Physics of Gravity

Posted on February 19, 2013 by YanruChen

What is physics? I have been studying physics since elementary school, but I was never really taught about the definition of physics. My personal understanding of physics is that it is a study of the law of the nature.

The nature of physics is truly mysterious. Why do things obey the same law? Why can they be represented by certain equations?

More amazingly, our grandiose universe also obeys physics laws we find on Earth. This is actually the concept of “isotropy” in Cosmological Principle, which means that the same law of physics applies everywhere in the universe.

For example, gravitational force presents everywhere in the universe. The universal law of gravitation holds that the gravitational force of an object on another object is directly proportional to the mass of the object and inversely proportional to the distance between these to objects.

http://filipinofreethinkers.org/wp-content/uploads/2012/05/Universal-law-of-gravitation.jpg

This law was discovered by Sir Isaac Newton, but was left unexplained until Albert Einstein came up with general theory of relativity.

According to general relativity, a mass distorts the space around it. All objects are trying best to follow a shortest straight route when moving through the space. In a curved space-time, however, the object might fall into the trap of the curvature, thus proceed in a orbital motion around the mass that causes the curvature.

http://www.thephysicsmill.com/blog/wp-content/uploads/relativity_curved_space_deflection.jpg

If you would like to learn more about general relativity, please watch this clip from The Elegant Universe, which explains much better than I do.
General Relativity & Gravity


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Archeoastronomy

Posted on February 19, 2013 by AlanL

Over the summer I was in Mexico and visited some Mayan ruins in Tulum and Chichen Itza. It was incredible to hear all about how the cities were built with regard to the sun’s movement in the sky. In Chichen Itza, there is an observatory where they had 20 sight lines each marking a different astronomical event. The most impressive structure however is the famous pyramid called El Castillo which was designed so that on the spring and autumn equinoxes, the sun shines onto the pyramid in a way that creates the effect of a serpent wriggling down the staircase.

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A view of El Castillo during the spring equinox

The Mayans weren’t the only civilization that built structures that were synchronized with astronomical events. Stonehenge is another very famous set of ruins in the United Kingdom believed to be connected to astronomy; however there are many opposing theories as to how it actually functioned. Additionally, the Egyptian pyramids are believed to have been oriented with the position of the overhead stars. As you can see archeoastronomy was used for various different reasons and it amazes me how something that seems so complicated was so commonplace among civilizations and how it was all done without any computers.


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Dark Matter vs Dark Energy

Posted on February 19, 2013 by fathomingthestars

In my previous post, I wrote about dark matter and how we can infer its existence through gravitational lensing.  Here, I will more fully explore what dark matter is and what dark energy is.

Dark matter, as the name implies, is matter that is dark and cannot be seen.  “Seen” here does not mean visible to the human eye; it means emitting electromagnetic waves.  For example, a dust cloud might not emit light in visible wavelengths, but with a telescope that can detect x-rays, that cloud can be seen.  Many things were initially considered to be dark matter, such as the x-ray gas or very faint white dwarf stars, but with better technology we can observe them.  Dark matter, on the other hand, is something that is impossible to directly observe.  So, if we cannot see it, how can we know it exists?  We can observe the effect of dark matter on other objects.  As I wrote in my post on gravitational lensing, dark matter does have mass, so it distorts space-time and causes gravitational lensing.  Another way to infer the existence of dark matter is through a galaxy rotation curve.

By looking at the amount of light for part of a galaxy, we can estimate the amount of mass in that section.  So if we can find the mass of all the matter from the galactic center to a particular object, we can tell how fast the object should be orbiting the center of the galaxy.  However, if you would do this, you would discover that there are places in the galaxy that are moving too quickly for the amount of matter they are orbiting.  Thus, there must be dark matter present to increase the rotation speed.  If you’re interested in dark matter, I highly recommend this SciShow episode on the topic.

So now we know what dark matter is (well, not really), what is dark energy?  Whereas the “dark” in dark matter comes from it  not interacting with electromagnetic waves, the “dark” in dark energy comes from the fact that we know very, very little about it.  With the knowledge that the universe is expanding, two teams of scientists observed a bunch of a certain type of supernovae*, calculated where they expected the supernovae to be, and then figured out how far away the supernovae actually were.  They found that the supernovae were farther away than they expected, meaning that not only is the universe expanding, the rate at which it is expanding is increasing.  These results were quite surprising, as we had previously assumed that gravity would eventually slow everything down, so the rate of expansion of the universe would decrease.  We call the thing that is accelerating the universe “dark energy.” If you’re confused, or want to learn more, SciShow also did an episode on dark energy.

I’d like to leave you with a final thought.  Think of all the regular matter in the universe.  All the planets, stars, gas, dust, galaxies.  All of that is just 4% of the total mass-energy in the universe.  everything else is either dark matter or dark energy.


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DETECTING OXYGEN!

Posted on February 19, 2013 by sharpew

According to a New Scientist article from FEBRUARY 19TH, 2013, a new telescope in Chile might be able to detect oxygen on exoplanets (planets outside our solar system). This means that it would be able to detect alien life!! According to the article, our currently developed telescopes can identify the different elements of exoplanet’s atmospheres by studying the substances that absorb particular wavelengths. However, until now, this was not able to be done on smaller, rocky planets (like other Earths). This new extremely large telescope (39-metre main mirror), will be big enough to filter the atmosphere in Earth-like planets. This new telescope should be completed within this decade. Here is what the telescope should look like upon completion:

Screen Shot 2013-02-19 at 6.36.36 PM

I wonder what the speaker who visited Vanderbilt thinks of this new telescope! It seems to open up a lot of possibilities for discovering life and it is certainly a very exciting time to be studying exoplanets!!


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Happy 540th Birthday Copernicus!

Posted on February 19, 2013 by juliettealper

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Today, February 19, happens to be Nicolaus Copernicus’s 540th birthday. Google honored him by making their icon a heliocentric model. I thought it was fitting to talk a little about his accomplishments. One of the most interesting facts about Copernicus was that he completed all of his observations with his naked eye. Copernicus was one of the only people at this time (early 1500’s) to go against the Ptolemaic approach to the theory of the universe, which said that everything in the heavens orbited the earth. Instead, Copernicus created a heliocentric theory that said everything revolved around the sun. He also claimed that the earth rotates around it’s axis every day and this rotation affected what people saw in the heavens. Because he only used his eyes for observations, he was unable to formally prove any of these theories with enough evidence to convince people to such an “outrageous” concept. It was not until Galileo that these theories were proven, but it is incredible impressive that Copernicus was able to think so far out of the box with nothing other than his own eye’s observations.

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Who Needs Telescopes When You Have Dry-Cleaning Fluid?

Posted on February 19, 2013 by wherrysg

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Image Source

For Raymond Davis Jr, this was a legitimate question that he proposed to the science community in the 1960s with his Homestake Experiment. This experiment was Davis’s quest to learn about neutrinos–a neutral subatomic particle with an almost-zero mass and that also rarely reacts with normal matter. According to this article, Davis’s research on neutrinos has been important in the astronomical community since this particle is the only ‘species’ that has the ability to penetrate from the center of the Sun’s core all the way to the surface and escape into the solar system. It is understandable why a scientist would want to learn so much about these particles as I’m sure they could unlock so many secrets about the Sun.

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Image Source

Davis’s experiment is so fascinating because he built an underground tank, his neutrino trap, and filled it with 100,000 gallons of dry-cleaning fluid. The way the experiment worked was when a neutrino collided with the fluid in the tank, a chlorine atom would transform into Argon (the radioactive isotope form) that could then be extracted from the solution and counted.

Because an average telescope in the 60’s couldn’t even hope to capture the movements of neutrinos since they move at the speed of light and are so hard to track, it seems Raymond Davis Jr. built his own kind of telescope. Innovation at its finest!


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A Young Black Hole?

Posted on February 19, 2013 by mirandaskunz

As viewed from Earth, most black holes are about 17,000 to 21,000 years old. Recently, however, NASA scientists discovered what may be an infant black hole (pictured below). This black hole is only about 1,000 years old as seen from Earth and is located 26,000 light years away. It is left over from the supernova explosion W49B of a parent star. The strange thing about this explosion is that, unlike normal explosions that cause matter to explode in all directions, the matter was observed traveling extremely fast along the poles of the parent star. Usually, supernovas leave behind a neutron star, which is a dense, spinning core that can be detected with x-ray or radio waves. Scientists were not able to find any evidence of a neutron star, leading them to believe that this supernova created a black hole. If this is the case, this black hole is the youngest black hole ever recorded in the Milky Way Galaxy and the  first to be observed while still forming.

For more pictures of the black hole, check this out! For more information, go here or here.


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A Young Black Hole?

Posted on February 19, 2013 by mirandaskunz

As viewed from Earth, most black holes are about 17,000 to 21,000 years old. Recently, however, NASA scientists discovered what may be an infant black hole (pictured below). This black hole is only about 1,000 years old as seen from Earth and is located 26,000 light years away. It is left over from the supernova explosion W49B of a parent star. The strange thing about this explosion is that, unlike normal explosions that cause matter to explode in all directions, the matter was observed traveling extremely fast along the poles of the parent star. Usually, supernovas leave behind a neutron star, which is a dense, spinning core that can be detected with x-ray or radio waves. Scientists were not able to find any evidence of a neutron star, leading them to believe that this supernova created a black hole. If this is the case, this black hole is the youngest black hole ever recorded in the Milky Way Galaxy and the  first to be observed while still forming.

For more pictures of the black hole, check this out! For more information, go here or here.


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Aliens Don’t Exist! Or Do they….

Posted on February 19, 2013 by wherrysg

Gliese 581d habitable BEST

Image Source

I’m sure at some point we have all considered the possibility of life on other planets. What would they look like? How would they communicate? How advanced or primitive would they be compared to us? And most importantly, where/what would they call home? Like many kids, I was one whose view of aliens was dramatically informed by television and movies–expecting a purple alien race living on a spaceship, traversing the far reaches of the universe.

Our (the scientific community of Earth) idea of a ‘home’ capable of sustaining intelligent life has many requirements. First, we need to understand the concept of the extrasolar planet (or exoplanet). Seeing as we have yet to discover a planet within our solar system capable of sustaining life much like Earth, exoplanets refer to those planets found outside of our solar system; and currently we have found 262 potentially habitable ones.

Some are possibly inhabitable. How do we define a habitable ? A recent article from NBC News shed some light on a few of those requirements for “habitable zones for alien planets”, including: ability to retain liquid, temperature, atmosphere, etc.

At the end of 2011, one planet in particular was discovered to have the potential to house extraterrestrial life. This planet is called Gliese 581d and is so cool and it is the first planet known planet beyond our world that scientists currently believe is capable of sustaining life. Check out the article on this planet here! The article suggests that current greenhouse gasses are causing changes in the atmosphere, and these observations inform the notion of possible extraterrestrial life! It is even more amazing to think about how we can collect this information–through telescopes! Seeing that Gliese 581d is more than 20 light years away, it’s amazing to think how a planet that is so microscopic from our viewpoint, was found only by a 3.6 meter telescope in Chile. As technology continues to advance, there’s no telling what we will really find next!


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Galileo: A Man with No Last Name

Posted on February 19, 2013 by mirandaskunz

Galileo Galilei. Click image to expand.

I have always wondered why we always refer to Galileo by his first name. We don’t have Johannes’ laws of planetary motion or Albert’s theory of relativity, but Galileo Galilei is just Galileo. I remember learning in elementary school that people are referred to by their last names as a sign of respect. Certainly, the man who ultimately disproved the Earth-centered model of the universe deserves the respect that comes with referring to someone by their last name.

There are two main reasons we call Galileo by his first name: Galileo referred to himself by his first name and last names were ambiguous in Italy during his lifetime. When Galileo was born in 1564, Italy did not have laws regarding the consistent use and documentation of last names. Some people used the town they we from as their last name (like Leonardo da Vinci, who was from the town of Vinci), while others used their father’s first names, their occupation, or a traditional surname. People even used different last names in different situations.

Galileo himself could go by several different names. His father’s name was Vincenzo and his family was associated with the traditional surnames of Galilei and Bonaiuti, so his full name was Galileo di Vincenzo Bonaiuti de’ Galilei. He was also known to go by Galileo Galilei Linceo, which identified him as a part of a specific group of scientists. Overall, it seems he preferred being called Galileo without any last name, which is why we still call him that today.

This ambiguous last name system made identification and legal documentation very difficult, so during Galileo’s lifetime, authorities in Italy began requiring parents to document a specific first and last name for their children. Laws like these had already been in place for years in other European countries, which is why Johannes Kepler is referred to by his established last name.

More information on why we call Galileo by his first name can be found here.


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