The origins of space and time

 


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Theories about the Origins of Space and Time.

1. Gravity as Thermodynamics
Entropic gravity is a theory in modern physics that describes gravity as an entropic force – not a fundamental interaction mediated by a quantum field theory and a gauge particle, but a consequence of physical systems’ tendency to increase their entropy.

2. Loop Quantum Gravity
According to Einstein, gravity is not a force – it is a property of space-time itself. Loop quantum gravity is an attempt to develop a quantum theory of gravity based directly on Einstein’s geometrical formulation. The main output of the theory is a physical picture of space where space is granular. More precisely, space can be viewed as an extremely fine fabric or network “woven” of finite loops. These networks of loops are called spin networks. The evolution of a spin network over time is called a spin foam. The predicted size of this structure is the Planck length, which is approximately 10−35 meters. According to the theory, there is no meaning to distance at scales smaller than the Planck scale. Therefore, LQG predicts that not just matter, but space itself, has an atomic structure.

3. Causal Sets
Its founding principles are that spacetime is fundamentally discrete and that spacetime events are related by a partial order. The theory postulates that the building blocks of space-time are simple mathematical points that are connected by links, with each link pointing from past to future. Such a link is a bare-bones representation of causality, meaning that an earlier point can affect a later one, but not vice versa. The resulting network is like a growing tree that gradually builds up into space-time.

4. Causal Dynamical Triangulations
The idea is to approximate the unknown fundamental constituents with tiny chunks of ordinary space-time caught up in a roiling sea of quantum fluctuations, and to follow how these chunks spontaneously glue themselves together into larger structures. The space-time building blocks were simple hyper-pyramids (four-dimensional counterparts to three-dimensional tetrahedrons) and the simulation’s gluing rules allowed them to combine freely. The result was a series of bizarre ‘universes’ that had far too many dimensions (or too few), and that folded back on themselves or broke into pieces.

5. Holography
In this model, the three-dimensional interior of the universe contains strings and black holes governed only by gravity, whereas its two-dimensional boundary contains elementary particles and fields that obey ordinary quantum laws without gravity. Hypothetical residents of the three-dimensional space would never see this boundary, because it would be infinitely far away. But that does not affect the mathematics: anything happening in the three-dimensional universe can be described equally well by equations in the two-dimensional boundary, and vice versa.

The Sombrero Galaxy (M104)

NASA’s Hubble Space Telescope has trained its razor-sharp eye on one of   the universe’s most stately and photogenic galaxies, the Sombrero   galaxy, Messier 104 (M104).  The galaxy’s hallmark is a brilliant white,   bulbous core encircled by the thick dust lanes comprising the spiral   structure of the galaxy. As seen from Earth, the galaxy is tilted nearly   edge-on. We view it from just six degrees north of its equatorial plane.   This brilliant galaxy was named the Sombrero because of its resemblance to the broad rim and high-topped Mexican hat.

At a relatively bright magnitude of +8, M104 is just beyond the limit of   naked-eye visibility and is easily seen through small telescopes. The   Sombrero lies at the southern edge of the rich Virgo cluster of galaxies   and is one of the most massive objects in that group, equivalent to 800   billion suns. The galaxy is 50,000 light-years across and is located 28   million light-years from Earth.

Hubble easily resolves M104’s rich system of globular clusters,   estimated to be nearly 2,000 in number — 10 times as many as orbit our   Milky Way galaxy. The ages of the clusters are similar to the clusters in the Milky Way, ranging from 10-13 billion years old. Embedded in the bright core of M104 is a smaller disk, which is tilted relative to the large disk. X-ray emission suggests that there is material falling into the compact core, where a 1-billion-solar-mass black hole resides.

In the 19th century, some astronomers speculated that M104 was simply an edge-on disk of luminous gas surrounding a young star, which is prototypical of the genesis of our solar system. But in 1912, astronomer V. M. Slipher discovered that the hat-like object appeared to be rushing away from us at 700 miles per second. This enormous velocity offered some of the earliest clues that the Sombrero was really another galaxy, and that the universe was expanding in all directions.

The Hubble Heritage Team took these observations in May-June 2003 with the space telescope’s Advanced Camera for Surveys. Images were taken in three filters (red, green, and blue) to yield a natural-color image. The team took six pictures of the galaxy and then stitched them together to create the final composite image. One of the largest Hubble mosaics ever assembled, this magnificent galaxy has an apparent diameter that is nearly one-fifth the diameter of the full moon.

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2015: A Year In Science


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The infographic created in collaboration with Tanja Rudez, European Science Writer of the Year 2015!
It was an exciting year in science, and some of its significant events attracted a lot of attention.
Despite persistent ethical dilemmas, it’s obvious that research in genetics is bringing us closer and closer to creating genetically modified people.
Until genes are able to take care of it, we will continue to need antibiotics to fight bacterial infections.
At the same time, we’re finding out more and more about our ancestors and discovering hominin species that lived millions of years ago.
Those ancestors knew very little about the cosmos, and since then, we’ve advanced to the point of organizing space missions that give us a view on the most distant parts of our solar system.
We’re looking for “new Earths” while trying to figure out how to save our own from global warming.
One way or another, 2015 has been a blast!

A Black Hole’s ‘Point of No Return’

 
 
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The most distinguishing feature of the supermassive black hole: its event horizon. The point of no return for in-falling matter, it is about 15 million kilometres across, or one-tenth of the distance between Earth and the sun – minuscule in astronomical terms.

In general relativity, an event horizon is a boundary in spacetime, most often an area surrounding a black hole, beyond which events cannot affect an outside observer. Light emitted from beyond the horizon can never reach the observer, and any object that approaches the horizon from the observer’s side appears to slow down and never quite pass through the horizon, with its image becoming more and more redshifted as time elapses. The traveling object, however, experiences no strange effects and does, in fact, pass through the horizon in a finite amount of proper time.

More on Event Horizons

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Nanomedicine

Both the academic community and the pharmaceutical industry are making increasing investments of time and money in nanotherapeutics. Nearly 50 biomedical products incorporating nanoparticles are already on the market, and many more are moving through the pipeline, with dozens in Phase 2 or Phase 3 clinical trials. Drugmakers are well on their way to realizing the prediction of Christopher Guiffre, chief business officer at the Cambridge, Massachusetts–based nanotherapeutics company Cerulean Pharma, who last November forecast, “Five years from now every pharma will have a nano program.”  Read More

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