# The directional derivative (for 3D & 4D complex numbers).

A couple of days ago all of a sudden while riding my bicycle I calculated what the so called directional derivative is for 3D & 4D complex numbers. And it is a cute calculation but I decided not to write a post about it. After all rather likely I had done stuff like that many years ago.

Anyway a day later I came across a few Youtube video’s about the directional derivative and all those two guys came up with was an inner product of the gradient and a vector. Ok ok that is not wrong or so, but that is only the case for scalar valued functions on say 3D space. A scalar field as physics people would say it. The first video was from the Kahn academy and the guy from 3Blue1Brown has been working over there lately. It is amazing that just one guy can lift such a channel up in a significant manner. The second video was from some professional math professor who went on talking a full 2.5 hour about the directional derivative of just a scalar field. I could not stand it; how can you talk so long about something that is so easy to explain? Now I do not blame that math professor, may be he was working in the USA and had to teach first year math students. Now in the USA fresh students are horrible at math because in the USA the education before the universities is relatively retarded.

Furthermore I tried to remember when I should have done the directional derivative. I could not remember it and in order to get rid of my annoyance I decided to write a small post about it. Within two hours I was finished resulting in four pictures of the usual 550×775 pixel size. So when I work hard I can produce say 3 to 4 pictures in two hours of time. I did not know that because most of the time I do not work that fast or hard. After all this is supposed to be a hobby so most of my writing is done in a relaxed way without any hurry. I have to say that may be I should have taken a bit more time at the end where the so called Cauchy-Riemann equations come into play. I only gave the example for the identiy function and after that jumped to the case of a general function. May be for the majority of professional math professors that is way to fast, but hey just the simple 3D complex numbers are ‘way to fast’ for those turtles in the last two centuries…

Anyway, here is the short post of only 4 pictures:

Should I have made the explanation longer? After all so often during the last years I have explained that the usual derivative f'(X) is found by differentiating into the direction of the real numbers. At some point in time I have the right to stop explaining that 1 + 1 = 2.

Also I found a better video from the Kahn academy that starts with a formal definition of the directional derivative:

At last let me remark that this stuff easily works for vector valued functions because in the above limit you only have to subtract two vectors and that is always allowed in any vector space. And only if you hang in a suitable multiplication like the complex multiplication of 3D or 4D real space you can tweak it like in the form of picture number 4 above.

That was all I had for you today, this is post number 166 already so I am wondering if this website is may be becoming too big? If people find something, can they find what they are searching for or do they get lost in the woods? So see you in another post, take care of yourself & till the next post.

# What is one-way light speed? + A plasma lamp in a magnetic field.

Lately the Veritasium guy from the Youtube channel with that name came out with a video that made me think. It seems that the only way light speed has been measured experimentally is by using a mirror and as such you always measure a so called ‘two-way light speed’ average. It is possible that in this universe light has some preferred direction and in that derection it goes faster compared to say the opposite way.

You might wonder as why that is but that is the old problem Mr. Einstein faced & solved: It is very hard to get two clocks synchronized when they are apart. Vertitasium explains that if light has a preferred direction, in that case it all gets even harder and rather complicated.

Anyway to make a long story short, he also claims there has never been such a ‘one-way’ experiment. That made me think about it and I think that I have found a solution that does not depend on the nasty synchronization problem. All you need is two atomic clocks that are always a fixed distance apart. It gets more complicated compared to where there is perfect sync but if the universe has a preferred direction for light to go in, from the data you collect you should be able to find it.

First let me show you via a screen shot from the video what the usual way is to experimentally measure the speed of light:

In the next six pictures I try to explain that using two atomic clocks on two satellites can pull the trick off. Both satellites have a laser or for that matter any em radiation would do like normal radio waves. And on both satellites there is perfect registration of the local time of the times a laser signal was put out or received. Both satellites should be in the same strength of the local gravity field so that their atomic clocks run at equal speeds. Every day both satellites send out one laser pulse on a fixed time and on a daily basis these send & receiving times are recorded.

We proceed with a video from the Brainiac channel. On Youtube there are more than one Brainac channels, I mean the guy with the big magnets. And with big I really mean big, the most heavy ones are a staggering 13 kg. A couple of years ago I wondered if I should buy a plasma lamp in order to study how my own set of small neodymium magnets should influence the plasma. These lamps cost only 20â‚¬ so that was not the problem. But I have already plenty of lamps so I decided not to do it. After all the photo’s from how an old television set reacts on the neodymium magnets should be enough.

Anyway that is what I thought: Given the fact the audience is composed of scientists, simply communicating the facts should be enough. And applying a bit of logic simply says electrons are not magnetic dipoles but in order to explain the behavior on an old television set is far better explained by electrons being magnetic monopoles. Of course now we are five or six years further down the timeline all I observed is that university people are still very good at just one thing: being important. And no no no, of course we do not talk about that. Electrons magnetic monopoles? Great minds from physics, also people who were very important, said it ain’t so. So no no no, we are important and those crazy people from outside science should shut up and pay the taxes we need for being so important.

Yet now a few years later the video from the Brainiac guy shows that the plasma in the plasma lamp does not react at all as you might expect from a bunch of magnetic monopoles. On the contrary: If he applies one of those 13 kg neodymium magnets, the plasma lamp stops working. So I am glad I never bought one of those lamps because that would make me doubt my own insights that were derived from the electron cannons in the old television set… But the Brainiac guy has much more electronic equipment and he soon found out that the plasma in a plasma lamp is steered by and alternating electric current. So the plasma shakes hin und her with a high frequency and it is not streaming in one direction or so…

Furthermore he explains perfectly why the lamp stops working: the applied magnetic field from the 13 kg magnet stops the transformator in the plasma lamp from working properly. And that explains why the lamp stops working… By the way, if electrons were really magnetic dipoles, the 13 kg magnet would never hinder the functioning of a transformator because a magnetic dipole the size of an electron is by definition neutral for external magnetic fields.

Well here is the perfect video if you want to understand a bit of nature and in case you are one of those fake scientist only occupied with the importance of self, why not walk to a mirror so you can look at yourself?

This post is getting far to long for the attention span people have in the present media environment. But I want to show you also a part that the Brainiac guy does not understand: the next screen shot from his video shows only electrons that are repelled by the giant magnet he uses. If he would have used an other direction you could have seen also the electrons that are attracted by the magnet. All of this stuff nicely confirming year in year out that it is impossible for electrons to be magnetic dipoles…

Ok, end of this far too long post. See you in the next post & thanks for having a long enough attention span for reading these very words.