Quantum world: Small scales, big questions - 2

This is the deepest part of the universe. It is dark and cold and strange and unknown. Do you have what it takes to dive in? I mean did you read about the universe and gravity and the previous post? Well then, get ready to be blowned to strings :)

I am not joking about this post being the deepest. In the previous posts i have explained the big picture, the universe. Then i have mentioned the gravity as the mind boggling force. This brought the studies of small scales, quantum physics, because we needed explanations. Now we will end up with String theory as the smallest particles in the universe to explain the universe. But before jumping into that, i will explain couple of strange phenomena and concepts. Because scientists that i have mentioned in the previous post were studying in 20th century and coming up with ideas or solutions. But those ideas were not tested because of the lack of technology. Over the last 4 - 5 decades, more experiments yielded more discoveries.

There are particle models

A particle used to be called an atom back in the beginning of the 20th century. Then physicists came up with mathematical models for atoms and discovered atoms are consisted of a positive charged subatomic particles called protons. But they need a glue to hold it together, which is neutron. Furthermore electromagnetism proved that atoms have electrons around them. This is the elementary school atom but after this point, it got a whole lot complicated. Here is what it looks like today.

Protons and neutrons are consisted of quarks with different properties and the universe is producing leptons in stars or supernovas. But you can't just hypothetically propose or predict subatomic particles. You need a solid base and provable ideas. Therefore, without the technology to detect them, all you can do is to come up with equations that can predict or mandate new particles. This is why scientists have been working on mathematical models to summarize the whole variety of particles in the known universe. Those mathematical models are based on quantum mechanics ideas. That resulted in the Standard Model above. I will explain the overall idea of this model through the next subtitles according to the video below.

Quantum Field Theory

Back in 1900s, the subatomic particles were discovered with the developments in electromagnetic studies (i have made this term up). But there were no evidence that can directly support these particles. There were no experiment (particle collider) to prove them right. But people like Paul Dirac noticed that Newtonian gravity and subatomic particles can't get together and started tinkering with the math. And Erwin Schrödinger literally set the basis for the standard model, without even knowing. His equation that describes probabilistic behaviour of the particles gave rise to Quantum Field Theory. This basically tells you that there are quantum fields and they oscillate to produce particles. Here is how it is originated.

There is a term called Gauge invariance. It assures that the measurement is not effected by the relative point of view. For example, you drop a ball and it will hit the ground zero. That ground can be the floor of your apartment or the center of the earth. It still obeys the same kinetic motion and energy laws. This is the starting point. If you take a deeper look at the Schrödinger equation, the momentum is not invariant and is effected by the local phase shifts of the probabilities. In simpler terms: If you somehow interfere with the momentum of the quantum particle, the equation breaks down. This is a crisis. The non-relativistic equation for a single particle is like the image below.

So they modify it with a new term (vector potential that re-establishes the balance) and that term gives rise to electromagnetic field. This was of course a surprise and it also proves there are more fields than we think. But in order to fully function, that equation must be upgraded with Dirac equations. This makes it compatible with special relativiy.

Now it is proven that there are new fields, electromagnetic field being one of them, with quantum electrodynamics, it is time to investigate new invariances or symmetries in the Schrödinger equation. In simpler terms: You must be able to change other properties of the particles and Schrödinger equation must still survive it. If you incorporate this logic, you get new symmetries that predict weak and strong nuclear force and the bosons.

So if i go back to the standard model, those particles are categorized by their interaction, spin, mass and charge. For example, leptons don't make strong interaction. The particles have a property called spin and it is basically alignment with momentum. Bosons are the particles that gives some sort of property to the particle (now this was a weird sentence) so that you can realise them. Basically gauge utilities. We can talk about them because they are all proven by experiments. The biggest of them is the Large Hadron Collider in Cern. It discovered even more.

Cern

When your children are smashing their toys and braking them apart they are conducting a tiny version of the particle colliding experiment. They get new parts of the toys by breaking them. Now if you have naughty and hardworking scientists, you get a collider almost as big as a small town that collides particles at like 99.999% of the speed of light. If you smash particles together, you get subatomic weird particles. The result is a mess if your children do it, but a revolution if scientists do it :) Here is what it looks like.

The most recent and maybe the biggest discovery in Cern is made in LHC (Large Hadron Collider), which was completed in 2008. Although there has been other discoveries in the other small particle accelerators in Cern, Higgs boson is fundamentally changing the structure of the standard model. They found out that mass is a consequence of particles interaction with higgs field. This was proposed by Peter Higgs in 1964. Higgs field is what gives mass, well mass. That mass then bends the spacetime and it is formulated by Einstein as general relativity equations. Also, the mass of the higgs boson will give us a clue whether there is a super symmetry in this universe (at particles level) or it is mostly random. The hunt is still on but there are technical challanges because you can only smash particles so hard. Anyways, these two worlds (quantum fields and relativity) can't come together without hurting each other.

That is why there is an imaginary particle called graviton since 1930s. They propose that this particle is responsible for gravity. Quantum fields can't define a spacetime fabric that can be bent and quantized. Remember quantization is important. So some sort of particle or field that sets the gravity in action is needed. Scientists think that if you smash particles hard enough, this graviton may just travel to a different universe :)

All these observations are made mostly in particle accelerators like Fermilab, Stanford Linear Accelerator Center or Cern. They have also discovered that there are antiparticles. Which is the same mass but the opposite charge of the subatomic particle. First positron (anti electron) discovered by Dirac in a magnetic field. Then particle accelerators produced others through a century. Particle and anti particle annihilate each other when they merge as you know from sci-fi movies.

Then these particles start showing weird properties. They are interacting with fields and transforming by giving off particles. Remember Feynman diagrams are defining these transformations. They also can be massless like photons. They can travel right through the earth like it isn't even there, like neutrinos. But the strangest behaviour of all must be entanglement.

Entanglement

I know it is all entangled in your mind now. But don't worry. You have witnessed how the particle science work and i won't go into much detail for the next part. I will mostly talk about the weirdnesses. Entanglement is the state that describes two particles' properties are bound to each other. Like in magical spells where you stick a needle to some toy and the some person gets hurt :D In quantum mechanics, it is the observation that causes one of the particles wave function to collapse. And it immediately causes the other particle to collapse too. This is instantaneous, in other words, way faster then the speed of light. Something like this:

Einstein called it "spooky action at a distance" because this instantaneous travel of information violates the speed limit of the spacetime. When one particle is observed, its properties (spin) will be exposed. Then the other entangled particle is immediately effected like it is observed too. This effect is real but it is hard to inject it into known quantum mechanics equations. Scientists also proposed experiments to prove this behaviour and Veritasium explains quantum entanglement in this video. He basically explains the probabilistic results of measurements that proves some spookiness is going on.

The weirdness does not stop there. These entangled particles are seemingly re-writing the past. If you copy these particles and observe them seperately, they make it look like they have traveled back in time and changed their state. The video below explains this and there is actually a quite simple explanation. No matter where and when do you make an observation, it is still an observation and causes the other entangled particles wave function to collapse.

Quantum leap

I know it is enough for this post but quantum leap is important. When an electron jumps among orbits, that jump is a quantum jumps and scientists are wondering if it is intantaneous or if it takes time. If instantaneous, copenhagen interpretation is right. If not, the determinitstic universe might be right. The video from PBS spacetime explains this phenomena and there is no direct conclusion, since the particle is always somewhat observed. I think this is important because it looks like the more you dig into the universe, the more backfire you get. The so called certain events or states are turning out to be deceptive. Here is the video that explains the quantum jump.

String theory again

Yes this all goes down to string theory. Scientists tried to bring general relativity and quantum mechanics together but mostly failed. String theory deserves a whole blog post to itself but it would also be futile to talk about an unproven group hypothesis. I have briefly mentioned it in earlier posts. Now you understand why scientists needed a theory of everything. String theory says that all these weird particles, fields and behaviours are results of strings vibrating in a certain frequency. Like violin string vibrating and making different sounds. This theory is really really hard to test, maybe even impossible.

But it doesn't stop scientists. First string theory is proposed around 1960s and got re-ignited with the inflation theory. It has explanations for the big bang, black holes, dark matter and energy and etc. But most importantly, gravity. It has different versions. Some of them have different dimensions or parallel universes or infinite universes. There are version with 10 dimension or 11 dimension (called M theory). Also one person worth mentioning is Edward Witten. He helped the scientists by simplifying the dimensions, which is a big deal when you think about it. More dimensions mean exponentially more complexity.

There are different string theory interperetations because of their approach to the problem. There are questions like, which interpretation (copenhagen or deterministic) do you accept, do you accept parallel realities, do you have a particle for gravity or something else and etc. You have strings in your pocket. How are you going to use them and why? These 2 question can create tons of different alternative string theories.

If you ask me

I don't have the solutions to these mysteries but i do have my own idea (not mathematical, purely theoretical) of the workings of the reality. I need some time to think :) And in order to understand or make sense of my view, you have to have some background of the struggle. This was a 4 part series, a journey from the biggest to smallest. I hope i have enlightened you. See you at the next post :)