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Cosmology

When Russian meteors attack

It appears a huge meteor has just struck somewhere over Russia. Phil Plait is posting frequent updates over twitter. What is amazing is how many cameras seem to have caught the entry, and subsequent breakup, of the meteor. In Russia most cars have dashboard cameras installed to collect evidence in case of accidents. There are some crazy videos of Russian driving on Youtube, but this is the most awe-inspiring dashcam footage I have seen yet. 

Also, check out this video shot after the meteor passed by. About 20 seconds in you can hear the awesome sonic boom caused by the meteor's entry

UPDATE: Phil Plait has posted a more in depth analysis of the meteor strike, including some impressive footage.

The blackhole firewall paradox

Excellent overview by Jennifer Ouellette of a new paradox that is taking the physics world by fire. I first heard about this a month ago from Patrick Hayden. It looks like this could turn into one of the great thought experiments that tackles the difficulties merging quantum mechanics and general relativity.

Paradoxes in physics have a way of clarifying key issues. At the heart of this particular puzzle lies a conflict between three fundamental postulates beloved by many physicists. The first, based on the equivalence principle of general relativity, leads to the No Drama scenario: Because Alice is in free fall as she crosses the horizon, and there is no difference between free fall and inertial motion, she shouldn’t feel extreme effects of gravity. The second postulate is unitarity, the assumption, in keeping with a fundamental tenet of quantum mechanics, that information that falls into a black hole is not irretrievably lost. Lastly, there is what might be best described as “normality,” namely, that physics works as expected far away from a black hole even if it breaks down at some point within the black hole — either at the singularity or at the event horizon.

Together, these concepts make up what Bousso ruefully calls “the menu from hell.” To resolve the paradox, one of the three must be sacrificed, and nobody can agree on which one should get the ax.

Physicists don’t lightly abandon time-honored postulates. That’s why so many find the notion of a wall of fire downright noxious. “It is odious,” John Preskill of the California Institute of Technology declared earlier this month at an informal workshop organized by Stanford University’s Leonard Susskind. For two days, 50 or so physicists engaged in a spirited brainstorming session, tossing out all manner of crazy ideas to try to resolve the paradox, punctuated by the rapid-fire tap-tap-tap of equations being scrawled on a blackboard. But despite the collective angst, even the firewall’s fiercest detractors have yet to find a satisfactory solution to the conundrum.

Joe Polchinski, one of the authors who published the paper on the blackhole firewall paradox, has a more technical write up of the subject over on Cosmic Variance.

Earlier this year, with my students Ahmed Almheiri and Jamie Sully, we set out to sharpen the meaning of black hole complementarity, starting with some simple `bit models’ of black holes that had been developed by Samir Mathur and Steve Giddings. But we quickly found a problem. Susskind had nicely laid out a set of postulates, and we were finding that they could not all be true at once. The postulates are (a) Purity: the black hole information is carried out by the Hawking radiation, (b) Effective Field Theory (EFT): semiclassical gravity is valid outside the horizon, and (c) No Drama: an observer falling into the black hole sees no high energy particles at the horizon. EFT and No Drama are based on the fact that the spacetime curvature is small near and outside the horizon, so there is no way that strong quantum gravity effects should occur. Postulate (b) also has another implication, that the external observer interprets the information as being radiated from an effective membrane at (or microscopically close to) the horizon. This fits with earlier observations that the horizon has effective dynamical properties like viscosity and conductivity.

I love that one of the postulates is called "no drama."

Sean Caroll's live blog of the Higgs announcement

After nearly half a century of looking, a particle that looks an awful lot like the Higgs Boson has been discovered. Sean Caroll live blogged the press conference. My favourite two quotes:

Peter Higgs is visibly moved at the final results. I hope people understand, and perhaps this helps make clear, how invested scientists are in this work.

and

A couple of people have mentioned supersymmetry. As Rolf Heuer just said, straightforward SUSY models have a remarkable feature: not a single Higgs boson, but five Higgs bosons. So we may have only have found 20% of the Higgs conglomerate.

A physicist's work is never done.

CMS result for four leptons

The power of exponential growth and M&Ms

The power of exponential growth and M&Ms

Exponential scaling demonstrated with doubling periods, a chess board, and M&Ms

I made an error in my recent TEDxWaterloo talk. Inspired by the legend of Paal Paysam, I used a chessboard and a bowl of M&Ms to illustrate the power of exponential growth. On the first square of the chess board I placed a single M&M, then two on the second square, four on the third square, and so on doubling the number of M&Ms on each subsequent square. Continuing this way I would need 2^63 = 9,223,372,036,854,775,808 M&Ms1 to fill the 64th and final square. If each M&M is approximately 1cm^2 the last square would contain nearly enough M&Ms to cover the surface of the Earth, oceans included, twice over! TEDxWaterloo Krister with Smarties: Photo by Darin White of Makebright.com

But this is not what I said in my talk. I claimed you would need enough M&Ms to fill a bowl the size of the Earth (a volume). There is a big difference between surface area and a volume for a planet-sized object. If we assume2 each M&M is approximately 1 cm^3, then I was off by a factor of about 100 million3. Fortunately, this error does not weaken the argument I was making about the power of exponential growth. A factor of 100 million is large, but how many more times would we need to double the number of M&Ms in order to fill a bowl the size of the Earth? The answer is 27; instead of playing the doubling game on a chessboard with 64 squares we would instead need one with 91 squares. If we are going to add squares, why stop at 91? Here are some interesting numbers that we reach as we continue to add squares to our "super" chessboard.

Exponential scaling demonstrated with doubling periods, a chess board, and M&Ms

  • 111 squares (2^110): Enough M&Ms to fill a bowl the size of the Sun. They will melt pretty quickly.

  • 144 squares (2^143): This is enough M&M to fill a bowl the size of VY Canis Majoris, the largest known star with a radius 2200 times larger than the Sun.

  • 229 squares (2^228): Enough M&Ms to fill a bowl the size of the Milky Way, the galaxy not the chocolate bar, with M&Ms.

  • 266 squares (2^265): More M&Ms than there are atoms in the observable universe!. Various estimates put the number of atoms at ~10^80.

Exponential growth is powerful stuff!


  1. 64 doubling periods corresponds to 2^(64-1)=2^63 M&Ms. The first square contains 2^0=1 M&M. The second square has 2^1=4 M&Ms and so on. For N squares there will be 2^(N-1) M&Ms. 
  2. The volume of an M&M is roughly 0.636 cm^3 (see here or here). However, when packing M&M's into a bowl their will be some gaps between them. M&Ms can occupy a maximum of 68% of the volume in a bowl, leaving 32% empty. Therefore an M&M will occupy roughly 1 cm^3 (.636/.68). As a side note, you can fit more M&Ms into a bowl than perfect spheres. This was only discovered a few years ago, but has had a dramatic impact on many different fields. 
  3. I originally calculated the right answer (surface area), but before the talk only glanced over my old notes. I somehow got it stuck in my head that I was dealing with the Earth's volume instead of surface area. of course if we lived in the dark ages when the when the Earth was assumed to be flat, then my answer would be correct. 

Spectacular time-lapse of the annular solar eclipse

Spectacular time-lapse of the annular solar eclipse

The sun

Cory Poole's timelapse of yesterday's annular solar eclipse using a Coronado Solar Max 60 Double Stack telescope and a GH2. The telescope has a built in notch filter that only allows light from the H-alpha line at 656.28 nm to pass through. This allows astronomers to see features from the surface of the sun. 

Cory will be posting photos from the eclipse to his website shortly. He has a beautiful collection of photos available. Check them out.

(Via Kottke.org)

The dark core of dark matter

The dark core of dark matter

Dark Matter Evidence from Nasa

The link above is an interview I did for CTV's National Affairs on a new result that could change our understanding of dark matter.

Previous evidence points to dark matter not being able to interact with other dark (or regular) matter except weakly through gravity. Researchers at UBC took a look at a "cosmic train wreck" that occurred when two galatic superclusters smashed into one another. These galatic superclusters, each containing hundreds or even thousands of individual galaxies, are mostly made up of free Hydrogen gas. During the collision the gas interacts and gets "stuck" in the middle while the stars, planets, and dark matter should keep on moving through.

In this case it appears that the dark matter gets "stuck" in the middle as well, something that was not seen in previous observations of other cosmic train wrecks. There are a number of possible explanations, all of which will teach us something new about nature of dark matter:

  • Some dark matter may actually be able to interact with other dark matter via some new force.
  • There may have already been a large chunk of dark matter, without much regular matter, sitting in the middle where the collision took place. In this case, we need to understand how so much dark matter can exists without much regular matter.
  • Dark matter has a filament-like nature, similar to how roots on a tree grow. In this case, we may be looking at one of the filaments end on. Imagine looking at a pencil end on. All you would see is the pencil point and not have any idea how long the pencil actually is. A similar thing could be happening with the dark matter–what we see as a small dense core in the center could actually be a an incredibly long filament of dark matter.

This result provides another puzzle piece in the mystery of what dark matter is, how galaxies form, and what our place in the universe is.

A big thanks to Adrienne Erickcek and Keith Vanderlinde for walking me through this exciting work.

Eleven months at the bottom of the Earth

Last week I had the chance to sit down with cosmologist Keith Vanderlinde, a CIFAR Junior Fellow at McGill, who spent eleven months straight living at the South Pole in Antartica. During the winter temperatures dip below -70 C and their is continual darkness for nearly six months straight. It gets so cold during the winter that planes cannot fly in–once the last plane takes off you are stranded there until the following sumer.

While in Antartica, Keith was in charge of keeping the South Pole Telescope running. Every day he had to walk 1 km to and from the telescope, often in white blizzard conditions. Keith took his camera with him and captured a series of incredible photos of the night sky and life in Antartica.

While at the South Pole, Keith maintained a fascinating blog about what life is like. My favourite entry is about the 300 club:

There's a tradition here at pole dating back decades, that whenever the temperature outside falls below -100F, the 300 club convenes & initiates new members. You gain entry into the club by first sitting in the sauna with the temperature turned up to 200F, then running outside (a 300F temperature differential, hence the name) and around the pole, all wearing nothing but boots and a smile.

Only once - in the half century for which we have records - has the temperature failed to hit -100F over the course of a winter. It's expected that the 300 club convenes at least once each winter, more likely twice or three times. Well, with the sun now up and temperatures already rising into summer, our low for the year is sitting at -99.9F, and there's no way that would count. Seriously.

,

The Astrophysics of Bedtime Stories

Chad Orzel's clever analysis of the children's book Goodnight Moon:

The attentive toddler will find a lot to look at in the pictures-- there's a mouse in every one that SteelyKid delights in pointing out-- but an inquiring adult might well ask "Just how long does it take this bunny to say goodnight to all this stuff, anyway?"

Well, we can answer this question with SCIENCE! You see, there are six pictures in the book showing the moon through one of the room's windows, and as the book goes along, the moon moves higher in the window. This provides a way to estimate the passage of time in the book.

Why the Higgs Boson Matters

Kelly Oakes' winning physics essay in this years Science Challenge:

The standard model describes the behaviour and interactions of all of the most fundamental particles we have seen — and one other particularly elusive one that, physicists hope, we will see in the near future. The model was developed throughout the 20th century and finalised when the existence of quarks, the particles that make up protons and neutrons, was confirmed in the 1970s. At the time many of the particles predicted by the standard model were yet to be seen. Over the years since then, physicists have ticked these particles off, one by one, like items on a shopping list. Now they are left with just one remaining unfound particle — the Higgs boson.