Monday, January 15, 2018

Why does entropy increase over time?

In this video I use an example of two mixing gases to explain why entropy increases over time. Entropy is a measure of disorder, and so it is zero when gases are nicely separated and then starts to increase when the gases start to mix. A situation of order – gases nicely sorted into their own chambers – is less probable than a situation of disorder – in which gases are mixed. And so, as the system evolves, a situation in which entropy is higher is more likely than a situation in which entropy is lower. This is why entropy has to increase. Entropy can also decrease, if accidentally the gas gets unmixed. But because order is less likely than disorder, a decrease in entropy is less likely than its increase.

To sum up, entropy is defined as a measure of disorder, which is often high and rarely low. And so, by definition, entropy is likely to increase and unlikely to decrease. There is no deep physics here. Just clever definitions.

Monday, January 8, 2018

Why does atmospheric pressure decrease with altitude?

In this video, I show how a gas - a bunch of particles bouncing in a chamber - forms a density gradient if there is a force pulling them in one direction. The force is to the right but you should have no problems imagining that it points downwards. There is no voice-over – the animation seems sufficiently self-explanatory.

Saturday, December 2, 2017

What happens when a gravitational wave passes by?

In this video I explain what exactly happens to the geometry of space when a gravitational wave passes by. I haven't seen many videos doing that (actually none). Most of them just say that a gravitational wave squeezes and stretches things but do not explain what does it actually mean. Or, they they show a nice animation of spreading waves, usually on a two-dimensional surface, which is very nice but does not have much to do with gravitational waves.

I do not discuss other details, like the sources of gravitational waves, their strength, recent discoveries, etc. because those topics seem to be discussed aplenty.

So, if you wandered, what gravitational waves were about, here you go:

Tuesday, November 14, 2017

General Relativity: curved spacetime and how gravity works

Here is yet another video. This time it is inspired by the question "why things fall?"

I have noticed that most of videos explaining general relativity make a mistake of showing how to visualize curved space and then claiming that this somehow explains how gravity works. Some (better) videos explain that gravitational attraction is mostly due to time slowing down closer to a massive object. But none seem to explain why and how variation in speed of time explains the downward movement. Until today. There you go:

Monday, May 8, 2017

Special relativity: time dilation, relativity of simultaneity, and length contraction

I have recently learnt Special Relativity and in the process of doing so I have noticed that the explanations of it available on YouTube are somehow lacking. Here are the features of my explanation which I have not seen in the videos produced so far:

1. Why squeezing object in one way is good but in another way is bad? Most explanations of time dilation using a mirror in a train tell the viewer that in order to keep the speed of time constant a clock on a moving train must tick slower. But nobody mentions that the speed of light can be also kept constant by squeezing the train. And since we have length contraction why should we ignore the possibility of width contraction? Therefore, I decided to discuss the possibility of width contraction and explain why it must be discarded.

2. Some people confuse the idea of “what actually happens” with “what appears to happen” and think that time dilation is some sort of optical illusion. To make sure that they do not have this impression after watching my video, I present them with a hypothetical experiment illustrating what it means that the time moves slower for a moving observer.

3. Relativity of simultaneity is rarely discussed and when it is discussed, the presentation is done poorly. Most explanations present results but do not present the logic and are often of the type: “for this person they are simultaneous, for the other they are not, deal with it!” This does not give viewer a chance to understand why exactly the concept of simultaneity fails. Instead, I came up with a thought experiment with two moving trains and firecrackers to illustrate the logic. I hope that after watching my video a diligent viewer will be able to answer a question: “WHY simultaneity is relative?

4. Virtually no video discusses length contraction. As with relativity of simultaneity, a person trying to understand “why there is length contraction?” will have hard time finding satisfactory answer in the existing non-scientific video material. I try to fill this gap. My experiment with two trains and firecrackers, once the relativity of simultaneity is established, very nicely demonstrates the logic of why must it be that there is length contraction.

5. I also try to explain why, as the speed of the object approaches the speed of light, the length of the object and the speed of time for it both decrease to zero. This point is often skipped in the currently available videos.

6. Finally, I decided not to use any equations in my explanations (ok, I use one equation “SPEED = DISTANCE / TIME” but it is not essential for the presentation) and I decided not to use specialist phrases like “frame of reference” which may confuse people who do not study physics. My explanations are designed in such a way so that they can be used in a discussion at a cocktail party. Indeed, I have tried these explanations in a social setting before making this video and they seemed successful. As my lab rats I used people who are not versed in physics or mathematics but are generally intelligent.

Thursday, December 1, 2016

Humanist definition of truth

I was recently reading Richard Rorty’s “Contingency, irony, and solidarity.” In the introduction, he delineates the core problem he is talking about: relationship between individualism and solidarity. Should people be altruistic or should they be antisocial? Following a common philosophical practice, Rorty completely ignores the entire scientific body of evidence related to this topic which was available to him at the time when he was writing the book. There is no mention of evolutionary basis for altruism or other scientific theories of human motivation and social interaction. Instead, Rorty discusses what people like Nietzsche or Hegel, ignorant of any scientific investigation into the topic, pulled out of thin air hundreds of years before. This is why I don’t like (most) philosophers.

In the following chapter Rorty explains what he thinks “the truth” is. The explanation contains statements like “The world can, once we have programmed ourselves with a language, cause us to hold beliefs” and culminates in a statement that “truth is a property of linguistic entities, of sentences.” As it turns out this is a common understanding of what the truth is, among people involved in humanities like, say, anthropologists. Rorty himself is a popular philosopher having his part in shaping of the modern liberal academic ideology. The book I am discussing here was cited over 10,000 times according to Google Scholar.

The aforementioned definition of truth made me come up with a quick example. Consider a dog. Show two cups to the dog and put a bone into one of the cups. Then, distract the dog and quickly swap the cups. Then, let the dog choose one of the cups. The dog will choose the cup it remembers to have a bone in it. That is, the dog believes that bone is in a certain cup. This belief is false if you swapped the cups and is true if you did not swap the cups. Since the dog cannot speak, the existence of beliefs and their truth or falsehood do not depend on existence of a language.

This definition of truth is an expression of anthropocentrism that seem to be central to the modern liberal academic ideology. Nothing but humans is important. Nobody bothers to question whether the reasoning presented would be valid for agents who do not share all human characteristics, in this particular case, the use of language. As a result, Rorty’s arguments depend on how he implicitly defines human nature. Yet he is explicitly against the notion of human nature. The whole structure is internally inconsistent.

Why is it important? Well, it shows how modern liberal ideology is grounded in ignorance. This ignorance gives rise to dogmatically defended stances like cultural relativism. It makes otherwise perfectly reasonable people to say things like “2+2=4” is no better than “2+2=5” if the latter is an inherent element of a culture which assigns truth to it. The intellectual discourse deteriorates. Harmful policies gets enacted.