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Alexa Dosk
Attended University of Buenos Aires
Lives in Bs As, Argentina
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Gravity Check

Newton’s law of gravity states that between any two masses there is a gravitational force.  The strength of that force depends not only on the masses, but on the distance between those masses, following what is known as an inverse square relation.  That is, if you double the distance between two masses, their gravitational attraction will be a quarter of what it was.  If you halve the distance between two masses, their attraction will be four times stronger.  Newton felt that this inverse square relation was exact, but is it?

One of the ways we know Newton’s gravity works is through the motion of the planets.  Masses like the planets and Sun are attracted to each other by gravity’s inverse square relation, and thus their motion follows a relation known as Kepler’s laws.  We have seen that this holds not only for the planets and moons in our solar system, but also for other stars orbiting each other, exoplanets orbiting their star, and even stars orbiting the supermassive black hole in the center of our galaxy.  So Newtonian gravity works very, very well.

For large masses we know that the inverse square relation for gravity isn’t quite exact.  For example, Mercury and the Sun are massive enough and close enough that Mercury’s orbit deviates slightly from a simple elliptical orbit.  This deviation was the first evidence of general relativity.  We also know that the orbit of massive neutron star orbiting with another star will decay in a way that violates Newtonian gravity (but agrees with general relativity).  Newtonian gravity works very well, but for massive objects general relativity is more accurate.

What about for small masses on very short scales?

We know that on very small scales Newtonian physics is inaccurate, and we need to use quantum mechanics. One common feature of quantum mechanics is that rather than being smooth and continuous, objects can be constrained into discrete (quantum) states.  We see this, for example, in the light emitted by an atom.  Rather than being a continuous range of wavelengths, the emitted light can only be at particular wavelengths.  This is due to the fact that an electron in an atom can only have particular energy levels.  When an electron drops from a higher energy level to a lower one, it releases a photon of a particular wavelength.

On very small scales, gravity is also be quantized. We don’t have a complete theory of quantum gravity, but for weak gravitational fields such as Earth’s, it can behave similar to the quantum energy levels of an electron in an atom.  In a new paper in Physical Review Letters, this fact was used to measure Newton’s inverse-square gravity to the highest precision yet.

What the team did was to create a “gravitational atom” by bouncing between two mirrors (not mirrors in the way we usually think, but rather a surface that can reflect neutrons). These particular neutrons were ultra-cold, so their bounces were very small and were very low energy.  Because of this the energy of these neutrons were quantized. Basically, instead of being able to bounce to any height like a rubber ball, they could only bounce to specific (quantum) heights.  In other words, the gravitational energy of the neutrons were quantized in much the same way that the energy of electrons are quantized in an atom.

The team was then able to measure these energy levels very precisely, using a method known as resonance spectroscopy.  Since the energy levels of the neutrons depend on gravity, any deviation of gravity from Newton’s inverse square relation would show up as a shift in the energy levels.  What the team found was that the energy levels matched Newtonian gravity to the limits of their measurements.

What’s interesting about this result is that it puts constraints on certain forms of dark energy and dark matter.  For example, one model of dark energy, known as quintessence, proposes that dark energy is a scalar energy field.  One prediction of quintessence is that it would cause gravity to deviate from an inverse square relation at small energy levels.  This experiment rules out quintessence unless its interaction is very weak.  One idea for dark matter is a particle known as an axion.  This type of particle would also interact at low energy levels, causing a deviation from Newton’s gravity.  This experiment rules out axions unless their interaction is extremely weak.

So it turns out that on very small scales Newtonian gravity still works, and that means that dark energy is not likely to be due to quintessence, and dark matter is not likely made of axions.

Image: The quantum gravity energy levels for a neutron. 
Credit: T. Jenke et al.

Paper:  T. Jenke, G. Cronenberg, et al. Gravity Resonance Spectroscopy Constrains Dark Energy and Dark Matter Scenarios. Phys. Rev. Lett. 112, 151105 (2014)
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CREATIONIST COSMOS  
h/t: iflscience

It was no surprise that creationists weren’t going to love Cosmos: A Spacetime Odyssey. Their actual response would be laughable if I wasn’t so busy slamming my head into my desk. 

On the night of the premiere, a Fox affiliate station in Oklahoma “accidentally” cut out a full 15 seconds of programming containing Tyson’s only reference to evolution that night. Instead, a promo piece about a teenage archer was played. Could this have been an honest accident? Maybe. But to make such a dumb mistake during the premiere of such a highly-anticipated series reeks of ineptitude, which isn’t that great of a defense.

Over the following weeks since the show’s premiere, many creationists effectively covered their ears, saying “La, la, la! I can’t hear you!” or have attacked the content of the show only to highlight the fact that they didn’t understand it and were closed off to learning. Now, it has hit a breaking point with Young Earth Creationists actually demanding equal air time to provide the “science” of divine creation. What would their show even look like? Thanks to the folks at Funny Or Die, we have an answer.
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NOTE: I'm not trying to say anything bad about UNESCO or Red Cross. They do some really great work. What I'm saying is, it's disingenuous and factually wrong to try to say that the Catholic Church is just some sort of money-making scam. People don't give their lives for mere profit scams and pyramid schemes.
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Question of the Day:
How can you take a picture of our Galaxy if we are in it?

Answer:
Since our solar system is embedded within our Galaxy, we can only show an artist's representation of what our Galaxy looks like from the outside, rather than show a true astronomical image, as produced by a telescope. From our vantage point in the plane of the Galaxy we only have an edge-on view of the Milky Way, but this view is still very useful, especially when combining information from different types of astronomical observations. Some observations are good for tracing the spiral arms of our Galaxy, while others are better for detecting the stars and still others are good for tracing the gas and dust. A picture of the Milky Way, as seen from the outside, can then be made by piecing together the information from these different observations.
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Conservation of energy :)
 
THIS GUY . . . right?!

Probably the best GIF ever made. #boop  
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Boop! -lmao
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New Hubble view shows objects a billion times fainter than your eyes can see. Astronomers say this image also offers a remarkable depth of field that lets us see more than halfway to the edge of the observable Universe.

Read more: http://buff.ly/QiBgTd
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Looks like Captain Obvious.....

cf: Hotels.com
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Hilarity and wisdom
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Muy bueno pero yo amo leer en el Reader. Además así cuido el medio ambiente y los arbolitos :-) 
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Witches everywhere :)
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Education
  • University of Buenos Aires
    Electronics Engineering
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I'm not a complete idiot. Some parts are missing ;)
Introduction
Hi! I'm not good at introducing myself.
I love travelling; I'm a #STEM enthusiast (Science, Technology, Engineering, Math), passionate about Astronomy and Physics. Studied Electronics and Mechanical Engineering but I don't formally practice. 
I'm a natural teacher and I love to help people -especially youngsters and elder persons- understand science, math and computing, and how they can be applied to real life problems. 
Don't believe in astrology, numerology or other pseudo-sciences, so perhaps asking about my sign is not a good idea 
Need to learn something new everyday. 
Prefer buying tools to shoes. 
I'm a nice, very nice and quiet person, but don't bug me ;) 
I'm an atheist. I respect everybody's beliefs; please respect my disbelief.I won't meddle in your religious posts, please don't preach on mine.  
Just take a look on my posts and you'll get an accurate idea about me. If you like what you see, feel free to circle me 
Thank you for stopping by and reading :) 
=============================================== 

¡Hola! No soy buena presentándome 
Me encanta viajar 
Soy una #STEM fan (ciencia, tecnología, ingeniería, matemáticas) , me apasionan la Astronomía y la Física. Estudié Ingeniería Electrónica y Mecánica. No ejerzo formalmente.
Soy docente por naturaleza, me apasiona ayudar a la gente, especialmente chicos y gente mayor, a entender las ciencias, las matemáticas y la informática y a descubrir cómo pueden aplicarlas conceptualmente en la vida cotidiana. 
No creo en la astrología, la numerología ni otras pseudo-ciencias, por lo que, quizás, preguntarme por mi signo del zodíaco no sea la mejor idea.  
Necesito aprender cada día algo nuevo. 
Prefiero comprar herramientas antes que zapatos. 
Soy tranquila, muy tranquila y agradable, pero no me molestes  ;) 
Soy atea. Respeto las creencias de todo el mundo, por favor respetá mis no-creencias. No voy a ir a entrometerme en tus posts sobre religión, por favor no vengas a predicar a los míos. 
Dale un vistazo a mis posts y tendrás una idea precisa acerca de mí. Si te gusta lo que ves, no dudes en agregarme a tus círculos. 
Gracias por pasar y detenerte a leer :)
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