# How slow can slow motion get?

Hi,
ever been wondering how slow can slow motion get? If you hang for a longer time on YouTube eventually you might notice the channel The Slow Mo Guys or Smarter Every Day, both of them feature „quite often“ slow motion videos, meaning videos that have many frames per second (FPS). If you then slow the frames down you will get very slow video showing detail of whatever you are filming, whether it is flame tornado or AK-47 under water.

The slowest I ever watched is this one: https://www.youtube.com/watch?v=xbuvcQrAOSk

It has FPS of 343 915. That is a lot and in the video they are cracking glass container with high temperature difference. The video is so dark because in the short amount of time, not much light can get into the camera and that is often the limit for such high speed filming. You can also see that even though the video is so slow, the crack still propagates through the glass in surprising speed.

But this is not the limit, you can go much slower but it requires whole different technique. With 1 trillion FPS you can actually see light traveling through medium, it looks pretty impressive but how can it be done?

The scientists use a laser to lighten up what they want to take photo of. They take a 1 dimensional pictures, basically line of pixels[1], couple hundred times and then with a smart mirror they move along the object that they photograph. This technique is called femto-photography and the event on stage has to be performed many times before one gets the picture.

To put it in different words, you take a titanium-sapphire laser. Lighten up the object for a short time. Capture the photons that bounce back to you. Repeat over and over again and with some mathematical reconstruction techniques you got your result:

Interestingly enough this kind of device is able to see around corners and has very high potential for use in many technical fields if we are able to make it work faster and in smaller devices.

Post based on TED talk.

Dragallur

[1]It is not really line of pixels as you can read in the next paragraph. You are getting back couple of photons and through the mathematical analysing you get the picture.

# How do bearings lower friction?

Hi,
The first time I really encountered object with bearings and was wondering about what they really are was about 3 years back when I was on inline skates with a classmate. There was a nice long and smooth downhill and we both drove down without much beforehand added speed. Soon he was going way faster and was still moving many seconds after me. At that point when we started to talk about it, I thought than my inline skates do not have any ball bearings, which I now think is not true, he only had clean ones since his skates were new. Probably without bearings the skates would not work.

Ball bearing. See how they do not slide, they rotate.

Ball bearings are small balls (often from metal) enclosed between two spaces that are supposed to rotate, for example on some axis. It is possible to just leave the two surfaces touching but then they just rub against each other which causes high friction. The important part is that the balls as you can see on the left, rotate, they do not slide and when circular object is only rotating instead of sliding it does not experience much of a resistance. Try it yourself. Take a pencil and toss it across table so that it does not start to turn (parallel with the direction of the movement). Remember the distance where it got and try the same thing but this time perpendicularly and see how far it gets, that is exactly what the bearings are doing.

There are lot of types made for different purposes. Since the bearings have much lower area with which they are touching they do not distribute pressure so well, also they might need cleaning often or lubrication. In fidget spinners you will of course find bearings. The ones that spin very long time are the ones with ceramic bearings.

Dragallur

# Knowing the future, brain twist?

Hi,
two weeks back I wrote about the movie Arrival. I did not really get into the problems that arise when somebody knows the future, I will try to settle this today.

Alright, lets say that you just acquired the ability to know what will happen in the future. Cool huh?

First problem, do you have free will (meaning if you can choose to do something or there is no way to actually choose anything)? Lets start with the answer: yes, you have free will. Basically two things can happen, if you truly know what will happen then you can not choose any other option which means that by knowing the future you and everybody else will lose free will if you could choose something else than what the ability tells you then it would not be telling the future. Something else could happen though, you could know all the possibilities that arise from your decisions and the decisions of others. Funny would be if you would see it for the decisions of others, then the ability would be useless for longterm predictions where people all across the globe would interconnect with their decisions (do animals have free will, which ones do and which ones do not?). You could for example see that in 40 years there are couple (a lot) of lines that go to Third World War but there would be so many people involved in changing couple of important people that you could hardly do anything with it. At the same time if your brain would be organized in the mess you would immediately know what option you need to take to optimize whatever you want to optimize. Much easier would be if everybody else lost their free will and you alone had it.

The real fun begins if you consider no free will aka determinism. You know exactly what will happen but you can not change it. Imagine standing on cross roads, you know you will turn to left, its the future and you can not decide otherwise but there does not seem to be anything that would actually prevent you from turning right. If you do it, it means that the ability was telling you exactly that from the beginning but then you would turn left…

Lets consider thought experiment:

There is a robot that has very strict type of thinking. It is standing in a hall way that splits into two corridors, left and right (it is driving towards the left). Nothing miraculous can happen there, nothing that would prevent the robot to go where it is programmed to go.

You are at the headquarters and know where the robot will turn or simply what will happen there. You tell this information to the robot and the robot will turn exactly the other way. For example you know that he will turn left. You send him the information and he according to his program turns right which means that your ability is not working and this simply can not happen, you can not tell him the direction because he would do the opposite. What will you tell him? What is the future?

There is one more line of code in the robot: if you get the information “you did not decide”, you will turn left. This is to make it harder, the future would switching between left and right indefinitely, meaning the robot would not do anything and we do not want it. The only solution that I came up with is that he will actually not decide, you will send him the information: “You will start going left but when you will get this information you will turn right. After hearing this you will turn left but when you hear this information you will turn right again…” it will continue and then it depends how the robot is made. If it waits until the stream of information halts then it wont ever decide and you will speak to him forever. If it will take the information and while it processes the next part it will start to act accordingly to it (meaning the opposite way), the robot will slowly move towards left or right. At some point it will be on the threshold which raises a problem of course and I guess there is nothing stable to tell him without destroying the ability that you gained, you know what he will do but you can not tell him.

The last part would be the same scenario as if the robot could teleport from the beginning but if you have to say the information then it will result in a paradox. In normal non-robot life you would probably run into more complicated scenarios where knowing the future would not alternate you decision which is the whole problem we are dealing with. But if you would not and your ability would HAVE TO work then… ???

Dragallur

# Pareidolia

Hi,
today I will write about pareidolia a commonly seen phenomena. People often see familiar objects in completely random things, like rocks.

Clearly there is face in the upper middle part of the picture on the left. There is definitely sign of both eyes, of nose and mouth, thats more than one needs to recognise face in something, consider the following one on the right. Do you see the black thick circle filled with yellow color, two ellipses and curved line extended in the ends? Yeah me too.

The point is that humans are great in recognizing (most often faces) in things that are actually not them. The first picture is photo of region Cydonia which is a area on Mars. It was taken in 1976 by Viking 1 and of course people thought that it was proof for extraterrestrial life! Well if you take enough photos of Mars there is high probability that some of the rocks there will resemble primitive faces.

“I am the evidence of life on Earth, beware!”

Pareidolia does not happen only in images but also in sounds. For example there is a group of people who listen to so-called “ghost boxes” (sub category of ghost hunters). Ghost box is a box that is skimming quickly through radio channels. This creates lot of background noise and static noise with mix of what you can hear from the actual radio.. they say that the ghost can easily communicate through it.

Simplest explanation is of course that they just interpret extremely bad audio as some kind of words, plus if they listen for many hours they will eventually pop out something that will be an answer to your question, here is a link so you can consider for yourself, remember humans are great in interpreting random noise as actual words[1] (skip like 3 minutes for actual talk).

The story of the original Mars picture got stretched over many years. 2 decades after taking the picture, there was much better one taken by Mars Express as you can see below it was just the low resolution of Viking spacecraft.

There are many things that can trick us so it is not best to take the first explanation that we can think of, be sceptical and do not share if you do not know anything about it.

Dragallur

Smiley: By en:User:Mystìc – Originally created by en:User:Mystìc at en:Image:SNive.gif. Vectorized by Psiĥedelisto, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=55079042

Hi,
today I will write about passwords and their security. Mostly I want to explain what “hashing” means in this context. Its certainly important issue considering that for example last year in May there were 164 million passwords from LinkedIn offered for sale.

This means that when you create your account instead of storing the password which could be simply stolen away, the website will run the string through one-way function that will put out some long combination of various letters and numbers, unrecognizable from the original password.

One-way function means that you can not take the nonsense, put it into the function other way around and get the password out, one-way function may for example lose some of the original information so that the process is not reversible.

Now on the server is only saved hash of the password[1] but even that is not enough to be quite secure. The thing is that there are only several commonly used hashing functions and crackers (correct term for hacker) can still break it…

What crackers can own is called rainbow table. That is huge (in terms of gigabytes easily) table of hashes. These hashes were made from random letters or from combination of words from dictionaries. When somebody cracks the database of some website and get hands on all those saved hashes they will start to compare them in huge amounts with their rainbow table. The hash functions always create the same string from the same password so the cracker only needs to have these rainbow tables for couple of most used hash functions.

This is of course why it helps from the side of the user to have long and random password, one can not have everything on the rainbow table because of its size and it takes a long time to compate a lot of hashes.

For extra protection most pages also “salt” hashes. That means that after your password they add some random characters and makes a stronger hash with it. Every password has to have original long salt. With the salt it does not matter if it is known or not because cracker can not precompute rainbow tables for all the possible strings and the technique will become unusable.

Sites might also add time that it takes to log into account, not noticable for user but catastrophic for cracker. For example if user has to use CAPTCHA or if simply you use hash function that takes longer time to go through, you will be way more secure from brute force attacks attacks which are cracking hashes one by one simply by trying random strings.[2]

Dragallur

[1]When you log in the password that you entered will be hashed again and compared to the hash that is already saved in the database.

[2]On the other hand you might me more fragile against attacks that try to make your site overloaded.

Source

# Book review 12) Thing Explainer

Hi,

Randall Munroe is a great guy. Creator of XKCD (totally free nerd comics) and the author of What If which you can also read on the internet maybe only some parts… Now one day about two weeks ago I noticed in our school library that they bought his “new” book Thing Explainer. I wanted to buy it earlier but I found out that it costs like almost two new books and was quite discouraged (and I did not have the money anyway). So for some reason the people in the library bought it and I have read it in few days.

### Rating: 10/10

Thing Explainer is a book that explaines complicated stuff in simple words, simple means ten hundred most used words. Great idea I admit. Randall says that when he was younger he purposefully used complicated words so that nobody thought about him, that he did not know them, but in this book he does not need to care about it.

Inside you can find explanations of: Saturn V (Up Goer Five), Keyhole (Shape Checker), Periodic table, Sun, Washing maschine, Car and many many more. There are I think two or three double pages which extend the books already giantic size to double and the page about Skyscraper (Sky toucher) is of the format A2

1000 words is not much. Most technical terms do not exist and even if you know them IRL (in real life) you may find yourself wondering what some things mean. “Fire water” took me some time indeed. Or helium is “kind of air that makes your voice funny”.

Basically there is no objection from me, hopefully the author will write 2nd part since there is lot of stuff outhere that still needs to be covered!

Here is in the same style Einstein and Theory of Relativit explained.
Here is Up Goer Five.

This video is from Minute Physics about getting to space:

Dragallur

# Do we see in 3 dimensions?

Hi,
its been quite long time since I wrote about dimensions. Just a quick recap since people do not click on links much: 0th dimension is point, 1st dimensions is line, 2nd dimension is plane and 3rd dimension is space. We are talking about spatial dimensions, another thing is atime dimension, but that is not important here.

So I got into this argument if humans see in 3 dimensions or not, I got no clear conclusion though so I am just going to discuss it here. We live in 3 spatial dimensions, proof, cubes exist. How do we see though? We can see cubes but I would argue that we see in 3rd dimension.

1. Retina does not capture depth, it is 2 dimensional detector so we simply can not have a 3 dimensional vision.
2. We have two eyes though, lot of people seem to like to point this out. With second eye you have what is called a stereoscopic vision.. the second eye has little bit different point of view and when brain combines it stuff gets depth. This does not mean that we see in 3D though. Still it is just two 2 dimensional pictures put together. Brain interprets this picture as 3 dimensional and based on experience judges distance. Also colors and shades can help us with that.

This is stereoscopic picture, disalign your eyes and match the pictures so you see 3 of them.

3. You can draw anything you see on piece of paper and it will be exact representation of what you see, all angles same and so on. This I think would be impossible if you actually wanted to transfer 3D image to 2D plane because by definition 3D space is made up of infinite 2D planes put on top of each other. Same as you can not take infinite picture and store it in 1D line.
4. If we could see in 3D we would see all angles as they actually are. If you look into corner you do not see 90° angles though because you remember the way that walls work you know that they are there.

Dragallur

# Sunset elevator

Hi,
today I will write about one particular physics problem that I was solving during weekend. It was pretty hard, but quite interesting set-up. (It is originally from Czech physics seminar called Fykos)

You and your boyfriend/girlfriend are sitting on a beach watching sunset. Luckily you are prepared to extend the romantic moment with elevator that will drive upwards. How fast does it need to drive for you two to be able to watch sunset continously?

Normally sunset related problems are about plane or car driving and how fast does it need to be for you to watch sunset all the time. That is freakin’ easy because you just need to drive at the speed that the Earth turns in your place. For Prague this is roughly 300m/s which is about the speed of sound.

This problem is way more unique. I do not know if my solution is correct since the people from seminar did not release solutions yet.

Basically you are standing on top of circle that is rotating at 300 m/s or also 0.00417°/s. You are soon leaving place from which you could see the sunset so you need to go up. The problem is that you are not actually going directly upwards to this place but as Earth turns your elevator rises in a line perpendicular to tangent of Earth at your paricular location, check out this desmos graph which helped me a lot to understand it (my creation): https://www.desmos.com/calculator/oftnm48s3b

Here is a picture though it is better to go on the original link which is very interactive:

(Check out complete end of post for explanation of picture) What does it mean for you in practice? In one hour you will be going almost 100 m/s. After 6 hours you will certainly be dead because the acceleration will kill you. At this point Earth would still be bigger on the sky though you would already be 500,000 kilometers away. After another three minutes from what I have considered last time you would be almost 3 million kilometers away and Sun and Earth would be the same size, at this point you would also ride in 1/3 of speed of light. But this journey still continues. After another 13 seconds you would go faster than the speed of light with acceleration of 14 km/s. There is not much time left but lets see.. 10 million kilometers would be reached by next 9 seconds. 5 seconds later you would go in freakin 10 million kilometers per second if it would be possible. One second before the journey would end you would reach 0.5 of AU. Soon after you would divide by zero which is dangerous[1]. After exactly 21600 seconds which is 1 quarter of day your elevator is perpendicular to this horizon, which sucks.

Dragallur

Explanation: black circle is Earth. Green line is elevator that with you turns left, after 21600 it will go 90 degrees. Red dot is the spot where you need to be in order to see sunset. Blue line is the original horizon.

[1]Do not be discouraged by only 0.5 AU. In the next mili and microseconds you would whizz through whole Milky Way and Observable universe as you would reach infinite speed.

# Why do stars twinkle (and planets not)?

Hi,
I felt so embarassed that I finally had to find it out and now I am writing this short post about it. For few years, roughly, I am studying astronomy yet, I never knew why stars twinkle and planets not. I confess.

Stars twinkle because the light that reaches us goes through atmosphere and atmosphere is not very homogenous – smooth. Air refracts light and there is different temperature once in a while, humidity and so on, I think that lot of factors play the role. This causes the light of star to scatter a bit and creates the twinkling effect.

Planets do not do it. This is great because you can identify them extremely fast on the sky and you do not mistake them for some other bright star. Why? Their light still goes through atmosphere. Because they are not “point sources”. Stars are so far away that even with best telescopes we see them only as points. Planets with simple telescope on backyard already have shape. Some of their light scatters one direction, some the other and it basically cancels out creating nice image. This is also why it is better to go star-gazing in the winter, colder air does not create so much “noise” on the picture.

Dragallur

# Why golden trash bins do not help (modern equipment in schools)

Hi,
(few days back) I am sitting in a classroom, slightly bored by the teacher saying what I heard the day back. After few minutes I am being offered to do experiments alone. I agree with the hope that it is going to be more fulfilling. Instead of getting full access to the laboratory[1] I sadly accept white box, aka trash bin.

This is kind of similar, the fact that it is chinese[2] kind of fits the situation since my german is not so good yet.

Such a box contains “scientific” equipment for the study of electro-magnetism. This consists of few cabels, power source, resistors, capacitors, all properly laid on green boards. Function generator, some frequency and amplitude thing, two coils, magnet and some stuff to hold it together. This is probably almost perfect list of things that costs the school hunderds of dollars. I took it with the manual that contained roughly 15 experiments and decided to do one of them. I put components together as it said, found out the thing it said I am supposed to find out, it gave me the formulas to calculate it.. that is all.

So now the rant against these boxes (thrash bins as my host-brother pointed out).
The problem is that such a box with set up equipment and set up experiments does not enhance any creativity in students. Especially building circuits could be one of the cool things where you try what happens when you connect this and that. That is probably the biggest problem, you can just follow some manual and not understand what is going on. Also these components are totally dependant on each other and you can use only this box alone, there is no room for expansion or only limited. Not speaking about the cost, there is another trash bin like this for 800 euro. It had wagon, line on which the wagon could drive, two movement sensors and some things to hold it together and so on. We used it during physics class to demonstrate Newton’s 2nd law (F=ma). It took so much time to set it up, to measure it all to 3 decimal places. Actually it took 90 minutes and we did not get even to the formulation of the law. People were bored and I bet that if you asked half of them what was this whole about they would not have a clue.

This is modern equipment.. and it is useless. If they bought separate components boards to built circuits on, they even have those in the school but they are not used anymore. These days teachers probably think that they can not get better with chalk and a board.

Dragallur

[1] I do not think it would be a good idea to let me there alone though I go there anyway every monday with my host-brother.

[2] I do not know if it is chinese.