What is the color of Universe?

today I want to write about the average color of the Universe.

The average color of the Universe is not black. I mean, when you look at the sky in night it seems that there is black everywhere, but that is actually no color. When we speak about color we say that something is red, that means that it reflects red light.

Right, light, but when there is nothing shining it does not have any color because it can not reflect anything.

The average color of the Universe was found in 2002, year before the same team discovered the color which you can see below but it was corrected several months later because there was mistake in the software.

So how do you find such a color? Well you take the color we see of various galaxies and stars and so on and make the average of all the photons wavelengths creating the color which you can see below:

This color gets redder over time as there are more red stars in the Universe. In RGB this color is: 255,248,231.

Meet the color of the Universe, Cosmic Latte.


Those two color were taken from here.

PS: Next week there wont be practicly any posts since I will be away learning some math.


Optics: 5) Magnifier and microscope

today I will finally continue to write about optics. Last time I was talking about dioptre and today I will explain how magnifier and microscope works.

Angle of view

Angle of view plays important part in magnifier, microscope and so on. The problem why we can not see individual cells in leaf with naked eye is that we are not able to distinquish things that are too close to each other. Human eye is able to distinquish things that are about 1′ (arc minute=1/60° degrees) apart.

You can easily try it when you draw something on paper and then walk away from it. Or you are not able to tell trees apart when you are hundreds meters away from them.

(On the picture you can see the angle of view for camera, it can be measure horizontaly, verticaly or diagonally).

To make this angle bigger so we can distinquish everything we can walk towards stuff. But when we have a leaf we can get only limitely close to its surface and our eye can not adjust to something so close. Look at your thumb when you put it three centimeters from your nose. It will be blurry even if you try your best, this is because your eye does not have enough dioptre to make the image clear, plus your eye is going to hurt because of the muscles in eye stretching to make the optical power of your eye bigger. Conventional visual distance is distance for which human eye has to release least effort, this is about 25 centimeters.

To know the distance two objects must be apart to distinquish them we can use tangens:

tg τ=y/d

τ is the angle of view which is for human 1′.
y is the distance of two objects which you are trying to distinquish.
d is the distance from you to the objects.

y=d * tg τ

So the limit of our eye is that it is not able to be powerful enough so we need something which will help us and it has to work the same way as our eye, magnifier!

The light rays are going too much away from each other and your eye is not able to change their direction to create picture.


There is thing called angular magnification.

γ=τ’/τ = tg τ’/tg τ =  y/f/y/d = d/f

γ is the angular magnification and is the distance to focal point.

Angular magnification says to us how much our magnifier is strong. The formula above works for objects that are right in focal point, otherwise there would be “a” which is the distance to the object. If the object is right in focal point our eye does not need anything to do and as it gets closer the light rays are more and more going apart so that at one point you will need better magnifier and then it just wont be enough so you will have to use microscope.


There are two lenses in microscope. The first one is close to the object and it has the largest dioptre possible, making its focal point small as possible. It is called objective lens.

The second one is not so strong and its role is to make finally adjustment of light rays so they create image in your eye.

Optics 5, Pic 1

The picture above which I drew is horrible wrong but I can describe what is going on there. On the right you have the small object (brown). There is light coming from it in all various angle but important is that the lens has enough dioptres to use them all. F’ is the focal point of second lens, this point should be at the distance where all the rays from first lens converge into one point but I was not able to draw it properly. This is the way microscope is designed. Those rays start to go apart again but soon they hit the second lens, converging again and entering the eye in proper angles so that they hit all the spots on red line creating much bigger image.

Microscope is not unlimited source of magnification since when you will try to make bigger something too small you will get into problem with the wavelength of light.


Book review 1) The Particle at the End of the Universe

I saw already lot of people to do book review, like Joseph from Rationalising the Universe or Abyssbrain from Mathemagical site. I have already used a lot of parts from this book in posts about dark matter, dark energy, particle accelerators and so on.

It is book: The Particle at the End of the Universe by Sean Carroll. It is about particle physics and the Higgs boson.

This book has 13 chapters and three extra three parts explaining some stuff around.
Author starts the book with short introduction to history of particle physics, what people thought that was making up everything. He mentions elements, atoms and so on, then he introduces higgs boson and his role in standard model of physics. He explains why he thinks that it is important to study it and what part LHC plays in this.

In second chapter Sean explains why Higgs is also called “god particle” and the relationship of physicists with god. There is also review of properties of Higgs and some things about fields.

In third chapter author introduces whole standard model and how higgs boson changes it. There are parts about all particles and all four interactions.

Fourth chapter is about the story of accelerators and how they work. This continues to next chapter where there is description of all the work that had to be done to build LHC with credit to all people. Author describes how are particles detected and how they decay.

Whole chapter is just about fields and gravitational waves continuing about symmetries and how they are broken. This is also probably the most complex part of the book which I had to read more times to really get to know what is it all about.

He continues with deep look into finding of Higgs boson with stories about all the people around, and the excitement about it.

There are stories about destroying the world with LHC creating black holes and author perfectly talks about the way news are used in magazines and how physicists were trying their best to not let spread a wrong news about Higgs.

In 11th chapter Sean is talking about Nobel awards for particle physics that led towards Higgs.

The book ends with text about the new things that are now opened for scientists to discover when they know that the particle really exists.

In three extra parts author adds some more context to spin, standard model and Feynman diagrams.


This book is really well written and I give it 10/10. I really recommend it to anybody who wants some introduction to particle physics because with all those analogies you will never be lost. I like how Sean also describes all those people around the great work and how all of this makes the whole picture and story behind “The Particle at the End of the Universe.”


Picture of Czech book
Picture of English book

The book review of: The Organized Mind
The book review of: On the Origin of Species

Higgs boson for dummies!

finally here it comes, here it goes, post about Higgs boson is coming. Lets look what the “god’s particle” is how physicists found it and what it means.


God’s particle

Lets see how Higgs boson was named the god’s particle.

One of the best particle physicists Leon Lederman who found out that there are more types of neutrinos and so on and on. He wrote a book named the “God’s particle”. The book was partially named like this because the publisher did not want it to be named “Damned particle”.

He did this and now all physicists can agree on one thing, they hate this phrase because Higgs boson has nothing to do with God.

While all journalists can agree that “God’s particle” is amazing phrase.

So if you want some physicist to be angry on you, just mention the God particle and he will never forget.

Higgs boson was found 4.7.2012 in Large Hadron Collider.

Higgs field

What is actually more important than Higgs boson, the particle, is the field from which it came, this is the Higgs field. I already talked in last post about fields and how specific vibrations can form particles. Higgs field can do this too and it makes the higgs boson which decay almost immediately and is really hard to detect.

Higgs field is a very different from other fields because other fields can get to 0 energy while Higgs field can not. What is more accurate to say is that non zero value of Higgs field is less energetic than zero so Higgs field does not want to fall on the value of 0.

What does it do?

Well you may have heard about Higgs field giving mass to matter. This is partially true since when particle interacts with Higgs field they are kind of slowed so they do not travel at the speed of light. Some particles interact more than others like some people interact with group of people more than others because they are well known [1].

At one post I wrote about symmetries, check it out if you did not already. There is symmetry in particles. They are all the same.
What? Now this symmetry is broken, this means that there are differences between particles, thanks Higgs field! This is the most important effect of the field with the effect that while it would not change much the mass of protons and neutrons, it would change the mass of electron rapidly if it would not exist. Now the space occupied by particles as electrons is set and such a light particles need to have a lot of space around them. If you would turn off Higgs field completely, things would probably gone exploding a lot since the size of atom would increase as the space around electron needed would get bigger.


[1] This does not mean that all the mass is from Higgs field, most mass of neutron and proton is made up of energy m=E/c^2.





Solar sails

have you ever wanted to be space pirate? To just fly through Universe close to speed of light and sometimes stop on some planet to steel some stuff? Well now, your space craft can even look like a ship, with huge sail!

Solar sails are sails like any ordinary sails. They even use wind, wind made of photons!

On the picture above, you can see IKAROS spaceprobe, the first succesful probe to use solar sails.

Those solar sails are powered by nothing more than the electromagnetic radiation coming from the Sun. It then pushes the probe because of photon’s momentum[1].

But photon has no momentum!

Yes according to Newton’s mechanics it should not have a momentum because it has no mass.


p is momentum, m is mass and v is velocity (speed).
If you would use this you would get that photon does not move and it does not have momentum but if you use theory of relativity as I already showed in the post about conservation laws you will get some real value, using what is called “relativistic mass” which is not zero for photon.

The IKAROS’s sail was 20 meters on diagonal and most of it was 7.5 µm thick so it was very light.

Whole probe had 315 kg while the sails had only 2 kg. This is about average mass for probes since New Horizons had about 450 kg while Jason-3 about 250 kg.

The pressure of the solar wind from Sun was 1.12 milli newton and it was able to gain velocity of even 400 m/s or 1440 km/h.

This method is not much useful for fast speedup and also for deep space travel since the radiation decreases with squared distance, but still you can be a local pirate.



[1] The photon’s momentum is transfered to the solar sail and because of conservation of momentum the sail must be pushed a little bit while the photon bounces away, this is the same effect as with a shooting rifle. When you shoot the bullet goes forward while the rifle backwards with the same momentum.

2nd picture
1st picture


Space NEWS #8 (Planet Nine and Flower on ISS)

why space news again? Well new planet has been found, if you know something about astronomy this would not really excite you since new planets are found “all the time”. Well what if I say to you that Solar System has new planet? The planet Nine?

Also on ISS first flower was able to bloom!

When I saw the message about planet Nine I was very excited, but most media made again a mistake to say that it was found, that is not right it was not found yet. There is a strong evidence that such a planet could exist in our Solar System (if this planet is really approved to have been found, I promise to make another post about for “Planets of our Solar System”).

This planet would have mass to about 10 times the mass of Earth making it about the same size as Uran and Neptune, which means that it would be ice giant.

Above you can see the artist’s impression of such a planet. The evidence for it is in the movemenent of TNOs (trans neptunian objects). Those are things like Sedna which you can see below.

Those objects as well as planet Nine have highly excentic orbit. It is clear that we can detect them only when they are close to Sun which means that there are surely more of them. The problem is with their orbit lined up in plane which is very improbably without planet Nine. It’s magnitude is very low, to about +20 or so making it really hard to see even if we were able to find it’s exact spot on the sky. It could orbit in distance ranging from 200 AU in afelion and 1000 AU in perihelion. Caltech is the institution that published about it 20.1.2016.

This week also for the first time flower called zinnia (it is on the picture) finally bloomed. Why this plant? Because it has longer growth of about 60 to 80 days which is more then plants which were planted before.

This flower is a big step forward to grow tomatoes.. tomatoes for food!

That is why it is so important, we need to be able to make a food in microgravity to sustain when traveling through deep space.



Gravitational waves

before I start to write about gravitational waves, let me explain how electromagnetic waves work.

Electromagnetic waves are just light which we see from candle for example. The thing is that in such a candle atoms oscillate and in the process of burning electrons are jumping on more energetic levels, orbitals. When this happens they want to go back right away, so they emit photon and fall back on the lower orbital. Such a photon then travels towards you and you can sense it with your eye.

But all of those atoms oscillate because there is huge temperature in the candle (800°C). They move back and forth creating waves of photons because some photons are closer together as the atom moves to the maximum of oscillation. As it goes back the photons are more stretched apart creating the gap in the wave. This is called electromagnetic wave.

If you had really good eye and somebody would walk away from you with candle, the light would not stop but you would observe the light come towards you in wave, in quantum. The frequency would get smaller and smaller but it would never disappear and would always appear with the same luminosity.

Now when you have gravity this can happen too in what is called gravitational wave. Such a wave is a result of shaking with something that interacts with gravity. The problem here is that gravity is such a weak force that you just can not observe it on candle and you need some kind of star.

Here comes two neutron stars which were found to be rotating rapidly around each other. As they rotate they create the ripples in space time, gravitational waves. In 1993 the Nobel prize was awarded to two guys who were able to indirectly observe how this system of two neutron stars was losing energy emitting those waves, they were observed to be slowly getting closer and closer to each other.

Physicists are trying to observe gravitational waves directly with tremendously precise methods using lasers but it was not yet achieved.


Picture is from here.


Various fields for dummies!

fields? Well yes, this is probably the last post before I will write about Higgs boson. Today you will learn that everything is made up of fields and that particle is just a special vibration.

Take for example magnet, it is something totally special if you think about it. Not that it sticks to stuff but that you can feel how it wants to stick without actually touching anything, just through EMPTY SPACE!

Magnet has his magnetic field all around, that is why we can feel it from some distance and the strength decreases with distance increasing.

On the picture above you can see lines of force around magnet.
This is electromagnetism and now we know that there is electromagnetic field around all the stuff that have charge. We know that we can magnetize needle using electric current.

This field is not only around magnets but also around all things that have mass, this is called gravitational field and even that it does not sound very exciting to us, in Newtonian age it was very cool when Newton found out that there is similarity between apple falling on his head and Moon orbiting Earth!

What happens when you start to rapidly move with source of electromagnetic field? Well you create waves. If you do it well enough such waves will create light! This light then comes to you in quantum! If you do it more rapidly you will get gamma rays and if you do it less rapidly you will get radio waves. This is just a vibration of field.

Or when you take radioactive decay. There is neutron which somehow changes itself into proton, electron and antineutrino. This is just a change of vibration in various fields.

Now there are 4 fields if I do not count Higgs field. What physicists want to achieve is the prove that all those fields are just one field and everything is just a various vibration of it, creating the effect of gravity, electromagnetism and so on. This would be the Theory of Everything.


Elements of Periodic table: 4) Selenium

why Selenium? Well I was not sure what element to choose, I did not want to write about some precious metal since last two time I have covered gold and palladium. I used random generator and I got 34, which is proton number of Se.


Selenium is one of those elements which were find in last centuries. This usually happens because the element is not enough common for some alchemists to find it or it is always well bonded with other element (here it is sulfur) and it took some time before we were able to extract it.

Jöns Jakob Berzelius and Johan Gottlieb Gahn were chemists in Sweden and they were working close to Falun mine [1], which you can see on the next pictureThe Copper Mine in Falun, the Great Pit

Guys there wanted to know what was it what they mined so they gave sample to those two chemists. It seemed to be some kind of arsenic compound but it was smelling strange and soon they found out that it is similar to sulfur and tellurium. Tellurium was named after Earth so they named Selenium (in Greece) after Moon, this happened in 1817.


  • Universe: 3.0×10-6 %
  • Earth’s crust: 5.0×10-6 %
  • Ocean: 4.5×10-8 %
  • Human: 5.0×10-6 %

You see it is not very common, at least it does not seem to be. But if I compare it’s occurrence in Universe with other elements it is not so bad. Most metals have one or two magnitudes less occurrence, from what I found selenium is not produced in solar fusion which means that it is created from supernovas, which would explain it’s  relative rarity.

On the picture above you can see some Se in piece of sandstone from uranium mines.

Usually you will find it with sulfur so you need to extract it using methods as SX/EW [2].


Se is non metal element which can exist in several allotropes [3]. SeBlackRed.jpg

It is usually red powder as you can see above but if you melt it rapidly you will get this kind of grey form which is usually sold. Se makes big and complex structures.

There are five Se stable isotopes and the couple of others with half life ranging to thousands of years, than there is Se 82 which has half life of 10^20 years which is considered relatively stable.

It has extremely important property of photo-conductivity, its conductivity depends on the amount of light hitting its surface.

Selenium is toxic element.


Selenium dioxide has a great usage during manganese electrolysis because it decreases the energy needed to get manganese (it works as catalyst). China is largest consumer of this compound for such use. For ton of manganese there are two kilograms of Se used. There are 31,200,000 tonnes of manganese produced each year.

Glass gets often kind of yellow or green color because of iron or other things accidentally mixed into it so Se is used to color it into red, this is the most common usage.

Also since lead is so toxic Se is used in brass with bismuth. At low concentrations it also improves machinability of lead, which is similar usage as of vanadium which improves the strength of steel.

Because of its photo voltaic property, it is used in photo voltaic cells called CIGS (copper indium gallium selenide solar cell).

There are other trace uses like radiography.

On the pie graph you can see the production of Se. While I did not find the graph of biggest consumers of Se, on the top is clearly China, as always.

Selenium in organisms

Organisms need selenium as we found out. It is important in some cellular processes but only really small amount like tens of micro grams.

At one time people thought that it is going to be good if they get more Se through some pills. Soon it was found out that more than 200 micro grams can cause cancer and so on. More accurately in one test, doctors got their patients 17% higher chance of prostate cancer which is number two of cancers killing male humans.

There are some illnesses with the lack of selenium but they are not very common even in places where is small amount of Se in the soil like New Zealand.

The price for Se is about 60$ for pound while at some times it lowered to about 30$.


[1] Falun mine was extremely important mine producing 2/3 of Europe’s needs of copper. It was working for almost 1,000 years and it is now cultural heritage with museum.

[2] SX/EW (Solvent extraction and electrowinning) is method used to get some metals like nickel, cobalt, zinc and uranium.

[3] Allotrope of carbon is for example graphite and diamond, both made up of only carbon but with different shape of molecules.

Symmetry for dummies!

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.



[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)