The Theory of Everything (2014): So, what did Stephen Hawking find out?

 The Theory of Everything 

(So, What did Stephen Hawking find out?)

    Hi! Winter in South Korea was getting warmer (I felt it clearly), but today it snowed a lot - with some rain drops. It was freezing, so I had to consistently provide myself a cup of hot matcha latte :) Thinking about the movie I would introduce to you in today's post, I decided to introduce you about the main character of the movie The Theory of Everything (2014) in depth since I didn't really talk about his achievements (what scientists, including myself, should appreciate!) in the previous post. I am very glad to write about Stephen Hawking, who is my role model of all time.

So shall we begin?

    Stephen Hawking peered behind the curtain of reality and glimpsed the true workings of the universe. His profound contributions across physics from quantum theory to cosmology constantly inspire people even after his death.  

Time was his main thing. 

    He shared his discoveries and thoughts in a Bestseller book "A brief Story of Time" people around the world, including myself or you maybe. 

Hawking Radiation

    Do you think that black holes emit no radiation? Well, I think most of the people will probably think like this because black holes absorb everything, even the light. Also, people strongly believed that black holes should exist forever, only growing, never shrinking. 

    However, Stephen Hawking was the first person to discover that black holes can actually shrink and that black holes should not be so black after all. 

What made him think like this?

    Whenever matter enters a black hole, it is totally lost from the rest of the Universe as the black hole absorbs it. This also removes a measure of disorder - what we call entropy.

    Since this removal of matter leaves the Universe with less entropy (less disordered), it breaks the second law of thermodynamics. A physics students from Princeton Jacob Bekenstein pointed out that a even horizon (the boundary surrounding the space most affected by a black hole's insane gravity) should increase in area whenever matter falls in. 

    He showed how this area represents the measure of entropy that would otherwise be lost, a suggestion that should solve the paradox. 

    Hawking wasn't not fully convinced. Entropy is a way of describing heat energy, which necessarily emits radiation. If an event horizon has entropy, it should glow in some way, meaning black holes wouldn't be completely dark at all! 

    The physical process behind the emission of particles from near a black hole's even horizon is a bit complex, relying on a solid understanding of the mathematics of quantum field theory. But don't worry, I will help you through. 

    Imagine twin 'virtual' particles - matter and antimatter. These particles naturally emerge from the vacuum being separated by gravity. Usually they spontaneously appear and then annihilate each other, briefly borrowing energy from the vacuum itself. But when this happens near a black hole, where the gravitational force is extremely strong, the split leaves one of every pair to escape as actual radiation.  One of the pair will be swallowed by the event horizon, leaving the other free to escape and taking its stolen energy with it. That energy can't come from nothing. And so the black hole itself pays the debt by slowly leaking away its mass (shrinking!).  

(Hawking's own popular explanation of the mathematics describes fleeting virtual particles affected by extreme gravity, with one half of the pair removing mass from the black hole thanks to extreme gravity providing the particle with negative energy) 

 

    While we'd need a complete theory of gravity's role in quantum mechanics to map this interaction properly, Hawking's conclusions show how curved space can upset the mix of quantum properties in the fields near an even horizon, to the point that black holes 'scatter' some features while leaving others intact. It's these intact properties that resemble specific temperatures of radiation, and cause a black hole to shrink. 

    He concluded: The smaller black hole is, the hotter it should glow. Although it has never been directly observed, Hawking radiation is a prediction supported by combined models of general relativity and quantum mechanics. He published about this theory in a paper titled <Black hole explosion?>. 

A video that will help you to understand better! 

Time Travel

Stephen Hawking, at the party for time travellers that he hosted. 

Hawking has also explored one of the world's favourite specific questions, whether time travel is possible. I want to introduce to you one interesting episode of this exploration to "time travel."

According to the theory of relativity, time travel to the future is definitely possible. 

How?

By time dilation! 

There are two ways:

a) If an object moves at a speed close to the speed of light, its time will flow slowly. 

b) Also, do you remember that one hour on Miller's planet was the same as 7 years on Earth? Like this, according to the theory of relativity, time passes relatively slowly in a space with strong gravity. 

Time travel to the future like this is theoretically possible in reality. All we have to do it run at a very fast speed or go to a place with strong gravity. 

What about time travel to the past? 

Many scientists are researching whether time travel to the past is possible. T-flow cylinders, black holes, wormholes, space strings etc. are suggested as methods. Stephen Hawking's answer was 

"No, it is impossible" 

Hawking has prepared an interesting experiment to prove that time travel to the past is impossible. He held a party and even made an invitation to time travellers. Click the image to read the invitation that he sent! 

Since the University of Cambridge may not exist in the future, the latitude and longitude were clearly indicated as well as the exact date and time. The space-time coordinates were written very clearly. Stephen Hawking prepared cold drinks and delicious food with the Discovery Channel and waited for the time traveller. The whole process was recorded by the Discovery Channel. (Here is the link for the videos! https://www.discovery.com/shows/into-the-universe-with-stephen-hawking/episodes/time-travel) 

June 28, 2009, at 12 PM, at the University of Cambridge, no one came to the party for time travellers hosted by Dr. Stephen Hawking. Now, how on earth did this happen? They say that no one, not even time travellers, but ordinary people, came. 

The truth is this. 

Stephen Hawking did not release the invitations until the day. (Wait, if they were not made public, then of course no one can come!!) It's a bit confusing, but this was all his plan. 

The reason why he revealed the invitations that had the date, location, and time of the party, after the party was to prove that time travel to the past is impossible. If time travel to the very distant past becomes possible in the future, the time travellers who have checked the invitations would have come. However, the fact that no one came to the party proves that time travel to the past is impossible even in the far future. 

Stephen Hawking explained that time travel to the past is impossible with 'Chronology protection conjecture.' 

This video will help your understanding. 

Singularities 

A singularity is a place where the curvature of spacetime becomes infinite. However unlike other physical theories the notion of singularity in General Relativity is rather subtle. For electromagnetism for example one can talk about points in spacetime where the electric field diverges. It is not so easy to talk about points in spacetime where the curvature diverges, because in General Relativity spacetime itself is given by solutions of Einstein's equations, which by definition are not defined where the curvature is infinite. Instead, singularities are characterised by points which are missing from the spacetime. These missing points can be detected by finding paths of particles/photons which terminate because they run into singularity.

 

A key ingredient of the singularity theorems is that of a closed trapped surface. This is a surface where the gravitational field is so strong that outgoing photons are dragged inwards. 

Researching about his accomplishments in depth, I couldn't stop myself from being surprised by all his creative and innovative thinking. And what I learned from him as a person is to be 'curious.; He did not simply accept the things that he was taught. His works reminded by favourite Einstein's quote

"Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning." - Albert Einstein  

As a person who loves sci-fi movies, I really appreciate his achievements that contributed to our understanding of cosmology that inspired a lot of movie producers and watchers. In the summer, I am planning to visit the University of Cambridge. When I get there, I will visit Hawking Building and other places that he words at. I will try to share my experiences in the summer !

I hope today's post has enhanced your interest to the world of physics. I will come back with a new sci-fi movie next week (in 2024, next year!!!) Until then, I hope you have the warmest winter and the happiest end of the year :) ☃️❄️🧣🧤