# Symmetry for dummies!

Hi,
as I said, I will continue with the explanation of what I mentioned in some earlier posts. Today I will try my best to learn you what physicists mean when they say something about “symmetry”.

First of all, when you say symmetry you probably mean that it is the same on both sides.

On the next picture you have some shapes with the right and left “lines of symmetry”.
This means that you can flip them around this line and they will be exactly the same pictures.

Square has more than one line of symmetry, there are four of them [1].

This is what we think as symmetry but physicists use it in more kind of complicated way.

When somebody makes experiment with coca-cola and candy [2] it will explode. And it will explode in New York, Prague, under water, upside down if you do it properly and even in space. This is symmetry, it does not matter where you do the experiment. But it does matter what you do it with, if you would have used water instead of coca-cola, or chocolate bar you would see that there is no symmetry [2.5]! Because it is not going to work!

When we talk about particles we can say that there is a symmetry in them, for example you can have 3 quarks, labeled as Paul, Rick and Nick. It does not matter which one you will use, because all of them have the same properties! This is symmetry all quarks are same, all electrons are same and so on.

There is a symmetry in fundamental forces. For example in strong nuclear force there is symmetry in quarks and their colors [3]. It does not matter how you label one of three quarks, it can be red, green or blue.

Also charged particles are created in pairs. This means that you have to conserve the charge so if you create electron you must create positron or something else with positive charge.

Only weak nuclear interaction of all fundamental forces has special kind of symmetry. Weak force is the only force which makes difference between particles which are right and left handed.

Such a particles  are in pairs:

• quark u ←→ quark d
• quark c ←→ quark s
• quark t ←→ quark b
• electron ←→ electron neutrino
• mion ←→ mion neutrino
• tauon ←→ tauon neutrino

This is also called the breaking of parity.

So weak interaction breaks symmetry and behaves differently with right and left handed particles while other forces do not do this, take for example gravity, everything is attracted by it and it does not matter if it is quark u or quark d.

Of course those particles are diametrically different their mass varies a lot, but this is only because of what is called: Higgs field, and I am going to talk about it another time.

Dragallur

[1] Star has 5 lines of symmetry, triangle has 3 and arrow only 1.
[2] I do not know if it is in English mentos.
[2.5] This is also called “broken symmetry” if it would not be broken, in this analogy anything would work as the mentos candy and there would be no difference between coca-cola and oil.
[3] Quarks have colors as I mentioned in last post and also in post about strong nuclear force.
[4] Maybe you remember from chemistry how you were filling the orbitals with pairs of electrons: ↑↓. Those arrows mean that one electron has negative and second positive spin (but still the same value: 1/2  .. -1/2)

# The Standard Model for dummies!

Hi,
last time I talked about some stuff like dark matter (1 & 2), dark energy and I did not explain a lot of things which I mentioned and this time I will talk about Standard Model.

Standard model or Standard model of particles and interaction is the model of all observed and proved particles.

The next picture shows how it looks like, you could say that it is the “modern” periodic table or some kind of holy grail of physics.

So in this standard model you have particles that make up everything we know [1].

There are four main groups which are sorted by the forces they interact with.

All of those particles interact with gravity. Quarks also interact through strong nuclear force while leptons do not interact that way, also all of them have whole numbers for charge.

The red part has inside particles which are what is called “force carriers” they carry the fundamental forces with graviton excluded because he is not proven yet.

The most mysterious is the yellow part with only Higgs boson inside, I will make sure to make a whole chapter only about it.

### Quarks

Already months and months ago I made post about quarks. Here I will cut it short so, quarks are particles that made everything there is except just a little part which is made from electrons. Quarks normally group together into hadrons – protons, neutrons, pions. Quarks have charge of either +2/3 or -1/3. They also have a property called color which is not color at all and they must group together so their colors cancel into white (white) [2].

### Leptons

There are three main particles called: electrons, muons and tauons. Only electrons are actually somewhere while we can create other in the particle accelerator.

All of those have -1 charge but there are other particles called neutrinos. Electrons, muons and tauons all have their neutrino.

I already wrote about neutrinos but they are actually extremely light particles sometimes called “ghost” particles because they can easily go through whole planet Earth without touching anything. They are also electrically neutral.

### Force carriers

Gluons are particles that are mass less and they carry the strong nuclear force.
Photons are also mass less and they carry electromagnetism.
Gauge bosons (W+- and Z) carry weak nuclear force.

Most of those particles have mass and that is because of Higgs boson, but that is whole new story which I will have to start with symmetries and fields, stay tuned.

Also main difference between force carriers and everything else is that they do not need any space to exist, there can be millions of them at one spot while only one lepton or quark.

Dragallur

[1] I do not talk about dark matter which I mentioned in earlier posts. WIMPs are not here since they do not belong into standard model, those are particles beyond the model even if they exist.

[2] Quarks have 3 basic colors: Red, Green and Blue but there are of course anti quarks which have just opposite colors: Antired, Antigreen and antiblue.

# How it started, featuring Big Bang!

Hi,
when you read the title of this post it is pretty clear that I am going to write about Big Bang, I already wrote about the ends of the Universe but it feels as lot of people are interested in the beginning and there are some misconceptions.
For example even the title is little bit wrong since you could assume from it that Big Bang was the start of everything..

So I will try to explain Big Bang and what happened right after and I want to start with first big misconception.
People think that Big Bang was explosion, nope it was not. It is thought that Universe expanded into space but actually Universe is already everything and it kind of expands into itself, if it makes sense.

On the picture above you can see the example of expansion where space expanded not the things inside but the fabric itself. The space in the grid increased while nothing happened to the objects except that they are further apart. This is what is happening all the time and even if the Universe was infinite it could get bigger, kind of, because everything is going away from the rest of the stuff and NOTHING can be the center of the Universe. There was no explosion.
For the rest of the post I will follow the picture on the left.

On the bottom of the picture is the start of the big bang. This is outside of the graph because we are not able to investigate it using the laws we know now. This is until Planck time passed (10^-43 seconds). After Planck epoch which is big unknown, the time of grand unification came. This is time with extremely high energies involved and it is assumed that 3 fundamental forces are working as one at this time: electromagnetism, weak and strong nuclear force. This is extremely important but we are not able to reach such energies even in particle accelerators while it could help us a lot with Theory of Everything.

Few really really short moment later strong force separated and started to work alone. This took some really long time before all the forces separated to the state we know today. This is one picosecond after big bang. Then quarks became grouping together into hadrons. Those are particles with zero “color” charge like neutron or proton.
Some time later finally deuterium is created and through big bang nucleosynthesis some heavier elements like lithium, beryllium and helium too.

Then it takes really a long time before everything calms down so that first stars and then galaxies form.