Physics

Cosmic Distortions & Gravitational Lensing

An Einstein Ring, LRG 3-757 was discovered in 2007 in data from the Sloan Digital Sky Survey (SDSS), the image shown above is a follow-up observation taken by the Hubble Space Telescope. Image credit APOD

An Einstein Ring, LRG 3-757 was discovered in 2007 in data from the Sloan Digital Sky Survey (SDSS), the image shown above is a follow-up observation taken by the Hubble Space Telescope. Image credit APOD

Cosmic rings are a dazzling gift provided by the laws of physics.

Just as the lenses in a pair of glasses can refract (bend) light to allow us to see better, large celestial objects can do the same. It’s like having a telescope built by nature. It occurs when light from distant background stars, galaxies, quasars or supernovas are distorted into rings or even duplicate images by interacting with the curvature of space-time. This is just another example why science is so fricken awesome!

Einstein acknowledged gravitational lensing in his general theory of relativity, in which he proposed that because space-time is curved by gravity, so too should light if it passes near a massive object. The first test of his claim came during the solar eclipse of 1919. Since the sun is the most massive object in our solar system it seemed a worthy place to find distortions due to gravity. Arthur Eddington photographed the sun while being eclipsed by the moon. The moon acted as a filter, blocking most of the sun’s light allowing him to view images of the universe behind the sun.

Astonishingly, he saw light shining in the background that should have been obscured by our star, instead the light was being lensed by the gravity of the sun. These stars weren’t just in the background; they were actually behind the sun.  It was the proof needed to get Einstein the Nobel Prize for physics in 1921. If it weren’t for the reality of space-time being malleable, we wouldn’t see the beauty of gravitational lensing.

THE PHYSICS BEHIND IT

The lensing effect acts as a magnifying glass allowing a viewer to see objects that lie behind a larger foreground structure. Let’s use a distant galaxy as an example. The light from that star is traveling through space in all directions. While on its journey if it happens to pass near a massive object, such as a foreground galaxy or group of galaxies, the light will follow the gravitational curve of the massive object(s). This will distort the light from distant objects.

In the words of Neil deGrasse Tyson, “some lenses are like fun house mirrors. They can take the background galaxy and flip it left, right, and upside down, distort it and make the image appear multiple times” (Star Talk Radio). If the background object is directly behind the massive galaxy we will see the background object in different locations with the same magnitude. The background image may appear as a halo, or a ring around a bright object; this is called an Einstein Ring. (Top photo).

If the background light is slightly askew, meaning that the background object’s center doesn’t match up with the center of the foreground object, it will cause the light to smeared out in the form of an arc, or we can see a duplicate image, one with more magnitude than the other(s).  This is because it takes some of the light a longer amount of time to travel from it’s original source to the viewer. As the light bends its way around the far side of the foreground object it essentially is taking the long route and reaches us later. Meanwhile, the light traveled farther from the massive object took the fast lane, this light will appear with more magnitude because of the off-center natures of the lens.

Watch the short clip to see how different types of foreground objects will produce different lensing outcomes. Galaxies produce different types of images than say, a black hole would.

Gravitational lensing comes in three types strong lensing, weak lensing, and microlensing.Strong lensing is what we have described until now. These are categorized by obvious light distortions. This occurs most often when massive objects such as galaxy clusters are used as the lens. In weak lensing shear (the stretching of light) and convergence (the light’s magnitude) are still present, but not in a drastic way. Scientists can use lensing to measure dark matter in large-scale structures within the depths of our universe. With gravitational microlensing there is no smearing of light or multiple images seen; rather the objects’s magnitude will change over time, it may appear brighter than stars relatively close, despite the object being great distances away.

SIMULATING GRAVITATIONAL LENSING AT HOME

 Have you ever stared through the bottom of a wine glass? Not because you’ve had too much to drink, but to watch the light twirl around the base. This is actually a great gravitational lensing simulation that you can do at home. Watch the video to see how you can create the illusion.

 

 

 

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What Matters About Antimatter

 

 

“On the big Bang theory: For every one billion particles of antimatter there were one billion and one particles of matter. And when the mutual annihilation was complete, one billionth remained – and that’s our present universe.”

– Albert Einstein

 

A brief history of how antimatter was first observed

To understand what antimatter is let’s begin with when it was first discovered. It was first predicted by mathematician, physicist, and true genius,  Paul Dirac, in the 1920s. Dirac did something quite profound and he actually created an equation, know as the Dirac equation, that combined both relativity and quantum mechanics, two worlds that don’t seem to want to play nicely with each other. He is credited with one of the most astonishing achievements in the last century:

“Paul Dirac developed a theory that combined quantum mechanics, used to describe the subatomic world, with Einstein’s special relativity, which says nothing travels faster than light. Through complex mathematical calculations, Dirac managed to integrate these disparate theories…He went on to assert that every particle has a mirror-image antiparticle with nearly identical properties, except for an opposite electric charge. And just as protons, neutrons and electrons combine to form atoms and matter, antiprotons, antineutrons and anti-electrons (called positrons) combine to form anti-atoms and antimatter”. (NewScientist)

This is incredible because the electrons we are used to here on Earth, and everywhere else we had looked in the universe up to this point in history, all had a negative charge, not positive. What is equally as absurd is the thought that if these positively charged electrons were to exist where was it to end?Antiatoms, anti molecules, antiMATTER? Was there a whole new world out there that humans had yet to access?

How to set up a cloud chamber. Photo credit: The Naked Scientist.

How to set up a cloud chamber. Photo credit: The Naked Scientist.

The cloud chamber

 It was five years after Dirac’s postulation of antimatter that Carl Anderson confirmed the existence of it, and all he had to do was peer into a device that had been around since the 1890s. By observing particles in a little contraption know as a cloud chamber, he found the proof of antimatter; he found the positron!

The box, which is sealed off to the outside atmosphere, has a bottom cooled by dry ice. The top contains a cloth soaked in alcohol; the combination creates an atmosphere inside the box of super-cooled alcohol vapor. The back of the box is often painted black to better see what happens inside. A light source is then introduced. What is observed is a series of vapor trails being created within the box; these trails are similar to those left behind by aircraft molecules condense in the air creating a trail hence, the name cloud chamber.

What makes the trails?

In two words:Cosmic rays. Essentially these are highly charged subatomic particles, mostly “…protons, electrons, and atomic nuclei which have had all of the surrounding electrons stripped during their high-speed” travels near the that of light. These cosmic rays are constantly bombarding Earth. They are smashing into you and me right now undetectable to us. Because subatomic particles have charges (protons=positive, electrons=negative) they will follow the lines of the magnetic fields found naturally surrounding Earth.

Click the following link for an excellent video from MIT that illustrates, once again, how a cloud chamber works in more detail and shows the cosmic rays as they pass through the cloud chamber! It is truly beautiful!

Examining the trails

Carl Anderson was not the first person to observe antimatter trails. He was, however, the first person to realize that some of the trails inside the chamber, that countless scientists before him had disregarded, were in fact positrons.

If you peer into a cloud chamber you will notice that the vapor trails don’t all look the same? In fact, according to Frank Close, professor of physics at Oxford University and Head of Communications and Public Education at CERN, says that “Light weight particles such as electrons leave thin wispy trails, quite different from the dense trails of bulky protons” as they pass through the atmosphere inside the chamber. When earlier scientists first saw the abnormality produced by positrons they missed the significance of them and simply brushed off the odd occurrence of antimatter trails.

So, in 1932, when American physicist Carl Anderson, first saw a wispy lightweight trail moving in the direction of only positively charged particles he knew he had observed the first proof of antimatter, a positron! Remember that positrons have all the same properties, in terms of weight, mass and spin, as an electron, only it has swapped its charge.

As stated by Dirac himself, antimatter is said to be a mirror image of matter.  What is amazing, in addition to the fact that antimatter exists at all, is that the mirror image description may be a bit of an oversimplification. Research scientists, James Cronin and Val Fitch won the 1980 physics Nobel Prize for discovering that matter and antimatter are not indeed exactly symmetrical and may interact with the laws of nature differently. This just goes to show that the universe is extremely complex in strange and mysterious ways. There is still much to learn about how antimatter works and how we as humans can benefit from it.

When a positron and electron meet they annihilate and release high energy photons (Image source).

When a positron and electron meet they annihilate and release high energy photons (Image source).

The Power of Annihilation

When matter and antimatter meet they annihilate one other. In doing so the material within each particle transforms from matter into energy, in the form of photons (aka the force carrying particle of light and the electromagnetic spectrum). E=MC² illustrates, on a basic level, that matter and energy are the same. The annihilation of matter and antimatter into gamma radiation is a perfect example of Einstein’s equation!

So, here is another way to think about it: The Anti/matter particles do not last long in the same area before they collide with each other. The outcome of this meeting is so great that it creates, for an instant, the highest form of energy in the universe a gamma burst. This type of light frequency is well beyond the spectrum of light that is visible to the human eye, however, it is strong enough to alter DNA and could pretty much destroy the entire planet if enough gamma radiation was concentrated in the small enough beam!

Yes, it is incredibly impressive, especially when you take into consideration that “..each gram of annihilation liberat[es] twice the energy of an Hiroshima-sized atomic bomb”,  this according to Frank Close, author of “Antimatter” published in 2009. That sure is a lot of energy that could be harnessed! Perhaps lucky for us, a gram of antimatter is exceptionally hard to come by here on Earth.

Modern applications

Currently, scientists and engineers are working on new applications  to exploit the enormous amount of energy released in an antimatter/matter annihilation, even if the amount we are able to produce in labs is quite small. Research into antimatter jet propulsion and antimatter guns have already started! Antimatter has been used for decades in medicine, PET scans, which stand for positron emission tomography, detect radioactive neutrons as they decay in the human body producing pairs of gamma rays. Using these rays doctors can map the human body.

Antimatter Fun Facts

  • In 1995 at CERN the first and largest antimolecule was created, nine atoms in fact, of antihydrogen! “Each one remained in existence for about 40 billionths of a second, traveled at nearly the speed of light over a path of 10 meters and then annihilated with ordinary matter” (CERN).
  • Over the last few years, scientists have been working on perfecting the methods of storing antimatter. In fact in 2011, the antiatom of hydrogen was stored for 16 minutes! This is particularly impressive knowing that antimatter annihilates instantly when it’s met with matter. 16 minutes is huge in comparison to its normal fraction of a second existence.
  • Research is currently being conducted to determine just how the Earth’s gravitational pull affects antimatter.
  • Antimatter is created in natures quite frequently by solar flares, thunderstorms, and by naturally occurring radioactive particles.

 

 

 

References and further reading

 Antimatter by Frank Close. Published by Oxford University Press, 2009.

Finding Antimatter in the Real World by Roger Highfield, 2009.

NASAs Fermi Catches Thunderstorms Hurling Antimatter into Space. 2011.