Cosmology and astrophysics
Loop quantum gravity ( LQG ) is a theory that attempts to describe the quantum properties of gravity . It is also a theory of quantum space and quantum time , because, as discovered with general relativity , the geometry of spacetime is a manifestation of gravity. LQG is an attempt to merge and adapt standard quantum mechanics and standard general relativity.
The cores of black holes may not hold points of infinite density as currently thought, but portals to elsewhere in the universe, theoretical physicists say. A black hole possesses a gravitational field so powerful that not even light can escape. A black hole generally forms after a star dies in a titanic explosion known as a supernova, which crushes the remaining core into dense lumps.
Hi, and welcome to my site “Of Particular Significance”. If you are an interested layperson, whether you have very little knowledge of science or quite a lot already, this website is mainly intended for you — although as you’ll see, it has a number of scientists among its readers. It’s still young and growing, so check back often for new material. You’ll see there’s a blog with up-to-date comments, but most of the web-pages are permanent or semi-permanent articles.
On Tuesday, scientists announced promising signs in the data from the Large Hadron Collider (LHC) near Geneva of the existence of the Higgs boson . If the discovery is confirmed with new data, what will it mean for physics and why should we care? First, the short answer. If the Higgs is discovered, it will represent perhaps one of the greatest triumphs of the human intellect in recent memory, vindicating 50 years spent building one of the greatest theoretical edifices in all of science and requiring the construction of the most complicated machine that has ever been made. That's the good news. But if the Higgs is all that is found at the LHC, it will mean that the other crucial empirical guidance that physicists now need to try and understand truly fundamental questions about our existence – from understanding whether all four forces in nature are unified in some grand theory, to determining what may have caused the big bang – will still be absent.
In 1929, cosmologists discovered that the universe is expanding — that space-time, the fabric of the cosmos, is stretching. Then in 1998, light coming from exploding stars called supernovas suggested that the universe is not only expanding, but that it has recently begun expanding faster and faster; its expansion has entered an "accelerating phase." This was bad news for the fate of the cosmos: An accelerating universe is ultimately racing toward a "Big Rip," the moment at which its size will become infinite and, in a flash, everything in it will be torn apart. The discovery was bad news for the state of cosmology, too.
Astrophysical ambulance-chasers everywhere got a bit excited this week, and why wouldn’t they? Here are some of the headlines we read: Wow. More evidence against dark matter? I didn’t know about the original evidence.
3:am magazine (yes, that’s what it’s called) has a very good interview with Craig Callender , philosopher of physics at UC San Diego and a charter member of the small club of people who think professionally about the nature of time. The whole thing is worth reading, so naturally I am going to be completely unfair and nitpick about the one tiny part that mentions my name. The interviewer asks: But there is nothing in the second law of thermodynamics to explain why the universe starts with low entropy. Now maybe its just a brute fact that there’s nothing to explain.
<img class="alignnone size-full wp-image-59358" title="Frame dragging" src="http://www.wired.com/images_blogs/wiredscience/2011/05/Frame-dragging.jpg" alt="" width="660" height="489" /> Four superconducting pingpong balls floating in space have just confirmed two key predictions of Einstein’s general theory of relativity, physicists announced in a press conference Wednesday. “We have completed this landmark experiment testing Einstein’s universe, and Einstein survives,” said physicist Francis Everitt of Stanford University, the principal investigator on NASA’s Gravity Probe B mission.
Sep. 30, 2011 — The Bolshoi supercomputer simulation, the most accurate and detailed large cosmological simulation run to date, gives physicists and astronomers a powerful new tool for understanding such cosmic mysteries as galaxy formation, dark matter, and dark energy. The simulation traces the evolution of the large-scale structure of the universe, including the evolution and distribution of the dark matter halos in which galaxies coalesced and grew. Initial studies show good agreement between the simulation's predictions and astronomers' observations. "In one sense, you might think the initial results are a little boring, because they basically show that our standard cosmological model works," said Joel Primack, distinguished professor of physics at the University of California, Santa Cruz.
Read full article Continue reading page | 1 | 2 | 3 A theory of reality beyond Einstein's universe is taking shape – and a mysterious cosmic signal could soon fill in the blanks IT WASN'T so long ago we thought space and time were the absolute and unchanging scaffolding of the universe. Then along came Albert Einstein, who showed that different observers can disagree about the length of objects and the timing of events.
The universe is littered with the weird and wonderful and GRB 060614 could turn out to be one of the weirdest and most wonderful of them all. GRB 060614, which we’ll call Ralph to smooth things along, was a gamma-ray burst with some very puzzling properties detected by Nasa’s Swift satellite on June 14, 2006. Gamma-ray bursts are the most powerful explosions in the universe. They usually come in two flavours: long bursts, which are normally caused by the sudden release of energy that occurs when a collapsing star forms a black hole in a massive supernova event, and short bursts, which occur when two neutron stars – the superdense remains of dead stars – collide.
What existed before the big bang? What is the nature of time? Is our universe one of many? On the big questions science cannot (yet?)
How far is each of these galaxies? Appearances may deceive. In my previous post , I described the little-known and somewhat counterintuitive idea that objects in the distant universe appear larger and larger the farther they are, in a reversal of the usual rules of perspective. I called it the cosmic magnifying lens. As promised, I will now explain the physics behind it.
“Despite its name, the big bang theory is not really a theory of a bang at all. It is really only a theory of the aftermath of a bang.” - Alan Guth So you finally understand it. The Big Bang tells us that the Universe was hotter, denser, and expanding at a faster rate in the past.
In the heart of MCG-6-30-15 , a galaxy 130 million light-years away, there is a hole. It’s as big around as the orbit of Mars. Into this hole stars and star stuff are always falling—a lot of stuff, the equivalent of a hundred million suns so far. From this hole nothing escapes, not even light. It is perfectly black, like the mouth of a long tunnel.