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December 2012 Archives

The Moon: Not Green Cheese After All

In 2011, the twin GRAIL space probes were launched to map what the moon is made of. Upon reaching the moon exactly one year ago, they began to carefully map the density of the entire crust of our largest satellite.

The mission was a complete success; the map was finished late this year. At that point, NASA put the probes into what's called a decaying orbit. The craft spiraled down towards the surface, falling lower each revolution until they crashed into the surface earlier this month to end the mission. The map they left behind (shown in the NASA image below) tells some interesting stories about the moon.

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The Power of Asteroid Impacts

When you look at the map, craters pop out dramatically. The rings of color are the patterns left in the moon's crust by space rock impacts. Blue areas are less dense and red areas are more so. Since the moon doesn't have erosion (no wind, rain, rivers, living organisms to shape its surface), craters stay forever. An amazing 12% of the moon's surface is actually empty space, smashed in by impacts. This level of destruction is even greater than expected by astrophysicists.

The early solar system was a place where massive space rock impacts were frequent. The moon's surface is an indelible map showing the ultra-violent ferocity of this time.

The Moon Grows and Shrinks

Some features on the density map resemble giant slashes or lines. These are called dikes, and they indicate volcanic activity related to the growing and shrinking of the moon's crust. During its first billion years, the moon was very hot, and grew in size from volcanic activity. Eventually it cooled down, and now it is actually shrinking. These maps are the only known way to find and study this phenomenon.

The Moon is Made of Earth

No one knows for sure where the moon came from and how it ended up orbiting the earth. The most likely theory however, is that early in the planet's history, an enormous object (roughly the size of the moon) smashed into it. The resulting explosion was so violent that a moon's-worth of earth's rock was blasted into space. All that rock slowly coalesced into the moon.

The GRAIL data supports this theory, showing that both the earth and the moon contain about the same amount of aluminum. This would probably not be the case if the moon formed in some far away place and was "captured" by the earth's gravity.

December 2012 Archives

Are We Living in The Matrix?

Can we know if we are actually living in a computer simulated universe? New physics research gives us some possible clues about how we might tell and how hard it would be to artificially create the world we experience. This work is at the fine border between scientific speculation and speculative science. Keep in mind that it is about as far from practical and testable as physics can get.

The heart of the matter is to determine whether the space we live in has infinitely small distances. What do I mean by that? Everyday intuition tells you that you can take one step, or half a step, or half of a half of a step, or a half of a half of a half (1/8) of a step, and so forth. The universe, so far as we know, probably allows you take smaller and smaller steps forever (infinitely).

However, when a computer simulates reality, it does things differently. It can't use infinitely small space because it can only store a limited (finite) number of things in its memory. This places a limit on the very smallest step you can take. So, if we were living in a simulation, we might find out that trying to take too small of a step is impossible!

One of the very best current computer simulations of reality is lattice QCD. QCD is the quantum theory of the strong force. It describes what protons and neutrons are made of and how they interact to form atomic nuclei and carry out nuclear processes. Computer simulations of QCD must use space with a limit on how small the size of a step can be. These simulations assume that space has a smallest possible step to move (or set of positions that you can occupy). Currently, the smallest step is somewhere around one tenth to one twentieth of a femtometer (10-16 m = 10-1 fm). This is about one hundred times smaller than the nucleus of an atom (2-15 fm).

To simulate a cube of space the size of the period on this page, you would need roughly 1035 possible steps you can take or locations you can be at in that space. Right now our fastest computers could never do this in a trillion years.


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Lattice QCD simulation (Brookhaven National Laboratory)


This work analyzes extremely high energy bursts from outer space, called cosmic rays. Based on the energy of these rays, physicists claim that the space they come from must have steps at least as small as one millionth of one billionth of a femtometer (10-27 m = 10-12 fm). So if we are being simulated by some future computer, it must be incomprehensibly powerful to be able to analyze this many possible steps. (Think trillions of years to simulate the size of an atom.)

This raises a new question. Is it even possible to build such a computer and carry out a simulation this powerful? While we have been experiencing approximately 50 years of unbelievably high (and consistent) increase in computer power, it would take centuries (or millennia or more) of growth continuing at the same rate for this to be possible for us. Furthermore, there are certain other problems, like whether there are enough atoms in the universe to build such a powerful computer, which no one has any idea about.

While this new evidence gives us something to think about, we are still back to essentially the same ancient conundrum. Before the computer age, philosophers wondered if we could all be living in someone else's dream. Like that old puzzle, the new practical conclusion is that we still can't tell, and so we might as well not worry about it.


December 2012 Archives

The Biggest Cash Prize in Science

What's the most lucrative prize a scientist can collect? The Nobel Prize has long been the premier award in all scientific fields. It nets each recipient a share of $1.2 million. The next most prestigious awards, such as the Israeli Wolf Foundation in physics and chemistry, pay around $100,000. This past year, styling himself after Alfred Nobel, Russian billionaire Yuri Milner decided to bestow prizes from his personal wealth. This is the Fundamental Physics Prize. Each winner's haul? Three million dollars.

Not only is this the largest monetary prize in physics (and all of science), but in some senses it carries the fewest strings attached. The first round of prizes were personally awarded by Milner. 3000 scientists do not vote by mail, unlike the Nobel selection process. 250 candidates are not discussed in secret; no reports are written and no committees meet. Future winners will be chosen by past winners and a very small board. Simple, quick, decisive, not bureaucratic.

The Fundamental Physics Prize has distinctive upsides. Being beholden to no large establishments, it is not caught up in politics or games. For example, Milner brushed off an idiotic New York Times question about the gender of recipients. (The overwhelming majority of physicists, and theoretical physicists, in particular, are male.) It can be awarded solely on merit and bypass politics.

The prize can change the life of a researcher in the heart of their career. A brilliant theorist waits, sometimes for decades, for experimental validation of their work before they can receive a Nobel. Peter Higgs is a perfect example. He published in 1964, and only now (thanks to the LHC), at age 83, is he eligible for the honor. 
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Milner's prize does have a glaringly unscientific facet however: it does not require experimental validation or realization of the honored work. Verification is essential to making sure that the prize honors scientific contribution. By choosing work that is speculative, the award can promote "creative output" more than strict scientific achievement. Additionally, this may promote ideological bias towards certain ideas regardless of their veracity. If string theory is some day rejected, several of the prize-winners may be seen as great thinkers who chased a red herring.

Taking money made from Farmville (Milner made millions from Zynga) and giving it to physics research is a great idea. Manny Pacquiao can make $23 million in a single night and not even be conscious at the end of it. Now a physicist can make $3 million for years of late nights working through math and physics textbooks and solving equations. It's about time.

(Image: Laser via Shutterstock)

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December 2012 Archives

The space probe Voyager 1 has flown through the asteroid belt, past Jupiter and Saturn, past Neptune and Uranus, beyond Pluto, and out to the very edge of the solar system. Along the way it has taken many famous pictures:


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Saturn and its Moons

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Neptune. Notice the giant blue spot, bigger than the Earth.

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Saturn

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Saturn's Moon Ariel

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Jupiter's atmosphere

The solar system is as huge as it is beautiful. But, it is tiny compared to the distance of the nearest star system. If the orbit of Pluto around the sun was the size of a dime, the diameter of the entire solar system would be a hockey puck with the sun at the center. Voyager has now reached the edge of that hockey puck. Alpha Centauri, the nearest solar system to ours, is like another hockey puck, one that is sitting almost three hockey fields (nearly two football fields) away.

Voyager's mission was not just to take pictures, but also to collect scientific data from the vast outer reaches of the solar system. This mission continues, as the probe still maintains continuous contact with the earth, from 11 billion miles away. 35 years in, most of the probe's instruments are still working, and only in the past few years have they begun to be intentionally shut down as the nuclear engine powering the craft slowly dies out. Some instruments will continue running all the way out to 2025, however.

Among these instruments are a magnetometer (which, as you might expect, measures magnetic fields), a cosmic ray detector, and a plasma wave measurement system (this essentially measures how many electrons are around). Astronomers use these instruments to learn about the area through which Voyager is now passing, the very furthest edge of the solar system. Astrophysicists have made theoretical predictions of what should be out there; now we get to find out firsthand.

Out beyond the planets, the main thing to see is the solar wind. This is a stream of charged particles (such as electrons) blasted out of the sun's atmosphere, into space and across the solar system. Howling past earth, it creates the auroras we see near the poles. The solar wind blows into the teeth of the interstellar wind, which is the general motion of charged particles throughout the space between stars. This has a different direction than the solar wind. The further from the sun Voyager travels, the weaker the sun's magnetic field and the solar wind should be. Soon, the spacecraft should reach a point where the two winds blow opposite each other to a standstill: the heliopause.

Voyager has begun to approach to this area over the past few years, and has been investigating it. Just this year however, things stopped going according to prediction. Instead of fading out, the solar magnetic field has leveled off and even grown stronger. It seems to merge with the interstellar field, in a way such that particles from the sun can be grabbed by the interstellar wind and whipped out far into space, and interstellar particles can find their way into the solar system.

As Voyager sails further, beyond the heliopause, the only thing we expect it to find out there is the cold lonely interstellar wind. After successful encounters with all four of the gas giant planets and now its work determining the composition of the outer solar system, this is already one of the most successful space missions of all time. Who knows though, further surprises may still be in store!