Big bounce with loops

I'm a sop for articles about fundamental physics. The October issue of Scientific American has an article about how loop quantum gravity might indicate that the universe didn't start with the Big Bang; instead, the Big Bang might actually be a Big Bounce, where the universe started expanding again after a collapse which erased all trace of its previous existence. It appears that at extremely high energy densities, gravity would no longer be an attractive force and instead becomes a repulsive force.

Continue reading "Big bounce with loops"

Alarming news from the LHC

Despite the successful beam circulation in the LHC with no apparent ill effects, it has been revealed the LHC only avoided destroying the Earth because the planet had already been destroyed:

It is our duty to inform you that as of 7:35:05am UTC on September 10, 2008, the Earth has been destroyed.

The destruction of Earth was first reported by Mr Jonathan Barber of Wisconsin, United States, who spotted that his home-made seismic Earth Detector had ceased to give readings at around 8:00am (2am local time). Several other amateur geocide spotters noticed this at the same time but Mr. Barber was the first to place a telephone call to the IEDAB's Geocide Hotline (+44 115 09Ω 4127, ask for Other Dave) at which point IEDAB officials performed an emergency check of their own instrumentation and verified Mr. Barber's report, as well as fixing the exact time of geocide.

Evidence is still being collated, but preliminary results suggest that the Earth was destroyed pre-emptively by scientists at the Large Hadron Collider at CERN, Geneva, Switzerland, before the commencement of their experiments to locate the Higgs Boson, as a precautionary measure to ensure that the experiment itself could not result in the destruction of the Earth.

Flood of data from the LHC

CERN Computing Center
CERN Computing Center

If all goes well with the Large Hadron Collider this week, it will finally have gotten a beam to go around a full circle almost a month after the first beam injection. While from a physics standpoint this will be quite exciting, although it will be much more exciting when they manage head-on collisions between two beams a couple of months later, the LHC is also very impressive in terms of the supporting computing infrastructure.

The LHC is going to generate an incredible number of collision events, too much to handle in a single computing center. And I mean a center with more than 100,000 computers. This means that they need a computing infrastructure distributed all over the world which is able to handle the flood of data that comes out of the collider. With about one DVD's worth of data being generated every five seconds, the data is first received by CERN's computing center, which then distributes the data to 11 computing sites in Europe, North America, and Asia. These then provide access to the collision data to scientists on their own computers, which will do the actual CPU-intensive work of analyzing the data for new discoveries.

And despite the incredible amount of data that comes out of the collider, it's mind-boggling how that is just a tiny fraction of what is originally produced in it. Out of the 40 million collision events that would occur, a lot of work is done to filter out "boring" and "well-known" events which our current theories of physics can already explain quite well, so that data for "only" about 100 potentially interesting events per second will come out of the collider. Without such filters, even all the computing power and network bandwidth in the world would not be able to handle all the data.

Matter over antimatter

Almost everything around us is made out of matter rather than antimatter. And this is not just true for our solar system or our galaxy, but appears to be true for the entire universe, or at least the observable universe. But except for having opposite charges, matter and antimatter are virtually identical. Then why should everything we see in the universe be made up of matter rather than antimatter? For that matter (pun intended), why is there any matter at all? Why shouldn't there have been an equal amount of matter and antimatter that all annihilated with each other and left nothing?

Electron-positron annihilation
Electron-positron annihilation

It is thought that matter and antimatter were formed in nearly equal amounts during the birth of the universe, but there was an extremely tiny excess of matter over antimatter, about one in ten million. Almost all of the matter and antimatter annihilated each other, and only the tiny excess of matter remained to form almost everything we see in the universe today. The process through how this tiny excess of matter was generated is called baryogenesis, which is still a mysterious process where speculation abounds.

Mark of Cosmic Variance is writing and editing a series of excellent posts about baryogenesis. Starting off with an introduction to the problem, so far he has talked about the theories of electroweak baryogenesis and leptogenesis. They are based on speculative theories of particle physics that have not yet been confirmed experimentally, which can be exciting for particle physicists since it means that they still have plenty left to do.

Whatever the mechanism, it must have happened uniformly across the universe after inflation, so mechanisms that are predicted to generate random amounts of excess matter or antimatter cannot be the vehicle for baryogenesis. Mechanisms for baryogenesis will have to take advantage of miniscule asymmetries between matter and antimatter, asymmetries that will have to arise in theories of physics that have yet to be discovered and confirmed.

Composition of the universe

One question about baryogenesis I had for the longest time was why it did not account for the existence of dark matter. If only the tiny excess of matter forms everything we can see in the universe, wouldn't the energy from the annihilation of the rest of the matter and antimatter be more than enough to account for the gravitational pull of dark matter? It turns out that I did not consider that light, which is the by-product of matter-antimatter annihilation, becomes less energetic with the expansion of the universe because the wavelength is stretched. This means that the energy density of light in the universe falls much faster than the energy density of matter, so gravitation due to light becomes negligible quite early in the life of the universe.

Where did all the energy in the light go? In a sense, the tens of millions of times more energy that used to be in light compared to matter literally all went into thin air; that is, into space-time itself. You could say that it all went into the gravitational energy stored by space-time as the universe expanded. The only caveat is that defining gravitational energy is a quirky thing to do in general relativity, which is the best theory we have so far for explaining gravitation.

Finally, an extra treat with a video from NASA showing the evolution of the universe since the time of the light-dominated period of the universe, when light had a significant gravitational influence, up to today, when light is no longer a major source of gravitation: