I have currently got computer issues so this week’s posting has not been written.😱 I’m writing this as a placeholder until I can catch up. The subject will be, as above, “upgrades”.
I have currently got computer issues so this week’s posting has not been written.😱 I’m writing this as a placeholder until I can catch up. The subject will be, as above, “upgrades”.
Now and then I fire up one of those programs that displays a fractal on the screen. These programs use mathematical programs to display patterns on the screen. Basically the program picks the coordinates of a pixel on the screen and feeds the resulting numbers to the program. Out pop two more numbers. These are fed back to the program and the process is repeated.
There are three possible outcomes from this process.
Firstly, the situation could be reached where the numbers being input to the program also pop out of the program. Once this situation is reached it is said that the program has converged.
Secondly, the numbers coming out of the program can increase rapidly and without bounds. the program can be said to be diverging.
Thirdly, the results of the calculation could meander around without ever diverging or converging.
A point where the program converges can then be coloured white. Where it diverges, the point or pixel can be coloured black. A point where the program seems to neither converge nor diverge can then be coloured grey. A pattern will then appear in the three colours which is defined by the equation used.
Anyone who has seen fractals and fractal programs will realise that a three colour fractal is pretty boring as compared to other published fractal images. Indeed the process that I have described is pretty basic. A better image could be drawn by colouring points differently depending on how fast the program converges to a limit. This obviously requires a definition of what constitutes convergence to a limit.
Convergence is a tricky concept which I’m not going to go into, but to compute it to say in a computer program you have to take into account the errors and rounding introduced by the way that a computer works. In particular the computer has a largest number which it can physically hold, and a smallest number. Various mathematical techniques can be used to extend this, but the extra processing required means that the program slows down.I’m not going to explain how this difficulty is circumvented, since I don’t know! However the fact is that the computer generated fractals are fascinating. Most will allow you to continually zoom in on a small area, revealing fantastic “landscapes” which demonstrate similar features at all the descending levels. Similar, but not the same.
The above far from rigorous description describes one type of fractal of which there are various sorts. Others are described on the Wikipedia page on the subject.
Another interesting fractal is created on the number line. Take a fixed part of the number line, say from 0 to 1, and divide it into three parts. Rub out the middle one third. This leaves two smaller lines, from 0 to 1/3 and from 2/3 to 1. Divide these lines into three parts and perform the same process. Soon, all that is left is practically nothing. This residue is known as the Cantor set, after the mathematician Georg Cantor.
This particular fractal can be generalised to two, three, or even higher dimensions. The two dimensional version is called the Sierpinski curve and the three dimensional version is called the Menger sponge.
One of the fractal curves that I was interested in was the Feigenbaum function. This fractal shows a “period doubling cascade” as shown in the first diagram in the above link. If you see some versions of this diagram the doubling points (from which the constant is determined) often look sharply defined.
I was surprised the doubling points were not in fact sharply defined. You can see what I mean if you look closely at the first doubling point in the Wolfram Mathworld link above. Nevertheless, the doubling constant is a real constant.
Another sort of fractal produces tree and other diagrams that look, well, natural. A few simple rules, a few iterations and the computer draws a realistic looking skeleton tree. A few tweaks to the program and a different sort of tree is drawn. The trees are so realistic looking that it seems reasonable to conclude that there is some similarity between the underlying biological process and the underlying mathematical process. That is the biological tree is the result of an iterative process, like the mathematical trees.
I’ve mentioned natural objects, trees, which show fractal characteristics. Many other natural objects show such characteristics, the typical example which is usually given is that of the coastline of a country. On a large scale the coastline of a country is usually pretty convoluted, but if one zooms in the art of the coastline that one zooms in on stays pretty much as convoluted as the large scale view.
This process can be repeated right down to the point where one can see the waves. If you can imagine the waves to be frozen, then one can take the process even further, but at some point the individual water molecules become visible and the process (apparently) reaches an end.
If you want a three dimensional example, clouds, at least clouds of the same type, probably fit the bill. Basically what makes the clouds fractal is the fact that one cannot easily tell the size of a cloud if one is simple given a photograph of a cloud. It could be a huge cloud seen from a distance or a smaller cloud seen close up. Of course if one gets too close to a cloud it becomes hazy, indistinct, so one can use those clues to guess the size of a cloud.
Fractals were popularised by the mathematician Benoit Mandlebrot, who wrote about and studied the so-called Mandlebrot set, wrote about it in his book, “The Fractal Geometry of Nature”. I’ve read this fascinating book.
While I was searching for links to the Mandlebrot Set I came across the diagram which shows the correspondence of the period doubling cascade mentioned above and the Mandlebrot set. This correspondence, which I did not know about before, demonstrates the interlinked nature of fractals, and how simple mathematics can often have hidden depths. Almost always has hidden depths.
Well, I don’t know really. Most programmers that I know seem about as happy as the rest of the population, but I was thinking about programming and that variation on “A Policeman’s Lot” from the Pirates of Penzance appealed to me.
Programming in often presented as being difficult and esoteric, when in fact it is only a variation of what humans do all the time. When you read a recipe or follow a knitting pattern, you are essentially doing what a computer does when it “runs a program”.
The programmer in this analogy corresponds to the person who wrote the recipe or knitting pattern. Computer programs are not a lot more profound than a recipe or pattern, though they are, in most cases, a lot more complicated than that.
It’s worth noting that recipes and patterns for knitting (and for weaving for that matter) have been around for many centuries longer than computer programs. Indeed it could be argued that computers and programming grew out of weaving and the patterns that could be woven into the cloth.
In 1801 Joseph Marie Jacquard invented a method of punched cards which could be used to automatically weave a pattern into textiles. It was a primitive program, which controlled the loom. I imagine that before it was invented the operators were giving a sheet to detail what threads to raise and which drop, and which colour threads to run through the tunnel thus formed. I can also imagine that such a manual process would lead to mistakes, leading to errors in the pattern created in the cloth. It would also be time consuming, I expect.
Jacquard’s invention, by bypassing this manual method would have led to accurately woven patterns and a great saving in time. Also, an added advantage was that changing to another pattern would be as simple as loading a new set of punched cards.
At around this time, maybe a little later, the first music boxes were produced. These contained a drum with pins that plucked the tines of a metal comb. However the idea for music boxes goes back a lot further as the link above tells.
The only significant difference between Jacquard’s invention and the music boxes is that Jacquard relied on the holes and music boxes relied on pins. They operated in different senses, positive and negative but the principle is pretty much the same.
Interestingly there is a parallel in semiconductors. While current is carried by the electrons, in a very real sense objects called “holes” travel in the reverse direction to the electrons. Holes are what they sound like, places where an electron is absent, however I believe that in semiconductor theory, they are much more than mere gaps, and behave like real particles.
It’s amazing how powerful programming is. Microsoft Windows is probably the most powerful program that non-programmers come into contact with, and it does so many things “under the hood” that people take for granted, and it is all based on the absence or presence of things, much like Jacquard’s loom and the music boxes. While that is an analogy, it is not too far from the mark, and many people will remember having been told, more or less accurately that computers run on ones and zeroes.
When a programmer sits down to write a program he or she doesn’t start writing ones and zeroes. He or she writes chunks of stuff which non-programmers would partially recognise. English words like “print”, “do”, “if” and “while” might appear. Symbols that look like maths might also appear. Depending on the language, the code might be sprinkled with dollar signs, which have nothing directly to do with money, by the way.
The programmer write in a “language“, which is much more tightly defined than ordinary language, but basically it details at a relatively high level what the programmer wants to happen.
The programmer may tell the program to “read” something and if the value read is positive or is “Baywatch” or is “true”, do something. The programmer has to bear in mind that often the value is NOT what the programmer wants the program to look for and it is the programmer’s responsibility to handle not only the “positive” outcome but also the “negative” one. He or she will tell the program to do something else.
When the programmer tells the program to “read” something, he or she essentially invokes a program that someone else has written whose only job is to respond to the “read” command. These “utility” program are often written in a more esoteric language than the original programmer uses (though they don’t have to be), and since they do one specific task they can be used by anyone who programs on the computer.
This program instructs other, lower level programs to do things for it. Again these lower level programs do one specific thing and can be used by other programs on the computer. It can be seen that I am describing a hierarchy of ever more specialised programs doing more and more specific tasks. It’s not quite like the Siphonaptera though, as the programs eventually reach the hardware level.
At the hardware level it will not be apparent what the programs are intended for, but the people who wrote them know the hardware and what the program needs to do. This is partially from the hierarchy of programs above, but also from similar programs that have already been written.
Without going into detail, the low level program might require a value to be supplied to the CPU of the computer. It will cause a number of conducting lines (collectively a “bus”) to be in one of two states, corresponding to a one or a zero, or it might cause a single line to vary between the states, sending a chain of states to the CPU.
In either case the states arrive in a “register”, which is a bit like a railway station. The CPU sends the chains of states (or bits) through its internal “railway system”, arranging for them to be compared, shifted, merged and manipulated in many ways. The end result is one or more chains of states arriving at registers, from whence they are picked up and used by the programs, with the end result being whatever the programmer asked for, way up in the stratosphere!
This is monumental achievement, pun intended, and is only achievable because at each level the programmer writes a program that performs one task at that level which doesn’t concern itself at all with any other levels except that it conforms to the requests coming from above (the interface, technically). This is called abstraction.
Suppose two men are marooned on a remote island somewhere. At first each is unaware that the other is there, but eventually they meet. Suppose that for some reason they don’t want to join up, but they do want to interact. So they set about working out ways to share the island, and obviously they want to live amicably until they are rescued.
So they might draw an imaginary line across the island. A can only go into B’s half as long as B is aware and approves, and vice versa. Maybe it turns out that food is easier to come by in B’s half, but there is plenty for both. B allows A to venture into parts of his half of the island and A drops off a few items that he has gathered as thanks.
Later on they find that A’s part of the island has the best spots to catch fish or something, and they come to an agreement about that. Slowly but surely they build up a set of rules on how to behave and live on the island in harmony.
One can imagine that an arbitrarily complex set of rules may be developed, and these rules could be further complicated if a third man, C, were to join them on the island.
You can probably see where I am going with this. As the population of the island rises, more and more rules will become necessary, or if not necessary, useful, and at some stage someone will have the idea of writing them down. The rules become laws and eventually attract all the mechanisms of a full legal system.
While browsing around while thinking about this sort of thing, I came across a review of “Day Z”, which the author of the review describes as “A Video Game Without Rules”. The author describes how the ability to do nasty things to others leads to characters in the game, especially established players doing nasty things to other players, usually new spawned players.
It’s possible that the behaviour of players in the game is merely an early stage in its evolution, and it may be that later on stronger players may band together to help the newly spawned players and the people who treat new players badly will be marginalised or persuaded to change their ways. One can hope.
Another dismal view of the island scenario was that of William Golding who wrote “The Lord of the Flies”, where a group of English schoolboys are marooned on an island, perhaps as the result of an atomic war. They soon revert to savagery and murder, overriding the civilised urgings of Piggy and Ralph. As Piggy says “Which is better—to have rules and agree, or to hunt and kill? … law and rescue, or hunting and breaking things up?” The rest of the boys obviously want to hunt and kill.
Nevertheless, the process of generating laws by discussion and agreement was probably along the lines that I have suggested above. No doubt there were many tries to achieve this process which failed in the manner that things appear to have failed in the video game and how they were depicted as failing in “the Lord of the Files”, before a working system of laws was achieved.
It’s possible that the magic ingredient was the evolution of system of magistrates and a method of enforcing the laws. With a supposedly impartial system to decide the rights of a matter, and a special force or police system to enforce the laws, the weak individual would be protected against the stronger.
In early days, the system of laws and the enforcement of them would have been vested in the priests and spiritual leaders, who would have controlled the enforcement system, probably “Temple Guards” or similar.
Where do kings fit in? The rulers were often not priests themselves, but the rulers were seen to rule by divine right, so there was a tight link between the rulers and the religious leaders. Kings such as Hammurabi supposedly led the way in law making, though no doubt there was much political to and fro between the kings and the priests.
These days, in many countries the law has been secularised and in many laws are decided by the government of the country, and are arbitrated by a separate branch of the administration called the justice system, and the enforcement is carried out by the police and retribution by the prisons system.
Lawmaking, justice and enforcement are in many countries legally independent of one another so that, for example, the government cannot manipulate the system for its own advantage. The principle is that justice should be independent of lawmaking and the enforcement systems.
How does all this affect the man in the street? Well, in practise, not very much, usually, at least not directly. When driving along the road, a motorist is aware that the speed limit is so-and-so, and usually keeps to it, more or less. He or she treats it as an advisory rather than a restriction, in that it is taken as the top speed that is safe for that road.
The man in the street also uses laws for his own protection. He will assume that the consumer protection laws back him up when he purchases something which it transpires is defective and will feel confident in returning it. In most cases the retailer would not be too upset by someone returning a defective product as in most cases the retailer would want a happy customer and can return the product to the manufacturer.
In general, laws work best when they conform with the principle of “natural justice” or what would generally be considered fair. It is not fair for example for someone to keep others awake by holding noisy all night parties, and in most cases the law will support the sleepless neighbours over the noisy one, but it could come down to a matter of perception.
Things like disputes about access to properties can hinge on such matters and are very often cannot easily be settled. The law has been evolving for thousands of years, but it can’t solve every dispute, although we would be worse off without it. It has to change as the world is changing, so it is constantly evolving. We cannot expect it to be perfect.
Well, I almost forgot to write my weekly post. My excuse is that Monday is a public holiday and this upset my schedule. Of course this is only an excuse.
It did start me thinking about forgetting things. We have probably all forgotten appointments at one time or another, though with cell phones being ubiquitous and possessing calendars, we probably should never do so in the future. Yeah, right!
The reasons why we forget appointments can be myriad, but I’d suggest that at least some of the appointments that we miss are ones that we would prefer to miss, such dentist appointments. I’d guess that we would be much more likely to remember lunch appointments or some other types of appointments that we would enjoy.
Some people seem to forget things that I am unlikely to forget, such as plane flights. It always amazes me that people can turn up for flights at the last minute. I’m usually in the airport, waiting, well before the official check-in time starts.
It is probably a consequence of our busy lives that we need calendars and other “aide memoires” like shopping lists. One can imagine that in earlier times to-do lists were shorter and the number things that one needed to carry on a normal life was a lot smaller and our memories were able to cope. But then again, that may be an illusion. Was life really simpler in the past?
If you miss an appointment that affects not only you, but the people with whom you have the appointment. The dentist will be looking at an empty chair, and while he may enjoy the break, it will cost him money. That’s why some service providers like dentists may charge you a fee if you forget an appointment. Some places get the receptionist to send you a text the day before as a reminder.
Although I’ve suggested above that maybe in simpler times the need for a calendar was less, the need was not non-existent. Farmers, for example, need to know the best time to plant seeds to ensure a good crop.
The Babylonian calendar for example was based on both lunar and solar cycles which would enable the priests to suggest the correct time for planting crops. This calendar has its origins around 2000 BCE according to Wikipedia.
The Mayan calendar is even older, with roots in the 5th century BCE. The Mayan calendar came to popular attention in 2012, when it was conjectured that the Mayan calendar would end on 21 December 2012, and that this would signal a global catastrophe.
Of course nothing significant happened and the Wikipedia article on the topic explains that the Mayan calendar did not end on that date. Surely very few people seriously thought that it would. Even the ancient Mayans did not predict a calamity at that time, so far as scholars are aware.
Forgetting important dates is a recipe for matrimonial disharmony. There seems to be a gender bias here as most males do not worry too much if you miss a birthday, but it seems more important to females. Whether or not this is real gender difference or merely a societal one, I’m not prepared to guess. Whatever the cause, it is best to remember one’s spouse’s birthday. I personally find it very difficult to remember dates other than the usual wedding anniversary, spouse’s birthday and my children’s birthdays.
There is another sort of forgetting though, one that creeps up on one as time passes. Some of that can be attributed to loss of facilities due to age, but memories do seem to fade regardless of ageing. Even in your twenties your recall of events ten years earlier can be faulty, though for some reason some things can be said to stick in your mind.
It’s difficult to work out what we have forgotten and what we have simply had no reason to remember. Something may, for some reason or other, trigger a memory, and we say “Oh, I had forgotten that!” when obviously, we hadn’t.
Equally, memories may be replaced by false memories. For instance, for years I believed that I had a memory of an event at a particular place involving my sister’s pushchair. When I visited the place many years later, it was apparent that the event could not have happened as I remember it. The slope of the path, the flower beds were all wrong.
It seems to me that memories can be true, or totally false, and that a memory of events may be completely lost, and this would make the study of memory very difficult and that relying on memory for veracity is impossible.
There are people who claim to have memories of a previous life. I don’t believe such claims, as I don’t believe that there is such a thing as reincarnation. If there were such a thing, one wonders why those who remember their previous lives were always important and powerful people in past lives.
But memory loss definitely gets worse as one gets older. Some unfortunate people suffer so badly from memory loss that they cannot recognise their own families and get lost in places with which they were once familiar. As people live for longer this phenomenon is becoming a big problem.
Of course there is research into both ageing and memory, so this situation will hopefully improve, but at the moment, it doesn’t seem attractive to live to 100+ and lose all one’s faculties.
Memory is one of the things that makes you you. You can remember many things from your past, and while you can’t completely remember being the person that you were, you can remember some of it. Maybe you can remember what you were feeling at the time, maybe not.
But you believe that the person that you remember was you, in spite of the forgotten things, the things that you remember wrongly, because there is a continuous thread of memory between the person that you remember and you in the here and now.
Yet in another sense, that person was not you. His memories only encompass the time up until his now. Your memories of the time from then on are of events that have changed you and your memory of events before that person’s now have also changed, or been lost. How could you be the same person?
The last post that I made was my 100th post on this blog. I’ve tried to keep blogs before now, but I’ve always failed at some point. There are blogs started by me at various places on the Internet, but this is the only one to have got past a few dozen posts.
I’m not sure of the reason why I’ve been able to keep this blog going and I’ve failed before. I don’t think that it is the fact that this is a WordPress blog, as I’ve not found significant differences between the various type of blog. They all do pretty much the same thing.
Of course, there are myriads of themes out there, but it is impossible to hide the underlying structure completely – you create a blog post, you post it and people are able to look at it.
There are no doubt those who have specific needs and need specific features, for example if they are selling something and need to accept payments, who find that a specific blogging platform is required to fill their needs, but most people will find, I think, that the blogging platform that they use is mostly irrelevant.
I have committed myself to creating blog post of around 1,000 words once per week and so far I’ve been able to achieve this. I plan to have a post ready to go on Monday evening. Below I’m going to describe how I write a post. It’s a creative process, with a small ‘c’. It’s not Creative with a large ‘C’, a work of Art, as I don’t aspire to such exalted levels. It’s just my small blog.
When I sit down to write a post, I usually, but not always, have a topic in mind. If I am lucky I will have been thinking about it during the week and I have some idea on what I am going to include in the post. However, I don’t plan it out as such. I just some ideas, some pretty well developed in mind.
Sometimes though, I sit down at the computer with maybe only a topic or not even that. I type the title and I’m away! So far I’ve not had any real difficulty in reaching the 1,000 words, and sometimes I have to leave things out.
It is usually reckoned that a work of this sort has a distinct beginning and end. I certainly open with a sentence on what I about to write about and then go on to write about it, but I don’t try to tag on a definitive conclusion, especially if I am running on, and the word count gets significantly higher than 1,000 words.
So anyway, I start writing. As I write I might plan ahead a little, but more often than not I put down my current thought which might take a sentence or three and I correct and formulate my sentences as I go. I look back a little too, and may revise a sentence or phrase in the current paragraph if it strikes me as being too ugly.
I don’t however have the whole thing in my mind, though I may remember and revisit thoughts that I have written earlier if something strikes me. I do think ahead a little, or maybe a paragraph or two, but in general, I compose as I write as I go.
Sometimes I pause, as I just did, to think my way ahead. This is an indication to me that I’ve said all that comes to mind on the point that I was making and that I should start another point.
I am not formal about references and in fact mostly use Wikipedia for any references, but I try to link to the work of others and sometimes to major references. If a reader has an interest in any of the topics that I touch on, Wikipedia, for all its faults, can be a good place to start.
The result, I suspect, is almost certainly more of a ramble through the topic in question than a serious analysis of it. Caveat Emptor! Of course, anything that I write is my opinion only.
When I have finished writing the post, I save it, and then start “decorating” it. By this I mean that I insert images every paragraph or so, to break up the post into more readable chunks. A single mass of text is off-putting I find. That’s also why I kept the paragraphs short too.
I choose the picture purely on their look. I don’t check the websites that the image come from, so people should not assume that I in any way agree or disagree with the authors of the websites that I borrow images from.
This is probably not a big deal, as I usually use Zemanta to provide the images and they provide links mainly from Wikipedia. Also using a source like Zemanta means that there should be no copyright issues with the images that I include.
When I have finished writing the post and I have inserted my images, I categorise the post using my usual categories and include tags. Doing this is supposed to help people looking for posts on particular topics and tagging in particular should enable my posts to come up in searches. Apparently tagging posts helps search engines.
The way that I write posts mean that there is a danger that I might meander through a topic rather than do a tight analysis of it. That’s OK by me. However I don’t know if the readers of my posts consider them to be rambling or whether I unconsciously put in there a structure that I am unaware of when I write a post.
Essentially, though, I write for myself, to get my ideas out there, to amuse myself and to test myself. When I write, I am, in my own mind, in a way, writing to myself, as if I the reader were a different person to I the writer. I know the occasional real person stumbles on my writing, and if they get something out of it, I am glad. If they don’t get something out of it, well, that’s fine, but I guess that they won’t be back!
There is a perception that electric cars are greener than petrol-driven cars. While I would not like to give the impression that I am against electric cars, as I am actually in favour of them, long term, in the short term I see some issues with them.
Firstly, consider the auto mobile. There are 250 million of them in the United States alone. That require a huge infrastructure which we don’t often consider. Firstly the crude oil is extracted from the ground using huge drills. While the technology is fairly basic, a lot of planning goes into a well before the hole is drilled, and then the drilling rig, and the workers are brought in and eventually crude oil flows.
It flows, ultimately to refineries where, apart from fuel oil, many other oil based products are extracted. The fuel is then trucked around the country or to other countries and ultimately to petrol supply stations (or gas stations as they are referred to in North America). Special equipment, the bowsers, are used to load the fuel into the cars.
The cars also require lubricating oil, which can be purchased in the petrol supply stations. More often the lubrication oil is supplied at special workshops set up to cater for the auto mobile users. These have special equipment to attend to and repair internal combustion engine. Replacement parts are manufactured and distributed to these workshops.
In contrast the fledgling electric car industry is small. There are few recharging stations, and the repair stations for electric cars are currently few and far between. Technicians who can work safely on electric cars are rare.
For electric cars to compete directly with petrol engined cars the infrastructure for electrical cars needs to match the current infrastructure for the petrol cars and that will require significant investments from someone. New electrical charging stations will need to be created or petrol supply stations will have to give up some space to electrical charging stations.
While charging stations are being created, there are less than 10,000 world-wide and a few thousand in the US. In the US there are approximately 3 charging points per station, so there are relatively few places to charge electric cars.
Charging an electric car at an outlet takes a minimum of 10 minutes and to do it this fast requires special equipment, for which special expertise is required. To provide this expertise requires special training, comparable to the expertise required to deal with petrol bowsers. Cross-training of petrol bowser experts in electrical outlets is of course possible, but the expertise is sufficiently different that a whole new pool of experts will need to be built up.
When an electrical car requires repair for any reason, it will need to be taken to a mechanic who knows how to deal with one. It’s likely that some repair locations will switch to electric rather than petrol, since the equipment is so different, though these days the petrol repair locations already use sophistic electronics in the diagnosis and repair of petrol engined cars.
So, in summary, electric car facilities will have to replace petrol car facilities as electrical cars become more common. This will not happen quickly and easily as the industry supporting petrol cars will no doubt resist. The electric car industry will have an expensive fight on its hands as all new equipment will have to be provided and a fledgling industry wont have a lot of financial backing.
What is needed is for the costs of the petrol car industry to climb significantly, and that will cause other significant societal problems. Then it will make sense to invest in the electrical car industry.
Another issue as regards electric cars is related to the charging of them. It takes significantly longer to charge an electric car as opposed to filling up a car’s tank with petrol. In a fast charging station, with special equipment in the charging “bowser” and special connections in the car, it could take anything from 10 minutes upwards.
Cars can be charged at home, and from standard electrical connections, but this would normally have to happen overnight when there is less other usage of electricity in the home. However, if you charge a car from a standard electrical connection, it will take a long time, up to eight hours or more. So those who charge their cars at home can expect not to use the car in the evening, and a flat battery is more of an issue than a flat battery in a petrol car.
The cables both in the house and in the supply connections needs to be robust because of the inevitable heating from the continual high current, and if you be chance draw too much current, either the car charging or the house will be temporarily cut off. If you were to have medical equipment in the house then this could be life threatening.
Of course there are mechanisms that can be ensured to reduce the impact of these problems, but that means that the wiring infrastructure in the house needs to be upgraded. It’s not a big problem until you multiply it by the number of houses that would need to be upgraded.
A bigger issue is that the electricity infrastructure is built for, really, quite light usage. If everyone in the street were to get an electric car, then the local infrastructure would come under stress. There are already “brown-outs” and “black-outs” of the infrastructure in the US at times of heavy demand. Add onto that the charging of numerous electric cars and one wonders if the infrastructure could be upgraded in a reasonable time or whether blackouts and flat batteries would become common.
This problem goes all the way back to generation, which currently depends mostly on fossil fuels in many parts of the world. It’s not much good if reducing fossil fuel usage at the consumer end results in increased fossil fuel usage at the generation end.
So while electric cars and fossil free generation should eventuate, at the moment there are high barriers to widespread adoption of electric cars and reduction of dependence on fossil fuels.