Partially Coherent

Time travel is a popular concept in works of fantasy, with many different flavors. In the Back to the Future trilogy, Doc Brown built a time machine out of a DeLorean just because he could. In Harry Potter and the Prisoner of Azkaban, Hermione Granger uses a time-turner  so she could study every subject in Hogwarts, and even Superman turns back time to undo the death of Lois Lane. Seems like Superman really is quite super. But scientifically speaking, how much sense does time travel actually make? Let's start from the most obvious type of time travel: forward in time. Clearly we are all automatically traveling towards future time by default, since we age and seasons shift and whatever. But the interesting thing is that according to the theory of relativity, it is possible to slow down the passage of time for yourself, while everything else around you continues to age normally. This effect is called time dilation , and it is an important effect in the universes dynamics....

When you whisk an egg and leave it alone, why doesn't the egg white and yolk separate on their own? If you light a fire, why does it keep burning? And why do we perceive that time never changes it's direction? All of these questions are answered by a single concept in physics: entropy. Simply put, entropy is a measure of the microscopic disorder of a system, and the second law of thermodynamics says that it can only increase or stay constant in a closed system. And all of this is just simple statistics. Let's put this in more concrete terms with a simple example: we flip three identical coins and record the outcome. First of all, what does this have to do with anything? In thermodynamics, we are interested in the energy of the studied system. That energy is made up of all of the individual energy states of the particles that make up the said system. The two sides of a coin represent the possible states of a two level system, which makes it quite a popular example. ...

After two papers on something that I did not receive an education for, I finally got a topic in photonics, my bread and butter to be. I started working as a part of the coherence coherence group of UEF in the summer of 2015 and my first task was to design and build an interferometer, which would be used to quantify spatial coherence. Thin film interference. Physics is pretty, ain't it? Now, one might ask, what is spatial coherence? The idea behind this concept is simple: it describes how well different parts from a beams cross-section correlate with each other. If the correlation is strong, then we talk about high coherence and low when the correlations are weak. A very good overview of spatial coherence and its measurement can be found  here . The usual way to measure it is to use the  Young's interferometer  (a double slit experiment, variations of this are used in quantum mechanics), but there are some problems. First of all, a single measurement is not eno...

Around two weeks ago I heard about a very interesting article called " Bose-Einstein Condensation in a Plasmonic Lattice ." I must admit, the first time I heard about it, I knew what all those words meant separately, but together it was some mumbo jumbo that made no sense to me. What exactly is condensing? Don't these condensates exist only at extremely low temperatures? And what do plasmons have to do with this? Reading the abstract didn't help at all. Going through the whole article, I understood maybe half of it. But apparently they had done something great, and it was going to be published in Nature Physics! By chance, I happened to be in contact with one of the authors and he explained everything to me in a way that I finally got what they were doing. And it really was something great. First of all, what is a Bose-Einstein condensate? About a century ago, Indian scientist Satyendra Nath Bose sent an article to Albert Einstein, humbly asking for his op...

Probably the biggest reason why I chose physics, was the belief that it is completely dictated by rational arguments. If you can show that from A comes B because of C, then everyone will accept it as being true. Given of course that you didn't mess up the calculations and the premise is realistic. However, a few years of work in this field has proven that belief to be false. You can prove your point rigorously with widely accepted mathematical tools and leave no wiggling room. And still there will be people who do not agree with your reasoning. It wouldn't be a problem if these doubters were some internet trolls who obviously have no idea what they're saying, since you can just ignore them. Unfortunately, they can also be esteemed scientists in the field. Senior researchers, award winning scientists, professors, even so called living legends. Sure, it's fine to make mistakes, and everyone does make them. I have been locked in several heated discussions ...

What did the MythBusters ultimately teach us? "Remember kids, the only difference between screwing around and science is writing it down." A picture is worth more than a thousand words, so I guess I was doing science after all, and lots of it! Got that "evil genius" -thing going on. I have been thinking of making a video series called: "Will it ablate?" in which I will put all kinds of things in front of an extremely powerful laser. I also have plans for some other videos as well, so stay tuned. I made a youtube channel for the blog, and here are the fruits of the first filming day at the lab, hope you like it! If you have some suggestion on what I should film next, throw me a comment!

One thing that we are taught very early on in physics lectures is that the speed of light in vacuum, c, is the fastest anything can ever move, period. But is that really true? Well, the short answer is yes, and the long answer has some ifs and buts. Probably the most popular reasoning behind this statement is that Einsteins theory of relativity does not allow for anything to exceed the speed of light. But what it actually says is that information or energy cannot travel faster than light. Of course, even this is a very strict condition, since every particle, physical system and any radiation can be used to carry information and/or energy, which means that none of those can travel faster than light. To achieve a speed faster than c, you need something that doesn't contain information or energy, but what could that possibly be? One entity that potentially carries neither, is the group velocity of light. In optical telecommunication, group velocity is the speed of the...