Gravity, relativity and brief story

This is the second part of the science series that broadly explains the current situation and the developments in the science of physics. Make sure you read the First Post before diving into this. As usual, i will ve giving you a little bit basic and a little bit complex information to start wondering about these subjects. All these subtitles can be a vast research area. This one will be about the gravity. I will try to explain what it is, what people think it might be and why is it important. I have to end with a little bit string theory but that part will be explained more detailed later. I will try to make it fun to read as much as i can :)

What is gravity

A brilliant movie from Alfonso Cuarón starring Sandra Bullock and George Clooney? Well yes but no. Is it the thing why flight tickets are so dorn expensive? Wll kind of but still no. Is it the force that causes the apples to fall? Getting closerrr... Is it the force of attraction between objects with mass? Yess, i knew you would figure it out Sir Isaac Newton. :)

Philosophers have been thinking about why objects are falling from the sky rather than hanging in the air and may just conclude that earth is pulling them down. But if you want to use and take advantage of this mechanism, you have to formulate it. When Newton figures out mass has influence on other masses, he formulates this cute little equation.

Which states that gravitational force is equals to mass (m1) times mass (m1) times gravitational constant (G) over distance squared (r). This explains why gravity becomes too weak too soon when you get away from the mass. This discovery was made around 16th century so there were no technology or advanced machines to do calculations. Newton used an inclined slope and rolled a ball over it. This way he did not need to go up in an empire state building to drop things down and calculate. He has also invented some of the calculus because the mathmetics were not enough to explain his workd :D He was basically a genius. This formula works very well for a long time. Scientists used this to send rockets to the space and this equation even explains orbits of planets around the sun.

But every dream must end, every perfect piece of code must fail when an exception occurs :) When astronomers realize that Mercury has a little bit weird orbit and does not exactly obey the laws of Newton, there was a need for a new theory for gravity. And then Einstein had his happiest thought of his life (He describes it with these exact words) and saved science of gravity. He imagines the worker working on the rooftop of a building in front of his office building, a patent office. And he realizes that when you are falling, you will basically feel weightless. This is what you feel in the plane while descending. Then he brings a new idea called spacetime and eventually wrote down this bogy equation. (General Relativity)

Oh this is nothing much complicated actually. You know with the Ricci Tensor (R) explaining the curvature with geodesics, Stress-Energy Tensor (T) explaining the effect of mass, 16 dimension (4x4 u and v indices) and Cosmological Constant plus Newtonian principle. Simple stuff :) This took Einstein 10 years to complete but not because he was not smart enough. The simpler explanation of this equation takes advanced high super level of calculus to understand, but it is not because Einstein is super smart :) The uniqueness of Einstein was his new perspective of gravity. He proposed that space and time are inseperable and called it spacetime. It is wobbly and curves and objects follow spacetimme curvature basically. He had help from mathematicians sure but he did not just add another constant or variable on top of Newtonian gravity. This is what makes the Einstein unique when it comes to general relativity. You probably know special relativity and mass-energy interchangeability and i can mention it in the upcoming posts. But 3D visualtization of spacetime is this:

The exreme version of this is a black hole. Here is how it works: If you throw a ball in the air, it will fall back to earth. This is because earth is able to keep the hold of the object before escaping its gravitational radius. If you throw it around 11 kilometers per second speed, you can go and apply for guinness world records, it will be able to go all the way up to the space. Imagine earth gets a lot bigger and gains mass and therefore gains more and more gravitation. It will require faster speeds to throw into space like 20 30 40... etc. Eventually you will reach the speed of light. You have to throw the ball with the speed of light up in the air to make it escape the gravity of the earth :D But don't even dream about it because at that point the gravity of the mass will be so powerful, it will crunch the earth into a black hole. Black hole is the result of extreme curvature around extreme mass. The subject of black holes are deeper than this but i think this much is enough within the context of gravity. And this is the result of the curvature from another perspective. Light is bending around a heavy cluster of galaxies and looks like a lens. Because light is also traveling through spacetime. It ends up looking like a lens gathering light around.

Here is something fascinating. Just like a fortune teller, this equation was telling that if you gather enough matter together, spacetime will be so dense and even the light will not be able go throug it. Sort of like a very strong lensing that actually traps light. And it will result in a black hole. This was one of the expected results of the equation. The second one is that because the spacetime is one single entity, it should be affected by mass inside it. There should be spacetime jiggles when to heavy objects move through spacetime. Like when you swim in a pool, you cause waves. This one is caused by gravity, hence they have called it gravitational waves. And both these prophecies are confirmed lately :) You probably know the picture of the black hole (which is a whole subject all by itself), but the image below explains what happens due to gravitational waves and you may not have seen it. Well, basically we are all wobbling due to waves of gravitation :)

LIGO

So far we have witnessed Einstein dropping the mike with his equations after Newton and the equations told us that we are bunch of John Snows who knows nothing i guess :) At this stage i want to seperate a subtitle dedicated to LIGO (Laser Interferometer Gravitational-wave Observatory). You would not be surprised if i tell you this structure is built to catch these gravitational waves. But you would be surprised to know that its arms are 4 kilometers long. You will be even more surprised to know that it detects movements with 10 thousands times smaller than an atomic nucleous. It is not "blink and you will miss", it is "you will miss it no matter what" kind of detail. The mechnanism is quite simple actually. It sends laser beams through the arms and beams merge when they reflect back from the mirrors. If they don't merge correctly, that means the spacetime is stretched or contracted.

This instrument is sooo sensitive, it is forbidden to do sudden moves around the compunds to prevent any noise in the data. It is as isolated as you can get from the ground but it is trying to detect subatomic vibrations. So it is inevitable to get lots of false data from cars moving around or just weather events. This is why i kind of like this instrument. The more sensitive you want to get, the more data you will have to handle. Just like sensitive people in real life. Anyways, with this insturment, Einstein has been proven right after 100 years.

Aside from proving Einstein right, there is a very interesting story of the detection of the first gravitational wave. There were this man (i think a janitor or some kind) trying to figure out what was wrong with some device towards the early morning in the night and the detectors were off. He can't figure out the problem and just leaves the place to work on it tomorrow. Procrastination basically. He starts the detectors again. After couple of minutes the machine detects the gravitational waves and if the guy were to be still working there, the millions of years old gravitational waves would have just passed by silently. There is a saying in Turkish i will try to translate it into English. Prefer the evil in the morning instead of good in the evening.

But why is gravity so important? Why is this centuries old obsession with gravity? Why isn't it enough to live with general relativity, which we can, satellites are using general relativity to adjust to the flow of spacetime literally. The reason is not just curiosity or necessity. There is a piece of the puzzle missin in the universe. I will jump to that subject with one of my favorite science puns:

The gravity of the situation

I was dying to make use of this pun :) Well, gravity is a pain in the butt. Not because scientists are sitting all day on their desks trying to figure out what it is. It is because there are 4 fundamental forces in the universe as we know. Electromagnetism, weak and strong nuclear force and gravity. Magnetism is basically result of electrons movement in electric field (Faraday). Weak nuclear force explains atomic decay. Strong nuclear force unfortunately describes Hiroshima and Nagasaki. This is also based on special relativity of Einstein and i have heard it kind of led him to minor depression.

3 of 4 fundamental forces can be explained with the particles that scientists know. But here is a problem. Gravity is basically the attractive force of mass but it is way way weaker then the magnetic force. Like 10 to the power of 40 times weaker. There is also the confusion of black holes which suggests that the gravity is infinite inside it but nothing can be infinite. So the mighty General Relativity explains gravity on very big scales almost perfectly, but when you go under subatomic realms, the general relativity and quantum mechanics (there will be more of this subject later) make a mess when combined. And also, general relativity explains how gravity works, it doesn't explain what is it with any sort of particle or mechanism. Magnetism is caused by electrons but what causes gravity to work? So todays sicence trying to find an answer to this question: How can we combine quantum mechanics and gravity get along together nicely?

This is a little bit advanced but Leonard Susskind explains his view of quantum gravity (the gravity that works in quantum realm).

A little bit of string theory

I think this much science is enough for this post but i should give you a teaser of upcoming posts in this series. Scientist are trying to explain all the reality and universe with simpler terms. Because the more they dive into quantum physics the more type or variety of particles comes into play. Some people believe there is only one structure causing all the laws of physics and subatomic particles. They call these things, Strings. Very small (actually the smallest) string like sturctures with vibrations like a guitar string. Take a look at this.

The different vibrations causes different subatomic particles, resulting different atoms and elements and everyting else. This theory also has crazy suggestions like 10-11 dimensiton and has its own branches but it has never been directly tested. It also suggests multiverse. It is kind of old, it has been thought around 1900 through 1940 and rekindled with the discovery of dark energy around 1980.

I will stop burning your brain here :) The previous post explained the big picture, this one explained the trouble when you go into the smaller scales. Next one will be about quantum physics (it sounds so cool when i say this :D) as much as i can. I hope i have given you enough basics to go further. All of the subtitles in this post are worthy research subjects. See you at the next post :)