that Hawking's proof is invalidated. Using the right configuration for the wave function of the universe, we provide a complete proof.

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Topological defects
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A simple way of perceiving particles is that they are products of FIELDS.
For EVERY particle there is a corresponding field. It is `Probabilities` in the field, that carry energy and momentum from one place to another, that we call particles. This connection between particles and fields is called the Standard Model

Particles were found to have discrete levels of energy (quantised), the amounts were always `whole numbers`. An electron, for example, has 1.5 bits of energy! Hence particles are also called quantum. The study of particles and their fields is often called quantum physics.
Physicists hypothesise a series of particles, like the Higgs particles, which create scalar fields. The standard model cannot alone explain the mass of particles.

The following particles were created by the big bang, some are hypothesised.
Lightweight particles (leptons): half integral spins (1/2, 3/2,)
Particles and antiparticles would have been created together. Antiparticles are the same as particles except they have the opposite electric charge. More matter was produced than antimatter; about one out of every billion particles of matter survives today!
The Higgs Particle is responsible for spontaneous symmetry breaking. Interaction of Higgs with all other particles leads to them acquiring MASS.


Time = 10-43 seconds; Temp = 1032The Planck epoch, During which all four fundamental forces were unified and "particles" as we known them could not have existedAt this time Gravity and the Strong Force are at the same scale. 1/R2is extremely large (R is very, very small)This is the time when our conventional physics breaks-down:
At the wall of the cosmos bubble, Supersymmetry was broken, making the bubble grow. Just inside this wall Higgs particles were releasing their energy as they decayed. So the bubble was gradually filled with energy. As bubbles of the "true vacuum" (with a nonzero Higgs field) percolate and grow, baryogenesis can occur at or near the bubble walls.
Cosmic strings are supermassive relics of the early universe that were form at phase transitions. Other relic objects known as topological defects can also form at such transitions, including monopoles, textures and domain walls.
Also note that the first results from the Supernova Legacy Survey (SNLS) project, an international effort to probe the nature of dark energy, suggests that Dark energy has remained constant over the life of the universe. The data shows that the strength of repulsion cannot have changed by more than about 20% over the past eight billion years, when the universe was just half of its current size. Many alternative theories predicted that dark energy fades in strength. One idea that was ruled out was that the repulsion comes from Topological defects fractures in space that might have been left behind as the universe cooled after the big bang. But the density of topological defects would fade too fast. The results, published in Astronomy and Astrophysics, fit the most conservative theory of dark energy that space has some inherent, and constant, energy density.


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A giant knot may have been found in the fabric of space-time - almost a decade after cosmologists abandoned the idea that such objects might exist.
Known as "topological defects", such esoteric entities were first proposed in the 1970s, when physicists realised that the processes that gave rise to particles and forces in the early universe could also fracture space, creating twists and knots, dubbed textures, or "cosmic strings" that stretch across the universe.
The idea attracted attention because Neil Turok at the University of Cambridge, and others, showed that such defects could help form galaxies by acting as gravitational seeds, pulling matter towards them and building a web of galaxy clusters.
But there was a rival concept, based on the idea that the early universe went through a rapid period of expansion known as inflation, giving rise to regions of relatively dense matter that could also act...

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RE: Space-time
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Title: Cosmological Scalar Fields Unification
Authors: Abdel Pérez-Lorenzana, Merced Montesinos, Tonatiuh Matos

We present a model where early inflation and late accelerating expansion of the Universe are driven by the real and imaginary parts of a single complex scalar field, which we identified as inflaton and phantom field, respectively. This inflaton-phantom unification is protected by an internal SO(1,1) symmetry, with the two cosmological scalars appearing as the degrees of freedom of a sole fundamental representation. The unification symmetry allows to build successful potentials. We observe that our theory provides a matter-phantom duality, which transforms scalar matter cosmological solutions into phantom solutions and vice versa. We also suggest that a complete unification of all scalar fields of cosmological interest is yet possible under a similar footing.

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Title: Time-like vs Space-like Extra Dimensions
Authors: Israel Quiros

Higher-dimensional theories with time-like and space-like extra dimensions are compared both from the conceptual and from the phenomenological points of view. In this context causality and unitarity are discussed. It is shown that additional time-like dimensions allow to recover four-dimensional phenomenology without invoking neither Kaluza-Klein compactification procedure nor brane world construct. It is shown, also, that contrary to scenarios with space-like extra dimensions, in higher-dimensional space-times with additional time-like dimensions the cosmological constant problem can be safely solved.

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Spacetime Geometry
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Title: Possible Connection between Probability, Spacetime Geometry and Quantum Mechanics
Authors: E. Canessa

Following our discussion  to associate an analogous probabilistic description with spacetime geometry in the Schwarzschild metric from the macro- to the micro-domain, we argue that there is a possible connection among normalized probabilities, spacetime geometry (in the form of Schwarzschild radii) and quantum mechanics (in the form of complex wave functions). We show how this association along different (n)-nested surfaces --representing curve space due to an inhomogeneous density of matter-- preserves the postulates of quantum mechanics at different geometrical scales.

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