Time Asymmetry

I read a short article in Discover magazine today, which can be found here, about a new discovery that some physicists made. What exactly happened was not very clear to me, and I think it would be confusing to the public as well. So I thought I’d try to re-explain what I believe is going on, using some relatable examples below. Hopefully I have the right idea now, and you can appreciate this discovery a bit more!

To quote the article title: Physicists discovered, as theoretically predicted, that time flows asymmetrically at the electron (very tiny particle) level. But what does this mean? Well first, let’s review how we perceive time. Time, to human beings, is a forward moving unchangeable entity. Time passes for us everyday, and we can’t ever go backwards in time. If we were to run time backwards, we should see ourselves re-experiencing everything that happened that day, just in reverse. For example, if I video taped you driving to work and walking into your office, then played the tape backwards, I should see you walking backwards out of your office and driving home from work in reverse. Therefore, for humans, time is symmetrical. What happens forward in time must happen exactly the same way, but backwards, if time were played in reverse. So what is this time asymmetry these physicists are talking about? Scientists at the CERN particle accelerator have been smashing tiny particles together at very high speeds, and watching what happens to them when they collide. They know that when you smash two particles together, you should see the pieces that the particles are made of as a result. Think of it like a car crash. You’re driving down the road and you see two cars collide in a head on collision. When these cars collide, the pieces of each car are strewn about the road. So when you collide two things, you’re left with the bits and pieces of the inner working of that object. So what does this have to do with time not being symmetric? Ok, let’s run this car crash scenario again. You see a SUV and a mini van crash on into each other. Time is flowing forward when the cars crash, and lets assume both cars crash and all their constituent pieces are on the road. Now, we can theoretically make time flow in reverse, by collecting all the pieces of the cars and rebuilding them.  Putting the cars back together is similar to flowing time in reverse, essentially arriving back at the pre-crash state with two unharmed and functional vehicles. Now, you would expect that if I have all the pieces and put both cars back together, I should end up with an SUV and a mini-van again. This would be an example of time symmetry. But what if I put all the pieces of the cars back together, and ended up with a small car and a truck, instead of a SUV and a minivan? Al cars are made of (essentially) the same parts, so in theory I could end up with two different cars than I started with. I’m essentially running time in reverse, but I’m not arriving back at exactly the same pre-accident state. The end result is two completely fixed vehicles, but not the SUV and mini-van I started with. This is time asymmetry. Running time in reverse does not get me back to my starting point. Physicists realized that if they watch a specific particle, which likes to “change state” (you can think of this like a coin, which can be heads up or tails up, depending on how the coin is sitting), when it changes state (flips from head to tails) it does not always change back to its previous state, if time is run in reverse (the coin is flipped again).

They also realized that time has a preferential direction. Let’s go back to our car crash scenario. The SUV and the mini-van crash. When time is run forward, the crash occurs and the pieces for the mini-van and SUV are on the road. When run in reverse (the cars are put back together), sometimes you end up with a mini-van and SUV, sometime you end up with two completely different cars. The fact that when time is run forwards, you almost always see the SUV and mini-van collide, means that the laws of physics, as we understand them, prefer time moving forward. Things don’t always “make sense” when time runs backwards. So in this example, time preferentially moves forward. It was unclear to me in the articles I read whether the scientists findings showed forward or reverse time as preferential, but it’s fascinating that they are not the same! Intuitively time running forward or backward should yield the same result, but it does not! Now remember, this only happen in the sub-atomic world. This doesn’t actually happen on car-size scales. But still, this result changes how we perceive time at the smallest level, and ultimately our understanding of the universe as a whole! 

Orion Proplyds

The Orion Proplyds were first discovered by the Hubble Space Telescope. Astronomers expected the Orion nebula to be a host for lots of star formation, and were amazed to see that Hubble could resolve individual young stars. The Proplyds are young stars surrounded by a gaseous circumstellar disk . In the image of the Orion Nebula above, the proplyds are enlarged so you can see the bright central star surrounded by a dark oval shaped ring. The disks appear dark because they are absorbing the light emitted by the nebula, and re-emitting it in the infrared, a wavelength of light that does not appear bright in these images. Portions of these disks will eventually fall onto the star, and the rest will either form planets, or be dispersed back into the nebula. Astronomers are using these, and other images of young stars, to learn about how stars form and how planetary systems evolve.

Image Credit:

NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA), the Hubble Space Telescope Orion Treasury Project Team and L. Ricci (ESO)

American Flags Fading on the Moon

Image of an American flag from the moon's surface during the Apollo missions

During each Apollo mission that made it to the moon, the astronauts  left behind an American flag. Each was attached to a poll, and designed to wave horizontally in the low gravity environment. Astronomers have been studying these flags over the years using moon orbiting satellites to take photos of them. Even though they are not able to resolve the flag in the images, they can see a color difference in the photo where the flags sit. In more recent photos, astronomers have noticed that the flags appear a little brighter than they expected. Why is this? They think that the flags are fading, big time! If you've ever flown a flag outside and left it out all summer long, then you might have noticed that the colors look a little less bright over time. Now imagine this same flag on the moon, where there is little to no atmosphere to protect the flags from being bombarded by harmful UV radiation. It's likely that the sun has not only faded these flags but sun-bleached them white! Regardless of what they look like today, they are still a symbols of the fantastic accomplishment of landing man on the moon. 

Image Credit: NASA/Apollo Mission

Shiny Martian Rocks

The Curiosity rover has been exploring Mars since early August, and has taken many beautiful photos of the Martian landscape. In early October, Curiosity took its first scoop of Martian soil to be placed inside SAM, an instrument which analyzes the composition of Martian soil. With the scoop of soil in hand, curiosity photographed the area where the sample was taken, and stumbled upon a strange looking shiny object (center of above image).  At first, astronomers who analyzed the photograph thought the object was a small piece of shrapnel from when the rover landed.  This brought testing to a halt, because astronomers did not want to run a piece of sharp shrapnel through a very delicate machine meant to filter and analyze soil. About a week prior, Curiosity photographed a piece of plastic with ChemCam that likely broke off during it's descent, so it was very possible that this was another piece. Just to be safe, Curiosity dumped the soil. Upon closer inspection of this shiny rock, astronomers realized that this was not a piece of metal or plastic, but rather a strange rock of Martian origin. What these rocks are made of is still unclear, but Curiosity can now safely use SAM to analyze soil samples and hopefully find out the composition of these rocks!

Image credit:

 NASA/JPL-Caltech/MSSS

Iapetus, the Dinosaur Moon

Iapetus is a moon of Saturn with a funny name and a funny geological feature. I always think of it as the "dinosaur moon", because it has a distinct ridge feature on its surface that reminds me of the back of a dinosaur. Orbiting at 2.2 million miles from Saturn's surface, it's farther away from Saturn than Titan is. The surface of Iapetus was imaged by the Cassini mission in 2004, and the images revealed the equatorial ridge, a 6 mile high mountain range. It's a bit unclear how this band of mountains ended up on Iapetus. One theory is that a long time ago, Iapetus had a ring similar to Saturn's ring. As the moon evolved, the ring began to collapse onto the surface, and this ridge is where all the material collected. A second idea is that the ridge formed during a time when Iapetus was spinning on its axis much faster than it does today. Bodies in space, such as the Sun and the Earth, spin on their axis. Because of this, they bulge just a little bit in the middle. So Earth and the Sun are not perfect spheres, but rather balls that are slightly wider at the center. If Iapetus was spinning really fast some time in the past, this ridge might be the result of the moon bulging in in the middle. Astronomers will have to take a closer look at the composition and orbital properties of this moon before they can determine exactly how the ridge formed.

Image Credit: NASA/JPL/Cassini

Astro Plans for 2013

It's that time of year when everyone is making new year resolutions, and I am no different. My goal this year for you, my readers, is to write a blog post at least once a week. So today, I thought I'd share with you some exciting events of 2013; a hint at blog posts to come.

This year is going to be just as exciting as years past for astronomy enthusiasts. NASA has many missions planned, including the launch of the Interface Region Imaging Spectrograph (IRIS), Lunar Atmosphere and Dust Environment Explorer (LADEE), and the Mars Atmosphere and Volatile Evolution mission (MAVEN). These instruments are designed to study the solar atmosphere, moon's surface, and Mars' upper atmosphere, respectively. Along with these new satellites, NASA and other agencies will continue  to support the International Space Station and science experiments being conducted there.  The ESA will also be very active in 2013, focusing on launching satellites to study the Earth as part of their Living Planet Programme. Work will continue on the James Webb Space Telescope (JWST), and the construction of the Atacama Large Millimeter/submillimeter Array (ALMA) should be completed. Data continues to pour in from the Great Observatories Hubble, Chandra, and Spitzer, along with various missions exploring our solar system. Astronomers are actively studying this information and continue to make discoveries pertaining to star, planet and galaxy evolution. The Kepler space telescope, along with ground based observatories, continue to discover new exoplanets on a weekly basis. Maybe an Earth analog will be uncovered in 2013? Towards the end of 2013, be on the lookout for comet ISON. It's expected to whiz by Earth in December, and will appear as a small dot as bright as the full moon traveling across the sky.

For more information on these events, and, of course, some basic astronomy topics explained, check back on a weekly basis!

Image Credit: NASA/JPL-Caltech, space.com

Can I See the Stars?

Clear skies are essential for astronomers, but depending on where you live they may be few and far between. If you want to do some star gazing, but aren't sure if the weather will cooperate, take a look at the clear sky clock (http://cleardarksky.com/csk/). All you need to do is click "find a chart" and enter your location (or chose a state then city). What you'll see is a chart telling you all sorts of weather predictions, but the most important one is the cloud cover. Above is a clear sky chart for Kitt Peak, AZ, and you want to look at the top row of boxes to see if the sky will be clear. The color of the box at a given time tells you if there will be clouds in the sky (white), or if the sky will be clear (dark blue). So it looks like the sky will be cloudy before midnight Saturday, and then crystal clear the next day and a half. Below the chart there will be a description of how to read the chart and what the colors correspond to exactly. The chart is usually very accurate and astronomers use it all the time while observing. So the next time you want to go to a local star party, but aren’t sure if you should bother going because it might be cloudy, take a look at the clear sky chart before you head out.