Waves of Spacetime- GW150914

On February 11th, 2016 the world was exposed to a shocking discovery that scientist’s have been questioning since the 1910’s. The idea of Gravitational Waves had been tossed around but never confirmed. This was mostly due to the fact that the detection of a GW seemed impossible because the technology simply did not exist. However, nothing is impossible in the scientific community. The first encounter with GW was with the Hulse-Taylor Pulsar, in which they observed the pulsar’s orbital decay which matched Einstein’s predictions of energy loss by gravitational radiation. This discovery would win them the Nobel Prize in 1993.

Not too many people are familiar with gravitational waves, so I will take this opportunity to clear things up. By the way, the name of the GW detected in the title of this post is the date that it was found! Fun fact for the day.

What is a GW? A gravitational wave is formed by a mass in motion. Think of a stone tossed into a lake. The stone creates ripples, or waves that propagate throughout the lake. The same idea can be applied in space. However, stones in a waternot all masses in space are strong enough to send ripples through spacetime. Only the large, energetic ones like a rotating binary system, supernova’s, black holes, etc. These massive objects are so strong that the space around them will “ripple” as they spin or explode while they are losing energy in the form of gravitational waves. This is why the detection of GW is huge. Only massive violent events in space cause them, therefore, we can study GW to learn more about the events that produced them, like mysterious black holes and possibly the big bang itself.

How do we detect gravitational waves? As previously stated, GW are nearly impossible to detect. As they pass through, they cause distances to change and periodic deformations. Their effect, however, is so small which makes it difficult to detect them. This is because gravity is a weak force and the period of the wave is extremely small. For example, a mass with a diameter of 1 meter would only be deformed by 10^-21 meters. This is why it is very difficult to detect GW. Nevertheless, physicist Albert Michelson came along to show us how we could measure such a small motion. Using the wavelength of light as a measuring device we are able to detect precise movements for exquisitely small distances, or periods.

How is light used as a measuring device? If you’ve ever taken a physics class then you’veinter probably learned about Young’s two slit experiment that allowed us to “see” the wavelengths of light. A single light beam that is shined through two slits can be seen on a blank screen some distance away as a pattern of light and dark “fringes.” This is known as interference. The distance between fringes is directly related to wavelength.

 

Laser Interferometer’s
obs
LIGO (Laser Interferometer Gravitational-Wave Observatory) is a collaboration between multiple physics institutes and research groups dedicated to the search for GW’s, which began in August 2002. Because the wavelength of a GW is directly related to the size of the cosmic event, detectors must be about the size of the cosmic event. Thus, we have two types of man-made devices: Ground Interferometer’s, designed for small cosmic sites w/ GW of a few thousand kilometers, and Space Interferometer’s, designed for large cosmic sites with wavelengths tens of millions of kilometers. The ground interferometers are located in Hanford, Washington and Livingston, Louisana.

Basically, an interferometer sends out a laser beam that hits a beam splitter, splits the light in two where the light is directed toward mirrors that finally send the light back to the beam splitter to form an interference pattern. The arms of the interferometer are the trajectory of the beams, so the pattern depends on the distance between the arms.

laser

If a GW goes through, the distance between the arms changes, leaving the interference pattern changing periodically!
In theory, LIGO could also detect hypothetical phenomena of GW caused by oscillating cosmic strings, and domain walls

LISAPathFinder
Lisa is the first space interferometer that was successfully launched on December 3, 2015. The mission is to map out the technical difficulties that may be experienced by eLisa, which will be launched with three satellites positioned 5 million km away from each other with laser beams connecting the three satellites. Any change in the distance of laser light will suggest a GW passing through.

To watch and learn more about this fascinating historic event, see the video below!

 

Are we really able to learn about the creation of the universe by studying a GW?
Because gravity is such a weak force, gravitational waves interact weakly with their environment. In fact, the effect is so small that they don’t change much because of their weak interactions. This makes them the perfect little “messengers” of distant cosmic events, providing us more information on gravity and how the universe works as gravity is turned into waves.

Side note- an interesting comment was made in the discussion post on GW so I thought I would share:
“gravitational waves, to me, would better explain some kind of déjà vù, because space time is being curved, it would be a variation on the time that maybe allows someone to look into the past or future for a few milliseconds (or the time it takes to the wave to pass)” -M.A
Something to think about!

That about sums up the discussion on gravitational waves, next time I will talk about black holes- their mysterious nature, escaping them and how GW will provide us with information we would never be able to gather otherwise!

This post is part of a series, for links to other posts, click here!

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The Implications of Gravity in Spacetime

The theories in which modern science rest heavily upon were presented hundreds of years ago by the scientists we have grown to learn about and love. Their theories have yet to be disproved, and that is why those theories are the platform on which modern science now rests. It is a strong platform, but as it ages, we must fill in the cracks. That’s where we are at in this day and age, filling in the cracks of an old foundation. Gravity is the most fundamental force in the universe, yet it is a very weak force. The series of posts I am about to share rely heavily on our concept of Gravity, so it’s important to get the basics down first.

We will start with Galileo. In a uniform gravitational field, Galileo believed that all Galileoobjects fall identically-irrespective to their mass. To prove his theory, he climbed up the Leaning Tower of Pisa where he dropped various masses. In doing so, he proved that when an object is in free fall, it will not experience a force in relation to it’s mass and that all objects, regardless of their mass will move in the same direction, at the same time. Think of an elevator- your head and shoes will “fall” at the same time, even though your head is heavier than your shoes. Galileo gave us the understanding of inertia; where an object that is set into motion stays in motion until it is acted upon by some external force.

Aristotle believed that the Earth did not move because if you threw a ball straight up in the air it would come straight back down, instead of going to the left/right etc. Galileo argued this idea giving an example of the cabin of a ship. Inside the cabin, if there are no windows, there is no way to tell if the ship is moving or not. Galileo concluded that the laws of physics are identical in all Galilean (intertial) reference frames, providing us with our first encounter with relativity.

newton

Next, Sir Isaac Newton comes along to explain the force that acts upon all objects. Newton’s first law of motion is essentially Galileo’s concept of intertia. The second law of motion tells us that the force needed to act upon an object depends on it’s mass and acceleration. If you have a large mass with a large acceleration, you will need a large force to act upon it and so on. Finally, Newton’s third law of motion state’s that for every action, there is an equal but opposite reaction.

Newton’s laws gave us a better understanding of the physical world around us. Einstein decided to apply his idea’s to the entire universe. On November 25th, 1915 Einstein
published his Theory of Special Relativity. This theory has Einsteinprovided us a profound understanding of our universe, and much of what we know has been found using Einstein’s theories. Special Relativity tells us that the speed of light is the same in all constantly moving frames and that Time slows down the faster you travel and vice versa.

To better understand the idea of special relativity, I will provide an analogy from the book “Hyperspace” by Michio Kaku: Continue reading “The Implications of Gravity in Spacetime”

Background

I randomly signed up for an online physics course that would last six weeks. Little did I know, I would become so intrigued by the end that I am now spending every spare second reading science blogs, science books, and re-watching the lectures of the course. I plan to share with whomever takes the time to read this, the exciting new things that I learned from the course.

Let me start with an introduction about the course.

The title of the course was “Gravity! From the big bang to black holes.” So, as you may assume, the topics ranged from Einstein’s general relativity, the big bang, inflation, dark matter, dark energy, gravitational waves, and black holes. Some old concepts, some new (to me). The best thing about the course was that you did not need to have any background in physics. Just an appetite for learning, and maybe some extra research on your own time if interested.

The course was taught by Professor Pierre Binetruy of Paris Diderot University. Pierre was the first director of the AstroParticle and Cosmology laboratory in Paris upon it’s creation. His main interests, according to a bio online, include cosmology and gravitation; connecting the theories of the early universe and fundamental interactions. He’s highly knowledgeable about inflation models, dark energy, and cosmological background of gravitational waves. Due to these areas of interest, he is highly involved in the eLisa mission- which I will go into more detail about later on.

I would just like to express how happy I am about taking this class. The course provided such lucid, comprehensible explanations on theories and concepts of physics. There was hardly any math involved, which was nice. The detailed explanations and demonstration’s made these unfamiliar concepts easy to grasp. Finally, Pierre arranged live hangouts where we were introduced to prestigious scientists, and we were able to ask questions during a live chat. George Smoot was one scientist that was present during the hangouts, and also recorded a lecture himself to explain the concept that won him the Nobel Prize in 2006. We were also able to meet key scientists that were actively involved in the LISAPathfinder mission, which was launched 12/03/2015. This mission will (hopefully) uncover another corner of the veil on the universe. I now anxiously await the discoveries that will be made from this mission. The series of blog posts that follow should explain why.

Here I will post the links to the series of posts I will be writing:

  1. The Implications of Gravity in Spacetime
  2. Waves of Spacetime- GW150914
  3. Black Holes: Part I